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Browsing by Subject "Stickstoff"

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Die Auswirkungen einer einmalig variierten Bodenbearbeitung auf Ertragsbildung, Verunkrautung und Bodennitratgehalt unter ökologischen Produktionsbedingungen
(2007) Häberle, Annette; Claupein, Wilhelm
Although organic farming is a very non-polluting kind of agriculture, nitrate leachate losses can also be found under this management. Restrictions in organic fertilization have the purpose to keep the nitrate leachate with soil tillage and crop rotation on a low level. Due to this aim field experiments were conducted to investigate the short-term effect of timing and method of cultivation after the harvest of legumes and crops with high-N crop residues on N mineralization, nitrate leaching, crop growth, diseases and weeds in wheat crops. The study was designed to compare the effects of the ?Schutz- und Ausgleichsverordnung? (SchALVO) in Baden-Württemberg and tillage strategies which are normally used in practice, like reduced and conventional tillage in autumn and to compare different times of conventional tillage in winter and spring in three different areas of Baden-Württemberg with typically soil types. The areas were located in the Main-Tauber-Kreis with soils from Keuper and shell lime, in the Gäu-Region with soils from löss and the Schwäbische Alb with soils of limestone. Especially organic farms use, for the admancement of yield und for the regulation of weed population, a timely and increased requirement of soil tillage. In the results of October 2002 till summer 2005 there was no significant influence of timing and method of cultivation, for example reduced tillage in autumn or tillage in winter or spring, on the productivity of organic farms. In the most cases the conditions on the experimental fields were very good resulting of a low weed density and a good farming management. On fields with a high density of perennial weeds the risk of multiplication of weed population persists even after a short-term variation of tillage. There were only a few, not significant differences in the development of wheat growth because of different soil tillage. The most differences were seen between the growth of winter wheat and summer wheat. The yield of summer wheat was not significantly lower than the yield of winter wheat. Summer wheat reached nearly the same yield potential with higher amounts of crude protein. Especially in areas with strong winters and low N-input the yield of summer wheat was higher than the yield of winter wheat. Because of a second peak of mineralization in spring there was a better adaptation of NO3-release to the growth of summer wheat after soil tillage in November, December and February. Because of the better utilization of soil-N from summer wheat the lower yield potential in comparison to winter wheat was relativised in the most areas. With regard to N mineralization a time displacement of soil tillage in winter or spring didnt reduce the N-mineralization before winter in all cases. But in this time displaced treatments there was a second peak in N-mineralization additional to the first peak in autumn. Short-term practice of reduced soil tillage did not reduce N-release in the field experiments. Altogether a time displaced soil tillage in winter or spring could be, based on the experiments, a practical alternative for N-conservation through winter with regard to N-mineralization as well as with regard to corn yield. With the cultivation of a fast-growing catch crop farmers could reach an additional reduction of mineralised N amount over winter. In the farming practice a well timed sowing of catch crops is not always possible, like it is shown in the experiments, but it should be kept in mind for N conservation.
Bedarfsgerechte Stickstoffernährung von Hopfen (Humulus lupulus L.) durch Düngesysteme mit Fertigation
(2021) Stampfl, Johannes; Ebertseder, Thomas
In terms of quantity, nitrogen is the most important and most yield limiting plant nutrient in hops (Humulus lupulus L.), whereby excess nitrogen not taken up by the hop plant is subject to various loss processes. Despite that, little is known about the exact effects of an N supply varying in rate and timing for the hop varieties and cultivation systems currently used in the Hallertau, the worlds most important hop-growing region. In the Hallertau, the required amount of nitrogen is largely supplied by surface spreading of granulated N fertilizers, whereas in semi-arid growing regions, high proportions are applied via irrigation water (fertigation). The aim of this thesis was to examine nitrogen fertilization systems with fertigation under the conditions in the Hallertau region with regard to a nitrogen nutrition that is based on the hop plant’s needs. Therefore, four research questions with different sub-aspects have been formulated, as explained below. From 2017 to 2019 the experimental research and the acquisition of empirical data has been conducted in various field trials consisting of three trial series examining the most important hop varieties at different locations. Apart from a variation in rate and timing of N fertilization, different fertilizer application forms (surface application of granulated fertilizer and above- or below-ground fertigation) have also been examined. In addition to the determination of yield, quality and N-uptake at the time of harvest, further analysis methods such as the 15N-Tracer-Technique, chlorophyll value measurements (SPAD-Meter) or passive reflection measurements were used in individual field trials to depict the N-uptake and N-distribution in different parts of the plant. a) Which effects have different nitrogen treatments varied in rate and timing? These studies found that the hop plant absorbs more than two thirds of the total amount of nitrogen over a period of 7 to 8 weeks between early June and end of July - during formation of main biomass. Despite the fact that only a low amount of nitrogen is accumulated in the plant prior to this stage, the varieties Perle and Tradition showed that a nitrogen deficit in early growth stages until end of May already leads to a decrease of yield potential. This is due to a change in the variety-characteristic formation of lateral shoots (side arms) - the later the application of nitrogen, the greater the formation of side arms was reduced, starting from the bottom to higher plant sections. Consequently, a nitrogen fertilization solely based on the hop plant’s N uptake curve cannot be recommended, neither regarding yield formation nor nitrogen utilization. Instead, an early application of the first nitrogen treatment in April is of vital importance for early maturing varieties such as Perle and Tradition. Late maturing varieties like Herkules show a higher potential of compensation due to prolonged growth phases which enables a higher adaption of N-Fertilization to the plant’s N uptake curve. The ideal amount of nitrogen fertilization with regard to yield optimization has been determined by the growth pattern - depending on variety, weather conditions and location - and therefore by the N uptake, the supply of mineral nitrogen in the soil as well as the location-specific N mineralization potential. A reduction of the nitrogen fertilization to a level significantly below the plant’s N uptake not necessarily led to a limitation of biomass and yield formation in the same year, however, it resulted in an accelerated ripening and a negative impact on external cone quality. Furthermore, it showed that the storage of nitrogen in specific storage roots declines if N levels are significantly reduced, leading to lower vitality as well as limited plant development and yield formation in the following year. With regard to the hop plant’s perennial properties as well as the goal to achieve a demand-oriented nitrogen nutrition of the hop plant it is also necessary to supply the storage roots with enough nitrogen. With respect to valuable contents of alpha acid it has been found that high N supply levels during the stage of alpha acid synthesis (starting from early August) can result in a reduction of alpha acid concentration in the variety Herkules. This decrease can be caused by late and excessive N fertilization as well as by high mineral N contents in the soil. However, this effect has not been observed in the aroma varieties Perle and Tradition. b) Is it possible to determine the current nitrogen nutritional status through non-invasive methods? The measurement of the chlorophyll value with a SPAD-Meter on the lower leaves of the main shoot generally reflected the N content and N supply status of the hop plant. However, short-term changes in the N nutritional status could not be recorded with sufficient accuracy at this measuring point, especially not during the stage of main biomass formation, since increased proportions of the applied nitrogen were transported to higher plant sections, as was shown by the use of 15N. Regarding the determination of threshold values a classification of the plant development into before, during and after main biomass formation independent of the measuring point, is considered appropriate, since the chlorophyll value correlates with the plant’s development stage. Vegetation indices, calculated on the basis of reflectance spectra, represent not only the N content but also the actual N uptake of the crop, which is why passive reflectance measurement methods have a higher informative value with regard to the current N supply status of the plant compared to chlorophyll value measurements. Therefore, this technology could be used to achieve a site-specific optimization of rate and timing of N fertilization and thus a more demand-oriented nitrogen nutrition of the hop plant in the future. c) What are the effects of surface and subsurface drip irrigation? In the period from 2017 to 2019, additional irrigation of the aroma variety Perle on sandy soil led to a stabilization of the agronomic parameters cone yield and alpha acid content every year. In addition, irrigation also achieved an improvement of nitrogen utilization. Compared to subsurface systems, surface drip irrigation achieved a higher efficiency if the horizontal water distribution was limited by hydraulic soil properties. It was shown that this is due to the fact that the majority of the hop plant’s fine root system is located in the hill formed along the hop rows and the soil layers beneath it. d) What are the effects of a nitrogen nutrition via irrigation water? A system comparison was made between N fertilization systems with fertigation and a solely granulated N application. The use of fertigation resulted not only in an improvement of cone yield and alpha acid content, but also in an increase of the plants nitrogen uptake and a reduction of Nmin content in the soil, which is also associated with a reduction of the risk of nitrate leaching into the groundwater. Fertilization systems with fertigation achieved a higher nitrogen utilization especially at low N-fertilization rates. If two thirds of the total amount of nitrogen were applied via irrigation water, the concentration over a 6-week period proved to have a positive impact on all analyzed varieties, especially under conditions of a limited N supply, since a higher proportion of N has been applied during main biomass formation and the stage of lateral shoot growth. For an efficient N-fertilization with fertigation the application should take place between mid-June and late July while no significant amounts of nitrogen should be applied after early August. For early maturing varieties such as Perle and Tradition, there is a risk of a late N application as it is hardly possible to lay out the drip tubes before the 25th week of the year. Therefore, in early maturing varieties, a higher proportion of N should be applied in earlier growth stages while the amount of N applied via fertigation should be less than two-thirds of the total amount of N fertilizer. A substantial advantage of fertilization systems with fertigation is that nitrogen applied via the irrigation water is immediately absorbed by the plants, which allows an effective short-term intervention in the plant’s nitrogen nutrition. On the basis of a reliable recording of the current N supply status with sensors during the main growth stage, fertigation could be used to adjust the N fertilization in order to achieve a site-specific and demand-oriented nitrogen nutrition of the hop plant.
Bedeutung der Stickstoffumsetzung und externer Stickstoffquellen für die Entwicklung von FFH-Mähwiesen in Baden-Württemberg
(2023) Kukowski, Sina Louise; Streck, Thilo
1. AIM AND OBJECTIVES OF THE STUDY. The condition of the species-rich lowland hay meadows (habitat type 6510) in Germany is increasingly deteriorating. One cause of the deterioration is the supply of reactive nitrogen (N). To counteract the ongoing deterioration, it is necessary to understand the relationships between external N inputs via the atmosphere and fertilization, internal N turnover in the soil, plant uptake and growth, as well as possible links to the conservation degree of this habitat type. The overall objective of this dissertation is therefore to contribute to a better process-based understanding of the complete N cycle of Fauna-Flora-Habitat (FFH) meadows. 2. MATERIAL & METHODS. The interdisciplinary structure of this thesis includes different approaches to study inputs, turnover and outputs of N. With respect to N input via the airborne pathway, the focus was primarily placed on the hitherto poorly studied relationships between ammonia concentration and specific N-sensitive species groups in FFH lowland hay meadows. These relations were analyzed by means of generalized mixed models (GLM) based on nationwide data. In addition, further site-specific factors with a significant influence on the conservation degree of FFH meadows were identified using GLM. For the quantification of soil-borne N turnover processes, an empirical approach was chosen, including the determination of gross N turnover rates using the 15N isotope dilution method. To record these N dynamics, an intensive monitoring of gross and net N fluxes (mineralization, nitrification, ammonium consumption, nitrate consumption) in soils from different primary substrate and with different meadow conservation degree was carried out in 2016 and 2017. The results were merged using a process-based agroecosystem model (EXPERT-N), which was adjusted for habitat type 6510 to the collected data. The adapted model was applied to other sites of habitat type 6510 distributed throughout the state of Baden-Württemberg, which served to investigate spatial and temporal patterns of relevant nitrogen fluxes over an extended time period (1996 until 2012) and had been characterized in terms of soil and vegetation. 3. RESULTS. The nationwide data show a statistically significant decrease of habitat-typical low-nutrient indicator species and an increase of N indicator species with increasing atmospheric ammonia concentration on lowland hay meadows in Baden-Württemberg. Whether this is an effect of the atmospheric ammonia concentration or whether differences in agricultural land use structure play the decisive role could not be clarified with the available data. The intensive monitoring on selected FFH lowland hay meadows showed that soil-borne gross nitrification rates on soils from calcareous parent substrate (high pH) differed significantly from those from decalcified substrate (low pH). Both gross mineralization and gross nitrification were characterized by high temporal variability at all sites, which could not be explained by measurements of soil temperature and soil water content. Determination of net N turnover rates showed almost no variability and could not be used to draw conclusions about actual gross turnover rates in soil. The N-turnover model adapted for habitat type 6510 was able to represent spatial and temporal patterns over an extensive period of time. Simulation results showed high spatial and temporal variability for most N cycle variables. Soil organic N mineralization has a critical influence on the amount of plant-available N and thus has a direct impact on yield and N removal. On high clay-content soils and sites with high organic matter content, the model overestimated mineralization. External N inputs, such as moderate organic fertilization or atmospheric N deposition, were less crucial for yield. Additional N input is always a driving factor for N turnover in soil in the short term. With already high turnover levels, N turnover continues to increase and thus the risk of nutrient imbalances also increases. In the long term, the decisive factor for the N balance of FFH lowland hay meadows is whether N supply exceeds removal, whether the mineralizable organic N pools are thus increased, or whether a balance between supply and removal can be achieved. If soil internal N turnover is high, as it was the case on most of the simulated sites, a longer depletion phase should be applied before. In summary, this dissertation provides insight into the complexity of N cycling of FFH meadows. Using various approaches (statistical analyses, field trials, process-based modelling), it contributes to a better understanding of site-specific N turnover and the role of external N sources for the development of this ecosystem.
Effects of elevated soil temperature and altered precipitation patterns on N-cycling and production of N2O and CO2 in an agricultural soil
(2016) Latt, Yadana Khin; Kandeler, Ellen
Both temperature and precipitation regimes are expected to change with climate change and are, at the same time, major environmental factors regulating biogeochemical cycles in terrestrial ecosystems. Therefore, crop water availability, soil nitrogen transformations, losses, and uptake by plants as well as CO2 emissions from soil are likely to be changed by climate change. Agriculture is known to be one of the most important human activities for releasing significant amounts of N2O and CO2 to the atmosphere. Due to global concern about the changing climate, there has been a great interest in reducing emissions of N2O and CO2 from agricultural soils. CO2 and N2O are produced in soil primarily by microbial processes. Their production and emissions from the soil are controlled by a number of environmental variables including inorganic N availability, soil temperature and water content. Agricultural management practices, such as irrigation, affect these environmental variables and thus have the potential to dramatically alter N2O and CO2 emissions from the soil. The present study is titled "Effects of elevated soil temperature and altered precipitation patterns on N cycling and production of N2O and CO2 in an agricultural soil". The objectives of this study were: to determine the effects of elevated soil temperature on N cycling in a winter wheat cropping system, to investigate the short-term response of N2O and CO2 fluxes during rewetting of soils after extended dry periods in summer, and to determine the effects of different degrees of rewetting on the CO2 emission peaks after rewetting in laboratory incubations. In the 1st experiment, we used the Hohenheim Climate Change (HoCC) experiment in Stuttgart, Germany, to test the hypothesis that elevated soil temperature will increase microbial N cycling, plant N uptake and wheat growth. In the HoCC experiment, soil temperature is elevated by 2.5°C at 4 cm depth. This experiment was conducted at non-roofed plots (1m x 1m) with ambient (Ta) and elevated (Te) soil temperature and with ambient precipitation. In 2012, winter wheat (Triticum aestivum) was planted. C and N concentrations in soil and aboveground plant fractions, soil microbial biomass C and N (Cmic and Nmic), mineral N content (NH4+ - N and NO3- - N), potential nitrification and enzymes involved in nitrogen cycling were analyzed at soil depths of 0-15 and 15-30 cm at five sampling dates. The plants were rated weekly for their phenological development and senescence behavior. We found that an increase in soil temperature by 2.5oC did not have a persistent effect on mineral N content and the activity of potential nitrification within the soil. Plant growth development also did not respond to increased soil temperature. However microbial biomass C and N, and some enzyme activities involved in N-cycling, tended to increase under elevated soil temperature. Overall, the results of this study suggested that soil warming by 2.5oC slightly stimulates soil N cycling but does not alter plant growth development. In the 2nd experiment, in 2013, the effects of a change in the amount and frequency of precipitation patterns on N2O and CO2 emissions were studied after the two dry periods in summer in the HoCC experiment. N2O and CO2 gas samples were taken from four subplots (1m x 1m) of each roofed plot exposed to ambient (Ta) or elevated (Te) soil temperature and four precipitation manipulations (ambient plot, reduced precipitation amount, reduced precipitation frequency, and reduced precipitation amount and frequency). We found that CO2 emissions were affected only by temperature, but not by precipitation pattern. It can be said that N2O and CO2 emissions after rewetting of dry soil were not altered by changing precipitation patterns during dry periods in summer. In the year 2014, using laboratory incubations, we also measured the short-term response of CO2 production to a rewetting of dry soil to different volumetric water contents for 24 hours. This study was conducted by manipulating microcosms with agricultural soil from the HoCC experimental site, which had been exposed to severe drought conditions of three months duration for each of the last six years. The results showed that CO2 production increased with increases in the water content of soils by rewetting at 5%, 15%, 25%, 35% and 45% VWC. With increasing water additions more peaks in CO2 production were detected and different temporal patterns of CO2 emission were affected by adding different amounts of water. It might be due to the fact that with greater water additions successively larger pore sizes were water filled and therefore different bacterial groups located in different pore size classes might have contributed to CO2 production. In summary, the results from field study suggested that climate warming will affect N cycling in soils in an agricultural cropping system. The results from both field and microcosm rewetting experiments contribute to a better understanding of C and N dynamics in soil by investigating the effect of varying soil water content on the emission of N2O and CO2.
Effects of monensin and tannin extract supplementation on methane production and other criteria of rumen fermentation in vitro and in long-term studies with sheep
(2013) Wischer, Gerald; Rodehutscord, Markus
Ruminants increasingly attract public concern due to their methane release and contribution to the greenhouse effect. One strategy to reduce the release of methane is to modify microbial fermentation in the rumen by the use of feed additives such as monensin and tannin extracts. However, other characteristics of fermentation including the synthesis of microbial protein may also be affected. The aim of the present studies was to provide a comprehensive evaluation of the effects of monensin and tannin extracts on ruminal fermentation and methane production. The ionophore monensin is known to increase feed efficiency in ruminants. Although the use of silages is common practice in cattle feeding, the effects of monensin on the fermentation of silages in the rumen and microbial protein synthesis are lacking. Monensin has often been described to have indirect effects on methane production resulting from its effects on feed intake, protozoa and Gram-positive bacteria. It has rarely been studied whether monensin can reduce methane production without adverse effects on other criteria of rumen fermentation. The first objective therefore was to investigate the effects of different dosages of monensin on methane production and microbial protein synthesis when supplemented to different silages in two in vitro systems (Study 1). In Experiment 1 of Study 1, 15 g of oven-dried grass silage alone or combined with a concentrate was incubated in a rumen simulation (Rusitec) over a period of 13 d to examine the effects of monensin supplementation (2 or 4 mg/d, n = 4) on the production of total gas, methane, volatile fatty acids (VFA), degradation of nutrients and microbial protein synthesis. In Experiment 2 of Study 1, different dosages of monensin (0.5, 1, 2, 6 and 10 µg) were supplemented to syringes containing 120 mg of grass silage alone, grass silage combined with concentrates, or maize silage alone. After 24 h of incubation the effects of monensin on total gas, methane and VFA production were determined. In Experiment 1 monensin inclusion to grass silage and grass silage combined with concentrate resulted in a decreased total gas, methane and acetate production, while propionate production was increased. Along with a decreased degradation of crude protein, ammonia concentration in the system was reduced. While microbial protein originating from solid associated microbes decreased with monensin inclusion, microbial protein from liquid associated microbes was increased, resulting in an increase in total microbial protein synthesis. In Experiment 2, different dosages of monensin reduced methane production in grass silage (17%), grass silage combined with concentrate (10%) and maize silage (13%) without adverse effects on total gas production. Based on these two in vitro experiments it was concluded that monensin is able to reduce methane production without a major decrease in total gas and VFA production and degradation of organic matter. Although microbial fractions were differently affected, the total microbial protein synthesis was increased upon monensin supplementation. Tannins are secondary plant compounds that are known to complex with feed and microbial proteins. Several products from this heterogeneous group have shown potential to affect rumen fermentation in vivo and, even more, in vitro, but are often accompanied by negative effects on digestibility, feed intake and microbial protein synthesis. In Study 2 of the present work, ten tannin extracts (chestnut, mimosa, myrabolan, quebracho, sumach, tara, valonea, oak, cocoa and grape seed) and four monomers of rapeseed tannin (pelargonidin, catechin, cyanidin and sinapinic acid) were screened in grass silage based diets in successive runs using the Hohenheim Gas Test. The objective was to determine the optimal dosage of each tannin extract to cause a maximal methane reduction without negative effects on total gas production. Whereas the supplementation of pelargonidin and cyanidin to grass silage did not reduce methane production; catechin and sinapinic acid reduced methane production without affecting total gas production. Except tara extract, all tannin extracts reduced methane production by 8 to 28% without adverse effects on total gas production. Based on these results, chestnut, grape seed, myrabolan, sumach and valonea extract were investigated in a second step in a Rusitec to determine their effects on degradation of nutrients, VFA and ammonia production, and particularly on microbial protein synthesis. All tannin extracts were supplemented at similar dosages of 1.5 g to 15 g of grass silage. The supplementation of chestnut resulted in the greatest decrease in methane production (63%), followed by valonea (35%), grape seed (23%), sumach (18%), and myrabolan (7%; not significantly different from the control). While chestnut extract reduced acetate production by 19%, supplementation with grape seed or myrabolan extract increased acetate production; however, degradation of fibre fractions was reduced in all tannin treatments. Degradation of dry and organic matter was reduced by all tannin extracts, but there were no differences between tannin treatments. Crude protein degradation and ammonia production were also reduced by tannin extract supplementation. Microbial protein synthesis and its efficiency were not affected by tannin supplementation, which indicates that a reduction in methane production due to tannin extract supplementation is possible without negatively affecting microbial protein synthesis. Chestnut and valonea extract had the greatest potential in reducing methane production without negative effects on rumen fermentation of grass silage and microbial protein synthesis. Therefore, these tannin extracts were investigated for their long-term effects in sheep (Study 3). In Experiment 1 of Study 3, sheep receiving the control, chestnut or valonea treatment (each n = 4) were fed 842 g/d of hay (fresh weight). The animals on the control treatment also received 464 g/d of concentrate, and animals on the tannin treatments received the same amount of concentrate but were also fed 20 g of the respective tannin extract. Following initiation of tannin feeding, methane release from sheep was measured in 23.5 h intervals in respiration chambers on day 1, 8, 15, 29, 57, 85, 113, 148, and 190. In three balances periods faeces and urine were collected for 6 and 3 days, respectively. Effects on nutrient digestibility, nitrogen and energy metabolism were evaluated, with microbial protein synthesis estimated from the urinary excretion of purine derivatives. Based on the results of Experiment 1, a second experiment was conducted four month after the start of Experiment 1. Experiment 2 had the same study design and data collected, but the dosage of tannin extracts was doubled compared to Experiment 1 (0.9 vs. 1.7 g tannin extract/kg body weight) and the duration was shorter (85 days). Hay and concentrates used in both experiments were also evaluated using the Hohenheim Gas for their effects on total gas and methane production. In both experiments, methane release was not significantly reduced by tannin extract supplementation when analysed over the whole experimental period. In Experiment 1 the supplementation of chestnut extract on day 190 resulted in a reduced methane release. In both experiments, on day 1 a numeric reduction in methane release for the tannin treatments was observed, with a greater reduction recorded for the higher dosage used in Experiment 2. This trend disappeared by day 57. In the third balance period of Experiment 1, digestibility of dry and organic matter was reduced by tannin supplementation. The digestibility of crude protein was reduced in both experiments, whereas the digestibility of fibre fractions was not influenced. In both experiments a long-lasting shift in nitrogen excretion from urine to faeces was observed, which occurred to a greater extent in Experiment 2. The urinary excretion of purine derivatives was not significantly affected by tannin supplementation, indicating that the microbial protein synthesis was not altered in either experiment. The in vitro methane production was reduced for concentrates containing tannin extracts, but it was not significantly affected when concentrates were incubated with hay. It is concluded that monensin added to different silages caused a decrease in methane production without affecting total gas production but with an increased microbial protein synthesis. Nine of the ten considered tannin extracts and two tannin monomers decreased methane production without affecting total gas production. The Rusitec study confirmed the great potential of chestnut and valonea extract to reduce methane production without negative effects on microbial protein synthesis. However, neither chestnut nor valonea extract reduced the methane release in sheep when fed over a longer period of time. It is assumed, that rumen microbes adapted to the tannin dosages in terms of methane release but not nitrogen metabolism, as there were long-lasting effects on nitrogen excretion. The shift in nitrogen excretion can have a positive effect on the environment due to the reduced potential of ammonia emission from the urine. Both in vitro systems used in the present studies showed effects of tannin extracts that were considerably different from those observed in sheep. The monomers investigated in the present study are the basic units of condensed tannins, whereas the tannin extracts selected in vitro only contain hydrolysable tannins. It is possible that monomers of chestnut and valonea extract may reduce methane production, whereas higher dosages of these tannin extracts cause negative effects on feed intake, digestibility and microbial protein synthesis. Further investigations should focus systematically on the transfer of in vitro studies to estimate in vivo responses. Therefore, a parallel implementation of different in vitro and respiration studies would be of great value.
Einfluss der Bearbeitungsintensität beim Umbruch von Luzerne-Kleegras auf die Stickstoffmineralisation zur Folgefrucht Winterweizen im organischen Landbau
(2003) Wald, Fabian; Claupein, Wilhelm
In the crop rotation of organic farming grass-legume mixtures play an important role due to the legumes´ ability to assimilate N. Ploughing-in of established grass-legume mixtures results in releasing the assimilated N by mineralisation of organic matter. In practice the mineralisation can only be controlled by means of soil cultivation. The aim of the present study is to analyse the relations between different intensities of soil cultivation and N-mineralisation. The data were used to test the simulation model CANDY. The field experiment of each 0.1 ha was set up at three sites in two different locations, which were cultivated from 1999 to 2001: Hohenheim (with trials 610 and 611) and Kleinhohenheim (with trial 660). In the beginning all sites had a three-year old grass-clover-alfalfa mixture, which was ploughed-in for trial 610 and 660 in the late summer of 1999 and in the year 2000 for trial 611. The factor soil tillage was varied in three stages as follows: RT+RT+plough: double rototill cultivation (RT, 10 cm deep) in intervals of approx. 2 weeks, followed by ploughing (plough, 25 cm deep); RT+plough: single rototill cultivation, followed by ploughing (depths as mentioned above); Plough: ploughing without any preceding cultivation (depth 25 cm). After uniform seedbed preparation with a rotary harrow, wheat was sown on all trial sites in autumn, and in trials 610 and 660 it was followed by oat in 2001. Nitrogen content in the soil was determined by repeated sampling at a depths of 0-10, 10-20, 20-30, 30-60 and 60-90 cm. Monitoring boxes were installed in 1 m depth in an undisturbed soil body from September 2000 until April 2001 to record nitrate leaching. Ploughing-in of the grass-clover-alfalfa by means of rototiller cultivation (treatments RT+RT+plough and RT+plough) was followed by a significant increase of mineralisation, which in case of the plough treatment was less pronounced. In this case the date of cultivation, 6 weeks after the rototilling, may have had an influence. Nmin-contents in autumn 1999 were higher after RT+RT+plough than after RT+plough. It has to be taken into consideration that there was a time gap between both treatments of 9 days. But also in the following year (611), when both treatments were cultivated the same date, there was a significant, slight difference of the Nmin values depending on the treatment. Nitrate leaching was only measured in trial 611. Quantities of 86, 84 and 64 kg N/ha were observed in treatments RT+RT+plough, RT+plough and plough, respectively during winter. Due to high Nmin-contents in autumn, for the rototill treatments higher nitrate losses can be assumed compared to the plough treatment for both years of experiment. Depending on the location, nitrogen uptake and yields of wheat turned out to be different. In Kleinhohenheim they were lower in treatments RT+RT+plough and RT+plough than in the plough treatment. It was the other way round in Hohenheim on a higher production level. Due to strong hail impact, this relation between the treatments was not to be proved in trial 611. Oat was the second crop. In this case no effects of intensity of soil cultivation on nitrogen uptake and yield could be observed between treatments and locations. The CANDY model was used for simulating the results of trials 610 and 611. First, the model seemed to be inadequate because it could not model the N-dynamic after soil cultivation. Adding fictitious organic material to the system helped to overcome this problem and then, on average, the N-dynamic model fit was satisfying. An estimate to overcome the general insufficient fit of the model could be mineralisation of parts of the physically protected organic matter (SOS), which is already implemented in the model, right at the moment of cultivation. Data of soil moisture of trial 611 served to calibrate the model successfully. With amended soil parameters the model was then easily applied to the corresponding data of trial 610. In contrast, CANDY did not predict well the nitrate leaching - possibly because the model did not consider preferential flow.
Evaluation and improvement of N fertilization strategies in the wheat/maize double-cropping system of the North China Plain
(2015) Hartmann, Tobias Edward; Müller, Torsten
The North China Plain (NCP) is the main production area of cereal crops in China. The intensification of agricultural systems and the increased use of chemical N fertilizers are contributing to environmental pollution. One of the objectives of this thesis was to apply an Nmin based approach for the calculation of N application rates to a previously over-fertilized farmers field of the NCP and to evaluate the potential of reducing N inputs while maintaining the grain yield of a summer-maize/winter-wheat double-cropping system; and to evaluate fertilizer strategies, aiming to reduce N inputs and loss. Using an Nmin based approach for the calculation of fertilizer application rates, a reduction of fertilizer input by up to 50% compared to farmers practice (550 kg N ha-1 a-1) is possible without negatively affecting the grain yield of a wheat / maize double cropping system. The extreme re-supply of N during the summer-vegetation periods of maize in the first two experimental seasons resulted in high yields of the control treatment (CK: 2009: 5.7 and 2010: 5.9 Mg ha-1), which did not significantly differ from the fertilized treatments. This resulted in a reduced recovery efficiency of N (REN: 0.09 kg kg-1 – 0.30 kg kg-1). According to the results of this field experiment there was no agronomic justification for the application of fertilizer N. The grain yield of maize of the control treatment finally decreased in the third vegetation period of summer-maize. While maintaining the yield level, the optimized application of N increased REN (0.37 – 0.58 kg kg-1) significantly compared to farmers practice (0.21 kg kg-1) in this final vegetation period of maize. Wheat, in contrast to maize, is dependent on the application of fertilizer N for yield formation. In both vegetation periods of wheat, REN of the reduced treatments (0.34 – 1.0 kg kg-1) was significantly higher compared to FP (0.26 and 0.27 kg kg-1). The highest cumulated (5 vegetation periods) agronomic efficiency of N, as well as cumulated grain yield of the wheat/maize double-cropping system was observed when ammoniumsulphate-nitrate was applied in combination with the nitrification inhibitor 3,4-dimethylpyrazolephosphate (ASNDMPP: AEN: 19 kg kg-1, yield: 35 Mg ha-1) and according to crop N demand and residual soil mineral N. The highest REN was observed when urea ammonium nitrate was applied in a shallow, banded depot (UANDEP: 40 kg kg-1). The results of this field experiment further show that the N surplus (fertilized N - grain N) as well as the N balance (N Input - N output) after harvest are significantly lower when an optimized approach to fertilizer application is followed. The over-application of N for an optimized application of urea or ASNDMPP (Surplus: -25kg to 98 kg N ha-1; Balance: -36 to 102 kg N ha-1) was significantly reduced compared to current farmers practice (Surplus: 156kg to 187 kg N ha-1; Balance: 56 to 262 kg N ha-1). This leads to lower residual N in the soil horizon from 0 - 90 cm in the reduced treatments (113 kg N ha-1 at end of experiment) compared to FP (293 kg N ha-1). The results of this experiment indicate that N contained in the residues of maize is available only to the subsequent summer-crop and may sufficiently supply N for the yield formation of maize. Should the over-application of N be effectively reduced in the cropping systems of the NCP it is therefore necessary to take the N mineralization potential of soils into account. Based on the results of this field experiment and others, a crop-soil interface model (HERMES) was calibrated and validated to the conditions of the NCP. Finally, this research observed the effect of wheat straw and the urease inhibitor (UI) N-(n-buthyl) thiophosphoric triamide (nBPT) on the turnover of urea, as well as the loss of ammonia and nitrous oxide from an alkaline soil of the NCP. UI inhibit or reduce the appearance of ammonia after the application of urea and almost completely prevent the loss of N as ammonia (urea: 12 – 14% loss). nBPT effectively reduces the rate of urea hydrolysis but does not down-regulate the process enough to completely inhibit nitrification, thereby maintaining the availability of N from urea for plants. Further, the addition of wheat straw prolongs the appearance of ammonium after the application of urea while the appearance of nitrate is reduced. Wheat straw may therefore either act as a stimulant of hydrolysis or as an inhibitor of nitrification. The addition of urea increases soil respiration and the emission of N2O drastically, possibly acting as a C and N source for microbial organisms and causing a priming effect on microbial activity in soils. This effect was increased further when wheat straw as well as urea were added to soil. nBPT, in contrast, prevents a significant increase in CO2-respiration and N2O-emission. The urease inhibitor may therefore generally restrict microbial activity or shift nitrification/denitrification processes towards the emission of N2.
Fermentations- und Syntheseleistung der mikrobiellen Gemeinschaft des Pansens in vitro bei Variation der Grobfutter- und Stickstoffquellen
(2017) Zuber, Karin Helga Renate; Rodehutscord, Markus
In the first part of this doctoral thesis five batches of maize silage (MS), five batches of grass silage (GS) and three batches of alfalfa silage were incubated in the Hohenheim gas test. The variation of silages based on in vitro gas production kinetics and ammonia-nitrogen-concentration (NH3-N-concentration) in the mixture of rumen liquid and buffer solution over time was determined. For this purpose, 10 glass syringes per silage batch were used per experimental run. 3 glass syringes were used to determine the gas volume over 72 hours. The remaining 7 glass syringes were removed from the incubator at 7 time points and the NH3-N-concentration in the mixture of rumen liquid and buffer solution was determined. Upon the incubation of the 13 silages both silage species and batch had an influence on the potential gas production and on the rate constant of gas production. The determined potential gas production was between 62.5–74.2, 56.0–64.9 and 39.9–59.6 mL/200 mg organic matter (OM) for MS, GS and alfalfa silages. The rate constant of gas production amounted to 5.5–7.3, 3.8–7.1 and 5.0–7.7 %/h for MS, GS and alfalfa silages. Both silage species and batch as well as the time point and their interactions had an influence on the NH3-N-concentration in the mixture of rumen liquid and buffer solution. In the second part of this work one MS and one GS were incubated in the rumen simulation Rusitec. The influence of the forage source without supplementation of concentrates on the NH3-N-concentration in fermenter liquids over time and the fermentation and synthesis characteristics of the ruminal microbial community were investigated in vitro. Degradation of nutrients, gas, methane and short chain fatty acid (SCFA) production as well as NH3-N in effluent and microbial protein synthesis (MPS) were measured. The NH3-N-concentration in fermenter liquids was determined at different time points within two periods. Upon the incubation of GS, degradation of OM and fibre fractions, amount of NH3-N in the effluent as well as MPS and its efficiency (EMPS) was higher than with incubation of MS. Degradation of crude protein (CP) and total amount of SCFA were unaffected by silage. N-efficiency was higher with incubation of MS than with incubation of GS. During period 1, NH3-N-concentration in fermenter liquids increased for all treatments within the first 24 hours and was not different between the treatments. For GS, NH3-N-concentration subsequently continued to rise up to a maximum value at the last time point of measurement in period 1. NH3-N-concentrations in fermenter liquids in period 2 remained on a relatively constant level for MS and GS, differing between the two silages at all five time points of measurement. Mean NH3-N-concentration in fermenter liquids measured in period 2 corresponded in level with NH3-N-concentration determined in the effluent of both silages. In the third part of this work, the influence of different N-supplements to MS compared to GS on fermentation and synthesis characteristics of the ruminal microbial community in vitro was investigated. GS and MS were incubated in a Rusitec, the latter being either unsupplemented or supplemented with urea, pea protein, pea peptone or a mixture of amino acids to adjust N-content of MS to that of GS. The NH3-N-concentration in fermenter liquids was determined 0, 2, 4, 12 and 24 hours after changing the feed bag on day 12. Results concerning degradation of OM, CP and N-free extracts showed a positive influence of N-supplementations except for MS+pea protein. Furthermore, degradation of detergent fibres were partially improved through N-supplementations. The values of MPS and EMPS were enhanced through all N-supplementations. Thereby supplementation of urea and pea peptone to MS resulted in the largest increase in EMPS. However, through none of the N-supplements the level of GS in EMPS could be achieved. The determined course of NH3-N-concentration in fermenter liquids was largely similar between the treatments. Variation in nutrient composition of MS, GS and alfalfa silages were reflected in a large variation both in gas production kinetics and curve shape of NH3-N-concentration in the mixture of rumen liquid and buffer solution. Upon the sole incubation of MS and GS in the Rusitec, GS promoted MPS and EMPS stronger than MS. Supplementation of MS with different N-sources resulted in an increase in MPS and EMPS compared to MS without N-supplementation. Thus the assumption of an insufficient N-supply of ruminal microbes during the sole incubation of MS in vitro was confirmed. However, through none of the N-supplementations level of GS in EMPS could be achieved.
Improved prediction of dietary protein use and nitrogen excretion in tropical dairy cattle
(2023) Salazar‐Cubillas, Khaterine; Dickhöfer, Uta
The overall objective of the present doctoral thesis was to evaluate the adequacy (i.e., accuracy and precision) of existing laboratory methodologies and modeling tools, originally designed for temperate systems, in predicting the nitrogen (N) supply and excretion of cattle in tropical husbandry systems. It was hypothesized that the adoption of laboratory methodologies and modeling tools from temperate systems without validating and adapting them for tropical systems may result in inaccurate estimations of N supply, utilization, and excretion, which will hamper the assessment of N use efficiency. An in vitro study was conducted to evaluate the adequacy of the chemical method (Sniffen et al., 1992; Kirchhof et al., 2010; Valdés et al., 2011) to predict rumen-undegraded crude protein (RUP) of tropical forages grasses and legumes (n = 23). The adequacy of the predictions was assessed by comparing them with RUP proportions measured in situ at rumen passage rates of 2, 5, and 8% per hour. Results showed that the RUP of tropical forages estimated with the in situ method can be predicted using the chemical method. However, regression equations developed for temperate forages were not adequate enough to predict RUP proportions of tropical forages consistently for all rumen passage rates. Instead, developed equations in the present thesis can be used to predict RUP proportion of tropical forages with a similar chemical composition than the reference forage sample set. A second in vitro study was conducted to evaluate the adequacy of the chemical (Sniffen et al., 1992; Zhao and Cao, 2004) and in vitro methods (Steingaß et al., 2001) to predict post-ruminal crude protein (PRCP) supply of tropical forages (n = 23). The adequacy of the PRCP supply with the chemical and in vitro methods were tested against PRCP supply estimated from in situ measurements at rumen passage rates of 2, 5, and 8% per hour and digested organic matter. Results showed that the in vitro method can be used as an alternative method to estimate PRCP supply in tropical forages at moderate to fast rumen passage rate but not at slow rumen passage rate. Available regression equations developed for temperate forages were not adequate enough to predict the PRCP supply of tropical forages from concentrations of chemical crude protein fractions. Instead, developed equations in the present thesis can be used to estimate PRCP supply of tropical forages with a similar chemical composition than the reference forage sample set. A third study was conducted to assess the adequacy of modeling tools to predict N excretion of cattle in tropical husbandry systems. These models, namely model A (based on AFRC, 1993), model G (based on GfE, 2001), and model I (INRA, 2019), were selected to predict fecal N (FN), urine N (UN), and total N (TN) excretion as well as FN fractions of dairy cows, heifers, and steers kept under typical tropical husbandry conditions. The adequacy of the model predictions was assessed against reference values of UN (total collection and creatinine method) and FN excretion (total collection, internal and external markers) (n = 392 observations). Adjustments were made to the models with the greatest potential to predict N excretion. The adjustments were focused on the input variables driving the variability in N excretion predictions, identified through a sensitivity analysis. None of the tested models predicts adequately the excretion of UN, FN, and of different FN fractions of individual cattle kept under tropical conditions. Instead, model I in the present thesis, adjusted for increased efficiency of rumen microbial crude protein synthesis and reduced intercept of FN prediction, can be used to estimate FN and TN excretion of individual cattle kept under tropical conditions. The findings from the present thesis partially support our hypothesis. The adjustment of laboratory methodologies, such as the chemical method used to estimate the protein value of temperate forages, to tropical forages, results in more adequate estimates of the proportion of RUP and PRCP supply of tropical forages. Model I is, therefore, able to predict the N excretion of cattle more adequately in tropical husbandry systems, because it is sensitive to differences in the RUP proportion and PRCP supply. In addition to increasing the adequacy of these input variables, adjustments made to the microbial protein synthesis and intercept of the FN excretion of model I results in a more adequate prediction of N excretion by cattle in tropical husbandry systems. However, not all adjustments to laboratory methodologies and modeling tools from temperate systems yielded adequate predictions. Specifically, challenges remained in predicting RUP proportion and PRCP supply for tropical forage legume with slow rumen passage rates, as well as urinary N excretion in cattle with low N intakes. Consequently, further research is required to identify the factors contributing to their poor adequacy.
Influence of biogas-digestate processing on composition, N partitioning, and N₂O emissions after soil application
(2023) Petrova, Ioana; Pekrun, Carola
The ever-growing need for agricultural products represents a global issue, particularly with a view to the limited availability of cultivable land. According to the latest estimates, the arable land per capita decreases and, in 2050, is expected to account for about 60% less than in the 1960s. In order to meet the demand, agriculture has evolved into industrial-like structures. This development often goes along with nutrient surpluses (e.g., excess of nitrogen and phosphorus) and increased emissions, caused by mismanagement and inappropriate agricultural practices (e.g., over-fertilization). Biogas plants offer a possibility to valorize organic residues and wastes, but potentially aggravate this problem since additional organic residues (referred to as digestates) with considerable nutrient contents are generated as by-products. A simple approach to adjust nutrient levels in the affected regions is the transfer of manures and digestates. However, to make this feasible, a reduction of water content (and consequently of total mass/volume) of digestates is required. Up to now, various techniques for digestate downstream processing are available. Previous research mainly addressed single processing stages or differences between feedstock mixtures. Only limited information was found about the influence of a completed downstream processing on total mass reduction and nitrogen concentration in digestate. Studies about the (gaseous) N losses that occur after the application of the respective intermediate and final products to soils were equally scarce. Therefore, the aims of the current doctoral thesis were to determine (i) the mass reduction achieved by the gradual removal of water within competing processing chains, (ii) the nitrogen partitioning after every single processing step and its recovery in the end products, and (iii) the amount of greenhouse gases (especially N₂O) released after the application of intermediate and end products to soils in comparison to untreated, raw digestate. For that purpose, two commercial, full-scale biogas plants were examined, which completely processed either the solid or the liquid fraction after mechanical screwpress separation of raw digestate. The separated solid fraction was subsequently dried and pelletized, while the liquid fraction was treated by vacuum evaporation with partial NH₃ scrubbing. As final products, digestate pellets and N-enriched ammonium sulfate solution were generated. Calculation of a mass flow balance served as the basis for determining (total) mass reduction, the partitioning of fresh mass and nitrogen during digestate processing, and the recovery of initial N in the products. Additionally, the environmental impact of utilizing digestate as an organic fertilizer was studied by measuring the N₂O release after application to soil under field and laboratory conditions. A further in-depth analysis was performed to observe the main factors influencing the production and release of climate-relevant N₂O from digestate pellets. It was found that the mass reduction caused by water removal during subsequent processing accounted for 6% (solid chain) and 31% (liquid chain) of the total mass of raw digestate. Liquid processing required 40% less thermal energy per ton of water evaporated than solid processing. At the end of the downstream processing, the recovery of initial nitrogen in pellets was 33% lower than in ammonium sulfate solution. Regarding the environmental impact of digestate application to soil, mechanical solidliquid separation showed the potential to reduce N₂O emissions. Contrary to expectations, pelletizing of dry solid boosted the emissions, which was linked to the properties and composition of the pellet. Here, indigenous microbial activity triggered N₂O production and release from denitrification immediately after wetting. Overall, the present work has shown that the subsequent processing of separated solid or liquid digestate generates different products with individual benefits and challenges. Solid digestates are characterized by a high share of recalcitrant organic compounds and therefore can serve, e.g., as soil improver. After processing to pellets, they can be easily transported, stored, and commercialized. However, it is questionable whether the pelletizing process is advisable, since pellets emitted a considerable amount of GHGs during utilization. Liquid processing produces ammonium sulfate solution, which can be utilized as a valuable inorganic fertilizer rich in plant-available N. Besides the discussed advantages, a final decision for or against digestate processing always depends on individual factors, such as local situation and financial means. Smart decision-making must include fertilizer properties, technological performance, and economic feasibility. With a view to future research, additional aspects were identified, such as returning to a laboratory-scale biogas plant for more accurate digestate sampling and analysis, consideration of digestate storage and transport, and economic evaluation of the entire digestate value chain including the assessment of digestate fertilizer value (expressed as e.g., N use efficiency or N fertilizer replacement value).
Interactions of nitrogen-related, growth promoting bacteria with Miscanthus × giganteus : impact and mechanism
(2020) Liu, Yuan; Ludewig, Uwe
The highly nitrogen-use efficient biomass grass Miscanthus is a host of the bacterial endophyte Herbaspirillum frisingense. While Herbaspirillum frisingense has the genetic competence to fix nitrogen, the plant-associated microbiome may also contribute to this nitrogen efficiency. Furthermore, the costly field establishment of the sterile perennial Miscanthus × giganteus from rhizomes is a severe constraint for expanding the production area of this commercial biomass crop. In this study, the effect of Herbaspirillum frisingense inoculation on stem-cutting sprouting, shoot biomass and other yield parameters was investigated. I studied how the inoculation impacts on the M. × giganteus associated microbiome and how the long term differences in nitrogen fertilizer amount modulated the M. × giganteus associated microbiome. This was studied in a 14 year-old field trial of M. ×giganteus fertilized with various amounts of nitrogen. Stem cutting inoculation improved the shoot sprouting and establishment success of Miscanthus × giganteus in the greenhouse. In a small field trial, plant height and biomass from inoculated sites were significantly larger in the second year after establishment, but already after one year after inoculation, the bulk soil, rhizosphere, root and rhizome microbiomes were almost devoid of Herbaspirillum. This beta-proteobacterium may colonize the shoot of Miscanthus × giganteus more efficiently. Major differences between bacterial communities were determined by plant-soil compartments and less by the plant organs, while both inoculation and nitrogen had little effects on these communities. Compared to the little effect on the soil, rhizosphere and root microbiomes, the rhizome microbiome was massively modulated by both inoculation and nitrogen level. In the rhizome, several proteobacteria, which are associated with plant growth promoting functions, were enriched by inoculation, while N2-fixing-related bacterial families were favored by long-term nitrogen-deficiency plots, but denitrifier-related families were depleted. The studies suggest that H. frisingense inoculation may improve establishment of Miscanthus stem cuttings and has long-lasting effects on the rhizome microbiome diversity, despite low rhizocompetence and low root abundance. Meanwhile, the rhizome could be a potential nitrogen fixation factory. The organ-specific, nitrogen-related bacterial communities are modulated by long-term different nitrogen supply and are mainly shaped by the plant, which provides guidance for optimizing Miscanthus sustainable cultivation.
Linking microbial abundance and function to understand nitrogen cycling in grassland soils
(2017) Regan, Kathleen Marie; Kandeler, Ellen
This thesis characterized spatial and temporal relationships of the soil microbial community, the nitrogen cycling microbial community, and a subset of the nitrogen cycling community with soil abiotic properties and plant growth stages in an unfertilized temperate grassland. Unfertilized perennial grasslands depend solely on soil-available nitrogen and in these environments nitrogen cycling is considered to be both highly efficient and tightly coupled to plant growth. Unfertilized perennial grasslands with high plant diversity, such as ours, have also been shown to have higher soil organic carbon, total nitrogen, and microbial carbon; greater food web complexity; and more complex biological communities than more intensively managed grasslands or croplands. This made the choice of study plot especially well-suited for characterizing the relationships we sought to identify, and made it possible to detect spatial and temporal patterns at a scale that has heretofore been under-examined. The first study used a combination of abiotic, plant functional group, and PLFA measurements together with spatial statistics to interpret spatial and temporal changes in the microbial community over a season. We found that its overall structure was strongly related to the abiotic environment throughout the sampling period. The strength of that relationship varied, however, indicating that it was not constant over time and that other factors also influenced microbial community composition. PLFA analysis combined with principal components analysis made it possible to discern changes in abundances and spatial distributions among Gram-positive and Gram-negative bacteria as well as saprotrophic fungi. Modeled variograms and kriged maps of the changes in distributions of exemplary lipids of both bacterial groups also showed distinct differences in their distributions on the plot, especially at stages of most rapid plant growth. Although environmental properties were identified as the main structuring agents of the microbial community, components of those environmental properties varied over the season, suggesting that plant growth stage had an indirect influence, providing evidence of the complexity and dynamic nature of the microbial community in a grassland soil. The second study took the same analytical approach, this time applying it to abundances of key members of the soil nitrogen cycling community. Marker genes for total archaea and bacteria, nitrogen fixing bacteria, ammonia oxidizing archaea and bacteria, and denitrifying bacteria were quantified by qPCR. Potential nitrification activity and denitrifying enzyme activity were also determined. We found clear seasonal changes in the patterns of abundance of the measured genes and could associate these with changes in substrate availability related to plant growth stages. Most strikingly, we saw that small and ephemeral changes in soil environmental conditions resulted in changes in these microbial communities, while at the same time, process rates of their respective potential enzyme activities remained relatively stable. This suggests both short term niche-partitioning and functional redundancy within the nitrogen cycling microbial community. The seasonal changes in abundances we observed also provided additional evidence of a dynamic relationship between microorganisms and plants, an important mechanism controlling ecosystem nitrogen cycling. The third study determined spatial and temporal interactions between AOA, AOB and NOB. These steps are related in both space and time, as the ammonia-oxidizers provide the necessary substrate for nitrite-oxidizers. Using a combination of spatial statistics and phylogenetic analysis, our data indicated seasonally varying patterns of niche differentiation between the two bacterial groups, Nitrospira and Nitrobacter in April, but more homogeneous patterns by August which may have been due to different strategies for adapting to changes in substrate concentrations resulting from competition with plants. We then asked a further question: was the microbial structure at sampling sites with high NS gene abundances fundamentally different from those with low NS gene abundances? Using a phylogenetic approach, the operational taxonomic unit composition of NS was analyzed. Community composition did not change over the first half of the season, but by the second half, the relative proportion of a particular OTU had increased significantly. This suggested an intraspecific competition within the NS and the possible importance of OTU 03 in nitrite oxidation at a specific period of time. Observed positive correlations between AOA and Nitrospira further suggested that in this unfertilized grassland plot, the nitrification process may be predominantly performed by these groups, but is restricted to a limited timeframe.
Managing crop health by mineral nitrogen fertilization and use of different chemical nitrogen forms
(2023) Maywald, Niels Julian; Ludewig, Uwe
Maintaining plant health is one of the most difficult but crucial challenges in crop production to realize plants’ full genetic potential. It is lowered by a variety of abiotic and biotic stresses that are becoming more severe and unpredictable due to climate change and its consequences. In addition, the use of chemical synthetic pesticides is increasingly criticized for endangering sensitive natural resources and possible pesticide residues in food and environment. Avoiding or reducing the use of chemical synthetic plant protection products makes the control of phytopathogenic pests even more difficult. Therefore, in addition to optimizing various management measures such as tillage, sowing time, row spacing or crop rotation, mineral nitrogen (N) fertilization and the targeted application of N forms must be utilized to reduce abiotic stress factors and the infestation pressure of certain pests to ensure high yield performance. Consequently, several experiments were conducted to better understand how mineral nitrogen fertilization and forms can improve plant health by increasing plant resistance to abiotic stressors, particularly repeated drought stress and nutrient (P) deficiency, and to biotic stressors, such as relevant phytopathogenic fungi. It was found that with respect to repeated drought stress, maize plants receiving supplemental nitrogen during the recovery period after an early drought stress were better able to cope with late drought stress. In this context, N fertilization could help the plant to maintain its photosynthetic activity under drought stress. Additionally, plants repeatedly exposed to drought stress recovered faster with N fertilization due to transiently higher antioxidant levels and higher production of reactive oxygen species. A further experiment revealed that depending on the maize genotype, ammonium as a form of nitrogen has a positive effect on the availability and uptake of phosphorus compared to nitrate, depending on the maize genotype. This observation could be attributed not only to the acidifying effect on the pH of the rhizosphere, but also to the increased abundance of various phosphorus-solubilizing bacteria and arbuscular mycorrhizal fungi under ammonium nutrition. Together this could provide an enhanced P availability, which ultimately reduces plant stress and improves physiologically resistance leading to a reduction in disease risk. Nevertheless, studies revealed that high N fertilization in most cases promotes disease attack and makes the plant more susceptible to pathogens. Scrutinization of this observation indicated that N fertilization enhances infestations of biotrophic pathogens, especially in wheat, while necrotrophic fungi were attenuated. Overall, the complex relationship between plant pathogens and nitrogen nutrition appears to be highly variable due to dynamic factors such as the soil, microorganisms in the rhizosphere, environmental factors, and the host plant, making it difficult to give definite statements about the effects of nitrogen nutrition on pathogen occurrence. Thus, the form of nitrogen could be a promising way to target nitrogen fertilization against individual pathogens. With regards to the previous research, experiments on the influence of N form on pathogen infection, revealed that wheat leaves inoculated with the foliar pathogen Blumeria graminis f. sp. tritici (Bgt) were comparatively less infested when fertilized with nitrate or cyanamide compared to ammonium. After contact with the pathogen, an enhanced defense response in form of increased production of protective substances, indicated by increased concentrations of hydrogen peroxide and superoxide dismutase, and increased antioxidant potential, was detected. Further, it was observed that ammonium fertilization resulted in lower bacterial richness in the plant rhizosphere and higher fungal richness compared to nitrate supplementation. Additionally, a pronounced effect of ammonium fertilization on rootcolonization by important fungal pathogens such as Gaeumannomyces graminis var. tritici (Ggt) and Bgt was found. Regarding the experiment with maize under low P conditions, it appears that ammonium is able to promote both pathogenic and beneficial fungi in cereal crops. Thus, nitrate fertilization appears not only to suppress the occurrence of fungi, but may also promote pathogen-antagonistic bacteria, which in turn have a positive effect on fungal disease suppression.
Microbial consortia as inoculants for improvedcrop performance
(2020) Bradácová, Klára; Neumann, Günter
The use of microbial consortia products (MCP) based on combinations of different strains of plant growth-promoting microorganisms (PGPM) and frequently also on non-microbial bio-stimulants (BS) with complementary beneficial properties, is discussed as a strategy to increase the efficiency and the flexibility of BS-based crop production strategies under variable environmental conditions. Moreover, MCP application aims at the restoration of plant-beneficial, soil biological processes disturbed by soil degradation and intensive use of agro-chemicals. This PhD thesis was initiated to characterize the modes of action and the potential advantages of a representative commercial MCP formulation over selected single strain PGPM inoculants, with documented effects on plant growth promotion and pathogen suppression. In total, nine pot and field experiments were conducted with three crops (maize, spring wheat, tomato) on seven different soils with three organic and inorganic fertilization regimes. Only in one out of nine experiments conducted in this thesis, clear evidence for superior MCP performance was detectable in a drip-irrigated tomato field experiment conducted under the challenging environmental conditions of the Negev desert in Israel (Bradáčová et al., 2019c). This finding demonstrates that MCP inoculants can exhibit an advantage over single strain inoculants but not as a general feature. Selective interactions with the type and dosage of the selected fertilizers, as well as avoidance of inhibitory effects on root growth during MCP rhizosphere establishment, have been identified as critical factors. A further characterization of the conditions, promoting beneficial plant-MCP interactions is mandatory for a more targeted and reproducible MCP application.
Nitrogen-rich and lignocellulosic biomass for biogas production : methane yield potentials, process stability and nutrient management
(2023) Morozova, Ievgeniia; Lemmer, Andreas
A sustainable energy supply and bio-based economic processes are of central importance for the future development of many Eastern European countries. Due to the large agricultural potentials of these countries, bioenergy systems can make a significant contribution to sustainable electricity and heat production if they are reasonably integrated into an energy supply structure based on various renewable energy sources. This requires the use of regenerative starting products and the complete utilisation of all by-products of the overall process. With such a cradle-to-cradle approach, biogas technology can be a central component of future energy systems. The focus of this study is on Ukraine. In the future, bioenergy villages can make a decentralised contribution to a sustainable energy supply in this country. This study aims to determine the methane yield potential of various energy crops from Ukraine, investigate the process stability during fermentation in biogas plants and derive concepts for optimized digestate management. Seven different crops with a total of 22 varieties were investigated for their specific biomass yields, methane yields and areal methane yields. The crops were cultivated in Ukraine. The biogas production potential of the collected crop samples was determined using the Hohenheim Biogas Test in Germany. The Ukrainian variety “Osinnii zoretsvit” of miscanthus, “Giganteus” species, from the 8th year of vegetation, harvested at the stem elongation stage, resulted in the highest areal methane yield of 7404.55 ± 199.00 m3*ha-1 and the lowest N requirement per unit methane produced (23.41 ± 7.18 gN*m-3) among all the studied crops. The maize variety "Svitanok MV" (FAO 250) had the highest value of areal methane yield of 6365.67 ± 55.49 m3*ha-1 among the annual crops when harvested at the stage of wax maturity; remarkable was its unusually high specific methane yield of 0.41 ± 0.00 m3*kg-1VS. The Ukrainian sugar sorghum variety "Favoryt", harvested at the beginning of flowering, had an areal methane yield of 5968.90 ± 82.70 m3*ha-1, making it an attractive alternative energy crop for Ukraine. In the second part of the work, experimental investigations were carried out to test how N-rich substrates influence the stability and efficiency of the biogas process. For this purpose, different variants with various N-increase rates of the input materials at two initial concentrations were evaluated in the laboratory. The continuous trials were conducted over a period of 33 weeks. The modelling procedure was applied to evaluate the effects of TAN (total ammonia nitrogen) and FAN (free ammonia nitrogen) on the degree of methane production inhibition for all scenarios studied. It was concluded that the higher the N-increase rate in the feeding regime, the more methane production is inhibited. The maximum nitrogen concentration in the digestate achieved during stable fermentation processes in this study was 11.5 g*kg-1FM, which corresponded to the values of TAN and FAN of 9.07 g*kg-1FM and 0.85 g*kg-1FM, respectively. These values are much higher than those reported up to now in the literature. At the same time, process efficiency decreased with increasing nitrogen concentrations. As a final step, the technology for nutrients recovery from digestate was developed and tested in this work. First, the digestate separation with a screw press separator was carried out as a "benchmark" at the research biogas plant "Unterer Lindenhof" on a technical scale. Subsequently, a methodology for digestate separation at laboratory scale was developed based on a tincture press, which corresponds to the technology used in practice. The effect of pretreatment of digestate with various biocoal-based additives was studied. In this study, six variants of biocoals synthesized at either 350 °C or 600 °C and partially impregnated with Mg or Ca before pyrolysis were produced. Different reaction times and conditions between the biocoals and the digestate were tested. The results on nutrient removal showed that the biocoals impregnated with Mg prior to pyrolysis had a positive effect on nutrient removal efficiency. The Mg-impregnated biocoal synthesised at 600 °C showed removal efficiencies for NH4+, P and K of 56.04%, 66.66% and 51.77%, respectively. These values were much higher than those for the control variant and much higher than the values found up to now in the literature. By using the nutrient-rich solid fraction of the digestate as fertiliser to cultivate bioenergy crops for further use in biogas production, the production cycle is closed, and the cradle-to-cradle approach is achieved.
Nitrous oxide emissions and mitigation strategies in winter oilseed rape cultivation
(2019) Kesenheimer, Katharina Anne; Müller, Torsten
After carbon dioxide and methane, nitrous oxide, is the third most important greenhouse gas in the atmosphere. Nitrous oxide contributes to the greenhouse gas effect as well as to ozone depletion. The major portion of anthropogenic N2O emissions are stimulated by the use of nitrogen fertilizers in agriculture. The main processes for N2O production in soils are nitrification and denitrification. Various environmental and management factors such as precipitation, soil type, tillage, and crop residues affect these processes. N2O emissions can occur substantially in the post-harvest period. In Germany, approximately 50 % of the annual N2O emissions can occur during winter. This exhibits the importance and necessity of annual data sets which prevent misinterpretations instigated by investigations limited to the vegetation period. Winter oilseed rape is the most important raw material for biodiesel in Germany. As of 2018, the framework of the European Renewable Energy Directive requires that the use of biofuels achieve GHG savings of at least 50 % compared to fossil fuels. Feedstock production for biodiesel contributes more than half of the total GHG emissions. To close the nutrient cycle with renewable energy, digestate from biogas plants can be used as a substitute for mineral N fertilizer permitting the reduction of GHG emissions in the production process of synthetic fertilizers. When compared to other crops, OSR has a high N demand. The low N removal by the seeds results in inefficient use of nitrogen and therefore a high N surplus in the soil which is susceptible to gaseous or leaching losses to the environment. Another potential risk for N2O losses are crop residues after harvest. The type of soil cultivation can have both positive and negative implications on N2O emissions which depend, among other things, on tillage depth, soil type and moisture. Results from studies measuring N2O emissions from different tillage systems are contradicting and site dependent. This study aims to investigate the effect of (a) N fertilization (mineral and organic), (b) nitrification inhibitors, (c) crop residues and (d) tillage on direct N2O emissions and, inter alia, yield and soil nitrogen dynamics in OSR production. N2O emissions were monitored for three years over a range of N fertilization levels at five study sites chosen so as to best represent typical winter oilseed rape production in Germany. Furthermore, the effect of the nitrification inhibitor (NI) TZ+MP (1H-1,2,4-triazole and 3- methylpyrazole) with digestate is investigated. Additional experiments for 15N labelled crop residues, nitrification inhibitor DMPP (3,4-dimethylepyrazole phosphate) with mineral fertilizer and soil tillage were implemented. A high spatial and temporal variability in N2O fluxes over all sites was observed. At each site, increased N2O fluxes were often detected after N fertilization in conjunction with rainfall events. During the first six weeks after harvest we frequently observed increased N2O fluxes following rainfall. In this postharvest period of winter oilseed rape, nitrate contents in the top soil were generally elevated. There were no considerable N2O pulses observed during thawing of frozen soil. Winters were mild without any severe frost periods in all three surveyed years which could be a reason for the generally low N2O winter fluxes observed in this study. On all examined sites, increasing N fertilization significantly enhanced N2O flux rates. Data obtained during the study were used to augment an existing model, wherefrom a new emission factor for OSR can be calculated. Assuming a quantity of 200 kg N ha-1 the global fertilizer-related emission factor derived from the exponential model was 0.6 %. This factor is within the uncertainty range of the EF1 IPCC emission factor (0.3 % – 3.0 %), but about 40 % lower than the 1 % IPCC default. The nitrification inhibitor (NI) TZ+MP combined with digestate mitigated the N2O fluxes significantly across all study sites and experimental years. As already noted in the fertilizer experiment, a high spatial and temporal variability in N2O fluxes over all sites was observed. The magnitudes of the N2O fluxes also showed similar trends. Over the entire investigation, the application of the NI significantly reduced annual N2O emission by a factor of three. During the fertilization period this mitigation effect was six times significant. This clearly emphasizes the importance of annual data sets to avoid overestimating NI effects.
Profiling of physiological responses and quality aspects in Vitis vinifera L. as influenced by aspects of N application
(2019) Lang, Carina Paola; Zörb, Christian
Viticulture and the vinification of vines (Vitis vinifera L.) to wine is an important branch in agriculture world-wide. Berry quality and the associated wine quality are the driving factors here. Nitrogen (N) is the most important plant nutrient for the grapevine. In addition to its influence on vegetative and generative growth, it determines significantly the metabolite composition and the oenological parameters of the grape berry. Nitrogen is present in various forms, such as nitrate, ammonium or amino acid, in the individual plant organs and is used differently by the grapevine. Grapevines are believed to have the ability to assimilate N in various forms, which in turn may affect the quality of berries and the resulting wine. For a better understanding of the effects of N on berry and wine quality, knowledge of which N-form can be assimilated by the vine and the way that this affects oenological parameters and quality-giving metabolites is essential. To this end, several investigations were carried out at various test levels, starting with hydroponic experiments, a pot experiment and a further field experiment, and on the matured wine. The various N-forms of nitrate, ammonium, urea and the amino acids arginine and glutamine were applied, following which the plant-physiological reactions of the grapevine and quality-determining parameters in berry and wine were measured. Furthermore, a metabolite profile with a focus on phenolic components was prepared and a sensory analysis of the wine was performed. The grapevines in the hydroponics and pot experiments were treated with 4 mM total N. The grapevines in the field experiment were fertilized with 60 kg N ha-1, calculated in relation to the block size. The rootstocks SO4 and RU140 showed similar patterns of N assimilation with respect to the N-form but differed significantly with regard to the level of growth and N content among all N-forms. The N-sensitive rootstock SO4 reacted more strongly than the rootstock RU140 and, therefore, SO4 was used for further experiments. This suggests that grapevines are able to assimilate the amino acids glutamine and arginine, as also shown by the enzymatic nitrate reductase activity and the increased abundance of the transcripts of nitrate reductase and nitrite reductase. Nevertheless, the N-forms NO3- and NH4+ were preferentially assimilated. The assimilation under urea treatment was significantly reduced. In addition to the N-form, the amount of N applied had an influence on N assimilation in the grapevine. With increasing amounts, the vegetative and generative growth increased up to a threshold. However, if this threshold was exceeded, both were significantly reduced. If the grapevine is overfertilized, the sink : source ratio changes, which will lead to a change in the biomass production and furthermore to a saturation and storage of N. In addition, competition for assimilates occurs, this alters the N distribution and N availability within the plant and the berries. The N-form has no influence on berry yield. The oenological and chemical parameters of the must and the wine are of enormous importance for product quality. The key components include pH and acidity, which contribute significantly to the organoleptic properties of wine. Both factors are influenced by the N-form and the amount of N offered. As the amount of N increases, the pH increases and the acidity decreases. The N-forms NO3- and urea and, the zero application (without additional N) show the highest influences. The must weight is a defining factor reflecting the berrys maturity and thus the time of harvest. As the amount of N increases, the must weight decreases. On the one hand, an increased N amount leads to lower acidity in the berry, indicating that more sugar is being stored and that the berry is in an advanced stage of maturity. On the other hand, an increased N amount leads to a decreasing must weight, which leads further to a maturation delay. The total phenolic content increases with increasing N amount, but is highest following zero N application. Tentative phenols measured in the metabolite profile are markedly down-regulated after urea treatment and are upregulated with NO3- following NH4+ treatment. This result might arise from reduced N assimilation in the root and thus reduced N availability for the berries. The influence of N on the aroma and sensory aspects of wine is controversial. The individual aroma attributes show both an increase and a decrease in their intensity attributable to N, mainly urea and NO3-. A marked influence between N-treated vines and the zero application is also apparent. However, these contrasting results clearly show that aroma and thus the sensory characteristics of wine can be influenced both positively and negatively. The results of the aroma and sensory evaluation in the agroforestry system underline once again the controversial influence of N on the sensory features of wine; no significant influence was measured. In summary, N has a significant influence on the vegetative and generative growth of the grapevine. The influence of N can be both positive and negative and is in part directly or indirectly linked to wine quality and should therefore not be ignored.
Rahmenbedingungen für eine vereinfachte „gabenreduzierte“ N-Düngung zu Winterweizen (Triticum aestivum L.)
(2018) Makary, Thomas; Müller, Torsten
The split N-fertilization with CAN in three or four doses was considered a measure to improve the nitrogen supply of winter wheat in the past and still is considered a guarantor for good yield and quality. The split N-fertilization with CAN is also recommended to synchronize and harmonize N-demand of the plants as well as soil N-content. The aim of the current study was to analyze simplified (reduced number of N-servings) CAN strategies to winter wheat and the necessity of split nitrogen servings in order to achieve yield and quality aims. This interest was occasioned by impressive results of experiments on farmers’ fields using simplified N- strategies with CAN. Simplified CAN fertilization strategies are able to produce high grain yield and protein contents with winter wheat when the N-supply is ensured. Therefore, the common split N-servings with CAN are not necessary. Simplified strategies with UAN seem to be possible, but this requires further research on application techniques to reduce NH3 losses. Simplified CAN fertilization strategies were tested based on modern wheat varieties and the high plasticity in the development of the yield compounds. Modern wheat varieties show low harvest-indices which is important to reduce the risk of lodging. Furthermore, these varieties are able to overcome omitted N-servings through remobilization of N in the plants. Suboptimal conditions during the development within one important growing stage can be compensated during later growing stages when the growing conditions are better. These properties in combination with a late first application (BBCH 29/31) of N turned out to be the “gold standard” in our experiments. Reduction processes during the tillering (BBCH 25/27) period when N is applied confirm these findings. In addition, the application date for the heading stages (BBCH 49/51) when temperatures are high and conditions very dry have to be considered. Simplified N-fertilization systems can also be applied on Luvisols if the soils are not long-term fertilized by liquid manure. The positive soil characteristics of these soils and the high soil-borne fertility support the approach with simplified CAN strategies. In this situation, N-leaching into deeper soil layers is not likely as high precipitation rates in a short time would be necessary to cause this. In fact, a long term liquid manure application with high rates is not necessary when simplified CAN treatments are applied. Moreover, high N amounts in soils caused by long term liquid manure applications are a risk for N-losses and environmental pollution. Notwithstanding the above, organic fertilizers like liquid manure show positive effects on the soil chemistry and the physical properties of the soil. It is important to apply a system to better include the N fertilization effect of liquid manure during the vegetation period. Additionally, simplified CAN fertilization reduces the work effort on the farms. Currently, especially for livestock farms, which rely on N-fertilization, simplified CAN treatments are a good alternative to the common practice. Whereupon on shallow or sandy soils the approach with simplified CAN treatments should be restricted since these soils mostly show low water holding capacities and high percolate water rates. Under suboptimal growing conditions with high precipitation rates simplified CAN treatments can be a risk for the environment and the groundwater. Apart from that, the volatile weather conditions are the most important factor for yield and quality outcome. Mild conditions during the early winter lead to prolonged growing of the plants. In spring the number of tillers per m-2 is already determinated. Therefore, a combination of N doses at the beginning of the growing season in order to promote the number of tillers doesn´t yield the aimed results. The properties of modern wheat cultivars, tested soils, weather conditions and constraints of simplified CAN treatments show the complexity of N fertilization of winter wheat. Standard measures like the common split CAN fertilization are neither wrong nor ideal to create high yield and protein contents with a minimum of input. The most important items for a successful wheat production are high knowledge and attention levels for the plants and growing conditions. Combining the fertilizer requirement calculation and the knowledge on the field yield potential, the yield and quality of winter wheat can be optimized with a minimum of input.
Reaktionen einer Weizen-Wildkraut Gemeinschaft auf erhöhtes CO2 im FACE Experiment: Proteomik, Physiologie und Bestandesentwicklung
(2006) Weber, Simone; Fangmeier, Andreas
The enhancement of the atmospheric carbon dioxide concentration in the last 150 years due to human activities is one of the main components of global change. For the future, different scenarios predict a steadily increase of carbon dioxide in our atmosphere. As carbon dioxide is the most important carbon source for plants, higher CO2 concentrations have the potential to cause direct effects on plant metabolism and vegetation development. Until now almost all of the studies concerning the effects of elevated CO2 on plants were carried out under controlled conditions, whereas the effects under natural conditions are in-vestigated at only 33 sites worldwide. The aims of this study were to investigate the effects of elevated carbon dioxide on a plant community under natural conditions with regard of (i) the plant proteome, (ii) the plant physiology, (iii) the vegetation development and (iv) the potential interactions between these criteria. Therefore a Mini-FACE system was used to expose a plant community composed of wheat and weeds to two different treatments: (a) Ambient (ambient CO2 concentration, circa 380 ppm) and (b) FACE (Ambient + 150 ppm CO2). The study mainly focussed on the bio-chemical and physiological reactions of spring wheat (Triticum aestivum cv. Triso) as a crop species and wild mustard (Sinapis arvensis L.) as a weed species on carbon dioxide enrich-ment. The SELDI-TOF-MS technology was applied for the first time in the topic of carbon dioxide impacts on plants. The technology provides the opportunity to quantitatively and qualitatively investigate low molecular weight proteins with low abundances, which has been difficult to realise with the standardized methodology in proteomics until now. In addition to the biochemical and physiological analysis, the vegetation development was investigated continuously during the vegetation period using non-destructive methods. This included the assessment of species phenology and species dominance. The results of the performed study show that the carbon dioxide enrichment affects the protein profiles of both species wheat and wild mustard. Interestingly, many alterations in the protein concentrations were found, but no protein could be detected to be exclusively ex-pressed under CO2 treatment. The degree of modification in both species was influenced by their developmental stage. Particularly the protein profile of wheat leaves was strongly in-fluenced during generative plant development, therefore the plants seems to be highly sensitive to environmental changes during this developmental stage. Altogether three proteins were identified which were affected by CO2 treatment. The first protein, the saccharose-H+-symporter protein, was detected in the grain of spring wheat and is associated with the plant?s primary metabolism. This protein plays an important role in controlling the import of saccharose in developing grain. Consequently, elevated CO2 seems to regulate the allocation of assimilates in an active way by influencing the saccharose-H+-symporter concentration in the grain of spring wheat. Furthermore, the remaining two proteins, the PR4 protein localized in the grains and the LRR-kinase protein accumulated in the leaves of spring wheat, are associated with the secondary plant metabolism and they also responded to the elevated CO2 concentrations. These proteins are linked with defense reactions of the plants against patho-gens. The elevated CO2 concentrations caused a decrease in defense recognition in the vege-tative tissue. If the plant is infected by pathogens this down-regulation could result in a ne-gative impact. The concentration of soluble proteins and of total nitrogen decreased in the leaves of spring wheat whereas the C/N ratio increased. Despite this the relative concentration of Chlorophyll a was not affected and therefore an accelerated growth of the plants due to the carbon dioxide enrichment can be excluded. Thus the detected pattern of responses suggests an enhanced nitrogen use efficiency under increased CO2 concentrations. The biomass of single spring wheat plants was unaltered during the vegetation period whereas other investi-gations in parallel showed an enhanced growth and a greater yield of spring wheat at the end of the vegetation period. Species dominance of wheat and weeds was neither influenced in the first nor the second year of investigation with regard to CO2 enrichment. The results indicate that annual crop systems under natural conditions indeed exhibit strong reactions concerning proteomics and physiology, but not concerning the plant development probably due to a relative short time of exposition. Based on long term considerations the detected reactions of the plant proteome may play an important role in the breeding of optimal adapted plants.
Regulation of ammonium transport in Arabidopsis thaliana
(2022) Ganz, Pascal; Ludewig, Uwe
The overarching question of this thesis deals with how plants ensure the selective uptake of ammonium while maintaining ion and pH homeostasis. A key component of this is ammonium transporters (AMTs) with high affinity towards their substrate, which are at the same time part of a multilayered protection system against uncontrolled ammonium influx. Conserved protein sequences inside the transporter were analyzed as well as the regulatory system based on post-translational modification of the transporter.

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