Browsing by Subject "Nordchinesische Tiefebene"

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    Air pollution by particulate matter and ammonia at suburban and rural sites in the North China Plain
    (2011) Kopsch, Jenny; Fangmeier, Andreas
    The thesis presented here was conducted at the Institute of Landscape and Plant Ecology at the University of Hohenheim within the scope of the first Sino-German International Research Training Group (IRTG) ?Modeling Material Flows and Production Systems for Sustainable Resource Use in Intensified Crop Production in the North China Plain?. The project is jointly performed by the University of Hohenheim and the China Agricultural University (CAU) Beijing and financed by the German Research Foundation and the Chinese Ministry of Education. The present study was performed in the framework of subproject 1.3 of the IRTG which had the major aim to study air pollution and atmospheric nitrogen deposition in the North China Plain (NCP). For that purpose data on concentrations of atmospheric pollutants were required in order to assess the level of exposure to pollution of both population and environment in the NCP. This study represents the initial work in the NCP in 2005 and 2006 in order to monitor air pollution and dry nitrogen deposition and its effects. Within this work experiments were conducted to monitor concentrations of PM2.5, PM10, TSP, NOx and NH3 in the NCP. Ammonia monitoring and biomonitoring were synchronised in order to study the potential effects of nitrogen deposition on Molinia caerulea. Since there was no air monitoring network existing in the NCP at the onset of this study, one major part of the work consisted of setting up and testing of European measuring devices under the special conditions in the NCP. The measurements have been therefore the starting point of field observations in the NCP and especially the PM monitoring operated at the agricultural study site Dongbeiwang (DBW) was a key element of the field campaign in order to study pollutant concentrations in the NCP but also the influences of the nearby megacity Beijing. Sampling with the High Volume Sampler Digitel DHA 80 proved to be suitable for the conditions in the NCP. The levels of daily PM10 measured in this study exceeded European (50 µg m-3) and Chinese (150 µg m-3) thresholds by far. Also the EU standard for the number of tolerated daily exceedances (35 times per year) was not met in the Beijing area. Results of PM10 measurements at DBW showed 126 exceedances of the daily mean European threshold in only 128 days in 2005 and 43 exceedances in 44 days in 2006. The maximum daily mean of 412 µg m-3 also reflects the high PM10 peak concentrations in the study region. Results of daily PM2.5 measurements at DBW in 2005 and in 2006 showed exceedances of the U. S. daily average air quality standard of 35 µg m-3 for 99 % of the data (mean value in 2005: 222 µg m-3 and in 2006: 123 µg m-3). High daily PM2.5 peak concentrations were observed especially during the winter. Overall, only under extreme meteorological conditions such as heavy rainfalls PM levels of less than 50 µg m-3 were detected at DBW. Diurnal and hourly variations of PM levels were demonstrated. Glass fibre filters proved to be suitable for the collection of high PM loads whereas quartz fibre filters are much more suitable for the laboratory analysis of N species. Determination of particulate ammonium and nitrate on glass fibre filters of spring season was tested and showed averaged concentrations of 2.4 and 13.1 µg m-3 (TSP) and 8.0 and 11.6 µg m-3 (PM10), respectively. The mass spectrometric measurements were challenging due to the filter material and δ15N/14N ratios were found to be very heterogeneous ranging from -3.0 ? to 44.3 ?, referring to both filter types. The simple and low-cost passive sampling method used (Radiellos®) also proved to be an appropriate tool for evaluating ammonia exposure in the NCP. The seasonal ammonia levels were in the range from 9 to 43 µg m-3 at DBW, Wuqiao and Quzhou, which indicates intensive agricultural activity in the whole NCP. No relationship was found between atmospheric ammonia levels and plant growth parameters of Molinia caerulea and thus, growth of these test plants was not related to gaseous dry deposition of ammonia. The NOx measurements in NCP did not yield reliable data within given time. Overall, multiple sources are assumed to interplay at the study site namely, local dust (such as harvest), traffic, biomass burning, coal combustion, secondary aerosol and industrial emissions from Beijing area. Long-range transported air pollutants such as pollutants from Hebei and Shandong province or deserts as well as the weather pattern greatly influence the atmospheric pollution at DBW and NCP in general.
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    Economic evaluation of nitrogen application in the North China Plain
    (2008) Barning, Roland; Zeddies, Jürgen
    Today, China had solved its long-standing problem of inadequate grain production, but there are two new targets for rural China. Firstly, one goal is rural development towards an improved income generation of rural households in order to slow down the increasing income disparity in China, especially between rural and urban residents. Secondly, decades of inefficient utilisation of resources and high consumption of materials led to overexploitation of water and land resources. Over-fertilisation and low nitrogen use efficiency are representative for the production system in the North China Plain, which is characterised by small-scale farm households who traditionally cultivate winter wheat and summer maize. This thesis is embedded in the Sino-German Research Training Group "Modeling Material Flows and Production Systems for Sustainable Resource Use in Intensified Crop Production in the North China Plain", a cooperation of the University of Hohenheim in Stuttgart and the Chinese Agricultural University in Beijing. The overall hypothesis of this project is that substantial changes in farming systems and management practices can reduce environmental pollution and at the same time stabilise or increase income of farmers. As a subproject, this thesis focuses on the identification and evaluation of applicable instruments for this goal. The final target of this thesis is the simulation of scenarios in order to estimate the impact of identified instruments on the nitrogen balance as well as on the net income of farm households. The literature review indicates that nitrogen application in the cultivation of wheat and maize in the North China Plain shows a broad variation. A considerable high share of farm households applies nitrogen input levels far beyond the crop demand. This situation raises the question, what do over-fertilising farm households have in common or in another way, which factors lead to nitrogen overuse. This question is the basis of the discussion on applicable instruments to reduce the described nitrogen overuse and finally the intended simulation approach. The analysis of impact factors on the nitrogen application level requires a broad analysis of the cultivation system, the farm household characteristics, and the income sources of the farm households. The descriptive results of the farm survey on 340 farm households in the North China Plain conducted in 2005 are presented in chapter 5. The farming system at the survey sites is characterised by farm households, who cultivate the wheat and maize rotation system. In most cases, it is extended by cash crops such as cotton or peanuts. The farm size is on average 0.5 ha of allocated farmland per farm household. About two thirds of the farm households have some kind of additional off-farm income source, which usually exceeds the income share from farming. Farm households without off-farm income sources generate only half of the average farm household income. The average farm household income reaches 10 150 ¥ (1 015 ?) per year, but there is a broad variation within the survey sites as well as between the surveyed townships. As mentioned already, over-fertilisation is prevalent for farming in the North China Plain. On average 360 kg of nitrogen per ha are applied in wheat and 220 kg in maize, while CHEN (2003) recommends 180 kg per ha for wheat and maize. Further, fertilizer costs are the major share of variable costs at all cultivated crops. The major nitrogen fertilizers are urea and ammonium carbonate. Nearly 80 per cent of the applied nitrogen originates from these fertilizers. Manure is only applied in wheat and it plays only a minor role as nitrogen source. About one third of the farm households cultivates wheat exclusively for own consumption and these farm households apply more nitrogen in wheat cultivation than the remaining farm households. The average yield of 5.7 t per ha in wheat and of 6.4 tons in maize enables gross margins of about 4 000 ¥ (400 ?) per ha, while in cotton and cultivation of peanuts the average gross margin is twice this amount. In chapter 6 the efficiency of the agricultural system is analysed. This analysis includes an impact analysis on nitrogen input and yield as well as an economic and ecologic optimum analysis of the nitrogen input. Nitrogen application rates show a broad variation at all cultivated crops. The impact analysis on nitrogen input does not show any clear and unique influence from the income structure of the farm household. Hence, additional cash income and less available family work force for farm work have no impact on the nitrogen application level. The analysis of the fertilizer costs instead of the amount of applied nitrogen confirms this statement. The nitrogen input analysis provides the nitrogen price as major impact factor. Higher nitrogen input levels are connected with lower nitrogen prices. Differences in nitrogen price result from the composition of the applied fertilizer, which differs in the ratio between fertilizer price and nitrogen content. The yield of wheat and maize indicates a high variation within the survey sites, but especially between the surveyed townships. A multifactorial regression analysis identified the location as the only significant influencing factor on yield. From the agronomic point of view, nitrogen is a major yield factor, but the survey data do not indicate a clear impact of nitrogen input on yield. The estimated relationship between nitrogen input and wheat yield provides a constant-shaped yield function. This result allows the assumption that due to the long term high nitrogen inputs the crop demand for nitrogen is fulfilled in the short term and additional nitrogen input is without impact on the yield. The quadratic regression models of nitrogen input and yield in wheat and maize fail to provide applicable economic optima of nitrogen input. For this reason, the concept of KRAYL (1993) is considered to estimate an applicable production function for wheat and maize. This concept is based on a location independent production function, which can be transferred into a location specific production function by the consideration of a location specific optimum nitrogen input and the corresponding yield. In this case the recommendations of ZHEN et al. (2005) are considered, which recommend for wheat a nitrogen input of 220 kg per ha in order to harvest 5.3 t per ha. The economic optimum nitrogen input levels are higher than the nitrogen recommendations of ZHEN et al. (2005), but still lower than the average nitrogen application rates. Hence, the present nitrogen price does not support the implementation of the recommended nitrogen application rates. The estimation of the economic optimum nitrogen input considers a production function based on the concept of KRAYL (1993) which is enlarged by factor and product prices. These are the crop prices and the costs of the other variable inputs, which are the variable costs excluding fertilizer costs. In this way, the gross margin can be described as a function of nitrogen input including the uniform factor crop price and the constant "other fertilizer costs". The calculated maximum gross margin in wheat of 4 057 ¥ per ha is achieved at a nitrogen input of 272 kg per ha. This level of nitrogen input is lower than the present average nitrogen input, but higher than the recommendations presented by ZHEN et al. (2005). Similar to the gross margin, the nitrogen balance is described as a function of nitrogen input, which considers the nitrogen input from fertilizer and straw left on the field from the previous cultivation as nitrogen inflow and the nitrogen content of the harvested crops as nitrogen outflow. Natural inflows and outflows are not taken into account. A nitrogen input of 205 kg per ha would result in the maximum accepted nitrogen surplus of 50 kg per ha and a gross margin of 3 365 ¥ per ha. Chapter 7 focuses on the estimation of the nitrogen balance and the analysis of relevant impact factors. The estimated nitrogen balances show at all crops, but especially in wheat cultivation a high level of nitrogen surplus, which is on average 200 kg of nitrogen per ha. The corresponding figures for maize, peanuts, and cotton are less than 100 kg of nitrogen per ha. Similar to nitrogen input, the nitrogen balance is indicated by a broad variation. This variation allows a classification of farm households into three nitrogen balance types: "equalized nitrogen balance", "slight nitrogen surplus", and "heavy nitrogen surplus". The farming system of "heavy nitrogen surplus" farm households can be characterized by low yields, high nitrogen input, and low calculated gross margin. These farm households have a share of 32 per cent of all farm households and cultivate about one third of the wheat of all surveyed farms, but their cumulated nitrogen input amounts to 50 per cent. Furthermore, this group of farm households accounts for 67 per cent of the cumulated nitrogen surplus. This situation leads to the question, which factors lead to that kind of nitrogen overuse. A binary logistic regression model is used to analyse the impact of pre-selected factors on the probability of a group membership interval, in this case to the "equalized nitrogen balance" as well as the "heavy nitrogen surplus" group. The covariates "family size", "education", "farmland", and "off-farm activities" do not show any significant influence. Similar to the nitrogen input analysis, a low nitrogen price and the application of manure increases the probability of a farm households of membership of the "heavy nitrogen surplus" group. Also, a low village average wheat yield and a high village average nitrogen input in wheat increases the probability. In order to identify parallel impacts of farm household characteristics on the nitrogen balance the group of farm households of "heavy nitrogen surplus" and "equalized nitrogen balance" are clustered. The farm households of the major cluster of the "heavy nitrogen surplus" group are characterized by less farmland and low farm households income without off-farm activities. Farm households of these characteristics are found at a minor cluster of the "equalized nitrogen balance" group, as well. A low income does not automatically lead to nitrogen application rates beyond the crop demand. Indeed, the combination of low income and high nitrogen input shows a higher probability than the combination of high income and high nitrogen input. Without doubt, the assumption that a lower income leads to a lower nitrogen input must be rejected. The nitrogen price might be a clear indicator for classification of farm households, but this criterion requires the analysis of the cultivation system of the considered farm household. For this reason, easy observable dichotomous variables are pre-selected and analysed whether a certain pattern can be used as criterion for identification as a part of a target group specific instrument. This approach does not provide applicable results. Chapter 8 deals with the simulation of scenarios of the nitrogen surplus reduction and the estimated impact on the net income of farm households. In the first step, the instrument independent potential nitrogen surplus reduction is estimated. The cumulated nitrogen surplus of wheat cultivation of all surveyed farm households can be reduced by more than 60 per cent, if all farm household would follow the nitrogen input recommendations and harvest the target yield of ZHEN et al. (2005). This scenario shows no changes in net income. However, the approach that all farmers would modify their present nitrogen application level to the recommended application rates might be too ambitious. Hence, it might be more realistic to consider a theoretical shift of half of the farm households belonging to the "heavy nitrogen surplus" group to the "slight nitrogen surplus" group. The nitrogen surplus reduction in wheat would be 18 per cent. The affected group of farm households represents 17 per cent of the wheat cultivation area, but accounts initially for 32 per cent of the total nitrogen surplus in wheat. This hypothetical shift considers the modification of the share of farm households belonging to a certain nitrogen balance type. The average nitrogen surplus and gross margin in combination with the share of farm households of nitrogen balance type is taken to estimate the overall nitrogen surplus and net income from farming of the considered nitrogen balance type. A change in the share of farm households modifies the overall nitrogen surplus and net income from farming of each nitrogen balance type and these modified values are considered as the impact of the evaluated instrument, which originate that change of share. The individual gross margin multiplied by the individual cultivation area of all farm households is summed up and it is considered as net income from farming. In the following step, the impact of an instrument on the nitrogen balance and the net income is simulated. The variable nitrogen price shows a highly significant influence towards the classification of nitrogen balance type. For this reason, a modification of the nitrogen price is selected as considered instrument. A higher nitrogen price reduces the probability of "heavy nitrogen surplus" and this difference in probability can be regarded as the share of farm households, which convert form "heavy nitrogen surplus" to "slight nitrogen surplus". In addition, a theoretical shift of "slight nitrogen surplus" farm households into "equalised nitrogen balance" farm households is considered. As instruments, a percental increase of the nitrogen price by 10 per cent is simulated. An increased nitrogen price by 10 per cent results in a reduction of the total nitrogen surplus of 4.9 per cent. The estimation of the impact on the net income from farming considers the described theoretical shift of farm households to another nitrogen balance type and a multiple regression model of the gross margin. The latter model considers all farm households and indicates a negative impact of the nitrogen price on the gross margin. A combination of both models results in a marginal reduction of net income from farming by 0.6 per cent, in case of a 10 per cent nitrogen price increase. In addition, a target simulation focuses on a more noticeable nitrogen surplus reduction. The average nitrogen price increase by 159 per cent to obtain a nitrogen surplus reduction of 50 per cent, but the net income from farming shows a reduction by 15.3 per cent. Summarized, the considered instrument "nitrogen price modification" fulfils the demand partly. It allows a nitrogen surplus reduction without a strong impact on the net income, but there are two major disadvantages. Firstly, huge nitrogen price modifications are required to gain a noticeable impact on nitrogen surplus reduction. Secondly, a nitrogen price modification affects all farmers, but there is a broad variation of the nitrogen balance and a high share of farm households actually has an equalized nitrogen balance. The discussion about the reasons for nitrogen overuse in the wheat and maize farming system in the North China Plain leads to the following results. This thesis cannot provide a comprehensive answer on the question, what the core reasons for the described surplus at the nitrogen balance are. The described high variation in nitrogen input and the reported low rate of farm households, which follow the recommended nitrogen application rates, leads to the assumption that an insufficient knowledge transfer system is the key reason for the inadequate use of the traditional cultivation system in terms of fertilizer application in the North China Plain. Lack of knowledge might be an explanation that low income farm households without off-farm activities do not have less fertilizer costs, but even have a higher probability to apply above average nitrogen rates than farm households, which have additional income from off-farm activities. The discussion about applicable instruments focuses on nitrogen tax, implementation of new agricultural technologies, and improvements in education and agricultural skills. The modification of the nitrogen price by a nitrogen tax is considered as an economically applicable instrument, but there are the described disadvantages. Furthermore, an economic instrument might not be suitable, if a noticeable share of the target group seems not to consider their farm level economic optimum as criterion in their determination of the applied nitrogen. In addition, a low nitrogen price is a suitable indicator for nitrogen overuse, but not its explanation. The nitrogen price represents the composition of the used fertilizer. An unfavourable composition can be regarded as an insufficient use of the cultivation system, which results in the described nitrogen overuse. Hence, an improvement in application of the cultivation technology might be more successful than an economic instrument. The discussion about new technologies focuses on their implementation. Only a minority of farm households follows the presently recommended nitrogen application rates and at a noticeable share of farm households the traditional cultivation system is not free of cultivation mistakes, especially in terms of nitrogen application. This raises the question, how successful a new agricultural technology can be implemented. The correct application present of the cultivation system and a proper working knowledge transfer system are the preconditions for the implementation of new technologies. For this reason, improvement in education and agricultural skills are the base instruments as well as the basis for all advanced instruments, because a sustainable cultivation system requires a sustainable implementation of its correct use.
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    Environmental and economic assessment of the intensive wheat - maize production system in the North China Plain
    (2016) Ha, Nan; Bahrs, Enno
    To ensure food security for its vast population input intensification in crop production has been one of China’s major strategies in the last decades. However, the negative environmental impact of the highly intensive crop production becomes apparent. Especially the emission of greenhouse gases (GHG) constitutes a major sustainability issue of crop production in China. The winter wheat - summer maize (WW-SM) double cropping system plays a crucial role for China’s national food security. Strong research efforts mainly focusing on field experiments insufficiently consider the economic viability of the proposed improvement strategies and farmers’actual crop management. Therefore this study aims to fill this void by assessing farmers’actual crop management in the WW-SM production system, with regard to its environmental and economic performance to derive suitable improvement strategies for more sustainable crop production in the North China Plain (NCP). This cumulative PhD thesis consists of three papers published or accepted with revisions in international peer-reviewed journals. A field survey conducted in 2011 interviewing 65 WW-SM producing farm households constitutes the core data base for the thesis’analysis. The data was supplemented by expert interviews and specific secondary data. Partial life cycle analysis and economic assessment were conducted, comprising GHG emission, product carbon footprint (PCF), gross margin (GM), variable cost per unit product and life cycle costing (LCC) as key environmental and economic indicators, respectively. The first article describes the status quo of single farm environmental and economic performance of 65 WW-SM producers. The results revealed a huge heterogeneity among farms. Astonishingly no trade-off between productivity and sustainability could be identified in the region. Building on cluster analysis, with farms grouped according to their economic and environmental performance into “poor”, “fair” and “good” producers, the regional GHG mitigation potential was estimated. Under the scenario assumption that all grain in the NCP is produced under “good” production conditions, 21% and 7% of GHG could be mitigated in wheat and maize production, respectively. To be able to address the existing heterogeneity and develop strategies towards attaining GHG mitigation in practice, the second article aimed at assessing the factors determining farmers’ current environmental and economic performance. Using stepwise multiple linear regression (SMLR) it was revealed that nitrogen (N) input and electricity for irrigation were responsible for 0.787 and 0.802 of variability (adjusted R2) in the GHG emission results of the WW and SM production, respectively. Electricity for irrigation and labor were the most significant factors explaining the differences in LCC of WW and SM production, with an adjusted coefficient of determination (adjusted R2) of 0.397 and 0.29. This finding indicates that N input, electricity for irrigation and labor are key target areas for lowering GHG emissions and production costs of the WW-SM production system in the NCP. As revealed in the second article overuse of N fertilizer, which actually constitutes a major current issue in China, offers great potential for reducing GHG emissions and production costs in the WW-SM production system. Therefore in the third article three simple and easily to apply N fertilizer recommendation strategies are tested, which could be implemented on large scale through the existing agricultural advisory system of China, at comparatively low cost. Building on the household dataset, the effects of the three N strategies under constant and changing yield levels on PCF and GM were determined for every individual farm household. The N fixed rate strategy realized the highest improvement potential in PCF and GM in WW; while the N coefficient strategy performed best in SM. The analysis furthermore revealed that improved N management has a significant positive effect on PCF, but only a marginal and insignificant effect on GM. On the other side, a potential 10 % yield loss would have only a marginal effect on PCF, but a detrimental effect on farmers’income. It will be of vital importance to avoid any yield reductions and respective severe financial losses, when promoting and implementing advanced fertilization strategies. Therefore, it is furthermore recommended to increase the price of fertilizer, improve the agricultural extensions system, and recognize farmers’ fertilizer related decision-making processes as key research areas. The presented thesis gives valuable contributions to the development of environmentally and economically more sustainable crop production systems in the NCP. The thesis concludes that an adjustment in the agricultural advisory system is required, supported by more interdisciplinary research, which is able to address the inherent complexity of realizing more sustainable crop production in China.
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    Grasping the complexity of intercropping - developing and testing an integrated decision support system for vegetable production in the North China Plain
    (2010) Feike, Til; Claupein, Wilhelm
    This cumulative dissertation consists of six papers published, accepted or submitted to international high standard journals or books. To detect and describe the status quo of vegetable intercropping in the North China Plain (NCP), a survey was conducted from autumn 2007 to spring 2008. The results of the interviews with researchers, extensionists and farmers embedded in the first article revealed a huge variety of intercropping systems being practiced by farmers in the region. The first article furthermore elaborated farmers? underlying motives and concepts and described the knowledge transfer systems involved. When evaluating the prevailing systems against the background of the rapidly changing socio-economic frame conditions for farming in rural China, it became obvious that a great proportion of the systems practiced nowadays are prone to extinction in a long run. Therefore the second article discussed possible adjustments of the intercropping systems to fit the demands of modern agriculture, while maintaining their potential agronomic and environmental benefits. To enable mechanization, it was suggested to either adjust the machinery to the traditional row intercropping systems, or adjust the cropping system to the prevailing and available machinery. The latter approach was then followed throughout the thesis, using an agronomic modeling approach. The combination of Chinese cabbage and maize was selected, as it is a traditional intercropping system, with strong interspecific effects. In the course of this study, the two crops were strip intercropped in four field experiments at three sites in Germany and in China in 2008 and 2009. To understand, explain and predict plant behavior under the impact of complex cropping structures, crop growth models present a viable and powerful tool. However, two constrains had to be overcome within the framework of this thesis i) Chinese cabbage is not integrated in the common process-oriented crop growth models, ii) a method had to be developed to quantify resource competition and simulate intercropping. Therefore the integration of Chinese cabbage, the number one field vegetable of China, into the CROPGRO model constituted the first step for the simulation of intercropping systems in China. Two greenhouse experiments, testing crop growth and development under different temperature regimes, served as the data base for the accurate parameterization of Chinese cabbage and built the baseline for the third article. Cardinal temperatures of Chinese cabbage were identified by correlating mean relative growth rates and mean leaf appearance rates to temperature. Minimum growth temperature was identified at 0 °C, optimum temperature ranges between 14 °C and 24 °C, and maximum temperature is 34 °C. The further adjustment and testing of the model, which was executed on up to six independent data sets, is presented in the fourth article. The key to successfully simulate intercropping systems is the knowledge on changes in resource availability compared to monocropping. Therefore, a method was developed to quantify the availability of the most crucial growth factor solar radiation at any location within a Chinese cabbage strip, presented in the fifth article. The method was extended in the sixth and final article to enable the estimation of available radiation in Chinese cabbage strips of different widths. The ?environmental modifications? option of CROPGRO was employed to simulate the effects of the estimated reduction in incoming radiation in Chinese cabbage strips of different width. Simulations were conducted over up to thirty years of weather data of 12 locations throughout the NCP, and were additionally tested on different soil texture types. The results were extended over the entire NCP by linking them to a GIS-system. The developed approach constitutes a reliable decision support for the optimization of the spatial arrangements in Chinese cabbage strip intercropping systems, according to local soil and climate conditions. The described approach can be extended to develop a comprehensive decision support system that allows testing of various intercrop combinations under a wide range of climate and especially radiation environments. The presented thesis is a valuable contribution to the development of sustainable vegetable production systems in the NCP. A new method to quantify availability of solar radiation in strip intercropping was developed, which can be applied in various other intercropping systems. The integration of Chinese cabbage into CROPGRO, offers great opportunities not only for studying intercropping systems, but also for improving input levels and resource use efficiency in Chinese cabbage production in China and throughout the world. Understanding farmers? concepts and estimating the production potential of intercropped Chinese cabbage created additional value, which substantially contributes to realizing the potential of intercropping in the NCP.
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    Real-time in situ measurements of trace gases from agriculturally cultivated soils by means of laser spectroscopic techniques
    (2008) Hillebrand, Malte; Haas, Ulrich
    Two devices to study the exchange of climate relevant trace gases between arable cultivated soils and the atmosphere in the North China Plain are presented in this thesis. They are based on Tunable Diode Laser Photoacoustic Spectroscopy (TDL-PAS). These devices are capable of real-time in situ detection of trace gases. For methane a detection limit of 85 ppb and for ammonia of 111 ppb was achieved, respectively. For the field campaign at the experimental field Dongbeiwang (DBW) in Beijing it was necessary to optimize the instruments due to the harsh conditions in China, e.g. high variation in temperature, high humidity and particulate matter emissions. This included accurate thermally stabilization of the system as well as long-term stability of the laser diode and the possibility of unattended operation over a period of several days. These prerequisites were fulfilled and evaluated in Germany before the devices were brought to China for the field campaign in the years 2006 and 2007. Additionally, mobile closed chambers for the trace gas exchange measurements were designed in Germany. They consisted of two parts: One frame installed permanently in the soil, therein agricultural crops could be planted, and a hood placed on it during the measurement and removed afterwards again. Altogether seven frames made from stainless steel were constructed by a company located in Beijing. Three hoods of different heights (250, 500 and 1000 mm) were made from 8 mm colorless Plexiglas and were built by a German company. The innovation of this design was the possibility to insert up to eight cooling packs that cooled down the enclosed air in the chambers by mixing it via two fans. By comparing measurements with and without applying cooling packs it was shown that the temperature difference between both situations was increasing up to 10 K. According to ambient air temperature measurements the test also showed that by applying cooling packs the temperature of the enclosed air could be adapted close to ambient conditions. After installation of the closed chambers in DBW a test checking the gas tightness had to be performed. With this test leakages of the frames, hoods and tubes should be discovered. This was done by injection of 2 ml ethane into the closed chambers and studying the concentration decrease within one hour of closure time. For this test the permanently installed gas chromatograph in the measurement container in DBW was used, connected by Teflon tubes to the closed chambers. All closed chambers showed leakages lower than 10% and therefore could be considered as tight. For methane measurements the chambers were operated in the dynamic mode, so the air inside of the chamber was circulated through the TDL-PA system and pumped back into the chamber. The increase or decrease in methane concentration with time was determined and flux rates were calculated. The obtained data confirmed that the soil in DBW, a Calcaric Cambisol according to FAO classification, could be considered as a methane sink. The exchange rate ranged from ?0.17 to ?3.33 mg CH4-C m-² d-¹ for winter wheat and from ?0.68 to ?2.07 mg CH4-C m-²; d-¹ for bare soil. For summer maize the exchange rate was slightly lower and ranged from ?0.51 to ?1.0 mg CH4-C m-² d-¹ and from ?0.53 to ?1.14 mg CH4-C m-² d-¹ for the control plot. Due to the fact that elevated methane concentrations at daybreak were detected during the exchange measurements at the plots planted with winter wheat as well as at the control plot a diurnal variation in methane concentration was assumed. To verify and quantify this diurnal variation in methane concentration at DBW, one plot was selected for a 24 hour measurement campaign. During this measurement campaign ambient air methane concentrations of up to 22 ppm were observed during nighttime, which was elevenfold the normal concentration. Because the previous exchange measurements revealed that methane was not emitted by the soil it must originated from somewhere else. After the 24 hour measurement campaign the ambient air methane concentrations in DBW as well as at other places in the vicinity of DBW were studied to detect the source of the methane emissions. For that purpose an ultrasonic anemometer for wind direction and wind speed measurement was combined with the TDL-PA system. A diurnal variation with maximum methane concentrations of about 40 ppm during nighttime and early morning and minimum concentrations of about 1.4 ppm during the afternoon were detected in DBW. Research conducted at the campus of the CAU, 3.2 km south of DBW, showed a similar pattern. These results confirmed the urban heat island effect where stable atmospheric layering dominates during the night and a mixing layer dominates during daytime. According to literature the height of this atmospheric boundary layer in Beijing in autumn was of 1 km thickness during daytime and of 200 ? 400 m during nighttime. Moreover the high methane concentrations in the night verified the assumption of a methane emission source in the vicinity of DBW and the CAU. The search for a potential emission source revealed a landfill approximately 6 km north-west of the CAU as well as 5.5 km west of DBW. Measurements conducted at the landfill site itself showed a diurnal methane emission pattern as well, with maximum concentrations up to 450 ppm during nighttime and minimum concentrations of about 10 ppm during daytime.
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    Reducing irrigation water supply to accomplish the goal of designing sustainable cropping systems in the North China plain
    (2007) Binder, Jochen; Claupein, Wilhelm
    An International Research Training Group (IRTG) of the University of Hohenheim and the China Agricultural University, entitled ?Modeling Material Flows and Production Systems for Sustainable Resource Use in the North China Plain? was launched in 2004. The major hypothesis was ?that adjustments in cropping systems and management practices provided potential for sustainable resource protection on a high yield level?. The research program was conducted in one of the most important economic and agricultural regions in China, the North China Plain (NCP). The NCP is one of the major maize (Zea mays L.) and wheat (Triticum aestivum L.) growing areas. A literature review indicated that over the last two decades yields for wheat and maize increased by more than 20%, which had mainly been achieved by augmenting the amount of irrigation water and fertilizer. Besides the positive effects on yield an increasing amount of these input factors leads to many environmental problems. Field experiments were carried out to compare different cropping systems. Currently, the double cropping of winter wheat and summer maize is the common cultivation system in the NCP. It consists of growing two crops mostly winter wheat and summer maize in one year. The winter wheat production depends on a supplemental irrigation, because rainfall is concentrated in the summer months during the maize growing season. An alternative to the intensive double cropping system could be the single cultivation of spring maize. Relative less irrigation water is required for spring maize production, because the rainy season coincides with the main part of the maize growing season. Due to the longer growing season spring maize normally realises higher yields in comparison to summer maize. However, the total yield of a double copping system of wheat and maize is higher. The evaluated system three harvests in two years (winter wheat and summer maize in the first year followed by spring maize in the second year) forms a balance between the double cropping system and the single cropping of spring maize. Due to the fact that three crops are grown in two years total yield is higher in comparison to single cropping of spring maize (two harvests in two years) but lower in comparison to the traditional double cropping system (four harvests in two years). However the lower cropping index in contrast to the double cropping of wheat and maize results in a lower demand of the input factors irrigation water and N-fertilizer whereas in comparison to the single cropping of spring maize a higher amount of input factor is required. Besides the conduction of field experiments for the collection of empirical datasets, the CERES-Maize and CERES-Wheat models were used to quantify the effects of different irrigation management practices on crop growth, productivity and sustainability of agricultural production. Results indicated that there is a considerable potential for reducing the irrigation amount for winter wheat. However, the results also showed that a supplemental irrigation at critical growth stages seems to be essential to maintain high yields and to ensure an adequate gross margin. In a more complex approach the CERES-Maize model was used to simulate the yield of summer maize and spring maize across the NCP. The spatial and temporal climate variability was taken into account by using up to 30 years of weather data from 14 meteorological stations. The simulated results were linked to a Geographic Information System (GIS). Results indicated that the yield distinction between summer maize and spring maize was partially very low as a result of water shortage at flowering stage. A delay in sowing and the use of adapted cultivars with a later flowering date could help to increase spring maize yields. Summarizing, the results of this study indicate that water is one of the most limiting factors for crop production in the NCP. Further, the reduction of total water consumption will become more and more important with water becoming increasingly scarce and thus costly. Consequently agriculture has to undergo and is already undergoing dramatic changes. The results of this study indicated that there are several possibilities optimize cropping systems in the NCP, focussing on a more sustainable use of water while maintaining high yields. In this context, crop models are valuable tools for e.g. irrigation planning or evaluating different cropping designs in the NCP.