Browsing by Subject "Erosion"

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    Compound-specific 13C fingerprinting for sediment source allocationin intensely cultivated catchments
    (2018) Brandt, Christian; Cadisch, Georg
    The loss of fertile topsoil due to soil degradation and erosion not only threatens crop productivity, but also induces sedimentation of aquatic systems and leads to social-, economical-, and environmental problems in many regions of the world. The abandonment of shifting cultivation in favor of intensive mono-cultural cropping systems on sloping land accompanied by rainfall detachment and surface runoff induced soil erosion is one of the most pressing environmental and agricultural problems in the highlands of Southeast Asia. Informed soil management strategies require knowledge on the main sediment sources in a catchment. Compound-specific stable isotope (CSSI) fingerprinting, based on δ13C values of fatty acid methyl ester (FAME), allows identifying hot-spots of soil erosion, particularly with regard to assigning sediment sources to actual land uses. In this regard, we assessed the potential of the CSSI – fingerprinting approach to assign sediment sources to specific land use types in various intensely cultivated catchments. In a first step we improved the statistical procedure to identify sediment sources in a heterogeneous agricultural catchment in the mountainous northwestern region of Vietnam. In a next step we tested the CSSI-fingerprinting under different agro-ecological conditions to evaluate its global applicability, using an aligned protocol. Finally, we integrated CSSI-fingerprinting and fallout radio nuclide (FRN, 210Pbex, 137Cs) analysis to estimate past net erosion rates linked to land use types. In conclusion, the integrated Bayesian SIAR-CSSI approach was an appropriate tool to identify and assign sediment sources to actual land uses in small and heterogeneous catchments. This methodology was also suitable to identify hot-spots of soil erosion in contrasting catchments of different sizes and agro-ecological zones. Integrating CSSI-fingerprinting and fallout radio nuclide analysis to determine past sediment budgets provided insight into the impact of specific land use changes on soil retrogression and degradation. Such knowledge is of great value for informed and effective soil conservation through evidence-based land management and decision making.
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    Development of management strategies to control soil erosion in field grown vegetables with a focus on white cabbage (Brassica oleracea convar. capitata var. alba L.)
    (2014) Übelhör, Annegret; Claupein, Wilhelm
    Soil erosion by wind and water is a widely recognized problem throughout the world. Field grown vegetables, such as white cabbage (Brassica oleracea convar. capitata var. alba L.), are particularly endangered by soil erosion because of high disturbance tillage, including deep inversion tillage by the mouldboard plough. Furthermore, wide row spacing and late soil covering by leaves intensify the problem. In light of this, field experiments were conducted from 2011 to 2013 in southwest Germany to investigate, develop and adapt soil erosion control strategies, in particular for field grown vegetables, with white cabbage as a model crop. Focus was placed first, on the use of row covers (fleece and nets), which are usually used as frost protection or for pest control in organic farming, and second, on the development and adoption of strip-tillage for field grown vegetables, which combine the benefits from conventional tillage (high yields) and no-tillage (erosion control). Artificial rainfall simulations demonstrated a high erosion control by row covers. Soil loss under fleece cover was reduced on average by 76% and under net cover by 48% compared to the uncovered control treatment. In 2012, fresh matter head yield was significantly higher under fleece (80 t ha-1) than control treatment (66 t ha1). The opposite was found in 2013, with highest yield under the non-covered control (64 t ha-1) and lowest under fleece cover (53 t ha-1). A higher prevalence of diseases under row covers compared to the control was only found in 2012 with Sclerotinia sclerotiorum on 4% of cabbage heads under fleece cover. Soil loss under strip-tillage during artificial rainfall simulations in 2011 was reduced by an average of 80% compared to conventional tillage (512 g m-2). In 2012, soil losses were reduced by an average of 90% under non-intensive strip-tillage and by 48% under intensive strip-tillage compared to conventional tillage (210 g m-2). The fresh matter head yield in 2011 and 2013 under strip-tillage (58 t ha-1 and 57 t ha-1, respectively) was similar to conventional tillage (59 t ha-1 and 58 t ha-1, respectively). In 2012, cabbage yield was significantly higher under strip-tillage (74 t ha-1) than under conventional tillage (65 t ha-1). The intensive strip-tillage treatments with broadcast and band-placed nitrogen fertilization did not show a yield increase. Yield potential under band-placed fertilized strip-tillage was, at 67 t ha 1 (2012) and 50 t ha-1 (2013), the lowest within the strip-tillage treatments. The CROPGRO cabbage model was evaluated for cabbage production under temperate European climate conditions. After calibration of main parameters of phenology and plant growth, the model showed a high accuracy with indices of agreement mostly above d=0.94. Observed dry matter cabbage head yields of the different years and different locations ranged between 6574 kg ha-1 and 11926 kg ha 1 which were predicted by the model with an accuracy of R2=0.98. Also the sensitivity analysis, conducted under different nitrogen fertilizer amounts and different fertilizer application strategies, generated realistic values from an agronomic point of view. Overall, row covers and strip-tillage seem to be suitable for minimizing the erosion risk in vegetable production. The hypotheses of high erosion control under row covers and strip tillage can be accepted. Due to the modified microclimate under row covers, the infestation with pests and diseases can increase and the influence on cabbage growth can result in either a yield increase or decrease. Based on the study results, there is no evidence that the intensive, double-tilled strip-tillage treatment or the band-placed nitrogen fertilization lead to a yield increase. The non-intensive strip-tillage with only soil preparation in autumn showed the highest yield potential within the strip-tillage treatments, with similar or even higher yields than under conventional tillage. Furthermore, the CROPGRO cabbage model is suitable to simulate growth parameters and yield potential of white cabbage under temperate European climate conditions. For the future, due to the prediction of increased frequency of heavy rainfall events, soil conservation will focus increasingly on intensive crop production and farmers, particularly vegetables growers, will be increasingly dependent on erosion control strategies. For this reason, the approaches presented in this thesis can contribute significantly to produce field grown vegetables in a sustainable way that promotes soil protection.
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    Modelling weed management effects on soil erosion in rubber plantations in Southwest China
    (2018) Liu, Hongxi; Cadisch, Georg
    Land use in Xishuangbanna, Southwest China, a typical subtropical rain forest region, has been dramatically changed over the past 30 years. Driven by favorable market opportunities, a rapid expansion of rubber plantations has taken place. This disturbs forests and land occupied by traditional swidden agriculture thus strongly affecting hydrological/erosion processes, and threatening soil fertility and water quality. The presented PhD thesis aimed at assessing farmer acceptable soil conservation strategies in rubber plantations that efficiently control on-site soil loss over an entire rotation time (25 – 40 years) and off-site sediment yield in the watershed. The study started with field investigations on erosion processes and soil conservation management options in rubber plantations (Chapter 2 and 3). Based on the field data, the physically based model “Land Use Change Impact Assessment” (LUCIA) was employed to assess long-term conservation effects in rubber plantations (Chapter 4) and scale effects on sediment yield in the watershed (Chapter 5). Specifically, the first study aimed at assessing soil loss in rubber plantations of different ages (4, 12, 18, 25 and 36 year old) and relating erosion potential to surface cover and fine root density by applying the Universal Soil Loss Equation (USLE) model. This study adopted the space-for-time substitution for field experimental design instead of establishing a long-term observation. Spatial heterogeneity of soil properties (e.g. texture, organic carbon content) and topography (slope steepness and length) interfered erosion at different plantation ages. To meet this challenge, namely account for possible impacts of soil properties and slope on erosion, the empirical USLE model was applied in data analysis to calculate the combined annual cover, management and support practice factor CP, which represents ecosystem erosivity. Calculated CP values varied with the growth phase of rubber in the range of 0.006 - 0.03. Surface cover was recognized as the major driver responsible for the erosive potential changes in rubber plantations. The mid-age rubber plantation exhibited the largest erosion (3 Mg ha-1) due to relatively low surface cover (40%-60%) during the rainy season, which was attributed to low weed cover (below 20%) and the low surface-litter cover favored by a high decomposition rate. Based on the results of the first study, the second study focused on reducing soil loss in rubber plantations by maintaining a high surface cover through improved weed management. Among the different weeding strategies tested, no-weeding most efficiently reduced on-site soil loss to 0.5 Mg ha-1. However, due to the low farmer acceptance of the no-weeding option, we recommend reducing herbicide application to a single dose at the beginning of the rainy season (once-weeding) to better conserve soil as well as inhibiting overgrowth of the understory vegetation. As the second experiment lasted only one-year, while rubber plantation is a perennial crop with a commercial lifespan of 25 – 40 years, the third study applied the LUCIA model to simulate the temporal dynamics of soil erosion in rubber plantations under different weeding strategies. The erosion module in LUCIA was extended to simulate both runoff and rainfall based soil detachment to better reflect the impact of the multi-layer structure of the plantation canopy. The improved LUCIA model successfully represented weed management effects on soil loss and runoff at the test site with a modelling efficiency (EF) of 0.5-0.96 and R2 of 0.64-0.92. Long-term simulation results confirmed that “once-weeding” controlled annual soil loss below 1 Mg ha-1 and kept weed cover below 50%. Therefore, this weeding strategy was suggested as an eco- and farmer friendly management in rubber plantations. Furthermore, LUCIA was applied at watershed level to evaluate plot conservation impact on sediment yield. Two neighboring sub-watersheds with different land cover were chosen: one a forest dominated (S1, control), the other with a mosaic land use (S2), which served to assess mono-conservation (conservation only in rubber plantations) and multi-conservation (conservation in maize, rubber and tea plantations) effects on total sediment yields. The model was well calibrated and validated based on peak flow (EF of 0.70 for calibration and 0.83 for validation) and sediment yield (EF of 0.71 for calibration and 0.95 for validation) measured from the two watersheds outlet points. Model results showed that improved weed management in rubber plantations can efficiently reduce the total sediment yields by 20%; while multi-conservation was largely able to offset increased sediment yields by land use change. In summary, while exploring the dynamics of erosion processes in rubber plantations, a physically based model (LUCIA) was extended and applied to simulate weed management effects over an entire crop cycle (40 years) and implications at higher scale level (watershed sediment yield). Once-weeding per year was identified as an improved management to reduce on-site erosion and off-site sediment yield. But to fully offset increased sediment yield by land use change, a multi-conservation strategy should be employed, which not only focuses on new land uses, like rubber plantations, but also takes care of traditional agricultural types. A conceptual framework is proposed to further assess the specific sub-watershed erosion (e.g. sediment or water yield) effects in large watersheds by spatially combining process-oriented and data-driven (e.g. statistic based, machine learning based) models. This study also serves as a case study to investigate ecological issues (e.g. erosion processes, land use change impact) based on short-term data and modelling in the absence of long-term observations.
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    Soil conservation methods and their impact on nitrogen cycling and competition in maize cropping systems on steep slopes in Northwest Vietnam
    (2015) Vu Dinh, Tuan; Cadisch, Georg
    Recent maize cultivation expansion into steep forested uplands in Vietnam led to severe erosion, soil degradation, and strong environmental impacts. Despite effectively controlling erosion, conservation measures often reduce crop yields due to resource competition. To foster uptake of soil conservation, a study including two experiments with bounded plots at two communes - Chieng Hac (21.02° N, 104.37° E, inclination: 53%) and Chieng Khoi (21.02° N, 104.32° E, inclination: 59%) - was carried out over a period of three years (2009-2911). The treatments included maize monocropping under intensive tillage and fertilization (T1, control), maize with Panicum maximum as grass barrier (T2), maize under minimum tillage (MT) with Pinto peanut (Arachis pintoi) as cover crop (T3), and maize under MT and relay cropped with Adzuki beans (Phaseolus calcaratus) (T4). Soil loss in 2010 and 2011 were also measured using sediment fences on unbounded maize fields under current farmers’ practice. The first part of the study assessed the magnitude of erosion and the mitigation potentiality of soil conservation measures. Under farmers’ practice, annual soil losses of bounded plots reached up to 174 t ha-1, being much higher than those from unbounded fields (up to 111 t ha 1). The majority of the soil loss occurred early in the season, when high rainfall intensities coincided with a low percent ground cover (<30%). To keep erosion rates below a tolerable soil loss (3 t/ha/yr) on steep slopes (53-59%) under an average annual rainfall of 1270 mm, a theoretical minimum ground cover of 95% is required at the onset of the crop season which was hardly achievable under monoculture system. Under conservation measures erosion was reduced by 39-84% in grass barriers or by 93-100% in MT with cover crops. A yield decline of 26% was observed in grass barrier treatments or up to 35% of cover crop plots if Pinto peanuts were not cut on time. Both options provided animal feed, up to 5.5 t/ha/yr dry matter of grass or 1.8 t/ha/yr dry matter of Pinto peanuts. Despite these potential benefits, constraints such as labour for grass barriers and cover crop establishment and cutting it afterwards, or difficulties in accessing and collecting maize cobs due to proliferate growth of Adzuki beans may hinder adoption by local farmers. To increase the incentive for adoption, the conservation system also has to use N fertilizer more efficiently. Therefore, the second part of the study examined the fate of applied 15N-labelled urea at the Chieng Hac site in 2010. At harvest, 21.6% of the labelled 15N was recovered by maize in T1, 8.9% in T2, 29% in T3, and 30.9% in T4. In T2, maize and P. maximum competed heavily for N with a total of 23.6% of the applied 15N found in the barriers next to application point. About 46-73% of the maize N uptake was derived from the soil, showing the important role of inherent soil N in these fertilized systems. MT reduced 15N translocation to deeper soil layers (40-80 cm), indicating a safety net function. Downslope translocation (>17 m) of applied 15N was <0.1 kg ha-1 as the majority of 15N added was vertically translocated and intercepted by plants along the slope. Despite implementation of an improved fertilization method, approximately 24-46% of N-fertilizer was unaccounted for, presumably lost via volatilization, denitrification, and leaching below 80 cm. Measured data for plot level showed that current farming practice (T1) induced a negative N balance of -142 kg N ha-1 in which residue burning and erosion were major pathways for N losses. A less severe negative N balance in T2 was attributed to reduced N losses by erosion while positive N balances of MT treatments were accredited to strongly reduced N losses via erosion and abandonment of burning plant residues in these treatments. The third part of the study investigated causes of competition in conservation systems three years after their establishment (2011). A pre-test at Chieng Hac in 2010 showed that abundance of water and the lack of N fertilization induced low grain N concentrations, enriched 15N;13C values in leaves, and reduced maize grain yield. This pattern was also observed in maize rows grown next to grass barriers or in cover crop plots at Chieng Khoi under good water availability conditions, indicating that these yield declines were mainly forced by lack of N. Additionally, a positive water balance throughout the maize cropping season further confirmed that water stress was absent. Moreover, enriched 15N values of maize rows close to the barriers suggested that these plants had to rely on soil N rather than on 15N derived from fertilizer N. Similarly, results of MT with simultaneous growth of A. pintoi pointed to N competition, resulting in a maize yield decline due to vigorous cover crop growth in T3. In contrast, MT with a relay crop (T4) had a similar maize yield, leaf N concentration, d15N, d13C as the control, suggesting N and water competition did not occur. In conclusion, soil erosion and nitrogen balances of current farming practice showed the urgent need to safeguard land resources, counteracting soil degradation but maintaining crop yields. The tested conservation techniques provide a range of characteristics to be considered as a sustainable system. The grass barrier as well as conservation systems controlled erosion, while minimum tillage with a cover crop further improved the nitrogen balance, and finally minimum tillage with a relay crop adds another advantage in maintaining crop production. Likelihood of adoption, however, may vary with how well appropriate incentives and land use policy fit to the area.
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    Soil erosion in Andean Cropping Systems: The impact of Rainfall Erosivity
    (2002) Sonder, Kai; Leihner, Dietrich
    Rationale and methods The Andean region of Colombia, 30% of the country, has about 15% of the tot. population and 50% of the rural population. A great part of the countries food-crops are grown on the hillsides of the region, which are severely degraded or threatened by degradation. The objectives of the present study were: a) to determine the applicability of the USLE rainfall erosivity factor to the Andean Region, particularly the energy-intensity term b) to calculate long-term erosivity data c) to establish the long-term erosivity of two soil types in the research area d) to evaluate the yield and soil conservation performance of several cassava-based cropping systems. Research was carried out at two sites in the Cauca department in the southwest of Colombia. Santander de Quilichao is located at 3o 6' N, 76 o 31' W, at an altitude of 990 m a.m.s.l., with an annual precipitation of 1,789 mm and an average temperature of 23.7 o C. Mondomo, which lies 2o 53' N, 76 o 35' W at an altitude of 1,450 m a.m.s.l., has an annual precipitation of 2,133 mm and an average temperature of 18.2 o C. The soils at both sites belong to the inceptisols, which form about 77% of the soils of the Cauca departments. In 1987 erosion plots were established at both sites on slopes of between 7% and 20% consisting of 8 treatments and 3 repetitions at Quilichao with 2 at Mondomo. During the research in this study, the 8 treatments comprised: 1) Continuous bare fallow, 2) Traditional cassava-based rotation, 3) Continuous sole cassava, 4) Cassava-based rotation with minimum tillage and mulch, 5) Cassava-based rotation with two previous years of bush fallow, 6) Cassava-based rotation with vetiver grass barriers, 7) Cassava-based rotation with legume strips, and 8) Cassava-based rotation with improved fallow element. Rainfall erosivity Drop size distribution measurements with a Joss-Waldvogel Distrometer showed that the USLE R factor is applicable for the research region as no significant differences were found between the measured kinetic energy of rainfall events and calculated values according to the USLE. The average annual r-factor values during the 12 year research period for Quilichao and Mondomo were 10,037 and 9,016 MJ ha-1 mm h-1 a-1 respectively. A highly significant relationship was found between a modified Fournier index based upon average monthly rainfall amounts and the equivalent monthly r-factor values. Soil losses K-factor values measured of 0.017 t h MJ-1 mm-1 at Quilichao and 0.011 t h MJ﷓1 mm-1 at Mondomo may be regarded as being between medium and low, although soil losses on the bare fallow plots were very high due to the extreme erosivity of the climate. Total soil losses in Quilichao on the bare fallow from 1986 to 1998 were 1,840 t ha-1. In Mondomo it was 2,380 t ha-1. From June 1994 to July 1997, the 7 cropped treatments in Quilichao showed susceptibility to erosion in the following order (from high to low): Sole continuous cassava, bush fallow >> farmer rotation, legume strips > improved fallow > minimum tillage, grass barriers. In Mondomo the susceptibility to erosion for the same period was: Sole continuous cassava >> legume strips >> bush fallow > improved fallow, farmer rotation > grass barriers, minimum tillage. When calculating soil loss for a representative plot only the minimum tillage and grass barrier treatments reached levels below the tolerable average annual soil losses under both the Quilichao and Mondomo conditions.The erosivity and erodibility values for the whole 12-year duration of this project showed that there is a highly significant relationship between annual soil loss amounts and the R-factor of the USLE. The continuous bare fallow plots showed strong declines of organic matter at both sites. Yield performance The two conservation treatments, minimum tillage and grass barriers, showed no significant differences regarding yield compared to the widely used continuous cassava system. The farmer rotation treatment showed the highest yield levels, but there were no significant differences between this treatment and the minimum tillage treatment at Mondomo and Quilichao. Conclusions The results confirm the high erosivity of the climate and support the necessity of maintaining permanent soil cover. The proven applicability of the R-Factor of the USLE for the region and the long-term soil erodibility values determined should enable the potential erosion risk to be estimated and appropriate soil conservation measures offered. Of the cropping systems evaluated, both the minimum tillage and the vetiver grass barrier treatments proved to be interesting alternatives to the local cropping systems as they reduced soil erosion to a sustainable level and at the same time reached or even surpassed the yields of the traditional cassava monocropping. All the other systems would lead to degradation if long-term permanent cropping was practised.