Marianne Ruidisch

Simulation of Runoff Patterns and Soil Erosion on Mountainous Farmland with and without Plastic-Covered Ridge-Furrow Cultivation in South Korea

Abstract. Plastic-covered ridge-furrow cultivation (plastic mulch) can substantially influence runoff and soil erosion on agricultural land. However, the impact of this management practice in combination with complex farmland topography has not been thoroughly investigated. The goal of this study was to identify how topography influences runoff patterns and erosion rates of plastic mulch cultivation. We measured runoff and sediment transport on two mountainous fields in South Korea, one with a concave topography and one with a convex topography, during monsoonal rain events. We used the EROSION 3D model to compare flow and sediment transport between plastic mulch, uncovered ridges, and a smooth soil surface. We found the highest runoff and erosion rates from both of the fields with plastic mulch due to the impermeable surface. For the uncovered ridges, we identified 140% higher erosion compared to the smooth surface on the concave field, but 20% lower erosion on the convex field. The simulated sediment transport patterns showed that the ridge-furrow system concentrated overland flow on the concave field, resulting in high erosion rates. On the convex field, the ridge-furrow system prevented flow accumulation and erosion. Our results demonstrate that the effect of ridge-furrow systems on erosion is controlled primarily by the topography. These results have practical consequences for watershed conservation planning and the application of large-scale erosion models. Nevertheless, further research is needed to fully understand the impact of this management system on runoff and erosion on mountainous farmland.

Is Ridge Cultivation Sustainable? A Case Study from the Haean Catchment, South Korea

Non-sustainable agricultural practices can alter the quality of soil and water. A sustainable soil management requires detailed understanding of how tillage affects soil quality, erosion, and leaching processes. Agricultural soils in the Haean catchment (South Korea) are susceptible to erosion by water during the monsoon. For years, erosion-induced losses have been compensated by spreading allochthonous sandy material on the fields. These anthropogenically modified soils are used for vegetable production, and crops are cultivated in ridges using plastic mulches. To evaluate whether the current practice of ridge cultivation is sustainable with regard to soil quality and soil and water conservation, we (i) analysed soil properties of topsoils and (ii) carried out dye tracer experiments. Our results show that the sandy topsoils have a very low soil organic matter content and a poor structure and lack soil burrowers. The artificial layering induced by spreading sandy material supported lateral downhill water flow. Ridge tillage and plastic mulching strongly increased surface runoff and soil erosion. We conclude that for this region a comprehensive management plan, which aims at long-term sustainable agriculture by protecting topsoils, increasing soil organic matter, and minimizing runoff and soil erosion, is mandatory for the future.

Estimation of annual spatial variations in forest production and crop yields at landscape scale in temperate climate regions

Simulating regional variations in gross primary production (GPP) and yields of major land cover types is complex due to differences in plant physiological properties, landscape topography, and climate gradients. In our study, we analyzed the inter-annual and inter-regional variation, as well as the effect of summer drought, on gross primary production and crop yields of 9 major land uses within the state-funded Bioenergy Region Bayreuth in Germany. We developed a simulation framework using a process based model which accounts for variations in both CO2 gas exchange, and in the case of crops, growth processes. The results indicated a severe impact of summer drought on GPP, particularly of forests and grasslands. Yields of winter crops, early planted summer grain crops as well as the perennial 2nd generation biofuel crop Silphium perfoliatum, on the other hand, were buffered despite drought by comparatively mild winter and spring temperatures. We estimated regional yield increases from SW to NE, suggesting a comparative advantage for these crops in the cooler and upland part of the region. In contrast, grasslands and annual summer crops such as maize and potato did not exhibit any apparent regional pattern in the simulations. The 2nd generation bioenergy crop exhibited significantly higher GPP and yields compared to the conventional bioenergy crop maize, suggesting that cultivation of S. perfoliatum should be increased for economic and environmental reasons, but additional study of the growth of S. perfoliatum is still required.

Transport of sulfonamide antibiotics in crop fields during monsoon season

Previous studies have documented the occurrence of veterinary sulfonamide antibiotics in groundwater and rivers located far from pollution sources, although their transport and fate is relatively unknown. In mountainous agricultural fields, the transport behaviour can be influenced by climate, slope and physico-chemical properties of the sulfonamides. The objective of this research is to describe the transport behaviour of three sulfonamide antibiotics (sulfamethoxazole, sulfadimethoxine and sulfamethazine) in sloped agricultural fields located in the Haean catchment, South Korea. During dry and monsoon seasons, a solute transport experiment was conducted in two typical sandy loam agricultural fields after application of antibiotics and potassium bromide as conservative tracers. Field measurement and modelling revealed that frequency and amount of runoff generation indicate a relation between slope and rain intensity during monsoon season. Since the steepness of slope influenced partitioning of precipitation between runoff and subsurface flow, higher loss of sulfonamide antibiotics and bromide by runoff was observed at the steeper sloped field. Bromide on topsoil rapidly infiltrated at high infiltration rates. On the contrary, the sulfonamides were relatively retarded in the upper soil layer due to adsorption onto soil particles. Presence of furrows and ridges affected the distribution of sulfonamide antibiotics in the subsurface due to gradient from wetter furrows to drier ridges induced by topography. Modelling results with HydroGeoSphere matched with background studies that describe physico-chemical properties of the sulfonamides interaction between soil and the antibiotic group, solute transport through vadose zone and runoff generation by storm events.