RESULTS Cont’d EFFECTS OF CROPPING AND TILLAGE SYSTEMS ON SOIL EROSION UNDER CLIMATE CHANGE IN OKLAHOMA X-C. John Zhang USDA-ARS Grazinglands Research Laboratory, El Reno, OK ABSTRACT Soil erosion under future climate change is likely to increase due to projected intensification in the hydrological cycles. This study shows that mean annual precipitation will decrease by some 6% while daily precipitation variance will increase by 12% in central OK in the next 30 years (P=0.05). Despite the projected decrease in precipitation, simulated mean runoff and soil loss will increase by 19.5% and 43.5%, respectively, due to increased occurrence of heavy storms. Soil erosion increases as tillage intensity increases. Conservation tillage systems such as delayed till and no-till are able to keep soil loss rates below the current levels of the conventional till in the next 30 years. Cropping systems play an important role in controlling soil loss rates under climate change. Simulated runoff and soil loss in the same tillage systems follow the order of cotton>soybean>sorghum>wheat> double cropping, showing that winter wheat is a preferred choice for controlling runoff and soil loss in the region. INTRODUCTION Intergovernmental Panel for Climate Change (IPCC, 2007) has projected that the frequency and magnitude of extreme precipitation events will increase in the contiguous US under future climate change. It is well documented that most soil loss in a year is caused by a few severe storms. The projected trend toward precipitation occurring in more extreme events will have an enormous impact on soil erosion and environmental protection. As summarized in a special report from the Soil and Water Conservation Society (SWCS, 2003), the projected climate change would be very likely to increase the overall risk of soil erosion and related environmental consequence. However, the potential impact is unknown, and needs to be assessed in a wide range of agricultural systems and physiographical conditions to provide policymakers information they need to better conserve soil and water resources. Soil erosion models are best tools available for simulating the potential impact of climate change on soil erosion and surface hydrology. In the past decade, many researchers simulated soil erosion with different models and reported that for a 1% change in daily rainfall amounts (or daily intensity) soil loss would change by 2 to 4%. OBJECTIVES To quantify the effects of common cropping and tillage systems on soil erosion and surface runoff during in central Oklahoma, and to provide land managers information they need to better adapt to climate change and to conserve soil and water resources. MATERIALS AND METHODS Study site: 4-acre watershed at El Reno, Oklahoma. Four tillage systems: IT (intensive till, 4 passes/yr, chisel as primary till); RT (reduced till, 2 passes/yr, disk as primary till following harvest); DT (delayed till, same tillage as RT but with primary till postponed to planting); NT (no-till, 0 passes/yr). Five cropping systems: annual monoculture of winter wheat, soybean, sorghum, and cotton; annual rotation of winter wheat- summer soybean Climate data: baseline ; future change Erosion model: Water Erosion Prediction Project (WEPP). Four GCMs: CCSR/NIES, CGCM2, CSIRO-Mk2, HadCM3. Three emission scenarios: A2, B2, GGa. Spatiotemporal downscaling: the method of Zhang (2005) for downscaling GCM climate projections to the target location. RESULTS CONCLUSIONS Compared with the present climate, annual precipitation will decrease by 6% while precipitation variance will increase by 12% (P=0.05) at the study location during Compared with the present climate, annual runoff and soil loss averaged over 18 cropping and tillage systems will increase by 19.5% and 43.5%, respectively, during (P=0.05). Annual runoff in each cropping system during follows the order of IT>RT>DT>NT except NT in cotton and soybean due to limited residue cover. Simulated soil loss in each cropping system follows the order of IT>RT>DT>NT except RT in cotton and soybean. DT and NT are able to keep soil loss rates in the next 30 years below the current levels of the conventional till. Averaged runoff and soil loss in each tillage system follow the order of cotton>soybean>sorghum>wheat>double cropping of wheat and soybean during , showing that wheat is a preferred choice for controlling soil erosion. REFERENCE IPCC (2007). Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to IPCC-AR4. Cambridge University Press, Cambridge, UK. SWCS (2003). Conservation implication of climate change: soil erosion and runoff from cropland. A report from Soil and Water Conservation Society, SWCS, Ankeny, Iowa. Zhang, X.C Spatial downscaling of global climate model output for site- specific assessment of crop production and soil erosion. Agric. For. Meteorol. 135: Figure 2.