Conservation tillage and nutrient management in dryland farming in China

Keywords: China,conservation tillage, crop residue, dryland farming, fertilizer,long-term,maize,manure,nutrient balance,nutrient dynamics,nutrient management, rainfall,soil fertility, soil organic carbon,wheatNorthernChinahas alargedryland area. Rainfed maize and wheat are the main cereals grown here, accounting for 28% ofChina's cereal production. Crop yieldsare constrained by low and variable rainfall, wind and watererosion, low soil fertility,and poorsoilmanagement. Some of these constraints can be diminished by conservation tillage practices and improved nutrient management practices. This thesis characterizes the relations between rainfall and crop yields, and examines the effects of various tillage and nutrient management practices on erosion, crop yields and water and nutrient use efficiencies. The thesis is based on desk studies, long-term field experiments and model calculations.The desk studies indicate that wind erosion in spring under conventional tillage removes on average between 50 and 1000 t ha-1yr-1of carbon (C) and between 5 and90 kgha-1yr-1of nitrogen (N) from the top soil of drylands in northernChina. This high loss is related to the monsoonal climate with very dry winters and spring and wet summers with incidental very heavy rain showers. Yields of maize and wheat were highly related to the rainfall distribution. Results of the long-term field experiments indicated that the observed decline in crop yields over time were related to changes in total rainfall and its distribution over the growing season, but also to depletion of the soil potassium (K) reserve. Returning crop residues and manure to the soilwashighly effective in restoring negative K and C balances.Reduced tillage, i.e. ploughing after harvest but not in spring before seeding, reduced wind erosion by 50-90%, and contributed to improved seedling emergence.The positive effect of reduced tillage on soil water availability to the crop was made stronger by use of crop residue, either incorporated or applied as surface mulch.Reduced tillage combined with improved nutrient management also increased water use efficiency (WUE) and nutrient use efficiency (NUE).The analysis of nutrient balances and soil fertility indices revealed that nutrient inputs in most treatments were far from balanced. It is concluded that the concepts of 'ideal soil fertility level' and 'response nutrient management' are applicable to the variable rainfall conditions of dry land areas.Simulations using the Century model wereconducted to forecast the effects ofmanagement on soil organic carbon (SOC) dynamics.