Fate of nitrogen from green manure, straw, and fertilizer applied to wheat under different summer fallow management strategies in dryland

Returning crop residues to soil is an effective approach for sustaining organic matter concentrations and increasing nutrient availability in soils. A 2-year micro-plot field experiment was conducted in dryland to determine the green manure, straw, and fertilizer nitrogen (N)-15 uptake by wheat, their residual N in soil and losses; the effect of straw application on the fate of N from green manure and vice versa was also determined, as well as the effect of crop residue additions on the fate of fertilizer N. All the micro-plots were treated with the same amount of 15N-labeled or unlabeled fertilizer. The green manure N uptake by wheat, residual N, and N loss were 22.4, 51.7, and 25.9 % of the total added green manure N over the 2-year experiment. Straw addition significantly decreased the green manure residual soil N but increased the cumulative losses. The straw N taken up by wheat, residual N in soil, and N loss were 8.3, 31.0, and 60.7 %, respectively. Green manure addition significantly decreased the straw N taken up by wheat, increased the residual soil N, and reduced the N loss. Furthermore, the fertilizer N taken up by wheat, residual N in soil, and N loss were 32.4, 32.3, and 35.2 %, respectively. Crop residue additions significantly increased the uptake of fertilizer N by wheat in the second year. The application of inorganic N fertilizer in combination with appropriate crop residues may be an effective approach to improve the long-term fertilizer N use efficiency, soil quality, and crop yield in wheat–summer fallow rotation systems in dryland.