Fate of each period fertilizer N in Mollisols under water and N management: A 15N tracer study

Abstract

For soil-crop systems, it is important to increase the retention of fertilizer N that is not effectively utilized by crops in stable forms in soil and reduce fertilizer N loss from agroecosystems through agricultural practices. However, it remains obscure how the fate of fertilizer N will be affected by water and N management. To further clarify the effects of water and N management on the fate of each period fertilizer N and residual fertilizer N amounts of different derived forms, a field experiment was conducted in Mollisols in Northeast China. This experiment combined a field plot experiment with a flied microplot 15N isotope experiment, and six treatments were performed: two irrigation management modes (controlled irrigation and flooded irrigation) and three fertilizer-N rates (85, 110 and 135 kg/ha). Additionally, the basal, tillering, and panicle fertilizer N were tracked by 15N-labeled urea to study the fate of each period fertilizer N. The present study showed that under controlled irrigation (CI), fertilizer-derived N in different forms increased with the increase N rate. Under flooded irrigation (FI), with the increase N rate, the residual organic nitrogen (NO) first increased and then decreased, and the other forms of fertilizer-derived N increased. In the total residual fertilizer N in soil, residual basal fertilizer N accounted for the highest proportion under the two irrigation modes, residual tillering fertilizer N accounted for the lowest proportion under FI, and panicle fertilizer N accounted for the lowest proportion under CI. NO accounted for the highest proportion of the residual amount of each period fertilizer N under CI and FI, while NO3--N accounted for the lowest proportion under CI, and fixed ammonium accounted for the lowest proportion under FI. Compared with FI, CI increased the total residual fertilizer N amount and promoted the conversion of residual fertilizer N into NO. The present study suggested that CI, as a water-saving irrigation mode, not only decreased agricultural water consumption but also increased fertilizer N retention in soil and enhanced the conversion of residual fertilizer N into NO. The establishment of appropriate water and N management has great potential for the regulation of residual fertilizer N in paddy soil.