Low N apparent surplus with higher rice yield under long-term fertilizer postponing in the rice–wheat cropping system

Abstract

Nitrogen (N) fertilization increases rice yield, but inappropriate N fertilizer application increases N loss and the risk of environmental pollution. Short-term fertilizer postponing (FP) generally reduces N apparent surplus and increases rice yields, but the effects of long-term FP on N surplus and rice yields remain unknown. Our study was the first to investigate the impacts of long-term FP (11 years) on N apparent surplus and rice yields. FP effects in the short term (≤6 years) did not affect rice yields, whereas FP effects in the long term (>6 years) increased rice yields by 13.9% compared with conventional fertilization (CF). FP did not affect panicles per unit area, 1000-kernel weight, and filled-kernel rate, but spikelets per panicle increased over time due to spikelet formation stimulation. FP also reduced the N apparent surplus over time more strongly than CF owing to higher N accumulation and N utilization efficiency. FP effects in the long term also significantly increased soil organic matter, total N, and NH4+-N content. Our results were supported by a pot experiment, showing that rice yields in soils with a history of FP were significantly higher than those for soils without a history of FP, indicating that FP increased rice yields more strongly in later years mainly because of soil quality improvement. Our findings suggest that long-term FP can reduce N loss while increasing rice yields by improving soil quality.