Recovery by crop and loss of nitrogen fertilizer applied in rice season in Taihu Lake region

Field micro-plot 15N labeled fertilizer experiment was conducted to investigate the fate of fertilizer N applied in rice season and the residual fertilizer N recovery in the succeeding wheat season in paddy fields in Taihu Lake region. Data showed that 29%–39% of the labeled fertilizer N was present in above-ground rice crop at harvest. Turnover rate of the residual fertilizer N by the succeeding crop was low and only 2.4%–5.2% of the residual soil N was present in the wheat crop. After two rice-wheat rotations, 11%–13% of applied labeled N remained in 0-60 cm soil (mostly in the 0-20 cm soil); leaching of labeled urea applied in rice season was little (only 0.6%–1.1% of the applied N accumulated in 20-60 cm soil), and the leaching of fertilizer N occurred in wheat season and the beginning flooding period of the next rice season; 47%–54% of applied fertilizer N was lost and ammonia emission and nitrification-denitrification were the main pathways. High N and high P inputs did not lead to the increase in grain yield and plant N use efficiency.