Distribution and fate of nitrogen fertilizer in various soil nitrogen pool at wheat seedling stage

The dynamics of various soil nitrogen pool after nitrogen fertilizer application at wheat seedling stage was studied by pot experiment and 15N trace technique. The results showed that soil nitrogen of crop uptake was 58.1% of total nitrogen of crop uptake, and fertilizer nitrogen was 41.9% of that at 28th day after N application. Fertilizer nitrogen recovery rate, residual rate and losses rate were 55.3%, 24.3% and 20.4% respectively. The NH + 4-N was 50.5% of applied nitrogen fertilizer in short time after application. NH4+-N in soil sharply decreased with nitrification and crop uptake afterwards. NO3--N in soil increased in short time after application and decreased afterwards. High NO3--N in soil appeared at 7th day after N application, which means strong nitrification before that time. The fixed NH4+ fertilizer nitrogen was 33.7% of applied nitrogen at second day after N application and 2.4% at 28th day, which showed that the fixed NH + 4 from fertilizer nitrogen at early period could be used by crop at late period. The microbial biomass N was 15.2% from fertilizer nitrogen at 7th day after N application and 2.4% at 28th day. The fertilizer nitrogen in various soil nitrogen pool significantly decreased with crop growth. Fertilizer nitrogen mainly existed as organic form when other soil nitrogen pools almost was exhausted at 28th day after N application. Soil nitrogen mineralization was low without crop system, and high in crop system. Soil nitrogen mineralization increased with nitrogen fertilizer application which showed positive priming effect.