Effects of nitrogen applications on soil nitrogen balance and nitrogen utilization of winter wheat in a rice–wheat rotation

To clarify characteristics of soil nitrogen (N) supply and N balance in soil–plant system, field experiments were conducted in Nanjing, China, to investigate the effects of N application rates (0, 120, 210, 300 kg hm−2) and basal–top-dressing ratios (30–70%, 50–50%, 70–30% at 210 kg N hm−2) on the temporal–spatial distributions of soil inorganic N, the apparent soil N surplus, the N utilization efficiency, and the grain yield of winter wheat (Triticum aestivum L.) in 2006–2008. NH4+N content in the 0–40 cm soil layer increased with N application rates at overwintering and booting stages due to basal and topdressing N application, then after rapidly declined to its initial level. NO3−N content in the 0–60 cm soil layer increased as the basal N rate increased before jointing and also increased with an increase of the topdressing N dose after jointing. NO3−N mainly accumulated in the 40–60 cm soil layer at jointing stage, which inferred that NO3−N leached significantly to deep layer soil before jointing. At maturity, NO3−N accumulated mainly in the 0–40 cm soil layer due to topdressing after jointing. In all treatments, the soil apparent N surplus (ANS) differed at different growth stages. Throughout growth duration, ANS increased as the N rate and basal N ratio increased, which was mainly related to a large N surplus before jointing stage. N utilization efficiency and grain yield increased at the appropriate N rate and topdressing N ratio. Data from two growth seasons showed that the N rate to 210 kg hm−2, with half applied as topdressing, improved grain yield, plant N uptake and N utilization efficiency, and reduced leaching loss of N fertilizer.

► N rate and topdressing ratio changed NO3−N and NH4+N content in soil layer during wheat growth period.
► NO3−N leaching increased with increase of N rate and basal N ratio before jointing.
► Apparent N surplus increased as N application rate and basal N ratio increased.
► The appropriate N rate and topdressing reduced N leaching and increased N utilization.