Inorganic N accumulation in soil
Table 2 shows the amounts of accumulated soil inorganic N(NO3− N and NH4+ N) at jointing and maturity stages.
Our results showed that NH4+ N accumulation did not differ at jointing and maturity stages among soil layers perhaps due to the rapid nitrification
(Liu et al., 2003) (Table 2).
At jointing stage, NO3 − N accumulation increased with soil depth, as did the basal N rate in all soil layers, which was highest in the 40–60 cm soil layer in all treatments except for N0.
Thus,soil NO3− N leached fast and deep as the basal N rate increased.
However, NO3− N mainly remained in the 0–40 cm soil layer at maturity. The high accumulation of NO3− N in the upper soil would be beneficial to crop later growth, but with risks to leaching.