Plant nitrogen utilization and soil nitrogen status in rhizosphere of maize as affected by various nitrogen rates in wheat-maize rotation system

A field experiment was conducted on fluvo-aquic soil (aquic inceptisol) in Hengshui of Hebei province. The objective was to investigate the effects of different nitrogen rates on inorganic nitrogen and microbial biomass nitrogen in rhizosphere and non-rhizosphere soils, and nitrogen utilization by maize plants under the rotation system of winter wheat and summer maize. The results showed that in comparison to farmers' conventional N fertilization (300 kg/ha for winter wheat and 240 kg/ha for maize), reducing nitrogen application rates by 25% and 40% in the rotation system of winter wheat and summer maize did not significantly affect total biomass and total nitrogen accumulation of summer maize, but improved nitrogen use efficiency for maize plants. The soil NH+4-N contents presented no significant difference among various nitrogen application rates. The NO-3-N contents in rhizosphere soils did not significantly decreased with N application reduction, but decreased in non-rhizosphere soils. Especially in tasseling stage, the NO-3-N contents in non-rhizosphere soils under conventional N rate were one times higher than that under 60% of conventional N rate. The concentrations of microbial biomass carbon and nitrogen in rhizosphere soils did not change under the treatments of different nitrogen application rates. However, the levels of microbial biomass carbon and nitrogen in non-rhizosphere soils were increased when reducing N application rates by 40%. It is suggested that in those area with excessive nitrogen application in the rotation system of winter wheat and summer maize, nitrogen application should be reduced to an appropriate rate.