Effects of nitrogen application rate on soil inorganic nitrogen distribution,microbial biomass nitrogen content and yield of wheat

Nitrogen plays an important role in grain yield elevation.In order to obtain high grain yield and efficient nitrogen utilization and reduce the possible environmental effects,it is essential to determine the appropriate nitrogen application rate,especially on high fertile soil.A research was conducted to determine the effects of nitrogen application rate on soil in organic nitrogen distribution,microbial biomass nitrogen content,nitrogen uptake and utilization in wheat.The field experiments were carried out on a high fertile soil in Longkou,Shandong,during 20022003.Seven treatments(CK1,CK2,N1,N2,N3,N4,N5) with N application rate being 0,0,105,150,195,240,285 kg/ha was setup.Apart from CK1,135 kg P2O5 and 105 kg K2O per ha was addressed before sowing for the other treatments.The content of nitrate,ammonium and microbial biomass nitrogen in soil,the nitrogen uptake of plant during wheat growing,and the grain yield and the protein content of wheat were analyzed.The results showed,during wheat growing,the amount of(nitrate) accumulation in 0100 cm soil layers of treatments with nitrogen addition was dramatically larger than that without nitrogen addition.When nitrogen application rate was higher than 150 kg/ha,the amount of nitrate accumulation in 0100 cm soil layers increased significantly along with nitrogen addition increasing.Nitrate in upper soil layers with nitrogen treatments moved down obviously with the progression of growing;as the result,at maturity stage,the nitrate content in 60100 cm soil layers of treatments applied nitrogen at the rate of 195285 kg/ha was dramatically higher than that of other treatments.During period of wheat growing,the amount of ammonium accumulated in 0100 cm soil layers showed no obvious change,and no significant difference was found among treatments with nitrogen supplied.Compared with treatments no nitrogen applied,application of nitrogen increased the content of soil microbial biomass nitrogen in 040 cm soil layers during wheat growing.With less than 240 kg/ha nitrogen applied,the content of soil microbial biomass nitrogen (increased) along with nitrogen addition increasing.With nitrogen addition increasing,nitrogen using efficiency of wheat decreased.Supply nitrogen at the rate of 105195 kg/ha elevated the nitrogen uptake amount,biomass,grain yield and protein content of wheat at harvest.With more than 240 kg/ha nitrogen supplied,the nitrogen accumulation rate at later growing period,the nitrogen uptake rate at harvest,biomass and grain protein content decreased.The results indicated, nitrogen applied at the rate of 105150 kg/ha could meet the need of wheat on the current growing season to obtain high grain yield and protein content.Applying more nitrogen would increase the content of soil microbial biomass nitrogen,but might result in large amount of nitrate residue in soil and suspected to leaching loss.