Nitrogen uptake and transpiration by plant effects on nitrate leaching from granitic regosol

Field and soil column experiments were conducted to analyze the effects of N uptake and transpiration by corn on nitrate-nitrogen (NO3-N) leaching in a granitic regosol and to evaluate the contribution of plant growth to the reduction of NO3-N leaching. In the field experiment, NO3-N leaching, N uptake by corn and retained N (inorganic N and microbial biomass N) were monitored in conventional planting density (CPD), high planting density (HPD) and no planting (NP) treatments. Nitrogen (N) was applied as (NH4)2SO4 at the rate of 300 kg N ha-1 and corn (Zea mays L.) was sown. In the soil column experiment, 1500 mg N column-1 was applied and corn was sown in four treatments; the no plant (NP), 1-, 2- and 4-plant column-1. NO3-N leaching, N uptake and transpiration by corn and retained NO3-N in the soil were measured. In the field experiment, cumulative NO3-N leaching in the NP treatment was 208 kg N ha-1 from 38 to 49 days after treatment. In the CPD and HPD treatments, NO3-N leaching was reduced to 148 kg N ha-1 and 73 kg N ha-1, respectively. N uptake by corn and retained N in the soil increased with increasing of planting density. Cumulative NO3-N leaching was negatively correlated with N uptake by corn (r = -0.940, P < 0.01, n = 10). NO3-N leaching decreased as N uptake by corn increased above 60 kg N ha-1. In the soil column experiment, cumulative NO3-N leaching was decreasing with increasing of planting density because of increasing of N uptake by corn and the amount of retained NO3-N in soil. The amount of retained NO3-N in soil was positively correlated with transpiration by corn (r = 0.943, P < 0.01, n = 12). We concluded that NO3-N leaching from a granitic regosol during the rainy season could be reduced by the increasing of planting density due to the increase of N uptake by plants and the increase of retained N in soil derived from the increasing of transpiration by plants