Nitrate leaching in granitic regosol as affected by N uptake and transpiration by corn

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)(2)SO4 at the rate of 300 kg N ha(-1) and corn (Zea mays L.) was sown. In the soil column experiment, 1,500 mg N per column was applied and corn was sown in four treatments: no plants (NP), 1-plant, 2-plants and 4-plants per column. 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. Nitrogen uptake by corn and retained N in the soil increased with increasing plant 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 decreased with increased planting density because of increased N uptake by corn and the amount of retained NO3-N in the soil. The amount of retained NO3-N in the 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 increasing the planting density because of the increase in N uptake by plants and the increase of retained N in the soil derived from the increase in transpiration by plants.