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)₂SO₄ 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.