No abstract

Reducing nitrogen (N) loss from agricultural soils as surface runoff is essential to prevent surface water contamination. The objective of 3-year study, 2007–09, was to evaluate surface runoff and N loss from different cropping systems. There were four treatments, including one single-crop cropping system with winter wheat (Triticum aestivum L.) followed by summer fallow (wheat/fallow), and three double-cropping systems: winter wheat/corn (Zea mays L.), wheat/cotton (Gossypium hirsutum L.), and wheat/soybean (Glycine max L. Merrill). The wheat/fallow received no fertiliser in the summer fallow period. The four cropping systems were randomly assigned to 12 plots of 5 m by 2 m on a silty clay soil. Lower runoff was found in the three double-cropping systems than the wheat/fallow, with the lowest runoff from the wheat/soybean. The three double-cropping systems also substantially reduced losses of ammonium-N (NH4+-N), nitrate-N (NO3–-N), dissolved N (DN), and total N (TN) compared with the wheat/fallow. Among the three double-cropping systems, the highest losses of NO3–-N, DN, and TN were from the wheat/cotton, and the lowest losses were from the wheat/soybean. However, the wheat/soybean increased NO3–-N and DN concentrations compared with wheat/fallow. The losses in peak events accounted for >64% for NH4+-N, 58% for NO3–-N, and 41% for DN of the total losses occurring during the 3-year experimental period, suggesting that peak N-loss events should be focussed on for the control of N loss as surface runoff from agricultural fields.

Shortage of water or nutrient supplies can restrict the high nitrogen (N) demand of processing tomato, leaving high residual soil N resulting in negative environmental impacts. A 4-year field experiment, 2006-2009, was conducted to study the effects of water management consisting of drip irrigation (DI) and non-irrigation (NI), fertilizer phosphorus (P) rates (0, 30, 60, and 90 kg P ha -1 ), and fertilizer potassium (K) rates (0, 200, 400, and 600 kg K ha -1 ) on soil and plant N when a recommended N rate of 270 kg N ha -1 was applied. Compared with the NI treatment, DI increased fruit N removal by 101 %, plant total N uptake by 26 %, and N harvest index by 55 %. Consequently, DI decreased apparent field N balance (fertiliser N input minus plant total N uptake) by 28 % and cumulative post-harvest soil N in the 0-100 cm depth by 33 %. Post-harvest soil N concentration was not affected by water management in the 0-20 cm depth, but was significantly higher in the NI treatment in the 20-100 cm depth. Fertilizer P input had no effects on all variables except for decreasing N concentration in the stems and leaves. Fertilizer K rates significantly affected plant N utilization, with highest fruit N removal and plant total N uptake at the 200 kg K ha -1 treatment; therefore, supplementing K had the potential to decrease gross N losses during tomato growing seasons. Based on the measured apparent field N balance and spatial distribution of soil N, gross N losses during the growing season were more severe than expected in a region that is highly susceptible to post-harvest soil N losses.