Crop and soil nitrogen responses to phosphorus and potassium fertilization and drip irrigation under processing tomato

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.