Effect of spatio-temporal deficit irrigation and nitrogen supply on water and nitrogen use of tomato

For sustainable water use in protected agriculture, crop-specific and water-saving irrigation techniques that do not negatively affect crop productivity must be developed. Globally, successful attempts have been documented regarding the use of deficit irrigation methods. Regulated deficit irrigation (RDI) and controlled alternate partial root-zone irrigation (CRAI) have been used to improve irrigation water use efficiency (IWUE) of various crops. Because nitrogen (N) has been the most widely used fertilizer, N demand was likely to grow in the future. Thus the optimization of water and fertilizer use in vegetable production was a critical water/fertilizer-saving strategy. Four irrigation treatments under CRAI and three N levels were explored for optimum modes of water and fertilizer supply in vegetable production under water-saving irrigation in a pot tomato experiment. The irrigation treatments were W_HW_H (high water level through out growth period), W_HW_L (high water level at flowering and fruit-setting stages with low water level at full-fruit stage), W_LW_H (low water level at flowering and fruit-setting stages with high water level at full-fruit stage) and W_LW_L (low water level through out growth period). Then the N levels included NH high N, 0.45 g(N)·kg^-1, N_M medium N, 0.30 g(N)·kg^-1 and N_L low N, 0.15 g(N)·kg^-1. Using conventional irrigation (CI) as control experiment, the effect of spatio-temporal of deficit controlled deficit irrigation (STCDI), which combined RDI and CRAI, and N rates on the vegetative parts of tomato dry matter accumulation (DMA), irrigation water use efficiency (IWUE), N accumulation (N_A) and soil water and mineral N distribution were studied. Compared with CI, the results showed that W_HW_H, W_LW_H, W_HW_L and W_LW_L under CRAI decreased tomato DMA by 4.52%, 11.93%, 17.76% and 23.94%, respectively. They respectively decreased N_A by 1.74%, 12.86%, 15.50% and 22.47%. The four irrigation treatments decreased N dry matter production efficiency (NDMPE) by 2.24%, 3.93%, 2.55% and 0.89% and increased IWUE by 12.39%, 8.99%, 15.02% and 12.96%, respectively. DMA, IWUE and N_A of N_A were highest under CRAI. Compared with N_L, N_M and N_H decreased tomato NDMPE by 6.87% 12.70% and 17.81% 24.38% while increasing soil NO₃^--N content by 31.64% 159.58% and 57.37% 297.37%, respectively. High DMA, IWUE and N_A were obtained under W_HW_H, CRAI and N_M. The optimum mode for water and N supply under CRAI was 80% of CI irrigation (which was 70% 85% of soil field capacity) and nitrogen rate of 0.30 g(N)·kg^-1(dry soil).