Alternate Partial Root-Zone Drip Nitrogen Fertigation Reduces Residual Nitrate Loss While Improving the Water Use but Not Nitrogen Use Efficiency

The efficient utilization of irrigation water and nitrogen is of great importance for sustainable agricultural production. Alternate partial root-zone drip irrigation (APRD) is an innovative water-saving drip irrigation technology. However, the coupling effects of water and nitrogen (N) supply under APRD on crop growth, water and N use efficiency, as well as the utilization and fate of residual nitrates accumulated in the soil profile are not clear. A simulated soil column experiment where 30–40 cm soil layer was (15)NO(3)-labeled as residual nitrate was conducted to investigate the coupling effects of different water [sufficient irrigation (W(1)), two-thirds of the W(1)(W(2))] and N [high level (N(1)), 50% of N(1) (N(2))] supplies under different irrigation modes [conventional irrigation (C), APRD (A)] on tomato growth, irrigation water (IWUE) and N use efficiencies (NUE), and the fate of residual N. The results showed that, compared with CW(1)N(1), AW(1)N(1) promoted root growth and nitrogen absorption, and increased tomato yield, while the N absorption and yield did not vary significantly in AW(2)N(1). The N absorption in AW(2)N(2) decreased by 16.1%, while the tomato yield decreased by only 8.8% compared with CW(1)N(1). The highest IWUE appeared in AW(2)N(1), whereas the highest NUE was observed in AW(2)N(2), with no significant difference in NUE between AW(2)N(1) and CW(1)N(1) at the same N supply level. The (15)N accumulation peak layer was almost the same as the originally labeled layer under APRD, whereas it moved 10–20 cm downwards under CW(1)N(1). The amount of (15)N accumulated in the 0-40 cm layer increased with the decreasing irrigation water and nitrogen supply, with an increase of 82.9–141.1% in APRD compared with that in CW(1)N(1). The utilization of the (15)N labeled soil profile by the tomato plants increased by 9–20.5%, whereas the loss rate of (15)N from the plant-soil column system decreased by 21.3–50.1% in APRD compared with the CW(1)N(1) treatment. Thus, APRD has great potential in saving irrigation water, facilitating water use while reducing the loss of residual nitrate accumulated in the soil profile, but has no significant effect on the NUE absorbed.