小麦开花期适量灌溉提高水氮利用效率减少土壤硝态氮淋洗的机理

  【目的】  探究开花期土壤水分含量对小麦植株氮素积累转移、土壤硝态氮含量、小麦产量及氮素利用率的影响，为小麦氮素高效利用及节水高产栽培提供理论依据。  【方法】  于2018—2019和2019—2020年两个小麦生长季，在大田条件下，供试品种为济麦22，在开花期设置3个水分处理:不灌水 (W0)、将0—40 cm土层土壤相对含水量补灌至70% (W1) 和85% (W2)。测定了小麦开花期和成熟期氮素的积累和转运、小麦产量及氮素利用率，并对小麦成熟期0—200 cm土层土壤硝态氮含量进行分析。  【结果】  1) W1处理中，两个小麦生长季开花期营养器官贮存氮素转移量比W0和W2处理平均提高11.63%和7.27%，氮素转移率分别增加9.49%和6.11%；成熟期籽粒氮素分配量平均提高22.5%和12.9%，但叶片和穗轴+颖壳中的氮素分配量显著低于W0和W2处理，因而提高了氮素收获指数。2) 补灌至70% (W1) 处理降低了60—120 cm土层土壤硝态氮含量，小麦氮素吸收量比W0和W2处理平均提高11.4%和6.5%，土壤氮素表观盈余量平均降低51.0%和40.9%，W1处理减少硝态氮向深层土壤淋溶的风险，降低了0—200 cm土层土壤中无机氮的残留量和土壤氮素表观盈余量，有利于小麦根系对土壤氮素的吸收利用。3) W1处理的小麦千粒重比W0和W2处理平均增加11.0%和5.4%，籽粒产量提高25.9%和11.8%，水分利用效率平均提高17.0%和12.7%，氮素吸收效率提高了11.4%和6.5%，氮素利用效率增加了13.0%和4.9%。  【结论】  在小麦开花期，将0—40 cm土层土壤相对含水量补灌至70%，可以显著提高小麦灌浆中后期营养器官贮存氮素向籽粒的转移量和转移率，提高小麦成熟期籽粒中氮素的积累量和分配率，进而提高了产量、氮素收获指数、氮素利用率和水分利用效率，同时降低了60—120 cm土层土壤硝态氮含量，因而减少了环境风险。灌溉过量导致硝态氮过多向下移动，影响根系吸收，水分不足则降低氮素向籽粒的运转。

Mechanism of improving water and nitrogen use efficiency and reducing soil nitrate leaching by suitable irrigation during the anthesis stage of wheat

  【Objectives】  This study investigated the effects of soil water content during the flowering period of wheat on N accumulation and transfer and soil NO₃?-N leaching to provide a theoretical basis for water conservation to promote high wheat yield and efficient N use.   【Methods】  Field experiments were conducted during 2018–2019 and 2019–2020 wheat-growing seasons using Jimai 22 as the test cultivar. Three water treatments were set up during the anthesis stage: no watering (W0), watering 0–40 cm soil depth to a relative moisture content of 70% (W1) and 85% (W2). The wheat N accumulation and translocation at anthesis and maturing stage were determined; wheat yield and N fertilizer efficiency were investigated at the maturing stage, and soil nitrate-nitrogen content in 0–200 cm soil depth was analyzed.   【Results】  After anthesis, the average N transfer in the vegetative organ of W1 at maturity was 11.6% and 7.3% higher than W0 and W2, and the N transfer rate in W1 was 9.5% and 6.1% higher than W0 and W2. At the maturity stage, the grain N distribution in W1 was 22.5% and 12.9% higher than W0 and W2, but the N distribution in the leaf and spike axis and glume in W1 was (P < 0.05) lower than in W0 and W2, thus increasing N harvest index. Compared with W0 and W2, W1 treatment reduced NO₃?-N content in 60–120 cm soil depth, increased wheat N uptake by 11.4% and 6.5%. The apparent excess soil N in W1 treatment was 51.0% and 40.9% lower than W0 and W2, reducing the risk of NO₃?-N leaching into the deeper soil layer. W1 reduced the residual inorganic N in 0–200 cm soil layer and the apparent excess soil N, which benefited absorption and utilization by wheat roots. Compared with W0 and W2, a thousand-grain weight of W1 treatment was 11.0% and 5.4% higher, grain yield was 25.9% and 11.8% higher, and the water use efficiency was 17.0% and 12.7% higher in the two growing seasons. Similarly, N use efficiency was 13.0% and 4.9% higher in W1 than W0 and W2, and the N uptake efficiency was 11.4% and 6.5% higher on average.  【Conclusions】  Irrigating 0–40 cm soil layer to a moisture content of 70% during the flowering period benefits N transfer from vegetative organs to grains in the middle and late grain filling stages and at maturity, thereby promoting grain N accumulation, yield, N harvest index, and water use efficiency. Irrigating to 70% of the soil water capacity at the flowering stage reduces the NO₃?-N content in 60–120 cm soil depth, thereby decreasing the risk of NO₃?-N leaching, which improves wheat N use efficiency and uptake for production. Excessive irrigation leads to excessive downward movement of NO₃?-N, which affects root absorption. Insufficient water, on the other hand, decreases the transport of N to the grains.