[Effects of water limiting and nitrogen reduction on nitrogen use and apparent balance of winter wheat in the Guanzhong Plain, Northwest China].

Effects of water limiting and nitrogen reduction on yield, nitrogen use efficiency and nitrogen apparent balance of wheat were investigated to explore whether it would be feasible to restrict water and reduce nitrogen in wheat production of the Guanzhong Plain and thus to provide scientific supports for yield-stable, high-efficiency, and environment-friendly developments in the irrigated production of winter wheat. Following a split-plot design with two water regimes as the main plots and four N addition rates as sub-plot factors, a field experiment (2017-2019) was conducted in Yangling, Shaanxi. The two water regimes were conventionally irrigating at the rate of 60 mm during the overwinter period and at the jointing stage, respectively (W, a conventional practice) and irrigating at a rate of 60 mm during the overwintering period (W, a restrictive irrigation practice). The four nitrogen addition rates were 300 kg·hm(N, a conventional N rate), 225 kg·hm (N, a nitrogen rate of 25% less than the convention), 150 kg·hm(N, a nitrogen rate 50% of less than the convention), and 0 kg·hm(N, no nitrogen applied). The decreased irrigation rate and nitrogen rate significantly increased nitrogen content in the plants and grains, yield, N output, nitrogen use efficiency, nitrogen harvest index, nitrogen recovery efficiency, and nitrogen agronomic efficiency, reduced nitrate leaching and N surpluses, and maintained nitrogen balance. With both W and N adopted, the increased irrigation rate and nitrogen rate did not affect yield and N output of winter wheat in 2017-2019. Plant nitrogen content with both W and N adopted increased by 0.1%-25.5% and 14.0%-31.6% and the grain nitrogen content increased by 0.1% and 4.6%, compared with those with both W and N adopted in 2017-2018 and 2018-2019, respectively. Nitrogen use efficiency, nitrogen harvest index, nitrogen recovery efficiency, and nitrogen agronomic efficiency were averagely increased by 95.3%, 4.2%, 81.7% and 33.0% respectively. The N surplus was decreased by 97.2% and 95.1%, which effectively alleviated soil nitrate leaching. Considering all the indicators, irrigating at 600 m·hm during the overwintering period plus applying nitrogen at 150 kg·hm could achieve high yield, high efficiency, and environment friendly development of winter wheat in the Guanzhong Plain of Shaanxi.