Effects of reducing water and nitrogen supplies in rotated wheat with previous plastic mulched maize

To combat low crop productivity in long-term continuous cropping systems, it is necessary to study the effects of no-tillage and continued mulched plastic to optimize cultivation and establish cost-saving and benefits-increasing technology in Hexi irrigated areas in Gansu Province. A field experiment was conducted in northwestern irrigated areas in 2016-2017 to evaluate the yield, light energy, irrigation water utilization, and economic benefits of all combinations of two tillage practices, two irrigation levels, and three nitrogen application levels on wheat. The two tillage practices included no-tillage and continued mulched plastic in previous maize (NT) and conventional tillage in previous maize after removing the mulched plastic from soil (CT). The two levels of irrigation included the local conventional irrigation amount, 2400 m³·hm^-2 (high: I2), and the local conventional irrigation amount reduced by 20%, 1920 m³·hm^-2 (low: I1). The three levels of nitrogen application included the local conventional nitrogen amount, 225 kg·hm^-2 (high: N3), the local conventional nitrogen amount reduced by 20%, 180 kg·hm^-2 (medium: N2), and the local conventional nitrogen amount reduced by 40%, 135 kg·hm^-2 (low: N1). The results showed that NT increased the leaf area duration (LAD) of wheat across all growth stages by 21.6% to 26.1%, and the LAD remained high from the wheat filling to the maturity stage, increasing by 41.3% to 45.2% (P < 0.05), compared with CT, and delaying senescence. A 20% reduction in irrigation and N application combined with NT (NTI1N2) resulted in a greater LAD (by 34.8% to 50.7%) from the wheat filling to the maturity stage than CT with conventional high levels of irrigation and nitrogen (CTI2N3). NT increased wheat grain yield, light use efficiency, and irrigation water use efficiency by 10.1% to 10.4%, 5.6% to 12.3%, and 10.1% to 10.3% (P < 0.05) compared with CT, respectively. The grain yield, light use efficiency, and irrigation water use efficiency were significantly increased by 15.2% to 22.0%, 8.1% to 18.5%, and 44.0% to 52.5% with NTI1N2 compared with CTI2N3, respectively. NT integrated with reduced irrigation and nitrogen application reduced the production cost and improved the net return and input-output ratio. The NTI1N2 treatment increased the net return and input-output ratio by 22.9% to 23.9% and 34.8% to 35.1%, respectively. In addition, the benefit per cubic meter of water increased by 53.6% to 68.9% with NTI1N2 compared with CTI2N3 treatment. These results suggest that no-tillage and continued mulched plastic in previous maize with low irrigation (1920 m³·hm^-2) and medium nitrogen (180 kg·hm^-2) can reduce costs and increase the benefits of wheat production in Hexi irrigated areas in Gansu Province.