To explore the effect of irrigation at the jointing stage on nitrogen (N) redistribution after flowering and productivity effects of water and N in winter wheat (Triticum aestivum L.), a 2‐yr field experiment was conducted between 2015 and 2017. Three irrigation regimes were designed as follows: rain‐fed (W0), irrigation at jointing and 7 d after flowering (W1), and irrigation at 7 d after flowering (W2). Compared with W2, W1 increased spike number, kernels per spike, and N and dry matter (DM) accumulation at flowering; delayed the senescence of flag leaves after flowering; increased the flag leaf photosynthetic rate, redistribution of N and DM from vegetative organs to grains in the middle and late grain filling stages, and grain yield; and decreased N and DM redistribution and grain weight during early grain development. This may be the reason why the N uptake efficiency and N productive efficiency were higher, whereas the productivities of water and N had no significant difference, and even water productivity was lower under W1 than W2. Therefore, on the basis of suitable water supply from jointing to flowering, achieving a high N and DM accumulation at flowering and high kernels per spike, if the grain development can be accelerated earlier and the redistribution of N and DM can be promoted, it is expected to further improve the productivities of water and N.
Latest published information is limited on agronomic responses of winter wheat to irrigation quantity and the necessity of irrigation at the anthesis stage. This study was conducted to (1) evaluate winter wheat yield, water use, assimilate redistribution and economic benefit with respect to water input and (2) quantify relationship between water input and yield to develop a standard for withholding irrigation at anthesis. A 4‐year long field experiment was conducted to evaluate winter wheat water use, yield formation pathway and farmers' income under three irrigation regimes: rainfed, irrigation at sowing and jointing (SJ‐W) and irrigation at sowing, jointing and anthesis (SJA‐W). The yield formation pathway was correlated with the water‐induced variation in assimilate redistribution and accumulation. Throughout the experimental period, wheat yield was 19–38% lower in rainfed than that under other irrigation treatments. Moreover, SJ‐W treatment substantially increased biomass accumulation at anthesis, accelerated assimilate redistribution in vegetative organs and eventually resulted in a similar wheat yield to that of SJA‐W. Simultaneously, the SJ‐W treatment had lower irrigation water, reduced additional irrigation cost, suppressed yield loss and obtained a similar farmer's net income to the SJA‐W treatment. Water‐induced variations in yield were determined by irrigation, rainfall and soil water storage. SJ‐W plots receiving 204–331 mm water input (rainfall + irrigation) before anthesis and holding 549–587 mm soil water during anthesis stage achieved higher irrigation water use efficiency and yield relative to the rainfed and SJA‐W plots. In contrast, water input under rainfed plots exceeded 200 mm before anthesis, limiting yield substantially even when seasonal soil water consumption exceeded 160 mm. Developing a standard for withholding irrigation at the anthesis stage should incorporate 204–331 mm of water input (rainfall + irrigation) before anthesis and 549–587 mm soil water storage at anthesis, which could achieve a high wheat yield and save water resources.
Crop nitrogen (N) uptake depends on the root absorption area and the soil N availability which are closely related to the soil water status. With the increasing water shortages in the North China Plain, supplemental irrigation (SI) to winter wheat is a promising technique. To clarify the relationships between water and nitrogen use, four SI regimes in Tritcum aestivum L. cv. Jimai 22 were set up: no‐irrigation after emergence (T1), SI at jointing and anthesis (T2), SI at sowing, jointing and anthesis (T3), and SI at pre‐wintering, jointing and anthesis (T4). The results indicate that T2 had higher root length density (RLD) and root surface area density (RAD) in the 0–20, 60–80, and 80–100 cm soil layers, as well as higher post‐anthesis N uptake from soil by 23–26% in 2012–2013 and 162–177% in 2013–2014, compared to T3 and T4. The grain yield under T2 was lower than T3 but was not significantly different from T4, whereas its water use efficiency (WUE) was higher relative to both T3 and T4. There were no significant differences among T2, T3, and T4 in N use efficiency (NUE). The N uptake after jointing and WUE were positively correlated with the RLD and RAD in the 0–20 cm soil layer. The NUE was positively correlated with the RLD and RAD in the 20–40 cm soil layer. These results indicate that timely SI at jointing and anthesis was dependent on a suitable water supply at sowing, which increased the soil water content in the upper soil layer after jointing and improved the absorption area of the roots in both the deep and surface soil layers; this further improved the post‐anthesis N uptake from the soil and the WUE. This approach can be a valuable way to maintain high grain yields and NUE in winter wheat while using less irrigation and achieving higher WUE in the North China Plain.
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