Optimizing the spatial distribution of roots by supplemental irrigation to improve grain yield and water use efficiency of wheat in the North China Plain

Soil moisture affects the yield and water use efficiency (WUE) of winter wheat (Triticum aestivum L.) by regulating the spatial distribution of roots. Therefore, appropriate supplemental irrigation (SI) schemes are essential to achieve high yield and high WUE of wheat by constructing a reasonable root structure. In this study, field experiments were conducted the North China Plain (NCP) from 2018 to 2020. Based on the soil moisture management at sowing on a consistent basis, four SI regimes were set up: no irrigation after seedling emergence (W0), SI at jointing (W1), SI at jointing and anthesis (W2), and SI at regreening, jointing, and anthesis (W3). The results showed that although the grain yield of wheat increased with the SI frequency, the WUE decreased with increasing SI amount. SI at jointing and anthesis significantly increased WUE without reducing or slightly reducing the grain yield. The grain yield and WUE in 2018–2019 were significantly higher than those of the corresponding treatments in 2019–2020, and the yield of Bainong 4199 was higher than that of Zhoumai 18. The grain yield and WUE in 2018–2019 were significantly higher than those of the corresponding treatments in 2019–2020. The root length density (RLD) in the 0–20-cm soil layer increased with increasing SI frequency, but the proportion of RLD in the 40–60-cm soil layer decreased. The average RLD in the 0–60-cm soil layer and grain yield of Bainong 4199 were significantly greater than that of Zhoumai 18. Correlation analysis showed that the grain yield and WUE was positively correlated with the RLD in the 0–20-cm soil layer, and reached a very significant level with RLD in the 0–20-cm soil layer between rows. W2 and W3 in terms of root vigor and the grain filling rate 30 days after anthesis were significantly higher than W1 and W0 and also increased the contribution of post-anthesis dry matter to grain, resulting in an increase in grain weight. These results demonstrated that SI at jointing and anthesis could optimize the spatial distribution of roots, maintain higher root activity and filling rate at the late stage, increase accumulation and translocation of post-anthesis dry matter, and finally improve the yield and WUE. Therefore, we propose that Bainong 4199 was the preferred cultivars for this experiment，under sufficient soil moisture conditions before sowing, SI at jointing and anthesis is the optimal irrigation scheme for wheat on the NCP.