Abstract
Unreasonably high irrigation levels and excessive nitrogen (N) supplementation are common occurrences in the North China Plain that affect winter wheat production. Therefore, a 6-yr-long stationary field experiment was conducted to investigate the effects of irrigation and N regimes on root development and their relationship with soil water and N use in different soil layers. Compared to the non-irrigated treatment (W0), a single irrigation at jointing (W1) significantly increased yield by 3.6–45.6%. With increases in water (W2, a second irrigation at flowering), grain yield was significantly improved by 14.1–45.3% compared to the W1 treatments during the drier growing seasons (2010–2011, 2012–2013, and 2015–2016). However, under sufficient pre-sowing soil moisture conditions, grain yield was not increased, and water use efficiency (WUE) decreased significantly in the W2 treatments during normal precipitation seasons (2011–2012, 2013–2014, and 2014–2015). Irrigating the soil twice inhibited root growth into the deeper soil depth profiles and thus weakened the utilization of soil water and NO3-N from the deep soil layers. N applications increased yield by 19.1–64.5%, with a corresponding increase in WUE of 66.9–83.9% compared to the no-N treatment (N0). However, there was no further increase in grain yield and the WUE response when N rates exceeded 240 and 180 kg N ha−1, respectively. A N application rate of 240 kg ha−1 facilitated root growth in the deep soil layers, which was conducive to utilization of soil water and NO3-N and also in reducing the residual NO3-N. Correlation analysis indicated that the grain yield was significantly positively correlated with soil water storage (SWS) and nitrate nitrogen accumulation (SNA) prior to sowing. Therefore, N rates of 180–240 kg ha−1 with two irrigations can reduce the risk of yield loss that occurs due to reduced precipitation during the wheat growing seasons, while under better soil moisture conditions, a single irrigation at jointing was effective and more economical.
Highlights
The North China Plain covers an area of 3.2 × 105 km2
With increased irrigation (i.e., W2), wheat yield was significantly increased by 14.1, 45.3, and 29.3% compared to W1 in the 2010–2011, 2012–2013, and 2013–2016 growing seasons, respectively, in which the rainfall was lower or unevenly distributed during the wheat growing seasons (Figure 1)
No significant differences were found between W1 and W2 in the 2011–2012, 2013–2014, and 2014–2015 growing seasons (Figure 2, Table 2)
Summary
The North China Plain covers an area of 3.2 × 105 km. Due to climatic conditions, a highly intensive winter wheat and summer maize double-cropping system is the dominant, high-yielding agricultural production system (Zhao et al, 2007), supplying more than 50% of the winter wheat (Triticum aestivum L.) and 33% of the summer maize (Zea mays L.) produced in China (National Bureau of Statistics, 2013). Water is the main limiting factor in the North China Plain, and crop production relies mainly on groundwater irrigation (Hu et al, 2010; Zhang et al, 2010; Li et al, 2015). There are 4–5 irrigations supplied by some farmers during the wheat growing seasons in this region, which leads to a lower water use efficiency (WUE; Sun et al, 2010). Appropriate irrigation regimes are fundamental to increase WUE so as to develop sustainable wheat production in the North China Plain (Li et al, 2015). It is important to obtain a balance between high yield and reduced water supply in winter wheat by increasing its WUE in this region (Zhong and Shangguan, 2014)
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