Straw mulching improves soil water content, increases flag leaf photosynthetic parameters and maintaines the yield of winter wheat with different irrigation amounts

In North China Plain, straw mulching is increasingly applied to the succeeding crops with winter wheat-summer maize double cropping system. However, research results on the effect of maize straw mulching on the yield of winter wheat are inconsistent, and the underlying mechanism of the effect remains unclear. Such information is helpful to guide the field water management for higher yield. In this study, soil moisture, plant growth, photosynthesis and yield of winter wheat field treated with no-till and straw mulching (SM) and non- mulching (N) and three irrigation amounts (high, middle and low irrigation, HI, MI and LI) in four growing seasons in 2013–2016. The results showed that straw mulching improved soil moisture by reducing the days of soil moisture less than 60% field capacity for 2–10 days. Straw mulching increased net photosynthetic rate, stomatal conductance, maximum carboxylation rate (Vcmax), and the maximum rate of photosynthetic electron transport (Jmax) of flag leaves, especially at the post-anthesis measurements, during which, the above parameters increased by 20.6%, 21.9%, 28.7% and 25.2%, respectively. Compared with pre-anthesis measurements, the post-anthesis Vcmax and Jmax values decreased, but the decrease percentage of the SM treatments (10.8–25.7% for Vcmax and 22.0%−49.6% for Jmax) was less than those of N treatments (19.6%−41.4% for Vcmax and 29.3%−61.3% for Jmax). Vcmax and Jmax were significantly linear correlating to leaf nitrogen content and the relationships between them were not affected by straw mulching. The yield was not affected by straw mulching. However, straw mulching significantly increased the intercept of the linear relationship between yield and canopy potential photosynthetic capacity (the productions of leaf area index and Vcmax, or Jmax), indicating that straw mulching may improve the harvest index of winter wheat. The overall net effect of straw mulching was a favorable environment that stimulated plant photosynthesis, which compensated the lower LAI and tiller density, in turn, maintained wheat yield. This study elucidated the physiological basis of straw mulching and no-till effect on yield and provided photosynthetic parameters of winter wheat under such soil management.