Effects of delayed irrigation during the jointing stage on the photosynthetic characteristics and yield of winter wheat under different planting patterns

To study the water-saving and high-yielding planting pattern in the North China Plain (NCP), a conventional planting pattern (C) and wide-precision planting pattern (W) were adopted during the 2015-2016 and 2016-2017 winter wheat growing seasons. For each planting pattern, the plants were provided with 60 mm irrigation either during the jointing stage or 10 days after the jointing stage. During both growing seasons, the chlorophyll content index (CCI) in the flag leaves, maximum photochemical efficiency (F-v/F-m), photosynthetic rate (Pn), transpiration rate (Tr), and grain yield (GY) of winter wheat were measured. The results showed that at the heading and flowering stages, W significantly increased the CCI and F-v/F-m in flag leaves. In both growing seasons, the highest value for both CCI and F-v/F-m was observed during the filling stage in W treatment with 60 mm irrigation 10 days after the jointing stage (WI2). The trend for Pn was consistent with the change in Tr, and both reached the maximum value at the flowering stage. At the filling stage, the leaf water use efficiency (WUEL) in WI2 reached the maximum value. Delayed irrigation at the jointing stage significantly increased the number of spikes as well as the kernel numbers per spike in W; as a result, the winter wheat grain yield was significantly increased in WI2. The results indicate that the use of W in combination with 60 mm irrigation 10 days after the jointing stage is an optimal method for winter wheat production in NCP.