Irrigation at appearance of top 2nd or flag leaf could improve canopy photosynthesis by regulating light distribution and LAI at each leaf layer

A high-quality population structure is the basis for the efficient utilization of light energy by plants. Irrigation strongly influences wheat type and canopy structure. The objective of this study was to determine the effects of irrigation at different leaf ages on (a) the leaf area index (LAI) and light interception (LI) in each leaf layer, (b) the canopy apparent photosynthetic rate (CAP), and (c) the wheat yield. A field experiment was conducted over two winter wheat growing seasons. Four irrigation treatments were applied in 2019-2020 and irrigation was conducted at the appearance of the 3rd, 4th, 5th, and 6th spring leaves, respectively (T3-T6). Five irrigation treatments (T2-T6) and a no-irrigation treatment (W0) were applied in 2020-2021. The results showed that the increase in leaf area at each leaf position tended to be greater when irrigation was applied earlier in spring. However, the nth internode achieved maximum increases in length when irrigated at the appearance of the spring-leaf n + 2 or n + 3. Unlike the earlier irrigation treatments (T2-T4), the LAI of T5 and T6 decreased by an average of 20.62% at anthesis. Moreover, the rates of decline in LAI decreased post-anthesis as well, especially for the top 3rd and 4th leaf layers. In response to postponed irrigation, the LI of the flag leaf layer and the organs above it gradually decreased whereas the LI for the top 2nd, 3rd, and 4th leaf layers and CAP increased. The T5 and T6 treatments realized the highest yield for both years.

Automated summary

Irrigation timing has a significant effect on the leaf area index and light interception capacity of wheat, with earlier irrigation in spring favoring greater leaf area. However, the effect of irrigation timing on internode length shows maximum results when irrigation occurs at the appearance of the spring-leaf n+2 or n+3. Among the different irrigation treatments, T5 and T6 achieved the highest yield in both years.