Photosynthesis and winter wheat yield responses to supplemental irrigation based on measurement of water content in various soil layers

• Moisture in the 0–40 cm soil profiles (M40) was the optimum basis for irrigation.
• Optimizing irrigation promoted the water consumption in deep soil layer by wheat.
• Higher photosynthesis was attributed to the M40 with 70% field capacity.
• Irrigation based on M40 at jointing and anthesis enhanced yield in winter wheat.

Optimisation of supplemental irrigation (SI) is necessary for achieving continual improvement in the yield of winter wheat in arid, semi-arid and semi-humid regions. However, finding efficient water-saving irrigation techniques based on soil water storage in different soil layers has been difficult. In this field experiment, three soil layers were tested for soil water content (SWC) prior to SI: 0–20 (D20), 0–40 (D40) and 0–60 cm (D60). The target relative soil water content of each tested soil layer was 70% field capacity at jointing and anthesis. The SWC of D40 was significantly lower than that of D20 in the 60–160 cm soil profiles and that of D60 in the 20–180 cm soil profiles at maturity, which indicates that the soil water consumption amount of D40 was higher than that of D20 and D60. The net photosynthesis rate (Pn), stomatal conductance (Gs), actual photochemical efficiency (ΦPSII) of photosystem II (PSII) and electron transport rate (ETR) of flag leaves in D40 were greater than those in D20 and D60. The highest grain yields of 9648.35 and 10032.17 kg ha−1 were attained in D40 with a higher water use efficiency of 20.7 and 22.2 kg ha−1 mm−1 in 2011–2012 and 2012–2013, respectively. These results indicate that the optimised SI regime based on measuring the SWC in the 0–40 cm soil layers at jointing and anthesis increased the Pn, Gs, ΦPSII, yield and water use efficiency of winter wheat, which was related to the soil water consumption.