Effects of straw mulching and drip irrigation scheduling on photosynthetic characteristic and yield of winter wheat

Abstract: Determining the photosynthetic parameters is the basis for understanding the physiological causes of water saving and yield increasing under drip irrigation modes. In this study, intrinsic photosynthetic parameters were determined during four years experiments in winter wheat field treated with six drip irrigation modes (T1 to T6, stands for treatments of lower irrigation amount with straw mulch, lower irrigation amount without straw mulch, moderate irrigation amount with straw mulch, moderate irrigation amount without straw mulch, higher irrigation amount with straw mulch, and higher irrigation amount without straw mulch, respectively). The differences in photosynthetic parameters among treatments were statistically analyzed, and the correlations between photosynthetic parameters and crop yield were analyzed. The results showed that increasing irrigation amount and straw mulch enhanced the apparent photon quantum efficiency (α), photosynthetic capacity (Amax), maximum carboxylation rate (Vcmax) and maximum electron transfer rate (Jmax), respectively. However, the interaction effects of irrigation amount and mulching on photosynthetic parameters were not significant (p > 0.1). The effect of drip irrigation on apparent quantum efficiency (α) was significant (P < 0.05) during the late periods of the heading and grain filling stages, while the effect of straw mulch on α was not significant (P > 0.1). The effect of straw mulch and drip irrigation on Amax did not show significant (P > 0.05) seasonal differences. The effects of drip irrigation on Vcmax and Jmax were significant (P < 0.05) during the mid-season periods of the heading and grain filling stages, while the effects of straw mulch were significant (P < 0.05) during the later periods of the heading and grain filling stages. The results of multiple comparisons showed that the photosynthetic parameters of T5 were the highest (P < 0.05). Except for the measurements in 2016, the corresponding values of T6 and T3 were slightly lower but with no significant difference from those of T5 (P > 0.1). However, the corresponding values of T2 were significantly lower (P < 0.05) than those of T5. These results suggested that, under higher irrigation amount, photosynthetic parameters were not affected significantly (P > 0.05) by mulching, but under lower irrigation amount, the parameters significantly (P < 0.05) decreased if treated with no mulching. The average values of Amax during the four years from T1 to T6 were 29.59, 26.45, 31.44, 28.68, 32.42 and 30.90 μmol/ (m2·s), respectively. The average values of Vcmax during the four years from T1 to T6 were 121.42, 107.68, 133.42, 113.55, 141.83 and 129.95 μmol/ (m2·s), respectively. From the point of view of reducing the amount of irrigation, T3 irrigation scheduling can be used as an optimal strategy for winter wheat under drip irrigation with straw mulch, indicating that 65% to 85% of the field capacity was used as the lower and upper limits of soil moisture control. The management practices of drip irrigation with straw mulch can keep the higher photosynthetic capacity of flag leaf for winter wheat. The differences in Amax and Vcmax among treatments could be explained by the leaf nitrogen content (Nmass). Grain yield for all years were also linearly related to Amax and Vcmax, respectively. Therefore, by measuring Nmass, one can estimate Amax and Vcmax, thus achieving the yield estimates of winter wheat field in this area. In addition, the photosynthetic characteristic parameters can also be applied to the crop model to improve the accuracy of model prediction under different water and mulch regimes.