Effects of long-term no-tillage with straw mulch on photosyntheticcharacteristics of flag leaues and dry matter accumulation and translocation of winter wheat in dryland

【Objectives】 Photosynthetic characteristics of winter wheat after flowering play an important role in dry matter accumulation and transportation, and soil moisture is the most important environmental factor which affects the crop photosynthesis. Application of no-tillage could improve the soil environment and increase the crop production. To study role of water reserving and soil moisture keeping under no-tillage with straw mulch practice in a long-term experiment, and transfer characteristics of canopy photosynthetically active radiation and their effects on photosynthetic characteristics and dry matter transportation of wheat, we conducted this experiment in the long-term plots. 【Methods】 These plots were established in a silt loam soil in the Loess Plateau of China in 1992, and consisted of no-tillage with straw mulch (NT) and conventional tillage (CT) with three replications. The soil of this semi-arid area is a Chromic Cambisol, which is low in organic matter and slightly alkaline and which is subject to frequent drying and wetting cycles. The soil moisture, and photosynthetically active radiation, flag leaf photosynthetic characteristics, dry matter accumulation and yield components of wheat were measured during the fallow period and wheat-growing period under different tillage practices. 【Results】 During the fallow period and wheat-growing period, a significant increase of water-storage capacity under the NT practice is found in 0-160 cm soil depth compared with CT, with an average increase of 12%. At its lowest point (at the pre-filling stage), soil moisture under the NT practice is 21% higher than that of the CT practice(P0.01). The canopy photosynthetically active radiation intercepted under the NT practice is 163 mol/(m2s) higher than that of the CT practice at the heading and filling stages, which reaches the maximum difference (19.3%) at the pre-filling stage (P0.05), and both upper and bottom wheat canopies under the NT practice have opportunity to use light energy. Compared with the CT practice, the NT practice increases the stomatal conductance with an average of 39% at the pre-filling stage, enhances the ability of carbon dioxide utilization by 11%, and improves WUE by 22%. From the heading to mature stages, the net photosynthesis rate under the NT practice is 39% higher than that of CT, the grain weight and total plant weight at the harvest stage are 57% and 46% higher than those of CT respectively (P0.01), and the contribution of dry matter accumulation into grain after the flowering reaches 64%. From the point of view of yield components, the NT practice had the significant effect on wheat spike number and thousand grain weights, 31% and 10% higher than the CT practice respectively. The yield under the NT practice was 41% higher than the CT practice (P0.01). The study indicates that the ability of water reserving and soil moisture keeping under no-tillage with straw mulch practice could alleviate the decline of net photosynthesis rate in midday due to the action of water stress, and keep wheat photosynthesis at a high level. Meanwhile, the NT practice enhances the ability of dry matter accumulation after the anthesis, and the dry matter accumulation after the anthesis is the main source of dry matter accumulation into grain under the NT practice, while under the CT practice the dry matter accumulated in vegetative organs before the anthesis is the main source of dry matter accumulation into grain. 【Conclusions】 The results indicate that the long-term no-tillage with straw mulch practice could significantly improve soil moisture and light interception ability, enhance wheat photosynthesis characteristics, WUE and dry matter accumulation and transportation, coordinate relationship between the yield components and increase wheat production in the dryland of the south of Shanxi Province.