Effects of amount and time of straw mulching on soil temperature, root growth and yield of winter wheat

In order to take full advantages of straw mulching and improve straw mulching benefits, the effects of different straw mulching practices on soil temperature, root growth and yield of winter wheat under irrigation condition in a typical site was explored through a field experiment with different straw mulching times and amounts in the North China Plain. Times of straw mulching included immediately after planting and after three leaves of winter wheat. The amounts of straw included total straw yield, 1/2 straw yield and 1/3 straw yield of preceding summer maize, and no mulching as the control (CK). The results showed that:1) compared with CK, the winter wheat yield of mulching after planting and after three leaves was reduced by 8.6% and 2.0%, respectively. The yield decrease for the treatment of mulching after planting was more than that of mulching after three leaves for winter wheat. The reason for yield reduction of mulching after planting was decreases in 1000-seed weight, kernel numbers per spike and harvest index, which were 4.1%, 6.6% and 2.4%, respectively. The reason for yield reduction of mulching after three leaves was the decrease in spike numbers per area, which was 5.8%. 2) Straw mulching significantly affected soil temperature at the earlier growth stages of winter wheat. The straw mulching increased mean daily soil temperature averagely by 0.56℃ at tillering and overwintering stages. Straw mulching decreased soil temperature, compared with CK, after regreening stage of winter wheat. The contribution of straw mulching to soil temperature increase in winter was mainly due to the increase in night soil temperature, while the cooling effects after regreening stage was due to reduction in daytime soil temperature. The temperature increasing/decreasing effects of straw mulching were enhanced with straw amount increase though no significant differences among different straw amounts treatments were observed. 3) Root growth of winter wheat was improved under straw mulching due to the higher soil temperature. The root length density (RLD) under straw mulching treatment was higher than that under CK before regreening stage, after that RLD was reduced due to lower soil temperature under straw mulching as compared with CK. At flowering stage, with the increase of canopy coverage, the effects of straw mulching on soil temperature was weakened or disappeared, resulting in similar RLD among treatments. Higher soil temperature at tillering and wintering stages and larger root system under straw mulching induced higher consumption of soil nitrogen of winter wheat, which lead to lower soil nitrogen content at regreening to jointing stages under straw mulch treatments. In conclusion, straw mulching at three leaves stage of winter wheat had less negative effect on grain production of winter wheat. One third or half straw yield of preceding summer maize was appropriate amount for maintaining yield of winter wheat.