Effects of different straw returning amounts on soil physicochemical properties, dry matter accumulation, and yield of wheat

As a main way to reuse straw resources in the farmland, returning straw to the soil can effectively alleviate the adverse effects of direct straw burning on the soil and environment. Although there are previous studies on this aspect, few studies investigate the impact of the annual return of rice and wheat straws on wheat yield and soil properties. In this study, wheat 'Annong 1124' was used as the material. The four experimental treatments include: neither rice nor wheat straw returned to the field (R0), wheat straw returned to the field (RW), rice straw returned to the field (RR) and, both rice and wheat straw returned to the field (R2) were set up. The effects of different amounts of straw returning on soil physical and chemical properties, soil nutrient content, dry matter accumulation, and yield of wheat were studied, to clarify the characteristics of wheat yield formation, soil properties, and nutrient content changes under the condition of rice and wheat annual straw return. The results showed that straw returning increased soil aggregate content and root activity of wheat at the jointing stage. Still, they decreased soil pH and root activity at the flowering stage and increased soil aggregate content at small particle size (d <= 0.5 mm and 0.50 mm < d <= 1.00 mm). Straw incorporation (R2, RR, and RW) decreased soil urease activity in the early growth stage, increased soil urease activity in the late wheat growth stage, and increased soil nutrient content. Straw returning improved the dry matter quantity of wheat at the jointing stage and had a great difference in the dry matter accumulation of wheat at the flowering stage. RR and R2 treatments reduced the dry matter accumulation of wheat at anthesis by 11.97% and 7.38%, respectively, while RW treatment increased the dry matter accumulation by 25.38%. Straw returning (RW, RR, and R2) decreased the number of wheat spikes but increased the number of grains per spike and 1000-grain weight. In 2019 and 2020, RW treatment increased wheat yield by 1.32% and 3.76%, RR and R2 treatment decreased wheat yield by 2.82%, 0.78%, and 1.70%, 0.42%, respectively. The results of path analysis showed that soil pH, soil biomass carbon, and soil urease activity had significant effects on wheat yield, especially soil biomass carbon. In summary, RW treatment increased soil nutrient content first and then increased dry matter accumulation at the flowering stage, which was beneficial to the transportation of dry matter from stem and leaf to grain. The grain number per spike and 1000-grain weight of wheat increased, but RR and R2 decreased the yield of wheat. Therefore, whether or not straw returning to the field can improve crop yield is related to the way straw returns to the field and crop type, as well as the time of straw returning.