Effects of straw incorporation on crop yield and dissolved organic carbon concentration at rice growing season in rice-wheat rotation cropping system

In recent years, straw incorporation as an important way of straw utilization and culture fertility has been applied widely to achieve sustainable development of agriculture. However, straw incorporation also creates some novel problems. One of the most important of these is a large amount of crop straw returned to the field affecting the growth of rice and wheat at seeding stage. Even though lots studies reported that straw incorporation increased crop yield, there were also many reports that had a negative effect on crop yield. Another problem is that straw decomposition in rice field can produce lots of dissolved organic carbon (DOC), which has a close relationship with water eutrophication. Many studies reported the effect of straw incorporation on DOC concentration of paddy field at harvest time or on the dynamic of DOC concentration in soil incubation experiment. But little is known about effect of straw incorporation on the dynamic of DOC in rice growing season with different rate of straw returned and soil types. A two-year pot experiment was conducted to investigate the effects of straw incorporation on the yield of wheat & rice and DOC concentration in soil solution in rice growing season in two types of soil, loamy soil (L) and clay soil (C). According to the level of straw incorporated into soil, each soil type consisted of three treatments:1) 0% straw returned from previous crop to soil (S0); 2) 50% straw returned from previous crop to soil (S1); 3) 100% straw returned from previous crop to soil (S2). Compared with no straw treatment, straw incorporation significant increased rice yield in most of treatments in both soil types (1.6%-11.9%), and the yield increases of S2 treatment were higher than those of S1 treatment (no significant in first year but yes in second year). However, straw incorporation had different effects on wheat yield for two soils:in loamy soil, wheat yield increased in straw incorporation treatments in both years but only significantly in first year (7.2%-10.6%), and there was no significant difference between S1 and S2 treatments; in clay soil, wheat yield decreased significantly in straw incorporation treatments in both years (5.0%-9.3%), and the yield decrease of S2 treatment were higher than that of S1 treatment (no significant in first year but yes in second year). As to the DOC concentration in soil solution in rice growing season, compared with treatment of no straw returned, DOC concentration of S2 and S1 treatments significantly increased by 141.7% and 61.9%, respectively, and DOC of loamy soil was 89.6% higher than that of clay soil on average in the early rice growing stage, but all straw treatments and soils would decrease quickly once intermittent flooding. In conclusion, straw incorporation had a positive effect on rice yield for both loamy and clay soil, but a negative effect on wheat yield for clay soil, and also increased DOC concentration significantly. The intermittent flooding could rapidly reduce the concentration of DOC in paddy soil.