Study On Decomposition Characteristics Of Straw Return To Soil And Soil Enzyme Activity In Cold

Nutrient content of straw is rich, it is the main source of agricultural nitrogen, phosphorus, potassium and organic matter in the current and future, straw returning to soil is the simple but effective method to improve the soil organic carbon content, soil fertility and nutrient recycling.Soil enzymes is an important participant of the soil material and energy cycle, which is one of the most active components in soil ecosystem. Its activity can not only reflect the level of soil microbial activity, but also characterize the strength of the soil nutrient transformation and transport capacity,which is one of the important parameters for evaluation of soil fertility. Soil enzymatic characteristics have been a potential indicator of soil quality.This work employed nylon net bags to study the decomposition rates and nutrient release patterns of straw returned to the soil, sand strainer tube method to study the effect of straw on soil available nutrients, the effect of combined with the laboratory experiment of straw returned to soil on soil enzyme activity, the subject of the study is cold and black soil, soils were sampled from plots with four variants of tillage methods:traditional tillage(TT), no-til lage(NT), no-tillage with straw cover (NTS) and minimum tillage with straw mulch(MTS). Our aim was to study the influence of soil enzyme activities (urease, invertase, acid phosphatase, alkaline phosphatase, and catalase) by soil depth and the system of rotation cropping and the seasonal changes. The results showed that:Straw decomposing and nutrient release are divided into three periods:the fast stage of decomposition (0-45days), the slow stage of decomposition (45-135days), the lag phase of decomposition (135-365days). The rates of cumulative release of soybean stalk carbon, nitrogen, phosphorus, potassium are58.66%,37.57%,54.27%,87.90%respective, the rates of cumulative release of maize stalk carbon, nitrogen, phosphorus, potassium are52.80%,35.49%,57.68%,93.00%respective, the results indicate that straw potassium has the fastest releasing above all the nutrients, followed by phosphorus and carbon, nitrogen is the slowest.In laboratory incubation experiment and sand strainer tube test, the soil organic matter and available nutrients had an increasing trend under straw returned to soil. In laboratory incubation experiment, soybean stalk treaments had more soil organic contents than maize stalk treaments. Low amount of soybean stalk to soil treament had the most soil available N, then maize stalk treaments and the lest in high amount of soybean stalk to soil treatment. However, high amount of straw to soil treament had more soil available P than low amount treament. soybean stalk to soil treatment had more soil available P than maize stalk treaments in the same amount of straw returned to soil. The content of soil available K of maize stalk to soil treatment was significantly higher than other treatments. In sand strainer tube test, an average increase of soil organic matter, inorganic nitrogen, available phosphorus and potassium were12.58g/kg,2.26mg/kg,13.16mg/kg,5.35mg/kg respective.In laboratory incubation experiment, straw returning increased the soil urease, invertase and acid phosphatase activity, soil enzyme activity was affected by the types of straw and the amount of straw returned to soil. Soil urease activity was affected significantly by high amount of soybean stalk to soil. Soil urease activity was significantly increased at the amount of9044kg/hm2soybean stalk. The amount of soybean stalk and maize stalk in9044kg/hm2, soil invertase and acid phosphatase enzyme activity were increased.0-10cm soil layer had the highest soil enzyme activity and then10-20cm soil layer,20-30cm soil layer had the lowest soil enzyme activity. The soil enzyme activity of0-10cm soil layer of MTS was significantly higher than the other treatments. Compared with crop at different growth stages, soil urease, invertase and catalase enzyme activity of soybean full blooming and maize heading stage were highest. Acid phosphatase activity was increased at crop maturity stage. Alkaline phosphatase activity had no significant changes. Soil enzyme activity of maize-maize-soybean(MMS) rotation system was higher than soybean-maize-maize(SMM) system compared with different rotation patterns. There was a significant or extremely significant correlation between soil enzyme, the same as enzyme and available nutrients in soil.