Effect Of Soybean Straw Returning On Decomposition Rate And Soil Nutrient And Enzyme Activity

China is one of the countries with the largest straw yield in the world,but the average utilization rate is only 32%,nearly 35% of the straw in production was discarded and burned,which resulted in serious air pollution and waste of resources,and also affected the agricultural ecological environment.Soybean straw is rich in carbon source,nitrogen,phosphorus,potassium and other nutrients.It can be used as a supplement or substitute of chemical fertilizer to improve the problems of soil cementation,acidification and soil fertility decline caused by excessive application of chemical fertilizer.The winter and spring temperatures in the northeastern region of China were low,and the decomposition of straw under natural conditions was slow,resulting in low utilization.In order to solve this problem,the research experiment of soybean straw returning to field was carried out through outdoor and indoor cultivation.In the plot test 1,two straw lengths(1-3cm,3-5cm),three nitrogen application rates(0,80kg/hm2,120kg/hm2),and two burial depths(15cm,30cm)were set for 12 treatments;In the plot test 2,two kinds of straw returning amount(0,4.5t/hm2),three kinds of nitrogen application amount(0,80kg/hm2,120kg/hm2),and two kinds of buried depth(15cm,30cm)were set for 8 treatments;Three factors(straw S,brown sugar T,nitrogen N)and 2 levels(addition of 1,no addition of 0)were set in the indoor culture test for 8 treatments.Based on the effects of soybean straw decomposition rate,soil physical and chemical properties and enzyme activity,the suitable length and depth of soybean straw returning to field and the optimum concentration of carbon and nitrogen were selected to realize the high efficiency utilization of soybean straw.Providing theoretical basis for sustainable development of agriculture.The test results were as follows:The decomposition rate of each treatment increased rapidly in the first two months during the one-year return period,and gradually slowed down in the later period.With the increase of nitrogen fertilizer,the decomposition rate of soybean straw increased with the increase of nitrogen fertilizer at the same time and at the same depth.Under the same nitrogen level,the decomposition rate of the treatment with 15 cm depth was greater than that of the treatment with 30 cm depth at the same time.Soybean straw returning to field can effectively reduce soil bulk density and increase soil porosity compared with non-returning soil.When the amount of straw returned to the field was constant,the soil bulk density decreased and the soil porosity increased with the increase of nitrogen fertilizer application at the same depth.Under the same nitrogen level,the soil bulk density of 30 cm treatment was lower than that of 15 cm treatment,and the soil porosity was higher than that of 15 cm treatment,but there was no significant difference among the treatments.The effects of straw returning treatments on the contents of soil organic matter,total nitrogen,total phosphorus and slow available potassium were relatively stable during the whole retur ning period,and the difference was significant compared with the control.The content of total nitrogen and total phosphorus were increased most significantly by W1N2D2(adding straw and nitrogen application was 120 kg/hm2,buried at a depth of 30 cm),W1N2 D1(adding straw and nitrogen application was 120 kg/hm2,buried at a depth of 15 cm)had the most significant effect on the content of slowly available potassium.The contents of available nitrogen and available potassium in soil of each treatment increased first and then decreased with the increase of soil returning time,while the content of available phosphorus in soil showed a change of M-type.When soybean straw was applied to soil,the rapid stages of increasing soil available nitrogen,available phos phorus and available potassium were 0 ~ 90 days,0 ~ 90 days and 0 ~ 30 days,respectively.The most significant treatments for increasing soil available nutrients and organic matter content were W1N2D1(adding straw and nitrogen application was 120 kg/hm2,buried at a depth of 15 cm).With the increase of culture time,the soil respiration rate of each treatment increased rapidly at the early stage,then decreased gradually after reaching the peak value,and the enzyme activity of each treatment showed a trend of increasing at first and then decreasing.When nitrogen application rate and straw amount were constant,brown sugar could significantly increase soil respiration rate and microbial biomass carbon content.The activity of three enzymes(sucrase,catalase and urease)could be increased by applying nitrogen fertilizer when the amount of brown sugar and straw were constant.Compared with non-returning treatment,soybean straw could promote three kinds of enzymes and microbial biomass carbon content.The increase of the soil respiration rate,sucrase,catalase activity and microbial biomass carbon content in straw+brown sugar+nitrogen fertilizer treatment were the most significant.The increase of soil urease activity in straw+nitrogen fertilizer treatment was the most significant.