Decomposition Characteristics Of Different Organic Materials Returning To Field And Their Effects On Nutrients In Yellow Soil

Organic materials play an important role in soil fertility,and their decomposition status in soil directly affects soil quality and fertility supply.This study used nylon mesh bag landfill method and laboratory analysis,in combination with first order kinetics equation fitting,without organic material as the control(CK),different organic material(corn straw(MS)and rice straw(RS)and pig manure(PM)and adjusting the carbon and two treatments of adjusting C/N(corn straw + nitrogen(MS+N),rice straw + nitrogen(RS+N))as well as their effects on soil fertility and enzyme activity were studied,which were aimed at providing theoretical basis for the application of organic material returned to field and resource utilization under the dry farming condition in Guizhou province with a soil type—yellow soil.The main research results as follows:(1)According to the different decomposition rates,the decomposition processes of organic materials can be divided into fast decay period(0~30d)and slow decay period(30~180d).After 180d's decomposition,the cumulative decomposition rate of each treatment was between 61.0% and 67.1%,presenting as RS+N>MS+N>MS+N>MS>PM,in which MS+N and RS+N were slightly higher than MS and RS(P>0.05).The fitting results show that the potential decomposition rate of each treatment is between 62.68% and 72.68%,among which RS+N is the highest.The decomposition rate constant(k value)of MS+N treatment is higher,and the time to reach the decomposition equilibrium is shorter.(2)During the period of decomposition,the nutrient release characteristics of different treatments showed a trend of rapid release of potassium and phosphorus,and slow release of carbon and nitrogen.In general,the nutrient release characteristics were showed with potassium>phosphorus>carbon?nitrogen.After 180 days,the release rates of potassium of all treatments were higher(93.5%~98.1%),followed by phosphorus(75.3%~91.7%),and the release rates of carbon and nitrogen were lower(58.1%~78.8% and 55.0%~74.0%,respectively).The fitting results showed that the nutrient release rate constant(k value)was between 0.012 and 0.074,and the potential release rate(y0)was between 51.05 and97.66.Under the condition of equal carbon content,the potential release rate of carbon of corn straw(MS,MS+N)was lower than that of rice straw(RS,RS+N)and pig manure(15.77~31.79%),which showed that application of corn straw had a bigger contribution to soil organic carbon,and was a better measure to improve the content of soil organic carbon of yellow soil in dry farming management.(3)During the period of decomposition,soil nutrients showed a trend of increasing first and then decreasing.After 180 days,compared with CK,the nutrient contents of all treatments(MS,RS,PM,MS+N,RS+N)has significantly increased(P<0.05).The contents of organic matter,total nitrogen,total phosphorus and total potassium increased by2.30%~3.97%,8.52%~13.07%,9.75%~44.10% and 7.83%~13.04% respectively.The contents of alkali-hydrolyzed nitrogen,available phosphorus and available potassium increased by 45.12%~55.20%,0.64%~94.57% and 31.55%~52.67% respectively.Among all treatments,MS treatment had the highest organic matter content.The contents of total nitrogen,alkali-hydrolyzed nitrogen,total phosphorus and available phosphorus of PM treatment were significantly higher than those in other treatments.The content of total and available potassium of RS+N treatment were significantly higher than those in other treatments.(4)Organic materials returned to field has increased the activity of soil urease,catalase and sucrase.After returning to the field for 180 days,the urease activity of each treatment was increased by 0.5~1.75 times compared with CK treatment(0.55 mg/(g·24h)),catalase activity was increased by 0.39~0.69 times compared with CK treatment(1.47 mL/g),and invertase activity was increased by 1.01~3.27 times compared with CK treatment(10.10 mg/(g·24h)).Among them,the effect of urease and sucrase in soil was the best,and the effect of catalase in corn straw + nitrogen treatment was the best.Among all treatments,PM has led to the biggest increase of activity of soil urease and sucrase,and MS+N has the biggest effect on soil catalase activity.