Effect of covering on nitrogen transformation and the quality of pig manure-straw compost

The aerated static pile method was used to investigate the effect of covering on nitrogen transformation and the quality of a pig manure-straw compost during the composting process.Nitrogen forms and other indexes were determined in the different layers,i.e.,the bottom layer and top layer,in the composts covered with and without matured compost.The results showed that: the covered composts had lower moisture,germination index(GI) of the end of composting,and pH value in heating and thermophilic phases;however,it increased EC value of the composts in cooling phase.The temperature in the composts had no significant difference.The covering delayed ammonia emission in the bottom layer at the beginning of composting period,while the percentage of accumulated ammonia in total nitrogen did not change.During composting,the increase rates of NO-3-N,organic-N,total nitrogen and total phosphorus in the bottom of the covered compost were 66.7%,33.8%,32.7% and 138.6% higher than the corresponding control,respectively.However,the degradation rate of organic carbon and contents of NH+4-N and humus decreased by 1.1%,8.0% and 3.7%,respectively.The changes of pH,NH+4-N and NO-3-N contents in top layer of the covered composts indicated that the released ammonia in the bottom layer can be absorbed and nitrified.The top layer of compost was mineralized,and influenced the process of nitrogen transformation and quality of composts in the bottom layer.