Nitrogen Transformation during Pig Manure Composting at Low Temperature

Discharge of animal manure without treatment not only pollutes environment but also influences people health. It also hinders further development of livestock industry. Composting animal manure is one of the solutions to this problem, in which content and morphous of nitrogen play important roles that affect the compost quality. Therefore it has great meaning to study nitrogen transformation during the pig manure composting, especially at low temperature which reduces composting turnover rate. In this study, pig manure was collected as compost material. Maize stover was chosen as attendant agent. Three kinds of microbial agents (A, B, C) were inoculated into the manure to start composting at 6°C. Contrast test was performed without microbial innoculant added. Acid nitrogen and non-acid nitrogen were included in total nitrogen in the composting process. Furthermore, Amide nitrogen, amino acid nitrogen, amino sugar nitrogen, ammonium nitrogen and other unknown form acid nitrogen were included in acid nitrogen. Total nitrogen (TN) content decreased rapidly with microbial agents (A, B, C) added during the early 6d of the composting. TN content was the lowest at the stage of high temperature (6-12d) and increased quickly between 12-18d, and it became stable after 18d. Dynamics of acid nitrogen content was the same as that of TN content. Non-acid nitrogen content varied as same as the nitrogen content in contrast test. These indicated that composting microorganisms could not utilize non-acid nitrogen, so the change of TN was due to the variation of acid nitrogen. In the early stage of composting (0-6d), contents of both amide nitrogen and amino sugar nitrogen increased slowly, while contents of amino acid nitrogen and the unknown form nitrogen decreased rapidly. Moreover, ammonium nitrogen content increased quickly. It suggested that amino acid nitrogen and the unknown form nitrogen transformed into ammonium nitrogen. The decrease of acid nitrogen and TN contents were resulted from the evaporation at high temperature. In the stage of high temperature (6-12d), microorganisms grew quickly so that amide nitrogen and amino sugar nitrogen increased rapidly, which were ingredients of microorganisms. Other form nitrogen changed a little. In the stage of maturity (12-18d), contents of amide nitrogen, amino sugar nitrogen and ammonium nitrogen decreased rapidly, while the content of unknown form acid nitrogen increased quickly. Content of amino acid nitrogen grew slowly, which suggested that amide nitrogen and amino sugar nitrogen changed into unknown form acid nitrogen as well as amino acid nitrogen. As temperature decreased, contents of unknown form acid nitrogen and amino acid nitrogen increased slowly, while contents of other form nitrogen decreased after 18d. The amide nitrogen and amino sugar nitrogen contents decreased quickly at the former stage of the composting but slowly later. Content of ammonium nitrogen decreased significantly over the composting process.