Effects of fertilizing organic materials on contents of carbon and nitrogen, enzyme activity of desertified soils and alfalfa biomass

Poplar branch, corn straw, and cow manure were selected from a local site in order to study the effects of these amended materials on desertified soil in Ningxia. Further, a microcosm experiment was set up to test the effects of individual material or mixed materials on contents of carbon and nitrogen, enzymatic activity of desertified soil, and alfalfa biomass. Results showed that both individual material (except cow manure) and mixed materials increased all fractions of soil carbon and nitrogen, except inorganic nitrogen, compared with control. Cow manure increased inorganic nitrogen, soil organic carbon (SOC), oxidized organic carbon, total nitrogen (TN), and available nitrogen of the soil relative to other treatments. However, cow manure decreased soil C/N (SOC/TN) and microbial biomass C/N (MBC/MBN). Mixed materials with poplar branch, corn straw, and cow manure were the best in increasing microbial C and N contents, and also showed the best tendency for increasing enzyme activity, including the activities of cellulase, catalase, sucrase, phosphatase, and urease. Mixed materials with poplar branch, corn straw, and cow manure was also the best in increasing alfalfa biomass. Individual treatment with cow manure resulted in lower alfalfa biomass compared with the control. In conclusion, mixed materials with poplar branch, corn straw, and cow manure showed the most significant effect on improving soil fertility in desertified soils according to principal component analysis. The study will be an example for desertified soil amendment in Ningxia and other similar sites in China.