Effects of long-term fertilization on carbon and nitrogen and enzyme activities of soil microbial biomass under winter wheat and summer maize rotation system

Fertilizer management has significant effects on both soil chemical and biological properties. This study was designed to examine the effects of continuous fertilization, straw incorporation, and manuring on the soil chemical fertility, microbial biomass and activities of enzymes involved in mineralization of C, N, and P on a long term (20 years) field trial with winter wheat and summer maize rotation system under temperate conditions in Shaanxi of China. Treatments at the site included applications of the recommended doses of nitrogen (N), nitrogen and phosphorus (NP), phosphorus and potassium (PK), nitrogen, phosphorus and potassium (NPK), wheat/maize straw (S) with NPK (SNPK), dairy manure (M) with NPK (M1NPK and M2NPK) and un-amended control (CK). Compared with the CK, the contents of soil organic carbon, total nitrogen, total phosphorus, available phosphorus, microbial biomass carbon and microbial biomass nitrogen are increased by 34.0%, 34.0%, 58.5%, 608.9%, 23.3%, and 54.0% under the long-term application of the NP, respectively, and the activities of invertase, urease, alkaline phosphatase and dehydrogenase are increased by 53.9%, 132.6%, 29.9% and 40.9%. Nevertheless, the NPK has similar effects on above parameters as the NP. In comparison with the NPK, the SNPK has no significant effects on levels of soil organic carbon, nitrogen and phosphorus, but considerably increases microbial biomass C (29.5%), alkalinephosphatase (23.0%) and dehydrogenase (26.9%) activities. The soils with long-term applications of MNPK have the maximum levels of soil organic carbon, nitrogen and phosphorus, and highest microbial biomass and enzyme activities, while, large concentration of phosphorus in MNPK soils is accumulated. It concludes that the application of the NP could enhance soil fertility in the circumstance of inorganic fertilization, the SNPK is superior to the NPK in improving soil biological health, and the MNPK is the best fertilizer management in enhancing both soil chemical and biological fertility on Lou soil.