Effects Of Long-Term Fertilization Regimes On Changes Of Microbial Biomass Carbon And Nitrogen And Enzyme Activitiy

Under the intensive agricultural systems, it always concerns problem about the effect of fertilization on soil biological fertility. Soil microbial and soil enzymes activity are important index of soil biological fertility. Which are related to not only the soil types, but also the land use, tillage and nutrient management practices. Therefore, it has much significance to study the effect of soil management regimes on soil microbial and soil enzymes activities for maintaining the soil biology health and sustainable soil productivity. This study investigated the effects of soil management regimes on the dynamic changes of microbial biomass carbon and nitrogen and enzyme activities in soil based on the 20-year long-term experiments on Lou soil in Guanzhong Plain, Shanxi province, China. Treatments at the site included application of 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). Besides two management regimes, fallow and abandonment were also included. The main results obtained are as follows:1. The soil with fertilizer application had lower pH values than the soil with no fertilizer application. M2NPK treatment had the lowest pH value. The tested parameters of rhizospheric soils gave much higher values than those of non-rhizospheric soils, the increments were -1%~52.5% for soil organic carbon, 2.6%~26.9% for total N, 1.49%~24.35% for total P and 25.8%~57.0% for Olsen P, respectively. The differences in soil chemical properties affected various fertilization regimes were more significantly for rhizosphere soils than non-rhizospheric soils. Long-term application of NP or NPK fertilizers could increase levels of soil organic carbon, nitrogen and phosphorus compared with CK. In comparison with NPK, SNPK had no significant effects on levels of soil organic carbon, nitrogen and phosphorus. The soils with long-term applications of MNPK had the maximum levels of soil organic carbon, nitrogen, phosphorus. Moreover, crop yield was highest under MNPK treatments.2. The invertase, urease, alkaline phosphatese, dehydrogenase activity of rhizospheric soils were much higher than those of non-rhizospheric soils in winter wheat growing season. In non-rhizospheric soil, the invertase activity was higher in seedling and flowering stages; urease, alkaline phosphatese, dehydrogenase activity were the highest in flowering stage. In rhizospheric soil, invertase, urease, alkaline phosphatese activity were the highest in jointing stage, dehydrogenase activity was similar to non-rhizospheric soil. The soils with long-term applications of N or PK had the minimum levels of soil enzymes. Long-term application of NP or MNPK fertilizers could increase the invertase, urease, alkaline phosphatese and dehydrogenase activity.3. Compared to CK, bare fallow reduced invertase, urease, alkaline phosphatese, dehydrogenase activity, they had a litter change from in October 2009 to May 2010. From in October 2009 to May 2010, the invertase activity of abandonment showed a declining trend, but urease, alkaline phosphatese, dehydrogenase activity varied, and the highest peak in May 9, 2010. Invertase activity of abandonment was lower than CK, but other enzymes had higher activities than CK.4. Microbial biomass C&N of rhizospheric soils were much higher than those of non-rhizospheric soils, the increments were 42.2%~154.6% and 10.5%~176.1% for microbial biomass C and microbial biomass N, respectively, at flowering stage, 48.2%~187.9% and 25.8%~221.8% for microbial biomass C and microbial biomass N, respectively, at maturing stage. The contents of microbial biomass C&N at flowering stage were higher than those at maturing stage. Long-term application of NP or NPK fertilizers could increase microbial biomass carbon and nitrogen contents over CK. SNPK had considerably increased microbial biomass C relative to NPK. The soils with long-term applications of MNPK had the maximum levels of microbial biomass.In conclusions: soils from rhizosphere could reflect better soil chemical and biological properties affected by various fertilization regimes than non-rhizospheric soils. Application of NP could enhanced soil fertility and crop yield in the circumstance of inorganic fertilization. SNPK was superior to NPK in improving soil biological health, and MNPK was the best fertilizer management in enhancing both soil chemical and biological fertility on Lou soil.