The Effect Of Soil PH And Fertilization On Thermo-Dynamics Of Microbial Metabolism

Soil microorganisms play an essential function in ecosystem, it has been used as sensitive indices to assess soil quality. Soil pH is considered to be a major factor affecting microbial communities and biomass on a global scale, but the relationship between soil pH and microbial activity is unclear. Fertilization has an important impacts on soil fertility, crop yield and soil ecological environment. In agricultural systems, farmers are often forced to make decisions about their fertilizer strategy that reflects economic rather than agronomic pressures, more mineral fertilizers and less organic fertilizers are now being used, and unbalanced fertilization is unfortunately widespread at the same time. Red paddy soils are major utility pattern in China, the knowledge about effects of long-term fertilization on microbial activity and community structure in red paddy soil could improve our understanding of soil process and thus help us to develop sustainable management strategies.25soil samples collected from different district and different landuse in a pH gradient (4.35-8.70) were investigated by microcalorimetric method. The effects of mineral fertilizer and organic matter on soil microbial activity and community were also investigated in a long-term (20-year) fertilizer experiment of red paddy soil by microcalorimetric technique combined with phospholipid fatty acid (PLFA) analysis. The experiment included nine treatments:the control (CK, without fertilization), straw returning to field and organic manure (O), O plus fertilizer NPK (NPKO), O plus fertilizer N (NO), fertilizer NPK (NPK), fertilizer NPK plus1/2straw (NPKS), fertilizer N (N), fertilizer NP (NP) and fertilizer NK.The results showed that soil pH had a close correlation with microcalorimetric indices of growth rate constant (k), the maximum thermal power (Pmax) and the time to reach the maximum of the peak (tmax), with less time reached the maximum thermal power (Pmax) implied a higher microbial activity. It indicated soil pH is an important factor affecting microbial activity on a large scale; it also validated that tmax,Pmax and k are all good indices to assess soil microbial activity. In addition, the soil microbial activity were extremely lower when the soil available P was less than1.5mg/kg.Long-term fertilization changed the soil nutrient status, microbial activity and microbial community in red paddy soil.(1) Long-term fertilization changed the soil nutrient status. Total N was significantly increased in treatment NO, NPKO and NPKS; total P increased in all treatment except for N and NK treatment, and available P decreased in N treatment.(2) Long-term fertilization changed the soil microbial activity. Fertilization decreased the tmax and heat dissipation per unit of MBC (QT/MBC). Fertilization increased the growth rate constant (k) and the maximum thermal power (Pmax) except for P deficiency treatment (N and NK). Fertilization also increased soil MBC except for N treatment. Those results indicated that balanced fertilization improved the microbial activity in red paddy soil; P deficiency had a negative effect on soil microorganisms, which also was confirmed by the result that total and available P had a good correlation with k, tmax and Pmax; K deficiency had a less impact on soil microorganisms than that of P.(3) Fertilizations improved the amount of total PLFAs and single PLFA which indicated different microorganisms. The highest amounts of total PLFAs appeared in the NPKO, NPKS and NPK treatment. Organic fertilization or balanced fertilization promoted the growth of fungi, in contrast, the lower amount of PLFAs appeared in CK, N, NP and NK. Total P and mineral N positively correlated with the amount of total PLFAs. The principal component analysis (PCA) revealed that NPKO, NPKS, NPK treatment were different from others. Those results indicated long-term fertilization changed the soil microbial community and balanced fertilization promoted the microbial growth. In conclusion, balanced fertilization especially organic plus mineral fertilizers are beneficial to improve and maintain the nutrient balance, promote the microbial growth and activity, and thus improve soil quality; P deficiency treatment had a greater negative impact than K deficiency in red paddy soil.