A large number of long-term application of organic fertilizer can effectively increase microbial biomass carbon and nitrogen in yellow paddy soil

ObjectivesSoil microbial biomass carbon(C) and nitrogen(N) are the easy-to-use nutrient pool and the driving forces of decomposition and mineralization of organic matter in soil, and are closely related to soil nutrient cycling. Changes of soil microbial biomass C and N can reflect the changes of soil tillage system and soil fertility. In this study, effects of a long-term fertilization on soil microbial biomass carbon (SMBC) and soil microbial biomass nitrogen (SMBN) were studied in yellow paddy fields, Guizhou Province, and a rational fertilization model was also discussed.

MethodsBased on the long-term located monitoring base of yellow soil fertility and fertilizer efficiency, the changes of soil microbial biomass C and N and their relationships with soil organic carbon and total nitrogen under different fertilization conditions were studied using the method of chloroform fumigation-K₂SO₄ extraction. The treatments were: no fertilizer (CK), chemical fertilizer (NPK), organic manure (M), low application rate of manure combined with chemical fertilizer (0.5MNPK) and high application rate of manure combined with chemical fertilizer (MNPK).

ResultsThe results showed that SMBC varied in the range of 423.87–695.04 mg/kg and SMBN was in the range of 44.36–91.65 mg/kg under different fertilization treatments. The application of chemical fertilizers (NPK) and organic manure (M, 0.5MNPK and MNPK) could increase the SMBC and SMBN contents, and compared with the CK treatment, the MNPK treatment had the highest SMBC increase rate of 64.0%, which was significantly higher than those of the NPK and 0.5MNPK treatments, but had no significant difference with the M treatment. Compared with the CK treatment, the SMBN content of the M treatment was increased by 106.6%, which was significantly higher than those of the NPK and 0.5MNPK treatments, but the difference between M and MNPK was not significant. The long-term application of the chemical fertilizers (NPK) only significantly increased the content of SMBN (44.1%), and its effect on SMBC was not obvious. The effects of long-term fertilization on SOC, total NL and microbial quotient (qMB) were consistent with SMBC, and their contents were increased with the increase of organic fertilizer application amount, and were highest under the MNPK treatment, followed by the M and 0.5MNPK treatments, and the lowest contents were in the NPK treatment. The ratios of SMBC and SMBN had no significant differences in the fertilization treatments, and were all lower than that of the CK treatment. SMBC and SMBN had a significant positive correlation with SOC, qMB and TN, and also had a significant positive correlation with each other.

ConclusionsSoil microbial biomass carbon, nitrogen and microbial entropy were significantly correlated with soil organic matter and total nitrogen content. The data from the experiment indicated that the application rate of single organic manure or the high application rate of manure combined with chemical is an effective way to improve soil microbial biomass.