Effects of the combination of fungal residue and chemical fertilizer on soil microbial biomass carbon and nitrogen and dissolved organic carbon and nitrogen in paddy soil

As an excellent organic material additive to soil,fungal residue can reduce the application of chemical fertilizer and also plays an important role in maintaining soil fertility. As the most active organic components,soil microbial biomass carbon（ MBC） and nitrogen（ MBN） and dissolved organic carbon（ DOC） and nitrogen（ DON） are usually regarded as important and sensitive indices for soil fertility change. Therefore,it is vital to evaluate the ecological and soil fertility significance of fungal residue application under different rates return to the paddy soil. In our study,a randomized complete block field experiment with nine treatments(0,50%,and 100% levels of chemical fertilizers（ C） and edible fungal residue（F） were considered,C100F50 stands for 100% of chemical fertilizer and 50% of fungal residue application,etc.) was set up. The changes of MBC,MBN,DOC,and DON,and ratios of these parameters to soil organic carbon（ SOC） and totalnitrogen（ TN） were analyzed. Results showed that the highest contents of MBC,DOC and DON were observed under treatment of C100F50,which were 49.40%,43.65% and 83.52% higher than that under the treatment of control. Meanwhile highest MBN content was found under treatment of C50F100 which was 207. 19% higher than that under the treatment of control. Both ratios of MBC and DOC to SOC were decreased with increased application rate of fungal residue and chemical fertilizer; the highest ratios of MBN and DON to TN were observed in C100F50. There were highly significant positive correlations between MBC,DOC and SOC,respectively,and between MBN and TN as well. The correlation between DON and TN was significantly positive too. In conclusion,application of fungal residue with chemical fertilizer in paddy soil could increase the contents of MBC,MBN,DOC,and DON,but over dosage of fungal residue or chemical fertilizer application could lead to a negative effect. Consequently,the appropriate application rate of chemical fertilizer combined with fungal residue was the optimum choice to improve the SOC turnover rate,microbial activity,and nitrogen supply capacity and efficiency in paddy soil.