Effect of different crop rotation systems and continuous fallow on soil microbial biomass carbon and nitrogen under different fertilizer treatments

Crop rotation affects the amount and quality of crop residue returned into the soil. In this study, a 17-year long-term field experiment was conducted to study the effect of different crop rotation systems continuous fallow(CF), wheat and summer fallow (WF), and wheat and maize rotation (WM) under various fertilization treatments on the contents of soil microbial biomass carbon (SMBC), soil microbial biomass nitrogen (SMBN), soluble organic carbon (SOC) and soluble organic nitrogen (SON). Compared with WF rotation, WM rotation increases SMBC, SMBN, SOC, SON, total organic carbon (TOC) and total nitrogen (TN) contents in the 0~10 cm layer soil, but this is not so obvious in the 10~20 cm soil layer. CF also significantly increases SMBC, SMBN, SOC, SON, TOC and TN contents in the 0~10 cm soil layer in comparison with treatments without fertilizer (CK) or with chemical fertilizer (NPK) under both WF and WM rotations. The effect of different fertilizer treatments on the level of SMBC, SMBN, SOC and SON is in the following order: MNPK>NPK>CK. Crop rotation systems and fertilizer treatments have insignificant effect on SMBC/TOC and SMBN/TN ratios in the soil.