Objective The aims were to study the effects of long-term application of different types of livestock manure on total organic carbon (C), different components of labile organic C and C pool management index in apple orchard soil, and to provide theoretical basis for promoting scientific fertilization and fertilizer utilization of livestock and poultry manure in apple orchard.

Methods Based on the long-term positioning fertilization experiment (started in 2017), six treatments were selected: no fertilization (CK), chemical fertilizer (CF), cow manure (CM), chicken manure (CHM), pig manure (PM) and sheep manure (SM). The total organic C and labile organic C components in fertilized and non-fertilized areas of orchard soil were determined, and the proportion of each component and the C pool management index were analyzed.

Results In the fertilization area, the total organic C contents of four kinds of livestock manure treatments were significantly increased, and the labile organic C content of cow manure and sheep manure treatments were increased by 112.96% and 60.82%. The contents of high, medium and low labile organic C in cow manure treatment were 1.66 g kg⁻¹, 1.27 g kg⁻¹ and 1.73 g kg⁻¹, respectively. The C pool management index of cow manure, chicken manure, pig manure and sheep manure were 203.53, 125.47, 113.00 and 152.54, respectively. In the non-fertilized area, compared with CK, the labile organic C contents of chicken manure and pig manure treatments decreased by 45.1% and 43.85%, and the C pool management index decreased by 54.37% and 52.49%. Under the same livestock and poultry manure treatment, the total organic C content, labile organic C component content and C pool management index in the fertilized area were significantly higher than those in the non-fertilized area. The contents of labile organic C in fertilized and non-fertilized areas under CM treatment were 4.65 g kg¹ and 2.56 g kg⁻¹. The C pool management indices of CM treated fertilized and non-fertilized areas were 203.53 and 111.38.

Conclusion The application of livestock and poultry manure can improve the quality of active organic C in the soil of the fertilized area of the orchard, but has no significant effect on the fertilized area. The effect of the four kinds of livestock and poultry manure is better than that of chemical fertilizer, and the effect of cow and sheep manure treatment is the best, and the effect of cow and sheep manure treatments is better than pig and chicken manure treatment.