Objective  The aims were to provide theoretical basis and practical support for the rational use of pruned branches in the orchard by exploring the effects of different composting treatments on the physical and chemical properties of orchard soil and the photosynthetic performance of plants.

  Methods  The pruned branches of the fruit tree were treated with different composting treatments. The amount of raw materials used for composting was different between the treatments, such as branch fragments∶urea∶bacterial agent weight ratio, treatment T1: 30∶0∶0, treatment T2: 30∶0, treatment T3: 300∶0∶1, treatment T4: 300∶10∶1, and composting for 60 days. Then, the compost under the apple tree row was covered and returned to the field. The cellulose content of the compost material, the content of soil organic matter and the net photosynthetic rate of the apple tree were measured respectively during the composting process.

  Results  The addition of urea and the bacterial agent was beneficial to promote the decomposition of branches, and the effect of adding urea and bacterial agent together was more significant. Compared with T1, the degradation rates of hemicellulose, cellulose, and lignin in T2, T3, and T4 treatments were significantly increased. There was no significant difference in the degradation rate of cellulose and lignin between T2 and T4. The degradation rates of hemicellulose, cellulose and lignin in T4 treatment were 15.60%, 25.85% and 26.83% respectively. After mulching and returning, the content of soil organic matter and available nitrogen, phosphorus and potassium could be increased, and they all showed the rule of ST4 > ST2 > ST3 > ST1 > CK. The effect on topsoil (0-10 cm) is more significant. In 0-10 cm soil layer, the contents of organic matter, available nitrogen, available phosphorus and available potassium in ST4 treatment were 44.98%, 36.57%, 51.47%, and 29.74% higher than those in CK, respectively. Branch compost mulching could improve the chlorophyll content and photosynthetic performance of plants, and ST4 treatment has the most significant effect. The chlorophyll content of the ST4 treatment was 12.01%, 5.72% and 10.80% higher than that of ST1, ST2 and ST3, respectively. Compared with CK, ST1, ST2, ST3, and ST4 treatments could improve the net photosynthetic rate of plants, and ST4 treatment has the highest photosynthetic rate, 29.85% higher than CK.

  Conclusion  The addition of urea and the bacterial agent is conducive to accelerating the decomposition process of the compost of branch fragments. After mulching and returning to the field, the physical and chemical properties of soil can be improved, and the photosynthetic performance of plants can be improved.