Effects of different mulching methods with apple branch fragments on soil nutrients, growth and development of apple trees and fruit quality

【Objective】Fruit trees as perennial plants, can produce a large number of branches in the annual production due to pruning, which are rich in lignin and polyphenols and other organic matter, and are a resource that can be used, but by the impact of traditional concept development of branch crusher and limitations by other orchard machinery and equipment level, most Chinese fruit growers will prune down the branches as a waste, discarding in the orchard outside or adopting direct incineration, which not only wastes the effective resources, but also causes the environment pollution. With the overall development of social economy and the emergence of small branch crusher and other modern machinery, waste branches can be crushed and return to the orchard, as a labor-saving practice, not only to solve the environmental pollution, but also increase soil porosity, raise soil organic matter content, and improve soil structure at the same time. It can effectively increase the content of available nutrients. In addition, it can increase the quick-acting nutrient content effectively and improve the soil structure, signifi-cantly improve the crop yield and fruit quality, and make the waste branches utilised in a resourceful way. This experiment aims to improve the utilization rate of waste branches and soil environmental conditions in the orchard, and to screen out the treatment methods suitable for the growth and development of fruit trees.【Methods】The crushed branch mulching experiment began in April 2022, using the branch fragments for mulching in the scientific research base of Shenyang Agricultural University, After the branches were crushed into fragments of about 2 cm with the GTS1300 model tree branch crusher, the seven-year-old Longfeng apple orchards were treated with mulching. In first and second year, the mulching treatments were carried out in May 2022 and May 2023. This experiment was a 2-year replicated experiment, with tree disk clearing as the control. Manual weeding was applied in the clearing area, and crushed branches were returned to the field, with bare land in a diameter of 20 cm in the centre of the base, and mulched 150 cm in length, 50 cm in width, and 2 cm in thickness. Three treatments were set up in the experiment: T1 treatment was surface mulching of crushed branches, T2 treatment was covering a layer of horticultural ground cloth on top of the T1 treatment, and T3 treatment was rototilling an equal amount of crushed branches into the soil layer of 0-20 cm. Five trees were selected for each treatment as five replications, totaling for 20 trees, and other management conditions like water and fertilizer management kept consistent. Sampling times were in April 2022, July 2022, October 2022, April 2023, July 2023, and October 2023, with advance planning to avoid rainy day sampling if continuous rain was encountered.【Results】The results showed that apple branch debris mulching can improve soil quality, promote tree growth and development, and enhance fruit quality. After 1 year of mulching, all the crushed branches were decomposed by microorganisms, and the mulching of branch fragments around the tree tray could improve the soil structure, and the wood chips in contact with the soil would gradually decompose and turn into organic substances to provide nutrients for the trees. In the 0-20 cm soil layer in the second year of the experiment, the treatment of crushed branches + ground cloth mulching increased the content of organic matter and quick-acting potassium, and the effect was more significant; all three treatments increased the contents of alkali- hydrolyzable nitrogen (AN) and available phosphorous (AP); and the treatment of mulching apple branch fragments had a promoting effect on the growth of fruit trees. In the second year of the experiment, the three treatments were able to promote the growth of new shoots; the treatment of crushed branches + ground cloth mulching could increase the net photosynthetic rate; and the treatment of mulching apple branch fragments could improve the fruit quality. In the 2nd year of the experiment, all the treatments can significantly increase the single fruit mass, soluble solids and soluble sugar contents, and basically the crushed branches + ground cloth mulching treatment had a better effect.【Conclusion】Different ways of mulching with apple branches fragments can create a more suitable growing environment for fruit trees by improving the soil conditions around the trees, thus favoring the growth and development of fruit trees, and improving economic benefits while saving production costs. Comprehensively analyzing the effects of different mulching methods with apple crushed branches on soil properties, it was found that crushed branches + ground cloth mulching may be a more beneficial mulching method for actual production.