Influence of peach branch compost on the yield, quality of No. 9 peach and organic matter content in the soil

【Objective】Peach (Prunus persica) is native to China, and currently, China leads the world in both peach cultivation area and production. Compared with other fruit trees, peach trees grow rapidly and produce a large amount of pruning branches annually. Calculations indicated that each hectare of peach orchard would generate 4500 kg to 7500 kg of pruning branches. In Pinggu district alone, the annual pruning of peach branches across all four seasons amounts to nearly one million tons, yet the re-source recycling rate for these branches does not exceed 30%. Most of these branches are piled up in the orchards, severely impacting the orchard environment, posing fire risks, and spreading the pests and diseases. In order to utilize the peach branches as a resource, Pinggu district implemented the“Ecological Bridge”project in 2017, encouraging peach farmers to collect the pruned branches and deliver them to designated organic fertilizer production facilities to produce peach-branch organic fertilizer for field application. However, there has been little research on the effect of long-term application of the peach-branch fertilizer on the tree growth, fruit quality of peach and organic matter in the orchard soil. Therefore, investigation of the long-term effects of the peach branch fertilizer is of great significance for the sustainable development of the peach industry.【Methods】The peach tree branches were crushed and mixed with livestock manure and subjected to aerobic high-temperature composting to produce organic fertilizer. Three application rates were used (Treatment T1: 15 000 kg · hm- 2 ; Treatment T2: 30 000 kg · hm- 2 ; Treatment T3: 45 000 kg · hm- 2 ), and compared with the conventional organic fertilizer. The study was conducted on 4-year-old peach trees of the“No. 9”variety from 2017 to 2024, investigating the effects of the peach branch fertilizer as a basal fertilizer on peach yield, quality, and soil organic matter over seven consecutive years.【Results】The 7 years application of the peach branch compost has no adverse effects on the peach tree growth. However, different application rates of the peach branch compost could lead to differences in peach tree yield, quality, and soil organic matter content. Among the treatments, the yield and single fruit mass of the 30 000 kg·hm-2 and 45 000 kg·hm-2 peach branch fertilizer application rates showed no significant differences compared with that of the 30 000 kg · hm- 2 application rate of ordinary organic fertilizer, but the soluble sugar content, titratable acid content, and sugar-toacid ratio of the peach were superior to those of the 15 000 kg · hm-2 peach branch fertilizer application rate and the 30 000 kg · hm- 2 conventional organic fertilizer application rate. As the planting years increased, the vitamin C content in the fruit showed a trend of increasing with the application rate of peach branch fertilizer, while the hardness decreased with the increase of the application rate of peach branch fertilizer. By the autumn of 2024, before the basal fertilizer application, the soil organic matter content in the 0-20 cm and 20-40 cm layers at the fertilization ditch for treatments T1, T2, T3, and CK reached 34.25 g·kg-1 , 35.88 g·kg-1 , 35.76 g·kg-1 , 33.97 g·kg-1 and 56.36 g·kg-1 , 65.25 g·kg-1 , 72.11 g·kg-1 , 63.58 g · kg- 1 , respectively, showing a significant increase compared with the beginning of the experiment. The rate of increase was positively correlated with the application rate of peach branch fertilizer, with organic matter content rising rapidly in the early stages and then slowing down. Due to the adoption of the inter- row cover crop return-to- field technology, the organic matter content in the inter- row soil showed a trend of increasing year by year. Based on the analysis of yield and quality data, soil organic matter content was not correlated with yield, but was positively correlated with the vitamin C content of the peach fruits and negatively correlated with the hardness.【Conclusion】Based on the results of seven consecutive years of experiments, at a dosage of 30 000 kg·hm-2 , the application of the peach branch fertilizer showed no significant differences from the application of the conventional organic fertilizer in terms of yield, fruit mass, vitamin C content, and hardness. However, it outperformed conventional organic fertilizer in terms of soluble sugar and titratable acid content, which are indicators of taste. The treatments using 30 000 kg · hm- 2 and 45 000 kg · hm- 2 of the peach branch fertilizer only resulted in the difference of vitamin C content and firmness. Therefore, in the actual production of Pinggu peaches, the recommended application rate of the peach branch fertilizer would be 30 000 kg·hm-2 , and the preferred fertilization method would be trench application combined with the inter-row grass returning technology. This approach can not only meet the growth needs of peach trees and ensure stable yield and quality but also reduce input costs while continuously improving the soil fertility of the peach orchard.