Comprehensive assessment of effects on fruit and soil quality of applica- tion of branch compost in a pear orchard

Abstract: 【Objective】Collection and utilization of agricultural waste is a difficult in China. Pruned branches from fruit trees are a special kind of agricultural waste, which is rich in organic matters and mineral nutrients. However, due to its hard texture and complex structure, it is difficult to be reutilized, and is carelessly discarded or burned in large quantities causing great environmental pollution and safety hazards. Aerobic composting is an effective method to transform biological wastes into valuable organic fertilizer, which can be applied to the field, bringing both economic and ecological benefits. There is still a lack of systematic and comprehensive reports on the application of compost from fruit tree branches to the field, especially on the changes in fruit and soil quality and tree productivity after application. Therefore, it is necessary to investigate the effects of application of branch compost and organic fertilizer on fruit yield and quality and soil physical and chemical properties in densely-planted pear orchards.【Methods】Four fertilization treatments including branch compost (BCT), branch compost combranches from fruit trees are a special kind of agricultural waste, which is rich in organic matters and mineral nutrients. However, due to its hard texture and complex structure, it is difficult to be reutilized, and is carelessly discarded or burned in large quantities causing great environmental pollution and safe- ty hazards. Aerobic composting is an effective method to transform biological wastes into valuable or- ganic fertilizer, which can be applied to the field, bringing both economic and ecological benefits. There is still a lack of systematic and comprehensive reports on the application of compost from fruit tree branches to the field, especially on the changes in fruit and soil quality and tree productivity after appli- cation. Therefore, it is necessary to investigate the effects of application of branch compost and organic fertilizer on fruit yield and quality and soil physical and chemical properties in densely-planted pear orchards.【Methods】Four fertilization treatments including branch compost (BCT), branch compost com-bined with bio-organic fertilizer (MT), sheep manure (ST) and chemical fertilizer (CT) were set up, and the yield and quality of fruit, and the physical and chemical properties of soils at depths of 0-20, 20-40 and 40-60 cm were investigated, and comprehensively evaluated with the principal component analysis. The amount of sheep manure in ST in the test site was taken as the standard, and the organic matter in BCT and MT treatments was equal to that in ST, and the amounts of N2O, P2O5 and K2O in all treat- ments were equal.【Results】The results showed that MT significantly increased yield, which was 19.78 percent higher than that of CT. BCT and ST significantly increased fruit firmness after continu- ous application for two years. Continuous application of organic fertilizer improved fruit quality signifi- cantly. Compared with CT, ST and MT increased the contents of soluble solids and vitamin C in fruit. MT also increased the content of soluble sugars, and ST and BCT enhanced fruit firmness and in- creased the content of organic acids. There was significant difference in fruit and soil quality in differ- ent treatments. Soil pH was increased by sheep manure application, and decreased by continuous treat- ment of MT in 0-20 and 20-40 cm soil layers. The total salt content in 0-20 cm soil layer significantly increased in MT, and was the lowest in ST, and that in MT was significantly lower than in the other treatments in 20-40 cm soil layer. The content of soil organic matter in each treatment increased with the extension of application and showed a decreasing trend with soil depth. The content of available ni- trogen increased in different soil layers with the continuous application in each treatment, and after 2 years, the available nitrogen contents in ST and MT in the soil layers of 0-20 cm and 20-40 cm were significantly higher than those in CT. Compared with CT treatment, MT and ST significantly increased the content of available iron in soil. MT was the highest in available iron the 0-20 cm soil layer, while in the 20-40 cm soil layer, ST was the highest. The changing trend of soil ammonium nitrogen content was different. It decreased gradually with soil depth in ST, BCT and MT. In CT, ammonium nitrogen was higher in the 0-20 cm and 40-60 cm soil layers than in the 20-40 cm soil layer. Besides, the con- tent of ammonium nitrogen in MT was significantly higher than that in the other treatments in both the 0-20 cm and the 20-40 cm soil layers. The maximum nitrate nitrogen content was found in ST, MT and CT in the soil layer of 0-20, 20-40 and 0-20 cm, respectively. The nitrate nitrogen content in MT in the soil layer of 40-60 cm was always significantly lower than that in ST.【Conclusion】According to the comprehensive evaluation by principal component analysis, three principal components with eigenval- ues greater than 1 were extracted. The contribution rates of the principal components 1, 2 and 3 were 58.67%, 26.371% and 14.959%, respectively. The contribution rates of cumulative variance reached 100%, and the three principal components could reflect the information provided by all indicators. The comprehensive score of different fertilization treatments was in the order of MT>ST>BCT>CT, and MT had the best effect.