[Soil health evaluation of loquat orchard based on soil quality index method]

Fruit quality and yield in orchards will decrease after long-term planting. To analyze the changes of soil quality under different planting years and identify the key factors of the declining of orchard soil quality could provide scientific foundation for optimizing fertilization management of orchard soil. In this study, we analyzed the changes of soil physical, chemical, and biological properties of loquat orchard under different planting years (<10 years, 10-15 years, 15-20 years, ≥20 years) in Ninghai County, Zhejiang Province, and evaluated soil health by using soil quality index, multifunctionality index, and sensitivity and resistance indicators. The results showed that, compared with the orchards planting less than 10 years, soil bulk density in the orchards with planting years of 10-15 years and over 20 years increased by 12.8% and 13.6%, respectively. Soil pH decreased by 8.8%, 8.6%, and 7.5% in the orchards with planting years of 10-15 years, 15-20 years and over 20 years, respectively. With the increase of planting years, soil microbial biomass carbon, soluble organic carbon, soluble organic nitrogen, available phosphorus, available potassium, total organic carbon, total nitrogen decreased, and the soil quality and multifunctionality index of loquat orchard soil decreased. Compared with the orchards planting less than 10 years, soil quality index and soil multifunctionality index decreased by 20.4% and 17.9% for the orchards with the planting years of 10-15 years, 38.1% and 25.2% for the orchards with the planting years between 15-20 years, and 50.7% and 35.5% for the orchards planting over 20 years, respectively. The key factors affecting soil quality of loquat orchards were soil soluble nitrogen, available potassium, and available phosphorus. Amongst the available nutrients, NH₄⁺ and NO₃^- were the sensitive indices in orchard soil. In conclusion, long-term planting decreased soil quality and available nutrient content in loquat orchards.