The Effects of Nitrogen Reduction and Sheep Manure Incorporation on the Soil Characteristics and Microbial Community of Korla Fragrant Pear Orchards

Excessive use of nitrogen fertilizer affects the sustainable development of the Korla fragrant pear orchard. Semi-decomposed sheep manure is favored because of its advantages of being pollution-free, containing more microorganisms, and being friendly to soil. However, the effects of nitrogen fertilizer combined with sheep manure on soil nutrient cycling and microbial community in pear orchards are still unclear. This study involved a two-year field experiment to investigate fertilization’s effects on the 0–20 cm soil layer of 10–12-year-old Korla fragrant pear trees at maturity. The purpose of this study was to explore the effect of reducing nitrogen fertilizer combined with sheep manure on soil fertility and microbial community in Korla fragrant pear orchard. The treatments of no nitrogen fertilizer (N0), conventional fertilization (N), 20% reduction in nitrogen based on conventional fertilization (N2), a combination of 20% nitrogen reduction with sheep manure F1 (22,500 kg·hm−2), and 20% nitrogen reduction with sheep manure F2 (33,750 kg·hm−2) formed the experimental treatment of nitrogen reduction with sheep manure, denoted as N2F1 and N2F2. The results showed that nitrogen application increased soil physicochemical indicators but decreased soil pH and bacterial community richness and diversity. After nitrogen reduction, soil total nitrogen (TN), alkaline hydrolysis nitrogen (AN), available phosphorus (AP), microbial biomass nitrogen (SMBN), bacterial community richness, fungal community evenness, and diversity were inhibited, but bacterial community diversity was increased. Nitrogen reduction combined with sheep manure treatment increased the content of nitrate nitrogen (NO3−–N), ammonium nitrogen (NH4+–N), soil organic matter (SOM), pH, microbial biomass carbon (SMBC), and SMBN and increased the evenness and diversity of the bacterial community but inhibited the richness of the bacterial community. Among them, N2F2 treatment had the best effect on SMBC and SMBN. Soil pH, NO3−–N, and SOM were the primary environmental variables influencing bacterial and fungal community levels. The application of nitrogen significantly influenced pear orchard yields, but the yield of pears treated showed no significant variation with nitrogen reduction and nitrogen reduction combined with sheep manure based on complete nitrogen application. In summary, 20% nitrogen reduction (300 kg·hm−2) combined with 22,500–33,750 kg·hm−2 sheep manure better promotes the stability and health of soil microbial communities, and the use of organic fertilizer represents the most efficient approach to quickly enhancing soil fertility and the variation of microbial communities. These findings are highly relevant when improving land productivity, ensuring food security, and promoting environmental sustainability in fruit tree farming.