Effects of orchard sod culture on soil environment and pomegranate fruit quality

【Objective】Grass cultivation is a contemporary and effective soil management strategy for orchards. Its success depends on the careful selection of suitable grass species and the implementation of scientifically sound management practices. By planting legumes or grasses between the rows of fruit trees and managing them appropriately, a harmonious coexistence between the grasses and fruit trees can be established. This approach enhances soil nutrient levels, which in turn positively impacts the growth of fruit trees and the quality of their produce. However, in the current pomegranate farming industry, the majority of farmers still rely on clear- cutting for orchard management. This practice degrades the soil environment, negatively affecting the growth and development of fruit trees and ultimately reducing fruit quality. In recent years, grass cultivation in orchards has gained increasing popularity both domestically and internationally. This technique serves as an effective orchard management model, reducing the impact of weeds while helping to maintain soil moisture. To identify grass species suitable for the local climate and cultivation conditions, this study investigated the effects of different grass spe-cies on soil properties and fruit quality in pomegranate orchards in Binchuan County, Yunnan Province. 【Methods】This study implemented grass cultivation in soft-seeded pomegranate orchards to assess the impact of different green manure species on fruit quality, soil nutrient content, soil enzyme activity, and soil microbial abundance. The pomegranate variety used in the experiment was Huaguang. The experimental design included six treatments: VS (Vicia sativa), LP (Lolium perenne), TR (Trifolium repens), VV (Vicia villosa), NG (natural grasses), and CK (clear tillage) as the control. Each treatment was cultivated and managed over a two-year period. Soil samples from the pomegranate orchards were collected under each of the six treatments. The pH value, organic matter content, nutrient content, enzyme activity, and microbial counts were analyzed in the rhizosphere soil samples. One-way analysis of variance (ANOVA) was used to examine differences in the rhizosphere soil environment among the six cultivation and management treatments. Uniformly sized pomegranate fruits were harvested two weeks prior to ripening. The weight, longitudinal and transverse diameters, fruit shape index, titratable acidity, soluble solids content, and solid-acid ratio of individual fruits were measured. One-way ANOVA was also employed to compare the external and internal quality of pomegranate fruits across the six cultivation and management treatments. The six cultivation and management modes were ranked based on evaluations of soil habitat and fruit quality, with the highest-ranked mode identified. Correlation analyses were conducted to explore the relationships between fruit quality and environmental factors, thereby revealing the underlying mechanisms through which the environmental factors influence fruit quality.【Results】Grass cover can improve the orchard environment, yet different grass species exhibit varying regulatory effects on it. Compared with CK, most grass treatments, except for NG, can enhance soil nutrient levels. Among them, the TR treatment showed the most significant improvement (P＜0.05). The pH value of orchard soil was adjusted to neutral, reaching the soil pH value suitable for cultivating softseeded pomegranate. The soil organic matter content, hydrolyzable nitrogen content, effective phosphorus content, quick- acting potassium content, exchangeable calcium content, sucrase activity, bacterial counts, and actinomycete counts were significantly higher than those of CK. Specifically, these parameters increased by 38.02%, 41.12%, 42.51%, 94.51%, 39.84%, 25.47%, 60.19%, and 60.66%, respectively. The LP treatment performed best in increasing soil exchangeable magnesium content, and alkaline phosphatase activity by 24.33% and 21.20%, respectively, compared to CK. In comparison of CK, all grass treatments except for natural grassing altered both the intrinsic quality and external quality of the fruit. Moreover, cultivation of different grasses had different effects on fruit quality. Among them, the TR treatment exhibited the most significant improvements in fruit weight, soluble solids content, and titratable acidity, with respective increases of 28.14%, 14.13%, and 32.72%. Based on the comprehensive impact assessment results, the TR treatment ranked first in enhancing the orchard soil environment and fruit quality. Correlation analysis showed that soil pH was significantly and negatively correlated with soil nutrient content, soil enzyme activity, and soil microbial quantity, and fruit quality was significantly and positively correlated with soil microbial quantity. Cultivation of grass in orchards can change soil water holding capacity, adjust the soil pH, increase the retention capacity of soil, soil enzyme activity, and soil microbial quantity, ultimately improving fruit quality.【Conclusion】Trifolium repens living mulch in pomegranate orchards significantly elevated soil organic matter, hydrolytic N, available P, quick-acting K, exchangeable Ca, invertase activity, and counts of bacteria and actinomycetes compared with other treatments. Concomitantly, fruit quality peaked under Trifolium repens: average fruit mass reached 425.34 g, transervse diameter 100.90 mm, total soluble solids 17.77% , and titratable acidity 0.72%-all markedly higher than others. Living mulch enhanced soil nutrients, enzyme activity and mi-crobial biomass, ameliorating the soil habitat and advancing fruit quality. Thus, white clover is the most suitable cover crop for pomegranate orchards in Binchuan County, Yunnan.