Study on the Effects of Planting Alfalfa (Medicago sativa L.) and Adding Biochar on Soil Fertility in Jujube Orchards

Soil fertility has an important impact on orchard yield and quality, and sandy soil limits the economic yield of orchards due to its low water and fertilizer retention capacity. Although biochar and alfalfa planting have been widely utilized separately in soil improvement, few studies have examined the effects of combined alfalfa planting and biochar application on jujube orchard soils. This study investigates the effects of alfalfa planting alone and alfalfa planting combined with different levels of biocarbon addition on soil properties. A field experiment was conducted in a jujube orchard in Yanchuan County, Shaanxi Province, with four treatments: clear tillage control (CK), alfalfa planting only (B1), alfalfa planting + 1.5 kg·m−2 biocarbon (B2), and alfalfa planting + 3 kg·m−2 biocarbon (B3). The results show that planting alfalfa significantly increased soil moisture content (SMC) and soil organic matter (SOM) content by 27.79% and 17.65%, respectively, and biochar addition significantly increased soil carbon, nitrogen, and phosphorus content by 8.11–37.7%, enhanced the soil moisture content (SMC) by 98.13–100.22%, promoted the growth of alfalfa, and increased vegetation cover (p < 0.05). The combination of biochar and alfalfa improves soil fertility more effectively than alfalfa alone. It can increase the soil N and P nutrient contents, improve soil available nutrients, promote alfalfa growth in a short period, and provide a feasible solution for soil improvement in the future.