Impact of cover crop and mulching on soil physical properties and soil nutrients in a citrus orchard

Background: Cover crops and mulching can ameliorate soil porosity and nutrient availability, but their effects on the physical characteristics and nutrients in the raised bed soils are unclear. Methods: The field experiment was conducted in a pomelo orchard from 2019 to 2021, with an area of 1, 500 m. The treatments included control (no cover crop), non-legume cover crop (Commelina communis L.), legume cover crop (Arachis pintoi Krabov & W.C. Gregory), and rice straw mulching (Oryza sativa L.). At the end of each year (2019, 2020, and 2021), soil samples were collected at four different layers (0-10, 10-20, 20-30, and 30-40 cm) in each treatment. Soil bulk density, soil porosity, and the concentration of nutrients in the soil were investigated. Results: The results revealed that soil bulk density at two depths, 0-10 and 10-20 cm, was reduced by 0.07 and 0.08 g cm by rice straw mulch and a leguminous cover crop, thus, increasing soil porosity by ~2.74% and ~3.01%, respectively. Soil nutrients (Ca, K, Fe, and Zn) at topsoil (0-10 cm) and subsoil (10-20 cm) layers were not significantly different in the first year, but those nutrients (Ca, K, Fe, and Zn) improved greatly in the second and third years. Conclusions: Legume cover crops and straw mulch enhanced soil porosity and plant nutrient availability (Ca, K, Fe, and Zn). These conservation practices best benefit fruit orchards cultivated in the raised bed soils.