Soil responses to different management practices in rainfed orchards in semiarid environments

Clean cultivation is a common practice in rainfed orchards; however, it may have detrimental effects on soil properties. This study examines the effect of different soil management systems on physical, chemical, and biochemical properties in a hypercalcic Calcisol in rainfed almond orchards (Prunus dulcis (Mill.) D.A. Webb) in SE Spain. Four types of soil management (main-plot treatments) were compared to a frequently tilled orchard system (FT: three or four tillages per year). The four types of soil management were: fencing (SF) of a flock of 130 sheep in 0.4ha and grass cover was kept throughout the growing season; native vegetation (NV) that was allowed to grow; cover crop (CC) composed of legumes and crucifers; and reduced tillage (RT) comprising autumn and spring chisel ploughing. Each type of soil management was split into two grazing treatments (subplot treatments): with and without grazing. Our results supported the hypothesis that clean cultivation, i.e., FT, has deleterious effects on soil properties compared with managed groundcover. Compared with FT treatment, at the end of the experiment, the rest of treatments had higher wet aggregate stability (except the SF treatment), soil organic carbon (10.6gkg⁻¹vs. 5.4gkg⁻¹, mean groundcover treatments vs. FT), total nitrogen (1.35gkg⁻¹vs. 0.83gkg⁻¹, mean groundcover treatments vs. FT), available potassium (332mgkg⁻¹vs. 187mgkg⁻¹, mean groundcover treatments vs. FT), and dehydrogenase (2.6μgINTFg⁻¹h⁻¹vs. 1.9μgINTFg⁻¹h⁻¹, mean groundcover treatments vs. FT), arylsulphatase (12.8μgPNPg⁻¹h⁻¹vs. 6.5μgPNPg⁻¹h⁻¹, mean groundcover treatments vs. FT), β-glucosidase (569μgPNPg⁻¹h⁻¹vs. 300μgPNPg⁻¹h⁻¹, mean groundcover treatments vs. FT), and phosphatase activity (394μgPNPg⁻¹h⁻¹vs. 220μgPNPg⁻¹h⁻¹, mean groundcover treatments vs. FT). Grazed plots had higher water content in soil (10gH₂Okgsoil⁻¹vs. 9.4gH₂Okgsoil⁻¹, grazed vs. not grazed plots) and greater levels of arylsulphatase (12μgPNPg⁻¹h⁻¹vs. 11μgPNPg⁻¹h⁻¹, grazed vs. not grazed plots), β-glucosidase (582μgPNPg⁻¹h⁻¹vs. 491μgPNPg⁻¹h⁻¹, grazed vs. not grazed plots), and phosphatase activity (396μgPNPg⁻¹h⁻¹vs. 345μgPNPg⁻¹h⁻¹, grazed vs. not grazed plots), in late spring, and this is attributed to the reduction of evapotranspiration and to the stimulation of root activity by means of plant defoliation. In conclusion, under the conditions of this study, managements including grass cover improved physical, chemical and biological properties of soil compared with frequent tillage, particularly when grass was early removed by grazing.