Protective green cover enhances soil respiration and native mycorrhizal potential compared with soil tillage in a high-density olive orchard in a long term study

Arbuscular mycorrhizal fungi (AMF), living in symbiosis with most food crops, improve plant growth and nutrition and provide fundamental ecosystem services. Here, the possibility of increasing root density and native AMF activity through appropriate soil management practices was investigated, comparing the long-term (10 years) effects of a permanent green cover (GC) with shallow tillage (ST) in a high-density olive orchard in a Mediterranean environment. Olive root density, AMF colonization, and soil mycorrhizal inoculum potential (MIP) were determined after trench excavations at different soil depths. Soil respiration was determined by infrared gas analysis. The activity of native AMF, as assessed by MIP bioassay, was higher in GC plots than in ST ones. Olive roots were well colonized by AMF in both management systems. Soil respiration rates of GC plots were often higher than those of ST, whereas soil moisture and temperature in the topsoil were similar in both treatments. Soil depth significantly affected root density, which peaked at 0.2 m soil depth in both soil treatments. The maintenance of a permanent plant cover appears to be a better option than shallow tillage as a soil management practice to preserve biological soil fertility in olive orchards.