Microbial Biomass and Enzymatic Activity in the Rhizosphere of Organically and Conventionally Managed Olive Orchards Under Arid Conditions

Organic agriculture is perceived as an alternative agricultural system that is assumed to be less harmful to the environment and provide healthy and nutritious food products. However, whether organic farming practices sustain crop yields or improve soil quality relative to conventional farming is both system and location dependent. Organic farming is an expanding practice in Saudi Arabia, emerging in late 1990s and firstly adopted in tree orchard cropping systems, such as olive. The extent to which the organic agricultural management practices under extreme environment conditions of Saudi Arabia can affect the arid soil quality and biochemical properties is still largely unknown. Therefore, this study aimed at comparing the temporal impact of organic vs. conventional management practices on microbial biomass and enzyme activities in the rhizosphere of olive trees. Rhizosphere soils were collected from organically and conventionally managed olive orchards located within short distances from each other and representing three plantation periods: 20, 15 and 10 years. The activities of β-glucosidase, N-Acetyl-Glucosaminidase and alkaline phosphatase enzymes in addition to microbial biomass carbon and nitrogen have been examined. The results indicate higher enzymes activities in the rhizosphere soil of organically managed olive orchards, especially those under the 20 years of cultivation. The 20 years of organic management practices also resulted in higher soil microbial biomass C and N content.