Chapter 10 - Effects of Carbon Inputs on Chemical and Microbial Properties of Soil in Irrigated and Rainfed Olive Groves

Abstract

Olive tree pruning residue and olive waste represent a great amount of organic materials that are produced during a short period. The application of organic materials to land is a common practice in sustainable agriculture in recent years. However, its implementation in olive groves under different irrigation regimes has not been systematically tested. The aim of this work was to study the effect of alternative carbon input techniques (e.g., wood shredded, pruning residues, returning of olive mill wastes the field with compost) on soil chemicals (e.g., pH, EC, total organic carbon, total nitrogen, inorganic nitrogen, humic and fulvic acids, available P, and exchangeable K), and microbial properties (e.g., soil basal microbial respiration and microbial biomass carbon) in relation to irrigation conditions (e.g., irrigated and rainfed olive orchards). The results showed that changes in soil quality in olive orchards due to carbon inputs depend on irrigation conditions. Soil carbon content remarkably reduced by the addition of organic material in irrigated plots compared to control whereas they were substantially increased in rainfed plots. Microbial parameters appeared to be reliable indicators of changes in soil management over the short period of this study. Nutrient concentrations and microbial properties of soil show a decreasing trend with increasing distance from tree trunk regardless the irrigation conditions and carbon input practices. This fact indicates the influence of a tree canopy area and root density on the soil surface properties. Soil depth significantly influenced soil attributes; major decreases were recorded for SOC, inorganic nitrogen, and microbial properties, indicating the high potential of surface soil in olive groves to sequester carbon. Conversely, the addition of organic matter and irrigation conditions did not contribute to subsoil C content. Proper management of alternative carbon inputs in soil can positively affect soil productivity in Mediterranean olive groves.