RESPONSE OF SOIL AND WHEAT CROP TO THE APPLICATION OF TWO-PHASE OLIVE MILL WASTE TO MEDITERRANEAN AGRICULTURAL SOILS

Abstract

The two-phase centrifugation system for olive-oil extraction produces approximately 4,000,000 Mg per year of semisolid olive mill waste (SOMW) in Spain. Soils under intensive cultivation in the Mediterranean region have a net deficit of C, and SOMW application may represent a solution to this deficiency. A 2-year greenhouse study using wheat (Triticum aestivum L.) was conducted to evaluate the potential use of SOMW as a soil conditioner and soil amendment. Two representative Mediterranean agricultural soils, a Cutanic Luvisol (CL) and a degraded Leptic Cambisol (LC), were used. Treatments included five SOMW rates, ranging from 0 to 40 Mg ha−1, combined with mineral fertilizer. Significant increases in organic carbon, aggregate stability, total N, available K, and cation-exchange capacity were observed in both soils. However, available P decreased significantly. The SOMW application significantly increased N, P, and K uptake by the wheat in the LC soil but decreased P and K uptake in the CL soil. In the second year of the experiment, the SOMW application significantly increased the yield in both soils, and grain yields were increased by 29% and 198% when 40 Mg SOMW ha−1 was applied to the CL and LC soils, respectively. Raw SOMW, thus, seems to be a potential soil amendment agent and a source of organic matter, N, and K, especially in degraded agricultural soils.