Long-term effects of olive mill waste waters spreading on the soil rhizospheric properties of olive trees grown under Mediterranean arid climate

Abstract

Context The spreading of olive mill waste waters (OMWW) could offer an appropriate management option to add value to this agricultural by-product, such as to increase soil fertility and plant productivity. Aims The main objective of this work was to evaluate the effects of the application of OMWW (at a fixed dose of 50 m3 ha−1), in the long term (20 years) on the soil rhizospheric properties and on old olive trees (80 years old) growth and productivity. Methods The experimental site consists of four plots treated with OMWW (T1, T2, T3 and T4) and four ‘control’ plots (C1, C2, C3 and C4), without any treatment. The treated plots have received each a fixed dose of 50 m3 ha−1 of OMWW in February of each year since 2004. Key results The results obtained showed that the addition of OMWW increased the soil water retention capacity (SWRC) and its organic matter content (OMC), as well as the augment of phosphorus (P) and potassium (K) levels. The activity of the soil rhizospheric microflora was significantly enhanced. Conclusions OMWW application to the soil surface in an olive orchard at 50 m3 ha−1, since 2004, had no negative effects on the tree’s vegetative growth and satisfied plant P, K and N requirement. Implications Our study showed that OMWW can enhance the soil properties and enrich the soil with necessary minerals.