Annual spreading of olive mill wastewater over consecutive years: Effects on cultivated soils' physical properties

Abstract

Several studies cautioned against potential negative effects of controlled olive mill wastewater (OMW) application on soil physical properties that could be associated with the possible adverse effects of K on soil structure stability. The objective of the study was to examine the effects of annual application of OMW over several years on selected physical properties of the upper soil layer (0-10 cm) and their link to exchangeable K levels. Two experimental field platforms were studied: field crops grown in a tilled clay soil (3 years of OMW application) and an olive orchard grown in a sandy-loam soil (5 years of OMW application). In the clay soil, OMW application did not affect organic carbon (OC) and only slightly increased exchangeable potassium percentage (EPP) from 3.3 in the control to~4.5 in the OMW-treated plots. In the sandy-loam soil, application of different rates of OMW resulted in an increase in both OC and EPP (>20) compared with the control (8). For both soils, addition of OMW improved aggregate stability; yet for the clay soil, the increase was not associated with changes in EPP or OC. In the sandy-loam soil, aggregate stability was positively correlated with OC and EPP. Soil hydraulic conductivity, tested for the sandyloam soil only, was not affected by OMW application. Overall, our study shows that consecutive 3 to 5 years of controlled OMW application in the range of 50-150 m 3 OMW ha −1 y −1 does not result in the deterioration of soil physical and hydraulic properties. reported a range of 5.5-12 dS m −1 for electric conductivity. In addition to the oil extraction process, the high variability in OMW properties was attributed to harvest date, irrigation level, cultivar type, and fruit water content (Aviani et al., 2012). Nonetheless, these unique characteristics of OMW prevent its direct discharge into domestic wastewater treatment plants (Laor et al., 2011;Rozzi & Malpei, 1996;Sayadi, Allouche, Jaoua, & Aloui, 2000 to the classic "wastewater treatment" approach, numerous studies advised the controlled spreading of OMW on cultivated soils as a viable recycling approach. It was further suggested that OMW could be considered as a useful, low-cost soil amendment and fertilizer (Chartzoulakis, Psarras, Moutsopoulou, & Stefanoudaki, 2010;Gargouri et al., 2013;Hanifi & El Hadrami, 2008;Laor et al., 2011;Tomati, Galli, Fiorelli, & Pasetti, 1996), although OMW application caused a drastic reduction in soil mineral-N indicating net N immobilization (Karpouzas et al., 2010). OMW showed its potential to serve as environmental friendly bio-herbicide (Boz, Dogan, & Albay, 2003;Boz, Ogüt, Kir, & Dogan, 2009), and finally, in regions having low soil organic matter (SOM) content and consequently low soil fertility, OMW can serve as a readily available organic matter (OM) source.Yet, great concerns have been raised regarding the adverse effects of OMW on and to seed development and germination (Aliotta, Fiorentino, Oliva, & Temussi, 2002;Aviani, Raviv, Hadar, Saadi, & Laor, 2009;Barbera, Maucieri, Iop...

Sustainable Management of Olive Orchard Nutrition: A Review

“…In the case of N, most of the unconsumed applied N will leach below the root zone [9] and part of it will reach the atmosphere as N 2 O [16]. In the case of K, most of the unconsumed K will find its way to the adsorbing complex of the soil, unless the cation-exchange capacity of the soil is very low, in which case it will also be leached below the root zone [17,18]. Excessive soil K load may lead to soil dispersion and reduced infiltration rate, as described for sodicity [19,20].…”

“…Savci [70] stated that over-fertilization with K can impair soil structure. However, Levy et al [17] found that aggregate stability, a measure of soil structure, increased with increasing levels of K, and that soil hydraulic conductivity was not impaired by elevated soil K concentrations when organic compounds were added to the soil. Over-fertilization with K can affect salinity indirectly as, in general, the source for K is KCl.…”

“…Potential risks of in-situ orchard application of OMW include negative effects on soil characteristics [104] or soil fauna due to phytotoxicity [105] and transport out of the orchard and into natural water sources during erosion events. Nevertheless, recent studies [17,18] have shown that controlled application of OMW to olive orchards over several years has no long-term adverse effects on soil properties or tree performance. Saadi et al [106] found quick recovery of soil microbial activity after OMW application and recommended this procedure as safe.…”

“…Zipori et al [18] found that at an annual OMW application of 50 m 3 ha −1 , the whole K requirement and 30% of the P requirement of the orchard were satisfied, suggesting substantial savings on chemical fertilizers. Controlled application of OMW in olive orchards seems to be a sustainable practice, especially if it is followed by shallow tillage to reduce soil hydrophobicity and improve water infiltration [17]. However, there is always the risk of a negative impact of OMW on soil properties.…”

Toward Balancing the Pros and Cons of Spreading Olive Mill Wastewater in Irrigated Olive Orchards

“…Olive mill wastewater (OMW) is the liquid by-product obtained from three-phase (solid, aqueous, oil) olive oil extraction systems. Up to 30 million m 3 OMW is generated annually in the Mediterranean region [1]. OMW consists of vegetation water, tissues of olive fruits, and process water used in different stages of the extraction.…”