Comparing the Response of Growth and Physiologic Variables of Onion to Olive Mill Wastewater Application and Arbuscular Mycorrhizal Fungi Inoculation

From plantations to farms, food safety is a major concern in food industry, particularly for perishable foods like onions. New environment friendly methods like the use of beneficial microbes and organic amendments became requirements to provide long-lasting alternatives. In this study, the impact of the direct use of olive mill wastewater (OMW) and native arbuscular mycorrhizal fungi (AMF) consortium on soil characteristics and onion plant (Allium cepa) growth and physiological responses as a mean to enhance soil quality and onion yield, was investigated. Two doses of OMW (4 and 8 L m⁻²) were directly applied once in a field experiment, one month after onion plantation. Soil characteristics and growth and physiological variables of onion were evaluated to assess the OMW impact and AMF on them. Among the measured variables, soil levels of phosphorus (Sp), leaf phosphorus (Lp), bulb phosphorus (Bp) and soil total organic carbon (TOC) were the manifestly improved traits with an increase of 108 to 409% for Sp, 60–102% for Lp, 39–74% for Bp and 50–139% for TOC. On the other hand, AMF colonization showed a decrease ranging from 23 to 50% under OMW treatments. In addition, the application of OMW and AMF improved the growth performances including the bulb weight, physiological (stomatal conductance and photosynthetic machinery) and biochemical (sugar, proteins and antioxidant enzymes activity) traits compared to the control. These findings highlight the importance of AMF and OMW, in improving onion agro-physiological, biochemical traits as well as soil characteristics under filed conditions.