The use of by-products from table olive preparation process as fertilizers in the processing tomato crop

This study evaluates the substitution of sodium hydroxide (NaOH) for potassium hydroxide (KOH), during the industrial treatment of olives. Both compounds are a form of alkaline bleach, however, potassium hydroxide can be easily neutralized and transformed into a salt, in the form of potassium sulfate, which is a primary agronomic macronutrient. To neutralize the olive effluents, two acids were used: phosphoric acid (H₃PO₄) and sulfuric acid (H₂SO₄). The companies in charge of supplying the by-products for the olive treatment were, Aceitunas Torrent, Estepaoliva and S.C.A. Santa Marta Virgen. The objective of this study is to evaluate the suitability of effluents from the table olive treatment industry for use as potassium fertilizers in the processing tomato crop. Fertilization trials carried out on the processing tomato crop consisted of 3 different treatments, olive treatment's effluents neutralized with phosphoric acid, effluents neutralized with sulfuric acid and finally, a commercial potassium fertilizer, as a control treatment. The tests were developed in the Extremadura Agroalimentary National Technological Center (CTAEX), Badajoz (Spain) during the 2016 and 2017 campaigns. It has been demonstrated that by-products from the treatment of table olives applied as fertilizer to processing tomato resulted in yields similar to the commercial potassium fertilizers without affecting the key quality parameters of the tomato crop, while also increasing lycopene concentrations in the fruits. The results suggested that olive treatment's effluents can be successfully employed as alternative potassium fertilizers in processing tomato's cultivation, at a dose of 1,570 L ha^-1 (150 K) when neutralized with phosphoric acid and at a dose of 1,430 L ha^-1 (150 K) when neutralized with sulfuric acid.