Revalorization of a two-phase olive mill waste extract into a micronutrient fertilizer

Micronutrient deficiencies in plants may be treated using metal complexes. A modified two-phase olive mill waste (OMWm) was characterized using FTIR spectroscopy. A study was also made of micronutrient (Fe, Zn, Mn and Cu) complexation and the stability of complexes. An evaluation was then made of the effectiveness of Fe(III)OMWm to supply Fe to soybean (Glycine max. cv Stine 0480) chlorotic plants through nutrient solution and foliar application. The OMWm presented structural similarities with the fulvic fraction of raw OMW containing abundant phenolic-hydroxyl and carboxyl groups able to form complexes. The OMWm could complex Fe, Zn, Mn and Cu, although the stabilities of the complexes under agronomic conditions were low. In dealing with Fe chlorosis, Fe(III)-OMWm improved the Fe nutritional status of soybean chlorotic plants when applied to the nutrient solution, while only regreening of leaves was observed in foliar applications. Hence, OMWm complexes constitute a promising eco-compatible and cheap alternative to synthetic chelates in dealing with micronutrient deficiencies when applied foliarly or to the nutrient solution, although further research is necessary to improve the stability and effectiveness of the complexes.