Controlled Release of Zinc from Soy Protein-Based Matrices to Plants

Controlled release systems are increasing their presence on the market. However, their use is not generating a great impact on horticultural production, mainly due to their price, which makes crop production more expensive. This work proposes a cheaper alternative for the manufacture of these devices. Thus, an agri-food byproduct (soy protein isolate) and a thermomechanical processing were used to create devices (matrices) that can compete in price with the use of conventional fertilizers (0.50–2.00 €/kg). First, different processing methods were evaluated to obtain the matrix with the most optimal mechanical, functional (zinc and water retention/release, biodegradability) and morphological (zinc distribution) properties for the supply of zinc (micronutrient). This was achieved by incorporating an ethanol immersion step into the processing to remove the plasticizer before its use in horticulture. Finally, the efficiency of these matrices was verified in crops (lettuce and peppers), improving up to 60% the assimilation of zinc by plants that conventional fertilization achieves. In addition, these matrices allow a 33% reduction in the water used during cultivation. This work has opened a new possibility of creating more efficient devices for the incorporation of fertilizers into crops, also having an affordable price for industrial use.