Agricultural use of two bioproducts based on pistachio waste as source of nitrogen in a pepper crop

The interest in developing sustainable agriculture is becoming increasingly relevant in recent times, seeking alternatives to synthetic chemical fertilizers and the revaluation of wastes through more environmentally friendly alternatives. During the last decade, the cultivated area of pistachio in Spain is growing very significantly, especially in Castilla-La Mancha (FAO, 2018). During the harvesting and processing of the fruit, residues such as shell and peel of the fruit are generated, remains of vegetables and water from the cleaning process, which have a marked phytotoxic character due to their high content of polyphenols. Therefore, the generation of pistachio wastes, which can reach 40% of the harvest, could be an environmental problem. For this reason, various research groups have used this waste to obtain different products such as active carbon, mulches, biofuels, etc. In the present study, we evaluate the effect of two bioproducts generated from the pistachio harvest residue and determine which of them has a greater agricultural interest (P1: product with less polyphenols, extracted by a thermal process, and P2: product with an additional Steam Explosion process). The bioproducts were evaluated in a pepper crop field with a randomized complete-block design, considering an unfertilized treatment as a control (T0 = Control, T1 = 50% of N needed with P1, T2 = 100% of N needed with P2, T3 = 50% of N needed with P2, and T4 = 100% of N needed with P2). The parameters controlled were: ETc calculated with the FAO methodology (ETc = ETo x Kc), irrigation water (NO₃), soil (NO₂, NO₃, P, K, pH and texture), drainage water (NH₄, NO₃, P, K, Ca, Mg and pH), crop growth control (LAI and LAD) and dry matter composition of leaf, stem and fruit (N Kjeldahl, P and K). As preliminary results of the first experimental trial, no significant differences in the growth parameters measured between the control and the treatments have been found, although analytical results are still in progress and further research experiments will be stablished in the next years.

Keywords: By-products, organic wastes, global warming, circular economy.

Acknowledgements: Project INIA-2019-0007 (Spanish Ministry of Economy and Competitiveness).