Recycling of guacamole production waste through composting

The utilization of organic wastes as soil amendments in local farms and nurseries could avoid environmental pollution linked to waste disposal and increase the sustainability of production of some crops. This could be the case of wastes generated in guacamole production, an emerging activity in the avocado production area in mainland Spain, although treatment of this doughy textured oily waste has not been previously reported. The aim of this work is to study the feasibility of co-composting guacamole production wastes with garden pruning residues (as bulking agent) and chicken manure (as nitrogen source) and the use of the compost obtained in local avocado farms. Two windrow composting trials with different volume ratios of the residues were carried out in order to maximize the use of guacamole wastes in composting piles. In the first trial, pruning residues: guacamole waste ratio was always 7: 1, and chicken manure ranged from 1 to 0.3 to obtain initial C/N ratios ranging from 29 to 35. In the second trial, the guacamole waste was increased to 1: 2 and 2: 1 (pruning residues: guacamole waste) in two experimental piles using a low manure volume, and a third pile, similar to those of the first experiment, was used as control. In both trials, pile temperatures at depths of 50 and 100 cm showed a proper evolution of the composting process, with scarce differences between volume ratios. The composts obtained were chemically stable and showed moderate nutrient contents, and, therefore, could be suitable for nursery plant production. Results from self-heating tests and germination of cress seeds in Petri dishes were satisfactory, with no signs of toxicity due to compost. Seeds from avocado cv. "Topa-Topa" were also germinated in the compost obtained and plant growth showed that, in some cases, commercial substrates could be substituted by compost in commercial nursery avocado plant production.