Increasing soil and crop productivity by using agricultural wastes pelletized with elemental sulfur and bentonite

Waste materials have many characteristics that can be useful to improve soil fertility and crop productivity. This study aims to investigate on recycling orange, olive wastes, elemental S residue to produce new and more efficient S-enriched organic fertilizers. The fertilizer power of the different pads was first assessed in vitro on germination of three crop species (red onion [Purple Allium cepa L.], cayenne pepper [Capsicum annuum], and dwarf French bean [Phaseolus vulgaris L. bronco]) to individuate the doses to be used in pot experiements. In vitro tests showed that germination was stimulated by all treatments up to a concentration of 0.88 mg L-1. Pot experiments evidenced that pads of S-bentonite plus agricultural wastes were more effective in lowering the pH of alkaline soils and in increasing the labile fraction of soil organic matter (SOM) than pads of S-bentonite as such. The greatest beneficial effect on soil chemical properties was observed by using pad of S-bentonite and orange wastes. Regarding crop productivity, all the species (red onion, cayenne pepper, and dwarf French bean) grew better in fertilized compared to unfertilized soils, and the best performance was observed in crop fertilized with S-bentonite with agricultural wastes. A fertilizer specie-specificity was also demonstrated, red onion and cayenne pepper grew better in the presence of S-bentonite with orange waste, while red bean performance increased with S-bentonite plus olive pomace. Agricultural wastes with S-bentonite represent a new formulation of fertilizer able to generate a soluble zone of nutrients while minimizing leaching losses to the environment.