Making novel substrates for vegetables cultivation by mixing crop residue compost with natural zeolites

Up to eight innovative growth media were designed combining two composts from tomato and pepper crops waste with two rock by-products rich in zeolites and using two mixing ratios (1:1 and 1:3, vol:vol). Blends (zeo-composts) were characterized and tested on tomato plantlets in a short-term development assay. Mineralogic analyses confirmed chabasites and clinoptilolites as the main framework of the two zeolitites. Compared to composts alone 13C NMR of zeo-compost showed different C distribution, with increase of alkyl-C components and decrease of O-Alkyl-C groups related to polysaccharides and carbohydrates. Zeolitites drastically lowered phytotoxicity of pepper-waste compost while buffering alkalinity and salinity; moreover, they modulated cations in the water solution and trapped part of labile C fraction within their nanostructure. Blends including tomato compost and clinoptilolites at lower dosage resulted the best performing in the short-term assay, showing good fertilizing features, and suitability as peat-free substrate for vegetable crops.