Spectroscopic and Physicochemical Characterization of Poultry Waste-Based Composts and Charcoal–Compost Mixtures for the Prediction of Dry Matter Yield of Giant of Italy Parsley

Plant growing substrates obtained by composting agro-industrial waste can serve as organic soil amendments. However, it is crucial to determine the maturity and quality of organic amendments before their application to soil. This study aimed to evaluate the suitability of compost obtained from poultry wastes combined with five different vegetal residues (tree trimmings, sugarcane bagasse, sawdust, cotton residues, and Napier grass) as growth media for container-grown Giant of Italy parsley. Fourier-transform infrared and laser-induced fluorescence spectra were used to characterize the humification extent in composts before and after the addition of charcoal at five inclusion rates (0%, 15%, 30%, 45%, and 60%, weight basis). Spectroscopic measurements identified absorption bands between 1625 and 1448 cm−1 specific to each of the 25 organic amendments evaluated. The most suitable amendments (composts made from sawdust and sugarcane bagasse) were associated with O–H stretching of phenols and aromatic rings. Charcoal addition to composts changed some of their physical characteristics, leading to increased nutrient availability in some cases. Experimental and calculated dry matter yield were compared via multiple linear regression and simple non-linear regression as a function of the spectroscopic and physicochemical (N, P, K, pH, EC, C, HLIF, C:N, CEC, HA:HA) properties of the organic amendments. Regression models accurately assigned high yields to the sawdust- and bagasse-based composts and low yields to the Napier grass- and cotton-based composts. Electrical conductivity (EC) was the main factor limiting potted-parsley productivity, an indication that efficient management of charcoal rate and compost EC levels can aid in predicting parsley yield