Effects of Sewage Sludge Soil Amendment on Paddy: Multi-parameter Monitoring of Plant Stress

The distribution of organic materials, such as semi-solid residue from wastewater purification, represents a valid possibility of applying circular economy strategies aiming to close the production cycle. The distribution of sewage sludge (SS) to crops can provide plants nutrition but, as with any input into the food cycle, it requires careful monitoring for potential impacts on plants, humans, and the environment. Traceability technologies, including those relating to block-chain, enable the transformation of observed aspects into quantifiable data, facilitating digitization and seamless information flow from production to the end consumer. Experimental activities were carried out in a rice field located in Basiglio (MI, Italy) to evaluate the impact of SS distribution (at 25 and 34 t/ha) on plant physiology and odor emission. The physiological performance of rice plants was studied by measuring the chlorophyll content, acquiring NIR spectra and analyzing the spectroscopic indices obtained from satellite data correlated with the chlorophylls content. Total chlorophylls content increased by +15% in plants treated with the highest concentration of SS, suggesting its positive effect on the crop. PCA model built with NIR spectra allowed a separation between control and treated samples based on the SS concentration. The two treatments did not show significant differences in any of the measured spectral indices, suggesting that, at these concentrations, the SS distribution did not reduce plant health status. The potential olfactory nuisance was evaluated using Gas Chromatography – Mass Spectrometry (GC-MS) on SS samples. The identified compounds (sulphides, skatole) indicated that the choice of appropriate mechanical operations may be effective in reducing olfactory nuisances.