Soil amendment with agro‐industrial byproducts: molecular‐chemical compositions and effects on soil biochemical activities and phosphorus fractions

Environmental pollution by agro‐industrial byproducts in developing countries can be alleviated by recycling into soils. However, little is known about their chemical composition and impact on soil fertility. Therefore, the objectives of the present study were (1) to characterize the molecular‐chemical composition of dry (COD) and wet (COW) coffee, sisal (SIS), barley malt of brewery (BEB), and sugarcane processing (FIC) byproducts, and filter cakes of linseed (LIC) and niger seed (NIC) and (2) to evaluate their effects on respiration, pH, enzyme activities, and P fractions of a tropical soil. The agro‐industrial byproducts significantly differed in their concentrations of plant nutrients and organic‐matter compositions. The highest proportions of lipids, phenols + lignin monomers, and alkylaromatics were observed in COD, N‐containing compounds in COW, sterols in FIC, peptides in LIC, suberin in SIS, and fatty acid in COW and FIC. The application of the byproducts at the rate of 40 kg P ha^–1 (1.1 to 13.2 g C [kg soil]^–1) significantly (p < 0.05) increased the rate and cumulative soil respiration, soil pH, acid phosphatase and urease activities, and labile inorganic P over the control treatment. Ranking the qualities of the agro‐industrial byproducts for soil amendment based on their composition and effects on soil properties revealed the order NIC > LIC > BEB > COW > SIS > FIC > COD.