Agronomic and environmental aspects of utilization of organic residues in soils of the Andean-Patagonian Region

Patterns of N mineralization and P release were determined in two characteristic soils of the Andean-Patagonian Region (Andisol) and the transitional zone to the steppe (xeric Mollisol) amended with fish residues and biosolids. Residues were applied to the soils at rates of 10–20 g kg-1 and incubated for 112 d under controlled temperature and soil moisture conditions using a non-leaching procedure. Nitrogen mineralized from the total added N depended mainly on the type of residues, while P release depended firstly on the soil type, and secondly on the residue type. Fish residues displayed a potential as slow-release N fertilizers, while biosolids showed a marked initial flush of mineralized N. Due to the high P content, fish residues might exert adverse environmental and agronomic effects on the xeric Mollisol when applied at the rates to meet crop N requirements. In the Andisol with a high P retention capacity, the applied rates would cover both Nand P crop requirements. Biosolids were unable to supply an adequate amount of available P in the Andisol, possibly due to the addition of Al-sulfate and, consequently, the formation of Al-P species with low solubility.