Combining biosolid and mineral sources of phosphorus and potassium in organomineral fertilizers influences the dynamics and efficiency of nutrient release.

Using urban residues to produce organomineral fertilizers (OMF) is an environmentally friendly strategy that can enhance soil fertility by adding organic matter and mineral nutrients. Herein we investigated the availability of N, P, and K, under organomineral fertilization in sandy soils. An incubation study was conducted using OMF formulated with biosolids as organic matrix and N source, rock phosphate, and potassium sulfate as P and K sources, respectively. Two forms of isolated N, P, and K sources (granulated and non-granulated), five N:P:K granulation proportions (1-2-0, 1-4-0, 1-0-2, 1-2-2, 1-2-4), and a control (unfertilized) were mixed with soil and assessed over a 112 days incubation period. Soil samples were collected at 0, 7, 14, 28, 56, and 112 days to quantify available soil concentrations of ammonium (N-NH), nitrate + nitrite (N-NO + N-NO), P, and K. The results showed that OMF formulated with NPK had better nitrogen efficiency indexes (NEI) than other formulations and did not induce N immobilization throughout the experiment. Regarding P and K efficiency, OMFs containing phosphorus and potassium increased the indexes compared to the single fertilizer sources. When comparing non-granulated potassium sulfate with granulated, the latter showed a steadier release due to the granulation process. In comparison with rock phosphate at the end of the experiment, the OMFs 1-2-0 and 1-4-2 had higher P available by 116 and 41%, respectively. Based on these results, OMFs have the potential to alter the dynamics of nutrient availability serving as a strategy for nutrient management in agriculture.