Phosphorus (P) is an essential nutrient for crops. Modern agriculture is dependent on P derived from phosphate rock, which is a non-renewable resource that is becoming increasingly scarce and expensive. Therefore, it is necessary to identify alternative sources of P and develop novel technologies for its recovery. Such technologies are increasingly focused on the recovery of struvite (MgNH4PO4·6H2O) (STR) from urban wastewater. A reduction of P in effluents decreases the risk of eutrophication while allowing this mineral to be recovered and reused. Here we applied STR recovered from urban wastewater to three different soils and examined its slow-release properties. We performed a soil column leaching study and compared the results of soil treated with STR with those of soil amended with conventional phosphorous fertilizers, namely NPK, ammonium phosphate (MAP), and superphosphate (SSP). Phosphate leaching capacity followed the order MAP ~ NPK > SSP > STR in the three soils and was consistent with its rate of water solubility. Analysis of the soils after the leaching process showed differences in available P, the highest content being found in soils treated with STR. The results were consistent with those obtained in the leaching assay. STR behaves as a slow-release fertilizer and reduces the risk of eutrophication compared to the conventional P fertilizers tested.
The global rise in population highlights the need for a greater production of quality food. In this regard, intensification of the agricultural sector and an increased use of fertilizers are key. Phosphorus (P), together with nitrogen (N) and potassium (K), is one of the essential elements for plant growth. Modern agriculture is dependent on P derived from phosphate rock, which is a non-renewable resource whose high-quality reserves are becoming increasingly scarce and expensive. In this context, alternative sources of P and the development of new recovery technologies are required. Such technologies are increasingly focused on struvite (MgNH4PO4·6H2O) (STR) from urban or livestock wastewater, whose accessibility is guaranteed. In this study, the medium–long term efficiency of STR from urban wastewater as a fertilizer was evaluated in three successive lettuce crops using a 25 kg pot trial. To this end, STR application was compared with the use of other conventional P fertilizers (NPK, monoammonium phosphate (MAP), and single superphosphate (SSP)) at a dose of 100 kg P ha−1. Crop biomass yield, P uptake, and the nutritional quality of the plants were determined. Moreover, the effect of STR on soil quality was examined using several soil biological indicators. In general, the STR treatment yielded similar biomass results to those obtained with NPK in the three successive lettuce crops. MAP and SSP treatments produced higher biomass in the first crop, but these values diminished in the next two. In relation to the effect on soil, STR treatment maintained the concentration of available P during the three growing cycles and enhanced microbial activity and functional diversity. On the basis of our findings, STR emerges as a sustainable P-fertilization strategy for lettuce production.
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