Medium/Long-Term Efficiency of Struvite for Lettuce (Lactuca sativa L.) Production: Effect on Soil Quality

Abstract

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.