Soil-specific effects of biobased fertilizers and struvite on phosphorus dynamics and wheat growth

Abstract

Biobased fertilizers are increasingly considered viable alternatives to mineral phosphorus (P) fertilizers, however their agronomic performance in calcareous soils remains insufficiently documented. This study aimed to assess the effectiveness of composted organic waste (olive mill pomace, OMP; solid urban residue, SUR, and sewage sludge, SWS), applied individually or in combination with struvite (STR) to increase soil fertility, enhance plant growth and promote crop biofortification. A pot experiment was conducted using wheat as a model crop in three Mediterranean soils (Entisol, Inceptisol, and Vertisol) differing in carbonate content and P phytoavailability. All treatments supplied 50 mg P per kg of soil, including the application of diammonium phosphate (DAP), while unamended soils received no P (CON). Soil type modulated the performance of the biobased fertilizers. SUR and SWS, applied alone in the Entisol and Vertisol or combined with STR in all soils, increased plant-available soil P (74-238%) relative to CON. SWS, applied alone or with STR, achieved wheat yields comparable to those of DAP in the Entisol and Vertisol and exceeded DAP yields in the Inceptisol. The combination of SUR or SWS with STR resulted in plant P use efficiencies comparable to or higher than those obtained with DAP. SUR and SUR+STR enhanced wheat biofortification in the Inceptisol. By contrast, OMP showed limited effectiveness as a biobased fertilizer due to insufficient stabilization during the composting process, although its performance improved when combined with STR. Overall, while SUR and SWS alone or in combination with STR, can substitute mineral P fertilizers, their effectiveness depends on soil type and compost stabilization.