Antonio Rafael Sánchez-Rodríguez

Micronutrient deficiency in crops is not only an agronomic problem but can also lead to severe health issues in humans with cereal-based diets. Phosphorus fertilization and drought stress exacerbate the problem. However, the effect of different P fertilizers obtained from recycling (biobased fertilizers, BBFs) on micronutrient uptake under water scarcity conditions remains poorly understood. A two-season field experiment under rainfed conditions in southern Spain was conducted to evaluate the effect of different P fertilizers on the Fe, Cu, Mn, and Zn nutrition of wheat. Micronutrient uptake and homeostasis varied depending on the fertilizer, which was not explained by the amounts supplied with fertilizers. In the first year, compost-type BBFs decreased the Fe concentration in grain by 20%, whereas fertilizers obtained by ashing increased it by 84.7% relative to superphosphate. Biobased fertilizers, except compost, decreased the P:Fe ratio by 48%, indicating increased Fe digestibility relative to superphosphate. Biobased fertilizers reduced the risk of P-Zn antagonism. Carbon-rich BBFs decreased the HI, affecting micronutrient remobilization. Severe drought during the second year led to no significant difference in the evaluated variables between BBFs. These results provide important insights into the impact of fertilizer type on micronutrient nutrition, with some showing positive effects on biofortification relative to soluble mineral fertilizers under drought conditions.

Urbanization generates significant amounts of sewage sludge (SS), with relatively high concentrations of plant nutrients such as phosphorus (P). When biochemically stabilized by composting, SS (composted sewage sludge [CSW]) can serve as a sustainable P source in agriculture, supporting a circular economy and reducing agriculture's dependence on finite phosphate rock. The objective of this study was to assess the ability of CSW to supply P to plants grown on calcareous and noncalcareous soils of contrasting properties. Compost quality was assessed to support the scaling up of this study for agronomic application. Durum wheat ( Triticum durum L.) was grown under controlled conditions, and three treatments were applied to the soils: (1) control without P (CON), (2) diammonium phosphate (DAP)—a common synthetic P fertilizer, and (3) CSW, the last two to supply 50 mg kg ⁻¹ of P. The P content was 46% higher in CSW than before composting (24.0 vs. 16.4 g kg ⁻¹ ). In the pot experiments, total soil P concentrations increased by 11% with DAP and CSW relative to CON. The highest P internal utilization efficiency was obtained with CON and CSW in the Entisol and CON in the Vertisol, while wheat grain yields were highest with DAP and CSW across soils. CSW increased harvest index and one‐grain weight in the calcareous soil relative to CON. Moreover, CSW and DAP led to similar P uptake in wheat, significantly higher than CON. Our results highlight the potential of CSW as an effective P source for wheat in soils of southern Europe and others with similar properties.