Recirculating Aquaculture Biosolids Are Comparable to Synthetic Fertilizers for Grain Protein and Yield in Durum Wheat

Nitrogen is essential for durum wheat (Triticum turgidum subsp. durum) production, yet conventional sources such as urea-ammonium nitrate (UAN) and monoammonium phosphate (MAP) are energy-intensive to manufacture and, when mismanaged, contribute to soil degradation, nutrient runoff, and greenhouse gas emissions. Organic alternatives such as dairy manure solids (DMS) may reduce reliance on synthetic fertilizers but risk phosphorus accumulation and nutrient imbalances. Recirculating aquaculture systems generate nutrient-rich biosolids (RAB) that remain underutilized as fertilizers despite the rapid expansion of global aquaculture. We conducted a field experiment in Tucson, Arizona, USA, during the 2023–2024 winter growing season to evaluate RAB as a nitrogen source for Desert Durum® wheat under irrigated arid conditions. Treatments supplied equivalent nitrogen rates using UAN, MAP, DMS, or RAB. Grain yields (3.6–4.8 t ha−1) were not significantly affected by fertilizer source, but grain protein concentration was: RAB (101 ± 4 g kg−1) was statistically comparable to UAN and MAP (96 ± 5 g kg−1) and significantly higher than DMS (83 ± 4 g kg−1) by ~20%. While this study was limited to small plots and a single season, these results demonstrate that aquaculture biosolids can maintain yields while enhancing protein compared with DMS, supporting their use as a supplement to or replacement for synthetic nitrogen fertilizers in arid wheat systems.