Impact of Starter Phosphorus Fertilizer Type and Rate on Maize Growth in Calcareous Soil Irrigated with Treated Wastewater

Phosphorus (P) is an essential macronutrient, but its limited availability in calcareous soils remains a major constraint to crop nutrition. Treated wastewater (TWW) offers a sustainable irrigation source in arid regions, enhancing water supply and contributing nutrients such as P. This study evaluates the effects of TWW and tap water (TW) irrigation, combined with varying rates of phosphorus fertilizers, such as single superphosphate (SSP) and diammonium phosphate (DAP), on maize (Zea mays L.) growth, nutrient uptake, and soil properties. A greenhouse experiment was conducted using maize grown in sandy calcareous soil. TWW irrigation with SSP (40 kg/ha) and DAP (20 kg/ha) resulted in the highest shoot dry matter (2.6 g), while TW with DAP at 20 kg/ha produced 2.2 g. Root biomass was generally higher, peaking at 8.3 g under TWW-SSP (40 kg/ha) and 5.7 g under TW-SSP (40 kg/ha). Nitrogen uptake was highest under TWW, with TWW-DAP (40 kg/ha) yielding the highest N content in shoots (1.9%) and roots (1.2%). Phosphorus content peaked at TWW-DAP (30 kg/ha) in shoots (0.52%) and roots (0.26%). Potassium uptake also improved with TWW, particularly in shoots (4.5%) under TWW-SSP (40 kg/ha) and roots (2.6%) under TWW-DAP (40 kg/ha). Post-harvest soil analysis showed TWW maintained stable EC (0.3–0.5 dS/m) and neutral pH (7.6–7.8). Higher DAP rates (40 kg/ha) with TWW increased soil organic matter, nitrogen (266.2 mg/kg), phosphorus (38.0 mg/kg), and potassium (385.3 mg/kg). In contrast, TW irrigation had lower nutrient enhancement, though high DAP rates still improved soil fertility. These findings highlight the potential of integrating TWW with phosphorus fertilizers to improve crop performance and soil fertility in calcareous soils. This approach offers a sustainable alternative to conventional practices, supporting sustainable crop production in water-limited environments. Further long-term studies are recommended to assess the sustainability of TWW irrigation in arid soils.