Media Composition and Phosphorus Application Regime Regulate Orthophosphate-P Leaching

Phosphorus (P) management in horticultural crop production requires balancing nutrient supply while minimizing P losses to the environment. This study evaluated orthophosphate-P dynamics in leachates from three growth media differing in P retention capacity: quartz sand, a 50:50 mixture of quartz sand and sandy soil, and sandy soil. Two P fertilization strategies delivering the same total rate of 135 kg P2O5 ha−1 were compared: a single application and six split applications of 22.5 kg P2O5 ha−1. Three trials were conducted; the first two quantified orthophosphate-P concentrations in weekly leachate samples, and the third examined orthophosphate-P at hourly intervals following fertilizer application. Data were evaluated using linear mixed-effects models for repeated measures (fertilization strategy, growth medium, sampling time). Orthophosphate-P concentrations were significantly affected by fertilization strategy, growth medium, sampling time, and their interactions. Split applications maintained lower and more stable orthophosphate-P concentrations, whereas a single application produced a pronounced initial peak followed by a rapid decline. The third trial further demonstrated that P retention occurred over days rather than hours. These findings suggest that P mobility is controlled by fertilizer application timing and growth media properties. In sandy horticultural systems, delivering P in split applications (e.g., through fertigation) may reduce short-term orthophosphate-P peaks susceptible to leaching, although this needs to be confirmed in field studies with crops.