Phosphorus fertilizer form and application frequency affect soil P availability, chickpea yield, and P use efficiency under drip fertigation

Background Phosphorus (P) fertilizer properties and nutrient management strategies substantially affect soil P availability as well as uptake and consequently crop yield. Aims The present study aims to study the potential use of inorganic soluble polyphosphates (Poly-P) as slow-release fertilizer under drip fertigation. Methods A pot experiment was conducted using an alkaline soil. Two Poly-P fertilizers, differing in their polymerization rate (Poly-53 with 53% and Poly-100 with 100% Poly-P of the total-P content), were compared to an orthophosphate (Ortho-P) and a treatment without P application (control) under three drip fertigation frequencies (F-sow: P fertilizer applied at sowing, F-week: once a week, and F-3days: every 3 days). Soil samples were taken at 40 days after sowing and at harvest from 3 layers (0-5, 5-10, and 10-20 cm) to determine P availability in soil (Olsen-P) and its relocation into deeper soil layers. Furthermore, plant growth, yield, P uptake, P use efficiency, as well as water productivity were investigated. Results Soil P availability varied significantly between fertilizer forms and fertigation frequencies. At higher polymerization rate of the Poly-P fertilizer, P becomes less mobile in the soil, but its availability is maintained until harvest. The analysis of Olsen-P at harvest showed that the higher P availability in soil was obtained with Poly-P forms with higher values in the 0-5 and 5-10 cm soil layers than in the 10-20 cm. In addition, weekly fertigation (F-week) revealed the best results in terms of P availability compared to other P fertigation regimes, and all P fertilizers significantly improved chickpea grain yield, seed quality, and water productivity, compared to the unfertilized control. Conclusion Poly-P fertilizers can be recommended as an effective source of phosphorus for plants, due to their slow-release properties. Using Poly-P, the frequency of P application through the drip fertigation system can be reduced while ensuring high crop yields.