Leachability and Phytoavailability of Nitrogen, Phosphorus, and Potassium from Different Bio‐composts under Chloride‐ and Sulfate‐Dominated Irrigation Water

Abstract Concerns over increased phosphorus (P) application with nitrogen (N)‐based compost application have shifted the trend to P‐based composed application, but focusing on one or two nutritional elements does not serve the goals of sustainable agriculture. The need to understand the nutrient release and uptake from different composts has been further aggravated by the use of saline irrigation water in the recent scenario of fresh water shortage. Therefore, we evaluated the leachability and phytoavailability of P, N, and K from a sandy loam soil amended with animal, poultry, and sludge composts when applied on a total P–equivalent basis (200 kg ha −1 ) under Cl − (NaCl)‐ and SO 4 2− (Na 2 SO 4 )‐dominated irrigation water. Our results showed that the concentration of dissolved reactive P (DRP) was higher in leachates under SO 4 2− than Cl − treatments. Compost amendments differed for DRP leaching in the following pattern: sludge > animal > poultry > control. Maize ( Zea mays L.) growth and P uptake were severely suppressed under Cl − irrigation compared with SO 4 2− and non‐saline treatments. All composts were applied on a total P–equivalent basis, but maximum plant (shoot + root) P uptake was observed under sludge compost amendment (73.4 mg DW −1 ), followed by poultry (39.3 mg DW −1 ), animal (15.0 mg DW −1 ), and control (1.2 mg DW −1 ) treatment. Results of this study reveal that irrigation water dominated by SO 4 2− has greater ability to replace/leach P, other anions (NO 3 − ), and cations (K + ). Variability in P release from different bio‐composts applied on a total P–equivalent basis suggested that P availability is highly dependent on compost source.