Effect of long-term irrigation with sodic waters on soil properties and phosphate fractions

The effect of irrigation with sodic waters of varying composition [EC 0.75–2.30 dS m⁻¹, SAR 3.7–19.5 (mmole L⁻¹)^1/2 and RSC 0.4–10.8 me L⁻¹] for 8 years was evaluated in terms of soil properties, inorganic phosphate fractions and availability of phosphorus (P). Analysis of 46 surface (0–0.15 m) samples showed that the tubewell-irrigated soils had higher pH, ESP, CaCO₃, EC, total P, saloid-P, Al-P, Ca-P and available P but lower organic carbon (OC) and Fe-P content as compared to the poorly irrigated and unirrigated soils. The Ca-P-and total P were significantly correlated (r = 0.72 and 0.75, respectively) with CaCO₃ content of the soils. The total P content of the soils was positively and significantly correlated with pH (r = 0.35). The saloid-P, AI-P, Fe-P and available P were not correlated significantly with any of the soil properties studied. Total P was positively and significantly correlated with AI-P (r = 0.41) and Ca-P (r = 0.94) but not with saloid-P, Fe-P and available P. The Ca-P was positively and significantly correlated with Al-P (r = 0.47), while it was non-significantly correlated with other phosphate fractions. Individually, none of the inorganic P fractions was significantly corelated to the available P. Soil properties (pH, EC, OC, CaCO₃ and clay) jointly contributed to 11.8% variation in saloid-P, 27.0% in Al-P, 18.5% in Fe-P, 61.3% in Ca-P, 64.3% in total P and 11.8% in available P.