Soil Testing Indices for Phosphorus Leaching in Selected Vertisol and Inceptisol of India

Little information is available on P leaching potential of Indian soils. The degree of P saturation (DPS) relating the extractable P to the P sorption capacity governed by soil constituents (Al, Fe, Ca) has been widely used to predict the potential to adsorb or release P. The aim of the present study was to determine DPS in two major cultivable soils of India and to evaluate routine agronomic and environmental soil test P as indicators of P leaching through column leaching experiment with different levels of P fertilization. The results of the study showed the variation in leachate reactive P (RP) content which was significantly affected by P rates and increased significantly above threshold DPS values. For vertisol and inceptisol, threshold DPS Ol was 25.07 and 12.43%, DPSA.O. was 7.87 and 3.76%, and DPSM3 was 18.66 and 6.79%, respectively. The RP concentration showed a strong correlation with DPS and environmental soil test like 0.01 M CaCl2 and water extractable P (WEP) suggesting that soil 0.01 M CaCl2 and WEP can be used as surrogate for RP concentration for risk of P loss via leaching. Thus, the use of Olsen P, Mehlich 3 and ammonium oxalate P for calculating DPS provides reliable criteria for identifying soils having high risk of P loss to surface water bodies and works well in all soil types. © 2016, The National Academy of Sciences, India.