Effect of phosphorus levels on comparison of soil test extractants for available soil phosphorus on soybean in vertisols

Abstract

Phosphorus (P) fertilization is commonly based on soil testing, for which a variety of different soil P extraction methods are in use. The experiment was undertaken on medium black soil on the experimental field of Soil Science Department JNKVV Research Farm, Jabalpur. Five treatments based on targeted yield was laid in randomized block design consisted of T1= control: T2= GRD (20.60.20): T3= Targeted Yield (2.5 t ha-1): T4= Targeted Yield (3.0 t ha-1): T5= Targeted Yield (3.5 t ha-1), followed under optimum agronomic management practices. It was recorded that the Bray 2 method has extracted more available phosphorus than Troug, Mehlich 3 and Olsen having extracted lowest of all. The highest available phosphorus in the soil was noticed with the application of 118 kg ha-1 of phosphorus as obtained from the equation derived for targeted yield of soybean. The Olsen P is significantly small than the other three extractants. This indicates that other extracting agent extracted some forms of P that are not immediately available to 0.5M NaHCO3 extractant. The methods of extraction for available Phosphorus, among the four extraction methods, the Bray 2 was found to extract high available P content followed by Troug, Mehlich 3 and Olsen in soils but it has not responded under field conditions as compared to olsen.