Evaluation of chemical extractants for predicting soil manganese availability and critical levels for berseem (Trifolium alexandrinum L.) grown on typic haplustepts

Greenhouse studies on twenty soils, having a range in DTPA extractable Mn, were conducted to determine the critical levels of Mn in Typic Haplustepts for predicting response of berseem (Trifolium alexandrinum L.) to Mn application. There were three levels of applied manganese i.e. 0, 20 and 40 mg Mn kg⁻¹ soil as MnSO₄.H₂O. Four [CH₃COONH₄ (IN), DTPA (0.005), Mehlich-3 and hydroquinine (0.2%) + CH₃COONH₄ (IN)] out of five extractants were found to be promising for the estimation of critical levels of available Mn in these soils. The highest coefficients of correlation between available Mn and relative yield was with 0.2% Hydroquinone + IN CH₃COONH₄ (r =0.592**) followed by IN CH₃COONH₄ (r = 0.555*), Mehlich-3 extractant (r = 0.509*) and 0.005M DTPA (r = 0.465*).The critical levels of soil available manganese estimated by CH₃COONH₄ (IN), DTPA (0.005M), Mehlich-3 extractant and hydroquinone (0.2%) + CH₃COONH₄ (IN) were 1.9, 3.8, 16.0 and 28.4 mg kg⁻¹ soil, respectively. The critical level of Mn in 45 days old berseem plants was found to be 21.3 μg g⁻¹ dry matter.