Correlation of Five Manganess Extractants with Soil Properties and Soybean Responses in Calcareous Soils of Fars Province

Twenty-two surface soil samples (0-20 cm) from Fars province were extracted by five extractants (i.e., DTPA, 1.5 M NH4H2PO4, 0.1 NH3PO4, 0.05 MNa2EDTA, and 1% Na2EDTA) and used in a 7-week greenhouse experiment which was a 22 × 3 factorial with 22 soils (clay 16-63%; pH 7.8-8.2; electrical conductivity 0.32-1.78 dS m-1; calcium carbonate equivalent 28-63%; organic matter 1.1-4.9%; cation exchange capacity 9-27 cmol kg-1; and DTPA-extractable Mn 4-24 mgkg-1), 3 levels of applied Mn (0, 10, 20 mg Mn kg-1 as manganese sulfate), 3 replications, and soybean [Glycine max (L.) Merr., cv. Williams]. Application of Mn significantly increased top dry weight by 4 to 104%, averaging to about 12% over the control. But the increase in Mn concentration was not significant. Total Mn uptake also significantly increased but the apparent recovery of the applied Mn was very low (i.e., 0.05%). Soil pH, calcium carbonate equivalent, and clay content were found to be the properties influencing the extractability of Mn. The DTPA-extractable Mn, alone (with a critical level of 13 mg Mn kg-1) or along with some soil properties, was the only form of Mn that could reasonably predict the plant responses.