Availability of Manganese in Calcareous Soil of Saudi Arabia

A total of 96 surface soil samples were collected from four major agricultural areas in Saudi Arabia to determine Mn availability in soils and Mn content of crops grown on these soils. Visual Mn deficiency symptoms were not observed in any of the crop samples and Mn concentrations in crops were adequate by accepted criteria. About 15 and 35% of the soils extracted with DTPA and NH4OAC, respectively, were considered deficient while less than 1% were deficient according to criteria for the NH4HCO3-DTPA extract. The level of Mn extracted by different extractants increased with increases in organic matter, silt and clay content but decreased with increases in CaCO3 content, soil pH, Ca+Mg/K and Fe/Mn ratios. Extractable Mn was the lowest in Qassim and Riyadh areas as these soils were low in organic matter and high in CaCO3 content. Correlation between extractable Mn and Mn concentration in various crops decreased in the following order: DTPA > NH4HCO3-DTPA>NH4OAC. Inclusion of pH, Ca+Mg/K and CaCO3 content in prediction equations for each soil test improved the correlation between extractable Mn and concentration in plants