Micronutrient status of agricultural soils in Bhutan

摘要

Micronutrients deficiencies in soils have been found to be widespread in South Asia. Deficiencies of micronutrients in human nu trition are also found to be widespread in South Asia. These deficiencies can have their origin in the soil. To date, no comprehensive analyses of the levels of micronutrients in soils of Bhutan have been carried out. In the present study, soil samples from 371 agricultural fields across five different agro- ecological zones (AEZ) and two land use types, sampled in 1999-2000, were analyzed for five micronutrients (B, Zn, Cu, Fe and Mn). The plant available concentrations were 0.22 (0.04 1.23)mg·kg for boron and 1.34 (0.11-20.47)mg·kg for zinc. These elements were identified as the micronutrients most likely to be deficient in Bhutan soils. The levels of DTPA extractable Cu, Fe and Mn were generally well above critical values. The frequency distri butions of the micronutrients and their association with other important chemical and physical properties showed strong correla tons between B and pH (r=0.66);B and CaCO (r=0.59);B and Zn (r=0.51);CaCO and pH (r=0.67);CEC and organic carbon (r= 0.60);and clay and CEC (r=0.54). The spatial patterns for these elements across the study sites were as follows: concentrations of B were found to be low in high rainfall areas;Zn concentrations were greater in the west than in the east;Cu was low throughout the country;and no pattern was discernable for Fe or Mn.