Distribution of different forms of Mn and their association with soil properties in arid zone soils of Punjab, India

Six pedons from arid zones soils of Punjab, north western India, were investigated for different forms of manganese (Mn): total Mn, diethylenetriamine penta-acetic acid (DTPA)-extractable Mn, soil solution plus exchangeable Mn, adsorbed Mn onto inorganic sites, and oxide surfaces, and Mn bound by organic sites. Total Mn content ranged from 241–517 mg kg⁻¹, DTPA-extractable Mn content ranged from 1.40–4.52 mg kg⁻¹, soil solution plus exchangeable Mn content ranged from 0.04–0.30 mg kg⁻¹, Mn adsorbed onto inorganic sites ranged from 34–109 mg kg⁻¹, and that onto oxide surfaces ranged from 28–173 mg kg⁻¹. The Mn bound by organic sites ranged from 14–56 mg kg⁻¹. The forms of Mn did not exhibit any consistent pattern of distribution. Irrespective of the different fractions of Mn their content was higher in the fine textured soils as compared to the coarse textured soils. The soil solution plus exchangeable Mn held onto organic site and oxide surface (amorphous) increased with increase in organic carbon, silt and clay contents. The Mn adsorbed onto inorganic site (crystalline) increased with only silt and clay content. The DTPA-Mn increased with increase in organic carbon content, whereas Mn adsorbed onto oxide surfaces increased with an increase in organic carbon, silt and clay. However, both these fractions decreased with an increase in calcium carbonate and pH. Total Mn was strongly correlated with organic carbon, silt and clay content of soil. Among the forms, Mn held on the organic site, water soluble + exchangeable and Mn adsorbed onto oxide surface were positively correlated with DTPA-extractable Mn. DTPA-extractable Mn and soil solution plus exchangeable Mn seem to be good indices of Mn availability in soils and are helpful for correction of Mn deficiency in the soils of the region.