Dynamics of potassium in selected black soil type of Haveri district, Karnataka

Potassium in soil exists in four forms such as water soluble, exchangeable, non-exchangeable and lattice potassium were studied in twenty representative randomly collected maize growing soils of Haveri district, Karnataka. The soils varied appreciably in their physico-chemical properties depending on nature and amount of parent material. The available potassium in black soil varied from 322.56 to 752.64 kg ha-1 in surface layer. The higher value of available potassium indicated that these soils were added with sufficient quantities of potash fertilizers. The water soluble K of black soils ranged from 2.83 to 8.13 mg kg-1 in surface with a mean of 4.60 mg kg-1. The reason for higher water soluble K in black soil was mainly due to intensive weathering of K bearing minerals and also due external application water soluble K fertilizers under intensive farming system. The higher exchangeable potassium at surface zone was mainly due to the fact that these soils had good amount of organic matter content which might have retained more K ions at exchange sites and also potassium retained through external source. The non-exchangeable potassium of black soils in surface samples varied from 566.37 to 790.84 mg kg-1. The black soils ranged lattice potassium of 1.38 to 2.03 per cent in surface layer. The type and nature of parent material present and degree of weathering are important for the rich lattice potassium content in the soils. The black soils total potassium ranged from 1.45 to 2.10 per cent. The higher values of total K obtained were mainly because of high lattice K concentration. Based on degree of weathering, type and amount of clay and fertilizer that has been applied, the various forms of potassium varied among the samples.