J. SWAMANNA, P. KAVITHA*, M. SREENIVASA CHARI AND M. SRINIVASA REDDY
Department of Soil Science and Agriculture Chemistry, Agriculture College, Mahanandi,
An investigation was carried out to study the different forms of potassium and their relationship with soil properties in rice growing soils of Kurnool district. The mean values of water soluble K, available K, exchangeable K, Non-exchangeable K and fixed K were of 20.42, 189.60, 169.18, 329.63 and 519.23 mg kg-1, respectively. Non-exchangeable K had significant positive relationship with other K fractions indicating that equilibrium exists between different forms of potassium in the soil. The order of dominance of different forms of potassium was Fixed K > Non-exchangeable K > Available K > Exchangeable K > Water soluble K. Among the different soil properties pH, CEC, organic carbon and percentage of clay showed positive correlation with all forms of potassium, indicating that soil properties are more influence on the exist of different forms of potassium.
Available K, Exchangeable K, Non-Exchangeable K, Water soluble K, Soil properties.
Potassium is the major nutrient and also a most abundant in soils but the K content of the soil varies from place to place based on physico-chemical properties of soil. Potassium exist in soil in different forms viz., water soluble, exchangeable, non-exchangeable (fixed), mineral, lattice and total. But these forms were not homogeneously distributed in soils. Its amount in soil depends on the parent material, degree of weathering, K gains through manures and fertilizers and losses due to crop removal, erosion and leaching. Usually the amounts of non-exchangeable and total K present in the soil were high as compared to water soluble and exchangeable K. The dynamics of potassium in soil depends on the magnitude of equilibrium among various forms and mainly governed by the physico-chemical properties of soil (Lalitha and Dakshinamoorthy, 2014). The present investigation was carried out to study the different forms of potassium in relation with the soil properties in rice growing soils of Kurnool district in Andhra Pradesh.
The surface samples collected from different locations in rice growing soils of Kurnool district were processed and analyzed for varioussoil properties such as particle size analysis by Bouyoucous hydrometer method. The pH and EC were determined in 1:2 soil: water suspension by using pH meter and EC meter, respectively. The organic carbon content, CEC and CaCO3were determined as per standard procedures outlined by Jackson (1973).
Water soluble potassium was determined in 1:5 soil: water extract, after 5 minutes shaking (Kanwar and Grewal, 1966). The available potassium was determined by 1N NH4OAC (pH 7.0) extract with 1:5 soil extract after 5 minutes shaking as described by Jackson (1973). The exchangeable potassium was obtained as a difference of the available and water soluble potassium. The fixed form of potassium was determined by boiling for 10 min with 1 N HNO3 (1:10 soil: acid ratio), (Wood and Turk, 1941). The Non-exchangeable potassium was obtained by deducting the available potassium from fixed potassium contents.
Relative proportion of sand, silt and clay fractions of soils ranged from 42.56 to 76.56 per cent (with a mean of 55.49 percent), 0.36 to 19.36 per cent (with a mean of 11.91 per cent) and 16.08 to 43.08 (with a mean of 32.60 per cent), respectively (Table 1). The texture of studied soils varied from moderately coarse to fine.The pH ranges from 7.2 to 8.52 with a mean value of 7.99, indicating that soils were neutral to slightly alkaline in reaction.The Electrical Conductivity ranges from 0.14 to 1.52 dS m-1 with a mean value of 0.52 dS m-1 (Table 2).
The CEC ranged from 11.21 to 26.91 c mol (p+) kg-1 with a mean value of 18.21 c mol (p+) kg-1. The organic carbon varied from 0.26 per cent to 0.94 per cent with a mean of 0.67 per cent (Table 2) indicating that most of the soils are belong to medium in organic carbon content.
The water soluble potassium varied from 10.5 to 39.5 mg kg-1 with a mean value of 20.42 mg kg-1. The available potassium varied from 69 to 431 mg kg-1 with a mean value of 189.60 mg kg-1. The exchangeable potassium content varied from 48.5 to 393.5 mg kg-1 with a mean value of 169.18 mg kg-1 where asnon-exchangeable potassium ranged between 190.5 to 711 mg kg-1 with a mean value of 329.63 mg kg-1. The fixed potassium in the selected soils varied from 261 to 1142 mg kg-1 with a mean amount of 519.23mg kg-1 (Table 3).The order of dominance of different forms of potassium was Fixed K >Non-exchangeable K > Available K > Exchangeable K > Water soluble K.
Water soluble K showed positive and significant correlation with available K (r = 0.468**), exchangeable K (r = 0.386*), non-exchangeable K (r = 0.526**) and fixed K (r = 0.533**) whereas available K showed positive and significant correlation with exchangeable K (r = 0.996**), non-exchangeable K (r = 0.754**) and fixed K (r = 0.924**) (Table 4). Similar results were reported by Singh et al. (2010). Exchangeable K showed a positive and significant correlation with non-exchangeable K (r = 0.733**) and fixed K (r=0.910**). These results were in conformity with the findings of Islam et al. (1994), Das et al. (2000) and Subhash and Ali (2011).Non-exchangeable K had positive relationship with other K fraction indicating the existence of equilibrium among the forms of K and a depletion of one form will replenishes the other forms of K (Prasad, 2010).
Coefficients of correlations were worked out to assess the influence of soil properties on various forms of K (Table 5).
Among the different soil properties pH, CEC, organic carbon and clay showed the positive correlation with all forms whereas EC, CaCO3 and sand showed negative correlation. Similar reports were made by Taleb et al. (2010). Available K showed positive correlation with CEC (r = 0.119), indicating that clay humus complex formed from increased organic matter provides more exchangeable sites and access to K (Basumatary and Borodoloi, 1992).
Exchangeable K showed positive relationship with clay (r = 0.273) but negative with EC (r = -0.096) and CaCO3(r = -0.112).High amount of clay (r=0.273) played an important role in increasing the exchangeable K level by holding more potassium in the exchange sites thereby preventing it from leaching.
The study brings out the importance of potassic forms in the soil and positive correlations among themselves indicates the dynamic equilibrium among the forms of K and majority of potassium is found in fixed form which replenishes soil solution potassium. Hence, if potassium not adequately supplied during plant growth, fixed K depletes and helps in attaining sustainability on a long term basis. Among the different soil properties pH, CEC, organic carbon and clay per cent showed positive correlation with all forms of potassium, it indicating that soil properties are more influence on the exist of different forms of potassium.