KAVITHA, PSWAMANNA, J2018-06-292018-06-292015http://krishikosh.egranth.ac.in/handle/1/5810055816D5364The present investigation entitled “Potassium release characteristics and response to potassium application in rice (Oryza sativa L.) growing soils of Kurnool district” was conducted with 30 soil samples (black and red) to study the different forms of potassium, release pattern of potassium with incubation studies. A pot culture experiment was also conducted to study the response of rice crop to different levels of potassium and uptake. Non exchangeable potassium release pattern was studied using 1N HNO3 and data presented cumulative K, step K and constant K. The soils under study are moderately coarse to fine in texture, neutral to slightly alkaline with a mean pH value of 7.99 and EC ranging from 0.14 to 1.52 dS m-1. The Cation Exchange Capacity of the soils was ranged as 11.21 to 26.91 C mol (p+) kg-1. The organic carbon content of the soils was in the range of 0.26 to 0.94%. The soils were low to medium in available N with the range of 186 to 327 kg ha-1, except one village all villages are high in available P which were in the range of 38 to 115 kg P2O5 ha-1 and medium to high in available K with the range of 185 to 1158 kg K2O ha-1 and the exchangeable cations were in the order of Ca+2 > Mg+2 > Na+ > K+. xiv Among the five extractants, the mean extracting efficiency of potassium was found to be in the order of 1 N HNO3 > Mehilich-3 > 1 N NH4OAc > 0.01M CaCl2 > Distilled water. The mean values of water soluble K, available K, exchangeable K, non-exchangeable K and fixed K were 20.42, 189.60, 169.18, 329.63 and 519.23 mg kg-1 soil. Positive correlation was observed among the forms of potassium. Non-exchangeable K had significant positive relationship with other K fractions indicating that equilibrium exists between different forms of potassium in the soil. In incubation study, the NH4OAc extractable K of most of soils at K applied (80 kg K2O ha-1) were increased from 0 DAI to 35 DAI, which indicates that solubilisation of added K and increase in the intensity factor. Later there was a gradual decrease from 60 DAI to 110 DAI indicating the conversion of available K in to non-exchangeable form. Whereas in case of control soils (0 kg K2O ha-1) K was released even though fertilizer K was not applied up to 110 days of incubation. It is supporting fact that the K will be released from the non-exchangeable sites when external K application was not there. In the study of potassium release parameters, the black soils released higher amounts of mean cumulative K (864.11 mg kg-1) and step K (773.32 mg kg-1) than red soils. Whereas mean constant K release was high in red soils than black soils. Lower amounts of cumulative K was observed in all soils except in Midthuru soil under present investigation. Lower cumulative K and continuous cropping would leads to depletion of soil K reserves and result in K deficiency. In pot culture studies a fertilizer K level of 80 kg K2O ha-1 was required for better yield of rice; significant difference was observed with soil K status, K levels and their interaction on different plant parameters. The response to the applied K in terms of yield and uptake was observed in Midthuru soils having high initial available K status indicating that even though soils are higher available K may not match with crop uptake, this need its external application particularly for high K requirement of crops. Among the 5 extractants tried, 1N HNO3 showed highly significant and positive correlation with grain yield (r = 0.744**) and uptake of K (shoot (r = 0.445*), grain (r = 0.780*) and whole plant (0.588**)) rice crop followed by Mehilich-3 and 1 N NH4OAc (pH 7.0) in rice growing soils of Kurnool district. The maximum positive correlation of plant parameters was found with fixed K and non-exchangeable K. The correlation coefficient with xv water soluble K and plant parameters was estimated to be lowest. Thus, it could be concluded that non exchangeable K and fixed K should be taken into consideration while giving fertilizer recommendation.en-USnullThesis