MSc

In the present investigation, attempt has been made to evaluate the chemical nature, distribution, fixation and availability of potassium in the soils of kole lands. Soil samples were collected from 15 locations in Chathankole – Puppilakkadkole area, seven from Chittilappilly village and four each from Adat and Chalakkal villages. In each location, from two nearby plots both surface (0 - 20 cm) and subsurface (20 – 40 cm) soil samples were collected and were analysed for the physic – chemical characteristics related to potassium availability.
A retention study and a laboratory incubation experiment of three month duration was carried out in order to find out the level of retention and transformation of applied potassium. In order to find out the most suitable extractant for assessing the available potassium in these soils, different chemical extractants were tried and its correlation with K uptake by rice in Neubauer experiment was carried out.
The soils collected from the three villages showed wide variation in the particle size distribution and majority of them were grouped under the textural class clay and sandy clay loam. The single value constants were showing variations depending on the clay content and organic carbon.
Soils were generally acidic in reaction. Organic carbon content varied among the samples and for certain sites subsurface accounts higher value. The total reserves of nitrogen, phosphorus and potassium were relatively low. Total potassium showed significant positive correlation with clay content, organic carbon and cation exchange capacity.
Water soluble, exchangeable and HNO3 solubleforms of potassium were low in these soils. These forms of potassium showed significant positive correlation with each other also with total K except for water soluble fraction.
From the retention study it was found that in soils with high saturation capacity the retention capacity is low and hence longer duration of time is essential for maximum retention. From incubation experiment it was found that on application of potassium fertilizer, the different fractions viz., water soluble, ammonium acetate extractable and nitric acid soluble potassium got increased at the end of the incubation period although fluctuations were noticed in all the fractions during this period.
In NH4 OAC extracted higher amount of potassium compared to Mathew’s extractant and 0.01 M CaCl2. The potassium extracted by these extractants and IN HNO3 – K were positively and significantly correlated with K uptake by rice in Neubauer experiment. Among all the four extractants maximum correlation was obtained for In NH4 OAC.