The division conducts research work on soil science and plant nutrition besides offering analytical service to the industry. The research activities include investigations on physico-chemical properties of soil, soil-plant interactions, response of tea to primary, secondary and micro nutrients and other related interaction effects, ways and means to increase the efficiency of applied nutrients, response to foliar applied major and trace nutrients and interaction effects of agronomic factors such as nutrient levels, their ratios, method and time of application with cultural factors like harvesting and pruning.

SOUTH INDIAN TEA SOILS These are classified as latosols. The tea soils extend along the western ghats and run in north to south direction parallel and close to the west coast of the peninsula. The whole region is classified into six major tea districts, which vary in elevation from 300 to 2500 m above MSL and the annual rainfall varies from 900 to 7500 mm. In geological origin, the soils are mainly derived from gneissic rocks, which had undergone considerable weathering as shown by their acidic nature and low calcium content. The soils are abundant in sesquioxides.

TEXTURE AND CLAY MINERAL The soils of High Ranges, Anamallais, central and south Travancore are light in texture, coarse and fine sand fractions comprising 62 to 67 per cent of soil. The soils of Wynaad and Nilgiris are of clay loam type with the clay fraction prepondering. Tea soils contain predominantly kaolinite as the clay mineral and the soils have no fixation sites for potassium. Therefore, the leaching loss of potassium is considerable and it increases with the decrease in the pH of soils. Tea soils of south India contain large amounts of free sesquioxides and hence phosphorus fixation is very strong. Our tea soils are basically poor and their fertility and productivity depend on the organic matter content which builds the structure and sustain microbial activity. About 50 per cent of the total cation exchange capacity of soils comes from the organic matter fraction. On an average about 150 kg N/ha will be released annually if organic matter is maintained at medium category appropriate to the elevation of the tea area of which 30 to 40 per cent are available to the plants.

pH AND K AVAILABILITY South Indian tea soils have low calcium content and hence they are suitable for tea growing. In soils with pH above 5.0, accumulation of calcium interferes with synthesis of carbonaceous materials and uptake of K. In soils with pH below 4.0, the H⁺ and Al3⁺ ions interfere with K uptake. Nitrogen efficiency is maximum in soils between pH 4.5 and 5.0 and hence liming is recommended to maintain the soil pH around 4.8. The availability of water to the plants will be of longer duration in the heavy soils of Wynaad, Nilgiris and Karnataka in comparison to lighter soils of other districts.