| The south Indian tea soil is classified as latosols. It extends along the western ghats, which run in north to south direction parallel and close to the west coast of the peninsula. The six major tea districts vary in elevation from 300 to 2500 m above MSL and the minfall varies from 900 to 7500 mm per annum. In geological origin, the soils are mainly derived from gneissic rocks. The soils have undergone considerable weathering as shown by their acidity and low calcium content. They are abundant in sesquioxides. 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. The disadvantage of higher clay content at Nilgiris is offset to certain extent by the presence of higher amount of organic matter in the soil. Chemically, all the soils are poor and the organic matter helps in building structure and microbial activity. About 50 per cent of the total cation exchange capacity of soils is contributed by organic matter fraction. On an average about 40-60 kg N/ha will be released from organic matter.
Kaolinite is the dominant clay mineral, which has a very weak bonding for potassium and low cation exchange capacity. Therefore, the leaching loss of potassium is considerable and it increases with decrease in pH of soils. Because of the base deficiency created by low CEC of soils in comparison to root CEC of tea plant, absence of fixation and decreased binding energies due to acidity, tea roots are placed in an unfavourable environment as far as cationic nutrition (ammonium and potassium in particular) is concerned. Hence, there is a need for regular and frequent application of nitrogen and potassium to even out the above effects. Thus splitting the application can increase the agronomic efficiency of nitrogen and potassium. As the tea soils have no fixation sites for potassium and the clay fraction is of non-expanding type, there is good percolation of water. The broadcasted fertiliser is therefore leached down to the root zone with ease. There is also a risk of leaching down of nitrogen and potassium below the root zone if the nitrogen and potassic fertilisers are placed in the subsoil. Hence nitrogenous and potassic fertilisers are recommended to be applied by broadcast method. Tea soils of south India contain large amount of free sequioxides, which results in strong P fixation.
South Indian tea soils contain low calcium content, which is preferable for tea growth. In soils with pH above 6.0, accumulation of calcium interferes with uptake of potassium. In soils with pH below 4.0, the H+ and Al3+ ions are likely to interfere with potassium uptake. Nitrogen efficiency is the maximum in soils between pH 4.5 and 5.0 and hence liming once or twice in a pruning cycle is recommended to maintain the soil pH around 4.8. As kaolinite and sesquioxide colloids present in tea soils are of non-expanding type, the retentivity of moisture of the colloids are comparatively lower. But the availability of water to the plants will be longer in heavy soils of Wynaad, Nilgiri- Wynaad, Nilgiris and Karnataka in comparison to lighter soils of other districts. The cation exchange capacity on an average varies between 4 and 10 meq% for Anamallais, Central Travancore and High Range and 8 and 15 meq% for Wynaad, Nilgiri-Wynaad and Nilgiris. Based on the texture, the infiltration rate is slow (5-12.5 mm/hr) for Wynaad, Nilgiri-Wynaad and Nilgiris and moderate (15-25 mm/hr) for Anamallais, Central Travancore and High Range. The major problem of tea soils of south India is severe soil erosion due to intense rain and steep slopes. Contour cultivation and bench terracing are found effective techniques against soil erosion.
| SOIL
PROFlLE AND LANDSCAPE OF TEA GARDENS OF
SOUTH INDIA |
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