Soil nutrient dynamics in tea agroforestry ecosystem ofGolaghat district of Assam

Abstract

The study was conducted in above 50 year old tea plantation in Naharoni, Golaghat district of Assam with the objective to know soil physicochemical properties under long term tea monocropping. A total of 48 soil samples were collected from the rhizosphere zone of tea bush in four seasons namely pre-monsoon, monsoon, post-monsoon and winter from three depths i.e.0-20, 20-40 and 40-60 cm. Soil profile study was also done in non-rhizosphere zone. Soil pH ranged from 4.1 to 4.8 in rhizosphere soils and 4.5 to 5.1 in soil profile. Soils are strongly acidic in reaction. Studied soils were rich in soil organic carbon. In 0-20 cm soil depth of rhizosphere soils organic carbon ranged from 1.32 per cent in monsoon season to 1.82 per cent being highest in winter season. And in subsurface soils it ranged from 0.79-1.25 per cent in 20-40 cm to 0.66-0.78 per cent in 40-60 cm soil depth. In soil profile study it varied between 1.71-0.20 per cent. Irrespective of any season significantly higher concentration of nutrient elements such as N, P and K were recorded in top layer (0-20 cm) of soil. Nutrient elements showed significant seasonal variations. Moderate quantity of available nitrogen was found in all the three depths in rhizosphere soils. Low to medium amount of available nitrogen was recorded in the soil profile of non-rhizosphere soils. Available Phosphorous was recorded high and it ranged between 64.22-71.35 kg ha-1 P2O5 in 0-20 cm soil depth and decreased significantly in the subsurface soils. Medium range of available potassium 185.56-232.68 kg ha-1 K2O was recorded in top soils and it was very low in 20-40 and 40-60 cm soil depth. Cations like exchangeable Ca and Mg were also found in low amount and did not show significant seasonal variation. From the results it can be concluded that the soils are poor to moderate in concentration and availability of major soil nutrients and also there is imbalance in their availability with soil depths and seasons.