Comparative assessment of soil moisture behaviour of Red Yellow Podzolic soils covered under forest species {Alstonia macrophylla wall) and Tea {Camellia siensis) compared to bare soil

Abstract

A comparative assessment of soil moisture behaviour by the Tea {Camellia siensis) and forest species {Alstonia macrophylla wall) compared to bear soil was conducted in Faculty of Agriculture, University of Ruhuna, Mapalana, Kamburupitiya, Sri Lanka, during June to August 2004. Diviner 2000, which is safety, potable and accurate soil moisture monitoring device based on dielectric capacitance is used to assess the soil moisture in 100 cm depth in different sites.The experiment had two sites with replicates having same topography and soil conditions. First site was a well manage tea plantation o£ 15 years old and second site is a site with 3 years old well grown Alstonia plants, bear spots were also maintained in the research site to measure bear land evaporation. Average moisture content in top 30 cm layer in all crops was highly varied compare to bear soil. In tea soil, moisture retention ability in 0 - 100 cm layer is high compare to bear soil, but Alstonia soil had lower moisture retention ability. In surface 100 cm depth soil moisture is highly fluctuate due to high soil moisture extraction and evapotranspiration by the Alstonia cover. Prior to saturation, soil moisture depletion rate in 20 cm depth recorded as 0.52 mm day'1, 0.72 mm day'1 and 0.93 mm day'1 for Tea, Alstonia and bear soil respectively. After considerable rain due to saturation, average soil moisture replenish in tea was 1.29 mm day"' which is low compared to Alstonia and bear soil. Alstonia soil shows highest replenish rate of 2.27 mm day'1 due to shortage of moisture in top layers, as a result of high evapotranspiration and evaporation. Bear soil had intermediate rate of soil moisture replenish. (1.40 mm day'1 in top 20 cm depth.) The highest evapotranspiration of 5.29 mm day'1 is observed in bear soil, it was remarkably low in tea with an average of 4.8 mm day'1 which is a 10 % decrement over the bear soil evaporation. The evapotranspiration of Alstonia is 4.86 mm day'1, which is 8 % lower compared to the bear soil evaporation. Well established and well managed canopy cover o f tea plantation helps to reduce surface evaporation, from tea plantation.