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.
