Abstract:
Tea is the major export crop in Sri Lanka and is grown as a rain-fed plantation crop. All
tea-growing areas receive rainfall, to satisfy the evaporation demand but rainfall
distribution is not uniform throughout the year and often-diy spells are experienced.
Under prolonged dry weather conditions, growth of the tea is adversely affected by
plant water deficits created by the lack of soil moisture and associated high saturation
vapor pressure deficit of the air. As there is no real understating of soil moisture
regime, its movement pattern and the lack of relevant information, it is difficult to offer
suitable agronomical practices to overcome the drought problem.
This study was conducted during June to October 2001, to collect relevant information
on soil moisture regime, and its movement pattern. Diviner 2000 method, which is
based on the dielectric capacitance, was used for the moisture assessment. The active
root distribution of tea was determined using the soil profile root activated method.
Soils were loamy sand with pH of 4.0 and had a compacted soil layer at 70 cm depth
and thick lateritic layer at 40 -50 cm depth. Average bulk density of the surface layers
was 1.4 g/cm3 which increased with the depth.
Results revealed that moisture-holding capacity of tea soils is higher (7.67 %)
compared to the bare land. The rapid increment of soil moisture in tea land was
observed after the saturation or heavy rains. Root development was concentrated in
upper 40 cm layer (95%) and at 8 0 - 100 cm depth. Rapid extraction of soil moisture at
an average of 3.93 mm/day by the plantation was observed in upper 40 cm soil layer
which was 47.31% higher than that of the bare soil. However, moisture depletion of the
surface layer was due to high heat flux and the well-established canopy cover acted as a
barrier to prevent surface evaporation. Soil moisture depletion was influenced by
soil/air temperature, rainfall, evaporation, soil texture, pH value and root distribution
pattern.
