Abstract:
Reddish Brown Earth (RBE) and Low Humic Gley (LHG) association extends great
part of the diy zone, Sri Lanka in the dominant landform appearing in the command
area of the tank based irrigation scheme. Reddish Brown Earth (RBE) occupies the
upper and the middle slope of the landscape where as Low Humic Gley (LHG)
occupies the lower part of the catenaiy sequence. Soil physical properties play a
significant role in effective nutrient and water management practices in both uplands
and lowlands. The physical properties largely determine the stability of a soil and they
usually control the suitability of the soil as growth medium.
At present most of the annual crops, cultivated in the university farm showed poor
performance especially in the maha season due to water logging condition. Therefore,
this study was carried out in the Agriculture Faculty farm of Rajarata University at
Pulliyankulama to determine the drainage classes by characterizing soil physical
properties along the undulating terrain. The physical properties studied included
texture, structure, colour, bulk density and infiltration of the soil. Structure and colour
of the soil were determined by in situ observations. Texture was analyzed by
sedimentation and decantation method in the laboratory. Bulk density was determined
from an undisturbed soil sample using a core sampler. Double ring infiltrometer was
used to measure the infiltration rates of different points along the slope.
It was observed that soil colour varies from reddish brown to dark brown from top to
bottom along the slope. When considering textural classes, the upper slop of the land
consists of sandy loam soils whereas lower part of the land is occupied by sandy clay
loam soils. There was a significant difference in bulk density values between the soils
associated with upper and lower part of the catena (1.86 gem 3 vs. 1.16 gem 3). Higher
organic matter content of 2.8% was reported for soils in the down slope compare to the
1.7% of organic matter content in the upper slope soils. At the same time a considerable
difference was observed in steady infiltration rates: 27.7 mm hr 1 in the upper slope soils
verses 16.6 mm hr'1 in the soils at the down slope of the catena.
The results of the study clearly revealed that well drained' soils occupied the upper
slopes of the university farm where as lower part was associated with poorly drained
soils. Therefore water management and other cultural practices presently adopted in the
farm have to be revised according to the findings of the study.
