Agriculture Reference
In-Depth Information
ing to Hasselo (
1965
), low-country tea plants contain, on an average, higher amount
of Mn as compared to tea plants in upcountry. Therefore, Mn in soil and groundwa-
ter is a significant factor which can influence tea productivity.
Nitrogen and phosphorus are the major nutrients absorbed by plants. A signifi-
cant part of the study area shows soil nitrate concentration above 18 ppm. Nitrate
content in groundwater is ranging from 0.7 to 40 ppm in the area. Hence, water
is safe for all domestic uses. Concentration of soil nitrate is ranging from 6.03 to
54.24 ppm, however, mostly it is over 18 ppm, and hence it is a favourable factor
for plant growth.
Most part of the study area shows less than 119 ppb of soil phosphate. Similarly,
it is less abundant in water where it ranges between 0.02 and 873 ppb. However,
according to Hasselo (
1965
) both nitrate and phosphate concentration in low-grown
tea is higher than upcountry. Therefore, there is no inherent limitation of those two
elements in the area. However, proper nutrient management is required to ensure
sustainable yield. Concentration of dissolved silica in groundwater was reported as
an indicator to understand the weathering characteristic of basement rock. There-
fore, it has been used in various geochemical studies to evaluate the factors af-
fecting chemical weathering rates in a natural environment. However, groundwater
mostly shows less than 6.5 ppm dissolved silica. Hence, it indicates the weathering
resistance of metamorphic basement rocks. Bicarbonate is a significant anion in
groundwater chemistry predominantly present at slightly acidic pH. Bicarbonate
ion distribution in the study area is highly correlated with water pH and higher
bicarbonate concentration was recorded in areas where groundwater pH is greater
than 6.5.
No result was observed for Cu, Ni, Fe and Zn in groundwater at the concentra-
tion range of mg/L or ppm. However, soil analysis shows satisfactory result at same
concentration ranges. All elements show positive trend toward southward direction
where Ratnapura town is located. However, Cu is showing inverse trend of which
low concentration was observed in Southern part of the study area. Therefore, high-
er concentration of elements might be due to anthropogenic influences like mining,
which is prominent in SW part near to Kaluganga River.
4.1 Supervised Land Use Classification
Supervised land classification was done in order to identify the areas which show
common reflectance characteristics. Based on the reflectance value correlated with
the Google earth image, a signature file was prepared for water bodies, paddy
fields, vegetation (other than tea and paddy), constructions (built up areas), mature
and young tea. Then, land use images were prepared using AOI for years 1992,
2002, and 2005 to identify the changes in land use and land cover over the period
(Fig.
4.8
).
According to the 1992 AOI image, total extent of paddy is 750.33 ha. However,
according to supervised classification paddy extent increased to 770.76 ha in 2002
