Environmental Engineering Reference
In-Depth Information
also taken. Soil samples taken were lightly crushed and passed through a 2 mm
sieve. The leaf samples were oven-dried at 70-80°C and finely crushed. Soil
pH, organic carbon, total nitrogen, available phosphorus, exchangeable
cations, and cation exchange capacity were determined. Soil pH was deter-
mined in INKCI at a soil:solution ratio of 1:2. Organic matter was determined
by the Walkey-Black method (Allison, 1965). Total nitrogen was determined
by the Kjeldahl digestion method (Bremmer, 1965). Exchangeable cations (Ca,
Mg, K, Na) were extracted by neutral 1 M ammonium acetate solution.
Potassium and sodium in solution were estimated by flame emission
photometry, and calcium and magnesium by atomic absorption spectropho-
tometry. Available phosphorus was determined by the Bray 1 method (Bray
and Kurtz, 1945) and cation exchange capacity (CEC) by ammonium acetate
extraction at pH 7.0 (Pleysier, 1982). Base saturation was calculated as
the sum of total exchangeable bases as a percentage of CEC. The values of the
chemical properties of the two soil types under the tree canopies and in open
grassland were pooled to assess the effect of the indigenous trees on the soil
chemical properties.
Results
Socio-economic importance of indigenous trees
From Table 15.1, one realizes that all the four indigenous trees have complemen-
tary uses. With respect to soil conservation, however, it is
F. albida
and
P. biglo-
bosa
that are important. All are important as fodder for animals and as fuelwood.
Even though farmers recognize the importance of all these trees, they still regard
them as hindrances and, therefore, cut them out of their farms to increase the area
for arable crops.
Analysis of leaf samples
Of all the trees,
F. albida
leaves had the highest total nitrogen, phosphorus,
and potassium contents, as shown in Table 15.2. There is an indication of the
usefulness of
F. albida
leaves in improving soil fertility and as fodder for ani-
mals.
Among the four indigenous trees, the chemical properties of both soil types
under their canopies were highest in
F. albida
, followed by
D. mespiliformis
,
P. biglobosa
, and
V. paradoxa
in that order. Significant difference in soil
