Environmental Engineering Reference
In-Depth Information
maximum
and
Chromolaena odorata
applied annually at the rate of about
five tonnes per hectare. The poultry manure was layer manure.
The results (Table 11.4) showed burning (T
0
) to have adverse effects on soil
chemical properties. Compared with the initial soil nutrient values, burning
depleted all the nutrients measured, namely N, P, K, Na, Mg, Ca, and depressed
soil pH. The reduction of organic matter by burning is of grave concern
considering that soil organic matter serves as a source of nutrients, improves
soil physical conditions, increases the CEC (cation exchange capacity) of the
soil, buffers the soil against pH fluctuation, increases the efficiency of nutrient
use, particularly applied fertilizers, and generally enhances the productivity of
the soil. As burning is an integral part of the farming systems of smallholder
farmers, it is not surprising that such farms are characterized by low soil fertil-
ity and declining yield.
The results demonstrated clearly that leaving crop or plant residues (T
1
) on farm-
lands makes more sense than burning them. The slash-and-no-burn without any
external input (T
1
) maintained the fertility of the soil. Soil nutrients at the surface
were either higher or the same under the residue than the initial content, although
the differences were not significant. The residue protected the soil surface
against any possible losses through erosion. The decomposition of the residue over
the years may have slowly released some nutrients to the soil.
When the residue was combined with poultry manure (T
2
), the initial soil
nutrients in both the topsoil and subsoil were significantly increased. The
increase was several orders of magnitude greater than that of the residue alone.
The increase was ascribed to the additional release of nutrients from the
decomposing poultry manure. The buffering capacity of increased organic
matter became evident under T
2
treatment. The initial pH of 6.8 was increased
to 7.2. The neutral conditions thus created could enhance the release and effi-
cient use of nutrients. It is also remarkable to note that under the poultry
manure and residue (T
2
), soil nutrients were maintained at the same level as
that under poultry manure
mineral fertilizer (T
3
). Even in some
cases, such as for organic matter, P, Mg, and Ca, higher levels were recorded
under T
2
than T
3
. This has important implications for the smallholder farmer
who, in the wake of increased prices of fertilizers due to the total withdrawal
of government subsidy, can no longer afford to buy mineral fertilizers. Where
poultry manure is available, as at Tano-Odumasi, farmers can use it for sus-
tained high crop yield, bearing in mind to apply supplementary mineral fertil-
izers as and when it becomes necessary. The cost of the farmer's soil fertility
replenishment can therefore be significantly reduced.
It must, however, be pointed out that the addition of mineral fertilizers
to poultry manure
residue
residue (T
3
) also significantly increased the initial soil
nutrient status in spite of uptake by the test crops, maize/cassava. Organic mat-
ter content was also increased, as well as the soil pH. It was expected that the
addition of mineral fertilizer (T
3
) would give a higher increase in soil nutrients
