| dc.description.abstract | Part one of this study involved the determination
of quantitative parameters for predicting
erosion rates using runoff plots. The treatments on
the runoff plots included: Bare fallow, maize with
minimum tillage, maize with 3 t ha-l of maize
residue, maize with conventional tillage, sole beans,
and maize intercropped with beans on alternate rows.
The highest runoff and soil loss was observed
on the bare fallow plots followed by maize with
conventional tillage, maize with minimum tillage,
maize intercropped with beans on alternate rows,
sale beans, and maize with 3 t ha-l of maize residue
during all the seasons. The best erosivity factor
for this area was found to be EI30, defined as the
product of the rainstorm's Kinetic energy and its
maximum 30 minute intensity, with a correlation
coefficient of 0.80 and a mean annual value of
-1 -1
154.92 MJ cm ha h .
The mean soil erodibility factor determined
using EI30 erosivity factor for the luvisol found
at the study site was 0.47 t h MJ-l ern-I The mean
soil erodibility factor was found to vary between
-1 -1
0.11 t h MJ cm for rainstorms that produced soil
-1 ~l -1 loss less than 0.5 t ha and 1~54 t h MJ cm for
rainstorms that produced soil loss greater than 30
-1
t ha .
- xxxvii -
The mean estimates of crop cover and residue
management factors C for maize with conventional
tillage, maize with minimum tillage, maize intercropped
with beans on alternate rows, sale beans, and
maize with 3 t ha-l of maize residue were 0.77, 0.45,
a~44, 0~30, and 0.15 respectively.
The soil at the study site was assigned soil
- ..1. -1 -1
loss tolerange value of 5.6 t ha y (0.37 mm y )
calculated using the estimated soil formation rate,
the available plant rooting depth, the present soil
depth, and the effect of topsoil thickness on maize
production.
The second part of this study aimed at the
I
determination of the effect of topsoil thickness on
maize production and involved simulation of erosion by
artificial removal of 0, 3, 6," 9, 12, and 15 cm of
the topsoil and application of different rates of
I
fertilizer and manure. The highest maize height and
maize grain and residue yields at each depth of
topsoil removed were achieved on plots that had
received 40 t ha-l of manure or 120 kg ha-l Nand
-1 .
40 Kg ha P. The highest reduction of the maximum
matze height and maize grain and residue yields per
centimeter of topsoil removed was obtained on plots
that had lost 12 cm of the topsoil at all fertilizer
and manure rates. Maize grain and residue yields
obtained from plots that had lost more than 12 cm of
the topsoil were significantly lower than those
- xxxviii -
obtained from plots that had lost less than 9 cm of
the topsoil at all fertilizer and manure rates. It
was therefore concluded that loss of more than 12 cm
of topsoil may result in partial or tota~ loss of
this soil as a resource from maize production standpoint
and any attempt to restore its productivity
by application of higher fertilizer and manure rates
would be uneconomical. | en |
