| dc.description.abstract | Preliminary work on availability of and
response to phosphorus in a range of Kenya soils
showed that availability is least in one particular
soil group, the strongly acid humic Andosols of the
high bracken zone in central Kenya. The scope of
investigation was therefore narrowed to the effects
of lime and manure on available phosphorus in these
soils.
A factorial experiment was conducted in the
glasshouse on an altitudinal transect of three soils
from the high bracken zone. Phosphate and manure had
the strongest effects on sorghum yield on all three
soi150 On the lower 8bil, Kigumo, an intergrade as
shown by its classification as ando-humic Nitosolf
dolomitic limestone and calcium silicate applied
together also increased yield, especially in~subsoil.
On the middle soil, Ikumbi, the soil amendments
depressed yield. On the uppe rsoil, Gituamba
they gave the largest increase in yield at rates
sufficient to meet the lime requirements On the first
two oils double supers and the soil amendments
markedly increased available phosphorus. On Gituamba
soil not only did double supers fail to increase it
significantly 'but the soil amendments caused highly
significant depressions in available P.
The experiment was repeated jn the field at
Gituamba. Coyer three years, both magmax and manure
had highly significant positive effects and interactions
on yields of hybrid maize& Double supers also ,had
positive effects on the components of yield. These
could be explained by the beneficial effects of
the applied treatments on leaf nutrient contents and
soil properties. As early as after the first season
however, it was apparent that while the low rate
of lime increased it the high rate of lime, calculated
to meet the lime requirement in three annuall instalments,
depressed available P. This trend was confirmed in
the two subsequent years. In the fourth season
potatoes, a highter phosphate demanding crop than maize
showed significant residual etrects of magmax and
manure on yield and finally a significant positive
interaction between magmax and phosphate.
It is concluded that both lime and manure can
increase the efficiency of phosphate fertiliser in humic
Andosol by improving soil properties thus allowing better
root growth which is reflected in higher yieldS of
staple rood crops. Because of the risk of depressing
·available phophorus and hence yield by overliming,
the optimum rate of lime needs to be carefully
determinede
*FAO classification here and throughout (FAO-UNESCO 1974,
Sombroek l' 1980) | en |
