| dc.description.abstract | This thesis is the subject of work conducted during
1980 short rains and 1981 long rains to investigate the
influence of nitrogen and phosphate fertiliser rates
and their interaction on growth, development and yield
of potatoes under Kabete conditions with a view to
evaluating the validity of current fertiliser recommendations,
A completely randomised block 32 x 2 factorial
experiment was laid in three replicates with three rates
of nitrogen: 0, 75, 150 KgN/ha; three phosphate rates:
0, 100,200 KgB205/ha (0,44,88 KgP/ha), and two
potato varieties: Anett (early maturity, 3-3~ months)
and B53 (medium maturity, 3~-4 months). Plants were
grown under field conditions and sampled at intervals
of two weeks from the time of emergence to maturity
and various growth parameters and yield components
assessed.
Results showed that provided tubers were adequately
sprouted and environmental conditions favourable,
application of moderate and proportionate rates of
nitrogen and phosphate fertilisers would promote crop
emergence, growth and early tuber formation. Both
nutrients enhanced tuber bulking rates during the early
stage of growth (upto eight weeks after emergence) b~t
phosphate tended to lower bulking rates towards maturity.
Nitrogen was found to have a beneficial effect of
ehhancing both leaf area index and leaf area duration
ii
and increasing both tuber number per hill and size.
Moderate phosphate application increased both tuber
number per hill and size, but the highest phosphate
rate caused premature senescence of plants and tended
to reduce the number of tubers per hill. The number
of stems per hill was mainly a varietal character and
was determined by the initial degree of sprouting
rather than the application of fertiliser.
During both short and long rains, the recommended
phosphate rate of 200KgP20S/ha (88KgP/ha) was found
to be in excess of optimal requirement. During the
long rains the recommended nitrogen rate of 75KgN/ha
was optimal, but d~ring the short rains, heavier
ni trogen application produced statistically higher
yield in the early variety only, than did the recommended
rate.
Uptake of the greater proportion of the total
nitrogen and phosphorus taken up was found to occur
early in the growing season, upto four weeks after
emergence. Uptake of nitrogen and its accumulation
in tubers was enhanced by phosphate application, while
that of phosphorus was decreased by nitrogen application.
The levels of these nutrients taken up varied with the
season.
From these results it was.concluded that both
nitrogen and phosphate fertilisers need be applied
at the time of planting as late applied fertiliser
may not be beneficially utilized since uptake of ~these
nutrients takes place early in the growing season.
The recommended nitrogen rate of 7SKgN/ha was found
optimal for Kabete but that of phosphate of 200KgP20S/ha
(88KgP/ha) was found to be excessive.
However, climate, nutritional and varietal
influences appeared to be superimposed on each other
with respect to potato productivity, so that heavy
fertiliser applications particularly phosphate, may
be a waste under unfavourable conditions, such as
drought.
Thus, although phosphate is known to promote
root growth, thereby increasing water uptake by many
plants under a drought environment, its negative effect
of promoting plant senescence and producing few and
small tubers, particularly when nitrogen level is low,
tends to annul this benefit. Similar experiments,
with more closely-spaced fertilizer rates and a
wider range of potato varieties are therefore,
recommended to ascertain the consistency of the
results of this experiment under different locations. | en |
