| dc.description.abstract | Kenya continues to spend large sums of the scarce foreign
currency on the importation of vegetable oil. Adequate
local supplies of sunflower would save the country such
expenditure. Besides, the protein-rich cake obtained
after extraction of oil would contribute towards the
improvement of the nutritional quality of livestock feed.
Vast areas of Kenya receive marginal rainfall and
are therefore unsuitable for cultivation of a large
number of cash crops. Sunflower is adaptable to these
areas because it matures relatively faster and has a low
water requirement. Successful cultivation of this crop in
such areas will, however, require appropriately
researched, site-specific information to guide farm
practices.
The objective of this study was, therefore, to
contribute towards this need through determination of the
rooting characteristics of sunflower in relation to water
extraction under various water and nitrogen regimes, and
generation of yield-water-nitrogen functions for
sunflower.
The study was conducted at two sites, one with
a deep, well-drained Humic Nitosol (at Muguga) and the
other with a shallower, saline-sodic soil (at Naivasha).
Two irrigated experiments each lasting approximately
four and a half months were conducted at every site:
during the driest part of the year. A line-source
sprinkler irrigation system was used to create
differential moisture regimes. Nitrogen treatments were
randomised at each "water level" perpendicular to the
direction of the water gradient. Root-length density was
estimated using Newman's line intersection method; seed
yield was related to water and nitrogen using a quadratic
model.
Results show that roots grew to depths beyond 2
meters in adequately fertilized but moisture-deficient
treatments and extracted significant. amount.s of water
from these depths. Maximum seed yield of 2329 kg/ha was
obtained with 90 kg N/ha and 445 mm of applied water at
Muguga. The corresponding figures at Naivasha were 2284
kg/ha, 60 kg N/ha, and 438 mm. Seed yield was related to
applied water and nitrogen through the model:
Y=557+4.7W+9.89N-0.04W2-0.4NL+0.002NW at Muguga, and
Y=488+4.1W+l0.3N-0.005W2-0.06N2+0.007NW at Naivasha. | en |
