| dc.description.abstract | Micronutrients deficiency especially (Zinc and Iron) have been identified as limiting in most
diets of people who depend on staple toads. Bean varieties high in Iron and Zinc have been
developed in East and Central Africa to combat micronutrient deficiency. However. the benefits
from these varieties depend on the environment where they are grown. Agronomic practices have
been known to in fluence micronutrient concentration in beans. However. Iittle work has been
done to develop management practices that will enhance expression of the high mineral density
trait.
Field experiments were conducted during 2006 short rain and 2007 long rain seasons to
determine the effect of supplementary irrigation and organic manure application on
micronutrient density of five bean varieties grown in Kabete and Mwea. The experiments were
laid out in a split-split plot design with irrigation as the main plot factor, organic manure
application as subplot and bean varieties as sub-sub plot factor. The treatments were replicated
three times. The irrigation treatments were: rain-fed and supplementary irrigation. The organic
manure treatments were control (0 t/ha), cattle manure (10 t/ha) and chicken manure (10 t/ha).
Micronutrient (iron and zinc) dense bean varieties tested in the study were: Gofta. AND 620,
Maharagi Soja, Nakaja and MLB 49/89A. Supplementary irrigation was provided by overhead
sprinkler in Kabete and by flooding using furrows in Mwea three hours daily three times a week.
Data collected included time to emergence, plant height, and time to 50% flowering, time to 50%
podding, bean stem maggot severity, number of nodules per plant pods per plant, seeds per pods,
grain yield. and iron and zinc content in leaves and seeds.
Days to 50% flowering, 50% pod formation were longer in Kabete than in Mwea sites.
Generally, higher yields were obtained under chicken manure treated plots than under cattle and
control plots. Bean stem maggot severity was higher under chicken manure than under cattle and
control. Under irrigated conditions. severity was lower by 18% than under rain fed conditions.
Supplementary irrigation and organic manures improved number of nodules per plant, pods per
plant and seeds per pod. On average, higher yields (39%) were recorded under irrigation than
under rain fed conditions.
Supplementary irrigation increased plant height, number of nodules per plant, grain yield and
leaf iron content of bean plants. However, seed iron content and zinc content in both leaves and
seeds were not influenced by irrigation. Organic manures increased number of days to flowering
and number of days to podding ill some varieties. Chicken manure increased severity of bean
stem maggot (BSM) in the short rains while cattle manure had no effect. Chicken and cattle
manure increased grain yield and yield components in most varieties. Chicken manure however
increased grain yield in more varieties than cattle manure. Ranking of varieties based on leaf
iron content. from the highest to the lowest, was AND 620 347.7 pprn, MLB 49/89A 339.\ ppm,
Maharagi Soja 329.4 pprn, Nakaja 322.6 pprn and Gofta 245.4.9 pprn. Variety MLB 49/89A had
the highest seed iron content 78.13 ppm while all other varieties did not vary much in both leaf
and seed zinc contents. Bean plants grown in Mwea site had higher leaf iron content (364.8.ppm)
than bean plants grown in Kabete site (282.7 pprn) while the converse was the case with respect
to leaf and seed zinc content. More iron was accumulated in leaves during the short rains (342.6
mean ppm) than during long rains (304.9 mean ppm) while more zinc was accumulated in leaves
in the long rains than in the short rains. In conclusion, iron content of bean plants can be
improved by supplementary irrigation. AND 620 variety had the highest iron in leaves and also
the highest grain yield and therefore a suitable candidate for dual-purpose use (leaf and seed
utilization). Leaf iron content of beans is influenced by location and soil iron content. | en |
