Influence of supplementary irrigation and organic manure application on micronutrient density and yield of five common bean varieties'
Itwari, F A
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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.