Effects of phosphorus and soil moisture on grain yield, leaf and grain tissue concentration of iron and zinc in three bean (phaseolusvulgarisl.) genotypes

Abstract

v ABSTRACT Common bean ( Phaseolus vulgaris L .) is an important source of protein, minerals and food for the majority of the poor population in sub - Saharan Africa. However, its contribution to grain yield and micronutrient level is constrained by moisture stress and low available soil phosphorus. A study was carried out to determine the effects of bean genotypes, P fertilizer and moisture regimes on bean ( P. vulgaris L. ) grain yield and tissue concentration of Zn and Fe in three bean genotypes at KARI, Katumani Research Centre in M achak os, located at 1560 masl. The study was laid out in a randomized complete block design with five P fertilizer treatments in split - split plot arrangement with three replications. The main plot was moisture regimes , subplots were genotypes and the sub - s ub plots were P rates. Data on concentration of Fe and Zn at flowering, grain yield and grain concentration of Fe and Zn at bean maturity were recorded. Data for grain yield, grain and leaf tissue concentration of Fe and Zn were analysed using ANOVA, Means were separated using LSD at significant ( P <0.05) level and correlation between grain concentration of Fe and Zn, as well as between grain yield and leaf concentration of Fe and Zn were determined.(SAS 8.2; SAS institute, 1999). The results of grain yield showed highly significant ( P = 0.0006) interaction between moisture regimes, genotypes and P application rates. Grain yield of the three genotypes increased with P application rate up to 60 kg ha - 1 regardless of the moisture regimes. The leaf and grain concentration of Fe and Zn showed h ighly significant ( P < 0.01) interaction between moisture regimes, genotypes and P fertilizer application rate. Similarly , percentage of leaf Fe and Zn accumulated to grain showed h ighly significant ( P < 0.0001) interactions between moisture regimes, genotypes and P fertilizer application rate. All genotypes had significantly (P < 0.05) higher concentration of Fe and Zn in leaves compared to the grain. Grain Fe concentration was higher in beans grown under adequate moisture co nditions than in moisture stressed condition . A highly significant ( n = 90; r = 0.79736; P < 0.0001) positive correlation between grain Fe and Zn concentration and highly significant ( n = 90; r = 0.53662; P < 0.0001) positive correlation between leaf Fe and Zn concentration were observed. It follows that an increase in grain Fe concentration correlates with an increase in grain Zn concentration, also an increase in leaf Fe concentration correlates with an increase in leaf Zn concentration. A significant ( n = 90; r = - 0.34860; P = 0.0008) negative correlation between the grain yield and leaf Fe concentration and highly significant ( n =90; r = - 0.58292 P = 0.0001) negative correlation between grain yield and leaf Zn concentration were observed. Hence an increa se in grain yield correlates with a decrease in leaf concentration of Fe and Zn. In order to increase the grain yield and grain concentration of Fe and Zn, applicati on of P fertilizer , maintaining adequate soil moisture and planting superior bean genotype is required.