Response of Common Bean (Phaseolus Vulgaris L.) and Maize (Zea Mays) to Zinc Fertilizers in Acidic Ferralsols of Western Kenya

Zinc deficiency persists in global food systems causing hidden hunger and disease burdens to vulnerable populations. Past research has demonstrated that agronomic bio-fortification could play a key role in averting the global disease burden associated with insufficient Zn intake. This study was undertaken in Western Kenya to: i) determine maize and common bean grain yield response to zinc oxide, zinc sulphate and chelated zinc and ii) establish the maize and common bean grain zinc concentration response to fertilizers. The experiment was laid in a randomized complete block design constituting twelve treatments in 7 m by 4.5 m plots replicated four times. The experiments were carried out during 2020 short rains, 2021 long rains and 2021 short rains. At sowing, all treatments received 90 N, 60 P and 60 K kg ha-1. The treatments were NPK only (No Zn application), NPK + nano-particulate ZnO (10, 15 and 20 kg Zn ha-1), NPK + zinc sulphate hepta-hydrate (11.4, 17 and 20 kg Zn ha-1) each as one-time and split application, NPK + nano-particulate ZnO foliar (2 g litre-1) and NPK + chelated zinc foliar (1 millilitre litre-1). The variables assessed during the study were maize and common bean grain yield and grain zinc content. The data were analyzed by ANOVA and means separated by Fisher’s Least Significant Difference at 95% confidence interval. Soil analysis before the trial layout showed that the pre-planting soil was moderately acidic (pH = 5.0), Zn deficient (DTPA Zn = 0.66 ppm), and P deficient (Olsen P = 3.60 ppm). Over the three seasons, maize grain yield ranged from 4.2 to 6.4 t ha-1 while bean grain yield was 0.32 to 1.68 t ha-1. Maize grain Zn ranged from 18.8 to 23.6 mg kg-1. Soil-applied ZnO, ZnSO4, ZnO foliar and Zn-chelate increased the maize grain Zn levels from 18.8 mg kg-1 in the control to 20.3, 22.3, 21.0 and 22 mg kg-1, respectively. The common bean grain Zn ranged from 23.03 to 30.3 mg kg-1 and was significantly increased (19.3%) by the application of zinc. This study demonstrated that Zn applications targeting grain Zn bio-fortification are more successful in common beans than maize. Therefore, the study recommends agronomic bio-fortification of the common bean by Zn application over maize in Western Kenya