Zinc enrichment of common bean grains by foliar fertilization in a field experiment

Common bean (Phaseolus vulgaris L.) is the grain legume crop most consumed worldwide. Grain enrichment with Zn through proper crop fertilization management may contribute for ameliorating the grain quality of pulse crops. The enrichment of the common bean grain nutritional composition may potentially improve the quality of human diet, mainly in poor countries. The mean out-of-home common bean consumption per capita per day in the Brazilian population is 129 grams per day, at home, this consumption is 42 grams. The work aimed to increase the Zn concentration in common bean grains through the fertilization management of the crop in a field study. Grain nutritional quality, as related to Zn concentration, was evaluated through the application of 5 kg ha-1 to soil, at planting, and 0, 5, 10, 20 and 40 kg ha-1 Zn via foliar spray at the R8 crop stage. The Zn concentration in the grain increased from 36.63 to 52.23 mg kg-1 when the foliar dose went from zero to 40 kg ha-1. No interference of Zn on the accumulation of P, Ca, Mg and Fe in the grains was observed. The grain phytate was 4.42 g kg-1 (zero foliar Zn), increasing to 8.4, in average, with foliar spraying. The grain phytate/zinc molar ratio (Phy:Zn) increased from 12.77 (treatment with 0.0 kg ha-1 Zn) to 19.43 (median ratio for 5, 10, 20 kg ha-1 treatments), dropping to 15.58 with 40 kg ha-1 Zn. The Phy:Zn 15.58 is associated to about 30 % Zn bioavailability in the human diet.