Response of French Bean (Phaseolus vulgaris L.) Cultivars to Foliar Applications of Magnesium

Magnesium deficiencies have been shown to be particularly dangerous to short cycled crops, both on sandy and clay soils. Such deficiencies may be corrected by foliar fertilisations, but in French bean (Phaseolus vulgaris L.) no experimental data may be found to support this hypothesis. Therefore this paper was aimed at studying the effect of foliar Mg-applications (56, 112 and 224 g ha-1 in single application at flowering or splitted half dose at 4-leaf stage and half at flowering) alone and with Zn (200 g ha-1) on yield and quality of two French bean genotypes (Bronco, Cadillac). Foliar Mg-applications significantly increased pod yield and, considering the highest rate with respect to the untreated, such an increase was 78% and 32% for Bronco and Cadillac, respectively. Split applications were also more effective, with yield increases of 109% and 50% for the two genotypes. Concerning quality, foliar Mg applications showed a significant effect particularly on sugars, calcium, phosphate, sulphate and Mg contents in pods. On the other hand, a significant effect on the accumulation of nitrates was noted, especially with split applications (144% increase vs. unfertilised) and, in some cases, an antagonistic effect on K content (10-20% decrease on average). Foliar Mg fertilisation of French bean seemed to be a promising practice with reference to human health and nutrition, tough some care is needed to avoid the accumulation of nitrates in pods. Split applications seemed to be more effective, while the addition of Zn to the fertiliser mix did not give any relevant effect.