Effect of zinc foliar spray alone and combined with humic acid or/and chitosan on growth, nutrient elements content and yield of dry bean (Phaseolus vulgaris L.) plants sown at different dates

• Flowering and pod set in dry bean are very sensitive to high temperatures.
• At late sowing date (25 Mar.), heat stress coincided with the reproductive phase.
• Delayed sowing date (25 March) decreased the dry bean yield.Zn with humic acid and chitosan enhanced the yield on normal or delayed sowing.

Dry bean (Phaseolus vulgaris L.) plants were considered sensitive to heat stress especially during the reproductive growth phase. Hence, the present study aimed to investigate the benefits of zinc foliar spray (100 ppm) alone and combined with humic acid (500 ppm) or/and chitosan (150 ppm) on growth, foliar NPK content and yield of dry bean cv. Nebraska from normal (20 February) and late sowings (25 March) where heat stress coincided with the reproductive phase. The study was conducted in Dakahlia Governorate, Egypt, during the two seasons of 2011 and 2012. A split plot design with three replicates was used. Although the 25 March plantation had the highest values of biomass production and its NPK content, it had the lowest values of seed yield (around 10% loss) as compared with that sown at normal date (20 February). Foliar application of zinc containing treatments had a tendency to increase all the studied parameters of dry bean plants over those untreated up to 25–33%. In addition, the interaction between the dates of sowing and different zinc foliar application treatments had significant effects on all studied traits. Overall, the results of this study indicated that sowing date was a very important management tool in minimizing the negative impact of high temperature during the critical flowering and seed filling periods. Moreover, the benefits of zinc foliar spray combined with humic acid and chitosan are inconsistent over both sowing dates, but may be more efficient in late-sown crops where heat stress coincided with the reproductive phase.