The study of foliar spraying of micronutrients (iron, zinc and manganese) on yield and yield components of red bean (Phaseolus vulgaris L.) under irrigation cut-off conditions

Red bean is an annual legume which has high nutritional value for human consumption. The yield of this plant is greatly reduced in arid and semi-arid regions due to water deficit stress. One of the negative impacts of drought stress is the reduction of micronutrient absorption by the plant root. Provision of micronutrients under drought stress conditions can greatly increase plant resistance to stress. In this regard, the aim of this research was to study the effects of foliar application of micronutrients (Fe, Zn and Mn) on yield and yield components of red bean under drought stress conditions. The experiment was laid out in a split plot scheme based on a randomized complete block design with three replications in a field located in Mobarakeh city, during the growing season of 2016-2017. Water stress consisted of control (no water stress), cutting of irrigation at flowering and dough stages), which were assigned to the main plots and micronutrients foliar application was comprised of five levels of treatments: 1-control (no use of micronutrients), 2- manganese, 3- zinc, 4- iron and 5- mixture of the three elements, which were allocated to the sub-plots. The investigated traits were plant height, pod number per plant, grain number per plant, pod length, 100-grain weight, grain, biological yield and harvest index. Statistical data analysis was performed with statistical software MSTATC. Significant differences between the means were separated by LSD test at the probability level of 0.05. Simple correlation between traits was computed using SPSS version 16 software. The results indicated that cut-off irrigation caused a significant decrease in the all studied traits, but the negative effects of it at flowering stage was more pronounced than those of dough stage. Cutting irrigation at flowering stage reduced the plant height, grain number per pod, length of pod and 100-grain weight by 36.1, 39.4, 12.5 and 24.7 percent compared with control treatment, respectively. In this regard, researchers reported that irrigation cessation at vegetative growth and flowering stages caused a significant reduction in plant height, number of seed in capsule and 1000-seeds weight of mung bean (Jafar dokht et al., 2015). Our results suggested that the foliar spraying of micronutrients increased the plant yield and yield components. The effect of mixture of the three elements was greater than the sole application of the elements. The highest plant height (61.8 cm), grain number per pod (6.2), pod length (11.1 cm) and 100-grain weight (33.3 g) was observed in combined application of micronutrients. The combined use of micronutrients increased the plant height, grain number per pod, pod length and 100-grain weight by 17.2, 34.7, 16.8 and 18 percent in comparison to control treatment, respectively. The maximum pod number per plant (15.3), grain yield (3759.6 kg.ha-1) and biological yield (8044.5 kg.ha-1) were obtained from normal irrigation and combined use of micronutrients, whereas the minimum values of the traits were observed in cut-off irrigation at flowering stage and foliar spraying with water. The combined application of three elements under normal irrigation and drought stress at flowering and dough stages resulted in significant grain yield increasing of 21.1, 41.8 and 9.8 percent compared with control treatment, respectively. In this regard, Varnaseri Ghandali & Nasiri Dehsorkhi (2017) reported that foliar application of micronutrients (Zn and Fe) under irrigation cut-off conditions at flowering and podding stages caused a significant rise in growth characteristics and yield of cowpea. Also, Nasiri Dehsorkhi et al, (2018) reported that water deficit decreased the yield and yield components of cumin but foliar application of Fe chelate in nano and common forms increased the yield attributes. Also the results indicated that under cut-off irrigation at flowering stage, the maximum correlation of grain yield was observed with pod number per plant (0.90**). Based on the results, it seems that in the studied region conditions, terminating irrigation at dough stage and combined use of micronutrients can give yields similar to normal irrigation. Among the micronutrients used in this study, iron and zinc elements had a greater positive effect on yield and yield components than manganese.Keywords: Dough stage, foliar application, legume, water deficit stress, 100-grain weight