effect of foliar application of manganese and zinc on grain yield and yield components of red bean (phaseolus vulgaris l.) in drought conditions

introduction grain legumes are considered as the second source of human nutrition after cereals and play an important role in community food supply, sustainable agriculture and economic profitability. among grain legumes, common bean has the most consumption in the world compared with others. however there are always some constraints in common bean production and drought is most important factor in yield reduction of this crop. in addition high sensitivity of common bean to some micronutrients shortage such as manganese and zinc is another limiting factor that will be exacerbated in drought conditions. in such situation foliar application could be considered as a suitable strategy to facilitate the absorption of these micronutrients by plant. materials and methods in order to study the effect of foliar application of manganese and zinc on grain yield and yield components of red bean(phaseolus vulgaris l.) in drought conditions the experiment was carried out at research station of agriculture and natural resources research center of shahrekord as a split plot factorial design in basis randomized complete block with three replications. drought stress considered as main factor including s1, s2 and s3 (irrigation after 50, 70 and 90 mm of cumulative evaporation from class a pan respectively) and subplots were the factorial combination of manganese and zinc foliar application both with three levels including foliar application of distilled water, 150 ppm and 300 ppm from manganese sulfate and zinc sulfate resources respectively. sowing date was may 27, 2010 and each experimental plot was included of 4 rows with 50 cm apart and 4 m long. between main plots a m-2 wide strip was left bare to eliminate influences of lateral water movement. according to soil test 100 kg.ha-1 n was used in the form of urea (50 kg.ha-1 n before sowing and 50 kg.ha-1 n before flowering) by hand broadcasting method. irrigation was done every 5 days and drought stress treatments along with foliar application treatments were applied at v 4 (third trifoliate leaf appearance) crop growth stage. during the growth season, weeds and pests were controlled. at the harvesting time (15th to 26th september) 1 square meter of each plot in different treatments was harvested and grain yield, number of pod per plant, number of seed per pod, 100 seed weight, biological yield and harvest index were investigated.data analysis performed by sas software and mean comparisons were done using the least significant difference test at 5% probability by mstat-c software. results and discussion the results showed that drought had a significant effect on all investigated traits and the highest values of pod number per plant (14.2), grain yield (3172.4 kg.ha-1) and biological yield (9124.1 kg.ha-1) were related to s1 treatment, whereas the highest values of seed number per pod (4.7), 100 seed weight (26 gr) and harvest index (36.4) were obtained in s2 treatment. the lowest values of all traits were observed in s3 treatment, so that pod number per plant (5), seed number per pod (3.6), 100 seed weight (21.4 gr), grain yield (774.5 kg.ha-1), biological yield (5451.7 kg.ha-1) and harvest index (13.6) decreased by 64.8, 20, 12.6, 75.6, 40.2 and 60.8 percent respectively compared with control. the simple effects of foliar application of mn and zn in all investigated traits except harvest index and weight of 100 seed were significant and these traits increased with increasing in application of micronutrients amount. so that grain yield in 300 ppm of mn and zn foliar application treatments increased 36.3% and 28.2% respectively compared with control. investigation of interaction effects of treatments showed that in severe drought stress condition foliar application of mn had a better effect than zn on number of pod per plant and grain yield.the positive effects of mn and zn micronutrients might be attributed to the favorable influence of them on metabolism and their stimulating effect on photosynthetic pigments and enzyme activity which in turn encourage growth and yield. conclusion generally, however foliar application of mn and zn caused to grain yield increasing but in drought stress mn had a better effect in drought impacts alleviation and could be considered as an applied method for yield improvement of common bean in water deficit conditions.