Effect of different irrigation regimes on gas exchanges and agronomy traits related to yield in bean (Phaseolus vulgaris L.)

Bean (Phaseolus vulgaris L.) is one of the most important food sources of human. It has a high nutritional value due to its protein, vitamins and fiber supply. Abiotic stresses are most important limiting factors to crop productivity that among these, drought stress is known to be the main limiting factor of bean production in worldwide. The bean has a low tolerance to water stress, while about 60% of the bean crop is obtained in areas under low water stress. It has been reported that about 25% reduction of yield bean is due to drought stress conditions. The use of modern irrigation methods in addition raise grain yield, because saves of water consumption.

In order to investigate the effect of different irrigation regimes on gas exchanges and agronomy traits related to yield in bean, a field experiment was carried out at the Research Farm of the Faculty of Agriculture, Zanjan University, Zanjan, Iran (36410N, 48290E) in spring 2012 years. The experiment was conducted at complete randomized block design with four replications. Experimental treatments included five level of irrigation (Traditional Irrigation with 100 % supply water requirement (I1), drip tape irrigation with 100 (I2), 80 (I3), 60 (I4) and 40 % (I5) supply water requirement. Each plot consisted of four rows, each measuring six meter long, distance of each rows and plants was 50 and 10 cm, respectively. Crop Evapotranspiration (ETc) of bean determined through calculation the evapotranspiration of the refrence crop (ETo) evaluated by FAO-Penman-Montith method and Crop Evapotranspiration (ETc) of plant. For of photosynthesis and other gas exchange parameters use IRGA Lci meter. At the physiological maturity stage, plants in an area of 1 m2 to measuring of  length of plant, number pod in plan, number seed in  pod, weight of thousand seeds, grain yield, biological yield and harvest index (HI) were harvested, then all aboveground dry matter were determined.

The irrigation regimes have significant effect all traits investigate except plant length and intercellular CO2 concentration (Ci). Reducing the amount of available water had adverse effects on the yield and yield components. The maximum of Stomatal conductance to water vapour (gs) observed in I1 and net CO2 assimilation rate (ACO2), mesophyll conductance (gm) in I1 and I2 treatment. The intercellular CO2 concentration (Ci) was not affected by the irrigation regimes. The maximum of grain yield (945.6 kg/h), number of  pod in plant (10.95) and harvest index (23.87 %) observed in I2 treatment and  the highest of stomatal conductance to water vapour (gs) with 0.43 mmol.m-2s-1 was in I1 treatment. There was no difference in other traits investigate between I1 and I2 treatments. The intercellular CO2 concentration (Ci) not significant in different irrigation regimes. The grain yield, number of pod in plant and harvest index in I2 treatment was more than I1 treatment to the amount 31.29, 59 and 18.93 percent, respectively.

According to this study, results showed that the physiological and agronomical traits that affected the growth and development of common bean disturbed whit reducing the available water content and ultimately the yield reduced. Since the no significant difference between more eco-physiological traits, in order to reducing of water consumption, suggested that in the field of bean culture, instead of traditional (leakage) irrigation, to use from of drip irrigation method with 100 percent supply water requirement. Result showed that the use of drip tape irrigation with 100 % water requirement was better than traditional irrigation with 100 percent supply water requirement, because in addition raise grain yield, cause saves of water consumption and reduces of hardness of work in farm conditions.