Water is the source of life and one of the important resources for the sustainable development of countries. Population growth and consequently the need for more agricultural commodities and food products, in addition to the limitation of water resources, have led human beings to optimize use of available water resources and the use of low-quality water. To make more efficient use of limited water resources in the agricultural sector, new strategies such as the use of unconventional and saline water in irrigation operations should be considered. Knowing how plants respond to different degrees of salinity of irrigation water, which is used in different stages of vegetative and reproductive growth, is necessary for proper and optimal management of the use of unconventional water resources in agriculture. Beans are one of the most important crops in terms of high protein content and use in the diet. This plant is one of the annual legumes and is sensitive to water salinity, which is cultivated for seed production. Bean is one of the plants sensitive to salinity and tolerates salinity up to 2 dS/m, but its yield reduction starts from 0.8 dS/m, according to previous studies.
In the current study, experiments were carried out to determine the effects of saline water irrigation on vegetative and reproductive growth stage of Derakhshan red bean cultivar, which is suitable for Shahrekord climatic conditions. The experiments of this pot study were performed in factorial form in a completely randomized design, with three replications in the field. The pots had the diameter of 40 cm and the height of 70 cm. The research farm was located in Shahrekord University with UTM coordinates of X = 482573 m and Y = 3579364 m and altitude of 2070 m above sea level. The first factor in the experiments was the use of saline water at the mentioned three levels in the vegetative growth stage, and the second factor was the use of the same salinity level for irrigation in reproductive growth stage. The collected data included yield, yield components and water productivity.
Analysis of variance showed that salinity stress in the vegetative and reproductive growth stage of bean plant significantly reduces yield, yield components, water uptake, water productivity and biological productivity index (α <0.01). Harvest index was not affected by salinity stress at vegetative growth stage; while, the effect of salinity stress at reproductive growth stage on harvest index was significant (α <0.01). The highest value of water productivity was achieved in the control treatment with a rate of 0.67 kg/m³; the lowest value of 0.39 kg/m³ was observed in the treatment of applying 2 dS/m saline water in two stages of vegetative and reproductive growth. Regardless of salinity level, the mean effects of salinity in vegetative growth stage led to the productivity of 0.64 kg/m³, and in reproductive growth stage led to the productivity of 0.59 kg/m³. The results also showed that the highest yield (3349 kg/ha) was related to the control treatment and the lowest yield with rate of 1779 kg/ha was related to the treatment of applying 2 dS/m saline water in two stages of vegetative and reproductive growth. Regardless of the salinity level, the mean effects of salinity led to the production of 3067 and 2892 kg / ha grain yield in the vegetative and reproductive growth stage, respectively. The highest amount of water uptake was observed in the control treatment with the rate of 10 mm/day. The lowest amount of water uptake was 9 mm/day, which was without significant difference related to the treatment with the salinity of 2 dS/m in the whole growth period, the treatment of 2 dS/m in the vegetative growth period, and 1.5 dS/m during reproductive growth.
The results of this experiment, like the results of Ben Usher et al., 2006, showed that increasing salinity during the vegetative growth period of the plant reduces the storage content of plant organs, which affects the yield and its components at the end of the period. Furthermore, the application of salinity stress during reproductive growth period has a direct negative effect on yield and its indicators. These effects will be exacerbated when salinity stress is applied simultaneously during the vegetative and reproductive growth stages. The effects of salinity stress on grain yield and water productivity were more significant in the reproductive growth stage. The result is that in conditions of limited water quality, in order to achieve higher yield and optimal use of water, water with suitable quality should be used in the reproductive growth stage; while, saline water could be used in the vegetative growth stage.