Improvement of physiological indices and biological yield by intercropping of Kochia (Kochia scoparia), Sesbania (Sesbania aculeata) and Guar (Cyamopsis tetragonoliba) under the salinity stress of irrigation water

Due to the low quality of water resources in arid and semi-arid regions of the world, selection and management of forage plants suitable for saline condition is of great importance. Intercropping systems with halophyte plants not only improve production efficiency but also reduce soil salinity. In this study, the effects of different levels of irrigation water salinity and intercropping system on physiological indices and biological yield of Kochia, Guar and Sesbania were investigated during the growing seasons of 2016 and 2017. A split plot experiment was conducted in a randomized complete block design with three replications. The main factor was salinity of irrigation water (4, 9 and 14 dS m^-1) and the sub-factor was different cropping systems that consisted of mono cropping of Guar, Sesbania or Kochia, intercropping of two species and intercropping of three species. Results showed that salt stress increased sodium in the leaves of Kochia, Guar and Sesbania. Compared to mono cropping of Guar, in intercropping of three species and in intercropping with Kochia, Guar leaf potassium content was increased by 33.3% and 19.9% respectively. Salinity levels of 9 and 14 dS m^-1 compared to salinity level of 4 dS m^-1 increased the soluble sugar content of Kochia plant by 65.7% and 52.7%, respectively. However, in similar salinity levels, the trend for soluble sugar changes in Guar was vice versa. Salinity treatment of 14 dS m^-1 decreased the relative water content of Sasbania and Guar leaves, but had a reverse effect on Kochia. Intercropping of two and three species also increased the relative water content of Sasbania and Guar leaves. Enhancement in salinity stress increased ionic leakage and malondialdehyde content of Guar leaf. On the other hand, at salinity level of 14 dS m^-1, intercropping of three species increased the carotenoid content and decreased the amount of Guar leaf malondialdehyde compared to the Guar mono cropping system. The results of this study showed that salinity stress had negative effect on Guar yield but intercropping with Kochia could partly improve the yield of both Guar and Sesbania. In addition Kochia showed relatively good yield potential under salinity stress. Therefore, to improve the production of Sesbian and Guar, and also physiological performance of Kochia, intercropping system of these plants is recommended under salinity stress conditions.