Evaluation of yield and drought tolerance indices in pure and mixed cultivation systems of different cereals under hot and dry ecological conditions

Due to the increase in world population and the need for food using traditional agricultural methods does not meet the needs of society. The Food and Agriculture Organization (FAO) predicts that by 2050, 60 percent more food production will be needed to feed the world's 9 billion population. This has concerned agroecologists to sustainable agriculture and encouraged them to do more research and design new sustainable agricultural systems. Therefore, the aim of this study was to examine different mixed cropping systems of cereals and evaluation of different drought tolerance indices using a mixture of winter cereals, wheat, barley and triticale and their response to end-of-season water stress in hot and dry ecological conditions.

In order to investigate the grain yield and drought tolerance indices of mixed culture of different cereal genotypes to water stress in hot and dry ecological conditions, an experiment was conducted as split plot design based on a randomized complete block design with three replicates during 2017-2018 cropping year in College of Agriculture and Natural Resources of Darab, Shiraz University. In this experiment, the first factor was irrigation regime in two levels of normal irrigation and water stress and the second factor was ten cropping systems of genotypes (tall barley line EB-95-97, dwarf barley line EB-95-97, dwarf bread wheat line S-92-19, tall bread wheat cultivar Khalil and a cultivar of Triticale called Juanilo) which were grown as double and pure row culture. Double mixed crops included of: dwarf barley- tall barley (one row of dwarf barley + one row of tall barley), dwarf barley - triticale (one row of dwarf barley + one row of triticale), tall barley - triticale (one row of tall barley + one row of triticale), dwarf wheat - triticale (one row of dwarf wheat + one row of triticale) and tall wheat - triticale (one row of tall wheat + one row of triticale) in a 50:50 planting ratio and their pure cultivation.

The results of this experiment showed that the highest grain yield was obtained in tall wheat-triticale mixed culture with 9472 kg ha-1 under normal irrigation and the lowest grain yield was achieved in pure dwarf barley with 3934 kg ha-1 under water stress condition. The results of correlation analysis of drought indices showed that positive and significant correlations were observed between STI (r=0.858**), GMP (r=0.747*) and MP(r=0.801**) with grain yield under water stress conditions. Alos, positive correlation coefficients were observed between STI (r=0.884**), GMP (r=0.922*) and MP (r=0.932**) with grain yield under normal irrigation conditions. The highest SIIG index in this investigation was observed for dwarf barley-tall barley cropping system which had the minimum yield difference in normal and water stress conditions. 3D-graph of cropping systems using SIIG index indicated that cropping systems of pure tall wheat, pure dwarf wheat and tall barley+triticale mixture demonestraed the highest grain yield both in normal and water stress conditions.

Tall wheat+Triticale mixed culture wheat cultivation system under normal irrigation conditions showed a 16% increase in yield compared to the tall wheat pure cultivation system, while it did not show a significant difference with the Triticale pure cultivation system. Some of the mixed cropping systems such as tall wheat + triticale mixed cropping systems produced higher yields that their pure cultivation systems. Alos, it was concluded that STI, GMP, MP and SIIG were the best drought stress indices to evaluate different cropping systems.