Evaluation of Weed Control on Biochemical Characteristics, Relative Water Content, and Grain Yield of Mixed Cropping of Wheat Cultivars

Wheat is the most important crop in the world, which has always been of particular importance since its domestication and has the highest cultivated area among crops. Wheat is the main food of most people in many parts of the world. Among the factors that reduce wheat production, weeds are of particular importance and according to the studies; the average weed damage in wheat fields is 23%. Mixed cropping systems based on carefully designed species mixtures reveal many potential advantages in terms of enhancing crop productivity, reducing pest and weed interference. Recently, mixed cropping of wheat cultivars by different morphological characteristics is a suitable approach in increasing crop productivity especially under biotic stress conditions. This study aimed to investigate the effect of weed control on some biochemical traits, relative leaf water content and grain yield of mixed cropping of wheat cultivars.

In order to study the effect of weed control on biochemical traits and yield in mixed cropping of wheat cultivars, a field experiment was laid out as randomized complete block design with three replications in Research Station of Agriculture College and Natural Resources of Darab, Shiraz University, in 2018-2019 growing season. Experimental treatments consisted of six levels of weed control including weed control at tillering, stem elongation, booting and ear emergence stages, weed-free and weedy check and cropping system consisted of Sirvan monoculture, Setareh monoculture, and  mixed  row intercropping of Sirvan and Setareh which were in a ratio of  row one to one. The sowing date was 4th Dec in 2018 and harvest date was 19th Jun 2019. At late flowering stage, chlorophyll a and b content, carotenoid content, catalase and peroxidase activity, relative water content and weed biomass was measured. In addition, at physiological maturity grain yield were determined by one square meter quadrat.Finally, data were analyzed by SAS ver 9.1 software and the means were compared by LSD test at 5% probability levels.

The results showed that the simple effects of weed control and cropping system had significant effect on chlorophyll a and b, carotenoid content, catalase and peroxidase activity, relative water content, weed biomass and grain yield . The amount of chlorophyll a, carotenoid and relative water content of leaf, catalase and peroxidase in weed control at tillering stage were 64.2, 38.97, 31.4, 93.10 and 88%, respectively, compared to weedy check and these traits in mixed cropping increased by 5.2, 7.2, 12.8, 15.8 and 20.7%, compared to Setareh monoculture, respectively. Also, weed biomass in mixed cropping decreased by 29.6% compared to Setereh monoculture. The highest grain yield was observed in mixed cropping of Sirvan with Setereh which had  29.6% increase compared to Setareh monoculture and the best time to weed control was at the tillering stage because it had the lowest reduction in grain yield compared to weed free treatment.Overall, weed control at late-season especially at ear emergence would be less effective in crop productivity while weed control at early growth stages and before flowering provided the best crop performance in terms of photosynthetic pigments and grain yield.

It seems that mixed cropping of wheat cultivars could be effective in weed competition compared to monoculture, so that weed biomass in mixed cropping decreased especially at tillering and only 11.9% grain yield was reduced compared to weed-free control. Overall, when plants exposed to weed interference up to late growth stages, chlorophyll a and b content and carotenoid content decreased while catalase and peroxidase activity and weed biomass increased, significantly. Also, mixed cropping treatment weed interference increased catalase and peroxidase activities and relative water content and caused grain yield increasing compared to monoculture.