Effect of Burial Depth, Duration and Temperature Storage of Rhizomes of Elymus repens (L.) Gould on their Survival and Growth

IntroductionElymus repens (L.) Gould, is a perennial, three-carbon, rhizomatous and morphologically diverse weed, with highly competitive and allelopathic ability which is considered a problematic weed in many crop lands. Plant growth is done through seed or rhizome germination, but due to the reserves in the rhizomes of this plant, the growth of seedlings from rhizomes is faster than the seedlings from seeds. The rhizomes of this plant are the main factor of reproduction. The seeds of this plant germinate in autumn or spring. At the 3 to 4 leaf stage, the plant begins to shoot and produce a new rhizome. By the end of May, a new plant is formed. Each shoot can produce 2 to 3 new rhizomes, allowing each plant to produce up to 50 rhizomes in one season. The propagation of this plant is done when these organs are placed at a depth of 2.5 to 8 cm in the soil and the rhizomes that are placed on the surface of the soil produce a small number of stems. The ability of double reproduction of perennial weeds, including Agropyron repens, has made their management and control difficult, and their successful management is almost impossible without knowledge of their biology and how they grow and reproduce. Today, weed science researchers have come to the conclusion that in order to increase the effectiveness of weed control techniques, they must be aware of their strengths and weaknesses, so that they can avoid providing strong points to the plant and hitting the Weaknesses should prevail over it, and this issue is more important in the case of perennial weeds. Studies conducted on other species of rhizomatous weeds show that the emergence of a branch from a piece of rhizome strongly depends on the size of the rhizome and the depth of the rhizome burial. Normally, deep burial of short rhizome fragments is expected to reduce stem emergence. Apart from these two elements, external factors such as ambient temperature can also affect the growth of new branches from rhizomes. An increase in temperature has a significant effect on the deterioration of the rhizomes of perennial weeds, and the high temperature and the duration of exposure of the rhizomes to high temperatures are the main factors in reducing their population in the soil. Materials and Methods In order to investigate effect of duration, temperature storage and depth of burial of vegetative means of Agropyron repens L. on its survival and growth, two separate experiments were conducted in the weed science laboratory of Faculty of Agriculture and Natural Resources of Mohaghegh Ardabili University in 2021. In the first experiment, effect of duration and temperature storage on survival of vegetative means was carried out as factorially based on a completely randomized design with three replications. Treatments included length of rhizome (3, 6 and 12 cm), temperature storage (10, 20 and 40 oC) and duration storage (7, 14 and 30 days). In second experiment, effect of burial depth on survival of rhizomes was done factorially based on a completely randomized design with three replications. In this experiment, the treatments included the length of rhizomes (3, 6 and 12 cm) and their burial depth (5, 10 and 20 cm). Results and DiscussionResults showed that with increasing temperature and duration storage, number of new formed rhizomes and their survival reduced, so that no new rhizomes were produced when rhizomes of the plant were kept at 40 oC. Even 14 and 30 days of exposure of the rhizomes at 20 oC reduced production of new rhizomes by 50 and 95%, respectively, compared to 7 days. Results also showed that even rhizomes with 12 cm long could not survive at 40 oC for 7 days. At lower temperatures (10 and 20°C), the chances of survival and the strength of rhizomes increased as their size increased, resulting in the production of more and longer rhizomes. Additionally, at these lower storage temperatures, smaller rhizomes (3 cm) exhibited weaker growth ability, and the dry weight of seedlings obtained from them was significantly lower than that of seedlings obtained from larger rhizomes (12 cm).The results showed that to increase in burial depth, the number of Agropyron repens seedlings that appeared decreased. Conclusion The results of this experiment showed that by keeping the plant's rhizomes at high temperature and small size or by burying them, the chance of regrowth of the rhizomes is significantly reduced and it accelerates their deterioration. Therefore, any agricultural operation, including tillage in hot seasons or deep plowing, which causes the burial of the rhizomes of perennial weeds, can play an important role in their control.