WEED CONTROL USING ALLELOPATHIC PROPERTIES OF RAPESEED RESIDUES AND CROP MANAGEMENT

Planting date, density and allelopathic properties are important tools of crop management in controlling weeds in crops. Allelopathy refers to any direct or indirect inhibitory or stimulating effect of one plant on another through the production and release of secondary metabolites in the environment. Two experiments performed separately, in order to investigate the effect of allelopathic properties of rapeseed residues and crop management on the control of rapeseed weeds and its yield. The first experiment was conducted during two agricultural years (2018-2019 and 2019-2020) in a factorial form of a randomized complete block design with 3 replications at the Qarakhil agricultural research station (QaemShahr). The treatments were included: planting date in 3 treatment levels (October 17, November 6 and November 26), seed rate in 3 treatment levels (3, 5 and 7 kg per hectare) and weed management in 2 treatment levels presence of weed (no control) and the absence of weed (control). The second experiment was conducted as a factorial in the form of a completely random design in three repetitions in the research laboratory of the Islamic Azad University, QaemShahr branch in 2020. The experimental treatments included weeds [wild oat (Avena fatua), darnel regrass (Lolium temulentum), phalaris (Phalaris minor)] and charlock mustard (Sinapis arvensis)) different concentrations of rapeseed root and stalk extracts (0, 25, 50, 75 and 100%). The results of the first experiment showed that, in general, the rapeseed seed yield was affected by the planting date and density, so that the rapeseed seed yield on the delayed planting date (November 26) decreased compared to the first planting date (October 17) by 49 and 59 percent, respectively in the first and second year of the experiment, and this decrease was more intense in the second year. Also, the results showed that the highest dry weight of weeds was obtained in both years at a density of three kilograms per hectare and in the cultivation of November 26 (except for the highest dry weight of wild oats that was observed in the cultivation of October 17). While the highest weight of seed yield was obtained in both crop years at a density of 7 kg per hectare. The results of the second experiment showed that the extract obtained from the root and stem of the rape plant had a negative and significant effect on the speed, percentage and inhibition of germination in all weeds. However, no significant difference was observed between the concentration of root and stem extracts at the 5% level. A significant negative linear regression relationship was observed between the concentration of the extract (root and stem) with the percentage and speed of germination. Also, a significant positive linear regression relationship was observed between inhibition percentage and extract concentration (root and stem). Therefore, the germination and seedling growth of the seeds of all three weed species had a negative reaction to the concentration of rapeseed extract, but the highest sensitivity was observed in wild oat seeds. Therefore, according to the results, rapeseed extract can be used in the biological control of weeds. In general, the results of two experiments showed that the planting date, density and rapeseed residues can be used effectively in controlling weeds in rapeseed fields.