Evaluation of Competitive Indices and Cultivation Efficiency of Cotton-Fodder Beet Intercropping under Weed Interference Conditions

Intercropping involves growing more than one crop in the same field at the same time. Intercropping increase diversity in the cropping system and enhance the utilization of resources such as light, heat and water. This practice can also help to suppress weeds and increase the likelihood of being able to reduce herbicide use in the cropping system. Alternatively, in organic systems where herbicides are not used, intercropping can reduce the yield loss potential and provide stability in the system. In recent years, native cotton growers in Khorasan region, especially in Torbat-e Jam region, using the intercropping of cotton-fodder beet (Beta vulgaris subsp. vulgaris L.), while facilitating the growth of fodder beet plant providing forage for livestock and increasing land income in the cotton crop. Placement of fodder beet plants in or between rows of cotton cultivation accelerates the conquest of space and resources compared to cotton monoculture. Little information is available on the cultivation of fodder beet - cotton intercropping and its effects on the yield of both plants, as well as the potential of this crop system in weed control. Therefore, this experiment was designed with the aim of the effect of cotton- fodder beet intercropping on weed control and evaluation of intercropping and competitive indices in Mashhad region.

In order to evaluate the effect of cotton-fodder beet intercropping on weed suppression, a split factorial experiment was conducted based on a randomized complete block design with three replications at Ferdowsi University of Mashhad research farm. Treatments include intercropping pattern at two levels of inter-row and intra-row intercropping and the ratio of cotton-fodder beet substitution intercropping at five levels including 75: 25, 50: 50, 25: 75 and monoculture of cotton and fodder beet as the main factor and weed interference at two levels including weeding and non-weeding throughout the weed season as a secondary factor. Land equivalent ratio for cotton, land equivalent ratio for fodder beet, total land equivalent ratio , actual yield loss for cotton, actual yield loss for fodder beet, total actual yield loss, relative value total for cotton, relative crowding coefficient for cotton, relative crowding coefficient for fodder beet, total relative crowding coefficient, aggressivity, competitive ratio for cotton, and competitive ratio for fodder beet were the indices which calculated and used as a basis for the evaluation of cotton – fodder beet intercropping. Analysis of variance was performed using generalized linear models through GLMMIX procedure in SAS 9.4 software environment. The effect of three factors: intercropping pattern, intercropping ratio and weed interference and their interaction with each other were considered as fixed effects and block and block effect, mixed intercropping pattern, intercropping ratio and total error were considered as random variables in the model. Comparison of means of the simple effects of factors and their interaction were performed using the least squares mean comparison method in the same procedure.

The results showed that the effect of intercropping pattern and intercropping proportion on total weed density was not significant, but was significant on total dry weight of weeds, although it was still not significant compared to monoculture of cotton. Accordingly, at a 25: 75 crop proportion of cotton - fodder beet, the dry weight of weeds was lower than other intercropping proportion. Also, the effect of intercropping pattern on both crop traits was not significant, but the ratio of intercropping on cotton and fodder beet traits was significant. In terms of interference or non-interference of weeds, at least 50% reduction in cotton lint yield and 83% reduction in fodder beet root yield was observed in intercropping conditions, compared to monoculture of each plant. The two indices of land equivalent ratio and actual yield loss showed the superiority of cotton monoculture over intercropping, but the relative value total index expressed the superiority of cotton-fodder beet intercropping over cotton monoculture. So that intercropping of cotton-fodder beet with a ratio of 75:25, in the presence and absence of weeds, the relative value total increased by 2.5 and 8.6 times, respectively, of cotton monoculture. Competitive indices including relative crowding coefficient, competition ratio and aggressivity index showed that fodder beet has higher competitive power than cotton. In general, the results of this experiment showed that cotton-beet forage intercropping, although it had no significant effect on weed control, is still recommended in terms of mixed crop evaluation indicators.

In general, the results of this experiment showed that the cotton-fodder beet intercropping, as replacement pattern, had no significant effect on weed control, and considering that it was suitable only in terms of one of the evaluation indices (relative value total), it is not generally recommendable.