Assessment of Competition between Mungbean (Vigna radiata) and Lambsquarters (Chenopodium album) under Soil Dust Condition

Dust storms are meteorological phenomena that usually occur in arid and semi-arid regions with an annual rainfall of less than 200 to 250 mm when strong winds blow with a high speed. Dust particles affect plants growth and development directly by depositing in shoot or indirectly by changing soil chemical properties (Maletsika et al., 2015). The interference of weeds with the mungbean (Vigna radiate) plant is one of the important factors limiting the production capacity of this crop, which leads to a decrease in yield and an increase in production costs. The competition between crops and weeds becomes more complicated when coincide with environmental stresses like soil dust. Compared to crops, weeds are more resistant to environmental stresses and have a high capacity to absorb more water and nutrients. The aim of this research was to evaluate the competitive balance between lambsquarters and mungbean under soil dust conditions in order to manage production of this crop with lambsquarters under soil dust conditions.

The pot experiment was carried out in the research greenhouse of the Faculty of Agriculture of Ilam University, Iran in spring of 2022. The experiment was conducted as a factorial based on a completely randomized design with four replications. The treatments were included soil dust at two levels (0 and 60 g dust.m-3 of air) and replacement planting pattern at five levels (mungbean monoculture, lambsquarters monoculture, alternative intercropping of 75% mungbean + 25% lambsquarters, 50% mungbean + 50% lambsquarters and 25% mungbean + 75% lambsquarters). Totally, four plants per pots were sown. The measured traits were included physiological characteristics such as photosynthetic pigments, photosynthesis rate, transpiration rate, leaf area, plant height, stem diameter, biological yield and grain yield components of mungbean and inflorescence yield of lambsquarters.

The results showed that soil dust has no significant effect on the morpho-physiological characteristics of lambsquarters weed, while it decreased the photosynthesis rate, leaf relative water content, leaf area, plant height, number of pods per plant, biological yield and grain yield of mungbean by 26.1, 9.7, 10.6, 19.3, 14.8, 24 and 23.2%, respectively. The highest amount of chlorophyll in mungbean leaves (4.65 mg g-1 fresh weight of leaves) was obtained in the intercropping patterns of 75% mungbean + 25% lambsquarters and monoculture of mungbean under no dust conditions. The highest photosynthesis rate, transpiration rate, leaf area and number of pods in mungbean plant were observed in monoculture and planting pattern of 75% mungbean + 25% lambsquarters. The highest seeds number per plant (10.4 and 10.1) was observed in monoculture of mungbean and planting pattern of 75% mungbean + 25% lambsquarters under the no dust condition, which was 30.5 and 65.8 percent higher compared to dust treatment, respectively. The lowest seed number per plant (3.3) was obtained in 25% mungbean + 75% lambsquarters. Under both dust and no dust conditions in all plant patterns, the actual mungbean seed yield was lower than the expected yield and the changes in curve of mungbean yield was concave; but the actual yield of lambsquarters was more than the expected lambsquarters inflorescence yield, and the curve was convex suggesting a commensalism relationship for lambsquarters and amensalism relationship for mungbean. The relative crowding coefficient and the competition ratio under both conditions of dust and in different planting patterns were obtained for lambsquarters weed, were greater than one, which indicates the superiority of lambsquarters competitive ability compared to mungbean. The aggressivity index of lambsquarters under dusty conditions was higher than under dust-free conditions, which shows that lambsquarters weed has more competitive capacity under environmental stress conditions including soil dust. The results also showed that the mungbean plant has a greater potential to absorb dust than the lambsquarters weed, which is due to the presence of trichome in mungbean leaves surface. In general, in this experiment the lambsquarters dominated the mungbean plant in competition for water and nutritional resources and had better growth compared to mungbean in different planting patterns.

In the presence of dust, lambsquarters weed may have higher efficiency to use environmental resources due to its higher adaptability compared to the mungbean and causes decreasing in the yield of crop plants including mungbean. The interactive effect of dust and the interference from lambsquarters caused a significant decrease in mungbean yield. Therefore, the management of lambsquarters under dusty conditions is of important value.