Competition between Mungbean (Vigna radiate (L.) Wilczek) and Redroot Pigweed (Amaranthus retroflexus L.) under Dust Conditions

The dust storm has become a regional phenomenon due to occurrence of severe droughts. Dust storms, recognized as significant atmospheric phenomena and associated with climate change, exert detrimental effects on plant growth and crop yield. This study aimed to assess the impact of soil dust on the competition between mung bean and red-root pigweed.

An experiment was carried out at the research greenhouse of Faculty of Agriculture at Ilam University during spring and summer 2022. The experiment was conducted as a factorial based on a completely randomized design with four replications. The experimental treatments were included five replacement ratios of mung bean and redroot pigweed (planting patterns 75% mung bean + 25% pigweed; 50% mung bean + 50% pigweed; 25% mung bean + 75% pigweed; monoculture of mung bean and redroot pigweed) and dust were at two levels (0 and 60 gr m-3).

The results showed that the dust causes symptoms of necrosis and leaf burn in mung bean and pigweed. The highest amount of carotenoids (3.59 mg g-1 fresh weight of leaf) was observed in the planting pattern of 75% mung bean + 25% pigweed under no dust conditions. The monoculture of pigweed under dust conditions had the lowest amount of carotenoids. Dust reduced the amount of total chlorophyll, leaf relative water content, plant height and length of inflorescence in Pigweed plant by 23.4, 12, 14.7 and 12%, respectively. Dust caused a decrease in the leaf area in pigweed in different patterns of intercropping. Photosynthesis rate, transpiration rate, leaf area, plant height, number of pods per plant and number of seed per plant in mung bean were respectively decreased by 31.2, 24.9, 28.8, 17.7, 29.7 and 36.7% due to dust application. The highest photosynthesis rate in mungbean (5.28 µmol of CO2 m-2 s-1), leaf area (129.1 cm2) and the number of seeds per plant (13 seed plant-1) were obtained from monoculture of mungbean. However, they were decreased under competition with pigweed. The biological yield in mungbean and pigweed under dust condition were, respectively, 42.6 and 16.8 % lower than that of no dust condition. Under dust conditions, the grain yield of mung bean and pigweed were, respectively, 32.8% and 42.6% lower than that of no dust condition. The actual yield of mung bean under competition with pigweed was lower than the predicted yield indicating the higher competitive effects of pigweed. In all planting patterns with and without dust, the total actual yields were higher than the predicted yield indicating a negative interference effects for mung bean. The relative total yield in most of the planting patterns was greater than one, suggesting increase in the partial relative yield and reduction of intra-species competition in pigweed. The negative effects of pigweed on mungbean were more visible in high densities of pigweed, which also showed a higher positive dominance index. The competition index showed a value greater than one for the pigweed indicating the greater competitive ability of this weed compared to mung bean. Under both conditions, with and without dust, pigweed exhibited the highest relative density coefficient in all planting patterns, establishing itself as the dominant plant compared to mung bean, which had a relative density coefficient less than one. The competition index for mung bean, across all intercropping patterns, was also less than one, indicating its lower competitive ability compared to pigweed. Interspecific competition with pigweed resulted in an actual yield loss for mung bean, highlighting that interspecific competition in mung bean surpasses intraspecific competition. Conversely, pigweed showed a greater susceptibility to intraspecific competition.

The results showed that pigweed has a higher competitive ability and by increased exploitation of environmental resources, cause a decrease in mung bean yield. Despite the high competition ability of pigweed, soil dust cause reduction in its growth and biomass.