s. hajinia

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.

Drought is one of the major abiotic stress limiting plants growth and productivity across the world. Intercropping increased the efficiency of water utilization. In arid and semi-arid regions, intercropping can improve water use efficiency and water conservation in soil. Because intercropped plants use water efficiently and caused increasing of water use efficiency. Intercropping of legumes and cereals compared with corresponding sole cropping is common and might be beneficial in semi-arid regions particularly in resource limiting conditions. Do and Goutan (1987) reported that millet can be planted in mixture with some plants such as cowpea, sorghum, peanut and soybean. The aim of the investigation was to study the impact of intercropping on the growth and yield of millet and soybean under deficit irrigation.

The experiment was carried out as a split-plot based on a randomized complete block design with three replications, at the Research Farm of Agricultural Faculty of Bu-Ali Sina University in 2015. The main factor included three levels of deficit irrigation (irrigation after 60 (well-watered), 90 (mild stress) and 120 (severe stress) mm by using of class A evaporation pan) and five levels of replacement intercropping consisted of monoculture of soybean, monoculture of millet, 67% soybean+ 33% millet (67S:33M), 50% soybean+ 50% millet (50S:50M) and 33% soybean+ 67% millet (33S:67M) as subplot.

Water stress decreased chlorophyll concentration of millet and soybean. In all intercropping ratios, the chlorophyll concentration of soybean was higher than its monoculture. The rate of increase in chlorophyll concentration in (67S:33M), (50S:50M), and (33S:67M) ratios compared to monoculture of soybean, were 8.43, 8.57 and 8.76 percent respectively. The highest total chlorophyll content of millet was obtained in (50S:50M) and (33S:67M) ratios, that was 12.34 and 12.09 percent higher than monoculture of millet, respectively. The highest number of panicles per plant of millet was obtained from (50S:50M) and (67S:33M) ratios under well-watered, and the lowest one was observed in monoculture of millet under severe water stress. The highest number of seed per panicles of millet was observed at intercropping of 33S:67M, 50S:50M and 67S:33M treatments under well-watered, and the lowest value was measured in monoculture of millet under sever water stress. Water stress decreased number of pods per plant, number of seeds per pod and 100-seed weight of soybean, compared to well-watered. Number of pods per plant, number of seeds per pod and 100-seed weight of soybean reduced in severe water stress were about 50.58, 33.68 and 26.09 percent, respectively, compared to well-watered. The number of pods per plant of soybean plants in all intercropping patterns was higher than monoculture of soybean. The rate of increase in number of pods per plant in (67S:33M), (50S:50M), and (33S:67M) ratios, were 6.38, 11.63 and 7.75 percent respectively, compared to monoculture of soybean. The highest seeds per pod of soybean was obtained in (50S:50M) ratio by 13.78 percent higher than monoculture of soybean. Water stress reduced grain yield of millet and soybean by 46.8 and 50.05 percent, respectively. Under well-watered condition, the highest yield of millet was obtained in (67S:33M) and (50S:50M) ratios. The highest actual yield of soybean was observed in (50S:50M) ratio by. Maximum value of LER (1.14) was achieved in (50S:50M) ratio intercropping in severe stress.

The best planting pattern to obtain maximum yield of millet and soybean was (50S:50M) ratio. The difference in rooting millet with soybean and better use of water in different soil depths could be reason to the high yield under water stress, the show millet and soybean intercropping were complementary