عنوان مقاله [English]
Introduction: Weeds represent the major biotic problem in wheat cropping systems, especially when are managed under conservation tillage practices. Indeed, the excessive use of herbicides in agricultural fields caused hazardous consequences, such as loss of biodiversity and resistant plants, therefore, nowadays there is a tendency to adopt ecological based weed control measures to improve the sustainability of the agro-ecosystems. Previous studies showed that cover crops could be successfully intercropped with main cash crops as living mulch to improve weed management. This experiment was performed to evaluate the effects of bitter vetch (Vicia ervilia (L.) Willd.) and grass pea (Lathyrus sativus L.) intercropped in additive series with winter wheat under different soil tillage systems.
Materials and Methods: Two field experiments were conducted at the Agricultural Research Station of Ilam University, Iran, in 2018-19 and 2019-20. The experimental treatments included three soil tillage systems (no tillage, reduced tillage, and conventional tillage), and two intercropping patterns (wheat+grass pea and wheat+bitter vetch). Moreover, a pure stands of bitter vetch, grass pea, and wheat was adopted. A split plot layout based on randomized complete block design with three replicates was applied where soil tillage systems and intercropping patterns were arranged as the main and sub plots, respectively. Weed species density was used to calculate the species diversity indices including Margalef, Shannon-Wiener, Brillouin, Evenness and Simpson dominance indices. The multivariate analysis was performed to discriminate the difference among species in response to tillage systems and intercropping patterns.
Results and Discussion: The results showed that based on relative abundance, in both studied years under the no-till system, wild barley and oat weeds accounted for the highest weed population with the frequency of 11.84 and 10.53%, in the first year, and 11.97 and 12.68% in the second year, respectively. Under the minimum tillage system, wild barley weeds in the first and second year with 10.62 and 8.29% relative abundance, respectively, had the highest weed population. Under conventional tillage conditions, in the first year, weeds of wild barley, Euclidium syriacum, wild oat, and Ceratocephalus falcatus were observed as the predominant weeds with the frequency of 10, 10, 9.4, and 9.4% respectively. In the second year, the highest relative abundance was related to weeds of wild oat and barley. The intercropping of wheat+bitter vetch reduces the weed density more than rest of the treatments under different soil tillage systems. The reductions in weed density due to intercropping of wheat+bitter vetch and wheat+grass pea were 77 and 69.9 % under no tillage, 80.1 and 76.1 % under reduced tillage, and 70.2 and 54.5 % under conventional tillage systems, respectively. This could be due to the density and competitive pressure by intercropping to reduce the ecological niche for weed species to occupy. The weed diversity indices (Shannon and Wiener, Brillouin, and Margalef indices) were highest in pure weedy and grass pea monocultures. Weed density and diversity were also highest under conventional tillage system. The highest Simpson dominance index (0.38) was found in wheat+bitter vetch intercropping in both years compared to the other treatments. No significant difference was found among the soil tillage systems in Simpson dominance index in the first year, while it showed a significant increase in no tillage (from 0.27 to 0.44), decreased in reduced tillage (from 0.24 to 0.17) and had no significant change in conventional tillage (0.21 to 0.20) systems in the second year. The pattern of Additive wheat+bitter vetch than wheat+grass pea intercropping reduced the density of weeds in different tillage systems. Probably due to the greater diversity of plants in intercropping patterns compared to monoculture, as a result, crops obtain more ecological niches and, by absorbing more available resources for growth, reduce growth and thus reduce population and weed density.
According to the multivariate analysis, 100% of the variances was explained by the first function in 2018-19, which showed Hordeum spontaneum L. as the dominant species. In 2019-20, 96.2 and 3.8% the variances were explained by first and second functions, respectively, which showed Hordeum spontaneum L. and Avena ludoviciana L. as dominate species. Therefore, these two weed species might be well adapted to the cropping systems.
Conclusion: The results of this study showed that intercropping patterns could reduce the weed density even if the reduction was higher in wheat+bitter vetch than wheat+grass pea intercropping. Therefore, bitter vetch can be considered as an efficient living mulch for intercropping with wheat to control weeds in different soil tillage systems. Similarly, weed diversity is also affected by soil disturbances and intercropping. Hordeum spontaneum L. and Avena ludoviciana L. tend to be the dominant weed species. It is concluded that weeds can be controlled to an appropriate level using wheat+ bitter vetch intercropping under conservation and conventional tillage systems. This approach can be used to design an efficient weed management strategies toward sustainable agriculture.