Allelopathic Effect of Wheat and Barley Residues on Yield and Yield Components of Cowpea (Vigna sinensis L.) and Weeds Control

Weeds are a major constraint limiting crop yield in agricultural systems and in organic systems in particular. Although herbicides are efficient for weed control, continuous use has caused the development of resistance in weeds against several herbicides. Furthermore, herbicides also pollute the soil, water and aerial environments and herbicide residues in food have deteriorated food quality and enhanced the risk of diseases. Allelopathy is defined as the direct or indirect harmful or beneficial effects of one plant on another through the release of chemical compounds into the environment. Wheat (Triticum aestivum L.) is known to be allelopathic against crops and weeds. The objective of this study was to investigate the allelopathic effect of wheat and barley residues on weeds control and cowpea yield.
An experiment was conducted as randomized complete block design with three replications at the research field (36° 25’E, 54° 58’N, 1349 m a.s.l.) of Agricultural Faculty, Shahrood University of Technology in 2015. Treatments were included; weeding all season, no weeding, trifluralin according to the recommended dose (2 ton ha-1), foliar application of wheat straw extract (concentration of 50%), foliar application of wheat straw extract (concentration of 100%), the application of wheat residue mixed with the soil at a rate of 2 ton ha-1, the application of wheat residue mixed with the soil at a rate of 4 ton ha-1, the application of wheat residue mixed with the soil at a rate of 8 ton ha-1, foliar application of barley straw extract (concentration of 50%), foliar application of barley straw extract (concentration of 100%). Statistical analysis of data was performed with MSTAT-C software and means were compared with LSD test at the 5% level of probability.
The results showed that the effect of treatments was significant (P 0.01) on weed density and dry weight. Soil incorporation with wheat residue at a rate of 4 and 8 ton ha-1 significantly decreased weed density than non-weeding treatment. Seed number per pod, biological and grain yield of cowpea significantly increased in the soil incorporation with wheat residue at a rate of 8 ton ha-1 compared to control. Our results showed that weeding and soil incorporation with wheat residue at a rate of 8 ton ha-1 increased cowpea yield by 78.23 and 80.79% compared to no weeding treatment, respectively. Wheat is a potent source of bioactive phytotoxic compounds representing three main classes as phenolic (hydroxybenzoic, vanillic, pcoumaric, syringic and ferulic acids being most frequently reported and transferulic and trans-pcoumaric acids being the dominant acids), cyclic hydroxamic acids (a class of alkaloids) and short chain fatty acids. It is reported that wheat extract compounds can interfere with basic processes of receiver plants as photosynthesis, cell division, respiration and protein synthesis and indirectly provoke other forms of stresses. Thus, these compounds can reduce weed germination and growth. Another important effect of these allelochemicals is the activation of cellular antioxidant system in response to uncontrolled production and accumulation of reactive oxygen species. The reason for increase in grain yield was the control of weeds and probably the allelopathic effects of crop water extracts promoted the wheat growth which ultimately increases grain yield.
Conclusions : The present study concluded that wheat phytotoxins in straw inhibited germination and seedling growth of weeds, and the inhibition was concentration-dependent. Also wheat straw added to soil increased yield and some traits of cowpea. In general, the results showed that wheat straw can reduce weed suppression and can improve characteristics of plant, moreover, decreased environment risks of chemical inputs and ensure sustainability of production in long time.