The effect of ultrasonic waves and seed priming in conjunction with weed management on yield and yield components of cowpea (Vigna sinensis L.)

IntroductionThe mechanism of seed priming is to initiate the repairing system for membrane and the metabolic preparation for germination through controlling water absorption rate of seed. As a result, the germination capability and resistance to unfavorable conditions of seed can be promoted obviously. Ultrasound is defined as acoustic waves at frequencies greater than 20 kHz that can be an effective method of improve germination and growth characteristics of plants. Mirshekari et al. (2013) found that treating common narrow seeds with ultrasonic irradiation increases its germination and primary growth. There is no knowledge about the effect of ultrasonic waves and seed priming on plant competition with weeds. Thus, the objective of this research was to study the effect of ultrasonic waves and seed priming on yield and yield components of cowpea (Vigna sinensis L.) in competition with weeds.
Materials and MethodsExperiment was conducted at the research field of Shahrood University of Technology (latitude of 36° 25 'N and longitude of 54° 57' E with an elevation of 1345 m) as randomized complete block design with four replications in during the growing season of 2013-2014. Treatments included; ultrasonic waves (ultrasound) no weeding, ultrasonic waves weeding (all season), ultrasonic waves reduced herbicide dose (trifluralin 1 L.ha-1), ultrasonic waves the recommended herbicide dose (2 L.ha-1), hydro-priming no weeding, hydro-priming weeding, hydro-priming reduced herbicide dose, hydro-priming recommended herbicide dose, no weeding, weeding (all season), recommended herbicide dose, and reduced herbicide dose. In hydro-priming treatment, seeds were treated with water before sowing for 7 hours. Also for ultrasonic treatment, the seeds before sonication (for 6 minutes) treated with water for 7 hour. Trifluralin used in recommended dose (2 L.ha-1) and reduced herbicide dose (1 L.ha-1), therefore immediate mixed with soil before planting. Statistical analyses of data were performed with statistical software MSTATC. Significant differences between means refer to the probability level of 0.05 by LSD test.
Results and DiscussionThe results showed that all treatments decreased significantly biomass and density of weeds in comparison to control (no weeding). No significant difference was observed in density and shoot biomass of weeds between the application of hydro-priming trifluralin 1 L.ha-1 and ultrasonic waves trifluralin 1 L.ha-1 with trifluralin 2 L.ha-1 treatment. Hydro-priming reduced herbicide dose and ultrasonic waves reduced herbicide dose treatments decreased total weed biomass by 61 and 46.5% in comparison to using reduced herbicide dose treatment. In this regard Abbasdokht et al (2012) reported that density and shoot biomass of weeds was similar between reduced herbicide dose (Nicosulfuron 40 g.a.i. ha-1) hydro priming and recommended herbicide dose (Nicosulfuron 80 g.a.i. ha-1). During priming, seeds are partially hydrated so that pre-germinative metabolic activities proceed, while radicle protrusion is prevented, then are dried back to the original moisture level (McDonald, 2000). Ghassemi-Golezani et al, (2008) suggested hydropriming as a simple and effective method for improving seed germination and seedling emergence of lentil in the field. Also the results indicated that the combined use of ultrasonic waves weeding (all season) treatment increased grain and biological yield by 62 and 52.3 percent in comparison to control (no weeding) treatment respectively. Rajabian (2013) reported that seed pretreatment of corn by ultrasonic waves increased the grain and biologic yield in comparison to control significantly. The results indicated that no significant difference was observed in grain yield between the application of hydro-priming trifluralin 1 L.ha-1 and ultrasonic waves trifluralin 1 L.ha-1 in comparison to trifluralin 2 L.ha-1 and weeding (all season) treatments. Whereas, sowing pretreated seeds by ultrasonic waves and hydro-priming in soil containing recommended trifluralin dose decreased the investigated traits in comparison to application of pre-treatments alone and recommended herbicide dose. In this regard, Moradbeygi and Khara (2011) observed a significant reduction due to increased trifluralin concentrations on root and shoot length and dry weight of sunflower plants. Based on Yaldagard et al, (2008), one of the possible explanations could be that the mechanical effects of ultra-sonication produced numerous small holes in the coating and after steeping in the water a significant rise in seedling moisture resulted. It has been suggested that the sonication process accelerates the imbibition of water through the pericarp. Sonication may create or enlarge fissures in the protective coating surrounding the seed and pericarp. The superiority of sonication may be due to a higher holding capacity and higher porosity, which increase oxygen availability. Generally it seems that pre-treatment of cowpea seeds by hydro-priming and ultrasonic waves can increase competitiveness of bean plant with weeds through increasing crop growth rate. The results showed that proper combination of trifluralin herbicide along with seed priming could be used to control the weeds in the bean and obtain seed yield comparable with weed-free conditions.
ConclusionBoth hydro-priming and ultrasonic waves had the effects on accelerating germination and improving competitive ability of bean plant. Hydro- or ultrasonic waves priming showed better plant growth than that without priming treatment when exposed to competition conditions. Pretreated seeds in combination to low herbicide dose had the best effects on the weed suppression and increasing crop yield. Based on our results, priming and sonication of seeds in combination with reduced dose of herbicide can be an effective method of weeds control and increase crop yield and also reduce herbicide consumption.