ABSTRACT
Some plants exhibit allelopathy by which they exclude other plants from their vicinity or limit their competitive ability. Allelopathy is achieved though the release of chemical substances which inhibit the growth of other susceptible plants. Effluents of milled cassava contain some levels of cyanide which have allelopathic properties. This study sought to investigate the exploitation of this property for weed management in some arable crops.
A laboratory experiment was conducted to evaluate the effect of cassava effluent (CE) at 120, 240, 360, and 480 grams cyanide per hectare (g CN/ha) on germination of kenaf (Hibiscus cannabinusL.), cowpea (Vigna unguiculataL.), okra (Abelmoschus esculentusL. Moench), maize (Zea maysL.), rice (Oryza sativaL) and tomato (Lycopersicon esculentumMill.). The experiment was laid out in Completely Randomised Design (CRD) with three replicates. Four screen-house experiments were each laidout in CRD with three replicates. These include three separate factorial experiments with CE concentration of 60, 120, 180, and 240 μgCN/kgsoil. The first factorial experiment evaluated the effect of CE concentration applied at pre-plant intervals of seven, fourteen and twenty-one days on growth and yield of okra. The second factorial experiment evaluated the effect of CE concentration that were pre-plant and post-plant applied one to four times on okra. The third factorial experiment evaluated the effect ofCE concentration applied one to four timeson weeds. Pre-emergence and post-emergence CE applications of 6, 12, 18, and 24 g CN/ha were evaluated on weeds in another experiment. The soil chemical properties, microbial (bacteria and fungi) counts, weed weight, weed density and weed flora composition were evaluated. Control treatments (where CE was not applied) were included in all the experiments. Field trials were conducted in 2017 and 2018 to determine the herbicidal efficacy of CE and the resulting weed index. The treatments were different weed control methods from CE, hoe weeding, and pendimethalin in okra plots. These were laidout in Randomized Complete Block Design in three replications.
The results showed that okra germination was more tolerant to CE. Pre-plant application of CE influenced growth of okra but did not significantly reduce okra yield. The phytotoxic effect of CE reduced with increasing pre-plant interval. CE application of 7 or 14-day pre-plant interval reduced the growth of okra but did not reduce the yield. There was an interaction between CE concentration and frequency of application on seedling growth but did not reduce the yield. Soil Na, K and Mn increased with application of CE irrespective of the frequency of application. These increased with increasing concentration of CE. Some weed species, mainly Mitracarpus hirtus(L.)were controlled by CE. Control tended to increase with increasing concentration of CE. Panicum maximum(L.) and Cyperus rotundus(L.)were tolerant to CE. Irrespective of the frequency of application, none of the CE concentrations applied to the soil could reduce both the weed density and the weed weight, whereas foliar application of 24g CN/ha did in the screen-house but was ineffective on the field. The CE has some level of weed control but it may not be a reliable method of weed management.
