Effect of Chlorine Treated Water on Germination and Growth of Cowpea Cultivars (Vignaunguiculata L. Walp)
Abstract
Effects of different water qualities (WQ1- WQ5) of varying chlorine contents were tested on the growth and germination of four varieties of cowpea (Vignaunguiculata) IT03k 131-2 (v1), IT99k -573-1-1(v2), UAM09 1046-6-1 (v3) and UAM09 1055-6 (v4). The experimental design was factored using Completely Randomized Design (CRD) with three (3) replicates for each treatment of the five (5) water qualities for four (4) cowpea varieties. Growth parameters, germination rate, seedling vigor indices and chlorophyll content were measured. The interactions of cowpea variety and water quality had no significant effect on the any growth parameter tested (p>0.05). Variety factor was largely insignificant (p>0.05) with minor exceptions. Water quality factor had significant effects on all growth parameters of cowpea (p<0.05). Germination rate was highest in pond water (no chlorine) but least in disinfected water when10g and 20g of chlorine were applied. Percentage germination recorded the high values of 98.6% and 95.8% in pond and river water respectively. Water-treated plant without additional chlorine had the same germination with river water (95.8%). 10gCl and 20gCl added to disinfected water reduced cowpea germination to 10.1% and 0.5% respectively. Chlorination had significant effects on seedling height from 7 day to 28 day after planting (p<0.05). Seedlings treated with disinfected water were the tallest at 28 day after planting (18.1cm) followed by river and pond water (16.2cm and 16.1cm respectively). Heights of seedlings reduced drastically to 0.5cm on addition of 10g and 20g of chlorine. The two best vigour indices were found among seedlings treated with pond water (1186) and disinfected water (1172). Vigour were significantly reduced when seedlings were treated with additional chlorination (p<0.05). The same trend was observed in the germination speed indices of seedlings. Shoot and root weight were also reduced by chlorine. Disinfected water +10g of chlorine and disinfected water +20g of chlorine recorded zero weight (0.000g). The highest chlorophyll content was found in the leaf of plant treated with disinfected water (1.799) followed by river water (1.658) and pond water (1.402). No chlorophyll test was conducted on plants treated with additional chlorine as they died off before maturity when treated with DFW+10gcl and DFW+20gcl. As a result, normal disinfection yielded the same result as pond and river water having no significant effect on the growth parameters evaluated. However, additional chlorination (DFW+10gcl and DFW+20gcl) significantly affected the cowpea cultivars (p<0.05).Therefore, municipal water treated with chlorine for drinking should be considered safe for irrigating the crop. However, high chlorine concentrations adversely affect the crop and this outcome may also be applicable to other commercially cultivated crops of huge importance to the economy.
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Introduction
Cowpea is of Africa and Asian origin (perrino et al., 1993, Ogunkanmi et al., 2005). In Nigeria, it is grown all over the country but with varying sowing dates. The major cultivation centre includes Kano, Katsina, Bauchi, Borno, Sokoto and Niger in the North, Ibadan, Owo, Benin and Asaba in the South (Rachie, 1985).The cowpea (Vignaunguculata) is one of several species of the widely cultivated genus Vigna. Four subspecies are recognized, of which three are cultivated (more exist, including textiles pubescens, and sinensis) (Perrino et al., 1993). Most cowpeas are grown on the African continents, particularly in Nigeria and Niger which account for 72% of world cowpea production (FAO, 2015). Cowpea are grown mostly for their edible beans, although the leaves, fresh peas and fresh pea pod can also be consumed, meaning the cowpea can be used as food source before the dried peas are harvested (Ehlers and Hall, 1997).Cowpea is an important source of food for humans in poor arid regions the crop can also be used as feed for Livestock this predominantly occurs in India, where the stock is fed cowpea as forage or fodder (Singh et al., 1997). Cowpea provides a rich source of proteins and calories as well as minerals and vitamins. A cowpea seed can consist of 25% protein and is low in anti-nutritional factors (Rangel, 2003). The diet complements the mainly cereal diet in countries that grow cowpeas as a major food crop (Philips, 2003).
The demand for cowpea production keeps increasing as it is one of the cheapest source of protein and as such the production cannot be narrowed only to seasonal (rainfall) production. The increase in cowpea production also depends on other production practices such as irrigation using other available water qualities (such as pond, river or disinfected domestic water). The roles of water in the seed germination, plant growth and physiological functions cannot be over emphasized (Taylor et al., 2007). In the commercial production of cowpea, different types of water from different sources are used in irrigation most of which are disinfected with chlorine. Poor yield may be ignorantly attributed to other factors without prior knowledge of the effect of chlorine content on the general well being of the plant. Water quality varies from source to source. Different sources of water are commonly used by growers to irrigate crops in Nigeria among which are: well water, municipal water and pond water. Chlorination is used to kill certain bacteria and other microbes in tap water as chlorine is highly toxic. In particular, chlorination is used to prevent the spread of water borne diseases such as cholera, dysentery, jaundice, typhoid etc. (EPA, 2014). Disinfection by chlorination can be problematic, in some circumstances. Chlorine can react with naturally occurring organic compounds known as disinfection by products (DBPs). The most common DBPs are trihalomethanes (THMs) and shaloacetic acids (HAAs), which mainly responsible for health hazard (WHO, 2011). This present study was designed to determine the effect of chlorine on germination and growth by comparing chlorinated water with municipal and natural water bodies. The most effective water quality would be recommended for cowpea irrigation.
Conclusion
In conclusion, this present study has revealed that the low level of chlorine in municipal water supply does not affect cowpea germination and growth with 95% confidence limit. Therefore, municipal water treated with chlorine for drinking should be considered safe for irrigating the crop. This may also be applicable to other crops. However, high chlorine concentrations adversely affect the crop. In addition more highly demanded crops should be tested under greenhouse and field conditions and at lower concentration of chlorine other than the level used in this experiment.
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