Evaluation of Seven Elite Rhizobial Inoculants on It99k5731-1 Cowpea Variety in Soils of Minna Niger State of Nigeria
Abstract
Cowpea (Vigna unguiculataL. Walp) is an important source of dietary protein for man, animals and improves soil fertility through biological nitrogen fixation. However, its production potential is limited by a number of factors, one which may below availability of Nitrogen in the soil which could partly be due to the inadequate numbers of effective rhizobial strains in some soils to fix the required nitrogen. Evaluation of seven rhizobial strains was carried out on yield and yield parameters of cowpea variety IT99K573-1-1 during the cropping season. Prior to the commencement of the trial, soil samples were collected (0-15cm2) from each filed and processed for routine soil analysis. The field trials were conducted in Randomized Complete Block Design (RCBD) with nine treatments replicated at five different locations in Minna. Each of the treatment plots was 36m2 consisting of six manually made ridges of 6m long and an inter-ridge spacing of 80cm. The treatments were; control (no inoculation nor N fertilizer), 60kgNha-1, rhizobial inoculants strains 2NAG53e, 2NAG91a, 2NAG9d, 2NAG5261, CB756 (ref), BR3262(ref) and BR3267(ref). Cowpea seeds were mixed with the inoculants as treatment at planting. All plots received a dose of 30kgPha-1 (as Single Super Phosphate) at planting. Destructive sampling was done at 50% flowering to obtain data on number of nodules, nodules dry weight and shoot dry weight. Data was collected for Pod load, pod weight, 100 seed weight, and grain yield at full maturity. From the fertility and suitability rating all the fields had one or two limiting factor for crop production. There was a significant difference between 2NAG5261and the 60kgNha-1 treatment but all treatments were not significantly different from the control in terms of number of nodules. However, there was no significant difference at (P<0.05) in all inoculated plants, urea fertilized plants and the control. Statistically, there was also, no significant difference at (P<0.05) in all inoculated plants, urea fertilized plants and the control in terms of nodule dry weight. There was a significant different (P<0.05) between strain 2NAG9d and BR3267(ref) but there was no significant different between the control and all the inoculated plants in shoot dry weight. Higher mean value obtained from plants treated with 2NAG9d, indicated percentage increase in shoot dry weight but was not significantly different from the control and the urea supplied plants. Means of statistical analysis indicated no significant difference (P<0.05) for pod weight per plant among all the treatments and the control. The 60kgNha1 treatments, rhizobia strains CB756(ref), 2NAG91a 2NAG53e, and 2NAG9d gave the highest mean values of (1067.2kg, 883.9kg, 878.9kg, 832.8kg and 819.4kg) respectively which were more than the control that had a mean value of 769.4kg. Statistically, there was no significant difference between the control and other treatments. There was no response to inoculation in terms number of nodules, nodules dry weight, shoot dry weight, pod weight per plant, pod weight per kilogram per hectare, one hundred seed weight and total grain yield of IT99K-573-1-1 cowpea variety. The evaluation of these inoculants should also be conducted using other cowpea varieties and other legumes in other places outside Minna in order to capture the differences that may exist in physical, chemical and biological properties of soils because inability of cowpea to respond to inoculation could be attributed not only to the crop variety but also environmental conditions and can be site specific.
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Introduction
Cowpea is avery important leguminous crop which serves as a major source of protein for man and his livestock in developing countries like Nigeria and even some developed countries (Singh 2005; Langyintuo et al., 2003). It is one of the legume crops commonly sown in rotation with both cereals and tubers to replenish nitrogen content of soil, reduces soil erosion and weeds as a cover crop (Sanginga et al., 2003).
Despite its environmental and economic contributions to human existence its production in Nigeria and other developing countries is still 50% below its estimated yield potential (FAO 2012). Many researchers and farmers attribute low yield of cowpea to degraded soil fertility, poor agronomic management and inadequate indigenous rhizobial strains in the soil to effectively convert the atmospheric nitrogen in a usable form through a symbiotic relationship between the cowpea and rhizobia. The application of urea fertilizer has many economic limitations but cowpea has the ability under favorable conditions to derive 65% to 70% accumulated nitrogen from biological nitrogen fixation (Jensen, 1997) which can lead to improved shoot biomass and consequently improved yield parameters and total cowpea yield. Many soils however, do not have adequate amount of native rhizobia in terms of quality or effectiveness to enhance biological nitrogen fixation (FAO, 2012). Adler (2008) also suggested that due to the facts that inoculants price is low compared to the potential benefits it provide, farmers should be encourage to inoculate legumes with effective strains. These situations call for the use of inoculants that are symbiotic effective and can enhance cowpea nodulation, growth and yield. Therefore, the objective of this research was to evaluate the effect and symbiotic effectiveness of seven elite rhizobia inoculants on yield and yield parameters of cowpea variety IT99K573-1-1 in Minna, Niger State of Nigeria.
Conclusion
From the fertility and suitability rating the soil texture and soil pH was suitable for cowpea production and microbes responsible for nutrient cycling. However, each of the fields (replicates) has one or two limiting factor for cowpea production and need more nutrient elements like phosphorus which is very important in nitrogen fixation and absorption.
There was no effect of inoculation in number of nodules, though plants treated with 2NAG5261 had high number of nodules than the plants treated with 60KgNha-1 but could not translate in nodules dry weight and grain yield. Shoot dry weight which is mostly considered to indirectly measure symbiotic effectiveness, nitrogen fixation in legumes had shown no statistical difference in all treatments and showed no significant difference in response to inoculation. There was no response to inoculation in terms number of nodules, nodules dry weight, shoot dry weight, pod weight per plant, pod weight per kilogram per hectare, one hundred seed weight and total grain yield of IT99K-573-1-1 cowpea variety.
This work therefore recommends that further trial of these inoculants should be carried out on other varieties of cowpea and other legumes because different varieties may respond differently to each inoculant due to genetic make-up. The evaluation of the these inoculants should also be conducted in other places outside Minna in order to capture the differences that may exist in physical, chemical and biological properties of soils because inability of cowpea to respond to inoculation could be attributed not only to the crop variety but also environmental conditions and can be site specific.
CONFLICT OF INTEREST The authors declare no conflict of interest.
