Effect Of N:P:K And Poutry Manure On Population Of Rhizobia Bacteria, Growth And Yield Of Cowpea
The attendant low yield of cowpea among smallholder farmers has increased the need for site specific fertilizer recommendation and integration of biological materials to increase the yield of the crop. The effectiveness of applied fertilizer is constrained by the use of the in appropriate rate and improper timing of sowing. Rhizobia inoculant, on the other hand, needs a balanced nutrient application to increase crop yield. The study was designed to: i) determine the effects of inoculant, P and K mineral fertilizers on N,P,K uptake, growth and grain yield of cowpea, ii) evaluate the effect of NPK fertilizer application on the growth and yield of cowpea in the Guinea and Sudan Savanna zones of Nigeria, and iii) simulate the potential yield, yield gap, best sowing date, growth and yield of cowpea using CROPGRO – cowpea DSSAT model. The response of cowpea to rhizobia inoculation and fertilizer application revealed that sole application of inoculant was not sufficient to raise cowpea yield except when combined with 30 kg P2O5 ha-1 and 20 kg K2O ha-1. The yield response to mineral fertilizer also showed that K is very essential in determining cowpea yield and should therefore, not be omitted in any fertilizer recommendation rate. CROPGRO – Cowpea model was used to simulate the response of cowpea to different N rates, potential yield and the best sowing dates for cowpea. The model was calibrated for Omondaw cowpea cultivar using data from the experiment carried out at Kwara (Ferric Lixisol) and Kano (Ferric Luvisol) during the 2012 and 2013 cropping seasons. The model performance was evaluated statistically using RMSE (0.13 tons ha-1), CV (RMSE) (9.9%) and Wilmott index of agreement d (0.97). A long term seasonal analysis using the model was able to detect that 15 kg N ha-1 is optimal for Ferric Lixisol while 20 kg N ha-1 was optimal for Ferric Luvisol. To avoid crop failure, sowing window for Kwara ranged from July 11 to July 21st while that of Kano was extended to 26th July with consideration for August 5th. The yield gap analysis revealed that a wide gap exists between climatic potential yields and yields obtained from farmers‟ fields. The gaps between potential and research station yields (yield gap 1) ranged from 1.05 to 18 % of potential yield, while that of the farmers field was 84.21 % for Kwara soil and 79.55 % for Kano soil. It is necessary to reduce the yield gap by using site specific fertilizer recommendation and appropriate timing of sowing dates.
1.1 Background of the study
Cowpea (Vigna unguiculata) is a leguminious crop with a very vast importance and plays an active role in maintaining the ecosystem, nutrient requirement and the economy of many countries. A considerable amount of cowpea of more than 5.4 million tons are produced in the world annually with Africa producing nearly 5.2 million tons and Nigeria recorded as the greatest producers accounting for about 61% of cowpea production in Africa and 58% of the world cowpea production [IITA, 2009].
According to Wikipedia on Cowpea (2012), and IITA,( 2009); cowpea is one of the most important food legume crop in the semi arid tropics covering Asia, Africa, Southern Europe, and Central America and originated and domesticated in Southern Africa and Asia. [wikipedia/cowpea, 2012. IITA, 2009].
However, some constraint such as agro-ecological constraint, cultivation in marginal and sub marginal land, unpredictable and poor distributed rainfall, lack of soil fertility, seasonal constraint, low productivity, susceptible to pest and disease, flower shedding, tendril formation, lack of adaptive high yielding varieties have been reported to inhibit production of cowpea in some area [Maria et.al,2008].
The practice of shift cultivation to improve soil fertility and enhance production can no longer be sustained due to rapid increase in the world population. Therefore it is necessary to device an improved ways by which the soil fertility can be improved and sustained within the posible shortest time to ensure continual productivity.[ Ayoola et.al 2007]. The use of cover crop such as cowpea have been known to improve the physical , chemical and biological properties of soil.
N:P:K, a mineral fertilizer produced artificially consisting of equal proportion of nitrogen, phosphorous and potassium which are primary macro minerals essential for optimum growth and development of plants. And also used to enhance the productivity of soil.
Poultry manure is an organic manure composed of feacal waste from domesticated birds [poultry] and wood shavings which is added to the soil to enhance the biological , physical and nutrient status of the soil.
Rhizobia are group of bacteria that forms association with the legumes and fix free atmospheric nitrogen to form useable by plants [Ovstyna,2005]. These organisms are usually enhanced by the presence of leguminious plants and organic matter in the soil [FAO, 2005].
Plants obtain nutrient from two natural sources i.e organic matter and inorganic minerals. Organic matter e.g poultry manure release its minerals to the soil through decomposition [FAO,2005]. In the decomposition process, both the soil nutrient and organism present in the soil is increased[Ingham,2000] And according to them, only carefully selected diversified cropping system or well managed mixed crop livestock system are able to maintain a balance in nutrient and organic matter supply and removal.
Changes in land use associated with deforestation and inappropriate land use management has had a negative impact on approximately 2 billion hectares of agricultural land [Pinstrup-Anderson and Pandy Lorch 1998]. Hence, need to improve the soil with organic and inorganic manure to bring about increased productivity. Some other researchers said that land degradation result in the productive decline of soil and can be attributed to changes in the physical, chemical [minerals], and biological attributes from some ideal state brought about by natural or anthropogenic influences [Latham 1994, Lal 1990].
1.2 Objective of the Study
The overall objective of this study was therefore, to improve yield of cowpea in the Guinea and Sudan savanna zones of Nigeria using rhizobia inoculant and site specific fertilizer recommendation.
The specific objectives were to:
- Assess the influence of inoculant, P and K fertilizers application on nutrient uptake, growth and grain yield of cowpea,
- Determine the effect of NPK fertilizer application on the growth and yield of cowpea in the Guinea and Sudan Savanna zones of Nigeria
- To simulate potential yield, yield gap, best sowing date, growth and yield of cowpea using CROPGRO – cowpea DSSAT model.
1.3 Hypotheses of the Study
The above specific objectives were formulated to test the following null hypotheses:
- Nutrient uptake, growth and grain yield of cowpea is not influenced by inoculant, P and K fertilizer application,
- Growth and yield of cowpea in the Guinea and Sudan Savanna zones of Nigeria is not affected by the application of NPK fertilizer,
- Potential yield, yield gap, best sowing date, growth and yield of cowpea cannot be simulated using CROPGRO – cowpea DSSAT model
Summary, Conclusions and Recommendations
The overall objective of this study was to improve yield of cowpea using rhizobia inoculant and site specific fertilizer recommendation.
The study contributed to this objective by:
- Determining the effect of inoculant, P and K fertilizer application on nutrient uptake, growth and yield of cowpea;
- Determining the effect of NPK fertilizer application on the growth and yield of cowpea in the Guinea and Sudan savannah zones of Nigeria;
- Simulating potential yield, yield gap, best sowing date, growth and yield of cowpea at different N rates using CROPGRO – cowpea DSSAT model.
Combined application of rhizobia inoculant with P2O5 and K2O significantly increased cowpea grain yield with both locations showing similar response. The application of inoculant with 30 kg P2O5 ha-1 and 20 kg K2O ha-1 enhanced cowpea yield than sole application of the inoculant. The yield obtained from IN – 30 – 20 kg
P2O5- K2O ha-1 was not different from that obtained with the use inorganic fertilizer (20 – 30 – 20 kg N-P2O5- K2O ha-1). The application of IN – 45 – 20 kg N-P2O5-K2O did not give a significantly higher yield than that obtained from IN – 30 – 20 kg P2O5- K2O ha-1on the Ferric Luvisol. Rhizobia inoculation increased biomass N content which was an indication of enhanced BNF by the inoculant. Application of IN – 30 – 20 kg P2O5- K2O ha-1 proved to be economically viable more than the other fertilizer application rates. This study has therefore evaluated the effectiveness of the inoculant in increasing cowpea grain yield in the Guinea and Sudan savanna zones of Nigeria and can therefore be introduced for use to the farmers in the area.
The application of NPK fertilizer significantly increased grain yield of cowpea at both study locations. Fertilizer rate equivalent to 30-0-30 kg N-P2O5- K2Oha-1 gave the higest grain yield on the Ferric Luvisol but not significantly different form the yield obtained from application of 20 – 30 – 20 kg N-P2O5- K2O ha-1. There was a marginal difference between low fertilizer rate application and high fertilizer rates for the Ferric Luvisol suggesting that a farmer could still break even with the low rate application of fertilizer. Application of 20 – 30 – 20 kg N-P2O5- K2O ha-1 gave the highest grain yield at both study locations. Grain yield was considered as the most important yield related variable while grain P uptake and grain K uptake for the nutrient related variables.
Grain P and K uptake contributed more to the yield obtained on the Ferric Lixisol while only grain K uptake proved to be important for the Ferric Luvisol.
Comparison between simulated and observed yield at harvest for the fertilizer rates used in calibrating the model showed good performance of the model. The RMSE value was 0.13 tons ha-1. The CV (RMSE) was 9.9% (<20%) while Wilmott index of agreement (d) however gave a value of 0.97. The seasonal analysis results for the Ferric Lixisol indicated that the level of starter N for optimal grain yield of cowpea was 15 kg N ha-1. However, 10 kg N ha-1 could also be beneficial depending on the resource availability of the farmer. There was no need applying up to 20 kg N ha-1 since 10 and 15 kg N ha-1 gave a higher yield at 50% level of probability. For the Ferric Luvisol, application of 5 kg N ha-1 gave a yield of 1.9 tons ha-1 followed closely by 15 kg N ha-1. Fertilizer rates of 10 and 20 kg N ha-1 gave same yield of 1.8 tons ha-1 which agreed with the result obtained from the field experiment. There were was marginal difference between the comparison of low fertilizer rate application and high fertilizer rates. Twenty kg N ha-1was considered as optimal for cowpea production in this area. A wide gap existed between climatic potential yields and the yields obtained from farmers‟ fields. The gaps between potential and research station yields (yield gap 1) ranged from 1.05 to 18.00% of potential yield, or 0.02 to 0.41 tons ha-1 (Table 4.23) while that of the farmer‟ field was 84.21% for Kwara and 79.55% for Kano.
On the basis of the studies conducted to improve cowpea production in the Guinea and Sudan Savanna zones of Nigeria using rhizobia inoculant and fertilizer application, the following conclusions were drawn:
- Sole application of the inoculant was not sufficient to increase cowpea yield in the study area except when combined with 30 kg P2O5 and 20 kg K2O ha-1. Inoculation increased the number of nodules, nodule dry weight and biomass N content which was an indication of increased BNF. The rhizobia inoculant therefore could be a viable replacement of N fertilizer and subsequently reduction in input cost.
- Phosphorus was not the limiting nutrient for the Ferric Luvisol soil as is common with soils of the savanna. However application of N should be accompanied with the application of P and K to avoid P deficiency through crop removal in the long run. The promising fertilizer rates selected for optimal cowpea yield at both sites were 20 – 30 – 20 and 10 –15 – 20 kg N-P2O5- K2O ha-1.
- The seasonal analysis (20 years) of CROPGRO-cowpea showed that 15 kg N ha-1 was the optimal starter N for the Ferric Lixisol while 10 kg N ha-1could also be considered. The Ferric Luvisol soil required 20 kg N ha-1 for optimum cowpea yield. Simulating potential yield for cowpea in the 2 locations revealed that a wide gap existed between climatic potential yields and the yields obtained from farmers‟ fields. Using the recommended fertilizer rate in isolation may not be enough to close the yield gap due to the climatic risks that exist. Proper timing of sowing will ensure that the crop will receive enough rainfall throughout its life cycle. The sowing window for Kwara was narrower than that of Kano due to the high variability of rainfall. Sowing should be done from July 11 to July 21 at Kwara and July 11 to July 26 at Kano with consideration for August 5th. Sowing outside these dates will be highly risky for the farmer. The analysis generally suggested that a credible pathway for increasing farmers‟ yields involved the use of site specific fertilizer recommendation and appropriate sowing dates.
This study tested the use of rhizobia inoculant as a cheaper source of N and also derived the optimal N rates for cowpea production. Inoculation and starter N application enabled remarkable improvement in grain yield. Hence it is recommended that inoculation with BR3267 or use of starter N fertilizer could be used by the resource-limited farmer to achieve the dual goals of improving yield and maintaining soil fertility in the Guinea and Sudan savanna zones of Nigeria. Promotion of site specific fertilizer recommendation should go hand-in-hand with advice on the best sowing date. This would contribute to achieving the green revolution in Africa.
This study has addressed some of the issues that will boost cowpea production in the study locations, prospective studies need to be carried out on the following aspects:
- Replicating this study in other benchmark soils located within the agroecological zones to capture variability that exists in soil.
- Assessing persistence of the introduced rhizobia strains in the soil after one cropping season to determine if there is the need for yearly inoculation and the N contribution of the inoculant to subsequent cereal crop following inoculation.
- Extrapolating the results of the CROPGRO-cowpea model to other areas not studied using Geographical Information Systems (GIS) tool.
- Simulating the optimal rate of P and K when CROPGRO-cowpea model have been well developed.
- Identification of other factors that contributes to widening the yield gap that exists for cowpea production.
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