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1.1 Background of the study

Soybean (Glycine max l.) is one of the most important leguminous crops grown for its high nutritive value. Soybeans are believed to have originated in East Asia and the site of domestication can be traced back to Northern china where it was one of the main crops in the 11th century B.C. It was then distributed to the USA and tested by the scientific Agricultural school and then worldwide by missionaries. It was introduced in African from china late in the 19th century and is now widespread across the continent (lance & Benson, 2005).In South Africa, soybean was firstly believed to be grown in the cedara memories of 1903 and research station at Potchefstroom in the early 1950s from where the cultivar Geduld was developed and released (DAFF, 2010). This was the most important cultivar up to the early 1980s. Initially, soybean production was limited to bapsfontein and the Northern lowveld areas and it became important in rotation with wheat in irrigation areas (DAFF, 2010.).

A research report by Rodney (201gt2). Shows that soybean production in South Africa is currently 655700 tons per annum with an average yield of 1.39t ha-1 under dry- land condition. According to DAFF (2010), Mpumalanga province produces the largest quantities of soybean (about 42%). The Free State produces 22% of the total harvest, while KwaZulu-Natal produces 15%, Limpopo 8%, the North West 5% and Gauteng 2%.This crops is given as a cash crop by both small and commercial farmers.

According to lance and Benson (2005), Soybean is one of the larger in terms of cash sales and the number one export crop as whole soybean, Soybean meal and soybean oil in the united states of American, while South Africa is net importers of soybean oil cake. Dugjie et al. (2009) .That soybean seeds contain about 18-20% oil on a dry matter basis, and this is 85% unsaturated and cholesterol- free. It is mainly used as a protein supplement, beneficial as building blocks in the bodies of both humans and animals (Merit & Jenks, 2004). Miniello and Moro (2003) and Giampietro et al. (2004) indicated that soybean can be used as protein substitute in various baby formulas in cases where infants are allergic to pasteurized cow milk which affect their growth and development. Not only soybean a food source for humans, but is also used as a fodder crop for animals.

Lance and Benson (2005) clearly stated that soybeans are often used as forage crop rather than harvested for seed which is rich in omega- 6 and important in animal health. This crop is first growing and high yielding if grown in soil with a good supply of essential nutrient, hence good soil fertility management, soil fertility, according to Rooyani and Badamchian (1986). Is the ability of the soil to supply essential in appropriate forms, quantities and proportions for optimum plant growth.

The nutritional requirement of soybean are moderately high in comparison with other grains and the crops does best in soils of medium to high fertility and with a favourable soil PH of around 6.5(franzen,1999) while making good use of applied fertilizers (Gregorire, 2005). Therefore, even when the best soybean varieties and cultural practices are used it could result in the crop not reading full potential unless soil fertility is properly managed (Alan et al., 2005). In addition, soybean plant soil that require a loose, well- drained loamy soil that allows for good aeration and water – holding capacity (Edumame, 2005).

A study by George (2001) also showed that the soybean plant has a strong tap-root system and is able to use nutrients on the subsoil very effectively. However, research on soil testing reported that about 28% of the soil samples for soybean cultivation, tested low to very low in available p and k (George, 2001.). Gregoire (2005.) also reported that, approximately 60% of p and 50% of k taken up by a soybean plant is removed from the field when the seeds are harvested .As such, if availability is low, a band application of 4.5 to 14 kg ha-1 is beneficial and if the soil is low is low in k, 2.5 kg ha- 1 is required to raise the soil k test by 1mg kg -1 with the recommended fertilizer source being potassium sulphate (Gregoire, 2005).

Some researchers have shown that a response to p fertilization should not be expected if the soil test for p is higher than 20-25 mg kg-1 (measured by bray-1 producer). As like phosphate use, the response to potash fertilization should not be expected if the soil test for k is higher than 120 mg kg-1 (George, 2011). Phosphate and potassium play an important role in the growth and development of soybean. They increase frost and disease tolerance, palatability, storage quantity as well as yield (Manitoba soil fertility Guide, 2004). Phosphate specially, enhances photosynthesis rates, enzymatic activity, root development, uptake and transfer of other nutrient and seed germination (Snyder, 2000. Phosphorus deficiency is reported to reduce nodule formation and growth while an adequate supply leads to good development of nodules (wall et al, 2000).

However, very high soil phosphate value may depress seed protein and oil content while yielding will be low if available phosphorus is less than 30 kg p ha-1 (DAFF, 2010). Similarly, k regulates several plant processes including; water and nutrient transport across cell walls, and regulation of water vapour and carbon dioxide (co2) exchange through stomata. Potassium deficiency is reported to cause stunted growth and chlorosis (George & Michael, 2002). University of Minnesota. Since soybean are very efficient in deriving most of their nitrogen needs through N- Fixation, no additional N fertilizer application is required (George 2011). For this reason, the application of other essential nutrient elements like p and k for soybean is often over looked with the myth being that soybean don’t need fertilizer management at all.

This culture of ignoring soybean p and k fertilizer application is a problem amongst farmers in south Africa resting in (1) incorrect p and k application rates used and (2) a lack of knowledge on how soil properties like soil PH, soil structures and /or drainage affect the availability of these nutrients. Research has indicated that low PHwater (<5.0) or very high phwater (> 8.0) affects the cycling and overall availability of N, p and k in the soil (Rooyani & Badamchina, 1986). They indicated that the micro-organisms that fix N survive well in a neutral to be conditions can combine with acids cations (Fe, cu and Zn) resting in plant inaccessible compounds (murata, 2003).

Therefore, soil amendment like application of lime to correct PH should not be neglected when applying p and k fertilizers (Adam, 1980..The fact is that if one wants to manage soybean for higher yields, a good long term fertility plan needs to be in place. Thus, to obtain higher yield levels, soil fertility status and plant nutrient concentration must be monitored and adjusted to ensure adequate nutrient availability (Venter, 2003). Thus, the study is aimed to detect the potential effect of direct applied p and k on the overall productivity and yield of soybeans.

1.2 Statement of the Problem
Soybean has become an important crop in Enugu state due to its supply of proteins and oil. In spite of its importance as a source of protein and oil, researchers have noted that its production is below potential (FAO, 2008). In the past, researchers have been emphasizing on inorganic fertilizer to foster the production of crops including soybean. However declining soil fertility and high fertilizer costs are major limitations to crop production in smallholder farms in Enugu state Maobe et al., 2004). This has been augmented by intensification of agriculture coupled with the reduction in farm sizes (Saha and Muli, 2000).

Requirements for nitrogen (N) exceed any other major nutrient. Soils in the tropics rarely have enough of this nutrient to produce high sustainable yields (Wringley, 1982). This lack of adequate amounts of nitrogen in most soils puts a limitation on the farmers’ goals of increasing yield per unit area. Rebuilding soil fertility in traditional agricultural systems has been achieved through long duration fallow periods (Poubom et al., 2005). However, with increased human population and land pressure, long fallow period are no longer feasible (Gichangi et al., 2002). The quantity of nitrogen needed for agriculture is projected to increase in the period up to 2030 (Tillman et al., 2001) and would lead to greater environmental degradation.

Reduced dependence on fertilizer nitrogen and adopting farming practices that favour the more economically viable and environmentally prudent nitrogen fixation will benefit both agriculture and the environment (Vance, 2003). There are several options which are available to manage nitrogen in farmers’ fields with chemical fertilizers often considered to be an immediate answer to the current nutrient deficiencies in soils (Woomer et al., 1997). Unfortunately, commercial nitrogen fertilizers are expensive and out of reach to most small-scale farmers. As a result cheaper sources of nitrogen need to be sought if yields are to be sustained and food security attained. Biological materials may offer a solution in alleviating soil fertility problems and hence increase in crop production.

The farm derived sources such as crop residue, compost, manure and household waste has commonly been used by farmers in the management of soil fertility (Kimani et al., 1998). Animal manure and compost are beneficial in soils because they can increase the water holding capacity and caution exchange capacity (Nandwa, 1995). Therefore, the use of organic inputs as external nutrient sources can be used as alternative to expensive fertilizer. In addition, countries where nitrogen fertilizers are imported and the technology for manufacturing them are limited or too expensive to afford (Mwangi, 1994).

1.3 Aims and Objectives of the Study
i. To determine the effect of the manurening on the vegetative growth soybean in Enugu State (Glycine max (I) merril).

Specific Objectives
I. To determine the effect of different soil fertility amendments on soybean nodulation and yield.

II. To assess the effectiveness of local isolates of slow and fast growing soybean rhizobia in nitrogen fixation.

1.4 Research Questions
i. What are the effect of the different soil fertility amendments on soybean nodulation and yield?

ii. What are the assess of the effectiveness of local isolates of slow and fast growing soybean rhizobia in nitrogen fixation.

1.5 Research Hypotheses
i. Soil fertility amendments have no effect on soybean nodulation and yields

ii. Effectiveness of nitrogen fixation in soybean is not influenced by different rhizobia isolates.

1.6 Significance of the Study

In the Economic Recovery Strategy (ERS) for wealth creation and employment creation, (Government of Kenya, 2004. Economic Recovery Strategy for Wealth and Employment creation, Government, printer, Nairobi, Kenya. The Enugu state government identified agriculture as an important vehicle for the realization of its employment creation and poverty reduction objectives. According to this strategy, the government’s vision is to transform Enugu state agricultural sector into a profitable economy (Government of Enugu state, 2016). This transformation calls for fundamental shift to market oriented production, diversification of soybean agriculture and adoption of greater use of appropriate farming practices.

Soybean is one such crop that has the potential to make significant contributions to healthcare (Government of Enugu state, 2006). To date, Enugu state is an importer of soybean since its production (5,000 MT) cannot meet the ever increasing demand of 100,000 MT (GTZ, 1996). Greater demand is being made on alternative and inexpensive sources of nitrogen (Mwangi, 1994). (By Mwani. Effect of Bradyrhizobium Inoculation and Nitrogen Fertilization on Growth, Nodulation and yield of Msc. Thesis, University Nariobi. Hence use of natural manure is seen as an answer to small scale farmers in soybean production in Enugu state as it does not only save on expensive farm inputs but also protects the environment from effects of commercial fertilizers.

This research was therefore formulated to assess the effect of soil amendment with manure (poultry and farmyard) on the plant growth, nodulation and yield respectively as compared with inorganic fertilizer and to establish the symbiotic effectiveness of slow growing Brady rhizobium and fast growing Sino rhizobium in fixing nitrogen with promiscuous and non-promiscuous soybean varieties. (By Otieno, Muthomi, Cheminingwa, and African Crop Science Society 8: 305-312.

1.7 Definition of Operational of the Terms
- is the one of a group of delicate and often colourless hair like outgrowths found in certain algae and the gametophyte generation of bryophytes and ferns?

Fastidious - being careful that every detail of something is correct.

Legume - any plant that has seeds in long pods. Peas and beans are legumes.

Flavonoid – one of a group of naturally occurring phenolic compounds many of which are plant pigments.

Inoculum – a small amount of material containing bacterial, virus or other microorganisms that is used to start a culture.

Lysimeter – an instrument used to measure the loss water from an area of land covered with vegetative.

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