CHAPTER ONE
1.0 INTRODUCTION
Soybean (Glycine max L. Merrill) is one of the leading leguminous crops in the world in terms of total production, with 352,643,548 tonnes in 2017 (FAOSTAT, 2019). It is high in protein and an abundant source of vegetable oil (Mahamood, 2008; Dogra et al., 2014; Yagoub et al., 2015). Soybean is cultivated in different Ecological Zones in Africa (IITA. 2008 cited in Kolapo, 2011). In Ghana, it is cultivated in nearly all ecological zones including semi deciduous rain forest, rain forest, Guinea savannah and costal savannah. Soybean production is done in Volta region, Upper West Region, Upper East Region, Central Region and Northern Region. Among these regions, Northern Region is known to be the largest producer of soybeans in Ghana (Lawson et al., 2008), producing about 77% of the national total production with the average yield of 509 to 642 kilograms per hectare (kg/ha) (SRID, 2012). Soybean production in Ghana is done on small scale with low yield because it is usually intercropped with other crops like maize and cassava by local farmers. Farmers produce an average yield of 1.9 metric tonnes per hectare (mt/ha) which is below the achievable yield of 2.3 mt/ ha in the country (Ministry of Food and Agriculture Ghana, 2013). In Sub Saharan Africa (SSA) the average soybean yield has remained at 1.1t/ha in the last forty years below the world average of 2.4t/ha (Khojely et al., 2018).
Fertilizer applications, varieties and lack of rhizobia inoculant application may contribute greatly to the small returns in soybean cultivation in Sub Saharan Africa (SSA) (Khojely et al., 2018). Another constraint affecting soybean production and yield is low soil fertility. Growth and nodulation of the crop is also affected by soil acidity and soil phosphorus status (Ferguson et al., 2013).
Despite the crop’s ability to grow on marginal soils, the genetic potential of improved varieties may not be fully exploited resulting in low yield as a result of nutrient deficiency which affects the growth and yield of the crop (Xiang et al., 2012). The tropical and subtropical soils are low in nutrients, caused by weathering, Erosion also causes low nutrients when rainfalls are erratic and immobilization and fixation of some major nutrients (FAO, 2005; Agwe et al., 2007; Muntala, 2012). Soybean does very well in fertile soil and it is capable of fixing nitrogen due to the symbiotic relationship with Bradyrhizobium Spp. Soils in Ghana are highly weathered soils and have a moderate to strongly acidic surface soil (Owusu-Bennoah et al., 1995; Ghartey et al., 2012;FAO, 2005; Issaka et al., 2012). These have resulted in low organic carbon content with nitrogen and phosphorous being the most limiting nutrients in the Ghanaian soils (Owusu-Bennoah et al., 1995). The presence of Aluminium ion (Al3+) that gets its way into the soil during weathering increases the pH of the soils. This results in the lack of pH dependent nutrients like phosphorus and nitrogen leading to high level of these nutrients not being available for plants to use. The most effective means of improving soil fertility is to increase productivity by the use of mineral fertilizers; however, usage is very minimal due to high cost (Bump, 1994 and Gerner et al., 1995 as cited in Quansah, 2010; Tetteh et al., 2002). In many places, the low level of fertility has a tendency of worsening due to leaching and erosion. There is a severe imbalance in nutrient resources of soils in the country causing a major problem to sustainable management of soils for improved crop growth and yield (Bumb, 1994 and Gerner et al., 1995 as cited in Quansah, 2010; Tetteh et al., 2002).
Biochar is a technology that ensures a retention of organic materials in the soil by preventing rapid degradation of organic materials. It provides conditions suitable for crop production by creating conducive environments for the activities of soil microorganisms, improvement of soil texture,
provision of some necessary nutrients especially P and K as a cheap source of organic fertilizer for growth, development as well as the yield.
Soybean is a heavy feeder of nitrogen and fixes more than 70% of its required N nutrient by forming a symbiotic association with effective rhizobia (Herridge et al., 2008). Soybean requires as much K as N, but P and K uptake are usually required in large amount in the early pod filling stages. Although fertilization is quint essential for the growth and yield of soybean, most farmers are unwilling to apply fertilizers to soybean due to high cost of fertilizers and irregular supply.
Soybean production is the greatest in the northern part of Ghana where the soils are generally poor in P and K which are necessary for nodulation and seed formation. Soybean production is the greatest in the northern part of Ghana where the soils are generally poor in P and K which are necessary for nodulation and seed formation (FAO, 2005). Inoculation with rhizobia has been introduced to farmers in the northern regions of Ghana and biochar has been found to increase nodulation when applied to either the soil or the inoculated seed (Kumaga, 2020). Hence, a huge amount of biochar needs to be applied to the soil aside the application of the biochar which requires much labor. Therefore, the essence of the seed pelleting is to use small quantity of the biochar which will be coated on the inoculated seeds thereby making the farmer reduce or avoid huge spending on purchasing of biochar and labor cost during application.
The objectives of this study were therefore:
- To assess the effect seed pelleting on nodulation, growth and yield of soybean
- To evaluate the impact of different types of amendments on growth and yield of soybean.
- To compare the growth response of the two soybean varieties to pelleting and soil amendments.
CHAPTER TWO
LITERATURE REVIEW
ORIGIN AND DISTRIBUTION
The origin of soybean is uncertain, but many botanists believe it to have been derived from Glycine ussuriensis, a legume native to Central China (Hymowitz, 2008). However, cultivation of soybeans which has been long confined mainly to China has gradually spread to other countries. Other articles have however stated that it originated from South East Asia, from where it spread into many parts of the world (Crawford et al., 2003 and Xu et al., 2002) and was introduced for the first time to sub Saharan Africa by Chinese traders in the 19th century. Cultivation as an economic crop was as early as 1903 in South Africa (Khojely et al., 2018). It was cited that about 70% of the world’s production of soybean was in the United States of America (USA) followed by Mainland China (Asamoah, 2009). The story is not so different from today because the United States of America is still the leading producer with 112.95 million metric tonnes for 2017/2018, China ranking fourth with Brazil and Argentina taking the second and third position respectively (USDA, 2019). Soybean is a native to East Asia and China is where the spread started from to Europe and America and other parts of the world (USDA, 2011). History shows its existence more than 5,000 years ago, being used as food and a component of drugs (Norman et al., 1995). The earliest known cultivation of the crop in Africa was in 1885, in Algeria (Shurtleff and Aoyagi, 2010). In 1908 there was increase in soybean cultivation in Africa and serious attempts to establish the crop in Ghana took off in the early 1970s (Mercer-Quarshie and Nsowah, 1975; Shurtleff and Aoyagi, 2010). This was as a result of collaborative breeding efforts between Ghana’s Ministry of Food and Agriculture (MoFA) and The International Institute of Tropical Agriculture (IITA) (Tweneboah, 2000). IITA has since introduced, different soybean varieties belonging to different
maturity groups into Ghana and are being cultivated together with some local varieties such as
“Salintuya I” and “Salintuya II” , Anidaso, Ahoto and Nangbaar released by Crop Research Institute (CRI) in 2005 (MoFA and CSIR, 2005). More new varieties have now been introduced namely Favour, Afayak, Quarshie, Jenguma, among others (SARI, 2017).
CLASSIFICATION
The genus name Glycine was originally introduced by a Swedish botanist Carl Linnaeus (1737) in first edition of Genera Plantrum (Hymowitz and Newell, 1981). The book Species Plantarum, (Published in 1753) reveals that the cultivated soybeans appeared in the species Plantarum, Linnaeus under the name Phaseolus max L.; and the other was Dolichos soja based on what have been described by Hermann and Kaempfer (Shurtleff and Aoyagi, 2010). The contribution, Glycine max (L.) Merr., as proposed by Elmer Drew Merrill in 1917, has become the name of this advantageous plant; Due to the confusion concerning the selection of botanical name for soybean plant, the combination name “Glycine max (L) Mer” as proposed by Elmer Drew Merrill in 1917, has since become the valid botanical name (Hymowitz and Newell, 1981). Appiah-Kubi (2012) revealed Glycine is the genus of the wild species of soybean which is composed of the subgenera Soja and max (Moench). Wild soybean of the genus Glycine is a group of about 6 species that are perennial (Singh et al., 1984). These wild types have varying forms, cytology and genetic makeup (Singh et al., 1988).
PHYSICAL CHARACTERISTICS AND DESCRIPTION
Soybean is an annual crop growing up to 2 meters (2m) tall, it is usually erect, (Townley-Smith, 1993). Kim et al. (1995) reported the crop varies in growth habit and height which may grow prostate, not higher than 20 centimeters (cm) or grow up to a height of 2 m. Soybean is an herbaceous plant ranging in height from 30 to 183 cm, depending on the genotype (Ngeze, 1993).
Various soybean genotypes have varied growth habits: determinate and indeterminate type (MoFA and CSIR, 2005). The intermediate genotypes grow taller; produce more leaves and pods right from the stem to shoot than the determinate type. However, many varieties have been developed to have the determinate growth habits (Norman et al., 1995). The main leaves of soybean are alternate, unifoliate, ovate and opposite. The stipules of the leaves are broadly ovate about 3 to 7 millimeters (mm) long, and the petioles of the lower leaves are about 2 to 20cm long. The secondary leaves of soybean are alternate and trifoliate which are mostly compound with approximately four leaflet (Appiah-Kubi, 2012). The flowers of the crop are mostly purple or white, or purple and white borne on the same plant, and these are borne in axillary racemes on peduncles found on the nodes of the plant (Appiah-Kubi, 2012). The flower which is papilionaceous in nature have a tubular calyx and corrolla of five sepals and petals respectively, a pistil, about nine stamens borne on separate single posterior stamen (Acquaah, 2007). The collection of stamen forms a kind of ring at the basal section of the stigma which elongate about a day to pollination, and the elevated anthers make a ring around the stigma (Townley-Smith, 1993). Soybean plants are self-pollinated and produce many flowers but only a few of about two-thirds or about 25% of the flowers produce pods which are pubescent and either light-yellow or black at maturity (Appiah-Kubi, 2012). The shapes of the pods are mostly curved or straight with varying length which ranges between 2 to 7cm and comprises of carpels which are fused by a dorsal and ventral suture in two halves (Asafo-Adjei et al., 2005). The pod of soybean mostly contains about one to three seeds and four sometimes. Soybean seeds are usually oval but some cultivars have flattened, spherical and elongated seeds which are typically straw-yellow, brown, green, black and sometimes greenish-yellow (Acquaah, 2007).
CLIMATIC REQUIREMENTS
Soybean is a grain legume that grows well in the temperate, tropical and subtropical climates (IITA, 2007). Cultivation is successful in climates with hot summer, with optimum growing conditions in mean temperature of 20- 30 oC (Nzege, 1993) the minimum temperature at which soybean develops is 10 oC and that of the optimum and the maximum being 22 oC and about 40 oC respectively. Optimum temperature for germination is 23 oC to 25 oC. For better seed production it is suitable to select a place having wide range of day and night temperature (cooler night in mountain foot areas) so that it can produce more fulfilled large seeds. From seed development stage to harvesting time it needs dry conditions but humid condition during pod setting. Through plant breeding, several varieties have been produced and have performed differently in the various climatic or ecological zones in the world (FAO, 2009).
SOIL AND NUTRIENT REQUIREMENTS
Soybean has the ability to adapt to broad-spectrum environment, also thrives best in thoroughly drained loose loam or sandy soil that are fertile. An optimum pH range of about 5.5 to 7.0 is ideal
due to nutrient availability within this range (Seiter et al., 2004).
Soybean is a heavy feeder of nitrogen hence fix more than 70% of its required N nutrient by forming a symbiotic association with Bradyrhizobium Japonicum bacterium. Nitrogen nutrient is usually applied as a starter dose to give the plant a good start while infection by the bacteria for nodulation takes place. The starter dose is applied at very low levels. Phosphorus and Potassium fertilizer are the recommended fertilizer at a rate of 60 to 70 kg per hectare while about 300 kg per hectare of K2O is required.
NUTRIENT ELEMENT EFFECT ON SOYBEAN GROWTH
In soybean production, any level of yield attainable on any farm is completely dependent on nutrient availability and water supply (Tamagno et al., 2016). High yields obtained in soybean is directly proportional to high level of nutrient in the soil and consequently high level of nutrient uptake in the plant (Tamagno et al., 2016). Soybean growth and yield is dependent on soil essential nutrients. While there is the need to supply other essential nutrients for soybean growth, the plant is able to fix its own nitrogen nutrient.
Soybean requires nitrogen (N) for growth, seed formation and for its oil and protein content making the plant a heavy nitrogen feeder. This N is supplied through fixation and also from the soil, however the soil N is mostly lost through leaching and immobilization. Biochar is able to make immobilized N available and also prevent the leaching of the fixed N and hence increase the availability of N for growth in soybean.
Phosphorus is also very essential in the growth of soybean and this is because phosphorus is needed in soybean to convert solar energy to chemical energy which is required in soybean for protein synthesis (Hellal et al., 2013).
The third most important element required by plants for growth is Potassium. Soybean plant uses potassium for photosynthesis, transportation of sugars, water and nutrient movement. It also uses potassium in protein synthesis and the formation of starch. Research has proved that adequate K levels in plants improves resistance to diseases, water stress tolerance, tolerance to pest and aids the uptake of other nutrients. Soybean requires as much K as N. However P and K uptake is usually required in large amounts during early pod filling (Usherwood, 1998).
