EFFECT OF SEED PELLETING AND BIOCHAR ON NODULATION, GROWTH AND YIELD OF SOYBEAN (Glycine max L.)

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.