CHAPTER ONE

Introduction

Background;

Cowpea (Vigna unguiculata (L.) Walp) is a legume crop of vital importance to the livelihoods of millions of people in West and Central Africa. It provides a nutritious grain and a less expensive source of protein for both rural poor and urban consumers (Inaizumi et al., 1999). Some 8 million hectares of cowpea are grown in West and Central Africa, especially in Burkina Faso, Mali, Niger, Nigeria and Senegal. Cowpea’s high protein content, its adaptability to different types of soil and intercropping systems, its resistance to drought, and its ability to improve soil fertility and prevent erosion makes it an important economic crop in many developing regions. The sale of the stems and leaves as animal feed during the dry season also provides a vital income for farmers. The grains contain 25% protein and several vitamins and minerals and being a legume, replenish low fertility soils when the roots are left to decay. It is grown mainly by small-scale farmers in developing regions where it is often cultivated with other crops as it tolerates shade. Cowpea cultivation is mainly under traditional systems and cowpea grain yields in farmers’ fields are low especially in the West African sub-region (0.025–0.3 Mg ha−1), which is caused by severe attacks of pest complexes, diseases, low soil fertility, drought, inadequate planting systems, inappropriate cultivars and lack of inputs (Ajeigbe et al., 2010a). In addition to biotic and abiotic stresses, existing planting practices limit crop yields. Grain yields ranging from 0.5 to 2.76 Mg ha−1 have been reported in sole crop (Ajeigbe et al., 2005, 2008), whereas grain yields ranging from 0.37 to 1.27 Mg ha−1 have been reported in intercrop in the savannas of Africa (Ajeigbe et al., 2005, 2010). Cowpea production in the northern Nigeria generally uses wide rows 75 cm apart, same planting distance as the local farmers in Fako Division. As suggested by Kamara et al., (2016) this planting distance may be like this, because equipments used for ridging are the same as for the other grain crops such as maize, soybean, sorghum and millet. This general row spacing does not consider individual crop and varietal requirements, with low density resulting from wide row spacing usually leading to low yields in grain legume crops, such as cowpea in West Africa (Kamara et al., 2014). Plant density is an important component of yield in grain crops such as cowpea and soybean and it is important to determine the optimum plant densities for different areas and varieties as they have different potential for crop growth (Kamara et al., 2014). Adjusting planting density is an important tool to optimize crop growth and the time required for canopy closure, and to achieve maximum biomass and grain yield (Liu et al., 2008). High plant density increases light interception, dry matter and yield components (pods and seeds) by both decreasing row spacing and increasing plant density (Bruns, 2011). Ezedinma (1974) reported that close spacing between and within rows increased biological and grain yields of cowpea, with Jallow and Fergusson (1985) reporting a linear response of seed yield to plant density between 40 000 and 250 000 plants ha−1. However, plant response to changes in density depends on the morphology of the cultivars. The implements used for ridging are made for ridges spaced 75 cm apart. This reduces the flexibility of adjusting the distance between ridges. Since cowpea like any other grain crop in SSA is grown on ridges spaced 75 cm apart, the only option to increase plant density is to increase the number of rows per ridge from 1 to 2 or 3 rows. Although there have been some reports elsewhere on cowpea response to plant density (Jallow and Fergusson, 1985; Kwapata and Hall, 1990), there is little information on the performance of current cowpea cultivars when grown at densities higher than the existing density of 133 333 plants ha−1 in the most regions in SSA. Thus, an understanding of how the modern cowpea cultivars will respond to increased plant density through increase in number of rows per ridges is very important. This will help growers’ select appropriate number of rows per ridge corresponding to specific plant density that will increase grain yield in their locations. The aim of this paper was to determine plant density effects on cowpea performance: Growth, Yield, Pest and Disease incidence.

Problem Statement

Local farmers in  Fako Division grow Cowpea but most of the time fail to get their optimal  yield due to certain factors such as; pests and diseases in the field, climatic conditions, soil properties etc. so, this experiment is designed to investigate, using a cultural practice such as varying plant densities to observe their effects on the growth, yield and pest and disease incidence of Cowpea in order to come out with the appropriate planting density that will give the local farmers their optimal yield.

1.5. Objectives

1.5.1. Main Objective:

This experiment is being carried out to investigate the effects of plant density on the Growth, Yield Pest and Disease incidence of Cowpea.

1.5.2. Other Objectives:

• To investigate the effect of plant density on the Growth of Cowpea
• To investigate the effect of plant density on the Yield of Cowpea
• To investigate the effect of plant density on the Pest and Disease incidences of Cowpea.

Hypotheses

Plant density will have an effect on the Growth of Cowpea

Plant density will have an effect on the Yield of Cowpea

Plant density will have an effect on the Pest and Disease incidence of Cowpea