CHAPTER ONE
INTRODUCTION
1.1. Background of the Study
In Nigeria, vegetable crops are produced in different agro-ecological zones through commercial as well as small scale farmers both as a source of income as well as food. However, the type is limited to few crops and production is concentrated to some pocket areas. In spite of this, the production of vegetables varies from cultivating a few plants in the backyards for home consumption up to a large-scale production for domestic and export markets (Dawitet. al., 2004). Recently, despite the ups and downs observed, the demand for vegetables especially for export is increasing (Tsegay, 2010). In fact, vegetables can generate high income for the farmers because of high market value and profitability. They also have high nutritive value compared to cereals (EARO, 2000) Vegetables are an important feature of Nigerian’s diet that a traditional meal without it is assumed to be incomplete. In developing countries, the consumption of vegetables is generally lower than the FAO recommendation of 75kg per year in habitant (206g per day per capita) (Badmus and Yekini, 2011). In Nigeria, vegetable production has been on-going for decades, providing employment and income for the increasing population especially during the long dry season. However production is constrained by inadequate infrastructure, agronomic and socio-economic variables (Sabo and Zira, 2008). It has been widely demonstrated that rural women, as well as men, throughout the world are engaged in a range of productive activities essential to household welfare, agricultural productivity, and economic growth. Vegetable crops are grown in many parts of the world contributing significantly to income security and the nutritive diet of many households. According to (Mofekeet al.2003) Vegetable crops constitute 30 to 50 percent of iron and vitamin A in resource poor diet. Vegetable crops such as tomatoes, okra, pepper, cabbage etc. are widely cultivated in most part of the Sub-Sahara Africa, particularly by small scale farmers in most states of Nigeria (Adeolu and Taiwo 2009; Giroh et al., 2010). Global production of fruits and vegetables tripled from 396 million MT in 1961 to 1.34 billion MT in 2003(International Institute of Tropical Agriculture, 2005) and Nigeria ranked 16th on the global tomato production scale, accounting for 10.79 percent of Africa’s and 1.2 percent of total world production of tomatoes (Weinberger and Lumpkin, 2007) Protective cultivation has been widely applied due to adverse climatic conditions unfavourable to warm season vegetable production. In many parts of the world, nets or screens are commonly used in crop production for reducing excessive solar radiation, weather effects on produce, and to keep away insects and birds. Vegetable production under protective structures such as netting reduces yield losses from insects, diseases, heavy rains and sunburn which results in higher productivity and returns per unit area (Ramasamy,2011). Protective structures provide protection to vegetable crops against biotic and abiotic stresses (Palada, 2011). Mangmang in 2002, reported that the total fruit yield and high returns of tomato crop was significantly enhanced by the plastic net covers. The net shade greatly reduced insect population by 80% and marketable yields were 1.5 to 2 times greater under than in the open field (Palada and Ali, 2007). Growing cabbage under nets reduced insect incidence by 38-72 percent and resulted in significantly higher returns (Neaveet al, 2011). Green house, the latest word in agriculture is one of such means, where the plants are grown under controlled or partially controlled environment resulting in higher yields than those that are under open conditions (Navale et al. 2003). Net houses and its variants have been used in some European, South American and Southeast Asian countries for producing egg plants (Kaur et al., 2004), leafy greens (Talekar et al., 2003) and cabbage (Martin et al., 2006). In Africa, mobile net houses made of mosquito nets (25- mesh) were effective as physical barrier against the diamondback moths, cut-worms and loopers providing 66- 97 percent control of moths, birds and caterpillars (Martin et al., 2006). Netting is frequently used to protect agricultural crops from excessive solar radiation (shade-nets), improving the thermal climate (Kittas et al., 2009), sheltering from wind and hail and exclusion of bird and insect-transmitted virus diseases (Teitelet al., 2008). The shading of crops results in number of changes on both local microclimate and consequently crop growth and development (Kittaset al., 2009). (Takteet al. 2003) reported that shade nets were used for protection of valuable crops against excess sunlight, cold, frost, wind and insect/birds. They experimented on the effects of shading on crop growth and development, it was found that shading increased leaf area index and total marketable yield production, reduced the appearance of tomato cracking about 50% and accordingly, the marketable tomato production was about 50% higher under shading conditions than under non-shading conditions. (Smith et al. 1984) observed that under shading nets the air temperature was lower than that of the ambient air, depending on the shading intensity. Shade netting not only decreases light quantity but also alters light quality to a varying extent and might also change other environmental conditions.