VOL. 6, NO. 8, AUGUST 2011 ISSN 1990-6145 ARPN Journal of Agricultural and Biological Science © 2006-2011 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com EFFECT OF SALINITY LEVEL OF IRRIGATION WATER ON THE YIELD OF TOMATO P. O. Boamah 1 , L. K. Sam-Amoah 2 and J. Onumah 1 1 Department of Ecological Agriculture, Bolgatanga Polytechnic, Bolgatanga, Ghana, West Africa 2 Department of Agricultural Engineering, School of Agriculture, University of Cape Coast, Cape Coast, Ghana, West Africa E-Mail: pierrodecota@hotmail.com ABSTRACT This research was conducted to determine the salinity level of irrigation water from a dug well, pond and tap water as well as its effect on the yield of a tomato crop at the University of Cape Coast Teaching and Research Farm. Water samples were taken at fortnight intervals to determine the electrical conductivity (dSm -1 ) using the TOA water quality checker 20A. The averages of the four batches were computed and used as the three sources for the period of assessment. Flowering and yield of crop were the parameters used to assess the effect of salinity level on the tomato crop. Electrical conductivity as a measure of salinity was higher in the pond (0.25 dS/m) than the well and tap water (0.07 dS/m and 0.02 dS/m, respectively). Flowering and yield of tomato was high with crops treated with well water (45.22%; 99.08kg/ha) followed by the pond (27.70%; 43.76kg/ha) and tap water (27.08%; 27.25kg/ha) in that order. There was no significant difference in flowering and in yield of crops between the tap and pond treatments at both 0.05 and 0.01 levels but there was a significant difference in yield between the well treated crops and other sources. However, the yield for all the three treatments was very low (lower than expected) because there was no fertilization, pests and disease control. Keywords: tomato, salinity, irrigation water, electrical conductivity, flowering, yield. INTRODUCTION Tomato (Lycopersion esculentum) is a member of the family solanaceae. It is cultivated throughout the country Ghana and all year round - sources of water for irrigation tomato in Ghana are well water, fresh water (pipe born water), domestic and industrial waste water. A major advantage of using wastewater is that it contains high levels of nutrients, reducing the need for and cost of fertilization. A medium amount of water well distributed through the growing season is essential for high yield. Tomato tolerates a wide range of soils and climate. It does not like excessive humidity and high temperature. It requires well-drained soils with a high organic content. Tomato production for income is a major agricultural activity in Ghana and its production is associated with the provision of adequate water for the plant growth and development. The source of water should be of the right salinity such that it would not affect production because salt stress responses in crop plants throughout their growth cycle depend on several interacting variables, including the cultural environment, the plant developmental stage, the salt concentration and the duration of the stress over time (Munns, 2002 as cited in Marchese et al., 2008). The maximum soil salinity tolerated by tomato, with basis on the electrical conductivity of the saturation extract (ECe), is 2.5 dS m -1 , with reduction of 9.9% in the production for each unit increase of salinity above this limit (Maas and Hoffman, 1977 as cited in Campos et al., 2006). On the other hand, Ayers (1977) reports that the use of irrigation water with electrical conductivity of 1.7, 2.3, 3.4, and 5.0 dS m -1 reduces 0, 10, 25 and 50% the tomato yield, respectively, assuming 0.15-0.20 leaching fractions. The effects of the salinity on the tomato may be either harmful, reducing the yield and increasing the incidence of blossom-end rot, or beneficial (antioxidant), increasing fruits concentration of soluble solids (Mizrahi and Pasternak, 1985; Cuartero and Muñoz, 1999; De Pascale et al., 2001) and acidity (Vinten et al., 1986; De Pascale et al., 2001), resulting in larger profit at processing. The damages to plants caused by saline irrigation may be enhanced by high temperatures and low relative humidity as well as long-term salinization of the soil that undergo to permanent modification of its physicochemical properties; as a consequence in applying saline water for irrigation, an integrated approach, which should account for soil, crop and water management should be adopted (Gad, 2005). Plant salt tolerance may be expressed by plotting the relative yield as a continuous function of root zone salinity (Maas and Hoffman, 1977 as cited in Marchese et al., 2008). This relationship is represented by two intersecting linear regions, which identify a threshold after which the yield begins to decline as well as the yield reduction slope (slope) at increasing salinity. The salinity tolerance threshold is a specific target for improving salt stress tolerance (Maggio et al., 2001; 2007) The ability of plants to tolerate excess salts in the rhizosphere is of considerable importance in the arid and semi-arid region where salinization of soils usually prevails. The adverse effect of salt stress on plant growth is attributed to the specific toxic effect of ions excessively salt ions that are observed from the saline soil to the process of building up the osmotic potential of the plant cells, or to the imbalanced of nutritional cations in tissues of the salt affected planted or due to reduction in carbon fixation during photosynthesis and to increasing carbon 49