Effects of nitrogen and spacing on fruit yield of tomato Afr. J. Hort. Sci. (2011) 5:50-60 50 EFFECTS OF NITROGEN AND SPACING ON FRUIT YIELD OF TOMATO Kirimi JK 1 ,*, Itulya FM 2 and Mwaja VN 2 1 Ministry of Agriculture, P.O. Box 2558, Meru. 2 Egerton University, P.O. Box 536, Njoro, * Corresponding: kirimijk@yahoo.com Abstract Tomato (Solanum lycopersicum) is popular in fresh market and processing industries. Production of tomatoes under greenhouse conditions is gaining popularity in Kenyan highlands. Yields are limited by poor soil nutrition with nitrogen being the most limiting nutrient required in large quantities. The study investigated the effects of nitrogen levels and spacing on tomato fruit yield and quality in a Quonset greenhouse at 2238m above sea level. Plants were grown in a greenhouse at Egerton University, Department of Horticulture research and demonstration field in two seasons. The first season commenced in October 2002, to February 2003, the second in February 2003, to July 2003. The nitrogen rates 0, 40, 80 and 120 kg N ha -1 applied in two equal splits. Spacing was 40x30, 40x40, 50x30 and 50x40 cm. The experimental design was a Randomized Complete Block Design, with a Split-Plot arrangement with main plots as nitrogen levels and spacing the sub plots in three replications. Fruit yield and quality data were taken after each harvesting. Number of marketable fruits was significantly affected by spacing in both seasons. Nitrogen of 80 kg ha -1 and spacing of 40 x 30 cm had the highest mean fruit numbers in season 2. Nitrogen of 80 kg N ha -1 and spacing of 50 x 30 cm had the highest fruit yield in season 1. Marketable unit fruit weight was highest in season 1, at 50 x 40 cm. The study was significant to farmers producing tomatoes under greenhouse, to maximize on profits by scaling down nitrogen fertilizer use to attain high yields and quality of marketable tomato fruits using appropriate spacing. Key Words: Greenhouse, Highlands, Indeterminate tomato, Nitrogen, Spacing Introduction Within the past century the cultivated tomato has become one of the most popular and widely consumed crops with an annual world production approaching 80 million metric tonnes (FAO, 2001). Its versatility in fresh or processed form has played a major role in its rapid and widespread adoption as an important food commodity (FAO, 2001). Tomato is an important source of vitamins A (900 IU), C (23 mg) and B2 (0.04 mg), and minerals such as K (244 mg), Fe (0.5 mg) and P (27 mg) per 100 g sample (Nonnecke, 1989). Tomato production in Kenya is mainly under field conditions, where changes in climatic conditions do not allow realization of economic yield. There are fluctuations in the supply of tomatoes in the market, which lead to market glut during in season and shortage during off-season. The use of greenhouses ensures constant supply of fresh market tomatoes by modifying crop environment to meet plant growth requirement at any time of the year. The off- season tomato production enables improved market prices. Low temperatures limit production of tomatoes in high altitudes of Kenya. Determinate cultivars may grow up to 2 m in height and are erect with restricted flowering and fruiting, and are suitable for field conditions. The stem of indeterminate cultivars grows indefinitely, reaching to more than 10 m within one year, making it ideal for long season continuous cropping in greenhouses as they flower and fruit regularly and evenly (Rick and Butler, 1956). Indeterminate tomatoes, vegetative growth and reproductive development proceed concomitantly during the greater part of the plant life. A strong competition