An experiment wa1 conducted in 199 -1994 In the greenhouse unit of Agr., Sana'a Univ. to study the effect of qat leaves on growth of tomato. Plastic pots 20 cm in diameter were filed with soil taken from the collage field. Treatments consisted of adding tile residues t the rotes of (0, 1, 3, 5., 7, and 10) g/pot. The residues were mixed with the soil in each pot to a depth of about 5 cm, then tomato seeds were planted directly after residue application. The results showed that qat leaves residues reduced growth of tomato plants compared to the control treatment (0 g /pot). The most significant and severe red action was caused by the 10g /pot rate and It was about 82%, 7%, 20%, 53 %, and 63 % In leaf area, No. of leaves, plant heigh t, Fresh weigh t, dry weight, and leaf chlorophyll contet, respectively. On the other hand, stem diameter of the treated plants was seen by visual observation to be severely stunted and yellowish in color. It was concluded that the effect of qat on tomato could be related to the phenomenon of allelopathy.

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