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Amaranth is a very important vegetable worldwide. Its leaves are consumed and the seeds are processed into various food products. Its production in the tropics is threatened by low yields which has a major impact on global production. A research aimed at improving the yield of this vegetable was carried out at lady bird organic farm Broga, 2.9450N 101.8740E, Semenyih, Selangor, Malaysia by studying the effect of genotype and organic fertilizer on the following growth indicators, red:far red ratio below canopy, stomatal conductance, leaf temperature, and dry weight. These growth indicators were monitored on a weekly basis over a period of six weeks. Three genotypes namely, Amaranthus caudatus, 3388 (green round leaf), Amaranthus caudatus, 3233 (green long leaf) and Amaranthus cruentus, 888 (red leaf) were grown on soils to which organic fertilizer was added at three different application rates (0 t/ha, 7.5 t/ha and 15 t/ha). There was no significant interaction effect of genotype and organic fertilizer on the growth indicators; however, each of these factors had significant effect on the growth of amaranth. A strong negative correlation occurred between dry weight and red:far red ratio below canopy likewise, between stomatal conductance and leaf temperature. Over a cultivation period of five weeks, the green long leaf genotype was superior showing that it is better adapted to growing in the rainforest agro ecological zone of Malaysia than the other two genotypes. Organic fertilizer application at a rate of 15 t/ha produced the lowest leaf temperature, after 4 weeks of cultivation implying better water status than 0 t/ha and 7.5 t/ha application rates. This study clearly shows that genotype and organic fertilizer have significant effect on the growth of amaranth. Therefore, these factors can be manipulated in order to enhance amaranth production. [ABSTRACT FROM AUTHOR]