Abstract: An 8 x 8 diallel cross experiment involving eight varieties/lines was planted in a randomized complete block design to ascertain the nature of genetic mechanism controlling different morphological traits under two different soil fertility regimes. Highly significant genotypic difference for all the characters were obtained under both recommended as well as half dose of fertilizer plantings. All varieties/ lines, as expected under a half dose of fertilizer planting, exhibited a reduction in the development of morphological and yield related characters. Plant height, under recommended dose of fertilizer planting, 1000-grain weight and grain yield under a half dose of fertilizer planting were controlled by partial dominance type of gene action. Whereas, over-dominance was exhibited by number of tillers per plant, grains per spike, and grain yield per plant under recommended dose of fertilizer. The positive coefficient of correlation of Wr+Vr with parental means indicated positive effects of recessive genes for the expression of number of tillers per plant under recommended dose of fertilizer.