1.4 REGRESSION OF FORAGE YIELDS AGAINST A GROWTH INDEX AS A TOOL FOR INTERPRETATION OF MULTIPLE HARVEST DATA OF ALFALFA GENOTYPES.

Twelve genotypes of alfalfa, Medicago sativa L., were evaluated for green and dry forage yields under calcareous soil in the farm of Nubaria Research Station during 2010 and 201lseasons. Yield was recorded for nine month separate per year, i.e.; winter (December, and February cuttings); spring (April, and May cuttings); Summer (June, July, and August cuttings) and Autumn season (September and November cuttings). Regressing yield against a growth index associated with harvest date was utilized to describe forage performance of a genotype in an easy and concise format. The growth index was calculated as the mean of all entries at a harvest date minus the grand mean. The obtained regression coefficient (b) described an entry yield response over several harvest dates and is indicative of entry performance over variable growth conditions. [ABSTRACT FROM AUTHOR]