Growth of Birdsfoot and Alfalfa. III Changes in Carbohydrates Reserves and Growth Analysis Under Field Conditions1

Abstract

The amount of total available carbohydrates (TAC) in the roots of 'Empire' birdsfoot trefoil were lower and the changes were less pronounced than in the roots of 'Vernal' alfalfa at similar growth stages. The difference on a weight basis was much greater than by percentage. Starch, sucrose, glucose, and fructose were the components of the TAC of both species. Relationships among the fractions of the TAC were similar for both species throughout the growing season.Alfalfa had a higher crop growth rate (CGR) than trefoil except at late stages of maturity when growth of trefoil continued by active upper axillary branching. CGR of alfalfa was higher than trefoil because there was a greater leaf area and it developed faster. Alfalfa was more efficient in the conversion of radiant energy into dry matter because it had a higher leaf area index than trefoil at comparable net assimilation rates. This advantage over trefoil was attributed to a higher photosynthetic rate for alfalfa leaves and to a better light distribution in the taller alfalfa canopy.