Dynamics of shoot and root growth of lucerne after seeding and after cutting

Abstract

The accumulation of above ground and root biomass of a lucerne crop was studied after seeding in spring and during two consecutive regrowth periods in summer and in autumn. Estimates of the quantity of PAR intercepted by the crops were made using measurements of LAI and a model of light interception. For each period of growth, a linear relationship between the accumulated above ground biomass and the quantity of intercepted PAR was established. The slope of the regression was interpreted as the radiation use efficiency for aerial biomass production. It varied from 0.79 g.MJ-1 for the growth period after seeding to 1.80 g.MJ-1 for summer regrowth, with an intermediate value of 1.13 g.MJ-1 for the autumn regrowth. The radiation use efficiency for total biomass production was constant and equal to 2.4 g.MJ-1 for the three periods considered. These results indicated that the seasonal variation of potential production of lucerne was not determined by variation in radiation use efficiency for biomass production, but by the pattern of the assimilate partitioning between shoots and roots as influenced by daylength or temperature.