Ground cover and leaf area index of maize and sugar beet crops

Leaf area index (L) is an important variable characterizing the development of a crop and its exchanges with the atmosphere. Direct measurements are destructive and tedious. The relations between L and the ground cover (C) can be described analytically by taking account of leaf angle distribution and leaf clumping. Because it is difficult to characterize these two variables, we have studied the stability of empirical relations between L and C. Ground cover was measured from vertical-view photographs. For both maize (Zen mays L, var Deal and sugar beet (Beta vulgaris, var Matador), we found the extinction coefficient (K) to be robust throughout crop development and only weakly affected by population density and sowing geometry. Thus, measurement of C appears to be a simple way to estimate L, once the relation has been established for the variety of interest, and excluding periods of water stress that may modify crop geometry.