LEAF-AREA DEVELOPMENT OF CORN AS AFFECTED BY WINDBREAK SHELTER

Windbreaks generally have positive effects on crop yield because of im proved growing conditions, To quantify these effects, leaf area and ve rtical leaf area distribution of corn (Zea mays L.; cv. Wilson 2100) w ere studied with and without windbreak shelter during 1991 and 1992. S imulation models for leaf area estimation were also evaluated for the two years. Leaf area, length, and width were measured for the whole ca nopy several times during each growing season. Two types of area predi ction models were developed and tested: a simple length-width model us ing a correction factor (C) and a statistical model, Although the stat istical model gave a slightly better overall estimate of leaf area, th e simple model was the preferred choice because of its simplicity and better area predictions when leaves were small. Regardless of, windbre ak shelter or year, values of C were stable. The average C for this co rn hybrid was 0.75, which is consistent with other reported values for corn. Windbreaks did not affect total leaf area nor alter the vertica l distribution of Leaf area for the two years, With or without shelter , the height of maximal leaf area was at 1/2 of the canopy in 1991 and in the lower 1/3 of the canopy in 1992, This downward shift of maxima l leaf area was probably due to lower temperatures and more evenly dis tributed rainfall in 1992 and may have been positive for plant product ivity. The variations of windbreak effect on leaf area development wit h species and environmental conditions indicate the need of similar fu ture studies on other major crops to formulate an effective strategy f or windbreak evaluation.