CORN LEAF-AREA RESPONSE TO EARLY-SEASON SOIL-TEMPERATURE UNDER CROP RESIDUES

Residue cover from conservation tillage modifies the soil temperature regime, compared with conventional tillage. This study was conducted to examine the influence of crop residue on the area of corn (Zea mays L.) leaves developed when the apical meristem is below the soil surface. Field studies compared the effects of residue-covered and bare soil (Conover loam in East Lansing MI in 1988 and Brookston clay in Woodlsee, ON, in 1990), on maximum area per leaf (LA(max)) at V6 and on leaf area index (LAI) after silking. LA(max) for Leaves 4 to 6 was 11 to 52% higher in plants grown in residue-covered soil than in bare soil. LAI after silking was similar in both treatments. LA(max) differences could not be related to differences in volumetric water content or N concentration. Thermal effects of crop residue on LA(max) and leaf appearance rates were tested in growth chamber. After emergence, the corn apical meristem was exposed to air. Nighttime air temperatures were maintained at 16-degrees-C and daytime air temperatures were controlled at 18, 21, and 25-degrees-C, simulating seed zone temperatures measured in the field. Daytime air temperatures of 21-degrees-C resulted in higher LA(max) for Leaves 4 to 6 on V6 plants than did 18 or 25-degrees-C. Appearance rates increased with temperature. These results suggest that seed zone temperature under residue from emergence to V6 (almost-equal-to 23-degrees-C) was more favorable for LA(max) than seed zone temperature under bare soil 26-degrees-C). Thus, for corn Leaves 4 to 6 the temperature optimum for LA(max) is lower than the temperature optimum for leaf development.