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 t o examine the influence of crop residue on the area of corn (Zea mays L.) leaves developed when the apical meristem is below the soil surfac e. Field studies compared the effects of residue-covered and bare soil (Conover loam in East Lansing MI in 1988 and Brookston clay in Woodls ee, 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 5 2% higher in plants grown in residue-covered soil than in bare soil. L AI after silking was similar in both treatments. LA(max) differences c ould not be related to differences in volumetric water content or N co ncentration. Thermal effects of crop residue on LA(max) and leaf appea rance rates were tested in growth chamber. After emergence, the corn a pical meristem was exposed to air. Nighttime air temperatures were mai ntained at 16-degrees-C and daytime air temperatures were controlled a t 18, 21, and 25-degrees-C, simulating seed zone temperatures measured in the field. Daytime air temperatures of 21-degrees-C resulted in hi gher 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 t emperature under bare soil 26-degrees-C). Thus, for corn Leaves 4 to 6 the temperature optimum for LA(max) is lower than the temperature opt imum for leaf development.