Soil temperature and planting date effects on corn yield, leaf area, and plant development

Early-season soil temperature has been reported to affect leaf appearance and expansion rates, and consequently corn (Zea mays L.) ontogeny. A 2-yr field experiment was conducted on a Drummer silty clay loam (fine silty, mixed, mesic Typic Haplaquoll) at the Agronomy and Plant Pathology South Farm of the University of Illinois at Urbana-Champaign. Treatments consisted of planting date (early May and early June) and soil temperature surrounding the corn growing point (5 degrees C below ambient, ambient, and 5 degrees C above ambient). Soil temperature was controlled using warm and cool water circulating through copper pipes buried next to the corn rows. Air temperatures were not controlled. Irrigation was used. The experimental design was a split plot in a randomized complete block with four replications. Ten plants were randomly selected within each replication and nondestructive measures of plant stage, individual leaf area, and leaf senescence were taken three times per week from emergence to V5, and once per week afterwards until complete leaf senescence. Growing degree days (GDD) were calculated using the modified growing degree day formula (MGDD). From planting to V5, MGDD were computed using the soil maximum and minimum daily temperatures from each treatment. After the soil temperature treatments were terminated, the MGDD calculations were based on maximum and minimum daily air temperatures. Lower early-season soil temperature delayed corn development and modified individual leaf area. Plants under these cooler conditions went through vegetative developmental stages faster per unit of accumulated MGDD, showing the effect of temperature on corn ontogeny. The results also show that the current method of calculating MGDD (with base temperature of 10 degrees C) does not adequately predict corn development under exceptionally warm or exceptionally cool soils. Warmer early-season soil temperature linearly increased corn yield (beta(1) = 0.14 Mg ha(-1) degrees C-1). Leaves in the lower half of the canopy were larger under cooler soil temperature treatments (beta(1) = -48.9 cm(2) degrees C-1). There was a linear increase in the size of the leaves in the upper half of the canopy of the plants under warmer temperatures (beta(1) = 28.8 cm(2) degrees C-1).