Corn Emergence as Influenced by Soil Temperature, Matric Potential, and Aggregate Size Distribution

The effects of soil physical parameters on corn (Zea mays L.) emergence were determined in a growth chamber experiment. The treatments included three different soils, four soil temperature regimes (5–15, 10–20, 15–25, and 20–30°C), four soil matric potentials (−10, −33, −100, and −500 kPa), and seven aggregate size distributions (geometric mean diameter = 0.5, 1.0, 1.9, 3.6, 5.6, 6.8, and 11.1 mm). Corn was planted at 50 mm depth in soil aggregate mixtures contained in aluminum cylinders 152 mm in height by 76 mm inside diameter. Cylinders were placed in a growth chamber with a 10°C diurnal fluctuation and time to corn emergence was determined. Based on the growth chamber study, guidelines are developed that define best seedbed conditions for corn emergence. Time to corn emergence was influenced by the independent variables in the following order: soil temperature » soil matric potential > soil aggregate size distribution. Emergence time was related to soil temperature by a power function. Corn emergence was most rapid at the warmest soil temperature (20–30°C) when soil moisture was at or above field capacity and when aggregate size distribution corresponded to a geometric mean diameter between 1.0 and 6.8 mm. Time to corn emergence was less than 21 d for all soils and matric potentials when mean soil temperature was at least 15°C. The negative effect of low soil temperatures on corn emergence was partially compensated by high soil matric potential. A corn emergence model was developed from the relationship between percent emergence and growing degree days at the seed zone depth. Relationships between percent emergence and seed zone growing degree days were approximately the same for three soils and varied with the soil matric potential. The corn emergence model indicated a requirement of 59, 62, 67, and 76 seed zone growing degree days for 75% corn emergence at soil matric potentials of −10, −33, −100 and −500 kPa, respectively. The model was tested using corn emergence data from a field study consisting of eight combinations of three tillage and three surface residue treatments. Field data on corn emergence corresponded well with the growth chamber results obtained with constant diurnal soil temperature cycles. Heat units needed for 75% corn emergence under various tillage and residue conditions at field moisture content (matric potential = 0 to − 10 kPa) corresponded to 52 seed zone growing degree days. This corn emergence model should be useful in predicting optimum planting dates based on measured or predicted historical seed zone temperatures.