EFFECTS OF RESIDUE-FREE BAND-WIDTH ON SOIL-TEMPERATURE AND WATER-CONTENT

In the Northern Corn Belt, corn crop emergence can be delayed due to slow soil warming and drying when residue is present above the seed furrow. This study was conducted to determine the effects of residue-free band width on soil temperature and water content. Residue-free bands of 0, 80, and 320 mm, as well as a 360-mm-wide residue-free furrow, were created in a field plot study. Also, residue-free bands of 0, 80, 160, and 320 mm were created in a controlled environment study. A thermocouple matrix was placed in the soil around the seed zone. Soil temperature was recorded on a hourly basis during the normal crop planting and emergence period. Soil water samples were also periodically taken during the time soil temperature was determined. In the field study, the width of the residue-free band had a significant effect on temperature in the seed zone and less effect on soil water content. Based on accumulated growing degree days, the theoretical time to corn emergence was modeled as a logarithmic function of band width. Initially, the gradient of this relationship was large, which indicated the accumulated growing degree days increased rapidly with increasing band width. But with band widths greater than 300 mm, the curve's slope became relatively flat. In the controlled environment study, soil temperature below residue was substantially less than that below bare soil. A 320-mm band width accumulated sufficient growing degree days for corn to emerge on the same day as a treatment with no residue cover. Residue condition (shredded and nonshredded) and residue density (6000, 8000, and 10 000 kg/ha) had no significant effect on soil temperature. Soil under residue, even at the bare soil/residue interface, was generally higher in soil water than that below the clear soil surface. A residue-free band width in the 200- to 300-mm range would produce sufficient accumulated growing degree days to result in corn crop emergence on the same day as a treatment with no residue cover.