Runoff and soil erosion during spring thaw in the northern U.S. Corn Belt.

Surface water runoff and erosion can be accentuated from partially frozen soil and result in loss of soil productivity. Runoff and erosion were assessed during spring thaw on a Hattie clay (Typic Hapluderts) in 1986 and 1990 and on a Barnes loam (Calcic Hapludolls) in 1987 and 1988 in Minnesota. Simulated rain was applied at 64 mm h -1 on four dates during spring thaw to field plots subjected to autumn moldboard plow or chisel plow. Corn (Zea mays L) residue was removed or retained on plots prior to tillage in the autumn. Runoffand soil loss after an application of 96 mm of rain was similar for Hattie clay (6.0 mm m- 2 of runoff and 1.43 kg m -2 of soil loss) and Barnes loam (5.8 mm m -2 of runoff and 1.90 kg m -2 of soil loss). Analysis of variance indicated that date of simulated rain and residue treatment influenced runoff while only residue treatment affected soil loss from both soil types. Regression analysis determined that runoff was accentuated by a wetter and smoother soil surface and from a soil frozen nearer the surface. In addition, nearly 60% of the variability in soil loss occurring from a 96 mm rain in the spring was explained by runoff, random roughness, soil water content, and residue cover. Rate of runoff and soil loss increased by at least 50% for Hattie clay and 100% for Barnes loam as a result of subjecting these soils to a subsequent rain within the same day. In cold regions where autumn tillage is utilized to expedite soil warming and planting of seeds in the spring, roughening and rapidly thawing of the soil or retaining crop residue on the soil surface may be desirable for minimizing surface water runoff and soil erosion during spring thaw.