Corn stubble height and residue placement in the northern US Corn Belt Part I. Soil physical environment during winter

Management of crop residue is important for sustaining biological activity in soils during winter and promoting soil water recharge and early spring thaw in cold regions. This study assessed the impact of stubble height and residue placement in a corn (Zea mays L.) production system on the soil microclimate during winter in the northern Corn Belt of the USA. Residue treatments were established in a randomized block design after corn harvest in the autumn of 1993–1995 near Morris, MN. Corn was harvested using a combine that cut stalks at 60, 30 and approximately 0 cm above the soil surface and uniformly spread harvested residue over the soil. Treatments included: (1) 60 cm stubble, (2) 30 cm stubble, (3) 30 cm stubble with alternating bare and residue covered inter-rows, (4) 0 cm stubble, and (5) 0 cm stubble with all residue removed from the soil surface. Snow cover, depth of soil freezing and thawing, soil temperature and water content at various depths in the soil profile, and reflected global and net radiation were monitored during winter from November to March each year. Taller (60 cm) stubble trapped more snow, reduced the depth of frost penetration by at least 0.5 m, and hastened thawing of the soil profile by at least 25 days during winter as compared with short (0 cm) stubble and 0 cm stubble without residue treatments. Near surface, winter soil temperatures were moderated by at least 2 °C in the 60 cm stubble versus 0 cm stubble without residue treatments. Linear regression analysis suggested that 52, 93 and 40% of the variability in soil water recharge caused by residue treatments during successive winters, respectively, could be explained by differences in snow cover, soil water content and thaw depth among treatments. On clear days in autumn and spring, albedo was highest for the 0 cm stubble and lowest for the 0 cm stubble without residue treatments. Net radiation, however, was lowest for the 0 cm stubble and highest for the 0 cm stubble without residue treatments as compared with other residue treatments. Results from this study suggest that corn production systems in the northern Corn Belt which retain tall stubble on the soil surface will promote warmer soils during winter and earlier spring thaw as compared with those which retain short or no stubble on the soil surface.