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Low spring soil temperatures commonly restrict the early growth of corn (Zea mays L.) in the northern Corn Belt. A quantitative assessment of the effects of tillage and residue management practices on soil temperature would improve tillage recommendations in this region. The effect of tillage and surface residue cover on seedbed soil temperatures and subsequent corn growth were studied at four sites in the northern Corn Belt that differed widely in soil characteristics including drainage, texture, slope, and organic matter content. Tillage systems included no‐tillage, chisel plow, moldboard plow, paraplow, ridge plant, and wheeltrack plant. A wide range of surface residue cover was imposed on each system at three sites. Corn emergence and leaf number to the six‐leaf stage were closely related to percent in‐row cover and air temperature growing degree days (air GDD) through their mutual relationship to soil temperature growing degree days (soil GDD) at all sites. For a given site and year, percent in‐row cover following planting was the major factor affecting corn growth rate until the six‐leaf stage. Corn planted under high percent residue cover required more time and consequently more air GDD to reach the six‐leaf stage. This added time represents a growth delay that can be expressed as the additional air GDD required to reach the six‐leaf stage. Such delays were related to increased grain moisture and decreased corn grain yield when net cumulative air GDD were less than the threshold value of 1319 and water stress was minimal. In‐row residue cover due to tillage and previous crop can have a major impact on the growth and development of corn in the northern Corn Belt. These factors should be considered in selecting tillage systems in this region.

Crop residues have low densities and are somewhat elastic in nature. The presence of these residues in the soil or at the soil surface might reduce the severity of soil compaction. The objective of this study was to investigate the compression and compaction behavior of soils in the presence of corn residue. Compression behavior of soil‐residue mixtures was studied in the laboratory using the uniaxial compression test. Treatments included three size fractions (0.25‐0.50, 1.00‐2.00, and 3.36‐5.66 mm) of corn residue, four amounts of residue addition, three soil water contents, and three soils (Webster clay loam, Sargent silt loam, and Zimmerman sand). Compression samples consisted of 60 g of wet soil mixed with 0.0, 0.5, 1.0, and 2.0 g of corn residue. The compression index of residue mixed Webster clay loam or Sargent silt loam was approximately the same for various amounts and sizes of corn residues. The compression index of Zimmerman sand increased slightly with an increase in the amount of corn residues. However, for a given amount of corn residue, there was no difference in the compression index of Zimmerman sand for various residue fractions. Bulk density at a reference stress (σk = 100 kPa) decreased slightly with an increase in the amount of corn residue addition. Assuming that the residues are uniformly mixed in the top 15 cm of soil or concentrated in the wheel track (one fourth of the surface area), calculations showed that corn residues available on the farm (6.7 t/ha assuming 100 bushel/acre corn yield) will have little influence on compression parameters and thus on compaction of soils. Influence of surface residues on field soil compaction was tested in an aboveground soil bin containing a top layer of Waukegan silt loam. Residue treatments included 0.0, 3.4, 6.7, and 10.1 t/ha of corn residues on the soil surface. Measurements included normal stress at 200‐mm depth under the center of a wheel track during the passage of a tractor, and soil sinkage and bulk density profile after the passage of a tractor. Differences in the maximum normal stress at 200‐mm depth were <80 kPa between bare and residue‐covered plots. This reduction in maximum normal stress is equivalent to a reduction in bulk density of 0.12 Mg m−3 due to the presence of corn residues. However, because of the soil variability, the bulk density profile showed no significant difference due to the presence of surface residues. In summary, both laboratory and field tests in this study showed minimal beneficial effects of using corn residues in reducing the compression and compaction of soils. This conclusion, however, assumes a maximum amount of 10.1 t/ha chopped corn residue that is approximately equal to a yield of 150 bushel/acre (assuming a grain to straw ratio of 1:1).

Surface crop residues lower soil temperatures delaying emergence of corn (Zea mays L.) under no-till tillage systems in the northern Corn Belt. This study evaluates the use of planting depth as a management tool to overcome the disadvantages of cool temperature under residue covered soils. Growth chamber experiments evaluated the effects of planting depths, ranges of soil temperatures, and soil matric potentials on corn emergence. The seeding medium was aggregates of Webster clay loam (fine-loamy, mixed, mesic Typic Haplaquolls). Deep planting (75 mm) delayed emergence from 2.8 to 18 d as the soil temperatures decreased from ranges of IS to 25 °C and 5 to 15 °C. Seed zone growing degree days (GDD) needed to achieve 75% emergence increased with an increase in planting depth and a decrease in soil matric potential. Relationships of corn emergence vs. seed zone GDD needed to achieve 75% corn emergence at various planting depths were tested in the field for three planting depths, three tillage and three surface residue conditions during 1984 and 1985. Predicted time to 75% corn emergence was within 2 d of the field-measured values for three planting depths, and seven tillage and surface residue conditions, over two seasons. Simulation studies were conducted to predict the effects of tillage, planting depth, and planting date on the probability of obtaining 75% corn emergence within 14 d of planting. Input data for simulation studies included 10 to 20 yr of daily maximum and minimum air temperatures from Morris, MN and Lexington, KY. Tillage treatments included moldboard plow, no surface residue, and no-till surface residues. Reducing the planting depth from 50 to 25 mm advanced the planting date from 2 d to several weeks, depending on the weather, soil matric potential, and tillage-surface residue conditions. When soil water is nonlimiting, the effect of cooler temperatures on corn emergence under a no-till tillage system (with surface residues) can be compensated for by reducing the planting depth by 25 mm or less from that of average planting depth under conventional tillage systems. C ONSERVATION TILLAGE practices in the U.S. northern Corn Belt have often delayed corn emergence, slowed corn seedling growth, reduced final population, and sometimes reduced corn yield (Olson and Schoeberl, 1970; Griffith et al, 1973; Olson and Horton, 1975). Poor crop performance has been attributed to depressed seed zone temperatures due to surface residue cover under conservation tillage systems. Philips (1984) showed that delayed planting frequently reduces corn yields in the Corn Belt. In Wisconsin, Imholte and Carter (1987) found that delayed planting decreased corn grain yields, and yields of both conventional and no-tillage planted corn were generally highest when planting was completed by early May.

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