Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1996
Publication Date: N/A
Interpretive Summary: Growers have been urged to leave a portion of the previous seasons' crop residue on the soil surface to protect the soil from erosion. While crop residue is effective in reducing erosion, it also affects other soil processes including reflectance and absorption of sunlight, evaporation, and soil warming. Other researchers have studied these effects, often only over short periods of time so the residue's characteristics don't change significantly. This study measured how different types of corn residue (fresh vs. weathered) and its placement (random or with a bare strip) affect soil evaporation and heat flow. Large soil blocks were collected from two sites. One soil is organic rich from central Iowa while the other soil is a silty soil from southwest Iowa. Sensors were installed to measure changes in soil moisture, temperature, evaporation, and thermal properties. Two blocks of each soil were put in a chamber where temperature, humidity, and lighting were controlled to simulate a field climate. Experiments were completed with no residue on the soil surface and with fresh residue, weathered residue, and weathered residue with a bare strip. Temperature cycles simulated both fall and spring patterns. Corn residue reduced evaporation by an average of 40%. Thicker layers (fresh residue) reduced evaporation the most. Residue layers acted like a layer of insulation in limiting changes in soil temperature. Whether these effects are beneficial or not for crop production depends on the weather. If rainfall has been limited, the residue layer will help save soil moisture and keep the soil cooler for young plants. If there is too much rain, especially in spring, then residue layers prevent the soil from drying quickly and warming up.
Technical Abstract: Crop residue age and placement have a significant effect on evaporation and soil temperature, yet there are few data regarding residue properties and their effect on soil moisture and thermal regimes. The objective of this research was to quantify the influence of corn (Zea mays. L.) residue age and placement on evaporation from heat flow in two soil types. Duplicate monoliths (0.45 by 0.35 by 0.5 m) of Nicollet loam (fine-loamy mixed, mesic Aquic Hapludolls) and Monona silt loam (fine-loamy, mixed, mesic Aquic Hapludolls) were placed in a controlled environment chamber and instrumented to measure soil temperature, thermal conductivity, heat flux, and moisture content. One monolith of each soil type was also fitted with a load cell to measure the change in mass, which was used to estimate evaporation. Experiments were completed with a bare soil surface and with 0.385 kg m**-2 of fresh or weathered corn residue. For two experiments, the fresh and weathered residue were evenly distributed while, for a third experiment, a 0.15-m wide bare strip was made by moving the weathered residue aside. Cooling and warming diurnal temperature regimes were simulated for each treatment during which mean air temperature shifted 4 deg C over a 96-h period. Cumulative evaporation followed the order Bare> Strip> Weathered> Fresh for both cooling and warming experiments as evaporation was reduced an average of over 40% across both soil types and all residue treatments under wet soil conditions. The chamber environment produced soil temperature and heat flux patterns similar to those observed in field studies including reductions in soil temperature and heat flux when residue is present.