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Flat Residue Loss by Wind for Different Crop Types: Field Experiments
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Soil Erosion Research Under a Changing Climate, January 8-13, 2023, Aguadilla, Puerto Rico, USA .(doi:10.13031/soil.23015)Authors: Jiaqiong Zhang, Larry E. Wagner, Katie Talley
Keywords: Flat residue, Portable wind tunnel, Standing residue, Wind Erosion Prediction System (WEPS).
Abstract
After harvest, flat residue can help protect the soil surface from wind erosion. However, flat residue itself can also be susceptible to wind erosion, if it is not anchored to the soil or is not sufficiently sheltered from the wind by the standing crop stalks left in the field. The loss of surface residue cover itself increases the susceptibility to soil erosion by both wind and water. In addition, it can cause environmental damage, not only from the loss of soil, but also due to loose residue leaving the field. This field study attempts to determine, under typical field conditions, the wind velocities under which different types of unanchored flat residue are either redistributed within the field or removed. Soybeans, winter wheat and grain sorghum were selected because they covered a range of residue classes, based upon the residue classification system used by the Natural Resource Conservation Service (NRCS). Each crop residue evaluated falls under one of the following toughness/size classes labeled: “fragile, very short residue”, “moderate, short residue” and “non-fragile, medium length residue” respectively. Field experiments were conducted with a portable outdoor wind tunnel at nominal free stream wind velocities of 4-6, 8, 10, 14, 17, and 19 m s-1 perpendicular to the crop rows. Experimental field conditions consisted of two separate mowed stem heights for winter wheat (6 cm and 10 cm), the harvest height for soybeans (6 cm) and a single mowed height for grain sorghum (11 cm). The results show that flat residue rearrangement (residue bunching up against adjacent crop rows) and removal of residue increased with increasing wind speeds for all tested crops. The loss of flat residue not only correlated to characteristics of standing crop stalks but also to the characteristics of the loose flat residue. For different types of standing stalks with similar Stem Area Index (SAI) values, increased stem height decreased the loss of flat residue, while the amount, water content and shape of the flat residue also affected the loss of residue from the field plots by wind. Most of the residue blown away first consisted of light leaves, small branches and short stems at the lower free stream wind velocities, which indicated the strong selectivity of the wind to the lighter loose flat residue components. Additionally, the remaining larger flat residue components that did not leave the field at higher wind speeds wound up being trapped against the downwind rows of standing stalk residues, demonstrating the additional protection from the wind provided by the standing stalks. Results of this study are valuable for the management of loose flat residue after harvest in the field and are potentially significant for the improvement of wind erosion models like the Wind Erosion Prediction System (WEPS).
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