|Morrison Jr, John|
|Torbert, Henry - Allen|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/9/1996
Publication Date: N/A
Interpretive Summary: Researchers often use "rainfall simulator" machines to produce artificial rainfall under controlled conditions to study its effects on cropland. A common part of such studies is evaluation of the amount of soil protection which is provided by straw and stubble residues from previous crops. This cover is characterized by the percentage of the soil surface which is covered and thus protected from the direct impact of falling raindrops. We evaluated three residue cover methods on 53 rainfall simulator sites to compare the consistency of values obtained among methods. The drop-pin method produced values which were about 5 percentage points higher than the average. A second method which projected color photographic slides onto dot-screens gave values which were only 1 percentage below average. The video image analysis method produced values about 4 percentage points below average. More consistent cover measurements seem to be needed because the results of these studies are typically used to support the improvement of computerized models. Such models are used to estimate the environmental impacts of cropland management schemes on soil resources and water supplies.
Technical Abstract: Video image analysis, drop pins, and dot-screen methods were used to measure wheat residue cover in 1 m**2 rainfall simulator boxes under undisturbed field conditions. The data set consisted of 53 sites and represented residue cover on chisel-till and no-till systems two months after wheat harvest. If the mean from the three methods is taken as the true cover, then there was a trend to produce 5 percent-cover above average cover values with the pin method and 1 percent-cover and 4 percent-cover below average values with the dot and video methods, respectively. For no-till conditions of cover in the 80 to 100 percent-cover range, the differences in values achieved with the three methods may be of little importance. For the low-residue cover chisel-till conditions, the differences were as much as 50 percent of the mean cover and could produce misleading information on the effect of residue cover on runoff, erosion, water quality, and other products of rainfall simulator studies.