Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
6/11/99
FOR IMMEDIATE RELEASE
Contacts:
Gerald A. Miller, College of Agriculture, (515) 294-4333,
soil@iastate.edu
Elaine Edwards, Extension Communications Specialist,(515)
294-5168, eedwards@iastate.edu
Measure Your Crop Residue for Soil Conservation
AMES, Iowa -- By now, most producers are close to wrapping up the planting season. That means now is a good time to measure your crop residues--the stems and stalks remaining from last year's crop. Crop residue provides the most important cover for the soil, protecting it from erosion until crops can produce a protective canopy.
Knowing how to measure existing residue will give you a good idea of how well your soil is protected against erosion. And measuring residue before this year's crop emerges helps ensure that you are in compliance with best management practices and the objectives of your farm's conservation plan, according to Jerry Miller, Iowa State University agronomist.
How much residue is enough at this time of year? For most soils, the higher the level of crop residue left, the greater the benefits. But the consensus of most experts is that the most effective conservation tillage plans show at least 30 percent or more crop residue remaining after planting, Miller said.
There are several methods for estimating residue. The most reliable is the "line-transect" method. The line-transect method involves counting the number of times a marked line intersects a piece of residue.
To do this, use a 100-foot tape measure (or a rope with marks spaced at one foot intervals). Stretch the tape between two stakes placed diagonally at a 45-degree angle from the direction of the crop rows. (Be sure to exclude end rows from your sample.) Walk along the tape and count the number of times the marks intersect a piece of residue. To guarantee the best accuracy, be sure to look from directly above the tape. When you are done, the result converts into the percentage of crop residue remaining in that sample area. It's important to get a minimum of five measurements using areas that are typical of the field you are measuring. Then average the estimates to obtain the most accurate overall assessment.
Another method is using a meter stick (or a yard stick with metric marks). Place the meter stick on the soil. Measure in centimeters the crop residue occurring along one edge of the meter stick, and total those measurements. For example, if the total residue occurring along the meter stick measures 35 centimeters, your percentage of residue remaining is 35 percent. Again, sample several areas of the field. Places where the measurements are taken can be determined randomly by throwing the meter stick over your shoulder.
The photo-comparison method can help you estimate your residue by comparing it to percentages in photo that show a known percentage of crop residue. Be sure to look straight down when comparing the photos in your fields, since your perspective from an angle will be misleading. Again, repeat your estimates at several sites and average them to ensure that you are getting a broad estimate for the entire field.
Miller said the calculation method is a good way to estimate residue without going to the field. But since there are many variables, including weathering and individual tillage operations, it is less reliable and provides only a rough estimate. Use the table for estimated cover remaining after each tillage operation.
Finally, remember that planning residue cover begins in the fall as you harvest, Miller said. Make certain that your combine is properly set to distribute residues evenly over the crop field. Residues are your only protection against fall, winter and spring precipitation. Also, consider reducing the number of tillage passes, since every tillage pass buries additional crop residue. If you have any questions about measuring your crop residues, please feel free to call your local Soil and Water Conservation District office.
Estimate Your Residue
Multiply each operation by the existing percentage of residue left to find how much ground cover will be left after each tillage operation.
|
Operation |
Soybeans (planted in corn residue) |
|
After Harvest |
|
|
Over Winter Decomposition |
|
|
Plow |
|
|
Chisel (twisted shank) |
|
|
Disk (off-set, deep) |
|
|
Paraplow |
|
|
Chisel (straight shank) |
|
|
Disk (tandem, shallow) |
|
|
Anhydrous Applicator |
|
|
Field Cultivator |
|
|
Plant |
|
|
Till-Plant |
|
An example of how to calculate:
|
After Harvest |
(.95) |
|
After Winter |
x (.90) |
|
Spring Chisel (straight shanks) |
x (.60) |
|
Spring Disk (shallow) |
x (.75) |
|
Planting |
x (.95) |
|
Percent Ground Cover After Planting = |
(.36) |
ml: isufarm
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