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Revisit How Residue is Calculated

Revisit How Residue is Calculated
Earlier article contained an error that needs explaining.

If you're a faithful Web reader and recall the Jan. 3 article about still time to enter the free seed contest, you may have caught an error. The contest ended Jan. 15, with a sizable number of entries buying for the free seed offered by Beck's Hybrids, Atlanta. Winners will be formally announced in the March issue of Indiana Prairie Farmer and will also be announced here on the Web when appropriate.

The article provided a 'freebie' answer to question 2 if you were filling out the 10-question quiz and sending it in to enter the contest. The only problem is there was an error in calculation, resulting in the wrong answer. As a result, both the right answer and the answer printed in the article for question 2 will be counted as correct as the entries are scored and graded.

Here's the rundown. The question was:

If 25 knots in a 50-foot rope with a knot each 6 inches touch residue (when stretched at random across the field), soil cover is: a) 100%; b) 25%; c) 50%; d) 75%.

The answer should be b, 25%, but in the article, it was reported as c, 50%. Even editors make mistakes!

If the rope was 100 feet and there was a knot every foot, it would be simple. Count the number of knots that directly touch or lie upon a piece of residue, and that would be the percent cover of the soil left in the field.

However, many people use 50 foot ropes with a knot every 6 inches because it's more convenient and practical to use a shorter rope, especially if you're limited on help. To have 100 knots, one for each percent, knots are now 6 inches apart. To get the percentage cover, you still count the number of knots touching the residue. If 25 of 100 total knots touch residue, the cover is still 25%.

To be 50% cover, you would need 50 of 100, or half, of all the knots touching or lying over a piece of residue.

The ropes became popular when the highly erodible land provision first came into the Farm Bill in the 1980s. It's useful again now to check residue levels behind some of the new minimum tillage tools.

For example, a study last spring indicated that vertical tillage tools run correctly only reduce total cover by a relatively small amount, although the pieces of residue on an individual basis are smaller.  

TAGS: Tillage
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