How Does Your Crop Residue Measure Up?

University research shows that soil erosion can be greatly reduced in fields that have a minimum 30% crop residue cover on the soil surface – the accepted threshold for conservation tillage – after all tillage and planting operations are complete. That means starting with considerably more residue on the ground at the end of harvest, ideally distributed evenly over the field.

There are several advantages to know how to estimate your residue levels, from after harvest all the way through planting: to determine how well your combine is spreading residue, how well the soil is protected and how your overall conservation plans are working, in addition to having the information required for some conservation programs.

You can estimate crop residue cover using one or more techniques between harvest and emergence of the next crop, according to guidelines from several universities. The first three listed here are done through field observation; the last, calculation, is more generalized and used mainly for conservation planning.

Line Transect

AGCO agronomist Jason Lee estimates the residue coverage of a field of young corn plants using the line transect method.

Jason Lee, North American agronomy and farm solutions specialist for AGCO, uses the line transect method by laying down a 100-foot tape measure (or staking down a rope marked at 1-foot intervals) at a 45-degree angle across the crop rows. He looks straight down at the tape and counts the number of times he finds a piece of crop residue at a foot mark. If 45 of 100 “foot” marks intersected with residue, the estimated residue cover is 45%. He recommends repeating the process in at least five different spots in the field to obtain a field average.

Meter Stick

An Iowa State University Extension guide to measuring crop residue lists another estimating method that uses a meter stick or a yardstick with metric markings. Determine random places to measure by throwing the meter stick into the air and, wherever it lands, note how many centimeter marks on the edge stick touch crop residue. The total out of 100 centimeters is the percentage coverage in that spot.

Photo Comparison

Another way to do a quick estimate of residue cover is to compare your actual field conditions to photographs of known percentages of cover available from Extension crop residue guides. It’s important to look straight down at a spot typical of the field when comparing to your residue to the reference photos, rather than from an angle or from the road or field edge.

Calculation

University researchers have developed calculation tables for how much various field operations influence surface residue cover, by crop, through the season. Growers can consult a table which shows average initial “after harvest” flat residue percentages based on soybean or corn yields in a field, then calculate how much residue may be removed by planned tillage and planting operations.