Crop residue, or stover, includes leaf and stalk tissues of field crops that have traditionally been returned to the soil as an important source of organic matter and plant nutrients. Since the Dust Bowl of the1930s, crop residue cover left at the soil surface by minimizing tillage has also been recognized as a key erosion control tool. Yet, current trends in field crop production systems are encouraging some producers to harvest more stover for use as bedding, forage and even bioenergy feedstock.
Higher average biomass yields, reduced tillage and new demand from the livestock and energy sectors are fundamental factors creating site-specific opportunities for profitable stover harvest. Growers with multiple years of no-till corn in rotation may even see modest yield benefits from removing residue that can otherwise inhibit soil warming and planting. Still, it is important to remember that removing too much crop residue from a field has the potential to increase risks of wind and water erosion and negatively impact soil organic matter concentrations. Maintaining a base level of surface cover and returning enough stover to maintain long-term soil organic matter pools should be paramount in residue management decisions. Estimating the amount of residue cover remaining in a field after tillage or planting is an easy way to strike an appropriate balance.
The line transect method generates an accurate estimation of residue cover using one simple tool, a measuring tape or marked rope. The line can be 100 feet long marked or knotted at one foot intervals or 50 feet long marked every 6 inches. In the field, the line is stretched diagonally to crop rows and each end anchored in place. Residue cover is evaluated at each marked point along the line to calculate a simple percent cover measure (X/100). A point can be counted if it is directly over crop residue, cover crop tissue, weeds, animal bedding or anything else likely to absorb the impact of a 3/32-inch raindrop. Observations must be made from a consistent perspective, walking along one side of the line and looking straight down at each recording point. Some find it helpful to count using a 3/32-inch diameter dowel to simulate the path of a raindrop. Calculating the mean of five separate cover measures taken at representative sites dispersed throughout a field provides an acceptable overall estimation.
The Natural Resource Conservation Service (NRCS) conservation compliance standard of at least 30 percent residue cover remaining immediately after planting is a general goal to shoot for, but strict no-till systems can maintain as much as 60 percent cover from corn and 40 percent from soybeans. Achieving the “perfect” amount of cover is difficult and dependent on the specifics of tillage and planting operations as well as environmental conditions. Fortunately, tools are available to estimate the impact of various field operations on residue cover and also the amount of stover that could be removed without compromising the soil.
Michigan State University Extension has a table available that shows the average impact of tillage and planting implements on residue cover. If line transect measures are completed in the fall, cover remaining at planting can be estimated by multiplying the fall cover by each accumulative factor associated with subsequent operations (see example). Michigan State University Extension recommends higher estimation values should be used for corn and small grain residue and lower values for more fragile residue such as soybean stover. Residue cover can also be measured directly after planting in the spring.
Another handy tool, the Lucas Soil Organic Matter Calculator available online through The Ohio state University South Centers, is a spreadsheet based calculator that uses baseline soil data and information regarding production practices like residue removal, tillage, manure and cover crop use to predict soil organic matter dynamics. With this basic information, growers can target specific stover removal and residue cover rates appropriate for their unique cropping systems. Line-transect and crop biomass measurements are then simple ways to confirm the short-term results of these efforts. When complimented by soil health monitoring using emerging analysis techniques, the tools available provide an unprecedented and comprehensive soil health management package for field crop producers.