Crop Residue Decomposition Explained
Key Points
 Residue decomposition plays
a role in both percentage of
residue remaining at planting
as well as nitrogen availability
during and after
decomposition.
 Immobilization occurs when N
is consumed by soil microbes
to fuel decomposition and is
not available to plants.
 Carbon to nitrogen ratio, time,
and temperature influence the
rates of decomposition.
While there are several factors that affect the resulting amount of residue at planting,
decomposition plays a role in both percentage of residue remaining as well as nitrogen
(N) availability during and after decomposition. In corn, it is estimated that approximately
95% residue cover remains after harvest. When no other fall or winter management
practices are factored in, winter decomposition alone has been found to drop the
percentage coverage to roughly 86%.4
Why is crop residue decomposition important?
The process of crop residue decomposition is important because of its influence on the
subsequent crop. There are three primary areas of risk that crop residue poses to the
next crop: seedbed conditions, disease potential, and N immobilization. The presence
of too much crop residue at planting puts the new crop at risk for soil conditions that
are too cool and moist for optimal emergence and can harbor disease-causing
pathogens. Additionally, if the bulk of residue decomposition is occurring during the
growing season, N required for that process can limit N availability for crop growth and
development. Understanding how crop residue breaks down and the factors that
influence it can help farmers manage crops and crop residues to their benefit.
How residue decomposition works
Crop residue is composed of lignin, cellulose, hemicellulose, and nutrients. In order for
residue to decompose, many biological and chemical processes take place that are
influenced by environmental and soil conditions such as air and soil temperature, soil
moisture, pH, oxygen level, and soil microbial community. This nutrient cycling is a complex process that takes differing amounts of
time based on the type of residue.
Residue decomposition includes the processes of N
immobilization and mineralization, both of which involve soil
microbes (Figure 1). During decomposition, soil microbes
feed upon the carbon (C) in crop residue and require N for
the process. Immobilization occurs when N is consumed
by soil microbes and is not available to plants.
Mineralization is a soil microbe mediated release of N from
organic to inorganic sources. A higher concentration of C
as compared to N will result in soil microbes taking a
longer amount of time to break down the organic material
and using more soil N to do their work.
Figure 1. The interaction between available N and microbial activity that aids in decay of
crop residue. (Adapted from Modern Corn and Soybean Production.)
Channel.com
Soil microbes prefer a C:N ratio of around 10:1, but the
ratios of different crop residues vary greatly. Soybean,
alfalfa, and other legumes generally have a C:N ratio near
15:1, thus resulting in faster mineralization. Crop residues
with higher C:N ratios, such as corn, take more time to
decay and result in higher amounts of N being required by
the microbes from the soil solution to lower the C:N ratio.2
For additional agronomic information, please contact your Channel Seedsman
Crop Residue Decomposition Explained
If not taken into account, the microbe requirement for N can compete with a growing corn crop for available N to maintain their
desired C:N ratio of 10:1.3 Nitrogen deficiency symptoms can occur during this period of immobilization.
How can I manage decomposition?
While cropping system and ecosystem management can influence the factors critical to the processes of residue decomposition,
there is little that can be done to “manage” for optimal decomposition. It has long been thought that influencing the size of the
residue or its amount of contact with the soil could hasten the decomposition process, but recent research has proven that is not
the case.
A three-year study conducted in Iowa evaluated the effects of tillage on residue breakdown. The study showed no significant
differences in decomposition or the percentage of residue remaining after 12 months among deep tillage, strip-tillage, and no-till
systems.5 Another practice thought to hasten decomposition was to apply N fertilizer to residue after harvest seeking to stimulate soil
microbes and speed the process. The Iowa research also evaluated the effects of both temperature and N application on the rate of
residue decomposition. Observations from both field and laboratory studies showed that temperature had an effect on the rate of
decomposition; a slower rate of decomposition was observed at low temperatures and it increased with higher temperatures. There
was, however, no difference in residue decomposition with different rates of N added.5 These findings confirm that neither the use of
tillage nor N application work to speed the decomposition process, and they may actually be counterproductive from an economic
and environmental standpoint.
That being said, although tillage does not hasten the decomposition
process, it does still serve a purpose in many cropping situations. One
example is the use of strip-tillage to remove residue from the row for
improved seedling emergence. Removal of debris from the strips of soil
where seeds will be planted can help to warm soil faster and eliminate
some of the physical barriers to seedling emergence (Figure 2.).
So, what can a farmer do to encourage residue breakdown in fields?
Use of management practices that enhance soil health and
microorganism populations can help encourage residue breakdown.
Use of cover crops can provide additional energy, C, and N to the soil
helping to sustain a wide range of soil microorganisms. It has also been
proven that both time and temperature influence the rate of residue
decomposition. While both of these factors are out of our control, one
way to use time to your advantage though is to consider crop rotation.
Rotation cycles that include legumes, such as soybean, can put N back
into the soil more quickly and give corn residue more time to
decompose.
Summary
Figure 2. Although strip-till does not hasten residue decomposition, it
can help improve seedling emergence by allowing soil to warm up
faster and removing physical barriers to emergence.
Many biological and chemical processes take place during the course of crop residue decomposition. Soil microbes feed upon the C
in crop residue and require N for the process. A higher concentration of C as compared to N will result in soil microbes taking a
longer amount of time to break down the organic material and using more soil N to do their work. Recent research findings have
shown that neither the use of tillage nor N application to residue contribute to increasing the rate of decomposition. However, the
use of cover crops and crop rotation can help to build healthy soils and microorganism populations that encourage residue
breakdown.
Sources:
1
Nielsen, R.L., Johnson, B., Krupke, C., and Shaner, G. 2007. Mitigate the downside risks of corn following corn. Corny News Network Articles. Purdue University Extension.
www.agry.purdue.edu. 2 Mannering, J. and Griffith, D. 1985. Value of crop rotation under various tillage systems. AY-230. Agronomy Guide. Purdue University Extension.
www.extension.purdue.edu. 3 Hoeft, R.G., Nafziger, E.D., Johnson, R.R., and Aldrich, S.R. 2000. Modern corn and soybean production. MCSP Publications. Champaign, Illinois. Pages
121-131. 4 Al-Kaisi, M. and Hanna, M. 2009. Residue management and cultural practices. PM 1901a. Iowa State University Extension. www.extension.iastate.edu. 5 Al-Kaisi, M. 2014.
Myths and facts about residue breakdown. Integrated Crop Management News. Iowa State University. www.extension.iastate.edu/CropNews/.
Web sources verified 10/5/15.
This publication was developed in partnership with Technology, Development & Agronomy by Monsanto.
Individual results may vary, and performance may vary from location to location and from year to year. This result may not be an indicator of results you may obtain as local growing, soil and
weather conditions may vary. Growers should evaluate data from multiple locations and years whenever possible. ALWAYS READ AND FOLLOW PESTICIDE LABEL DIRECTIONS. Channel®
and the Arrow Design® and Seedsmanship At Work® are trademarks of Channel Bio, LLC. All other trademarks are the property of their respective owners. ©2015 Monsanto Company.
140909011101 091514JMG
Channel.com
For additional agronomic information, please contact your Channel Seedsman