Impact of Tillage and Crop Rotation Systems

on Soil Carbon Sequestration

by Mahdi Al-Kaisi

What is carbon (C) sequestration? of greenhouse gases from the soil are: (1) the potential
Carbon sequestration can be defined as the capture and increase of CO2 emissions from soil contributing to the
secure storage of carbon that would otherwise be emitted increase of the greenhouse effect, (2) the potential increase
to or remain in the atmosphere. The idea is to (1) prevent in other gas emissions (e.g., N2O and CH4) from soil as a
carbon emissions produced by human activities from consequence of land management practices and fertilizer
reaching the atmosphere by capturing and diverting use, and (3) the potential for increasing C (as CO2) storage
them to secure storage, or (2) remove carbon from the into soils, which equals 1.3 – 2.4 × 109 metric tons of
atmosphere by various means and store it. carbon per year (Tans et al., 1990), and to help reduce
future increases of CO2 in the atmosphere.
What is the importance
of carbon sequestration? Carbon benefit to the soil
The scientific consensus is that the levels of greenhouse Soil carbon, or organic matter in general, is important
gases in the atmosphere are increasing. These changes in because it affects all soil quality functions (Fenton et al.,
greenhouse gas emissions generally are linked to human 1999):
activities. The concern is that the mean global level of
greenhouse gases in the atmosphere is increasing to a level  Sustaining biological activity, diversity, and productivity
that can trigger serious climate changes in air temperature  Regulating and partitioning water and solute transport
and violent weather cycles.
 Filtering, buffering, degrading, immobilizing, and
Carbon sequestration by agricultural land has generated detoxifying organic and inorganic materials, including
international interest because of its potential impact on industrial and municipal byproducts and atmospheric
and benefits for agriculture and climate change. Where deposition
proper soil and residue management techniques are
implemented, agriculture can be one of many potential  Storing and cycling nutrients and other elements within
solutions to the problem of greenhouse gas emissions. the earth’s biosphere
Additionally, agriculture conservation practices such as
the use of different cropping and plant residue management, The impact of soil organic matter on the soil qualities listed
as well as organic management farming, can enhance above and soil functions can be summarized as follows:
soil carbon storage. Farmers, as well as the soil and  Physical effects: soil aggregation, erosion, drainage,
environment, receive benefits from carbon sequestration. aeration, water-holding capacity, bulk density, evaporation,
Agricultural ecosystems represent an estimated 11% of and permeability.
the earth’s land surface and include some of the most  Chemical effects: cation exchange capacity; metal
productive and carbon-rich soils. As a result, they play complexing; buffering capacity; supply and availability of
a significant role in the storage and release of C within N, P, S, and micronutrients; and adsorption of pesticides
the terrestrial carbon cycle (Lal et al., 1995). The major and other added chemicals.
considerations of the soil C balance and the emission

PM 1871 Reviewed and Reprinted September 2008

Biological effects: activities of bacteria, fungi, practices that minimize soil disturbance and optimize
actinomycetes, earthworms, roots, and other plant yield through fertilization. It is possible that
microorganisms.Different sources of organic matter supply improved land management can result in a significant
soils with carbon to replenish their C and nutrient pools. increase in the rate of carbon into the soil. Because of the
However, organic materials added to soils contain a wide range relatively long turnover time of some soil carbon fractions,
of C compounds that vary in their rate of decomposition. this could result in storage of a sizable amount of carbon
The biological breakdown of the added organic material in the soil for several decades.
depends on the rate of degradation of each of the carbon-
containing materials. Changes in environmental factors Processes affecting carbon
can cause changes in the rate of decomposition of organic sequestration in soils
materials in soils, such as soil moisture status, soil Several processes can affect the storage of carbon in soils.
aeration, soil temperature, pH, and availability of minerals. The amount of carbon stored in the soil system depends
on the rate and magnitude of the process. These processes
Carbon pools and sinks can be influenced by agriculture management systems and
Soils store a significant amount of carbon. It has been practices.
estimated that global soils contain approximately 1.5
× 1012 metric tons of carbon (Post et al., 1998). As a Organic production
component of the carbon cycle (Figure 1), soils can be Carbon production can be increased through
either net sources or net sinks of the atmospheric carbon photosynthesis, in which the permanent vegetation cover
dioxide. Changes in land use and agricultural activities can store a significant amount of carbon dioxide as
during the past 200 years have made soils act as net organic carbon. The volume of vegetation acts as a sink
sources of atmospheric CO2. Evidence from long-term for capturing CO2 and secures storage of it as carbon.
experiments suggests that carbon losses due to oxidation Farming practices and and land use can greatly affect the
and erosion can be reversed with soil management carbon status in the soil system. During plant growth, CO2

Atmospheric carbon
Photosynthesis

Photosynthesis

Decomposition
Net uptake

Respiration
Deforestation
Decay

Respiration
Fossil fuel use

Changing land use

Consumption
Water Plants Animals
(oceans, lakes, etc.) and humans
Formation
Soil

Wastes
Sedimentation

Fossil fuels
Geologic

Soil system
time

Soil
Sediments erosion

Figure 1. Carbon cycle aspects (modified from Paul and Clark, 1996)

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from the atmosphere will be fixed in the plant as carbon
compounds. Therefore, the primary source of carbon is the Benefits of Organic Matter
plant, in which the carbon has been manufactured initially Source of nutrients for crops
through the photosynthesis process.
Provides the major natural source of inorganic
Minimize organic carbon breakdown nutrients and microbial energy
The oxidation and breakdown of plant residue will
Promotes soil aggregation and root
accelerate the loss of carbon as CO2. Several factors can
development
accelerate organic carbon breakdown and production
of greenhouse gases. They include soil moisture, soil Favors the development of antagonistic
pH, the oxidation-reduction process, soil temperature, organisms that serve to combat certain plant
chemical and physical soil properties, nutrient status, diseases
and plant residue quantity and quality. The breakdown of
residue through conventional tillage and soil disturbance Improves water infiltration and water use
must be minimal to fully store carbon in the soil system. efficiency
Carbon stored in the soil can help improve soil physical
Improves soil water-holding capacity
properties such as infiltration rate, water-holding capacity,
aggregate stability, soil structure, soil aeration, and a host Increases soil aggregate stability to resist
of other physical properties. In addition, carbon storage erosion
can contribute significantly to improving soil nutrient
pools and other chemical properties. Plant residues play
Impact of conservation practices and fertilizer use on
a significant role in providing a positive environment for
carbon storage in soils
improving soil microbial populations, which in turn play
Conservation tillage practices can minimize the rapid
a significant role during the decomposition process of
breakdown of plant residues, reduce CO2 emission, and
organic materials. Keeping plant residues intact is a critical
reduce the production of inorganic dissolved nitrogen (i.e.,
component of soil management, not only for nutrient
nitrate and ammonium) in soil. When conventional tillage
value, but also for soil protection from wind and water
is converted to conservation tillage, both CO2 emission
erosion.
from soil and N-uptake by crops are reduced. Reduction
Soil erosion in CO2 emission from soils enhances soil organic carbon
Improper soil and residue management results in increased (SOC) content, but reduction in N-uptake decreases
erosion by water and wind. Soil erosion is a leading cause residue production and hence, organic C storage in soils.
of soil degradation due to the loss of organic matter, which is Also, it was found that reducing tillage significantly
the “glue” or binding factor in soil. In Iowa, water erosion decreases SOC loss from soils with high organic matter
contributes significantly to the degradation of soil quality. content.
The most effective way to minimize soil erosion is through
The Morrow plots at the University of Illinois were
the use of conservation tillage practices. The impact of
established in 1876 to study the effects of crop rotations
no-tillage practices in improving soil quality in terms
and fertilization on yield (Table 1). Crop sequences, in
of carbon content at the upper part of the soil profile is
a single replication, were continuous corn, corn-oats
evident where permanent vegetation has been established
rotation, and corn-oats-clover rotation, with and without
in grassy areas. Tillage can cause the loss of significant
lime, manure, and rock phosphate (Stauffer et al., 1940).
amounts of carbon (lost as CO2 bursts) immediately after
The results show that continuous corn plots with no
tillage. The exposure of soil organic carbon to aeration
fertilizer decreased soil organic matter (SOM) content
during soil erosion increases CO2 emissions. In addition,
by 45.6% in 55 years as compared with the adjacent
soil erosion can cause carbon to accumulate with soil
sod (Table 1). Neither the cropping system nor the soil
sediments and be removed from the soil carbon pool. The
treatment had much effect on soil organic carbon below 9
removal of carbon from the soil will lead to a decline in
inches.
soil fertility and aggregate stability.

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Table 1. Effect of rotation and treatments on organic carbon content in Morrow plots, 1876–1940,
University of Illinois (after Stauffer et al., 1940)

Rotation Treatmenta % Organic C % Organic Matter % C changeb

Corn None 1.74 2.99 –45.6

MLP 2.09 3.59 –34.7

Corn-Oats None 2.14 3.68 –33.1

MLP 2.44 4.20 –23.6

Corn-Oats-Clover None 2.28 3.92 –28.7

MLP 3.35 5.76 +4.0

Sod None 3.20 5.50 0.0

MLP = Manure-Lime-Phosphorus
a

% C changes based on sod C value

b

Figure 2 summarizes the long-term impact of different should have soil organic matter of approximately 4.5–5%
crop rotations on soil carbon content. The data showed (Fenton et al., 1999). Figure 3 shows another long-term
a higher rate of soil carbon decline under continuous crop rotation system. The rate of decline was the greatest
corn compared to corn-oats-meadow crop rotation. The during the period of 1916–1938 and then the rate of
plots were located on 9% slope gradients and some loss change decreases. The average loss of soil organic carbon
of soil organic carbon can be attributed to erosion. The during 1946–1956 was 2.1%.
uncultivated Marshall soil on which the plots are located

C-O-M = Corn-Oats-Meadow C-SG = Continuous Small Grain

C-C = Continuous Corn C-RC = Continuous Row Crop
A-RC = Alternative Row Crop and Fallow
Figure 2. Changes in organic matter in Iowa (after
Van Bavel and Schaller, 1950) Figure 3. Influence of cropping system on organic
carbon (Hays, KS) (after Hobbs and Brown, 1965)

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Summary References
This publication is intended to explain carbon Fenton, T. E., J. R. Brown, and M. J. Maubach. 1999.
sequestration, present facts about the carbon cycle, present Effects of long-term cropping on organic matter
concerns related to elevated atmospheric CO2 levels, content of soils: Implication for soil quality. Soil and
and show the relationship between current agriculture Water Con. J. p. 95–124.
practices and the carbon cycle. Carbon sequestration is
highly related to soil and management systems. Research Hobbs, J. A. and P. A. Brown. 1965. Effects of cropping
on the impact of tillage practices and crop rotation has and management on nitrogen and organic contents
demonstrated that no-till and permanent vegetation are of a western Kansas soil. Tech. Bull. No. 144. Kansas
more effective in storing carbon in the soil. The use of crop Agric. Exp. Stn., Manhattan.
rotation and conservation tillage, in addition to effective Lal, R., J. Kimble, E. Levin, and B. A. Stewart (Eds.).
manure and nitrogen management systems, contributed 1995. Advances in soil science: Soil management and
significantly to improving soil carbon status. The value of greenhouse effect. Bocan Raton: Lewis Publishers. P. 93.
storing carbon through conservation practices can be very
significant in improving soil quality and productivity as Stauffer, R. S., R. Muckenhirn, and R. T. Odell. 1940.
listed earlier. Organic carbon, pH, and aggregation of the soil of
the Morrow plots as affected by type of cropping and
Farmers can benefit from carbon sequestration through manurial addition. J. Am. Soc. Agron. 32:819–832.
the use of conservation tillage, crop rotation, the use of
buffer strips, and permanent vegetation for highly eroded Tans, P. P., I. Y. Fung, and T. Takahashi. 1990.
soils. These benefits include improved soil productivity, an Observational constrains on the atmospheric CO2
improved environment due to less erosion, and improved budget. Science 247:1431–1438.
physical and biological properties of soil. Carbon credit is
another benefit that has been explored recently by many Van Bavel, C. and F. Schaller. 1950. Soil aggregation,
different entities. Carbon credit is worth exploring but organic matter, and yields in a long-time experiment
needs careful consideration. The issues of market value, as affected by crop management. Soil Sci. Soc. Am.
policy, carbon monitoring procedures, and management Proc. 15:399–408.
entities are among those that need to be addressed when
considering carbon sequestration and credits.

The availability of recent carbon sequestration data in

Iowa is very limited although many projects currently
are addressing this issue. Carbon sequestration must be
viewed as a long-term process in order to see meaningful
impacts of conservation tillage, residue management,
manure and fertilizer use, crop rotations, etc. Farmers,
crop advisors, and others who deal with carbon
sequestration need to recognize that carbon sequestration
is a reversible process. They must adopt a system that
improves soil carbon sequestration as a long-term
management tool because any short-term disturbance,
such as a change from conservation tillage to conventional
tillage, will not achieve significant improvement in soil
carbon status. Therefore, farmers need to think long-term
when thinking about carbon sequestration.

The overall benefits of soil carbon sequestration need to be

viewed as an opportunity to improve soil quality as well as
the environment.

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Prepared by Mahdi Al-Kaisi, associate professor of Soil Management, This institution is an equal opportunity provider. For the full non-
Department of Agronomy, Iowa State University discrimination statement or accommodation inquiries, go to
www.extension.iastate.edu/diversity/ext.
File: Agronomy 8