crop residue and tillage effects on carbon sequestration in a luvisol in central ohio

Crop residue and tillage effects on carbon

sequestration in a Luvisol in central Ohio

S.W. Duiker, R. Lal*

School of Natural Resources, Ohio State University, 2021 Coffey Road,Columbus, OH 43210-1085,USA

Received 3 July 1998; received in revised form 2 March 1999; accepted 1 June 1999

Abstract

Soils play a key role in the global carbon cycle. They can be a source or a sink of carbon and in¯uence CO2 concentrations in

the atmosphere. In order to calculate the carbon budget of a region, the effect of soil management practices on carbon

sequestration in soils needs to be quanti®ed. Objectives of this experiment were to determine: (i) the effects of ridge till, plow

till and no-till on the soil organic carbon (SOC) pool; (ii) the SOC loss or sequestration for mulch rates of 0±

16 Mg haÿ1 yearÿ1 wheat (Triticum aestivum L.) straw applied in combination with each tillage method, and (iii) impacts of

tillage and crop residue treatments on soil physical quality, including aggregation and porosity. The experiment was initiated

in 1989 on a Crosby silt loam (Stagnic Luvisol) in Central Ohio. Seven years after initiation of the experiment, there was a

positive, linear effect of residue application rate on SOC contents in all tillage treatments. In the eighth year of the experiment

these trends were con®rmed for plow and no-till, but not for ridge till. Linear-regression equations, relating SOC content for

the 0±10 cm soil depth to mulch rate, were: for no-till: SOC (Mg haÿ1) � 15.21 � 0.32 [Residue (Mg haÿ1 yearÿ1)] (r � 0.68)

and for plow till: SOC � 11.95 � 0.27 [Residue] (p � 0.72). The carbon conversion ef®ciencies were 8% per year for plow till

and 10% per year for no-till. Detailed sampling at different depths revealed that increases in SOC content were only signi®cant

for the 0±5 cm depths of plow and no-till treatments. Effects of crop residue application on water stable aggregation in the 0±

10 cm layer were most pronounced with plow till and ridge till but not with no-till. Water retention characteristics, a measure

of pore size distribution, was not in¯uenced by tillage system, but crop residue application had a signi®cant effect on water

retention in the 0±10 cm layer at matric suctions of 30±300 kPa. This means that residue application increased macropores of

diameters 1±10 mm. It is concluded that, depending on the amount of crop residue returned to the soil, the large numbers

of farmers converting from plow to no-till cultivation in the Corn Belt may create an important sink for atmospheric CO2.

# 1999 Elsevier Science B.V. All rights reserved.

Keywords: Soil organic matter; Aggregation; Carbon sequestration; Mulching; Conservation tillage; Greenhouse effect; Soil quality

1. Introduction

Concern with global warming has led to a surge of

interest in evaluating the effect of management prac-

tices on carbon sequestration in soils. This interest is

justi®ed because soils play a key role in the global

Soil & Tillage Research 52 (1999) 73±81

*Corresponding author. Tel.: +1-614-292-9069; fax: +1-614-

292-7432

E-mail address: [email protected] (R. Lal)

0167-1987/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.

PII: S 0 1 6 7 - 1 9 8 7 ( 9 9 ) 0 0 0 5 9 - 8

carbon budget, containing 3.5% of the carbon reserves

of the earth, compared with 1.7% in the atmosphere,

8.9% in fossil fuels, 1.0% in biota and 84.9% in the

oceans (Lal et al., 1995). Land use change is still a

major source of carbon emission due to burning and

decomposition of vegetation and declining soil

organic carbon (SOC) contents in soils. Depending

on management, soils can be an important sink for

carbon. However, realization of the sink capacity of

soils requires adoption of appropriate soil manage-

ment practices that increase SOC content.

In the U.S., many farmers have shifted from plow

till to conservation tillage systems. The area under

conservation tillage (leaving >30% of crop residue on

the soil surface) has increased from 29 million ha

(26% of planted area) in 1989 to 40 million ha

(35%) in 1994 (Bull and Sandretto, 1996), and is

expected to increase to 75% by the year 2020 (Lal,

1997). The Corn Belt and Northern Plains are the

regions where conservation tillage (especially no-till)

is most popular. In 1994, about 14 million ha of

cropland in the Corn Belt had >30% residue coverage,

while 17 million ha had <30% residue coverage (Bull

and Sandretto, 1996). The implications for carbon

sequestration of the change to conservation tillage

are far reaching and need to be clari®ed for different

ecosystems.

Conservation tillage impacts the soil environment

in different ways. Crop residue returned to the land can

increase or maintain SOC content (Larson et al., 1972;

Havlin et al., 1990; Paustian et al., 1997). Many

studies have shown that SOC content increases soil

aggregation (Christensen, 1986; Skidmore et al.,

1986; Unger, 1997a). Further, SOC in microaggre-

gates is usually more resistant to decomposition and

has a longer turnover time compared with SOC in

macroaggregates or labile fractions (Beare et al.,

1994; Carter, 1996). Results of many studies con®rm

that plow till reduces SOC contents relative to no-till

in the topsoil (e.g. Angers et al., 1997; Paustian et al.,

1997; Unger, 1997b), although the reverse may be true

deeper in the pro®le (Dick, 1983).

Although the positive effect of crop residue on SOC

content is well established, only a limited number of

studies has evaluated the effect of different residue

application rates on SOC content under a range of

tillage systems (e.g. Larson et al., 1972). The objec-

tives of this experiment were to determine:

1. the effects of ridge till, plow till and no-till on the

SOC pool of a Crosby silt loam of central Ohio

(the eastern part of the Corn Belt);

2. the SOC sequestered or lost for mulch rates of 0±

16 Mg haÿ1 yearÿ1 wheat straw with each tillage

method, and

3. impacts of tillage and crop residue treatments on

soil physical quality including aggregation and

porosity.

The hypotheses tested were:

1. plow and ridge till result in more decomposition

and less carbon sequestration than no-till;

2. residue application increases SOC content;

3. aggregation and porosity increase more due to crop

residue application under no-till compared with

ridge and plow till treatments due to decreased

soil disturbance.

2. Materials and methods

2.1. Experimental site and statistical design

The experiment was located on Waterman Farm

of the Ohio State University (408000 N latitude and

838010 W longitude). Average annual temperature

is 118C and precipitation 932 mm. The soil is a

Crosby silt loam (Stagnic Luvisol in the FAO classi-

®cation and a ®ne, mixed, mesic Aeric Ochraqualf

in the USDA classi®cation). The experiment was

initiated in the summer of 1989 as a split plot design

with three replicates. Tillage was the main plot and

residue rate was the sub-plot (2 � 2 m). Tillage

treatments were: ridge till, plow till, and no-till.

Residue treatments (based on air-dry weight) were

0, 2, 4, 8 and 16 Mg haÿ1 yearÿ1 wheat straw.

The typical composition of wheat straw is: 44% C,

0.6% N, 0.2% S, 0.6% K and 0.1% P (Russell, 1973;

Lal, 1995). Soil tillage was performed each spring

after which crop residue was applied. It was observed

that residue rapidly compacted after a rainstorm

(very frequent around the time of residue application)

and, therefore, no special measures were taken to

keep it on the plots. Plowing and ridging were

done with a multiple and single moldboard plow,

respectively, to a depth of �20 cm, after which

74 S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81

the soil was not tilled any more during the year. No

crop was planted and no fertilizer applied. Herbicides

(usually glyphosate) were used to control weeds when

necessary.

2.2. Measurements and analyses

Soil physical properties and SOC content were

measured from September to November 1996 and

from May to July 1997. In fall 1996, one core

(7.62 cm high, 7.62 cm diameter) and one bulk soil

sample were taken in the center of each plot at 0±

10 cm, 10±20 cm and 20±30 cm depths. Total carbon

content of samples passed through a 100-mesh

(149 mm) sieve was determined by the dry combustion

method (Nelson and Sommers, 1986), neglecting car-

bonate content (pH of the Crosby silt loam is ca. 7). In

summer of 1997, SOC content at 0±1, 1±3, 3±5 and

5±10 cm depths was measured. A total of three or

four samples were taken per plot at each depth with

a 5-cm diameter auger, removing soil layer by layer.

Samples were taken halfway up the ridge in the

case of ridge till treatments to obtain a representative

sample for the ridge. The pipet method was used to

determine USDA particle size distribution (Gee and

Bauder, 1986). Bulk density was determined using

the Troxler density probe in summer 1997 (Blake

and Hartge, 1986). Volumetric SOC content (kg mÿ3)

was calculated by multiplying the SOC content

(g gÿ1) by bulk density (kg mÿ3). Water retention

characteristics were determined using core samples

on a tension table (0±6 kPa) and pressure plates (30±

300 kPa) (Klute, 1986). Water retention was included

because it is a measure of pore size distribution

(Marshall and Holmes, 1979). Percentage water stable

aggregation (%WSA) was determined on �50 g air-

dry aggregates of diameters 5±8 mm obtained from

the bulk samples taken in fall 1996. A sample was

placed on the top sieve of a set with diameters of 5, 2,

1, 0.5, and 0.25 mm, wetted under tension and then

oscillated submersed in tap water for 30 min. The

water stable aggregates in each size fraction were

dried at 1058C and corrected for the coarse fraction

(Yoder, 1936). The %WSA >0.25 mm and mean

weight diameter (MWD) were calculated according

to the method described by Kemper and Rosenau

(1986).

2.3. Calculations and statistical analysis

Calculation of SOC contents on a per-hectare basis

used weighted averages for each sampling layer of the

volumetric SOC content of the 0±10 cm layer deter-

mined in 1997. Calculation of carbon application rate

involved the assumption that the water content of

wheat straw was 10% and that its carbon content

was 44%, i.e. Carbon � (Residue/1.10) � 0.44 (Lal,

1995). Stepwise linear regression analysis related total

%WSA to clay, silt and SOC content. Analysis of

variance (F-test) determined signi®cant residue or

tillage effects or interactions between tillage and

residue rates. Polynomial regression analysis was

employed to detect linear, quadratic or cubic relation-

ships between residue rates and the dependent vari-

ables. Means of tillage treatments were compared

using Tukey's test.

3. Results

3.1. Soil organic carbon content

Measurements in 1996 indicated that seven years of

residue application had a positive effect on SOC

content in the 0±10 cm layer of the soil, but not in

the 10±30 cm depth (Fig. 1). Similar results were

reported by Dick et al. (1986b) and Havlin et al.

(1990). Some authors (Blevins et al., 1983; Dick

et al., 1986a; Angers et al., 1997) have reported higher

SOC levels at deeper depths under conventional tillage

Fig. 1. Residue rate effects on SOC at different depths after seven

years of residue application.

S.W. Duiker, R. Lal / Soil & Tillage Research 52 (1999) 73±81 75

at the 10±20 cm depth compared with no-till. Climatic

factors, drainage, texture, type and depth of soil tillage

may be among important factors responsible for dif-

ferences among locations and experiments.

The most signi®cant relationship of residue appli-

cation rate and SOC content at 0±10 cm depth was

linear for all three tillage treatments (Table 1). The

data indicated that, on a weight basis, the rate of SOC

increase with residue application was lower with plow

till then other tillage treatments, and the rate of SOC

increase with residue application was comparable in

ridge till and no-till treatments. The range of SOC

contents in the 0±10 cm layer varied from 7.5 to

18.6 g kgÿ1.

More detailed measurements of SOC content

made in 1997 in the 0±10 cm layer are presented in

Fig. 2. Analysis of variance indicated signi®cant

effects of tillage methods, residue application rate

and interactions between them. With plow till and

no-till, signi®cant linear relationships were observed

in the 0±5 cm layer. However, no signi®cant relation-

ship was observed between residue application rates

and volumetric SOC content with ridge till. The

most signi®cant linear regression equations relating

SOC content in the top 0±10 cm depth to residue

application rates are presented in Fig. 3. A reasonable

linear relationship was observed for plow till and

no-till. No signi®cant relationship was observed

with ridge till, only the intercept was highly signi®-

cant. These regression equations indicate that the

rate of SOC sequestration for each Mg of residue

applied was more for no-till than for plow till. The

results obtained in 1997 are different from those

in 1996, partly because bulk density of no-till treat-

ments (average 1.49 Mg mÿ3) was higher than that of

plow till and ridge till treatments (both 1.34 Mg mÿ3).

The different results for ridge till treatments remain

unexplained. For carbon sequestration purposes, how-

ever, preference should be given to the 1997 data

because sampling was more detailed and repeated

and because results are expressed on a volumetric

basis.

Results of this experiment are comparable with

reported SOC increases on a Typic Paleudalf (silt

loam) in Kentucky (Blevins et al., 1983), on a Mollic

Ochraqualf (silty clay loam) in northwest Ohio (Dick

et al., 1986a), on Typic Fragiudalfs (silt loam) in

Northeast Ohio (Dick et al., 1986b; Bajracharya

et al., 1998) and on an Aeric Aqualf in Ohio (Bajra-

charya et al., 1998). In these studies, SOC content in

the top 5±7.5 cm of the soil was higher with no-till

compared with plow till. Therefore, the results of the

present study can be extrapolated with reasonable

con®dence to determine effects of changes in soil

and crop residue management on carbon sequestration

in silt loams of the eastern Corn Belt.

To calculate the conversion ef®ciency of carbon

applied in the residue into SOC, conversion of residue

in the equations into carbon is necessary (see Sec-

tion 2.3). Carbon can be obtained by dividing the

slope of the regression line by 0.4 giving the conver-

sion ef®ciency of C applied into SOC. This needs to be

divided by the number of years of application (eight

years) to obtain the ef®ciency on an annual basis.

Following this procedure, the conversion ef®ciency

was 0% with ridge till, 8% with plow till and 10% with

no-till. Most studies ®nd conversion ef®ciencies in the

range of 14% to 21% (Rasmussen and Collins, 1991).

Low conversion ef®ciencies in this experiment may be

the result of a lack of nutrients necessary for decom-

position, since no fertilizer was applied (Himes,

1998).

Table 1

Tillage and residue rate effects on SOC (g kgÿ1) at 0±10 cm depth, 1996 data

Tillage Residue rate (Mg haÿ1 yearÿ1)

0 2 4 8 16 significance

Ridge till 9.4 11.1 10.7 14.1 14.9 La

Plow till 8.3 10.3 9.9 11.2 11.5 La

No-till 9.1 11.5 10.3 13.3 15.4 Lb

Significancec ns ns ns ns ns

a Significant at p � 0.05 level, L � linear.b Significant at p � 0.001 level, L � linear.c Comparison of means using Tukey's test (p � 0.05); ns � not significant.


3.2. Water stable aggregation

The %WSA data for the 0±10 cm layer are pre-

sented in Table 2. There were no treatment effects on

%WSA for soil below the 10-cm depth (data not

shown). Even in the 0±10 cm layer, the data are

variable and differences often not statistically signi®-

cant. The range of %WSA was 30±60%, and that of

MWD 0.23±1.12 mm. There was a linear increasing

trend in %WSA with increase in residue rate for plow

till and ridge till treatments. In contrast, increase in

residue application with no-till produced no consistent

increase in %WSA. There were no signi®cant effects

of tillage methods on the observed %WSA (averaging

across all residue treatments: 41.4% for PT, 44.7% for

RT, and 47.1% for NT). The MWD increased linearly

with residue rate in ridge till treatments only. Average

MWD was 0.45 mm with plow till, 0.55 mm with

ridge till and 0.66 mm with no-till. The data show

that residue application had a small positive effect on

%WSA with plow till and ridge till, and on MWD only

with ridge till. Residue application had no effect on

%WSA with no-till.

Reports in the literature on the effect of residue on

WSA are also mixed. Skidmore et al. (1986) did not

observe a positive effect of residue incorporation on

%WSA in the top 5 cm of a Kansas silty clay loam. In

Denmark, Christensen (1986) reported an increase in

mass of dry aggregates of 1±20 mm after 11 years of

straw incorporation compared with that of no straw of

Fig. 2. Residue rate effects on SOC at different depths with three different tillage systems after eight years of crop residue application. Note:

L, linear, ns, not significant differences between mulch rate effects across one depth, p � 0.1 (*), 0.05 (**) or 0.001 (***).


a loamy sand, but no effect on aggregation of a sandy

clay loam. Unger (1997b) found no difference in

MWD of WSA between no-till and cultivated Torrer-

tic Paleustolls in Texas. However, he observed that in

some cases the percentage of small aggregates was

larger in the no-till than in the plow till treatment. In a

study on a high clay Orthic Humic Gleysol in Canada,

Angers et al. (1993) observed a decrease in MWD of

WSA after four years of plow till compared with no-

till. Beare et al. (1994) reported that plow till reduced

the size of WSA compared with no-till on a well-

drained sandy clay loam in Athens, Georgia. In their

study, tillage effects on WSA disappeared below the

5 cm depth, except that the stability index of large

aggregates (>2 mm) was higher in the 5±15 cm layer

of the no-till compared with the plow till treatments.

Multiple regression equations showing the in¯u-

ence of clay, silt and SOC on WSA are presented in

Table 3. The SOC content was a determinant of

%WSA in the topsoil, but not in the subsoil. The

SOC, clay and silt contents explained only 50% of the

variation in %WSA. These results differ from those

reported by Chaney and Swift (1984) for the surface

layer of 26 soils in Britain. In their study, organic

matter content explained almost 100% of the variation

in MWD of WSA. However, they report soils with a

wide variation in SOC contents (0.25±5.8% SOC).

Unger (1997a) reported a highly signi®cant, positive

relationship between SOC and %WSA >0.25 mm.

However, Unger (1995) did not observe a positive

relationship between SOC and WSA, and attributed

this to the fact that differences between treatments

were small, while differences between soils were large

(Unger, 1997a). For a uniform Crosby silt loam of the

present study, there was a signi®cant effect of texture

on aggregation. However, the range of SOC contents

was limited, which may be an explanation of the lack

of differences in %WSA. The results of the present

and other studies also indicate a lack of understanding

of the factors determining aggregation. Biological

factors like micro- and macro-¯ora and fauna are

not included in most studies but may play a critical

role. Additionally, organic matter quality (e.g. lignin

and nitrogen concentrations) may also be an important

determinant of WSA.

3.3. Water retention characteristics

Statistical analyses of the data showed that water

retention of soil for 0±10 cm depth at some matric

suctions was signi®cantly in¯uenced by the residue

rate, but not by tillage treatments, and no consistent

Fig. 3. Regression equations of SOC vs. residue application rate

with three different tillage systems after eight years of residue

application.


interaction effects were observed between tillage and

residue rate. Below the 10-cm depth, however, no

consistent treatment effects on water retention were

observed (results not shown). Soil water retention

increased with increasing residue rate for soil water

suction >30 kPa for depths of 0±10 cm (Table 4).

Using the relationship � 2 /�gr (where is the

matric suction, the surface tension, � the density of

water, g the acceleration due to gravity and r the radius

of largest pores still ®lled with water), the water

Table 2

Tillage and residue rate effects on water stable aggregation in top 0±10 cm depth

Till Residue

(Mg haÿ1 yearÿ1)

%WSA (mm) MWD

(mm)

Total

%WSA5±8 2±5 1±2 0.5±1 0.25±0.5

Plow till 0 0.3 0.8 3.0 9.8 15.5 0.23 29.5

2 0.5 3.4 5.0 9.0 14.9 0.35 32.8

4 1.1 4.2 7.3 12.2 18.9 0.49 43.8

8 0.3 5.3 11.2 16.9 17.9 0.57 51.6

16 1.1 6.4 10.6 14.1 16.9 0.62 49.1

Significance Ca Lb Lb nsd nsd Lb Lb

Ridge till 0 1.9 3.5 4.7 7.7 14.1 0.43 31.9

2 0.7 5.6 7.4 13.5 18.6 0.53 45.8

4 0.9 5.3 7.4 12.4 17.5 0.52 43.6

8 0.6 5.5 9.1 9.5 24.9 0.53 49.5

16 2.1 7.1 9.7 16.4 17.4 0.72 52.7

Significance nsd nsd Lb nsd Qc nsd La

No-till 0 0.5 2.3 5.6 12.6 18.5 0.36 39.4

2 6.3 9.9 11.4 17.6 15.6 1.12 60.6

4 1.5 4.2 6.3 7.8 19.2 0.47 39.0

8 2.6 7.6 7.7 11.8 16.7 0.70 46.4

16 2.9 5.7 7.3 7.8 26.5 0.65 50.1

Significance nsd nsd nsd nsd Lb nsd nsd

a Significant at p � 0.1 level, C � cubic.b Significant at p � 0.05 level, L � linear.c Significant at p � 0.001 level, Q � quadratic.d ns � not significant

Table 3

Stepwise regression analysis of WSA vs. clay, silt and SOC content

Depth (cm) Regression equation r

0±30 WSA � 0.306 � 0.0039 clay 0.26

WSA � ÿ0.688 � 0.016 clay � 0.013 silt 0.59

WSA � ÿ0.852 � 0.126 SOC � 0.018 clay � 0.013 silt 0.57

0±10 WSA � 0.151 � 0.267 SOC 0.50

WSA � ÿ0.058 � 0.260 SOC � 0.005 silt 0.57

WSA � ÿ1.039 � 0.296 SOC � 0.015 clay � 0.015 silt 0.68

10±30 WSA � 0.219 � 0.0060 clay 0.40

WSA � ÿ0.863 � 0.0192 clay � 0.014 silt 0.65

WSA � ÿ0.823 ÿ 0.069 SOC � 0.019 clay � 0.015 silt 0.66

Note: WSA is expressed as a fraction in these equations, not a percentage. The other parameters (clay, silt, SOC, are in percent).


retention curve can be used to assess pore size dis-

tribution. At 208C, the relationship becomes: r � 0.15/

(where both, and r are in cm; Marshall and

Holmes, 1979). The higher water content at suction

ranges from 30 to 300 KPa indicates that residue

application increases the amount of macropores with

diameters from 1 to 10 mm. Increased macroporosity

is a result of higher SOC content and possibly of

higher microbial and earthworm activity.

4. Conclusions

A linear relationship was observed between the

residue application rate and volumetric SOC content

for plow till and no-till, but not for ridge till. The

conversion ef®ciency of residue carbon into SOC was

lower for plow till (8%) than for no-till (10%), con-

®rming the ®rst hypothesis that carbon sequestration

rates under no-till are higher than under plow till. The

SOC levels increased with residue level in both, no-till

and plow till, con®rming the second hypothesis. No

increases in SOC contents were observed for ridge till

(1997 measurements), the reasons for which remain

obscure. There was no increase in %WSA with residue

rate in case of no till, but a slight increase with the

other tillage treatments. Water retention was not sig-

ni®cantly different between tillage treatments, but

residue application rate had a positive effect on water

retention at matric suctions between 30 and 300 KPa,

indicating an increase in macropores (1±10 mm) due to

residue application. There was no increase in aggre-

gation and porosity with residue application under no-

tillage compared with the other tillage treatments, thus

leading to rejection of the third hypothesis. There was

a positive effect of residue application on aggregation

in plow till and ridge till treatments and on porosity in

all treatments.

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Table 4

Residue effects on soil water content (volume %) for 0±10 cm depth

Suction (kPa) Mulch rate (Mg haÿ1 yearÿ1)

0 2 4 8 16 significance

0 45.25 43.19 43.72 45.15 45.45 nsc

0.01 43.94 42.69 41.53 41.99 42.82 Qa

3 42.70 41.65 40.17 40.60 41.89 Qa

6 43.02 40.46 39.67 39.84 41.00 nsc

30 28.55 30.09 30.09 31.25 33.57 Lb

100 26.03 28.92 28.03 29.33 31.66 Lb

300 23.83 27.06 26.18 28.55 30.03 Lb

a Significant at p � 0.05 level, Q � quadratic.b Significant at p � 0.001 level, L � linear.c ns � not significant.


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