impacts of agricultural management practices on c sequestration in forest-derived soils of the...

Impacts of agricultural management practices on C sequestration in

forest-derived soils of the eastern Corn Belt

W.A. Dicka,*, R.L. Blevinsb, W.W. Fryeb, S.E. Petersc,D.R. Christensond, F.J. Pierced, M.L. Vitoshd

a School of Natural Resources, The Ohio State University, Wooster, OH 44691-4096, USAb Department of Agronomy, University of Kentucky, Lexington, KY 40546, USA

c Rodale Institute Research Center, 611 Siegfriedale Road, Kutztown, PA 19530, USAd Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824, USA

Abstract

Soil organic matter has recently been implicated as an important sink for atmospheric carbon dioxide (CO2). However, the

relative impacts of various agricultural management practices on soil organic matter dynamics and, therefore, C sequestration

at spatial scales larger than a single plot or times longer than the typical three year experiment have rarely been reported.

Results of maintaining agricultural management practices in the forest-derived soils of the eastern Corn (Zea mays L.) Belt

states of Kentucky, Michigan, Ohio and Pennsylvania (USA) were studied. We found annual organic C input and tillage

intensity were the most important factors in affecting C sequestration. The impact of rotation on C sequestration was primarily

related to the way it altered annual total C inputs. The removal of above-ground plant biomass and use of cover crops were of

lesser importance. The most rapid changes in soil organic matter content occurred during the ®rst ®ve years after a

management practice was imposed with slower changes occurring thereafter. Certain management practices, e.g. no-tillage

(NT), increased the soil's ability to sequester atmospheric CO2. The impact of this sequestration will be signi®cant only when

these practices are used extensively on a large percentage of cropland and when the C-building practices are maintained. Any

soil C sequestered will be rapidly mineralized to CO2 if the soil organic matter building practices are not maintained. # 1998

Elsevier Science B.V. All rights reserved.

Keywords: Carbon sink; Soil carbon; Tillage; No-tillage; Conservation tillage; Plow tillage; Soil organic C; Crop rotation; Cropping systems;

Carbon storage

1. Introduction

Carbon dioxide is the primary greenhouse gas that

contributes to climate change by accumulating in the

atmosphere and trapping the sun's heat. Atmospheric

CO2 concentration reached a record high in 1995 due

to ever increasing emissions of CO2 from fossil fuel

burning (Tunali, 1996a). Global average temperature

also reached a record high in 1995 (Tunali, 1996b).

These results have prompted studies evaluating how

farming practices, such as tillage intensity and rota-

tion, alter C sequestration in soil and thus help to

alleviate or possibly reverse the trend towards increas-

Soil & Tillage Research 47 (1998) 235±244

*Corresponding author. Tel.: +1-330-263-3877; fax: +1-330-

263-3653; e-mail: [email protected]

0167-1987/98/$19.00 # 1998 Elsevier Science B.V. All rights reserved.

P I I S 0 1 6 7 - 1 9 8 7 ( 9 8 ) 0 0 1 1 2 - 3

ing concentrations of CO2 in the atmosphere. How-

ever, the short-term and site speci®c nature of most

®eld experiments has limited our ability to assess the

impact of agricultural management practices on C

sequestration on a regional level.

Sequestration implies seclusion or temporarily set-

ting aside of something. In this paper, C sequestration

means the removal of CO2 from the atmosphere to soil

where it is secluded (stored) as part of the soil organic

matter. The stability of this stored C in soil is a related

but separate topic and will not be speci®cally

addressed.

The use of conservation tillage, de®ned as systems

having at least 30% or more crop residues covering the

soil at planting (Conservation Technology Informa-

tion Center, 1996), has increased rapidly in the United

States. In 1995, approximately 44.4 million hectares

were under some form of conservation tillage. No-

tillage (NT) is the most extreme form of conservation

tillage and is a management practice where the soil is

left undisturbed from harvest to planting except for

seeding and possible nutrient injection. Planting or

drilling is accomplished in a narrow seedbed or slot

created by coulters, row cleaners, disk openers, in-row

chisels or roto-tillers. Weed control is accomplished

primarily with herbicides.

Farmers adopt NT management practices because

NT saves labor, fuel and equipment costs while pro-

viding soil, water and wildlife bene®ts. The applica-

tion and maintenance of various management

practices, especially those having NT as a component,

alters the soil properties which in turn leads to a

new equilibrium distribution of organic C and

nutrients.

In 1995, NT was the only conservation tillage

system that showed an increase over 1994 in the

amount of land to which it was applied. No-till

increased 0.77 million planted hectares in the United

States to a total of 16.6 million hectares (Conservation

Technology Information Center, 1996). Ohio ranked

third in the United States in total amount of land using

NT (1.6 million hectares). Based on percentage of

total cropland planted to NT, Kentucky ranked ®rst

(47%) and Ohio ®fth (38%).

The eastern edge of the Corn (Zea mays L.) Belt in

the United States (de®ned in this paper as the states of

Kentucky, Michigan, Ohio, and Pennsylvania) contain

large areas of soils formed under forests. The soil and

climatic conditions that originally created the forests

are unique. New soil equilibrium conditions in this

region of the United States, created by the continuous

maintenance of various cropping and tillage systems

will, therefore, also be unique. Several management

system studies conducted in the eastern Corn Belt of

the United States have been continuously maintained

for 25 years or more. The combined information from

these long-term studies is valuable not only because of

the investment in time and money, but because col-

lectively they provide insight into how these systems

affect C sequestration. This paper reviews several

long-term studies conducted in the forest-derived soils

of the eastern Corn Belt of the United States and

reports common trends that emerge related to C

sequestration in soils of this region.

2. Materials and methods

Long-term ®eld studies were conducted at sites

located in the states of Kentucky, Michigan, Ohio,

and Pennsylvania. Soil and climate at these sites are

representive of the eastern Corn Belt of the United

States which originally was primarily under forest.

Selected characteristics regarding location, soil type,

and climate at each site are provided in Table 1.

Experimental treatments at each site are presented

in Tables 2±7 with more detailed descriptions in Paul

et al. (1997). The management systems are represen-

tative of those practiced in the eastern part of the Corn

Belt with corn predominating as a grain crop and other

crops sometimes being rotated with corn. The earliest

studies for which current data are reported began in

1962 at two sites in Ohio and thus represent a history

of more than 30 years. The most recently established

study began in 1981 and was located at the Rodale

Institute Research Center in Pennsylvania.

Soils were sampled and analyzed for organic C at

each site as described in Paul et al. (1997). Soil cores

(®ve minimum) ranging from 25 to 75 mm diam. were

brought to the laboratory and oven-dried for 48 h at

1058C. In most cases, bulk density measurements

(mass of dry soil per volume of ®eld-moist soil) were

also made at time of sampling. Where bulk density

measurements are not available, the organic C data are

presented in terms of concentration on a mass soil

basis.

236 W.A. Dick et al. / Soil & Tillage Research 47 (1998) 235±244

Tab

le1

Sel

ecte

dch

arac

teri

stic

so

fth

eex

per

imen

tal

site

sin

the

fore

st-d

eriv

edso

ils

regio

nof

the

Eas

tern

Corn

Bel

t,U

nit

edS

tate

s

Sit

eG

eog

raphic

allo

cati

on

(lat

itude,

longit

ude)

Soil

type

Dat

e

esta

bli

shed

Mea

nan

nual

pre

cipit

atio

n

(mm

)

Mea

nan

nual

tem

per

ature

(8C

)

Mic

hig

an

(A)

Eas

tL

ansi

ng

(fer

tili

zer

and

man

ure

exp

erim

ent)

4284

00 N

,8582

80 W

Met

ealo

amy

sand

(Are

nic

Hap

ludal

fs)

1963

782

(396)

a8.6

(B)

Eas

tL

ansi

ng

(til

lag

ean

dco

ver

cro

p

exp

erim

ent)

4284

00 N

,8482

80 W

Cap

aclo

am(A

eric

Och

raqual

f)1980

728

(379)

8.8

(C)

Sag

inaw

Co

un

ty(c

rop

pin

gsy

stem

s

exp

erim

ent)

4382

00 N

,8480

70 W

Mis

teguay

silt

ycl

aylo

am

(Aer

icE

ndoaq

uen

t)

1972

788

(422)

8.7

Oh

io

(A)

Wo

ost

er4

084

80 N

,8280

20 W

Woost

ersi

ltlo

am(T

ypic

Fra

giu

dal

f)1962

905

9.1

(B)

Ho

ytv

ille

4180

30 N

,8480

40 W

Hoytv

ille

silt

ycl

aylo

am

(Moll

icO

chra

qual

f)

1964

845

9.5

(C)

So

uth

Char

lest

on

3984

80 N

,8383

00 W

Cro

sby

silt

loam

(Aer

icO

chra

qual

f)1962

952

11.9

(D)

Cosh

oct

on

4082

40 N

,8184

80 W

Wes

tmore

land

silt

loam

(Typic

Hap

ludal

f)

1964

999

10.5

Pen

nsy

lvan

ia

(A)

Ku

tzto

wn

4083

30 N

,7584

30 W

Sil

tycl

aylo

am(9

0%

Typic

Fra

giu

dal

for

Hap

ludal

f,10%

Typic

Dyst

roch

rept)

1981

1045

12.4

Ken

tuck

y

(A)

Lex

ing

ton

3880

70 N

,8482

90 W

Mau

rysi

ltlo

am(T

ypic

Pal

eudal

fs)

1970

1140

13.0

aV

alu

ein

par

enth

eses

isp

reci

pit

atio

nre

ceiv

edd

uri

ng

the

gro

win

gse

ason

def

ined

asth

em

onth

sof

May

thro

ugh

Sep

tem

ber

.

W.A. Dick et al. / Soil & Tillage Research 47 (1998) 235±244 237

3. Results

The studies conducted in the eastern part Corn Belt

of the United States, which was originally primarily

under forest, provide information related to several

factors that impact C sequestration in soil. Tillage

intensity, soil type, C inputs, cropping systems and

length of time a management practice is maintained

are all important controlling variables that interact to

create new equilibrium levels of soil organic C.

3.1. Tillage intensity

One of the most important agricultural management

practices controlling C concentrations and amounts in

soil in managed agroecosystems is tillage intensity.

Amount of organic C in the 0 to 30 cm soil layer of a

Wooster silt loam (Typic Fragiudalf) soil located in

Ohio was 17 Mg haÿ1 greater when continuously

managed (i.e., for 30 consecutive years) by NT as

compared to plow tillage (PT) (Table 8). Similar

Table 2

Tillage and rotation experiments conducted in Ohio, USA. Soil samples were collected from all sites in late fall of 1980 and from the Wooster

site in late fall of 1991

Site location and soil classification Experimental design Tillage a Crop rotation b

Wooster A Wooster silt loam (Typic Fragiudalf) Randomized block (four replications) NT, CT, PT CC

Wooster B c Wooster silt loam (Typic Fragiudalf) Factorial, randomized block (three replications) NT, CT, PT CC, CS, COM

Hoytville c Hoytville silty clay loam (Mollic Ochraqualf) Factorial, randomized block (three replications) NT, CT, PT CC, CS, COM

South Charleston Crosby silt loam (Aeric Ochraqualf) Randomized block (four replications) NT, CT, PT CC

Coshocton Westmoreland silt loam (Ultic Hapludalf) Single replicate NT, PT CC

a NT�no-tillage, CT�chisel tillage and PT�plow tillage (fall plow at Hoytville and spring plow at all other sites).b CC�continuous corn, CS�corn and soybean in a two-year rotation and COM�corn, oat and meadow (hay) in a three year rotation.c Sufficient plots were established at Wooster B and Hoytville so that each crop in each rotation has an annual entry point.

Table 3

Tillage and cover crop experiment conducted on a Capac loam (Aeric Ochraqualf) soil (East Lansing, MI, USA). Initial treatments were

established in 1980 and were replicated four times. Soil was sampled 14 July 1987 and 28 September 1991

Treatment abbreviation Treatment description a

PT Fall plowed every year since 1980

NTP86 No-tillage with the rye (Secale cereale L.) cover crop strip-killed prior to planting. Spring plowed in 1986 and

then reverted back to NT

NTP87 No-tillage with the red clover (Trifolium pratense L.) cover crop strip-killed prior to planting. Fall plowed in 1986

and then reverted back to NT

NT No-tillage every year since 1980 with rye cover completely killed prior to planting

a Cover crop for all treatments in 1985 was clover and the use of cover stops was terminated after 1985. Corn was grown from 1980 to 1988

and a corn±soybean (Glycine max L.) rotation began in 1989.

Table 4

Tillage and mineral N fertilizer experiment conducted on a Maury silt loam (Typic Paleudalf) soil (Lexington, Kentucky, USA). The

experimental design was a split-block with tillage being assigned to the whole plots and N fertilizer rates to the subplots. Treatments were

replicated four times a

Variable Variable description

Tillage Plow tillage ± spring moldboard plow 20 to 25 cm deep 1 to 2 weeks prior to planting. Secondary tillage consisted of

two trips with a tandem disk harrow to a depth of 8 cm

No-tillage ± the only soil disturbance was that caused by the NT planter equipped with a fluted coulter opener

Nitrogen fertilizer Ammonium nitrate was applied to subplots at rates of 0, 84, 168 and 336 kg haÿ1

a Soil samples were collected 23 August 1989 from depths of 0 to 5 cm, 5 to 15 cm and 15 to 30 cm and analyzed for organic C concentrations

and bulk density.


results were observed in Kentucky (Fig. 1) where

amounts of organic C in the top 30 cm of soil were

4.2 Mg haÿ1 greater under NT than PT after 20 years.

Plowing a soil that has been managed using con-

tinuous NT stimulates rapid mineralization of the

organic C accumulated in the surface soil layer. A

Table 5

Cropping system experiment (Rodale Institute Research Center, Kutztown, PA, USA). Treatments were first applied in 1981 and were

replicated eight times. Soil was sampled in the fall of 1991

Cropping system Cropping system description

LIP-A Low input/animal system which simulated the cropping system of a beef or dairy operation. Crops grown included red

clover/alfalfa (Medicago sativa L.)/orchardgrass (Dactylis glomerata L.), hay, oats, winter wheat (Triticum aestivum L.),

corn grain, corn silage and soybeans. Nitrogen was provided by cattle manure and third year hay crops were plowed

down prior to planting corn. Soils were moldboard plowed every 4 to 5 years with secondary tillage applied for weed

control

LIP-CG Low input/cash grain system did not contain an animal component and produced a cash grain crop every year. Crops

grown included corn, soybean, oats, winter wheat and spring barley (Hordeum distichum L.). Nitrogen was provided

primarily by plowdown legumes. Primary tillage was moldboard plow once per year with secondary tillage applied for

weed control

CONV Conventional cash grain system which simulated an intensive sequence of corn and soybean production and mineral

fertilizers were added at rates recommended by the Pennsylvania State University. Primary tillage was once per year

with herbicides applied for weed control

Table 6

Fertilizer/manure and corn grain/silage harvest experiment conducted on a Metea loamy sand (Arenic Hapludalfs) soil (East Lansing, MI,

USA). The experimental design was a randomized split-block with corn harvest being assigned to the whole plots and fertilizer and manure

treatments assigned to the subplots. Treatments were replicated three times a

Variable Variable description

Fertilizer (kg haÿ1) and Manure (Mg haÿ1) application rates b A-179 (N); 20 (P); 37 (K)

B-179 (N); 94 (P); 177 (K)

C-11 (N); 20 (P); 37 (K); 22 (manure)

D-11 (N); 20 (P); 37 (K); 45 (manure)

E-11 (N); 20 (P); 37 (K); 67 (manure)

Corn harvestb Corn grain ± Grain was removed at harvest

Corn silage ± Above ground biomass was harvested for silage

a Soil samples (0 to 20 cm depth) were collected in June of each year following a spring moldboard plow treatment to a depth of 20 to 23 cm

and a light secondary tillage treatment.b Manure and fertilizer treatments were discontinued in 1982 and plots were maintained in a corn±soybean rotation with grain removal.

Table 7

Cropping system experiment conducted on a Misteguay silty clay (Aeric Endoaquent) soil (Saginaw County, MI, USA). The experimental

design is a randomized block with treatments replicated four times. Soils were sampled in the fall of 1972, 1981 and 1991

Cropping system a Cropping system description b

C-SB (140) Two year rotation of corn (C) and sugar beet (Beta vulgaris L.) (SB)

NB-SB (65) Two year rotation of dry beans (Phaseolus vulgaris L.) (NB) and sugar beet (SB)

O-NB-SB (45) Three year rotation of oat (Avena sativa L.) (O), dry bean (NB) and sugar beet (SB)

C-C-C-SB (140) Four year rotation of corn (C) for three years followed by sugar beet (SB)

C-C-NB-SB (105) Four year rotation of corn (C) for two years followed by dry beans (NB) and sugar beets (SB)

O-A-NB-SB (45) Four year rotation of oat (O), alfalfa (A), dry bean (NB), and sugar beet (SB)

a In parentheses are the nitrogen inputs (annual mean in kg haÿ1) for each cropping system.b Each crop in each system has an annual entry point.


tillage study was conducted in East Lansing, MI in

which a well established NT ®eld was plowed. After 7

years, soil organic C in the 0 to 5 cm surface soil layer

was 8.7 kg mÿ3 greater in the NT as compared to the

PT soil (Pierce et al., 1994). Spring plowing (NTP86)

or fall plowing (NTP87) a NT ®eld in 1986 and then

sampling in the fall of 1987 revealed that some of the

organic C had been redistributed to lower depths. At

this time, the NTP86 and NTP87 treatments had

signi®cantly more organic C in the 5 to 10 cm and

10 to 15 cm soil layers than did the NT treatment. The

NTP86 and NTP87 plots were then reverted back to

NT and in 1991 they were again sampled (Fig. 2).

Differences among treatments were no longer statis-

tically different except in the 0 to 5 cm soil layer

where the NT, NTP86 and NTP87 treatments con-

tained signi®cantly higher amounts of organic C than

did the PT treatment (Fig. 2). This suggests that

organic C amounts are trending back towards the

levels present in the continuously maintained NT soil.

3.2. Soil type

Identical tillage treatments were applied to two

different soils at the Wooster and Hoytville sites in

Ohio. Although the treatment trends were similar, in

that the NT treatment sequestered greater amounts of

organic C than did the PT treatment, the pattern of

distribution within the soil pro®le was somewhat

different between the two soils (data not shown). In

1980, after 19 years of continuous application of NT to

the Wooster soil, the differences in organic C amounts

caused by tillage were not evident at depths below

15 cm (Dick, 1983; Dick et al., 1997). In contrast,

organic C amounts were lower in the NT soil pro®le

than in the PT pro®le at depths below 15 cm in the

Hoytville soil. This soil difference was attributed, in

part, to the shrink-swell properties of the Hoytville

silty clay loam soil which develops cracks when the

soil dries. Exposure of soil subsurfaces and increased

aeration at depth, may have extended the mineraliza-

tion of soil organic C deeper into the pro®le of the NT

Hoytville soil than into the Wooster soil.

3.3. Carbon and nitrogen inputs

Soil organic C levels for the experiments conducted

in the forest-derived soils region of the eastern Corn

Table 8

Carbon storage in the 0 to 30 cm layer of Wooster silt loam (Typic

Fragiudalf) soil in 1991 after 30 years application of tillage and

rotation treatments. Bulk densities were measured at the same time

(late fall) soil was sampled for organic C measurements

Treatment Mean organic C

concentration a

(g kgÿ1)

Carbon

stored

(Mg haÿ1)

Tillage

No-tillage (NT) 22.7 (20.9) b 95a c(88)

Plow-tillage (PT) 18.5 (19.0) 78b (86)

Rotation

Corn±Oats±Meadow (COM) 21.9 (21.3) 92a (89)

Continuous corn (CC) 21.5 (20.5) 90a (86)

Corn±Soybean (CS) 18.4 (18.1) 77b (76)

Rotation and tillage

PT/CS 16.8 71a

PT/CC 19.1 80ab

PT/COM 19.6 82ab

NT/CS 20.0 84ab

NT/CC 23.8 100b

NT/COM 24.2 102b

a Mean values representative of the 0±30 cm soil layer.b Values in parentheses are those determined from data collected in

1980 from the same field plots.c Means followed by the same letter for each set of treatment means

at Site A or Site B are not significantly different at the P�0.05

level.

Fig. 1. Organic C in the 0 to 30 cm soil layer of soil under

bluegrass sod and corn at the Kentucky (Maury silt loam) site using

plow tillage (PT) and no-tillage (NT) averaged across N rates 5, 10

and 20 years after treatments were first imposed.


Belt (USA) were directly related to the C inputs to the

soil. This statement is illustrated using data from

Michigan (Table 9). After 20 annual applications of

manure (1982 data), soil organic C concentrations (0

to 25 cm soil layer) in the manured plots (Treatments

C, D, and E) were higher than in non-manured plots

(Treatments A and B). The greater the input of C as

manure, the higher the concentration of organic C in

soil. However, once addition of manure was discon-

tinued, soil organic C concentrations rapidly

decreased as is evident by comparing 1982 data with

1991 data.

Also at this Michigan site, removal of the above

ground biomass for silage had a noticeable effect on

total soil organic C (Table 9). This was determined by

comparing organic C concentrations in the silage

versus grain plots in 1982 and 1991. The removal

of corn residues as silage had an impact on soil organic

C even during the 20 years when manure was applied

(compare grain and silage plot data for 1982). Annual

manure input ranged from 22 to 67 Mg haÿ1 which is

considerably larger than the approximately 6 Mg haÿ1

amount of corn residues returned to soil after grain

harvest (Dick et al., 1992).

Grain and residue yields were increased by fertilizer

N additions in Kentucky (Ismail et al., 1994). This

increase in yield also resulted in greater residue inputs

leading to greater amounts of soil organic C when N

application rates are optimized for crop productivity.

3.4. Cropping systems

The impact of management practices on C seques-

tration re¯ects a combination of factors that are part of

the system. For example, after 10 years a low input

animal system (LIP-A) and a low input cash grain

system (LIP-CG) in Pennsylvania accumulated higher

Fig. 2. Organic C amounts vs. soil depth increments as affected by tillage intensity and cover crop (East Lansing, MI, USA). Treatments (i)

were continuous NT since 1980 (NT); NT from 1980 to 1986, (ii) spring plowed in 1986 and then again NT (NTP86); NT from 1980 to 1986,

(iii) fall plowed in 1986 and then again NT (NTP87); and (iv) continuous plow tillage since 1980 (PT). Soil was sampled 28 September 1991.

Table 9

Soil organic C concentrations in the plow layer (0 to 25 cm) of a

Metea loamy sand as affected by long-term fertilizer and manure

applications (East Lansing, MI, USA)

Treatment a Grain plots Silage plots

1972 1982 b 1991 1972 1982 b 1991

g C kgÿ1 soil

A 9.1 7.9 7.5 9.7 7.2 6.2

B 9.5 8.2 7.8 9.7 7.8 6.4

C 12.4 10.7 9.8 12.0 10.0 7.3

D 12.7 14.0 10.8 12.1 11.1 8.5

E 14.9 15.0 12.3 14.5 13.8 10.6

Mean 11.7 11.2 9.7 11.6 10.0 7.8

a A�179±20±37 (N±P±K fertilizer), B�179±94±177 (N±P±K

fertilizer), C�11±20±37 (N±P±K fertilizer) and 22 (manure),

D�11±20±37 (N±P±K fertilizer) and 45 (manure), and E�11±

20±37 (N±P±K fertilizer) and 67 (manure). Fertilizer rates are in

kg haÿ1 and manure rates are in Mg haÿ1.b Plots were first treated with manure and fertilizer in 1963,

treatments were discontinued in 1982 and plots were then

maintained thereafter in a corn±soybean rotation with grain

removal.


organic C concentrations than did a high input cash

grain system (CONV treatment) (Table 10). These

systems are complex with multiyear rotations which

included crops other than cash grain, supplemental

manure additions and tillage variables.

Several cropping systems were evaluated at a site

near Saginaw, MI. After 9 years of application, all

cropping systems caused a decline in soil organic C

concentrations as compared to when the cropping

system was ®rst imposed (Fig. 3). Since all plots were

plowed on the same day, bulk density at time of soil

sampling was assumed to be approximately equal and

organic C concentrations would correlate with organic

C amounts in the soil. As treatments are compared

from left to right in Fig. 3, there is an increase in

residue input due to addition of oat and then corn into

the rotation at increasing frequency. Annual residue

inputs to soil were estimated as 10, 6.0, 3.0, 5.5 and

8.0 Mg haÿ1 for corn, sugar beet, navy bean, oat and

alfalfa, respectively (Zielke and Christenson, 1986).

Decline in soil organic C was less where residue inputs

were greatest, i.e. for the corn±corn±corn±sugar beet

rotation as compared to the navy bean-sugar beet

rotation. There seemed to be little additional change

between 9 and 19 years of maintenance of the crop-

ping systems.

3.5. Time

The length of time tillage intensity or management

practices are imposed on a soil is also important when

estimating the soil's ability to sequester C. For exam-

ple, Fig. 4 clearly indicates that a soil to which NT and

PT treatments were imposed for 19 years (1980 data)

had a different distribution of C than a soil with 30

years (1991 data) of these same tillage treatments. The

amount of organic C in the 0 to 30 cm soil layer of the

PT Wooster soil pro®le continued to decrease through-

out the entire measured depth of the pro®le, but the

change was rather slight and not statistically signi®-

cant. In contrast, the NT soil had signi®cantly

increased soil organic C concentrations at the soil

surface, but showed a signi®cant decrease in soil

organic C concentrations below 15 cm.

Similar results of time have been reported in Ken-

tucky (Fig. 1). Comparison of NT and PT effects on

organic C concentrations after 5 and 20 years on a

Maury silt loam soil were clearly evident. In contrast

to the Ohio data, the Kentucky data show that

increases in organic C concentrations occurred simi-

larly for both the NT and PT treatments.

4. Discussion

Improved agronomic practices such as higher seed-

ing rates, improved pest control, and improved ferti-

Table 10

Soil organic C concentrations in soils as affected by three different

management systems (Rodale Institute Research Center, Kutztown,

PA, USA). Treatments were first applied in 1981

Management System a Year

1981 1990 1991

g C kgÿ1 soil

LIP-A 22.7a b 23.4ab 21.4a

LIP-CG 23.6a 24.5a 22.3a

CONV 22.3a 21.3b 19.8b

a LIP-A�low input animal system, LIP-CG�low input cash grain

system, and CONV�conventional cash grain system.b Means followed by the same letter in each sampling year are not

significantly different at the P�0.05 level.

Fig. 3. Organic C concentrations after 9 and 19 years of applying

various cropping systems (Saginaw County, MI, USA). NB�navy

bean, SB�sugar beet, O�oat, A�alfalfa and C�corn.


lizer practices have the potential to increase photo-

synthetic C capture, and thus C input, into the soil.

Increased C input, however, is just one component of a

complex set of variables that affect C sequestration in

soil. Our studies, conducted in the forest-derived soils

of the eastern Corn Belt of the United States, reveal

that C sequestration is due to the combination of C

input to soil and management factors.

A rapid decrease in soil organic matter occurs when

virgin grassland or forest soil is ®rst cultivated (Paus-

tian et al., 1997). The rate of loss depends on several

factors including tillage intensity, soil texture, rotation

and soil drainage. These same factors are important

controlling variables in systems that are known to

sequester C in soil.

Rotation, manure additions and removal (harvest)

of residues for silage all lead to variable amounts of C

input to the soil and thus, indirectly, the amount of C

ultimately sequestered. However, tillage interacts with

these variables to further modify the ability of a soil to

sequester C. For example, in Ohio, Dick (1983)

reported that NT is more ef®cient in storing C when

applied to a relatively low C input corn±soybean

rotation than when applied to a corn±oats±hay or a

continuous corn rotation where C inputs are greater.

Similarly in Kentucky, NT seemed to be more ef®cient

in storing C in the control treatment which had low C

input in Kentucky than where N was applied and C

inputs were increased (Ismail et al., 1994).

When NT was continuously applied to a Wooster

silt loam soil in Ohio, the amount of C sequestered in

the surface layer became greater and extended deeper

into the pro®le (Fig. 4). In the lower portion of the soil

pro®le, however, C is no longer replenished by inver-

sion tillage and its concentration continues to decline.

The questions still to be answered are (1) how will

organic C be distributed and (2) how much organic C

will be sequestered in the soil pro®le when equili-

brium that re¯ects long-term NT management is

®nally achieved? There is obviously a limit to the

decline that will occur in the subsurface soil layers, but

the depth of C accumulation from the surface down-

ward when NT is continuously maintained is still an

unknown result and will require additional years of

observation.

Termination of conservation tillage practices or

manure inputs will result in rapid loss of C stored

during the previous years' applications of these prac-

tices. The termination of manure applications in

Michigan, for example, resulted in a rapid decline

in amount of stored soil C (Table 9). Similarly, when a

NT ®eld was plowed in Michigan (Fig. 2) or Ohio

(Dick et al., 1992), soil organic C was rapidly miner-

alized. However, after a single tillage treatment, the

process of sequestering C and rebuilding soil organic

C levels once again occurs. When a NT soil is inverted,

C stored in the surface soil layer is buried and remains

buried until the next soil inversion or tillage. The

frequency of tillage or soil inversion may affect both

the rate and amount of C stored in the soil surface layer

as well as the rate of decay in the C buried from the

previous inversion. Whether infrequent inversion til-

lage is more effective in sequestering C than contin-

uous NT is not yet known. If infrequent tillage is

shown to be an effective management practice for

Fig. 4. Organic C distribution in the Wooster soil profile 19 years

(1980) and 31 years (1993) after tillage treatments were first

imposed.


sequestering C, the optimum frequency of tillage will

need to be determined.

5. Conclusions

Cropping system impacts on C sequestration in

forest-derived soils of the eastern Corn Belt of the

United States were due to the combination of various

management factors. Optimum N fertilization, choice

of crop rotations, supplemental C inputs (e.g., animal

manures) and crop residues left in the ®eld can clearly

lead to increased sequestration of C in soil. Conserva-

tion tillage or low input crop production systems,

especially use of NT practices, has the ability to

sequester C in the soil surface as well as provide

excellent erosion control, which holds in place or

conserves any C sequestered. When combined with

use of cover crops, crop rotation, fertilizer strategies

and supplemental C inputs, NT is the most ef®cient

management practice for sequestering C in soil.

Time scales of 15 to 30 years are required for C

concentrations in soil to reach equilibrium when a new

cropping system is imposed on a soil. As little as ®ve

years, however, is suf®cient to begin to see trends in

organic C level changes in some situations.

Carbon sequestered in soil as a result of NT is

thought not to be highly stable. The effect of infre-

quent tillage on C mineralization and C sequestration,

as compared to continuous maintenance of NT is still

unresolved.

Acknowledgements

Long-term experiments, by their very nature,

require the involvement of many people. We wish

to acknowledge those people who established the

research sites and those who have managed the plots

or conducted measurements. Financial support has

also been obtained from numerous sources so that

research on these sites could occur and this support is

acknowledged.

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