[advances in agronomy] volume 124 || opportunities and challenges of soil carbon sequestration by...

CHAPTER ONE

Opportunities and Challengesof Soil Carbon Sequestrationby Conservation Agriculturein ChinaHai-Lin Zhang*,1, Rattan Lal†, Xin Zhao*, Jian-Fu Xue*, Fu Chen*,2*College of Agronomy and Biotechnology, China Agricultural University, Key Laboratory of Farming System,Ministry of Agriculture, Beijing, China†Carbon Management and Sequestration Center, School of Environment and Natural Resources, The OhioState University, Columbus, Ohio, USA1The senior author was a visiting scholar at C-MASC, The Ohio State University, Columbus, Ohio, USA2Corresponding author: e-mail address: [email protected]

Contents

1.

AdvISShttp

Introduction

ances in Agronomy, Volume 124 # 2014 Elsevier Inc.N 0065-2113 All rights reserved.://dx.doi.org/10.1016/B978-0-12-800138-7.00001-2

3
2. CA in China 6
2.1
CT systems in different agroeco regions 6 2.2 Challenges to adopting CA in China 11
3.
Effects of CA in China 13 3.1 Soil bulk density 13 3.2 Soil water and temperature regimes 15 3.3 Crop yields 17 3.4 Soil organic carbon 18 3.5 SOC stock 21 3.6 SOC sequestration and soil quality 24 3.7 Limitations of SOC research under CA 25
4.
Potential and Opportunities for CA and SOC Research 27 4.1 Intensive farming problems 27 4.2 Soil erosion control 28 4.3 Residue management 28 4.4 Rural development and economic profit 28 4.5 Labor shortage 30
5.
Conclusions 30 Acknowledgments 31 References 31
1

http://dx.doi.org/10.1016/B978-0-12-800138-7.00001-2

2 Hai-Lin Zhang et al.

Abstract

Conservation agriculture (CA), an emerging technology for sustainable agriculture,has been practiced in China for more than 30 years and is increasingly being adoptedon cropland. CA system has four components: (i) no-till (NT), (ii) residue mulch,(iii) complex/diverse cropping system, and (iv) integrated nutrient management. Con-servation tillage (CT, main technology of CA) methods, relevant to a range of croppingsystems, are practiced on 6.67 million hectare (Mha) in China. With growing concernsabout global warming, soil organic carbon (SOC) sequestration is an important strat-egy to offset anthropogenic emissions. This chapter collates and synthesizes availableresearch literature on SOC sequestration under different tillage systems in China. Spe-cific focus is on the SOC dynamics, SOC stock, rate of SOC sequestration, and soil qual-ity under different tillage systems in diverse agroeco regions. The research on CTeffects on SOC sequestration has been conducted in China for more than 20 yearssince the 1990s. The review of the literature indicates that NT can increase SOC con-centration in the surface layer under dryland farming and rice (Oryza sativa L.) paddysoils. The average rate of increase of SOC (g kg�1year�1) in 0–20 cm depth under NTsystems is 0.60–3.74, 0.14–4.15, 0.50–5.94, and 8.81–17.95 for the Northeast, North,Northwest, and paddy fields of Southern China, respectively. However, most researchresults indicate that SOC under NT is concentrated more in the surface soil(8.6–31.3 g kg�1 in NT vs. 5.3–26.8 g kg�1 in plow tillage (PT)) and is relatively lessin the subsoil (6.9–17.6 g kg�1 in NT vs. 10.2–24.5 g kg�1 in PT). Residue managementis the key factor in SOC sequestration, which also influences SOC dynamics. Croppingsystem and rotation also affect SOC sequestration. Further, NT can improve soil qualityby enhancing and stabilizing aggregation. Because of relatively short duration, soil pro-cesses under CA management are not clearly understood and are confounded by thediverse cropping systems. There is a need to study pedospheric processes affectingSOC sequestration and soil quality under long-term use of CA in diverse cropping sys-tems and complex agroeco regions of China. Potential and limitations of CA, andresearch priorities in China are discussed.

ABBREVIATIONSC carbon

CA conservation agriculture

CT conservation tillage

GHG greenhouse gas

N nitrogen

NT no-till

PT plow tillage

PT0 plow tillage with residue removed

RiT ridge tillage

RoT rotary tillage

SOC soil organic carbon

WUE water use efficiency

rb bulk density

3Conservation Agriculture Effects on Soil Organic Carbon in China

1. INTRODUCTION

Mechanical soil tillage is a method of seedbed preparation, seeding, or

transplanting. The plow-based method has been practiced since the dawn of

settled agriculture (Lal, 2009a). Tillage can modify soil physical, mechanical,

and biological properties by cutting, mixing, overturning, and loosening.

Thus, it has been an important technological development in the evolution

of agriculture and in food production (Benites and Ofori, 1993; Derpsch,

2004; Lal, 2009b; Lal and Kimble, 1997). Soil tillage can also drastically

influence the environment. During the 1930s, for example, wind erosion

in the Dust Bowl era blew away millions of tons of topsoil from the barren

fields in the Great Plains of America, which degraded more than 40 million

hectare (Mha) of farmland (Lal et al., 2007; Logan et al., 1991). Over and

above the adverse effects of drought, continuous intensive tillage, which

aggravated drought and wind erosion, was among the principal reasons of

the catastrophy (Lal et al., 2007). After this disaster, conservation tillage

(CT), such as no-till (NT), has increasingly been used in the United States,

and elsewhere (e.g., South America). Presently, conservation agriculture

(CA, based on CT) is widely regarded as an important part of sustainable

agriculture and adopted by many countries (Baker et al., 1996; Derpsch,

1998, 2004). The CA system comprises of four components (Fig. 1.1),

and a judicious management of each component is important to its success.

By 2011, about 125 Mha of croplands were planted by CA (Friedrich et al.,

2012). Indeed, CA has numerous advantages, such as conserving soil, saving

water, along with fuel and energy, and enhancing the environment

(Azimzadeh, 2012; Derpsch et al., 2010; Holland, 2004). Presently, global

warming has become the focus of attention of scientists and policy makers.

Therefore, the technologies which could alleviate greenhouse gas (GHG)

emission and improve soil organic carbon (SOC) sequestration are being

widely recognized. The effects of CA on GHG emissions and SOC seques-

tration are also researchable and outreach priorities. Numerous studies indi-

cate that adoption of CA could enhance SOC sequestration, especially in the

surface layer because of reduction in soil disturbance and increase in residue

retention (Lou et al., 2012; Pacala and Socolow, 2004; Stewart et al., 2012;

West and Post, 2002). In general, CA can reduce carbon (C) footprint and

increase capacity of ecosystem services as the environmental benefits (Clay

et al., 2012; Crowley et al., 2012). However, some studies show that CA

may not always increase SOC sequestration (Alvaro-Fuentes et al., 2012;

Residuemulch No-till

Integrated nutrients management

CA

Diverse croppingsystem

Figure 1.1 Conservation agriculture (CA) comprises of four principle components:(1) no-till or complete absence of mechanical seedbed prepare; (2) residue mulch toprovide continuous soil cover to minimize water runoff and erosion, and conserve soilwater; (3) diverse and complex cropping systems involving a range of crop species; and(4) integrated nutrient management to improve soil fertility.


Powlson and Jenkinson, 1981), because of the short duration of CT, specific

methods of SOC assessment, the depth of sampling, and soil characteristics

(Baker et al., 2007; Blanco-canqui and Lal, 2008).

China has a long agricultural history, and intensive farming has been

practiced for millennia. Because of a wide range of soil types and climate,

the cropping systems practiced in China are also diverse. Single cropping

system (one crop per year) is practiced only in the Northeast and some parts

of the Northwest China. Multiple cropping systems, such as double

cropping (two crops per year) and triple cropping (three crops per year),

are dominant systems in China. In accord with the diversity of cropping sys-

tems, a wide range of tillage systems have been practiced (Fig. 1.2). Some

CA systems date back to ancient times (e.g., mulch tillage, ridge tillage

(RiT)). Several ancient agricultural books, such as Lvshichunqiu (Buwei

Lv, circa (ca.) 239 AD) and Qiminyaoshu (Sixie Jia, ca. 540 AD), have

described these CAmethods (Liu, 2008). However, conventional tillage sys-

tems, plow tillage (PT) along with some secondary tillage methods, have

been the predominant tillage systems used in the historic past. Although

adoption of PT based on conventional tillage promoted crop production,

B

D

F

H

A

C

E

G

Figure 1.2 Examples of tillage practices used in China: (A) traditional ridge tillagein Northeast (RiT); (B) spring ridge tillage in Northeast (RiT); (C) traditional plow tillage inThe North region (PT); (D) no-till for summer corn under winter wheat straw return inThe North region (NT); (E) rotary tillage in The North region (RoT); (F) traditional plow till-age in paddy fields of Southern China (PT); (G) rotary tillage for paddy in Southern China(RoT); and (H) rice transplanting under no-till in paddy fields of Southern China (NT).


there have been numerous problems in different regions. Soil fertility deg-

radation and labor shortages in PT system are among the common problems

encountered in different regions of China.

The CA research in China commenced during the 1970s. Over and above

the environmental issues, increasing soil productivity and crop yields are

important benefits in China because of the large population and the necessity

of achieving food security. In comparison with other countries, however,

there are some challenges in adopting CA in China because of diverse

cropping systems and relatively more residues and stubbles retained in the

field. Yet, demand for CA has been increasing because of the economic ben-

efits, shortages of natural resources, and decreasing availability of farm labor in

China. Yet, CA has become an important agricultural technology in China.

According to Agricultural MechanizationManagement, theMinistry of Agri-

culture of China, the area under CT in China exceeded 6.67 Mha in 2012

(Wang, 2012). Effects of CT on soil physical, chemical, and biological char-

acteristics and crop growth have been widely studied. Further, SOC seques-

tration and GHG emissions under CT have been monitored in different

regions (Bai et al., 2010; Zhang et al., 2009, 2011). Studies on SOC seques-

tration under CT and some related research have been conducted since ca.

2000. Because of the large differences in climate, soil types, cropping systems,

as well as experiment duration, results from different regions are also highly

diverse. Thus, there is a strong need to collate, synthesize, and infer data from

these studies.

Mechanisms of the tillage effects on SOC sequestration are not well

understood. Thus, understanding of the basic mechanisms is important to

validating, adapting, and promoting CA systems under soil/site-specific sit-

uations. Thus, it is the right time to summarize the relevant research results

of CA in China, and to identify its potential and challenges. Therefore, the

purpose of this chapter is to (1) review available literature on CA and its

adoption in China, (2) describe the impact of CA on soil properties and

SOC sequestration, (3) identify constraints to adoption of CA, and (4)

explain future research and development priorities in adopting CA in China

in the context of climate change and food security.

2. CA IN CHINA

2.1. CT systems in different agroeco regions
Intensive tillage dominated in most agricultural areas of China before the
1970s when moldboard plow was the most widely used implement.


Although intensive tillage has greatly contributed to China’s historic crop

production, it required numerous steps prior to sowing, such as residue

removal, plowing, harrowing, land leveling, and seeding. Indeed, the com-

plex process adversely affected soil and the environment by accelerating ero-

sion, increasing SOC loss, decreasing profit, and prolonging the time

involved. The CA technology (e.g., NT) has been researched in China since

the late 1970s. However, for several reasons, such as low yield, the rate of

adoption of CA has been rather slow.

The geographical focus of this chapter is on Northeast, North, Northwest,

and Southern paddy regions of China. This review is based on more than 400

articles and reports concerning CA from Chinese National Knowledge Inter-

net (CNKI) and Scidirect database. Of these, about 100 reports on CA are

related to its effects on SOC concentration based on 5 experiments in North-

east, 5 in North, 7 in Northwest, and 9 in paddy fields of Southern China

(Table 1.1). Most of these experiments are <20 years in duration. Some typ-

ical experiments of SOC under CA were outlined in Table 1.2 to represent

different agroeco regions of China.

The data in Tables 1.1 and 1.2 indicating some characteristics of CA on

SOC research in China can be summarized as follows:

1. A wide range of CA systems are practiced in different agroeco regions of

China because of the diverse cropping systems and large differences in

climate, soil type, and crops.

2. Compared with other countries, most of the farms are relatively small

(about 0.3 ha per household), except in the Northeast (NBSC, 2011).

Thus, demands for small seeders for CA have been increasing in

most areas.

3. Most of experimental duration is relatively short (�5 years). Only a few

experiments on CA have been conducted for more than 20 years.

Hence, results from short-duration experiments cannot provide a strong

foundation to infer the effects of CA on SOC dynamics.

4. In contrast with traditional soil science research, most of the research on

CA is based on soil sampled from a shallow depth, usually within the

plow layer (<30 cm).

The Northeast region includes Heilongjiang, Jilin, Liaoning province, and

eastern part of the Nei Monggol Autonomous Region, with cold temperate

zone and continental monsoon climate. The annual temperature ranges

from �1 to 10 �C and the cold season is relatively longer among other

seasons. The annual precipitation varies from 500 to 1000 mm, and most

rain falls in summer (June to August). Only one crop is grown every year,

Table 1.1 Distributions of conservation tillage experiments on soil organic carbon(SOC) in different agroeco regions of China

Agroeco regionsTotal experimentnumbers

Experimentalduration (years)

Experimentnumber

Northeast 5 3–5 1

6–10 1

11–15 2

16–20 0

>20 1

North 5 3–5 2

6–10 1

11–15 1

16–20 0

>20 1

Northwest 7 3–5 0

6–10 3

11–15 2

16–20 1

>20 1

Paddy fields of

southern region

9 3–5 5

6–10 2

11–15 1

16–20 0

>20 1

Source: These data are from the literature in CNKI and Scidirect database.


and spring corn (Zea mays L.), soybean (Glycine max L.), spring wheat

(Triticum aestivum L.), and potato (Solanum tuberosum L.) are the major crops.

The farm size is relatively larger than in other regions of China, nearly

0.6–0.7 ha per household (NBSC, 2011). Soil fertility depletion is a serious

problem in this region. Meanwhile, with the protected climate change, the

probability of spring drought has been increasing in recent years. Because of

cold and semiarid climate, RiT (Fig. 1.2A and B) is practiced by most

Table 1.2 Some conservation tillage experiments in China

References Location Soil typeExperimentaldurationa Cropping system Treatmentb

Depth ofsampling(cm)

Liang et al.

(2011)

Dehui (44�120, 125�330E), Jinlinprovince, Northeast region

Clay

(Chinese

Mollisol)

2001–2011 Single cropping: corn

and soybean rotation

NT, RiT,

and PT

30

Jiang et al.

(2012)

Yucheng (36�570N, 116�360E),Shandong province, North region

Salinization

fluvo-aquino

soil

2003–2010 Double cropping: spring

wheat and summer corn

NT0, NT,

and PT0

60

Han et al.

(2010)

Luancheng (37�530N, 114�410E),Hebei province, North region

Silt loam soil 2001–2010 Double cropping: spring

wheat and summer corn

NT, RoT,

and PT

30

Xu et al.

(2009)

Dingxi (35�350N, 104�370E), Gansuprovince, Northwest region

Loessal soil 2001–2009 Single cropping: spring

wheat and pea rotation

NT0, NT,

and PT

30

He et al.

(2010)

Ningxiang (28�070N, 112�180E),Hunan province, paddy fields of

Southern region

Stagnic

anthrosol

2005–2009 Double cropping: double

rice (early rice and late

rice)

NT, RoT,

and PT

20

aExperimental duration means the initial time to the last sample time of the experiment in the paper.bNT, no-till; RiT, ridge tillage; PT, plow tillage; NT0, no-till with residue removed; PT0, plow tillage with residue removed; RoT, rotary tillage. Residue retention inNT, RiT, PT, and RoT.


farmers as a means of improving soil temperature regime and conserving soil

water. Fall PT, spring PT, rotary tillage (RoT), and subsoiling in combina-

tion with RiT are also practiced in the Northeast region. Currently, some

CA systems, such as NT under original ridge and subsoiling, have been

developing gradually to improve soil fertility, enhance water use efficiency

(WUE), and control soil erosion.

The North region includes Beijing, Tianjin, Hebei, Shandong, Henan,

parts of Shanxi, parts of Anhui province, and parts of the Nei Monggol

Autonomous region. With predominantly temperate monsoon climate,

the average temperature is 11.6–12.5 �C and precipitation is 480–500 mm.

However, the rainfall is unevenly distributed during the seasons and most

is received in summer. Water scarcity is a serious problem limiting crop

production in this region. The ground water table in some areas of North

region (e.g., Cangzhou, Hebei province) has dropped at the rate of �1 m

year�1 with a total cumulative drop of over 100 m (Qiu, 2010; Zhang,

2011). The overuse of ground water on a large scale will become a severe

“bottle neck” to agricultural development in the future.Double cropping sys-

tem, winter wheat plus summer corn, is the typical cropping system in the

North. Historically, the farmers tilled the soil with moldboard plow before

seeding (Fig. 1.2C).Then,NT systemwas introduced in summer corn system

during the 1980s (Fig. 1.2D). Subsequently, the traditional tillage system

changed into NT for summer corn and PT for winter wheat. Until now,

NT for summer corn has been practiced over 90% of the area. During the late

1990s, most of crop residues were burned to facilitate timely seeding,

which influenced the environment quality and even public safety. Residue

retention became a serious issue for crop production in theNorth at that time.

The RoT system (Fig. 1.2E) for winter wheat became a dominant tillage

method that could chop corn stalk, mix the residue into the soil, and level

the land simultaneously. Presently, NT for summer corn andRoT for winter

wheat are the dominant soil tillage systems in the North. Application of NT

for winter wheat started in this region since ca. 2000, but it has not been

adopted on a large scale because of the poor seeding quality and low

agronomic yield.

The Northwest region is located in the innermost central region of the

Eurasia and includes Xinjiang Uygur Autonomous Region, Xizang Auton-

omous Region (Tibet), Qinghai, Gansu province, Ningxia Hui Autono-

mous Region, and part of the Nei Monggol Autonomous Region. The

long distance from oceans leads to a dry climate with favorable radiation

and higher diurnal fluctuations indicated by large temperature differences


between day and night. The average temperature is 7.9–10.0 �C. Theannual precipitation is <500 mm, which is a limiting factor for productive

agriculture. Accelerated soil erosion is the main problem for agricultural

intensification and both single and double cropping systems are practiced

in this region. Wheat and corn are the dominant crops in this region, along

with rice (Oryza sativa L.) in some parts of Ningxia. Cotton (Gossypium

hirsutum L.) is also a major crop in Xinjiang. Tillage systems are diversified

with different crops and agroeco regions, such as PT, subsoiling, mulch

tillage, and contour tillage.

Southern paddy fields refer to the region south of the Yangtze River,

which is the dominant rice growing region of China. This region has a sub-

tropical monsoon climate, with high temperature and high rainfall. The

average temperature is 16–18 �C and the annual precipitation is

1600 mm. The cropping systems are diverse, and double- and triple-

cropping systems are popular. Expectedly, PT (Fig. 1.2F) has been the pre-

dominant tillage in traditional farming. Presently, RoT (Fig. 1.2G) has

become the dominant tillage method because of its simplicity in preparing

the seedbed. However, labor-saving technologies have become a necessity

in most areas as a result of increasing migration to urban centers. With ben-

efits of labor and fuel savings, CA is also used in most paddy fields. No addi-

tional tillage operations are conducted before transplanting and rice seedling

are thrown in the standing water (Fig. 1.2H). In relation to the residues and

weeds problems, NT for both early and late paddy fields has been conducted

only in small parts of this region, and that also not on a large scale.

2.2. Challenges to adopting CA in ChinaAlthough the research and demonstration of CA system has used for more

than 30 years, it is still at a developmental stage in China. Numerous factors

for nonadoption have challenged the research and extension of CAwith ref-

erence to climate, soil type, diverse cropping systems, amount of crop res-

idues, specific suitable machinery, and skills of the farmers.

2.2.1 Diverse cropping systemsA wide range of temperature, precipitation, and soil results in diverse prac-

tices of cropping systems among different agroeco regions. Single-, double-,

triple-, and even quadruple-cropping systems are practiced in different

agroeco regions. The large diversity of cropping systems requires a range

of tillage systems. The diversity of previous crops also accentuates the com-

plexity of tillage systems. For example, the cropping systems in the Southern


region are based on rice, and systems vary with in this region. In double rice

paddy (rice–rice) cropped areas, late rice is transplanted after early rice. But

in the rice–wheat cropped areas, rice–wheat rotation is followed. Radically

different soil conditions from previous crops increase the difficulty of pre-

paring a good seedbed. Various climate, soil, and cropping systems give rise

to practicing of complex CA systems in China.

2.2.2 Low yield under some CA technologiesBecause of the large and affluent population, food security is a perpetual issue

in China. Thus, improving the crop yield has been an arduous task for

China’s agriculture. However, the crop yield under NT can be reduced

because of poor seeding, which also influences the extension of CA in some

regions. While CA is considered a revolutionary farming system, it is still

evolving throughout China. Meanwhile, it also requires a special set of

appropriate cultivation practices that are different from those for the

PT-based systems. Therefore, a set of appropriate package of cultivation

practices for a range of soils, crops, and agroecological environments for

the different CA systems should be identified/adapted according to specific

demands based on site-specific conditions. Some of the cultivation practices

should be specifically developed for CA (e.g., irrigation, pest control, and

fertilizer system). But, most farmers continue to apply the traditional culti-

vation operations in CA systems, and these farm operations also affect the

agronomic yield.

2.2.3 Suitable small-size seeders for small farm holdingsThe most important and difficult operation to be accomplished under CA

system is a good seeding and an adequate crop stand. In general, soil surface

under CA is uneven and mulched by the presence of crop/weed residues,

which increases the difficulties of seeding. Therefore, developing suitable

seeders is important to the success of CA. Mulch management is a key tech-

nique in CA that also greatly influences the seeding efficiency. Further, the

amount of crop residues is increasing over time. Based on the successful

experiences from other countries, large and heavy machinery can ensure

a good seeding even with high amount of crop residues. However, a large

seed drill is not suitable for Chinese farmers because of the small farm size.

The average farm size in China is about 0.3 ha per household and the plots of

cultivated land are scattered farther apart. Thus, small-size seeders are

required to meet the needs of scattered small plots, large residues, and diverse

cropping systems.


2.2.4 Understanding and perceptions of CAIt is well known that intensive farming is a major characteristic of China’s

agriculture (e.g., intensive labor, fertilizer, and irrigation). Most people with

perceived knowledge of intensive tillage consider CA as a “lazy

technology,” which reduces crop yields. Concurrently, the yield reduction

under CA in some regions also reinforces the negative mindset toward CA

extension. On the contrary, CA is not a “lazy technology.” It is an emerging,

modern technology that deserves the attention of farmers and policy makers

with a specific focus on the use of essential inputs needed, such as suitable

machinery and related agronomic techniques (e.g., seeding, irrigation, fer-

tilization, and weed/pest control). With numerous demonstrable environ-

mental and social benefits, CA is regarded by most farmers as a beneficial

technology. Besides improving the CA system, there is a need for taking

a series of measures to promote a widespread adoption of CA. Thus, a firm

resolve is needed to convert PT into an appropriate and site-specific CA sys-

tem. Thus, providing some incentives, along with strengthening of educa-

tion and demonstration programs, is needed to encourage farmers,

technicians, extensionists, and researchers to adopt CA.

3. EFFECTS OF CA IN CHINA

Some examples of CA-induced changes in soil properties are discussed

in the following sections.

3.1. Soil bulk densityConversion of PT to a CA system can lead to drastic changes in soil physical

properties. Soil bulk density (rb), a vital parameter that influences the SOC

estimation and nitrogen (N) pools, is strongly affected by tillage

managements.

In general, soil rb in the upper soil layer is significantly higher under

CA/NT than PT systems (Yang and Wander, 1999). However, in other

soils and cropping systems, soil rb under NT can be equal to or lower than

that under PT systems (Ussiri and Lal, 2009). Such a variability in rb may due

to the specific site, probably depending on climatic regime, soil type, residue

management, duration of the experiment, and the time of sampling.

Although results differ among tillage treatments, most data show insignifi-

cant differences in rb between NT and PT system (Table 1.3).

Regardless of tillage practices, rb changes with soil depth. In general, soil

rb increases with increase of soil depth and may attain the highest value

Table 1.3 Soil bulk density (rb) under different tillage systemsReferences rb (g cm�3)

Liang et al. (2011) Depth (cm) NTa RiT PT

0–5 1.22bb 1.31a 1.31a

5–10 1.46a 1.51a 1.47a

10–20 1.37a 1.35a 1.38a

20–30 1.38a 1.32b 1.33b

Jiang et al. (2012) Depth (cm) NT0 NT PT

0–5 1.27a 1.28a 1.30a

5–10 1.44b 1.52a 1.43b

10–20 1.45b 1.56a 1.54a

20–40 1.41b 1.48a 1.48a

40–60 1.43a 1.44a 1.46a

Han et al. (2010) Depth (cm) NT RoT PT

0–5 1.40a 1.30a 1.32a

5–10 1.50a 1.39b 1.35b

10–20 1.56a 1.56a 1.53a

20–30 1.60a 1.58b 1.57b

Xu et al. (2009) Depth (cm) NT0 NT PT

0–5 1.17a 1.01b 1.14a

5–10 1.20a 1.19a 1.24a

10–30 1.20a 1.27a 1.28a

He et al. (2010) Depth (cm) NT RoT PT

0–5 0.84a 0.85a 0.84a

5–10 1.11a 1.05a 0.88b

10–20 1.24a 1.15b 1.19b

aNT, no-till; RiT, ridge tillage; PT, plow tillage; NT0, no-till with residue removed; RoT, rotary tillage.Residue retention in NT, RiT, PT, and RoT.bDifferent lower case letters (a or b) in a row designate significant differences (P<0.05) among same soildepth.



corresponding with the depth of the plow pan. Furthermore, NT reduces the

depth of soil disturbance to merely 5 or 10 cm. Thus, adoption of NT may

eliminate the plow pan in croplands. However, NT may enhance the risks

of N leaching, especially with long-term flooding of the paddy fields.

Changes in soil rb are also influenced by the amount of crop residues.

Whereas Du et al. (2010) reported that residue removal alone did not signif-

icantly change the soil rb, other studies have indicated statistically significant

effects of residue management on rb. Such a discrepancy may be attributed to

the differences in quantity and quality of residues returned (Shaver, 2010).

3.2. Soil water and temperature regimesData from several studies indicate that adoption of NT saves water because of

the less soil disturbance, a higher proportion of retention and continuous

pores, higher infiltration rate, and low evaporation under the mulch cover.

Adoption of NT increases soil water storage and improves WUE of most

crops compared to that under PT. Increasing soil water storage is beneficial

for some regions with limited water resources in China (e.g., Northeast,

North, and Northwest). Soil water storage can be increased by 10% with

adoption of NT when compared with PT (Zhang et al., 2005). Further, soil

evaporation is reduced under NT system because of the residue mulch.

Thus, plant-available water is favorable under NT, which improves crop

growth and increases agronomic yield in drought-prone soils. He et al.

(2007) reported that NT enhances WUE by 11.42% (data from 1993 to

2000) in Shouyang compared to PT with residue removed (Table 1.4).

Residue retention in CA systems reduces soil evaporation, improves

water infiltration, and reduces runoff. Generally, water infiltration is more

than that under PT because of numerous and continuous macropores, cre-

ated by the activities of microbes, earthworms, and burrowing animals in the

soil (i.e., drilosphere) (Brown et al., 2000; Lal and De Vleeschauwer, 1982).

However, NT can improve soil pore continuity due to the minimum soil

disturbance and biological activities (Fig. 1.3, Lv and Zhou, 2012).

Further, CA influences water distribution in the soil profile over time,

and soil temperature dynamics under CA systems are also changed by

changes in soil properties. Soil properties under NT (e.g., surface residue

reflectance, thermal conductivity, soil moisture, and air porosity) likely

influence soil temperature regime. Generally, NT has dual effects on soil

temperature relative to PT soil, either decreasing or increasing temperature.

For example, maintaining crop residues on the surface slows soil warming

Table 1.4 Water use efficiencies (WUE) for corn under different tillage system inShouyang

Tillagea

WUE (kg ha�1 mm�1)

1993 1994 1995 1996 1997 1998 1999 2000 Average

PT0 6.3ab 10.8a 8.1a 8.6a 8.0a 10.2a 8.4a 7.9a 8.5

NT 8.3b 12.3b 9.4b 8.8a 8.4b 12.2b 8.5a 8.2a 9.5

aPT0, plow tillage with residue removed; NT, no-till, residue retention in NT.bDifferent lower case letters (a or b) in a row designate significant differences (P<0.05) among same soildepth.Source: Data adapted from He et al. (2007).

A B

C D

Figure 1.3 Soil pores under no-till systems: (A) pores at 0–5 cm depth, (B) pores andearthworm holes at 0–5 cm depth, (C) pores and flyspeck of worms at 5–10 cm depth,and (D) pores at 5–10 cm depth. Photos were taken with photomicrography methodafter fixed imaging of the undisturbed soil sample. Photos adapted from Lv and Zhou(2012). Experiment was conducted from 2001 in Lucheng, Hebei province.



during the early spring compared to a PT seedbed. Chen et al. (2009b)

observed that the cumulative soil temperature within 20 cm depth under

CA was several degrees cooler than that under PT during winter wheat

elongation stage of growth in the North region. The low soil temperature

under NT can be unfavorable to the regrowth and stem elongation of winter

wheat in spring, which can delay maturity. Radical elongation and phenol-

ogy of some winter and spring crops are delayed under conditions of sub-

optimal soil temperatures, which reduce crop yield potential and increase

risks of yield loss. Indeed, suboptimal soil temperature is one of the main

reasons of low grain yield of winter wheat (Li et al., 2008; Yang et al.,

2006). However, lower soil temperature under NT than PT is favorable

for summer corn growth in the North region (Wang et al., 2001). The aver-

age soil temperature under NT can be 2–4 �C lower than that under PT

during the hottest summer months. In contrast, NT with residue cover

maintains higher soil temperature during the winter compared with PT soil,

which is beneficial to overwintering of winter crops. Also, with more soil

water under NT, the soil temperature changes more gradually than in the

PT soil. Further, diurnal fluctuations are relatively smaller and the time

lag for heat transfer from surface to subsoil is longer under NT than that

under PT (Chen et al., 2009a).

3.3. Crop yieldsCrop yield response to CA is a controversial and debatable topic in China.

Xie et al. (2008) reviewed the published literature regarding the effects of

CT on crop yields in China between 1994 and 2005. In general, crop yield

under CT is more than that of PT on experimental plots. The data from field

experiments show that on the average crop yield was 12.5%more under CT

over that of PT, by 9.0% for wheat, 6.2% for corn, and 15.9% for rice (Xie

et al., 2008). However, 10% of experimental results indicated decline in crop

yield under CT, including that of wheat, corn, rice, as well as that of cotton,

soybean, canola (Brassica juncea L.), and hulless barley (Hordeum vulgare L. var.

nudum Hook. f.). Xie et al. (2008) indicated the decline in yield under CT by

16.5% for wheat, 10.1% for rice, and 8.9% for corn in these experiments.

The relative magnitude of decline in crop yield in different regions of China

by CT over PTwas 9.2% in theNortheast, 18.5% in theNorth, 14.8% in the

Northwest, and 16.9% in the paddy regions of Southern China among these

yield decreasing experiments. The highest decline in yield was observed in

wheat and the least in corn (Table 1.5).

Table 1.5 Themagnitude of yield decline by CT over PT in field experiments indicating anegative response to crop production

Agroeco regions

Yield decline (%)a

Wheat Rice Corn

Northeast region – – 10.68

North region 27.59 – 6.67

Northwest region 20.73 – 9.57

Paddy fields of southern region 5.56 13.77 –

aThe value of the total decline <100% is due to other crops not listed in this table.Source: Data adapted from Xie et al. (2008).


Many factors influence crop yield under CA. Decrease in crop yield under

NT may be attributed to suboptimal soil temperatures during spring, higher

bulk density and resistance to penetration, phytotoxicity problems, and high

weed infestation. Among these factors, poor seeding efficiency and low crop

stand are the most critical factors influencing crop performance and yield.

Thus, improving seeding efficiency and obtaining optimum crop stand are

the key issues to increasing crop yield under NT systems.

3.4. Soil organic carbonTillage system strongly impacts soil physical, chemical, and biological prop-

erties. Soil disturbance bymechanical tillage (PT) is the principal cause of the

historic loss of SOC. Thus, conversion of PT to CT could substantially

enhance SOC sequestration (Lal, 2002; Reicosky, 2003; West and Post,

2002). Regardless of upland or paddy fields, tillage can affect SOC and its

distribution in the soil profile (Table 1.6). Several studies indicate that the

most drastic effects of tillage systems on SOC concentration are observed

in 0–5 cm layer (Liang et al., 2011). Similar observations on stratification

of SOC in the surface layer have been reported from elsewhere (Alvarez

et al., 1995; Dolan et al., 2006; Franzluebbers, 2002; Puget and Lal,

2005; Sa and Lal, 2009). Tillage-induced differences in SOC concentration

between NT and PT diminish with increases in soil depth. Further, some

studies have indicated higher SOC concentration in PT than NT below

5 cm depth (Han et al., 2010; He et al., 2010; Jiang et al., 2012; Xu

et al., 2009). In comparison with PT, conversion to NT not only enhances

SOC concentration in the surface soil but also increases the stratification

ratio (Franzluebbers, 2002). Plowing under the crop residues incorporates

Table 1.6 Concentration of soil organic carbon (SOC) under different tillage systems indifferent agroeco regions of ChinaReferences SOC concentration (g kg�1)


0–5 18.0ab 18.1a 17.2a

5–10 16.1b 16.4ab 17.3a

10–20 15.4a 15.4a 15.6a

20–30 12.2a 13.4a 14.2a


0–5 7.0b 9.0a 5.3c

5–10 5.9b 8.2a 5.9b

10–20 9.6a 11.1a 10.94

20–40 17.0a 14.0b 18.2a

40–60 10.7b 9.2b 15.9a


0–5 13.2aA 11.8bB 9.8cC

5–10 9.9bB 11.8aA 10.3bB

10–20 6.9cC 9.1bB 10.2aA

20–30 4.1cB 5.8bA 6.2aA


0–5 9.8b 11.6a 10.0b

5–10 10.0a 10.0a 9.9a

10–30 9.8b 9.9a 9.9a


0–5 31.3a 28.3b 26.8c

5–10 23.9b 28.9a 28.5a

10–20 17.6c 26.0b 24.5b

aNT, no-till; RiT, ridge tillage; PT, plow tillage; NT0, no-till with residue removed; RoT, rotary tillage.Residue retention in NT, RiT, PT, and RoT.bDifferent lower case letters (a, b, or c) in a row designate significant differences (P<0.05) among samesoil depth. Different capital letters (A, B, or C) in a row designate significant differences (P<0.01) amongsame soil depth.



biomass C into the subsoil, thus changing the distribution of SOC in the soil

profile. In contrast, crop residues are left on the surface and soil is

undisturbed, thereby enhancing the concentration of SOC in the surface

layer. Therefore, PT leads to distribution of SOC and nutrients in the plow

layer, whereas NT leads to its stratification and concentration in the

surface layer.

Similar to crop yield, the data on CA from China also indicate a differ-

ential response of tillage systems to SOC concentration in the soil profile.

Liang et al. (2007) reported that NT enhanced SOC concentration only

in the 0–5 cm layer and decreased it in the subsoil compared with other till-

age treatments. Some other studies indicate that NT increased SOC concen-

tration in 0–20 cm or even deeper layers (Xu et al., 2009; Zhang et al.,

2008). Such a differential response among these experiments may be attrib-

uted to different cropping systems, site-specific tillage methods, amount of

crop residues returned, soil type, and profile characteristics.

Comparisons of the available data indicate that, in addition to tillage sys-

tem, residue retention and crop rotation also influence SOC dynamics and

its depth distribution. Residue management is the key determinant of SOC

sequestration, with a strong effect on SOC concentration (Rasmussen et al.,

1980). Huang et al. (2010) concluded that reduced tillage or NT practices

had no effect on levels of SOC sequestration in the paddy fields, but crop

residues and animal manure applications enhanced SOC over periods of

about 20–40 years.

In addition to the amount, location or placement of crop residues in the

soil also impacts SOC concentration. Such a response is termed “spatial effect”

of SOC under NT characterized by a higher concentration in the surface soil

but lower in subsoil. Furthermore, the amount of residues returned differs

among tillage systems and crops grown (Liang et al., 2007; Luo et al., 2011).

The range of SOC accretion in the surface layer is much larger than that

under other tillage methods. The data from tillage experiments in Dehui,

Jilin province (Fan et al., 2011; Liang et al., 2010) were analyzed to assess

the impact of residue management on profile distribution of SOC. Concen-

tration of SOC in the surface layer (0–5 cm) under NT was higher than that

under PT, but this trend was reversed in the subsoil layers. Results of this

experiment showed that the mean SOC concentration in 0–30 cm layer

under NT was higher than that under PT (Fig. 1.4). Yet, the overall rate

of SOC sequestration under NT was higher than that of PT, with the mean

SOC sequestration rate to 30 cm depth of 0.081 g kg�1year�1 for NT and

0.013 g kg�1year�1 for PT. The annual rate of increase in SOC for the

200014.0

14.5

15.0

15.5

16.0

16.5

17.0

2002 2004 2006

Year

SO

C g

kg

-1

2008

NT

PT

2010

Figure 1.4 Temporal changes in soil organic carbon (SOC) concentration in 0–30 cmdepth for NT versus PT systems (Dehui, Northeast China). NT, no-till; PT, plow tillage.Residue retention in NT and PT. The SOC of 0–30 cm was the average value of 0–5,5–10, 10–20, and 20–30 cm. Error bars stand for LSD (P<0.05) for comparison betweentillage treatments. Sources: Data of 2001, 2004, and 2006 adapted from Liang et al. (2010);data of 2009 adapted from Fan et al. (2011).


surface layer (0–5 cm) was 2.36% for NT compared with 0.30% year�1 for

PT. For 0–30 cm depth, the annual rate of increase was 0.53% and 0.10% for

NT and PT, respectively.

Amount and quality of crop residues strongly affect the rate of SOC

sequestration. Comparing different treatments between 2001 and 2008

(Fan et al., 2011; Liang et al., 2010) indicates that the SOC sequestration

rate was negative in PT without residue return to soil (Table 1.7). But with

residue return and across PT and NT systems, the SOC concentration

increased with the mean SOC sequestration rate of 0.56 and

0.63 g kg�1year�1, respectively.

Calculations of the rate of increaseof SOCfromthepublisheddata inChina

indicate that the average annual rate for 0–20 cm depth under CA systems are

0.60–3.74, 0.14–4.15, 0.50–5.94, and 8.81–17.95 g kg�1 for the Northeast,

North, Northwest, and paddy fields of Southern China, respectively.

3.5. SOC stockSome management techniques (e.g., adoption of CT, growing cover crops,

and incorporating crop residues) can increase the SOC stock. However,

Table 1.7 The rate of SOC sequestration different tillage system between 2001and 2008

Years

SOC sequestration rate (g kg�1year�1)

NTa NT0 PT PT0

2001–2002 0.95 0.55 0.50 �0.10

2002–2003 1.05 0.55 1.35 �0.05

2003–2004 0.10 0.35 �0.15 0.03

2004–2005 0.05 �0.08 0.20 �0.05

2005–2006 0.75 0.13 0.03 0.04

2006–2007 1.25 2.45 1.82 �0.03

2007–2008 0.25 0.15 0.20 �0.09

Average 0.63 0.59 0.56 �0.04

aNT, no-till; NT0, no-till with residue removed; PT, plow tillage; PT0, plow tillage with residueremoved. Residue retention in NT and PT.Sources: Data adapted from Liang et al. (2010) and Fan et al. (2011).


the results of computed SOC stock on equivalent mass basis under different

tillage systems are inconsistent among experiments conducted in different

regions (Table 1.8). With an exception of the experiment reported

by Liang et al. (2010), the SOC stock in the surface 0–5 cm depth is

reported to be higher under NT than that in other tillage methods.

The data of most experiments show that the SOC stock in 0–20 cm

depth tends to be higher in NT than that for other tillage treatments.

For soil below 30 cm depth, however, the SOC stock under NT is gen-

erally lower than that of soils under PT. Comparing the data for all depths,

the SOC stock is higher with residue return than with residue removal.

Differences in SOC stock among different experiments may be attributed

to differences in climate, soil, farming system, and duration since conver-

sion to CT/NT.

Although the SOC stock to 30 cm or deeper depths is lower under NT

than that under PT, the stock under NT exhibits an increasing trend over-

time when compared with the antecedent stock. This trend implies that

SOC stock under NT has not yet attained the equilibrium, and would

increase in the future. Furthermore, the effect of NT on SOC sequestration

is often the highest in soil under paddy cultivation in Southern China with

an average rate of increase of 1.93 Mg C ha�1year�1 and is generally the

lowest in Northeast with an average rate of 0.37 Mg C ha�1year�1.

Table 1.8 Soil organic carbon (SOC) stock on equivalent mass basis under differenttillage systemsReferences SOC stocks (Mg ha�1)


0–5 11.70ab 11.86a 11.27a

5–10 23.81a 24.24a 24.29a

10–20 44.56a 45.16a 45.51a

20–30 60.79a 62.98a 64.40a


0–5 4.51b 5.81a 3.43c

5–10 9.11b 11.99a 8.03b

10–20 25.28b 29.32a 25.50b

20–40 73.65ab 70.73b 79.19a

40–60 104.58b 97.20b 125.01a


0–5 9.24a 8.26b 6.88c

5–10 16.67a 16.83a 14.59b

10–20 27.43b 30.68a 29.93a

20–30 33.99b 39.96a 39.85a


0–5 5.73b 6.66a 5.85a

5–10 11.78a 12.70a 11.84a

10–30 36.87b 38.04a 37.18ab


0–5 13.25a 12.03b 11.41c

5–10 26.37a 27.86a 26.63a

10–20 48.14b 60.09a 57.04a

aNT, no-till; RiT, ridge tillage; PT, plow tillage; NT0, no-till with residue removed; RoT, rotary tillage.Residue retention in NT, RiT, PT, and RoT.bDifferent lower case letters (a, b, or c) in a row designate significant differences (P<0.05) among samesoil depth.



3.6. SOC sequestration and soil qualityContinuous use of mechanical tillage (PT) can disrupt aggregates and

adversely impact soil quality (Karlen et al., 1994; Lal, 1993; Lal and

Kimble, 1997). In contrasts, continuous use of a CA system maintains soil

structure, enhances biotic activity, increases SOC concentration in the sur-

face layer, and improves soil aggregation (Karlen et al., 1994; Lal, 1993). Dif-

ferentiation of SOC stock into fractions is an important indicator of SOC

sequestration and changes in soil quality in relation to soil management

and control (Kay, 1998; Melero et al., 2009; Miller and Jastrow, 1990;

Tan et al., 2007). Zhang et al. (2012) reported that the use of RiT increased

SOC in different fractions of aggregate-associated SOC, whereas conversion

to NT increased the SOC only in the microaggregates. Therefore, Zhang

and colleagues suggested that CA (RiT andNT) is beneficial to soil structure

through its positive effects on aggregation processes in the black soil of the

Northeast region (Zhang et al., 2012). From the data of a long-term tillage

experiment conducted in the North region, Zhao et al. (2012) reported that

PT resulted in a greater SOC concentration in 50–500 mm aggregates, but

NT and subsoiling increased the active or labile C and decreased the passive

or recalcitrant C fraction in 500–1000 mm aggregates. Huang et al. (2010)

concluded that levels of intra-aggregate particulate organic matter associated

with microaggregates and microaggregates occluded within macroaggre-

gates were more inNT than that in CT. This trend is beneficial to long-term

SOC sequestration in paddy soil. Overall, NT can increase soil aggregate

stability, leading to enhancement of SOC sequestration and improvement

of soil quality.

Despite the availability of a large literature on CA in China, there are

few studies on the impact of tillage system on SOC fractions in diverse

soils. In general, light fraction C is sensitive to farming operations, while

heavy fraction is more stable (Bremer et al., 1994; Cambardella and

Elliott, 1992; Golchin et al., 1994; Gregorich et al., 1996). With specific

reference to soils of China, however, it is still unclear how tillage impacts

soil C fractions under different cropping systems. Light and heavy

C fractions reflect the sensitivity to the environmental factors, which is

the key indicator of principal mechanisms of SOC sequestration. There-

fore, partitioning of SOC stock into different fractions or pools and quan-

titatively analyzing changes in these pools are critical to a better

understanding of the C and N dynamics and its response to climate change

(Song et al., 2012).


3.7. Limitations of SOC research under CADespite approximately 30 years of research on CA in China, there are several

knowledge gaps especially with regard to SOC sequestration, whichmust be

addressed. Important among knowledge gaps are research topics, sampling

depth, and study sites distribution, etc.

3.7.1 Research topicsSoil erosion is reduced or controlled under CA because of less soil distur-

bance and continuous ground cover on the soil surface. However, mecha-

nisms of increase in SOC by reduction of erosion under CA are still not fully

understood. Increase of SOC under CA in China has mostly been reported

on soils, which are relatively less erodible or nonerodible. However, SOC

dynamics upon conversion of eroded lands to CA is not understood. Yet,

understanding the fate of SOC transported by erosional processes (i.e., emis-

sions, burial, deposition, and redistribution) is an issue of global importance

(Lal, 2003, 2004a,b).

The CA-induced alterations in soil quality affect nutrient and water

dynamics, and productivity and sustainability of agroecosystems (Carter,

2002; Du et al., 2010; Reynolds et al., 2002). Nonetheless, assessment of soil

quality is complex, and demands a comprehensive and systematic research.

Conversion to CA affects soil’s physical, chemical, and biological properties,

and therefore, soil quality. The SOC concentration is an important index of

soil quality (Dalal and Chan, 2001). Yet, little, if any, research has been done

in China with reference to SOC dynamics and soil quality. Most of the stud-

ies on soil quality assessment under different tillage systems are based on

some sole parameters, rather than following a comprehensive, holistic,

and a systematic approach. The lack of a holistic approach has limited the

applicability of the results to other soils and agroeco regions and undermined

transfer of the CA technology.

The SOC sequestration is influenced by a wide range of factors, includ-

ing climate, soil type, cropping system, and farming operations (Eghball

et al., 1994; Jiang et al., 2007; Zhou et al., 2005). A tillage system can alter

the microenvironment, which changes soil biochemical processes and SOC

sequestration. Crop growth can also impact SOC sequestration. How tillage

methods influence the mechanisms of SOC sequestration and soil biochem-

istry are complex questions and become even more intricate with highly

diverse cropping systems practiced in China. Most studies conducted in

China are based on a single parameter or some simple index, such as a soil


physical or chemical property, rather than a whole soil–plant–atmosphere

continuum. Over and above these complexities, the impact of crops and

cropping systems is studied relatively less than that of soil characteristics.

Therefore, the mechanisms governing tillage impacts on SOC sequestration

have not been clearly identified. The soil C cycle involves complex processes

related to C input and output, and is influenced by climate, plant, soil, and

anthropogenic activities. As an important farming operation, tillage drasti-

cally changes the SOC stock, while there is still consensus regarding SOC

sequestration under CA;most scientists believe that CA enhances soil quality

and restores degraded soil (Dai et al., 2010; Liang et al., 2010; Zhang et al.,

2009). However, neither the SOC dynamics nor that of its fractions (e.g.,

C sequestration, GHG emission, and biomass) have been critically and

intensively assessed. Therefore, the relationship between GHG emission

and SOC sequestration under different tillage systems remains to be among

high researchable priorities in China.

The duration of most research on CA conducted in China is rather short.

Some experiments are conducted for only about 5 years. However, tillage-

induced changes in soil properties, especially soil physical properties, occur

over short- and longtime periods. Therefore, conversion to a CA system

may play a very important role in SOC sequestration for several years to

come. Thus, it is only the data from long-term experiments which can illus-

trate the impact of a CA system on SOC sequestration (Deen and Kataki,

2003; Huang et al., 2010; West and Post, 2002).

3.7.2 Soil C study methodThe SOC stock can be assessed on equivalent mass basis or fixed depth basis.

Ellert and Bettany (1995) indicated that SOC stock could be assessed on

equivalent mass basis especially when determining management-induced

changes in the quantities of SOC and other elements stored. This is neces-

sitated by changes in soil rb as influenced by tillage, irrigation, and other

farming and management operations. However, most of the available results

on SOC stock in China have been reported on fixed depth basis and are thus

biased to some degree.

Because of the small size of farm holdings in China, the mechanical

power of tillage implements is relatively small. Further, the depth of plowing

is also shallow in most farm fields in China. For example, the plow depth

with moldboard plow is about 20 cm compared with hardly 10 cm in

RoT system. Thus, the sampling depth for assessing SOC is about 30 cm

in majority of studies. On a long-term basis, however, tillage can affect soil


properties of even a subsoil layer. Baker et al. (2007) synthesized the available

literature on this topic and reported that most studies are based on sampling

from shallow depths. Assessing SOC stock to shallow depths has limitations,

and data are often not comparable, necessitating additional research. Du et al.

(2010) indicated that tillage did not affect the SOC sequestration in deep soil

(50 cm depth) in the North region. But Xu et al. (2013) observed that tillage

could affect SOC sequestration in subsoil under paddy fields in Southern

China. Such differences in results may be due to diverse cropping systems,

tillage durations, sampling depth, etc. It is also widely recognized that NT

enhances stratification ratio of SOC and other nutrients (Du et al., 2010; Lou

et al., 2012; Sa and Lal, 2009). Thus, improving the distribution of SOC and

nutrients throughout the profile remains to be a challenge.

There are several models to simulate SOC sequestration potential (e.g.,

DNDC, CENTURY, Roth C, and EPIC) and can be used to assess SOC

dynamics under different tillage systems (Izaurralde et al., 2001). Use of these

models would necessitate adjustment of appropriate parameters, since a

majority of research in China is conducted on multiple cropping systems

for which it is difficult to use simple models. Therefore, it is necessary to

adapt and fine-tune suitable models and determine localized parameters

for predicting the SOC sequestration potential.

4. POTENTIAL AND OPPORTUNITIES FOR CAAND SOC RESEARCH

Because of the strong environment, economic, and social benefits, CA

is gaining global acceptance toward achieving sustainable aquiculture

(Kassam et al., 2012). Accordingly, the CA technology has also a vast poten-

tial of improving China’s agriculture and the environment.

4.1. Intensive farming problemsFeeding 22% of world’s population on 7% of the world’s cultivated land area

is a great achievement for China’s agriculture (Zhang, 2011). This success is

attributed to intensive farming which uses 32% of world’s chemical fertil-

izers, 25% of pesticides, and 25% of total irrigation (Yan et al., 2011). Con-

sequently, China’s agriculture has paid a heavy price of intensive farming.

For example, the groundwater table has declined at the alarming rate of

1 m year�1 in some areas of the North region (Qiu, 2010). Thus, severe

resource depletion has raised concerns about sustainability of such farming

practices. Therefore, CA can be an important innovation for China because


of the savings in energy, labor, time, and other input, and improvement in

the environment and SOC sequestration benefits.

4.2. Soil erosion controlThe land area prone to accelerated erosion in China is estimated at 356 Mha

(Liu et al., 2011). It has been predicted that the surface soil could be blown

away on severely eroded lands within 50 years with the high rate of soil ero-

sion (0.5–1 cm year�1 surface soil) from the Mollisols region in Northeast

China (E, 2008). Soil erosion and dust storm are still important issues and

threaten the balance and stability of agroecosystems in China (Fig. 1.5). Fur-

ther, water runoff can decrease concentrations of SOC, N, and other essen-

tial nutrients, declining soil fertility, and reducing crop yield. In this context,

CA is an efficient measure to control wind and water erosion, increase SOC

stock, and improve soil quality.

4.3. Residue managementXiao et al. (2010) reported that the amount of crop residues produced was

700 Tg in 2008, and it could increase to 900 Tg by 2015. In 2005, only

9.81% of residues were returned to croplands as mulch/fertilizer, but

>20% of residues were burned directly in the field or thrown away. In con-

trast, a large amount of chemical fertilizers are being used. As much as 30% of

chemical fertilizer of the world is used in China’s agriculture resulting in

severe environment pollution and GHG emission. Besides, residue manage-

ment is a key factor in SOC sequestration. A judicious use of crop residues,

important to enhancing SOC stock, reduces GHG emissions, improves soil

quality, and has strong policy implications.

4.4. Rural development and economic profitSince implementation of reforms and opening up as a global economy,

China’s GDP has increased drastically. However, farmer income has

increased only modestly, and has been estimated at <$400 per person in

2011 (NBSC, 2012). With the increasing cost of chemical fertilizers, irriga-

tion, seed, and sowing, identification of economic techniques has become an

urgent priority for farmers in China. Conversion of PT to NT for winter

wheat can save $35 ha�1 in the North region. Thus, achieving a similar

or better yield by NT can lead to its rapid adoption.

A

B

C

Figure 1.5 Soil erosion and dust storm in some regions of China: (A) wind erosion fromthe Mollisols in the Northeast region, (B) the erodible relief of Loess Plateau, and (C)spring dust storm in Xinjiang in 2011. Photo (A) was provided by Mr. Liu, W.R., photo(B) was from http://image.cpst.net.cn/upload/2009-04/03/238740573.jpg, and photo (C)was provided by Mr. Zhai, Y.L.


http://image.cpst.net.cn/upload/2009-04/03/238740573.jpg


4.5. Labor shortageIndustrialization increased migration of younger population from rural areas

to urban centers, leaving the old people engaged in farming. Thus, labor-

saving techniques are urgently needed. Therefore, CA has numerous ben-

efits of saving in labor, time, and energy and alleviating the constraints of the

labor shortages.

Major challenges lie ahead to development of CA system in China. Yet,

future of China’s agriculture will be in the direction of low soil disturbance,

low input, and high energy-efficient production systems. In this context,

CA is a promising technology for improving the environment and the over-

all profit margin. A coordinated effort is needed to improve research, exten-

sion, and education about CA in China. Researchers must focus on

knowledge-based crop production systems for CA. The crop production

system must be high yielding, and profitable but simple to use. Farmers must

be always prepared to learn new innovations and be familiar with recent

developments. Policy makers must support researchers to study effects

of CA on a long-term basis and must also encourage farmers to adopt CA

through payments for ecosystem services.

5. CONCLUSIONS

Research on CA in China has been conducted since late 1970s and

CA is likely to become a dominant technology in the future. A wide range

of CA systems is needed in relation to diverse climate, soil, and cropping

systems. For some soils and cropping systems (e.g., dryland farming or paddy

fields), conversion from PT to CA can increase SOC concentration and

stock. In general, SOC under CA is concentrated or stratified in the surface

soil layer. Increase in SOC by CA can also improve soil quality by enhancing

soil aggregation and improving water and nutrient storage. However, most

of the research conducted on SOC sequestration under CA in China based

on a short-duration experiments and the underpinning mechanisms are not

clearly understood. Further, prevalence of diverse cropping systems makes it

difficult to conduct in-depth research in contrasting agroeco regions. There-

fore, it is necessary to study the underpinning mechanisms which govern

tillage effects on SOC sequestration in the subsoil layers.

In view of the characteristics and demand of China’s agriculture,

researchable priorities include the following: (1) establish and improve

CA systems, taking into consideration diverse soils, climates, crops, and


cropping systems; (2) identify suitable equipment for the small land holders

and diverse cropping systems; (3) establish CA research networks and links

involving multidisciplinary teams; and (4) link food security with environ-

mental protection, sustainable soil management, SOC sequestration, and

climate change.

ACKNOWLEDGMENTSThis research was funded by Special Fund for Agro-scientific Research in the Public Interest

in China (200903003) and National Natural Science Foundation of China (31171510). The

logistic support provided by CarbonManagement and Sequestration Center, The Ohio State

University, is greatly appreciated.

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