www.elsevier.com/locate/still

Soil & Tillage Research 94 (2007) 346–352

Soil biochemical response to long-term conservation

tillage under semi-arid Mediterranean conditions

E. Madejon a,*, F. Moreno a, J.M. Murillo a, F. Pelegrın b

a Instituto de Recursos Naturales y Agrobiologıa de Sevilla (IRNAS-CSIC),

Avenida Reina Mercedes 10, P.O. Box 1052, 41080 Seville, Spainb Escuela Universitaria de Ingenierıa Tecnica Agrıcola, University of Seville, Spain

Received 14 February 2006; received in revised form 18 August 2006; accepted 24 August 2006

Abstract

We studied the effects of long term conservation tillage (CT) versus traditional tillage (TT) on soil biological status of a semi-

arid sandy clay loam soil (Xerofluvent). The study was conducted in a wheat (Triticum aestivum, L.)–sunflower (Helianthus annuus,

L.) crop rotation established in 1991 under rainfed conditions in SW Spain. A fodder pea (Pisum arvense, L.) crop was introduced in

the rotation in 2005. Soil biological status was evaluated by measuring the microbial biomass carbon (MBC) and some enzyme

activities (dehydrogenase, alkaline phosphatase, b-glucosidase and protease) in autumn of 2004 and in summer of 2005, before and

after the fodder pea crop, respectively. Soil analyses were performed in samples collected at three depths (0–5, 5–10 and 10–25 cm).

In general and in both samplings, increases in the organic matter content, MBC and enzymatic activities were found in the more

superficial layers of soil under CT than under TT. Values of MBC were lower in summer, whereas values of enzyme activities were

similar in both samplings. Biological properties showed a pronounced decrease with increasing soil depth. Statistical differences in

biochemical properties between soils under the different tillage were not found in the deeper layer (10–25 cm). Enzymatic activities,

MBC and organic matter (water-soluble carbon (WSC) and soil organic carbon (SOC) contents) were strongly correlated

( p < 0.01). Conservation tillage improved the quality of soil in the superficial layer by enhancing its organic matter content

and, especially, its biological status, as reflected in the values of stratification ratios for MBC and enzymatic activities.

# 2006 Elsevier B.V. All rights reserved.

Keywords: Tillage; Soil quality; Enzymatic activities; Microbial biomass carbon; Soil organic matter

1. Introduction

Agronomic practices influence soil organic matter

(SOM) dynamics and may increase or decrease SOM

content by altering above and below-ground biomass

production, and the rates of top soil erosion and organic

matter decomposition. Conservation and increase of

SOM levels are crucial for biological, chemical and

* Corresponding author. Tel.: +349 546 24711;

fax: +349 546 24002.

E-mail address: emadejon@irnase.csic.es (E. Madejon).

0167-1987/$ – see front matter # 2006 Elsevier B.V. All rights reserved.

doi:10.1016/j.still.2006.08.010

physical soil functionality (Bradford and Peterson,

2000). However, changing soil organic carbon (SOC) in

arid climates is a great challenge (Lal, 1997; Martens

et al., 2005).

Tillage causes a rapid loss of SOM content leading to

a decrease of soil biological activity, impairment of

physical properties and over time, a possible reduction

of crop productivity. The efficiency of conservation

tillage (CT) to reduce soil erosion and to improve soil

organic matter content and water storage is universally

recognized. This is particularly important in arid and

semi-arid zones, where SOM content is frequently low

and climatic conditions leads to continuous losses.

E. Madejon et al. / Soil & Tillage Research 94 (2007) 346–352 347

Under these conditions, water is the limiting factor for

crop development under rainfed agriculture and

management of crop residues is of prime importance

to obtain sustainable crop productions (Du Preez et al.,

2001).

An increase of soil water content under CT, has

been reported for the semi-arid conditions of southern

Spain (Moreno et al., 1997), and for northern Spain

(Lampurlanes and Cantero-Martınez, 2006). Contents

of SOC, carbonates and nutrients in soil have also

been improved by CT (Murillo et al., 2004; Moreno

et al., 2006). Furthermore, under arid conditions CT

has increased aggregate stability and reduced erosiv-

ity in the more susceptible surface layer (Mrabet,

2002).

Concomitant with the goals of erosion reduction

and physico-chemical improvement, there is a

growing belief that CT benefits crop-enhancing soil

biota, and in general, soil ecology (Kladivko, 2001).

Soil management influences soil microorganisms and

soil microbial processes through changes in the

quantity and quality of plant residues entering the

soil, their seasonal and spatial distribution, the ratio

between above and below-ground inputs and through

changes in nutrient inputs. Soil biological and

biochemical properties have been suggested as early

and sensitive indicators of changes in soil quality.

Several studies have indicated that CT increases soil

microbial biomass, SOC, ratio of biomass C to SOC

and the activity of several enzymes (Dick, 1984) in

top soil (0–10 cm) but these differences are not

consistent and even more often commonly reversed in

the subsurface layers.

Under semi-arid climatic conditions the simple

determination of SOC may not be the best indicator

of the improvement caused by CT. More interesting

relationships may be found by computing stratification

ratio for SOC and of the other biochemical properties

(i.e. SOC at 0–5 cm/SOC at 5–10 cm or SOC at 10–

25 cm) (Franzluebbers, 2002; Moreno et al., 2006).

Stratification of SOM with depth under CT systems has

consequences on soil functions beyond that of

potentially sequestering more C in soil (Franzluebbers,

2004).

The aims of the study were to determine the effects

of the 14-year CT practices on chemical properties and

on microbial function and on their stratification ratios

under semi-arid conditions. Results were compared to

those obtained under traditional tillage (TT). We

hypothesized that CT would have a positive effect by

increasing SOM and soil fertility and enhancing soil

microbial functionality.

2. Materials and methods

2.1. Study area: climatological characteristics and

tillage treatments

Field experiments were carried out on a sandy clay

loam soil (Xerofluvent, USDA, 1996) at the experi-

mental farm of the IRNAS (CSIC) located 13 km

southwest of the city of Seville (Spain). Climate is

typically Mediterranean, with mild rainy winters

(484 mm mean rainfall, average of 1971–2004) and

very hot, dry summers. Rainfall in 2004 and 2005 were

450 and 222 mm (lower than the mean rainfall),

respectively. Year 2005 was especially dry. Rainfall

was obtained from the weather station located at the

experimental farm (200 m from the experimental plots).

An area of about 2500 m2 was selected to establish

the experimental plots in 1991. During the autumn of

that year wheat was grown under rainfed conditions.

The tillage operations applied were the traditional ones

used in the region. After harvest of the wheat in June

1992, the area was divided into six plots each of

approximately 300 m2 (22 m � 14 m). Two tillage

treatments were established: traditional tillage used in

the area for rainfed agriculture and conservation tillage.

The TT consisted of mouldboard ploughing (to a

30 cm depth), after burning the straw of the preceding

crop. Straw burning did not occur since 2003. The CT

was characterized by not using mouldboard ploughing,

by reduction of the number of tillage operations and

leaving the crop residues on the surface (for more

details see Moreno et al., 1997). A wheat (Triticum

aestivum, L.)–sunflower (Helianthus annuus, L.) crop

rotation was established for both treatments. In 2005 a

fodder pea crop (Pisum arvense, L.) was included in the

rotation. Three replications per treatment were used,

distributed in random blocks. Sunflower and fodder pea

crops were not fertilized (as is traditional in this zone),

while wheat received a deep fertilization with

400 kg ha�1 of a complex fertilizer 15N–15P2O5–

15K2O before sowing and a top dressing with

200 kg ha�1 urea (46% N). Since 2002, fertilization

was reduced to 100 kg ha�1 (fertilizer complex), and no

top dressing fertilizer (Murillo et al., 2004).

2.2. Soil sampling and analysis

Soil sampling was carried out in November 2004

(before sowing of the fodder pea, in December 2004)

and in June 2005 (after harvesting fodder pea crop) at

two sites of each individual plot (total of six samples

per tillage treatment), and at depths of 0–5, 5–10 and

E. Madejon et al. / Soil & Tillage Research 94 (2007) 346–352348

10–25 cm. Field moist soil was sieved (2 mm) and

divided into two subsamples. One was immediately

stored at 4 8C in plastic bags loosely tied to ensure

sufficient aeration and to prevent moisture loss until

assaying of microbiological and enzymatic activities.

The other was air-dried for chemical analysis.

The SOC content was determined according to

Walkley and Black (1934), WSC was determined in an

(1/10) aqueous extract using a TOC-V-CSH/CSN

analyser. The MBC content was determined by the

chloroform fumigation-extraction method modified by

Gregorich et al. (1990). Dehydrogenase activity was

determined by the method of Trevors (1984), alkaline

phosphatase according to Tabatabai (1994), b-glucosi-

dase activity as indicated by Tabatabai (1982) and

protease activity according to Ladd and Butler (1972).

Response variable between CT and TT were assessed

by the Student’s t-test. Data normality was tested prior

to analysis; and when necessary, variables were

transformed logarithmically. All statistical analyses

were carried out with the program SPSS 10.0 for

Windows.

3. Results and discussion

3.1. Soil properties

In general, soil under CT had higher SOC content

than soil under TT, especially in the second sampling

(summer sampling) in which differences were sig-

nificant to 10 cm (Table 1). Conservation tillage

systems have been shown to maintain soil organic

Table 1

Mean values of soil organic carbon (SOC) and water soluble carbon

(WSC) in soil under conservation tillage (CT) and traditional tillage

(TT) at the different depths

Treatment Depth (cm)

0–5 5–10 10–25

November 2004

SOC (g kg�1) CT 13.5 12.3 7.00

TT 13.2 10.5 6.50

WSC (mg kg�1) CT 326* 151 90.4

TT 183 136 138

June 2005

SOC (g kg�1) CT 14.8* 12.7* 8.80

TT 10.0 9.80 7.50

WSC (mg kg�1) CT 126 114 45.0

TT 161* 129 97.4

Differences between treatments are indicated by (*) ( p < 0.05).

matter at higher levels than traditional tillage (Dıaz-

Zorita and Grove, 2002). This increase is particularly

important in Andalusia, the region of our study, where

the levels of organic matter in agricultural soils

(normally around 10 g kg�1) are low in semi-arid soils

(Acosta-Martınez et al., 2003).

Conversely, WSC concentrations were higher in soils

under CT than under TT only in the first sampling

(autumn sampling) (Table 1). In the second sampling

values of WSC were similar in both treatments and even

higher in TT for the 0–5 cm depth. Probably the

elevated temperatures in spring and summer led to

greater mineralization of the labile fraction of SOM as

shown by the significant ( p < 0.05) decrease of WSC

contents between samplings in both treatments. More-

over, WSC also decreased with soil depth and this

decrease was more noticeable in CT. The great

enrichment in available C caused by CT mainly occurs

in the top soil layer whereas the tillage practices in TT

distributed available C along deeper layers.

The MBC is among the most labile pools of organic

matter and it serves as an important reservoir of plant

nutrients, such as N and P (Marumoto et al., 1982).

MBC was higher under CT than under TT to 10 cm

depth, especially in the first sampling in which

difference was significant at 0–5 cm depth (Table 2).

This enrichment was generally related with SOC and

WSC contents (Garcıa-Gil et al., 2000), and these two

parameters were positively correlated with the MBC

(Table 3). In both treatments MBC decreased sig-

nificantly ( p < 0.05) in summer probably due to

decrease of available C and also for the low soil

moisture which may have affected microbial growing.

Other authors have also found lower values of MBC in

summer than in winter. They attributed this effect to the

water deficit that took place in this season (Alvear et al.,

2005). As occurred with SOC, MBC decreased with soil

depth.

Enzyme activities have been used in a variety of

ways to assess issues of agronomic and environmental

quality. They have been tested as indices of soil fertility,

soil quality, soil productivity, pollution effect and

nutrient cycling potential (Dick, 1994).

Dehydrogenase is an oxidoreductase only present in

viable cells and it is considered as a sensitive indicator

of soil quality (Skujins, 1976). In the superficial layer

(0–5 cm depth) dehydrogenase was significantly higher

in soil under CT than under TT in both samplings; in the

first sampling differences were significant to 10 cm

depth (Table 2), indicating a consistent improvement of

soil quality under CT. Other authors have reported

similar results under no tillage or reduced tillage under

E. Madejon et al. / Soil & Tillage Research 94 (2007) 346–352 349

Table 2

Mean values of microbial biomass carbon (MBC) and enzymatic activities in soil under conservation tillage (CT) and traditional tillage (TT) at the

different depths

Treatment Depth (cm)

0–5 5–10 10–25

November 2004

MBC (mg kg�1) CT 316* 151 90.4

TT 183 136 138

Dehydrogenase (mg INTF kg�1 h�1) CT 3.95* 2.07* 1.22

TT 2.96 1.51 1.07

Alkaline phosphatase (mg PNP kg�1 h�1) CT 435 249 295

TT 402 213 260

Protease (mg Tyr kg�1 h�1) CT 92.6* 15.6 9.52

TT 49.6 25.6 12.2

b-glucosidase (mg PNP kg�1 h�1) CT 203 86.0* 40.0

TT 172 67.1 39.0

June 2005

MBC (mg kg�1) CT 90.7 62.0 44.6

TT 78.0 59.0 97.4

Dehydrogenase (mg INTF kg�1 h�1) CT 5.54* 1.61 0.62

TT 2.95 1.98 0.68

Alkaline phosphatase (mg PNP kg�1 h�1) CT 350 211 184

TT 313 186 167

Protease (mg Tyr kg�1 h�1) CT 92.7* 23.9 8.97

TT 59.4 22.7 12.3*

b-Glucosidase (mg PNP kg�1 h�1) CT 198* 140 65.4

TT 125 125 56.0

Differences between treatments are indicated by (*) ( p < 0.05); INTF: iodonitrotetrazolium formazan; PNP: p-nitrophenol; Tyr: tyrosine.

semi-arid conditions (Roldan et al., 2005). Dehydro-

genase activity was highly correlated with WSC and

especially with SOC contents (Table 3).

Soil hydrolases can provide indication about soil

fertility since these enzymes are closely related to

nutrient cycling. In general, CT had a positive effect on

hydrolase activities (Table 2). At the superficial layer

Table 3

Correlation coefficients between soil chemical and biochemical properties

SOC WSC MBC

SOC 1 0.403** 0.381**

WSC 1 0.763**

MBC 1

DHA

Prot

b-gluc

Phosph

SOC: Soil organic carbon; WSC: water-soluble carbon; MBC: microbial bi

b-glu: b-glucosidase activity; Phosph: phosphatase activity; n = 48 (numbe** p < 0.01

(0–5 cm depth) alkaline phosphatase, b-glucosidase

and protease were higher in soil under CT, and in some

cases the differences were significant. This increase of

hydrolases in the top soil under reduced tillage and no

tillage have been observed elsewhere (Kandeler et al.,

1999). No consistent effect of any treatment could be

detected in deeper layers. This result seems to confirm

DHA Prot b-gluc Phosph

0.721** 0.687** 0.819** 0.470**

0.485** 0.542** 0.528** 0.607**

0.372** 0.496** 0.391** 0.544**

1 0.908** 0.779** 0.581**

1 0.811** 0.651**

1 0.613**

1

omass carbon; DHA: dehydrogenase activity, Prot: Protease activity;

r of samples used to calculate correlation coefficients).

E. Madejon et al. / Soil & Tillage Research 94 (2007) 346–352350

that organic material buried after ploughing is

responsible for the higher rate of soil microbial

processes in deeper layers of soil under TT (Angers

et al., 1993).

In this study, significant correlations between

enzymatic activities, SOC and WSC were found

(Table 3). In general, a high response to soil enzyme

activities was observed under CT. Moreover, a

significant correlation was found between enzyme

activities (Table 3), indicating a general relationship

between soil microbiological properties. In general, soil

enzyme activities did not show seasonal changes.

3.2. Stratification ratios

Climatic conditions of southern Spain (high tem-

peratures during summer) are the limiting factor for the

accumulation of SOC. Thus, the simple determination

Fig. 1. Stratification ratio values (mean values � standard error) for

soil organic carbon (SOC), soluble organic carbon (WSC), microbial

biomass carbon (MBC), and dehydrogenase (DHA), phosphatase

(PHOS), b-glucosidase (GLUC) protease (PROT), activities under

TT (white bars) and CT (grey bars). For each variable, significant

differences are marked by asterisk ( p < 0.05). (a) Sampling Novem-

ber 2004; (b) sampling June 2005.

of SOC may not be the best indicator of the

improvement caused by conservation tillage. In general,

high stratification ratio of SOC indicates a good quality

of soil (ratios lower than two are frequent in degraded

soils, Franzluebbers, 2002). This approach could also be

applied to other variables, as shown in Fig. 1(a and b).

In this study, slight increases in SOC and SOC

stratification ratio occurred under CT, but more

significant increase of stratification ratios of MBC

and dehydrogenase activity were observed (Fig. 1a and

b). This corroborates the adequacy of the stratification

ratio concept for defining benefits derived from CT

under semi-arid conditions. Soils with low inherent

levels of SOM can be the most functionally improved

with CT, despite modest or no change in total standing

stock of SOC within the rooting zone (Franzluebbers,

2004). In general, the enrichment of the soil surface

with crop residues usually leads to significantly greater

macroaggregation (water-stable macroaggregates

>0.25 mm), especially in soils with coarse texture

(Franzluebbers, 2004). Other authors have also con-

firmed the relation between biochemical parameters

such as dehydrogenase and MBC and the macroag-

gregation. In our case (a soil with about 20% clay)

macroaggregation at the surface was expected to be

greater in CT than in TT, which can affect many soil

variables at this layer.

3.3. Crop yield

Fodder pea yield was determined weighing the yield

harvested by hand in a selected area (4 m2) of each plot;

thus, data in Table 4 may suggest higher than normal

yields compare to mechanical harvesting of pea crops

under field conditions.

Table 4

Pea kernel yield, weight of 1000 kernels, kernel N content, straw yield

and N incorporated by straw under CT and under TT

Variable Treatment

Kernel yield (kg ha�1) CT 4300 � 320

TT 4050 � 540

1000 kernels weight (g) CT 834 � 88

TT 904 � 57

Kernel N (g kg�1) CT 34.9 � 0.3*

TT 31.9 � 1.2

Straw yield (kg ha�1) CT 4740 � 130

TT 4060 � 540

N added by straw (kg ha�1) CT 45 � 2.4

TT 42 � 4.6

* p < 0.05.

E. Madejon et al. / Soil & Tillage Research 94 (2007) 346–352 351

Tillage system did affect crop yield. In this study,

kernel yield, was greater under CT (Table 4).

Tillage effects on crop yield are greatly dependent on

climate and soil type (Linden et al., 2000). Advantages

of conservation tillage systems for crop production

under these semiarid conditions were observed earlier

in this study. The most extreme situation corresponded

to 1995, a very dry year in which grain yield of

sunflower under CT was 1520 and only 473 kg ha�1

under TT (Moreno et al., 1997, 2001).

Soil suitability classification schemes for conserva-

tion tillage consider that timing of tillage and crop

establishment are important strategies for removal of

constraints to crop productivity (storage of water under

semiarid conditions). Shifting the time of the tillage

event can be used to circumvent or remove constraints,

and also provide soil conservation benefits.

4. Conclusions

Long-term conservation tillage was more effective

than traditional tillage for increasing organic matter

and, especially, for improving biochemical quality at

the soil surface (0–5 cm depth) under rainfed condi-

tions, in an extremely dry year. Despite slight increases

in SOC and SOC stratification ratio under conservation

tillage, more significant increases of stratification ratios

for MBC and dehydrogenase activity were observed.

This improvement may greatly contribute to long term

sustainability of agricultural systems under semi-arid

conditions by maintaining soil quality.

Acknowledgements

CICYT Projects (AGL2004-03684/AGR and

AGL2005-02423), and Andalusian Autonomous Gov-

ernment (Junta de Andalucia, AGR 151 Group)

supported these works.

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