006) 388–403

www.elsevier.com/locate/geoderma

Geoderma 131 (2

Micromorphological characterization and monitoring of internal

drainage in soils of vineyards and olive groves in central Italy

Edoardo A.C. Costantini*, Sergio Pellegrini, Nadia Vignozzi, Roberto Barbetti

Istituto Sperimentale per lo Studio e la Difesa del Suolo, Firenze, Italy

Available online 13 June 2005

Abstract

Internal drainage class is an interpretative soil quality that derives from the field evaluation of other soil qualities and

characteristics, i.e. soil permeability, texture, structure, redoximorphic features, and may not match the results of measurements

of the actual soil water status.

The aim of this work was to investigate whether a better characterization of standard field assessments of internal drainage

of 12 soils in vineyards and olive groves could be achieved through the qualitative and quantitative micromorphological

analyses.

The results of field and laboratory analyses, as well as of 34 months of monitoring of soil moisture and temperature, and 21

months of water table and redox potential, were related to the micromorphological estimation of the hydromorphy degree,

following the methodology of Aguilar et al. (2003) [Aguilar, J., Fernandez, J., Dorronsoro, C., Stoops, G., Dorronsoro, B.,

2003. Hydromorphy in soils. http://edafologia.ugr.es/hidro/indexw.htm], and to the quantification of porosity using image

analysis.

It was found that soils were only occasionally saturated with water and for short periods, although redox potentials

during autumn and winter indicated probable Mn reduction. Water content monitoring differentiated soils with values far

beyond field capacity throughout the year, and soils with values close to, or higher than, field capacity during rainy

seasons.

Results showed that hydromorphy degree was related to seasonal soil water content and redox potential. An improvement in

this method should consider the presence and the nature of calcite pedofeatures.

The statistical analysis associated the abundance of elongated and irregular macropores, which favor water drainage, to

scarceness of macro- and microhydromorphic features and lower bulk density. The quantity of regular pores, which are less

efficient for downward water transmission, was on the other hand correlated to an average high soil water content and to lower

mean redox potentials. The relevance of elongated and irregular macropores for the internal drainage of this kind of soil

(intensively cultivated, poorly structured, and with low total macroporosity) was also confirmed by the proportion of elongated

and irregular macropores to total macroporosity (PR index). In soils of vineyards and olive groves, optimal drainage conditions

in Mediterranean climate seem to be ensured by PR higher than 0.80.

0016-7061/$ - s

doi:10.1016/j.ge

* Correspondi

E-mail addre

ee front matter D 2005 Elsevier B.V. All rights reserved.

oderma.2005.03.029

ng author. Tel.: +39 55 2491222; fax: +39 55 241485.

ss: costantini@issds.it (E.A.C. Costantini).

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403 389

The study demonstrated, by means of a field experiment, the unfavorable effect of the common practice of deep plowing

before tree planting in increasing the formation of redoximorphic features, micritic calcite nodules and infillings, within the

deeper horizons of calcareous soils.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Soil; Micromorphology; Drainage; Vineyard; Olive Grove; Italy

1. Introduction

In prime viticultural and olive tree growing areas,

soil hydrological characteristics and water regime

contribute to the quality of wine and olive oil, because

they affect nutrient and oxygen supplies. The rationale

is based upon the observation that environmental

factors influence the hormonal equilibrium of each

variety, which in turn regulates the expression of the

genotype (Van Leeuwen and Seguin, 1997). The fre-

quency and duration of periods of soil wetting are

typically estimated in routine soil survey by the bclassof internal drainageQ. This indicator provides a first

rough approximation. Several strategies can be ap-

plied and combined to improve the routine estimation.

If technical reasons exclude the possibility of a con-

tinuous monitoring, as is generally the case in unre-

stricted and periodically cultivated fields, it is possible

to relate field evaluations to measurements of mois-

ture coming from benchmark soils (Costantini et al.,

1996), use simulation models calibrated on specific

environments (Costantini et al., 2002a), perform a

number of laboratory tests, e.g. measurements of

soil water content at different matric tensions, hydrau-

lic conductivity, etc. The use of the Epic model, in

particular, has produced rather good results in terms of

the water content simulation in some experimental

vineyards and olive tree plantations in central Italy

(Costantini et al., 2002b). Epic estimated a saturated

condition within the soil similarly to monitoring, but it

gave different results in terms of times of the satura-

tion period.

Quantitative analysis of the pore system through

image analysis appears to be another promising tech-

nique enabling a better understanding of soil hydro-

logical properties (e.g. Schaap and Lebron, 2001;

Vervoort and Cattle, 2003). In addition, the thin sec-

tion description for the assessment of hydromorphic

degree (Aguilar et al., 2003) has been proposed as a

method to validate the classification of internal drain-

age and to relate micromorphological redoximorphic

features to soil hydrological regime.

The present work assesses whether the routine

appraisal of soil internal drainage can be refined by

soil thin section analysis, using 12 soils representative

of different wine and olive oil bterroirsQ in the prov-

ince of Siena (central Italy).

2. Area description, methods and materials

2.1. Study area and soils

The trial was conducted in the Province of Siena

(central Italy), in the ambit of a vine and olive tree

zoning. On the basis of a reconnaissance soil survey of

the entire province, 12 representative fields, situated

on 8 farms, were chosen as benchmark soils. Five out

of eight farms are situated in the sub-humid climatic

region, two in the bordering humid region and one in

the dry sub-humid (Fig. 1). Long-term mean annual air

temperature ranges between 13.5 and 14.8 8C, withmaximum in July and minimum in January, and little

yearly and monthly standard variation of the long-term

means. The long-term mean annual rainfall is between

730 and 850 mm, with high yearly and monthly stan-

dard variations. Moister months are usually October,

November and December. Climatic adversities, such

as sudden downpours and hail-storms, can combine

with severe summer drought.

The hilly territory, where vineyards and olive

groves are most widespread, was formed in different

geological eras, and presents extremely variable char-

acteristics. For this reason, it is difficult to make gen-

eralizations that can be widely applied. The low-lying

areas consist of soils with a deep rooting layer, formed

by the deposit of alluvial material dating from the

Quaternary Period. Further uphill, on the Pliocene

PISA

LUCCA

MASSA

SIENA

AREZZO

PISTOIA

LIVORNO

FIRENZE

VITERBO

GROSSETO

LA SPEZIA

40 0 4020 KilometersClimate

Perudic: mm > 1400

Udic: mm > 1200

Sub-humid: mm > 800

Dry sub-humid: mm > 600

Semi-arid: mm < 600

Experimental farm

Fig. 1. Climatic regions and experimental farms in Tuscany (central Italy). Some experimental farms host more experimental plots (see Table 1).

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403390

and Miocene marine sediments, soils are mainly clay-

ey and enriched by calcareous fossil material, often

rather thin, due to the severe erosion. In the upper part

of the territory, soils are formed in older geological

formations, they are usually moderately stony and

sandy, rich in lime, mingled with wide areas with

clayey and rocky soils. Residual portions of paleosols

are rather widespread, although scattered in the terri-

tory. Long-time agricultural activities make soil distri-

bution and properties even more complex.

The experimental plots lay on slopes and did not

have any permanent groundwater table (Table 1). In

line with typical agricultural practice, on these special-

ized farms all the studied vineyards and olive groves

Table 1

Experimental settings, soil classification, macromorphological redox features, and class of internal drainage

Farm and crop Soil profile

number

Geomorphology and parent material Soil classification

(Soil Taxonomy, 1998)

Depth (cm) and

quantity (%) of

redoximorphic

featuresa

Class of

internal

drainageb

Le Fonti vine 1 Medium part of a slope, 20%; elevation

260 m; aspect 2808; clay schist

Typic Ustorthent,

loamy-skeletal

Absent 2

Le Fonti olive tree 2 Anthropically terraced slope, 30%;

elevation 260 m; aspect 2938; clay schist

Typic Ustorthent,

clayey-skeletal

Absent 2

Le Fonti vine 3 Medium part of a slope, 20%; elevation

260 m; aspect 2808; clay schist

Typic Haplustept,

fine-loamy

Absent 3

Barbi vine 4 Tread, 3%; elevation 480 m; calcareous

sandstone

Typic Calcixerept,

fine-silty

Absent 3

S. Angelo vine 5 Alluvial terrace, 4% slope; elevation

255 m; aspect 1808; alluvial depositswith clayey marl

Typic Calcixerept,

fine

30–60; 1% 3

Le Fonti olive tree 6 Upper part of a slope, 18%; elevation

280 m; aspect 1138; calcareous medium

and fine sands

Udic Calciustept,

coarse-loamy

35–80; 2% 3

80–140; 35%

Trecciano vine 7 Terraced bottom part of a doline, 2%

slope; elevation 400 m; colluviated

residual clay

Typic Haploxerept,

fine

100–150+; 8% 4

Modanella vine 8 Alluvial terrace, 2% slope; elevation

330 m; aspect 1808; alluvial depositswith sandstone

Aquic Haplustept,

loamy-skeletal

10–50; 25% 4

50–90; 20%

90–150+; 7%

Campriano vine 9 Convex slope, 2%; elevation 280 m;

aspect 1588; clayey marl

Aquic Haplustept,

fine

0–30; 5% 5

30–55; 2%

55–100+; 10%

Campriano vine 10 Medium part of a slope, 25%; elevation

275 m; aspect 1358; silty marl

Haplic Ustarent,

fine-loamy

0–30; 15% 5

30–60; 23%

Cetona vine 11 Convex slope, 2%; elevation 328 m;

aspect 458(NE); silty marl

Aquic Haplustept,

fine silty

0–20; 5% 5

20–75; 8%

75–120+; 18%

Strove olive tree 12 Alluvial terrace, 15% slope; elevation

240 m; aspect 3398; alluvial depositswith clay and quartzite

Aquic Paleustalf,

fine

40–90; 25% 5

90–145; 23%

a Redox features are mainly iron depletion on faces of aggregates and pores, and masses of iron and manganese concentrations inside

aggregates. Modal Munsell colors are respectively 10YR 6/1 or 7/2, and 10YR or 7.5 YR 5/8.b 2: Somewhat excessively drained, 3: well drained, 4: moderately well drained, 5: somewhat poorly drained.

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403 391

were deeply ploughed or backhoed before plantation,

up to a depth of about 0.8 m, resulting in a certain

homogenization of the profile and a fixed rooting

depth. Agricultural husbandry of the crops includes

surface cultivation (harrowing at about 0.1 m depth),

aimed at weed control, several times during the year.

2.2. Field routine description

The soils of the experimental vineyards and olive

tree plantations were routinely described, sampled,

analyzed and classified according to Soil Taxonomy

(Soil Survey Staff, 1999). Main physical, hydrological

and chemical soil characteristics are reported in Table

2. A field assessment of soil internal drainage for the

whole profile was obtained modifying the attributes

suggested by the Soil Survey Division Staff (1993).

The definition of the classes of internal drainage used

was the following: class 2, somewhat excessively

drained: water moves through the soil rapidly. The

soils are commonly coarse-textured and lack redox-

imorphic features. Class 3, well drained: water is

removed from the soil readily but not rapidly. Wet

periods are not so long during the growing season that

Table 2

Main physical, hydrological and chemical soil characteristics

Profile

number

Layer Sand

(dg kg�1)

Clay

(dg kg�1)

Field

capacity

(g g�1)

Wilting

point

(g g�1)

Permeability

classaCOLE

(m m�1)

MWD

(mm)

BD

(g cm�3)

CaCO3 (%) pH O.M.

(dg kg�1)

C/N

Total Active

1 1 18.3 23.3 0.222 0.091 3 0.031 0.48 1.49 10.4 1.1 8.2 0.63 7.2

2 1 21.3 40.3 0.263 0.157 3 0.033 0.93 1.44 10.2 2.3 8.1 1.23 7.1

3 1 27.1 23.6 0.208 0.090 3 0.033 1.20 1.46 14.7 2.2 8.1 1.05 10.2

2 20.8 36.6 0.216 0.116 3 n.d. n.d. n.d. 9.1 1.9 8.2 0.86 n.d.

4 1 17.7 35.3 0.237 0.098 3 0.028 0.27 1.33 28.6 6.1 8.0 0.45 7.3

2 18.2 35.4 0.250 0.108 3 0.022 n.d. 1.51 27.0 4.5 8.1 0.40 n.d.

5 1 24.2 43.7 0.272 0.137 3 0.025 0.55 1.26 7.7 3.6 7.8 1.64 9.4

2 27.8 45.3 0.264 0.132 3 0.025 n.d. 1.47 11.7 4.2 7.9 1.02 n.d.

6 1 46.9 18.2 0.172 0.066 2 0.010 1.57 1.33 25.0 4.2 8.1 1.29 8.2

2 51.0 12.3 0.176 0.083 3 n.d. 1.55 1.45 27.7 6.2 8.3 0.23 n.d.

7 1 15.7 38.9 0.226 0.146 3 0.026 1.86 1.56 0 0 6.0 2.12 108.8

2 11.6 46.0 0.231 0.103 4 0.027 1.15 1.42 0 0 6.2 0.86 n.d.

8 1 39.2 28.2 0.189 0.100 4 0.037 0.38 1.63 traces 0 7.9 0.21 55.4

2 52.4 19.6 0.157 0.083 4 n.d. 0.22 n.d. traces 0 8.0 0.21 n.d.

9 1 15.4 42.3 0.263 0.155 5 0.031 1.77 1.65 13.1 3.9 8.1 1.47 98.0

2 7.2 47.6 0.276 0.162 5 n.d. 0.39 1.78 1.40 0.1 8.6 0.27 n.d.

10 1 24.3 22.6 0.192 0.071 4 0.010 0.51 1.59 34.6 6.0 8.3 0.50 78.4

2 24.5 18.7 0.193 0.068 4 0.012 0.30 1.52 34.6 5.9 8.2 0.66 n.d.

11 1 8.8 28.6 0.254 0.124 4 0.022 0.35 1.45 17.3 4.1 8.2 1.13 90.5

2 5.3 25.7 0.263 0.102 4 0.024 0.21 1.56 17.9 8.1 8.4 0.64 n.d.

12 1 23.2 51.2 0.282 0.160 5 0.030 0.39 1.58 0 0 5.8 0.40 5.3

2 15.5 62.1 0.279 0.156 5 n.d. n.d. 1.50 0 0 6.4 0.20 n.d.

a 2: high (10–100 Am s�1). When moderately moist or wetter, structure that is moderate or strong granular, strong blocky or prismatic smaller

that is very coarse and no stress surfaces or slickensides. Common medium or coarser vertical pores that extend through the layer; 3: moderately

high (10–1 Am s�1). Strong very coarse blocky or prismatic and no stress surfaces or slickensides. z35 percent clay, soft, slightly hard, very

friable or friable. 4: moderately low (1–0.1 Am s�1 ). Few stress surfaces and/or slickensides. 5: low (0.01–0.1 Am s�1). Common or many

stress surfaces and/or slickensides (Soil Survey Staff, 2001).

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403392

they significantly affect crop behavior or choice of the

crop. These soils are mainly free of redoximorphic

features within the rooting depth. Class 4, moderately

well drained: water is removed from the soil some-

what slowly during some periods of the year. The soils

are wet for only short times during the growing

season, but long enough for crops and agricultural

husbandry to be affected. They commonly have a

moderately low or lower saturated hydraulic conduc-

tivity in a layer within the upper 1 m and show

common redoximorphic features (more than 4–5%),

at least in the lower part of the rooting depth. Class 5,

somewhat poorly drained: water is removed slowly so

that the soil is wet at a shallow depth for significant

periods during the growing season. Crops and agri-

cultural husbandry are deeply affected. The soils com-

monly have a low saturated hydraulic conductivity or

additional water from seepage. They show common

redoximorphic features within the rooting depth.

A field estimation of saturated hydraulic conduc-

tivity class of each horizon was obtained following the

USDA methodology, based upon specific soil proper-

ties, i.e. particle size, structure, consistence, macro-

porosity, presence of pressure faces and slickensides

(Soil Survey Staff, 2001).

2.3. Laboratory analysis

Besides routine physical and chemical analyses,

soils were characterized by bulk density (core meth-

od, replicated samples), moisture content at field

capacity (�33 kPa) and wilting point (�1500 kPa)

by Richards pressure plate extractor (Kassel and

Nielsen, 1986), and coefficient of linear extensibility

(COLE) (Grossman et al., 1968). Active CaCO3 was

analyzed with a solution of ammonium acetate. This

is the more active fraction of CaCO3, which easily

dissolves and precipitates. To evaluate soil aggregate

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403 393

stability, the mean weight diameter (MWD) of water

stable aggregates was determined by the procedure

described by Kemper and Rosenau (1986). Air-dried

aggregates in the range of 4–2 mm were put directly

on the top of a column of sieves of 2, 1, 0.5, 0.25

mm immersed in water. The column of sieves was

then vertically oscillated in water per 10 min, at a rate

of 30 complete oscillations per minute, by machine

with a stroke of 40 mm. The mass of oven-dried

particles (105 8C for 24 h) in each sieve resisting

breakdown was determined. The respective dry

masses were used to compute the MWD according

to Van Bavel (1949).

2.4. Soil thin section analysis

Three thin sections (55�85 mm) of undisturbed

samples for soil horizon were analyzed to quantify

macroporosity using image analysis. Two images

were captured with a video camera from each section.

These images covered 45�55 mm of the thin section,

avoiding the edges where disruption could have oc-

curred. The images were analyzed by means of the

image analysis techniques using the Image-Pro Plus

software produced by Media Cybernetics (Silver

Spring, MD, USA). Pores larger than 50 Am were

measured. Pore shape was expressed as perimeter2/

(4k area), and pores were divided into regular (shape

factors 1–2), irregular (2–5) and elongated pores (N5).

These classes correspond approximately to those used

by Bouma et al. (1977). Pores of each shape group

were further subdivided into seven size classes (class

1: 50–100 Am, class 2: 100–200 Am, class 3: 200–300

Am, class 4: 300–400 Am, class 5: 400–500 Am, class

6: 500–1000 Am, class 7: N1000 Am) according to

either the equivalent pore diameter for regular and

irregular pores, or to the width for elongated pores

(Pagliai, 1988). According to their sample position,

thin section analysis results were elaborated consider-

ing two functional layers: 0.1–0.3 m (layer 1) and

0.4–0.7 m (layer 2). Stony soils, namely profiles 1, 2,

3, and 4, were only sampled in layer 1.

The same thin sections were used to classify hydro-

morphism degree (Aguilar et al., 2003). This index

ranges from stages 0 to 4 according to groundmass

color, accumulation and depletion features, and some

macromorphological attributes such as color of soil

horizon, mottle presence and their color. The thin

section description followed the codes of Bullock et

al. (1985).

2.5. Moisture and temperature monitoring

Soil water content was measured by the gravimet-

ric method (three samplings with a hand auger) at 0.1–

0.3 m and 0.4–0.7 m depth, as experimental plots

were unrestricted and the use of permanent equip-

ment, like neutron probes or transducer tensiometers,

was not possible, soil temperature at 0.5 m depth

(portable pt100), and redox potential at 0.15 m

(hand-held Barnant pH/mV/ORP meter, two measure-

ments). Measurements were replicated every 2–4

weeks from February 1999 until February 2000 and

from April 2002 until December 2003. Layers 2 of

profiles 1 and 2 were not monitored because of the

excessive stoniness. Results of the trial years were

averaged on a seasonal basis. Electrode calibration

followed the instruction of Barnant Company (Bar-

rington, IL, USA) using solutions buffered to pH 7

and 4 with Quinhydrone. Redox potentials, measured

only during rainy seasons, were normalized at pH 7

according to Patrick et al. (1996).

Water table occurrence was monitored from April

2002 with piezometers in four experimental fields

(profiles 7, 9, 10, and 11), and inside auger holes in

the other soils, with the same observation periodicity.

Tube wells were made of plastic and had the follow-

ing characteristics: 0.04 m diameter, 1.25 m length,

perforated for 10% of the area in the lower 0.4 m,

sealed at the bottom and lined externally with metal

net. They were installed at a depth of 1 m in a 0.07-m-

diameter borehole filled by gravel from the bottom to

a depth of 0.5 m and surrounded by a collar of plastic

film covered by tamped clay.

2.6. Field simulation of deep plowing

In Italy, deep plowing and leveling of slopes al-

most always precedes new plantations of vineyards,

olive groves and orchards in hilly environments. This

operation, aimed to obtain a better macroporosity is

justified by the prevalent microporosity of clayey

soils, which are dominant. Deep plowing is usually

carried out with a mould board plough at 0.8–1.0 m,

but it can also be made by a backhoe. Moreover, land

leveling, aimed at obtaining wide and regularly slop-

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403394

ing fields, provokes the movement and redistribution

of high quantities of soil, and the burial of surface

horizon in correspondence of concavities along the

slope.

We then simulated the practice of deep plowing

before tree planting, which turns soil horizons upside

down, to check the occurrence of redoximorphic fea-

tures as a consequence of this agrotechnique. Layer 1

of profile 6 was buried at layer 2 depth at the end of

autumn 2002 (30th of November). A 2�2�2 m pit

was dug with a backhoe; layers were separately accu-

Profile 1

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Profile 3

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10-30 cm 40-70 cm red10-30 cm 40-70 cm redred

Fig. 2. Gravimetric soil water content and normalized redox potential. Prof

years 1999–2000 and 2002–2003.

mulated and then immediately resettled, layer 1 at

layer 2 depth, and vice versa. In late spring 2003

(6th of June), a new pit was dug and layer 1 exhumed

and described macro- and micromorphologically.

2.7. Statistical analysis

The bulk of data was submitted to Principal Com-

ponent Analysis (PCA) test by means of the software

Statistica (StatSoft Inc., Tulsa, OK, USA). The same

software was used to perform analysis of variance and

Profile 2

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FC 10-30 FC 40-70ox

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FC 10-30 FC 40-70ox FC 10-30 FC 40-70oxox

iles 1 to 6: monitoring years 2002–2003; profiles 7 to 12: monitoring

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10-30 cm 40-70 cm FC 10-30 FC 40-70redox

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0.10

0.15

0.20

0.25

02_99

04_99

06_99

08_99

10_99

01_00

04_02

06_02

08_02

10_02

12_02

02_03

04_03

06_03

08_03

10_03

12_03

100

200

300

400

500

600

700Profile 7

Gra

vim

etr

ic w

ate

r c

on

ten

t

0.00

0.05

0.10

0.15

0.20

0.25

0.30

02_99

04_99

06_99

08_99

10_99

01_00

04_02

06_02

08_02

10_02

12_02

02_03

04_03

06_03

08_03

10_03

12_03

100

200

300

400

500

600

700Profile 7

Gra

vim

etr

ic w

ate

r c

on

ten

t

0.00

0.05

0.10

0.15

0.20

0.25

0.30

02_99

04_99

06_99

08_99

10_99

01_00

04_02

06_02

08_02

10_02

12_02

02_03

04_03

06_03

08_03

10_03

12_03

100

200

300

400

500

600

700

0.00

0.05

0.10

0.15

0.20

0.25

0.30

02_99

04_99

06_99

08_99

10_99

01_00

04_02

06_02

08_02

10_02

12_02

02_03

04_03

06_03

08_03

10_03

12_03

100

200

300

400

500

600

700

Profile 8

Re

do

xp

ote

nti

al

(mV

)0.30

0.00

0.05

0.10

0.15

0.20

0.25

02_99

04_99

06_99

08_99

10_99

01_00

04_02

06_02

08_02

10_02

12_02

02_03

04_03

06_03

08_03

10_03

12_03

100

200

300

400

500

600

700

Profile 8

Re

do

xp

ote

nti

al

(mV

)0.30

0.00

0.05

0.10

0.15

0.20

0.25

02_99

04_99

06_99

08_99

10_99

01_00

04_02

06_02

08_02

10_02

12_02

02_03

04_03

06_03

08_03

10_03

12_03

100

200

300

400

500

600

7000.30

0.00

0.05

0.10

0.15

0.20

0.25

02_99

04_99

06_99

08_99

10_99

01_00

04_02

06_02

08_02

10_02

12_02

02_03

04_03

06_03

08_03

10_03

12_03

100

200

300

400

500

600

700

10-30 cm 40-70 cm FC 10-30 FC 40-70redox10-30 cm 40-70 cm FC 10-30 FC 40-70redoxredox

Fig. 2 (continued).

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403 395

compare macroporosity of layer 1 of profile 6 before

and after burying.

3. Results and analyses

3.1. Main chemical and physical soil characteristics

affecting saturation conditions and redox potential

The majority of the soils were alkaline or moder-

ately alkaline (Table 2), only profiles 12 and 7 had acid

or moderately acid reaction. The normalization at pH 7

of measured redox potentials resulted in a narrowing of

the values between acid and alkaline soils. Of the three

soils without carbonates, profile 7 and 12 were two

very old and leached paleosols, while profile 8 was

formed on pre-weathered alluvial materials.

All soils showed low or very low organic matter

content, with the exception of layer 1 of profile 7

which, according to Italian and international standards

(EUROCONSULT, 1989; SILPA, 1994), had a mod-

erately high value. C/N ratio of the upper layer was

low in profiles 1, 2, 4, 5, 6, and 12, normal in profile 3

and elevated in profiles 7, 8, 9, 10 and 11. The very

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403396

high C/N values indicate a slow decaying of the or-

ganic matter. High C/N ratio often corresponded to a

very low nitrogen content. The reduced microbiolog-

ical activity could, however, also be due to temporary

periods of water excess. Actually, soils with a high C/

N ratio almost always belonged to class 4 or 5 of

internal drainage and horizon permeability, and

showed mottles in the upper part of the profile.

The COLE values were always slight or moderate

(Shafer and Singer, 1976), thus excluding a high

shrink–swell activity and strongly expressed vertic

properties; nevertheless, the fine-textured soils

showed pressures faces and slickensides.

The aggregate stability index MWD indicated a

moderately good structure only in profiles 2, 6 and

7, and in layer 1 of profile 9. All the other horizons

presented low or very low aggregate stability (Cost-

antini et al., 2002b). This result is rather characteristic

of soils in the Mediterranean region, when poor in

organic matter and intensively cultivated; however, as

MWD did not result being significantly correlated to

the other variables, it was omitted from further ela-

borations. Bulk density values were, on average, rath-

er high, confirming the poor quality of the structure of

these soils.

3.2. Monitoring of water table, moisture, temperature

and redox potential

The regional climate during the trial showed years

1999 and 2000 with normal rainfall, whereas 2002

had a moister summer and 2003 was much drier than

the normal year. A bnormalQ year has rainfall total

amount in the range of Fstandard deviation of the

long-time mean, but a normal year in the Mediterra-

nean climate is most of the time bnot normalQ as

regards monthly precipitation (Costantini et al.,

2002a).

From April 2002, free water occurrence was only

observed in the experimental fields of Trecciano

(profile 7), during December 2002 and January

2003, at 0.45 m and 0.4 m depth, respectively; and

at Cetona (profile 11) in January 2003 at 0.55 m. It

was never observed in the other plots. However, due

to the fact that sampling was carried out on a fort-

nightly schedule we cannot exclude that some short

period of saturation could have occurred between two

measurements.

The main results of the monitoring activity are

reported in Fig. 2 and Table 3. Two groups of soils

can be clearly distinguished. The first group, formed

by profiles 1, 2, 3, 4, and 5, always showed water

contents well below their field capacity. All the other

soils showed moisture conditions during the rainy

seasons that in one or both layers, at the time of

sampling, were near to, or exceeded, field capacity.

The first group corresponds to soils with classes of

internal drainages 2 and 3, the second group to 4 and

5. The only exception is constituted by profile 6,

which belongs to the second group, although it was

estimated class 3.

Redox potential values, normalized at pH 7,

showed slight diversity in the studied soils, and the

observed differences were not always correlated with

the moisture content. Profile 6, for instance, which had

a relatively high water content, also showed a rather

high redox potential. Redox values pointed out that all

soils experienced weak reducing conditions during

autumn and winter times. If we consider Mn and Fe

oxides becoming reduced at 395 mV and 180 mV,

respectively (Sequi, 1989), figures indicated that

redox potentials at 0.15 m depth were low enough to

cause the vanishing of oxygen and nitrate, as well as

Mn2+ formation, but only in few cases induced Fe3+

reduction.

3.3. Thin sections macroporosity analysis

Total macroporosity and the sum of the seven size

classes of regular, irregular and elongated macro-

pores, are reported in Table 4. According to the

micromorphometric method (Pagliai, 1988), the

only soil having a moderate macroporosity (10–

25%) below the tilled horizon was profile 3, while

all the other were dense (5–10%) or very dense

(b5%). This result is not surprising for these kinds

of soils, which are poor in organic matter and fre-

quently passed over by farm machinery. The mor-

phological shape of macropores indicated that

regular pores were on average less abundant and

variable than the others (mean 1.15%, standard de-

viation 0.41). Irregular pores had an intermediate

position (mean 2.28%, standard deviation 1.31),

while the elongated were the most represented

(mean 2.30%, standard deviation 2.40). These last

two kinds of pore are the most important for vertical

Table 3

Main results of the hydrological monitoring

Profile

number

Layer Month of the year

when soil

Seasonal mean gravimetric water content (g g�1) and soil temperature at 0.5 m (8C), andmean redox potential at 0.15 m during Autumn and Winter (mV)

temperature at

0.5 m was lower

than 8 8C

Spring Summer Autumn Winter

1 1 Feb_03 0.11 16.5 0.08 27.6 0.14 11.9 278 0.15 6.4 341

2 1 Feb_03 0.15 14.9 0.12 25.1 0.17 14.3 327 0.18 7.3 329

3 1 Feb_03 0.13 15.7 0.10 26.3 0.16 13.6 304 0.17 6.8 338

2 and Dec_03 0.14 0.10 0.14 0.16

4 1 Jan and 0.14 14.7 0.13 25.3 0.18 12.9 279 0.20 5.9 285

2 Feb_03 0.14 0.13 0.17 0.20

5 1 Feb_03 0.15 17.2 0.14 26.9 0.19 15.4 269 0.20 7.8 349

2 0.18 0.15 0.20 0.20

6 1 Feb_03 0.16 15.7 0.10 25.5 0.17 14.7 318 0.20 8.2 324

2 0.16 0.08 0.15 0.20

7 1 Jan and 0.17 15.7 0.15 25.0 0.20 13.2 245 0.21 5.6 269

2 Feb_03 0.20 0.16 0.20 0.21

8 1 Feb_03 0.13 14.3 0.11 25.0 0.17 13.5 273 0.18 6.5 285

2 0.14 0.11 0.17 0.17

9 1 Feb_03 0.17 15.5 0.12 26.6 0.22 14.1 235 0.22 6.5 295

2 0.19 0.13 0.20 0.23

10 1 Feb_03 0.13 16.4 0.08 25.8 0.16 14.1 313 0.17 7.2 304

2 0.14 0.09 0.15 0.17

11 1 Feb_03 0.18 14.5 0.14 24.3 0.22 13.5 281 0.24 6.7 294

2 0.20 0.13 0.21 0.23

12 1 Jan, Feb 0.16 13.5 0.15 24.0 0.18 12.6 232 0.21 4.8 229

2 and Mar_03 0.19 0.17 0.20 0.25

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403 397

water movement, and could explain the different

hydrology of the studied soils.

The proportion of elongated and irregular macro-

pores on total macroporosity (PR index) ranged from

approximately 0.49 to 0.95. When PR was 0.80 or

more, the elongated pores generally predominated

over the other two kinds of macropores, and the

water content of the layer, apart from layer 1 of profile

8, was never found close to field capacity.

3.4. Micromorphological evidences of hydromorphy

The stage of hydromorphism of the studied soils

ranged between 0 and 3, that is from nil to high

hydromorphism (Aguilar et al., 2003); stage 4, mean-

ing extreme hydromorphism, was never found. Stage

1, indicating an incipient hydromorphy, corresponded

to layers with red or brown color, scarce presence of

Mn mottles and accumulation features, both in macro-

and micromorphology. Stage 2 corresponded to layers

which were yellow in color and had few bleached

mottles and depleted areas, and common Fe–Mn ac-

cumulation features, such as masses with diffuse

boundaries. Stage 3 was characterized by dominant

grayish, reddish and yellowish mottles, abundant

bleached and Fe–Mn depleted zones, and many Fe–

Mn accumulations. The combination of particular

micro- and macromorphological features suggested

by Aguilar et al. (2003) to typify hydromorphism

stage was sometimes difficult to find, thus intermedi-

ate degrees were envisaged.

In general, micromorphological evidence of hydro-

morphy was consistent with soil field description,

although quantitative and qualitative estimation of

redoximorphic features differed.

Besides groundmass color and Fe–Mn accumula-

tion–depletion features, micromorphological analysis

pointed out the presence of crystalline pedofeatures,

namely micritic calcite nodules, infillings and coatings,

in profiles 4, 5, 6, 9, 10 and 11, often associated to

depletion pedofeatures. The abundance of calcite crys-

talline pedofeatures was occasional (layers 1 and 2 of

Table 4

Soil thin section analysis results

Profile number Layer Stagea Total macroporosity (%) Regular pores (%) Irregular pores (%) Elongated pores (%) PR indexb

1 1 0.5 5.05 0.98 2.25 1.82 0.81

2 1 0.5 4.94 1.17 2.22 1.55 0.76

3 1 0 16.99 0.82 6.55 9.62 0.95

4 1 1 7.13 0.68 2.56 3.89 0.90

2 1.5 6.62 0.77 2.92 2.93 0.88

5 1 1 9.03 1.01 3.09 4.93 0.89

2 1 10.20 1.04 2.88 6.28 0.90

6 1 1 5.99 1.33 3.58 1.08 0.78

2 2.5 3.26 0.90 1.19 1.17 0.72

7 1 1 5.03 1.63 1.92 1.48 0.68

2 1 3.21 1.21 1.45 0.55 0.62

8 1 2.5 6.21 1.09 2.26 2.86 0.82

9 1 2 6.54 1.58 2.48 2.48 0.76

2 3 1.98 0.93 0.86 0.19 0.53

10 1 2 1.80 0.85 0.88 0.07 0.53

2 2 1.48 0.76 0.65 0.07 0.49

11 1 2 4.39 1.89 1.67 0.83 0.57

2 2.5 2.36 0.62 1.27 0.47 0.74

12 1 1 4.29 1.75 1.64 0.90 0.59

2 2.5 7.94 1.92 3.10 2.92 0.76

a Degree of hydromorphism according to Aguilar et al. (2003).b Elongated+ irregular pores/total porosity.

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403398

profile 9), many (layer 1 of profiles 5 and 6, layers 1 and

2 of profile 11), or abundant (layer 2 of profiles 5 and 6,

layers 1 and 2 of profiles 4 and 10). The occurrence of

calcite pedofeatures was proportional to calcium car-

bonate content and, when they were abundant, carbo-

nate tended to invade the whole groundmass. Although

Fig. 3. Soil sample of layer 1 of profile 6, buried at layer 2 depth in wint

features (arrow).

hydromorphic horizons with carbonate always had

calcite crystalline pedofeatures, their abundance was

not correlated to the quantity of redoximorphic fea-

tures and to the stage of hydromorphism.

The stage of hydromorphism was somewhat relat-

ed to the monitored water content of the layer. When

er and exhumed in late spring, showing neo-formed redoximorphic

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403 399

hydromorphy degree was 2 or more, in particular, the

water content during the moister seasons was found to

be higher, or very close, to field capacity.

3.5. Checking the occurrence of redoximorphic

features as a consequence of deep plowing

Layer 1 of profile 6 was found lacking in redox-

imorphic features during the field survey. The horizon

was brown (Munsell 10YR4/3), coarse-loamy, and its

estimated permeability was high (Table 2). Chemical

and physical analyses indicated that the structure was

rather good, bulk density not very high and C/N ratio

equilibrated. Thin section analysis had only evidenced

an incipient stage of hydromorphy, but many micritic

calcite nodules, infillings and coatings. Macroporosity

b

a

Fig. 4. Microphotographs of soil thin sections of exhumed layer 1 of profil

occupy the whole groundmass (25�, frame size 4.5�3 mm); (b) micritic

calcite (100�).

analysis, however, had pointed out a rather low total

quantity of pores, as well as a low incidence of

elongated pores, and elongated plus irregular, on the

total (Table 4). Mean redox potential during the rainy

seasons was quite high, in spite of the number of wet

periods.

When exhumed after having been buried for 6

months, the layer showed an outstanding change in

its macromorphology (Fig. 3). Many dark grayish

brown mottles (Munsell 10YR4/1), and pale brown

(Munsell 10YR6/3), 20 to 60 mm in size, had oc-

curred around main roots. Their examination in thin

section revealed that grayish mottles were constituted

by micritic calcite nodules and infillings, which

tended to occupy the whole groundmass, whereas

pale brown mottles corresponded to somewhat iron

c

e 6 (plain light). (a) Micritic calcite nodules and infillings tending to

calcite stuffing the groundmass (100�); (c) infilling of soft micritic

Table 5

Results of the PCA: eigenvalues of factors and factor loadings of the

variablesa

Factor 1 Factor 2

MOTTLES 0.251 �0.617HYD 0.548 �0.650PERM 0.841 �0.318SAND �0.587 �0.137CLAY 0.721 0.452

BD 0.456 �0.591aut_REDOX �0.760 �0.133win_REDOX �0.756 0.188

REG 0.568 0.235

IRREG �0.420 0.703

ELONG �0.366 0.675

spr_MOIS 0.754 0.225

sum_MOIS 0.743 0.574

aut_MOIS 0.795 0.356

win_MOIS 0.814 0.259

Eigenvalue 6.339 3.108

% of total variance 42.262 20.720

Cumulative eigenvalue 6.339 9.447

Cumulative% of total variance 42.262 62.982

In bold values higher than j0.500j.a MOTTLES stands for percentage of redoximorphic mottles of

the layer in macromorphological description, HYD for hydromor-

phic degree in micromorphological description, PERM for class of

permeability in soil survey, BD for bulk density, aut_REDOX and

win_REDOX for mean autumn and winter redox potentials, REG

for total regular macropores, IRREG for total irregular macropores,

ELONG for total elongated macropores, spr_MOIS, sum_MOIS,

aut_MOIS, and win_MOIS for spring, summer, autumn, and winter

mean soil water contents.

Fact

Facto

r 2

SANDaut_REDOX

win_REDOX

IRREG ELONG

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0

Fact

Facto

r 2

SANDaut_REDOX

win_REDOX

IRREG ELONG

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

0.8

1.0

-1.0 -0.8 -0.6 -0.4 -0.2 0

Fig. 5. Results of the PCA:

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403400

bleached areas (Fig. 4). Micromorphological image

analysis showed that, as a consequence of burial,

total pores passed from 3.27% to 1.99%, however,

elongated pores diminished more than irregular ones

(from 1.17% to 0.56% versus 1.19% to 0.72%),

whereas regular macropores remained almost un-

changed (from 0.80% to 0.70%).

3.6. Principal component analysis

The first step in the statistical analysis was the

computing of a correlation matrix for all variables.

Selecting from the variables that had been found

significantly correlated to at least one other indepen-

dent variable, we chose the most relevant ones, that is,

total regular, irregular and elongated macropores;

stage of hydromorphy in micromorphology; seasonal

mean redox potentials and mean water contents; bulk

density; sand and clay content; estimated percentage

of mottles and permeability of the layer. Other signif-

icant variables, such as field capacity and wilting

point, were omitted from the successive steps, because

they were closely related to clay content.

Eigenvalues of factors are reported in Table 5,

together with factor loadings of the variables. Factor

loadings are the basis for imputing a label to the

different factors. Loadings higher than 0.5 are usually

considered at least bmediumQ (Garson, 2004). The

first factor is highlighted by the variables total regular

or 1

MOTTLESHYD

PERM

CLAY

BD

REGspr_MOIS

sum_MOIS

aut_MOIS

win_MOIS

.0 0.2 0.4 0.6 0.8 1.0

or 1

MOTTLESHYD

PERM

CLAY

BD

REGspr_MOIS

sum_MOIS

aut_MOIS

win_MOIS

.0 0.2 0.4 0.6 0.8 1.0

plot of factor loadings.

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403 401

macropores, clay, permeability class, spring, summer,

autumn, and winter soil water contents, which contrast

against sand, autumn and winter mean redox poten-

tials. The second factor indicates that variables esti-

mating percentage of mottles, bulk density and stage

of hydromorphy oppose irregular and elongated

macropores.

It must be noted that the two factors explain most

part of the total variance (about 63%), and they are

both related to soil properties affecting soil water

holding capacity and to morphological consequences

of waterlogging, which contrast with variables asso-

ciated to aeration. This is better shown in the plot of

factor loadings (Fig. 5), which indicates two main

contrasting clusters of variables. The first cluster

groups the variables with a direct relationship with a

high water status, i.e. macro- and microhydromorphy,

soil water content and permeability class, with regular

macropores. The second cluster relates variables

pointing to a good aeration, i.e. sand content, autumn

and winter redox potentials, to irregular and elongated

macropores.

4. Discussion and conclusions

All the experimental vineyard and olive groves are

located on slopes and have rather high external drain-

age (runoff), increased by the up and down slope

tillage, which impedes the permanence of a water

table for long periods. We must moreover consider

that farmers usually avoid unfavorable morphological

positions for these crops (e.g. foot slopes, concavities,

flat plains). Short and occasional water saturation nev-

ertheless occurred when the permeability of a soil

layer, or of the underlying layer, was moderately low

or low. The short period of saturation, however, seems

to have been long enough to cause reductive processes

in some soils. This was probably due to the rather

elevated soil temperature during rainy seasons, foster-

ing anaerobic microbial degradation of organic matter.

Redoximorphic features, however, could have been

formed also as a consequence of plantation. In fact,

the common practice of deep plowing before planta-

tion caused a sudden enhancement of organic matter

in depth, which may have boosted iron and manga-

nese reduction and the formation of a redoximorphic

pattern. The burial of the upper layer, moreover,

seems to lead to a reduction of elongated and irregular

macropores, thus affecting the internal drainage of the

horizon.

Besides iron and manganese oxides, the reducing

conditions could have also affected calcium carbonate

dissolution and precipitation in calcareous soils like

profile 6. When the upper layer of this profile, rich in

total and active carbonates, and medium in organic

matter, was buried at a depth with less macroporosity,

the release of CO2 probably led to over-saturation of

the soil solution with respect to calcite, favoring the

formation of crystallized micrites. A similar process is

reported by Bouzigues et al. (1997) for calcareous

soils on a plateau in the south of France, occurring

in relation to the rising and lowering of groundwater.

Also Tassinari et al. (2002) found calcareous soft

masses correlated to duration of water saturation,

but only in soils of a specific environment, a Pliocene

plateau in the south of France, and not in the other

examined soils.

Our results indicate that micromorphological anal-

ysis could refine the characterization of the internal

drainage through both the qualitative and quantitative

approaches. The first one is relatively cheap and easy,

therefore it is recommended for all horizons which

have a problematic assessment of internal drainage.

The micromorphometric characterization of macro-

porosity instead, being more time consuming and

costly, could be limited to selected benchmark soils.

The estimation of the hydromorphy degree follow-

ing Aguilar et al. (2003) resulted correlated to all the

other variables of interest: directly with bulk density,

regular macropores and the variables indicating a high

water status, inversely with mean seasonal redox

potentials and total irregular and elongated pores.

Our experience, however, suggests that improvement

to this method should consider the presence and the

nature of neoformed calcite, in particular when asso-

ciated with depletion pedofeatures.

The PCA associated the abundance of elongated

and irregular macropores, which favor the water

drainage (Pagliai and Vignozzi, 2002; Pellegrini et

al., 2000), to the other variables pointing to a good

aeration, that is sand content, autumn and winter high

redox potentials. The quantity of regular pores, which

are less efficient for downward water transmission,

was on the other hand grouped together with an

average high seasonal soil water content, a low per-

E.A.C. Costantini et al. / Geoderma 131 (2006) 388–403402

meability class, and macro- and microevidences of

hydromorphy.

The relevance of elongated and irregular macro-

pores for the internal drainage of this kind of soil,

intensively cultivated, poorly structured, and with low

porosity, has been also confirmed by the PR index. In

soils of vineyards and olive groves optimal drainage

conditions seem to be ensured by a PR value higher

than 0.80.

Special care should be given to soils apparently

well drained, but showing many micritic calcite

nodules, infillings and coatings, as well as a PR

value lower than 0.80 and a strongly contrasting

O.M. content between the topsoil and the lower hor-

izons. If deep plowed before the new plantation of a

tree crop, they may experience a severe impairment of

the internal drainage and the occurrence of reductive

conditions.

Acknowledgments

This research was supported by a financial contri-

bution from the Agriculture Department of the Prov-

ince of Siena and by the Special Project bSUOLOQ ofthe Italian Ministry of Agricultural and Forestry Pol-

icies. Thanks are extended to the farms which hosted

the experimental plots.

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