Changes of soil properties and tree perf (2)

Europ. J. Agronomy 41 (2012) 18–27

Contents lists available at SciVerse ScienceDirect

European Journal of Agronomy
journal homepage: www.elsevier.com/locate/eja

Changes of soil properties and tree performance induced by soil management
in a high-density olive orchard
Riccardo Gucci a,∗ , Giovanni Caruso a , Claudio Bertolla a , Stefania Urbani b , Agnese Taticchi b ,
Sonia Esposto b , Maurizio Servili b , Maria Isabella Sifola c , Sergio Pellegrini d , Marcello Pagliai d ,
Nadia Vignozzi d
a

Dip. di Coltivazione e Difesa delle Specie Legnose, Università di Pisa, Via del Borghetto 80, 56124, Pisa, Italy
Dip. di Scienze Economico-Estimative e degli Alimenti, Università di Perugia, Via San Costanzo 1, 06126, Perugia, Italy
c
Dip. di Ingegneria Agraria e Agronomia del Territorio, Università di Napoli Federico II, Via Università 100, 80055, Portici, Italy
d
CRA-Centro di Ricerca per l’Agrobiologia e la Pedologia, Piazza D’Azeglio 30, 50121, Firenze, Italy
b

a r t i c l e

i n f o

Article history:
Received 12 September 2011
Received in revised form 20 February 2012
Accepted 1 March 2012
Keywords:
Olea europaea L.
Oil quality
Plant cover
Soil macroporosity
Tillage
Water infiltration

a b s t r a c t
Long-term effects of plant covers on yield and oil quality in olive orchards are poorly known. We compared
performance of Olea europaea trees grown under either tillage (CT) or permanent natural cover (NC) in

a sandy-loam soil over five years and determined changes in soil properties. The soil was tilled from the
year of planting until the end of the second growing season, when both soil management treatments
were established. The CT treatment was kept weed-free using a harrow with vertical blades (0.10 m
depth), whereas the NC was obtained by letting the natural flora grow. Trees were fully irrigated until
year 3 after planting, when deficit irrigation (about 50% of full) was started for both soil treatments.
Trunk cross sectional area (TCSA) of NC trees was 77 and 87% to that of CT trees at the end of the 2006
and 2010 growing seasons, respectively. Fruit yield and oil yield of NC trees were 65 and 69% to those of
CT ones, respectively (means of five years), however, when expressed on a TCSA basis, they resulted 87
and 95%, respectively. The fruit number of NC trees was lower than CT ones, whereas the oil content was
similar. There were no differences in free acidity, peroxide value, spectrophotometric indexes, and fatty
acid composition, but phenolic concentrations of the NC treatment were slightly higher than those of CT
oils. Soil macroporosity in the topsoil was 5.2 and 2% for the NC and CT treatments, respectively. Water
infiltration rate in CT plots was lower than in NC ones because of soil surface crusting; NC had higher
values of total organic carbon and total extractable carbon than CT, whereas the humic carbon content
was unaffected.
© 2012 Elsevier B.V. All rights reserved.

1. Introduction
Water scarcity and soil degradation are major threats to agricultural production in the Mediterranean basin, where over 95% of
total olive trees are grown. Soil management can markedly affect

soil properties (Gómez et al., 1999, 2009; Hernández et al., 2005)
and moisture (Hernández et al., 2005) although responses vary
depending on soil type, slope, equipment used, and environmental
conditions.

Abbreviations: ANOVA, analysis of variance; CT, tillage; DW, dry weight; ET0 , reference evapotranspiration; FW, fresh weight; HC, humic carbon; Kfs , field saturated
hydraulic conductivity; LAI, leaf area index; LSD, least significant difference; MI,
maturation index; NC, natural cover; PLWP, pre-dawn leaf water potential; TCSA,
trunk cross section area; TEC, total extractable carbon; TOC, total organic carbon;
VOO, virgin olive oil.
∗ Corresponding author. Tel.: +39 050 2216138; fax: +39 050 2216147.
E-mail address: rgucci@agr.unipi.it (R. Gucci).
1161-0301/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.eja.2012.03.002

Conventional tillage causes soil losses, runoff, structure
degradation, acceleration of organic matter mineralization with
consequent formation of compacted layers and negative effect on
porosity along the profile (Gómez et al., 2004, 2009; Moreno et al.,
2009; Pagliai et al., 2004; Rodrıguez-Lizana et al., 2008). Compacted

layers decrease water infiltration which, in turn, increases runoff
on slopes and waterlogging in flat areas. The effects of tillage are
time dependent: after tillage porosity and water infiltration initially
increase, but the loose structure does not persist due to compaction,
aggregate instability, and surface sealing driven by external and
internal forces (Zhai et al., 1990). It has been shown that positive effects of tillage on water infiltration in the interrow are lost
within eight weeks, but they last longer in the zone beneath the
tree canopy in a clay-loam soil (Gómez et al., 1999). All these processes inevitably lead to plant stress, depletion in soil fertility, and
increasing dependence on chemical inputs for plant protection and
fertilization with potentially negative effects on yield and product
quality.

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

In recent years there is evidence of an increasing occurrence
of heavy rainfall events associated with climate change (Brunetti
et al., 2001; IPCC, 2007) that further exposes the soil to erosion and
degradation (Phillips et al., 1993; Nearing et al., 2004). Sandy-loam
soils are particularly susceptible to crusting due to the impact of
raindrops when the soil is bare and dry, with resulting clogging of

pores by dispersed clay or slaked fragments (Dexter, 1997). It has
been observed that single rainfalls of high intensity are sufficient
to determine the above changes, whereas the impact of successive
events is less (Zhang and Miller, 1996). In spite of all these problems, periodic tillage is still the most commonly adopted method
to control weeds in olive orchards (Gómez et al., 2003; Ramos et al.,
2011).
The use of a plant cover is currently the recommended practice
for protection of the orchard floor. The presence of a cover crop
not only has positive effects on soil properties (Gómez et al., 2004,
2009), but also determines better biochemical fertility (Hernández
et al., 2005) and greater bacterial biomass and diversity (Moreno
et al., 2009) than tilled soils. A permanent plant cover decreases soil
erosion, compaction, surface crusting, improves traffic corridors,
and increases water infiltration and accumulation of organic matter
down the soil profile (Gómez et al., 2004, 2009; Pagliai et al., 2004;
Schutter and Dick, 2002). Olive groves managed with grass cover
have lower soil losses and a lower average annual runoff coefficient
than ones where weeds are eliminated by either tillage or herbicide applications (Gómez et al., 2004; Taguas et al., 2010). On the
other hand, complete sod covering the orchard floor competes with
tree roots for water and nutrients and, hence, may reduce growth

and yield of trees (Atkinson, 1980). For instance, grasses and weed
ground covers reduced vegetative growth, yield and leaf nitrogen of
two peach cultivars compared to herbicide treatment (Tworkoski
and Glenn, 2001). Little information is available on the long-term
response of yield to soil management in olive orchards. Although
there is some evidence that a natural cover does not reduce yield
compared to conventional tillage under rainfed conditions (Gómez
et al., 1999; Hernández et al., 2005) more studies are needed to
quantify the effects, if any, of plant covers on yield and oil quality.
These effects are likely to be mediated by water availability. Gómez
et al. (1999) reported a significant decrease in yield of olive trees
when the soil was managed by tillage plus herbicide in a year of
very low precipitation.
Olive trees for oil production are traditionally not irrigated, but
in recent years irrigation has been extensively used to stimulate
growth during the training phase and increase yield once trees
attain maturity. Deficit irrigation is currently expanding due to
the growing concern about the efficient use of water. Deficit irrigation consists in supplying less water than that needed to meet
the full requirements of the crop. Many recent studies have shown
the advantages of deficit irrigation practices in the olive orchard,

as they achieve considerable water savings while maintaining high
yields (Caruso et al., 2011; Gucci et al., 2007; Lavee et al., 2007;
Moriana et al., 2003). The controlled distribution of suboptimal
volumes of water is also beneficial to obtain oils with high concentrations of phenolic compounds and long shelf-life (Motilva et al.,
2000; Servili et al., 2007).
Most studies on the effect of different soil management practices
have been conducted in traditional, rainfed, mature olive orchards
focusing mainly on either soil physical or chemical properties
(Gómez et al., 1999, 2004). In this work we used a comprehensive approach to contrast a high-density olive orchard managed
with a natural plant cover with one tilled to 0.1 m depth in terms of
plant performance and soil characteristics over five growing seasons. In particular, the objectives were to determine effects on:
(i) soil (macroporosity, water infiltration rate, fractions of organic
carbon content) and (ii) vegetative growth, yield components
(flowering, fruit set, fruit weight, oil accumulation, fruit number),

19

and oil quality (free acidity, peroxide values, spectrophotometric
indexes, phenolic concentrations and fatty acids composition) of
deficit-irrigated trees cultivated either with a natural plant cover

as the orchard floor or tilled to 0.1 m depth in a sandy-loam
soil.
2. Materials and methods
2.1. Plant material and site
We used an olive (Olea europaea L. cv. Frantoio) orchard planted,
at a density of 513 trees ha−1 in April 2003, on flat land at the
Venturina experimental farm of University of Pisa, Italy (43◦ 10′ N;
10◦ 36′ E) between 2004 and 2011. Cultural practices were aimed at
keeping labour and chemical input to a minimum. Minimum pruning criteria were used for canopy management (Caruso et al., 2011)
and pruned wood was shred and distributed on the soil surface
using a VKD 170 mulcher (Nobili, Bologna, Italy).
Prior to planting 147 t ha−1 of cow manure were applied into
the soil profile. In the first year each tree received about 15 g of N,
P2 O5 and K2 O. Since 2005 (3rd year after planting) fertilizers were
distributed only via the irrigation system for a total of 25, 50, 85,
25, 50 and 35 g of N, P2 O5 and K2 O per tree in 2005, 2006, 2007,
2008, 2009 and 2010, respectively.
All trees had been fully irrigated since planting until the 2006
growing season, when deficit irrigation was started using subsurface drip lines (Caruso et al., 2011). Trees received about
half the volume needed to fully satisfy their requirements, corresponding to 469, 677, and 893 m3 ha−1 in 2006, 2007, 2008,

respectively; in 2009 and 2010, due to summer rains, the water
applied was only 23 and 12% to that of well irrigated trees (497 and
109 m3 ha−1 in 2009 and 2010, respectively). The water requirement of well irrigated trees was calculated according to Doorenbos
and Pruitt (1997) using a crop coefficient of 0.55. The coefficient of ground cover was adjusted annually according to tree
size (0.6, 0.8, 0.9, 1 for 2006, 2007, 2008, and 2009–2010, respectively).
The climate at the study site was sub-humid Mediterranean
(Nahal, 1981; Caruso et al., 2011). The climatic conditions over the
study period were monitored using a weather station iMETOS IMT
300 (Pessl Instruments GmbH, Weiz, Austria) installed on site since
May 2006. Reference evapotranspiration (ET0 ), calculated according to the Penman–Monteith equation, was 948, 993, 1101 and
1001 mm in 2007, 2008, 2009 and 2010, respectively. Annual precipitation was 708, 1107, 771 and 1140 mm in 2007, 2008, 2009
and 2010, respectively (Fig. 1). Rains during summer months were
160 mm (2006), 39 mm (2007), 74 mm (2008), 87 mm (2009) and
140 mm (2010), as reported in Fig. 1.
2.2. Soil type and management
The soil was a deep (1.5 m) sandy-loam (Typic Haploxeralf,
coarse-loamy, mixed, thermic) (Soil Survey Staff, 2006) consisting of 600 g/kg sand, 150 g/kg clay and 250 g/kg silt. The pH was
7.9, average organic matter 1.84% and cation exchange capacity
13.7 meq/100 g, all measured at 0.4 m depth. The soil was high in
Ca and Mg, medium for N, K, Na and low in P.

The soil was periodically tilled at a depth of 0.1 m until October
2004 when two management treatments were started: CT, tillage
by a power take off-driven harrow with vertical blades (Breviglieri,
Nogara, Italy); NC, permanent plant cover periodically mown with
a VKD 170 Nobili mulcher. Subsequently, treatments were maintained by either tilling or mowing the green cover three or four
times a year. Both treatments received the same amount of water
since planting.

20

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

2.4. Water infiltration rate
Steady-state infiltration tests were performed in situ using
a thin-walled metal ring of 0.3 m diameter, partially inserted
(40 mm) into the soil to cause as little disturbance of the surface as
possible. To prevent the clogging of the soil surface due to careless
water application, one piece of cheesecloth was placed under the
water outlet tip. A Guelph Permeameter (Model 2800 – Soil moisture Equipment Corp., Santa Barbara, USA) was used to measure
the rate at which the water entered the soil. The measurements

were carried out in May 2010 with four replicates for each treatment, about six months after the last tillage (CT) when the inter-row
soil surface was sealed due to the compacting effect of winter and
spring rainfalls. A hydraulic head of 25 mm was used in each test
and field saturated hydraulic conductivity (Kfs ) calculated according to Eq. (2). According to Guelph Permeameter technique, Kfs was
calculated using Richards’ analysis (Reynolds, 1993):
Kfs =

Fig. 1. Monthly precipitation (mm) at the experimental site in Venturina, Italy, from
2007 through 2010.

The percentage of soil surface covered by the natural cover
was measured at 10 different positions (below the tree canopy
and in the interrow) along three transects (total of 30 positions)
in February, May, July and October 2007 by using a 1 m2 grid
(1 m × 1 m) subdivided into 100 squares. The plant cover was complete in all the NC plots during the wet months, but typically dried
out in the summer to recover naturally upon late summer rainfall.
Soil moisture at 0.06 m depth was measured at three locations per
soil management treatment twice a day in 2007 and 2010 using a
ML2x ThetaProbe (Delta-T Device, Cambridge, UK).

2.3. Soil porosity and structure
In order to characterize soil structure, vertically oriented thin
sections (55 mm × 85 mm) were obtained from undisturbed soil
samples collected in May 2010 at different depths (0–0.1 and
0.1–0.2 m) along the profile of the two soil management systems
(six thin sections per treatment and depth). The undisturbed samples were dried by acetone replacement (Miedema et al., 1974) and
impregnated under vacuum with a polyester resin. The impregnated blocks were cut into 60 mm high × 70 mm wide × 30 ␮m
thick vertically oriented thin sections (Murphy, 1986). Two images
of the 0–0.1 m layer were taken for each soil thin section: one representative of the section as a whole and the other at 0–5 mm depth to
evaluate soil crusting. The images were analyzed using the ImagePro Plus software (Media Cybernetics, Silver Spring, MD, USA), total
porosity and pore distribution were calculated from measurements
of pore shape and size (the instrument being set up to measure
pores larger than 50 ␮m). A shape factor [perimeter2 /(4 area)]
was used to divide pores into three classes: regular (rounded, shape
factor 1–2), irregular (shape factor 2–5), and elongated (shape
factor > 5), corresponding approximately to the classification used
by Bouma et al. (1977). Pores of each shape group were further
subdivided into size classes according to either their equivalent
diameter (regular and irregular pores), or their width (elongated
pores) (Pagliai et al., 1984). Thin sections were also examined using
a Zeiss ‘R POL’ microscope at 25× magnification to observe soil
structure.

C(X, Y )R
[2H 2 + a2 C + 2H/˛]

(1)

where C is the dimensionless shape factor of the measuring well
that depends primarily on the H/a ratio and soil texture/structure
properties, (X or Y) R is the steady-state flow rate depending on
whether the combination reservoir (X) or the inner reservoir (Y) of
permeameter was used, H is the hydraulic head of water in the ring,
a is the radius of the ring, and ˛ is a soil texture/structure parameter
(Elrick et al., 1989). The C factor value (Reynolds, 1993) used in the
calculation was obtained according to the empirical equation of
Zhang et al. (1998) for sandy soils.
Since the metal ring prevented the field-saturated component
of lateral flow, Eq. (1) was modified as follows:
Kfs =

C(X, Y )R
[a2 C + 2H/˛]

(2)

2.5. Soil organic carbon fractioning
At the same time and position of undisturbed soil sampling, bulk
samples were collected to evaluate organic carbon in both soil management treatments. Total organic carbon (TOC) was determined by
oxidation at 170 ◦ C, with potassium dichromate in presence of sulphuric acid. The excess potassium dichromate was measured out
by Möhr salt titration (Yeomans and Bremner, 1988).
Total extractable carbon (TEC) and humic carbon (HC) organic
matter fractioning were determined according to the official
method of the Italian Society of Soil Science (Sequi and De Nobili,
2000). The TEC was obtained by 0.1 M NaOH + 0.1 M Na4 P2 O7 (1:10
soil to solution ratio) at 65 ◦ C for 24 h. The humic and fulvic
acids (HA and FA, respectively) were separated from the extract
by acidification to pH 2.0 with H2 SO4 . The purification of FA
from non-humic substances was carried out by adsorption onto
polyvinylpyrrolidone columns. The purified FA fraction was then
combined with the HA fraction to give the humified carbon (HC).
The quantification of TEC and HC in the extracts was performed by
K2 Cr2 O7 + H2 SO4 hot oxidation (Yeomans and Bremner, 1988).
2.6. Leaf water potential and vegetative growth
Tree water status was determined by measuring pre-dawn leaf
water potential (PLWP) on six trees per treatment every 7–10 days
during the vegetative season using a pressure chamber (Caruso
et al., 2011).
Vegetative growth was assessed as trunk cross sectional area
(TCSA) and canopy volume. Trunk circumference was measured
0.4 m above the ground and the TCSA calculated since the year of
planting at the beginning and at the end of the growing season.

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

21

Table 1
The effect of soil management on canopy volume of young olive trees (cv. Frantoio). Values are means ± standard deviations of six or eight trees per treatment. Least significant
differences (LSD) between soil management systems were calculated after analysis of variance within each year (p < 0.05).
Treatment

Canopy volume (m3 )
January 2006

November 2007

November 2008

December 2009

Natural cover
Tillage

7.42 ± 2.13
9.69 ± 1.10

12.76 ± 2.86
23.60 ± 3.17

15.19 ± 2.67
27.16 ± 4.07

21.27 ± 7.15
30.48 ± 6.99

LSD (0.05)

2.22

3.74

The average canopy volume was calculated from measurements of
height and width of the canopy taken in November 2007, November
2008 and December 2009, assuming an elliptic shape. The leaf
area was determined destructively at two dates in 2007. Four trees
were harvested, wood and leaves separated and their fresh and dry
weights determined. The leaf area of a subsample was determined,
prior to oven-drying at 50 ◦ C, by scanning the freshly cut leaves
and using the “UTHSCSA Image Tool” program (University of Texas,
Health Science Center, TX, USA). The regressions between leaf area,
leaf dry weight and wood dry weight and branch diameter were
used to estimate the total leaf area of each tree, from which the leaf
area index (LAI) was calculated.
2.7. Fruit set, yield components and oil quality
The total number of one-year-old shoots, the number of flowering shoots bearing at least one inflorescence and the number of
inflorescences were measured in spring on three selected branches
per tree of six trees per treatment, as previously reported (Caruso
et al., 2011). Fruitlets present on each selected branch were counted
about 30 days after full bloom and fruit set expressed as the number
of fruits per inflorescence. At harvest, 50–100 fruits were randomly
sampled to measure average fruit weight and maturation index
according to standard methodology (Gucci et al., 2007). The total
number of fruits per tree was calculated by dividing the crop yield
by the average fruit weight (Caruso et al., 2011).
The oil content of the fruit mesocarp of five fruits per tree was
measured by nuclear magnetic resonance using an Oxford MQC-23
analyzer (Oxford Analytical Instruments Ltd., Oxford, UK) (Caruso
et al., 2011). The oil yield of individual trees was calculated after
measuring the mesocarp oil content on a dry weight basis, the fruit
fresh yield, the pulp/fruit ratio, and the ratio between dry and fresh
weight, as previously reported (Gucci et al., 2007).
Harvest occurred on 20 November in 2006, 6 November 2007, 21
October 2008, 19 October 2009 and 25 October 2010. Each tree was
harvested individually by hand and final crop yield was expressed
on the basis of TCSA to account for differences in tree size and
vegetative growth.
About 250 cc of oil were obtained using a laboratory scale system
from about 3.5 kg of fruits, which were crushed by a hammer mill,
the resulting olive paste malaxed at 25 ◦ C for 20 min, and the oil
separated by centrifugation (Servili et al., 2007). The oils were then
filtered and stored in the dark at 8 ◦ C until analysis. The free acidity,
peroxide value, fatty acids composition and UV absorption characteristics at 232 and 270 nm of the oils were measured in accordance
with the European Official Methods (UE 1989/2003 modifying the
ECC 2568/91). The total phenols and ortho-diphenols were determined by the Folin-Ciocalteu method according to Montedoro et al.
(1992).
2.8. Experimental design and statistical analysis
Each treatment was assigned to 36 trees, divided into three plots
of 12 trees each. Each plot included three rows of trees. To avoid
border effects only the central row of each plot was used and all

4.17

8.90

measurements and samples were taken on the inner trees of the
central row. Treatment means were separated by least significant
difference (LSD test) after analysis of variance (ANOVA) using five
or six replicate trees. Since tree size was not uniform between treatments when different soil managements were put into action, the
TCSA measured in April 2004 was used as a covariate in the analysis of covariance (MedCalc software, Mariakerke, Belgium). Soil
macroporosity and organic matter fractions data were analysed by
2 × 2 factorial ANOVA with six replicates.

3. Results
3.1. Tree performance
The PLWP of CT trees, measured during the irrigation period,
was often significantly lower (more negative) than that of NC trees
(Fig. 2). In the last four years of the study, the cumulated leaf water
potential of CT trees was on average 13% lower than that of NC trees
with differences ranging from 7 to 20% in 2009 and 2007, respectively. The soil humidity of NC plots measured at 0.06 m depth was
significantly greater than that of CT ones during summer months
of 2010, but differences disappeared since autumn 2010 (Fig. 3).
These data are consistent with soil humidity values measured at
0.5 m depth beneath the tree canopy (1.1 m from the trunk), which
were higher in the NC than in the CT treatment (data not shown).
The TCSA of NC cultivated trees was smaller than that of trees
growing in CT plots. Differences were established early after soil
treatments had been put into action and the effect was evident at
the end of each of the five growing seasons (Fig. 4). Significant differences in leaf area per tree between the two soil management
systems were found at the beginning (35.3 and 57.2 m2 for NC and
CT, respectively) and end (45.8 and 68.6 m2 for NC and CT, respectively) of the fourth year after planting. These values corresponded
to a LAI of 1.81 and 2.92 for NC and CT, respectively (beginning of
2007) and 2.36 and 3.67 for NC and CT, respectively (end of 2007).
The canopy volume of CT trees was significantly higher than that
of NC trees by 23, 46, 44 and 30% in 2006, 2007, 2008 and 2009
(Table 1).
The number of flowering shoots per branch was similar for both
treatments. Some differences in fruit set appeared since 2008, but
they were not consistently maintained in the following two years
(Fig. 5). The fruit and oil yields of trees managed by tillage were
significantly higher than those of trees grown with a permanent,
natural cover (Table 2). However, when yields were expressed on
a TCSA basis, there were no significant differences between the
two soil treatments both in the initial three years of production
(2006–2008) and when full production was attained (2009–2010).
The fruit yield of trees with a naturally covered floor was 87% that
of trees under periodic tillage (average of five years). The number of fruits borne by NC trees was about half that by CT ones and
remained significantly lower even when the number of fruits per
tree was expressed on a TCSA basis (Table 2). The oil content in the
fruit pulp was similar for both treatments (Table 2). There were no
significant differences in maturation index between the soil treatments, but fruits harvested from the NC trees were usually more

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

22

Table 2
Yield, yield components, yield efficiency (fruit yield/TCSA or oil yield/TCSA), and maturation index (MI) of young olive trees (cv. Frantoio) subjected to two different soil
management systems. Values are means of three (2006–2008) or two (2009–2010) years. Least significant differences (LSD) at p ≤ 0.05 were calculated after ANOVA within
each period (n = 4–6 trees per treatment).
Soil management

Years

Fruit yield
(g tree−1 )

Fruit
yield/TCSA
(g dm−2 )

Fruits
per tree

Fruits/TCSA
(no dm−2 )

Oil yield
(g tree−1 )

Oil
yield/TCSA
(g dm−2 )

Fruit
FW (g)

MI

Oil in
mesocarp
(% DW)

Natural cover
Tillage

2006–2008

9588
16,342

12,602
14,818

4617
10,252

6077
8901

2269
3470

2903
3062

2.13
1.70

3.17
2.47

71.4
71.0

3445

4408

2472

2396

805

855

0.24

0.86

18,013
25,148

11,047
12,423

8636
14,278

5124
6858

3371
4555

2172
2308

2.29
1.87

2.48
2.24

6903

2267

5115

1935

849

565

0.37

1.04

LSD (0.05)
Natural cover
Tillage

2009–2010

LSD (0.05)

1.15
61.1
65.4
4.90

TCSA: trunk cross sectional area; FW: fresh weight; DW: dry weight.
Table 3
Free acidity, peroxide value, K232 , K270 , total phenols, ortho-diphenols, and fatty acids composition of virgin olive oils (VOO) from olive trees (cv. Frantoio) subjected to two
different soil management systems. Values are means of four different VOO replicates (n = 4). Different letters indicate least significant differences at p ≤ 0.05 after analysis
of variance (ANOVA) within each year. Data of fatty acids were transformed by arcsine transformation prior to ANOVA.
Soil management

Year

Free acidity
(% oleic acid)

Peroxide value
(meq O2 kg−1 )

K232

K270

Total
phenols
(mg kg−1 )

Orthodiphenols
(mg kg−1 )

Palmitic
acid (%)

Oleic acid
(%)

Linoleic
acid (%)

Linolenic
acid (%)

Natural cover
Tillage

2006

0.25
0.25

10.2
12.7

1.775
1.975

0.123
0.125

520
443

133
132

N.A.
N.A.

N.A.
N.A.

N.A.
N.A.

N.A.
N.A.

Natural cover
Tillage

2008

0.37
0.40

9.7
10.2

1.730
1.645

0.295
0.141

605
530

205
192

13.3 a
12.8 b

73.5
74.4

8.4
7.9

0.6 b
0.7 a

Natural cover
Tillage

2009

0.34
0.31

7.2
5.3

2.000
1.897

N.A.
N.A.

702 a
505 b

325 a
238 b

14.0
14.2

73.0
73.4

7.9
8.0

0.6
0.7

Natural cover
Tillage

2010

0.23
0.20

9.3
9.6

1.875
1.888

0.109
0.107

130
119

65
60

N.A.
N.A.

N.A.
N.A.

N.A.
N.A.

N.A.
N.A.

N.A.: not available.

pigmented than those picked from the CT trees (Table 2). There
were significant differences in fresh weight between treatments:
fruits from the CT treatment were smaller than those from the NC
treatment (Table 2).
Soil management did not influence free acidity, peroxide value,
K232 , and K270 in any of the years of study (Table 3). The fatty acid
composition of the oil showed a significant increase in palmitic
acid at the expense of linolenic acid of the NC treatment only in
one out of two years. Other fatty acids (myristic, palmitoleic, margaric, eptadecanoic, stearic, arachic, eicosenoic, behenic, lignoceric)
present in olive oils are not reported in Table 3, as they did not differ
between soil management treatments. Total phenolic concentrations of the NC treatment were slightly higher than those of the CT
one, although differences were significant only in 2009 (Table 3).

3.2. Soil properties and water infiltration
Soil porosity, determined according to micromorphometric
methods (Pagliai, 1988), was low in both treatments (Fig. 6). In
particular, NC and CT soils can be classified as dense (macroporosity between 5 and 10%) and very dense (macroporosity lower than

5%), respectively. Soil macroporosity was significantly affected by
soil management only at the surface (0–0.10 m) where NC showed
higher values than CT. This difference resulted mainly from the
higher frequency of irregular pores and elongated pores, which dramatically decreased in CT. Macrophotographs of the upper part of
soil (0–5 mm) and the corresponding pore size distribution of the
two soil managements confirmed the above differences and evidenced the presence of a compact surface crust in the CT treatment
only (Fig. 7).
The water infiltration rate of NC treatment was similar to what
FAO (1990) considers a standard steady rate for sandy loam soils
(20–30 mm h−1 ) (Fig. 8). On the contrary, the infiltration rate measured in CT plots was about eight times lower than that in the NC
treatment, in agreement with the low value of macroporosity at the
surface of CT soil.
Total organic carbon and TEC in NC plots were higher than
in CT ones, the former at both depths, the latter only at the
0–0.1 m depth (Table 4). The TEC values significantly decreased
at 0.1–0.2 m depth in both management systems. The humic
fraction, the more resistant pool of soil organic matter (Tate,
1987), was quite low and unaffected by soil management
(Table 4).

Table 4
Effect of soil management on the different fractions of soil total organic carbon (TOC). Different letters within each column indicate significant differences between soil
management treatments and depths after analysis of variance (p < 0.05).
Soil management

Depth (m)

TOC (%)

TEC (%)

HC (%)

Tillage

0–0.1
0.1–0.2
0–0.1
0.1–0.2

1.14 b
1.04 b
1.33 a
1.35 a

0.55 b
0.31 c
0.68 a
0.38 c

0.19 a
0.12 b
0.18 a
0.10 b

Natural cover
TEC: extractable carbon; HC: humic carbon.

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

23

Fig. 3. Seasonal changes in soil moisture, measured at 0.06 m depth, in a highdensity olive orchard managed either by natural plant cover or tillage. Symbols are
means of two measurements (dawn and solar noon) of three replicate trees during 2010 and 2011. Vertical bars represent least significant differences at p ≤ 0.05,
calculated after analysis of variance within each date of measurement.

Fig. 2. Seasonal course of pre-dawn leaf water potential (PLWP) of olive trees subjected to different soil management in 2007 (A), 2008 (B), 2009 (C), and 2010 (D).
Symbols are means of six trees. Vertical bars represent least significant differences
at p ≤ 0.05, calculated after analysis of variance within each date of measurement.
Horizontal lines indicate the irrigation period. H, harvest.

Fig. 4. Trunk-cross sectional area (TCSA) of young olive trees grown under either
natural cover or tillage conditions. The soil was tilled from the year of planting (2003)
until October 2004 (A), when two soil management treatments were established.
Trees had been fully irrigated until the 2006 growing season (B), when deficit irrigation was started. Symbols are means of 5–6 trees. Means were transformed after
analysis of covariance using TCSA measured in April 2004 as covariate.

24

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

Fig. 6. Total macroporosity (pores > 50 ␮m) values (n = 6), expressed as a percentage
of area occupied by pores of the three shape groups (regular, irregular and elongated pores), at two different depths (0–0.1 m and 0.1–0.2 m) in natural cover (NC)
and tillage (CT) treatments. Different letters indicate least significant differences
between treatments and soil depths after analysis of variance within each shape
group at p ≤ 0.05.

et al., 2004; Moreno et al., 2009) despite the fact that our CT
treatment was intended to be less aggressive than conventional
tillage. Conventional tillage of olive orchards typically involves
mechanical disturbance of the 0–0.2 m layer, the use of heavy
equipment (mouldboard plough or chisel plough), periodic disking
or harrowing (Gómez et al., 2009; Moreno et al., 2009), whereas we

Fig. 5. Number of flowering shoots and fruit set of olive trees (cv. Frantoio) subjected to two different soil management systems. Fruit set was measured about 30
days after full bloom and expressed as number of fruits per 100 inflorescences. Measurements were made every spring, before the beginning of irrigation. Values are
mean of 5–6 replicate trees. Different letters indicate least significant differences
between treatments after analysis of variance (ANOVA) within each year at p ≤ 0.05.
Data of fruit set were transformed by arcsine transformation prior to ANOVA.

4. Discussion
Soil management had a major impact on soil physical properties. The NC treatment had greater soil macroporosity in the
0–0.1 m upper layer and water infiltration rate than CT plots. The
dramatic decrease in soil macroporosity of the CT treatment was
essentially due to a significant reduction in elongated and irregular pores, which are critical for root penetration, water movement
and gas diffusion. The vegetation cover likely protected the soil
surface from the raindrop impact, thus reducing mechanical disruption of soil aggregates and preserving the continuity of elongated
pores (Panini et al., 1997). There was also evidence of soil crusting in the CT treatment, which was presumably responsible for
the low values of infiltration rate. These results confirm the occurrence of surface sealing and low infiltration in tilled soils (Gómez

Fig. 7. Macrophotographs of vertically oriented thin sections from the surface layer
of naturally covered (A) or tilled (B) soil and corresponding pore size distribution,
according to equivalent pore diameter for regular and irregular pores and width
for elongated pores in the upper part of soil (0–0.05 m). The presence of a compact
surface crust is evident in the tilled treatment.

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

Fig. 8. Water infiltration rate measured in the interrow of a high-density olive
orchard during the sixth growing season after establishment of different soil management. Histograms are means of four replicates (bars = standard deviations).

tried to minimize disturbance by limiting tillage to 0.1 m depth and
abstaining from using rotary tillers.
The bare soil of the CT plots was vulnerable to crusting and,
therefore, susceptible to waterlogging. Olive trees are sensitive to
hypoxia conditions which may negatively influence tree growth
and production (Aragues et al., 2004; Dat et al., 2006), but the periods of waterlogging that occurred in part of the CT area in the
autumn of 2008 and 2010 due to the abundant precipitations of
November and December were too brief to affect tree performance
(Fig. 1). The increasing number of heavy rainfall events (Brunetti
et al., 2001) exacerbates the problem of soil crusting and compaction in tilled soils. Over the 2006–2010 period there was an
annual average of 7.5 heavy rainfall events (intensity between 15
and 40 mm h−1 ) in the experimental area, at least two of which
in the autumn. In 2010 there were 11 events, five of which in
the autumn. When surface sealing of the CT treatment occurred
and hindered water infiltration, even rainfall events of moderate
intensity (3–15 mm h−1 ) could cause waterlogging.
The difference in infiltration rate between NC and CT treatments was much greater than that reported (about 2-fold) between
conventional tillage and a barley crop cover in a clay-loam after
seven years of differentiated soil management (Gómez et al., 2009).
Besides differences in soil type and time of measurement after last
tillage the differences we reported were probably amplified by having measured infiltration only in the middle of the interrow. In olive
orchards soil properties and hydrological parameters in the zone
beneath the tree canopy are distinct from those in the interrow.
In particular, it has been shown that water infiltration beneath the
canopy was about four times that of the interrow in a clay-loam
soil in southern Spain (Gómez et al., 1999).
Soil structure is positively affected by TOC content (Aranda et al.,
2011; Hernández et al., 2005; Hernanz et al., 2002), but it is necessary to quantify the different fractions of TOC to better evaluate the
effect of soil management (Vittori Antisari et al., 2010). In fact, we
found that while TOC was different between NC and CT treatments
at both depths (0–0.1 and 0.1–0.2 m), differences in TEC were significant only in the more superficial layer, and HC was unaffected
by soil management in both layers. The use of plant covers determines an increase of easily mineralizable organic matter, namely
fresh herbaceous plant residues such as leaves, root debris and exudates (Berry et al., 2002). Such fraction enhances biological activity,
thus favouring soil aggregate formation (Tisdall and Oades, 1982).
This is particularly important in weakly structured, coarse textured
soils and was clearly shown by our macroporosity results. Under the
pedo-climatic conditions of our study, five years of natural plant
cover were not sufficient to affect the HC content of the 0–0.2 m

25

topsoil. This is not surprising because longer periods are necessary to increase the soil content of organic matter along the profile
under Mediterranean climate conditions. Gómez et al. (1999) did
not find differences in the organic matter of the 0–0.09 m topsoil
beneath olive canopies between conventional tillage and no tillage
(plus herbicide) after 15 years. The formation of stable organic compounds is largely determined by either soil organic matter turnover
or soil minerals (Buurman et al., 2009). The low value of HC we
measured in both soil management treatments was likely due to
the rapid turnover of organic matter in the topsoil and to the specific textural characteristics. The abundance of the labile fractions
versus the humified ones suggested that this soil had a poor humification capacity (Vittori Antisari et al., 2010).
The presence of a permanent sod reduced trunk growth and
the number of fruits per tree with respect to CT-cultivated trees.
Differences in TCSA and canopy volume between treatments were
apparent every year and determined a greater LAI and fruiting surface of the CT management, which can explain why CT trees had
more fruits than NC ones. In olive trees fruit yield is positively
correlated with total fruit number (Gucci et al., 2007; Trentacoste
et al., 2010), which is not altered by thinning as in the standard
commercial practice of other fruit trees. The effect on fruit number
was still significant when the larger size of CT canopies was taken
into account. Although it is impossible from our data to determine
what caused the drastic reduction in fruit number/TCSA for the NC
treatment, we hypothesize that it was due to reduced shoot length
rather than fruit set (Fig. 5). Changes in initial fruit set or fruitlet
abscission have been reported to occur only when severe water
deficit develops (Gucci et al., 2007), but the differences in PLWP we
measured between NC and CT trees were too small to affect fruit
abscission. The overall negative effect of NC on fruit or oil yield was
largely diminished and no longer significant when yield efficiencies
(yield/TCSA) were calculated, indicating that differences in canopy
size were mainly responsible for the lower yield of NC-grown trees.
Gómez et al. (1999) did not find any yield differences between olive
trees grown with conventional tillage or no tillage under rain-fed
conditions.
The increase in fruit weight and maturation index for the NC
treatment are consistent with effects due to crop level rather than
tree water status (Gucci et al., 2007; Trentacoste et al., 2010). In
addition, the small differences in maturation index or plant water
status did not appear relevant to affect oil quality. A clear negative
correlation between tree water status and oil phenolic concentrations has been reported (Motilva et al., 2000; Servili et al., 2007)
but, in our study, the PLWP of NC trees was never lower than
that of CT ones (Fig. 2). It remains to be ascertained whether
the higher polyphenols concentration of the NC treatment measured every year (although significant only in 2009) is confirmed
over longer periods and, if so, why this increase since cannot be
explained by tree water status or stage of ripening. Phenols and
ortho-diphenols are very important for quality characterization of
virgin olive oil (VOO) since they are closely related to their sensory
and health properties (Servili et al., 2004). Oils of both soil treatments exceeded the 200 mg kg−1 value, currently considered the
threshold above which phenolic compounds exert their nutraceutical effects as antioxidants, except in 2010, when abundant rains
during fruit development determined low phenolic concentrations
in the oil (Servili et al., 2007).
In conclusion, the positive effect of NC on the strength of surface structural elements (peds and aggregates) can be mainly
attributed to the physical protection against raindrop impact and
to the stability enhancement due to enmeshing of soil particles and
microaggregates by grass fine roots rather than to the increase of
TOC content. The marked decrease in vegetative growth for the NC
treatment was likely due to the early establishment of the green
cover which competed for water and nutrients against the young

26

R. Gucci et al. / Europ. J. Agronomy 41 (2012) 18–27

root systems of trees. Hence, the establishment of permanent covers should not be recommended in the first two years after planting
but delayed to the third or fourth year depending on tree growth.
A natural plant cover significantly decreased the number of fruits
and yield, but did not affect yield efficiency, mesocarp oil content or
oil quality; these effects did not depend on a greater water deficit
developing in NC trees based on PLWP and soil moisture measurements.

Acknowledgments
We are grateful to Michele Bernardini, Rolando Calabrò,
Maurizio Gentili, and Stefania Simoncini for excellent technical
assistance. We also thank Netafim Italia for the supply of the
subsurface irrigation system. Research supported by Unaprol-Italy
(project Reg. UE no. 2080/2005 and no. 867/2008) and PRIN 2004
“Carbon Cycle in Tree Ecosystems” (project no. 2004074422 004).

References
Aragues, R., Puy, J., Isidoro, D., 2004. Vegetative growth response of young olive trees
(Olea europaea L. cv. Arbequina) to soil salinity and waterlogging. Plant Soil 258,
69–80.
˜
M.J., Domínguez-Vidal, A., Martín-García, J.M., Calero, J.,
Aranda, V., Ayora-Canada,
Delgado, R., Verdejo, T., González-Vila, F.J., 2011. Effect of soil type and management (organic vs conventional) on soil organic matter quality in olive groves in a
semi-arid environment in Sierra Mágina Natural Park (S. Spain). Geoderma 164,
54–63.
Atkinson, D., 1980. The distribution and effectiveness of the roots of tree crops. Hort.
Rev. 2, 424–490.
Berry, P.M., Sylvester-Bradley, R., Phillips, L., Hatch, D.J., Cuttle, S.P., Rayns, F.W.,
Gosling, P., 2002. Is the productivity of organic farms restricted by the supply of
available nitrogen? Soil Use Manage. 18, 248–255.
Bouma, J., Jongerius, A., Boersma, O.H., Jager, A., Schoonderbeek, D., 1977. The function of different types of macropores during saturated flow through four swelling
soil horizons. Soil Sci. Soc. Am. J. 41, 945–950.
Brunetti, M., Colacino, M., Maugeri, M., Nanni, T., 2001. Trends in the daily intensity
of precipitation in Italy. Int. J. Climatol. 21, 299–316.
Buurman, P., Nierop, K.G.J., Kaal, J., Senesi, N., 2009. Analytical pyrolysis and thermally assisted hydrolysis and methylation of EUROSOIL humic acid samples—a
key to their source. Geoderma 150, 10–22.
Caruso, G., Rapoport, H.F., Gucci, R., 2011. Long-term evaluation of yield components of young olive trees during the onset of fruit production under different
irrigation regimes. Irrig. Sci., doi:10.1007/s00271-011-0286-0.
Dat, J., Folzer, H., Parent, C., Badot, P.M., Capelli, N., 2006. Hypoxia stress: current
understanding and perspectives. In: Teixeira da Silva, J.A. (Ed.), Floriculture,
Ornamental and Plant Biotechnology: Advances and Topical Issues, vol. 3. Global
Science Books, Isleworth, UK, pp. 664–674.
Dexter, A.R., 1997. Physical properties of tilled soils. Soil Till. Res. 43, 41–63.
Doorenbos, J., Pruitt, W.O., 1997. Crop water requirements. FAO Irrigation and
Drainage Paper 24. Rome, Italy, 144 pp.
Elrick, D.E., Reynolds, W.D., Tan, K.A., 1989. Hydraulic conductivity measurements
in the unsaturated zone using improved well analyses. Ground Water Monit.
Rev. 9, 184–193.
EU. Off. J. Eur. Communities, 2003 November 6, Regulation 1989/03 amending Regulation (EEC) No 2568/91 on the characteristics of olive oil and olive-pomace oil
and on the relevant methods of analysis modifies the CEE n◦ 2568/91 on olive
oils and pomace olive oils characteristics and relative analysis methods. Official
Journal L 295/57 13/11/2003.
FAO (Food and Agriculture Organization), 1990. Irrigation water management: irrigation methods. In: Brouwer, C., Prins, K., Kay, M., Heibloem, M. (Ed.), Training
manual n◦ 5, Rome, Italy.
Gómez, J.A., Giraldez, J.V., Pastor, M., Fereres, E., 1999. Effects of tillage method on
soil physical properties, infiltration and yield in an olive orchard. Soil Till. Res.
52, 167–175.
Gómez, J.A., Battany, M., Renschler, C.S., Fereres, E., 2003. Evaluating the impact of
soil management on soil loss in olive orchards. Soil Use Manage. 19, 127–134.
Gómez, J.A., Romero, P., Giraldez, J.V., Fereres, E., 2004. Experimental assessment of
runoff and soil erosion in an olive grove on a Vertic soil in southern Spain as
affected by soil management. Soil Use Manage. 20, 426–431.
Gómez, J.A., Sobrinho, T.A., Giraldez, J.V., Fereres, E., 2009. Soil management effects
on runoff, erosion and soil properties in an olive grove of Southern Spain. Soil
Till. Res. 102, 5–13.
Gucci, R., Lodolini, E., Rapoport, H.F., 2007. Productivity of olive trees with different
water status and crop load. J. Hort. Sci. Biotechnol. 82, 648–656.
Hernández, A.J., Lacasta, C., Pastor, J., 2005. Effects of different management practices on soil conservation and soil water in a rainfed olive orchard. Agric. Water
Manage. 77, 232–248.

Hernanz, J.L., Lopez, R., Navarrete, T., Sanchez-Giron, V., 2002. Long-term effects
of tillage systems and rotations on soil structural stability and organic carbon
stratification in semiarid central Spain. Soil Till. Res. 66, 129–141.
IPCC, 2007. Intergovernmental Panel on Climate Change Fourth Assessment Report
(AR4 released in 2007). http://www.ipcc.ch/.
Lavee, S., Hanoch, E., Wodner, M., Abramowitch, E., 2007. The effect of predetermined
deficit irrigation on the performance of cv. Muhasan olives (Olea europaea L.) in
the eastern coastal plain of Israel. Sci. Hortic. 99, 267–277.
Miedema, R., Pape, T., Van de Wall, G.J., 1974. A method to impregnate wet soil
samples, producing high quality thin sections. Neth. J. Agric. Sci. 22, 37–39.
Montedoro, G.F., Servili, M., Baldioli, M., Miniati, E., 1992. Simple and hydrolyzable phenolic compounds in virgin olive oil 1. Their extraction, separation, and
quantitative and semiquantitative evaluation by HPLC. J. Agric. Food Chem. 40,
1571–1576.
˜
Moreno, B., Garcia-Rodriguez, S., Canizares,
R., Castro, J., Benìtez, E., 2009. Rainfed
olive farming in south-eastern Spain: long-term effect of soil management on
biological indicators of soil quality. Agric. Ecosyst. Environ. 131, 333–339.
Moriana, A., Orgaz, F., Pastor, M., Fereres, E., 2003. Yield responses of a mature olive
orchard to water deficits. J. Am. Soc. Hortic. Sci. 128, 425–431.
Motilva, M.J., Tovar, M.J., Romero, M.P., Alegre, S., Girona, J., 2000. Influence of regulated deficit irrigation strategies applied to olive trees (Arbequina cultivar) on
oil yield and oil composition during the fruit ripening period. J. Sci. Food Agric.
80, 2037–2043.
Murphy, C.P., 1986. Thin Section Preparation of Soil and Sediments. AB Academic
Publishers, Herts.
Nahal, I., 1981. The Mediterranean climate from a biological viewpoint. In: Di Castri,
F., Goodall, D.W., Specht, R.L. (Eds.), Mediterranean-type Shrub Lands Ecosystems of the World, vol. 11. Elsevier, Amsterdam, pp