land degradation & development

Land Degrad. Develop. 21: 132–138 (2010)

Published online 31 March 2009 in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/ldr.917

EFFECTS OF SOIL-PROTECTING AGRICULTURAL PRACTICES ON SOILORGANIC CARBON AND PRODUCTIVITY IN FRUIT TREE ORCHARDSy

G. MONTANARO*, G. CELANO, B. DICHIO AND C. XILOYANNIS

Department of Crop Systems, Forestry and Environmental Sciences, University of Basilicata, 85100 Potenza, Italy

Received 19 September 2008; Revised 8 January 2009; Accepted 13 February 2009

ABSTRACT

This 4-year on-farm study reports the effects of different agricultural practices on yield and soil organic carbon (SOC) in kiwifruit and apricotorchards grown in a Mediterranean area. Groups of plants under local orchard management (LOM,x) practices (i.e. soil tillage, removing ofpruning residues and mineral fertilisers) were compared with plots under soil-protecting orchard management (SPOM) actions (i.e. cover crop,no-tillage, compost application and mulching of pruning residues). In the SPOM blocks fertilisation rate was based on plant demand andirrigation volumes calculated on the evapotranspiration values, while they were empirically calculated in the LOM plots. Results show thatyield was 28–50 per cent enhanced by SPOM practices while SOC remained close to the initial values. In comparison with LOM plots, changedpractices increased up to 28–90 per cent the amount of P and K, and 13 per cent that of N annually incorporated into soil increasing theirreservoir in the soil. The study demonstrates that appropriate land management can increase the mean annual carbon soil inputs from about 1�5to 9�0 t ha�1 per year. Copyright # 2009 John Wiley & Sons, Ltd.

key words: crop residues; land use; organic matter; soil carbon input; SOC; Mediterranean soil; soil organic carbon

INTRODUCTION

Depletion of soil fertility is one of the major constraints to

crop production. Soil organic carbon (SOC) is widely

associated with soil fertility status. Although there is no firm

evidence of a critical threshold for SOC below which

fertility is compromised (productivity is depressed, soil

becomes physically instable and prone to erosion) the lower

limit of about 2 per cent SOC has been reported to avoid

significant structural deterioration of soil and to sustain

yields at about 90–95 per cent of the maximum, assuming

sufficient supplies of inorganic fertilisers (see Loveland and

Webb, 2003 for review). In modern agricultural production

systems inputs are increased to adequately compensate for

yield reductions due to SOC decline (Reeves, 1997).

However, maintaining or improving agricultural pro-

ductivity by improving soil fertility is desirable and crucial

to improve soil resources for future generations.

In Mediterranean cultivated soils, intensive agricultural

practices (continuous tillage, high inputs of mineral fertilisers,

* Correspondence to: G. Montanaro, Department of Crop Systems, Forestryand Environmental Sciences, University of Basilicata, Via Ateneo Lucano,85100 Potenza, Italy.E-mail: giuseppe.montanaro@unibas.ityThis article was published online on 31 March 2009. An error wassubsequently identified. This notice is included in the online version toindicate that this has been corrected 2 April 2009.xCorrection made here after initial publication.

Copyright # 2009 John Wiley & Sons, Ltd.

irrigation method and application of low-quality irrigation

water, removal of pruning residues) combined with the

aggressive climate characteristics (i.e. low precipitation and

high summer air temperatures) have dramatically degraded

some soil and reduced SOC to about 1 per cent in several areas

(Trinchera et al., 1999; Bastida et al., 2006). Such poor soil

condition negatively affects a large number of soil charac-

teristics creating unfavourable soil conditions for plant

physiology and preventing achievement of high yield and

fruit quality. It is widely known that increasing SOC content

can be achieved by both increasing the carbon input by

beneficial practices (e.g. manure and organic additions,

adequate fertilisation, return of crop residues to the soil, crop

rotations and optimal fallow frequency) and that soil carbon

emission can be curtailed by reducing soil disturbance (i.e.

minimum or no tillage) (Reeves, 1997; Kong et al., 2005).

However, in some cultivated Mediterranean areas suffering

water shortages, soil tillage is currently perceived as essential

to minimise the competition for water and nutrients between

weeds and crops, reducing considerably the appeal of

conservation tillage and hampering soil fertility remediation.

Quantitative informationonbiomass inputandon thepotential

increases of the carbon stocks are available for a number of

annual crops (Lal, 1997; Oelbermann et al., 2005), but there

are relatively fewer studies published on fruit tree orchards

under improved management practices. This hinders devel-

opment of effective policies to support sustainable land use.

SOIL-PROTECTING PRACTICES IN FRUIT TREE ORCHARDS 133

Therefore, the present study was intended to quantify carbon

input in two fruit tree orchards (kiwifruit and apricot) under

soil-protecting management practices in contrast to conven-

tional ones. The hypothesis behind this work is that

improvement in soil fertility (via increasing carbon input)

enhances crop yields.

Figure 1. Monthly precipitation (mm) and potential evapotranspiration(ET0) (mm) in the study area. Data are mean of 17-year period. (Source:

Agrometeorological Service—ALSIA, Basilicata Region).

MATERIALS AND METHODS

Study Sites

This study was conducted in South Italy during four growing

seasons (2004–2007) at two private farms. Maximum annual

temperature at this region is 368C and rainfall recorded over

a 17-year period averaged 550 mm y�1 (Agrometeorological

Service, ALSIA Basilicata Region) with rains occurring

from late August until January (Figure 1). This rainfall

pattern implies a seasonal water deficit of 855 mm during the

growing season (March–September) (Figure 1). Trials were

carried out at a kiwifruit site (N 408 23’ E 168 45’) on a

Haplic Luvisols, and at a apricot orchard (N 408 08’ E 16838’) on a Haplic Revosols. Soils were classified according to

WRB, 2006. The experimental sites were 25 and 7 m above

sea level for the kiwifruit and apricot orchards, respectively,

and further details are reported in Table I.

Experimental Design

In each site, the research compared the local orchard

management (LOM) practices with a soil-protecting orchard

management (SPOM) actions (see below for details) in an

experimental area of 2 ha with three replications per

treatment. The average area of the single plot was

approximately 0�3 ha. Prior to start the experiment, in both

sites the orchards were managed according to LOM practices.

In the SPOM treatments, soil including the tree row was

left untilled and weeds were mowed to 3–4 cm height in

March, May and September. Fertilisation was based on plant

demand and on availability in the soil of the various essential

plant nutrients (Xiloyannis et al. 2001; Xiloyannis et al.

2006). The Table II reports the annual amount of N, P and K

applied in the different plots. In particular, the concentration

of N (NO�3 ) was monitored (Nitracheck1) and N distributed

via fertigation each time the concentration in the top 40 cm

of soil fell below 20 ppm. Each year in January, 15 t ha�1

Table I. Characteristics of the orchards used for the experiment

Kiwifruit orchard

Specie Actinidia deliciosa, cv HayPlanting year 1985Training system Pergola, 494 p ha�1

Irrigation method Microjet, 120 L h�1 per pla

Copyright # 2009 John Wiley & Sons, Ltd.

(fresh weight, 24�8 per cent moisture content) of compost

were distributed (22�2 C/N; Eco-Pol SpA—Italy) contain-

ing, on a dry matter basis, 2�02 per cent total N, 1�8 per cent

organic N, 1�86 per cent K2O and 0�9 per cent P2O5 (see

Table II for doses annually applied). Pruning occurred each

year (November–December) and the resulting biomass was

subsequently chipped and evenly distributed on the soil

surface as mulch.

In the LOM plots, soil was tilled including the tree row

using a 18-disc plough, 4 times per year to 10–20 cm depth.

Pruning residues were removed and burnt. The mean

annual LOM treatment fertiliser rates are reported in Table II.

Irrigationvolumes for the SPOM plotswerecalculatedon the

basis of ETo values (potential evapotranspiration) measured at

a standard meteorological station located within 500 m

(Regional Meteorological Service, ALSIA) and using specific

crop coefficient (Kc). The Kc values (May–September) were

0�9, 1�1, 1�3, 1�2, 0�8 for kiwifruit and 0�4, 0�5, 0�6, 0�3, 0�3 for

apricot. The within-irrigation interval was 3–7 days for both

species. In the LOM blocks, irrigation volumes were

determined empirically according to local commercial

practice, and the irrigation interval time was 7–10 days.

Soil and Orchard Residue Sampling and Analysis

At the beginning of this study, an initial composite soil

sample was taken in autumn across the two sites for soil

texture, N, P, K, pH and organic carbon (SOC) analysis. Nine

Apricot orchard

ward Prunus armeniaca, cv S. Castrese1985

Palmette, 740 p ha�1

nt�1 Drip, 16 L h�1 per plant�1

LAND DEGRADATION & DEVELOPMENT, 21: 132–138 (2010)

Table II. Mean annual amount of mineral elements (kg ha�1) from different sources and applied to field under soil-protecting (SPOM) andlocal (LOM) orchard management practices

Source SPOM LOM

N P K N P K

KiwifruitIrrigation water 3�4 Trace 117�0 2�7 Trace 92�0Crop and weed residues 29�4 3�7 85�0 20�2 1�8 48�4Mineral fertilisation 40�0 — — 108�0 17�5 37�4Compost 75�0 33�0 70�0 — — —Total 147�8 36�7 272 130�9 19�3 177�8

ApricotIrrigation water 1�0 Trace 30�0 0�6 Trace 22�0Crop and weed residues 34�3 6�5 127�8 8�6 1�1 16�2Mineral fertilisation 17�0 — — 90�0 22�0 108�0Compost 75�0 33�0 70�0 — — —Total 127�3 39�5 227�8 99�2 23�1 146�2

134 G. MONTANARO ET AL.

soil cores (15, 30, 60, 90 cm depth) were randomly collected

from each treatment (3� plot) with a manual soil probe in

the middle of the inter-row space after removing visible crop

residue from the soil surface. Soil cores from the same depth

in each plot were mixed and kept at a workable wet

conditions to pass through a 2-mm sieve and left to

completely air dry afterward. Soil characteristics (texture,

total nitrogen, extractable POlsen and water soluble K) were

assayed according to Official Methods of Soil Analyses

(Black, 1965), and the total SOC was determined by

combustion using a LECO-SC apparatus. At the end of trial,

in order to evaluate any variation in SOC, and minerals

content, soil treatment replicates were sampled again using

the same methods described above.

The total pruning biomass obtained from kiwifruit and

apricot sites was measured each year on 10 plants per plot

(30� treatment). Trees for sampling were selected from the

middle of treatment plots to avoid border effects. The same

plants were used to measure yield and determine canopy

biomass annually by collecting total leaves at leaf fall. For

each mowing operation, a weed biomass sample was taken

from a 1 m2 sample-area randomly distributed on each plot

(3� plot). Subsamples of about 500 g for each tree

Table III. Cumulative yield (fresh weight, t ha�1) and irrigation volumewater use efficiency (m3 water per t yield) and yield/residues ratio (dry w(LOM) plots of apricot and kiwifruit orchards

Yield (t) Irrigation (m3)

SPOM LOM SPOM LOM

Apricot 69�0 53�5� 8937 667Kiwifruit 136�7 91�6� 35 411 27 68

Comparing treatments in the same parameter � indicates a significant differencexCorrection made here after initial publication.

Copyright # 2009 John Wiley & Sons, Ltd.

component and weed were oven dried at 708C until a

constant dry weight was reached. The dried samples were

weighed and ground in a mixer ball mill to a fine powder

which was used for carbon determination (dry combustion

method, LECO-SC). Carbon inputs were calculated for each

biomass component by multiplying the carbon fraction by

the amount of biomass (dry matter) produced per component

and expressed as kg ha�1 y�1 using the respective tree

densities. On the same dried samples, concentrations of K

and P were spectrophotometrically determined (Varian, AA-

40) on the acid digested samples (H2SO4þHNO3), while N

was assayed using Kjeldhal’s method.

RESULTS AND DISCUSSION

Increase in net primary productivity and agronomic yields

has been associated with soil fertility remediation through

improvement of a number of soil properties leading to more

favourable conditions for plant physiology (Lal, 2006).

Throughout this 4-year experiment, the beneficial manage-

ment practices increased cumulative yields in the SPOM

treatment for apricot and kiwifruit orchards by 28 and 50 per

cent compared to the LOM (Table III). In each year of this

(m3 ha�1) throughout the 4-year experiment, mean annual specificeight) in the soil-protecting orchard management (SPOM) and local

Water use efficiency(m3 t�1x)

Yield/residues

SPOM LOM SPOM LOM

9� 129�5 124�8 0�25 0�67�

3� 303�2 403�9� 0�75 0�93�

at p< 0�05 (Student’s t-test).

LAND DEGRADATION & DEVELOPMENT, 21: 132–138 (2010)

Figure 2. Seasonal variation of nitrogen (ppm NO�3 ) in the 0–40 cm layer insoil under SPOM and local (LOM) management of kiwifruit orchard during

2007 year. Each point represents the mean of three soil cores� SE.

SOIL-PROTECTING PRACTICES IN FRUIT TREE ORCHARDS 135

experiment, the annual carbon input units (t ha�1) from crop

residue application resulted in 0�1–1�0 t ha�1 y�1 of

additional yield in apricot, while it ranged from 1�1 to

5�6 t ha�1 y�1 in kiwifruit. The positive yield response to

residue addition is in accordance with findings in annual

crop systems, but it is difficult to compare with fruit tree

cropping systems because of limited information available

in literature on this specific topic. Wilhelm et al. (1986)

among others (Gebrekidan et al., 1999; Mesfine et al., 2005)

reported significant linear relationship between crop residue

returned to the soil and grain production in corn and

soybean, concluding that it was mainly due to increased

stored soil water and reduced soil temperature. Carbon

inputs play an important role in supplying plant nutrients

(via mineralisation) which are critical to adequately sustain

crop production (Wilhelm et al. 1986; Kong et al., 2005).

Therefore, for the present research the improved soil

reservoir of some nutrients (Table IV), conceivably due to

the abundance of carbon inputs as coupled with irrigation,

can explain the increased yield in SPOM treatments although

a lower mineral fertilisation rate (Tables II and III).

Annual nitrogen incorporated in the soil of SPOM plots

was approximately 13 and 28 per cent higher than LOM

treatments for kiwifruit and apricot, respectively, while

phosphorous increased by about 90 per cent (kiwifruit) and

70 per cent (apricot) (Table II). The amount of potassium

was about 55 per cent increased in field under SPOM actions

in both kiwifruit and apricot, and based on chemical analyse

of water (not shown) irrigation noticeably contributed to K

increase (Table II).

Application of supplemental (mineral) nitrogen is

essential especially during the first years of the use of

residue and organic fertilisers because of its large use by soil

microorganisms to effect decomposition (Gebrekidan et al.,

1999). Generally, in soil under the SPOM treatment nitrogen

(NO�3 ) was detected at a mean concentration lower than that

observed in LOM treatment soils (i.e. about 20–30 ppm). As

an example, variations of NO�3 in kiwifruit plots are reported

in Figure 2 showing that nitrogen was on average 25�6 ppm,

Table IV. Total nitrogen, phosphorous and soluble potassium of soilmanagement practices

Initial

N (%) POlsen Ksolu

Kiwifruit0–15 cm 0�13 5�0 25�15–30 cm 0�10 3�0 33�

Apricot0–15 cm 0�12 8�2 14�15–30 cm 0�10 6�6 4�7

Comparing values of each element at the beginning and after 4 year in the same

Copyright # 2009 John Wiley & Sons, Ltd.

however in few dates (i.e. 7 May, 9 and 24 August) it was

detected at 11–19 ppm. By contrast, the mean NO�3 in

the LOM plots was 35�8 ppm excluding some peaks

(i.e. 26 May, 21 and 31 July). Thus, mean available soil

nitrogen in SPOM treatment was 70 per cent of that in LOM

one although N applied by mineral fertilisation was just 37

per cent of that distributed in LOM plots (Table II). In

addition, we noted that nitrogen concentration in SPOM

treatments was quite stable throughout the growing season

(except in some occasions) while in LOM soils it was more

variable and peaked at 90–110 ppm, increasing leaching risk

(Figure 2). This suggests a better balance between release

and use of nitrogen in the SPOM compared with the LOM system.

Figure 3 reports the allocation of the above-ground annual

carbon observed in the plots. The soil-protecting agricultural

actions significantly increased the biomass of weeds in both

kiwifruit and apricot orchards, the pruning material and

leaves biomass were comparable, while the fruit biomass

was significantly increased by SPOM techniques only for

kiwifruit (Figure 3).

Mean annual carbon inputs from crop biomass were 3�9and 2�0 t ha�1 y�1 in the SPOM and LOM kiwifruit treatments,

of kiwifruit and apricot orchards after 4 year of soil-protecting

After 4 year

ble N (%) POlsen Ksoluble

3 0�15 11�0 � 41�1�4 0�15� 6�1 39�0

2 0�18� 17�1� 25�1�0�16� 10�5 21�0�

orchard � indicates a significant difference at p< 0�05 (Student’s t-test).

LAND DEGRADATION & DEVELOPMENT, 21: 132–138 (2010)

Figure 3. Annual carbon allocation (kg ha�1 y�1) in different componentsof (A) apricot and (B) kiwifruit orchard under soil-protecting (SPOM) andlocal management practices (LOM). Data are 4-year mean� SE; comparingtreatments in the same specie � indicates a significant difference at p< 0�05

(Student’s t-test).

Figure 4. Total annual carbon (kg ha�1 y�1) (C INPUT) from above-groundweed and tree residues (biomass) and compost in (A) apricot and(B) kiwifruit orchard under soil-protecting (SPOM) and local management(LOM). Data are 4-year mean�SE; comparing treatments in the same specie

� indicates a significant difference at p< 0�05 (Student’s t-test).

136 G. MONTANARO ET AL.

while they were 4�5 (SPOM) and 1�3 (LOM) t ha�1 y�1 in the

case of apricot (Figure 4). Grass mowing and pruning

residues retention accounted for a large part (50 per cent for

the kiwifruit and 90 per cent for the apricot) of that inputs. A

limited amount of weed biomass (0�1–0�2 t ha�1) was

incorporated also in the LOM plots due to within-tillage

weed growth. Application of compost caused the total

carbon input to be considerably greater at 9�6 and

8�4 t ha�1 y�1 for apricot and kiwifruit, respectively

(Figure 4). These rates were 8–4 times higher than the

total carbon input received by LOM treatments. In plots

under LOM, carbon was returned to soil at a mean rate of

Table V. Soil texture (%) and soil paste pH of kiwifruit and apricot or

Texture (%

Sand Silt

Kiwifruit orchard0–15 cm 62�2 18�315–30 cm 60�0 20�630–60 cm 65�2 19�460–90 cm 40�8 19�4

Apricot orchard0–15 cm 25�4 49�215–30 cm 24�6 48�630–60 cm 22�1 49�460–90 cm 25�9 45�6

Copyright # 2009 John Wiley & Sons, Ltd.

1�3–2 t ha�1 y�1 that corresponded almost entirely to crop

leaves biomass (Figure 3). It has been reported that under

conservative land use, a minimum charge of carbon from

crop residues left to decompose on the soil surface of 6–

12 t ha�1 y�1 is required to maintain soil quality (Reeves,

1997), therefore the amounts of carbon returned to soil in

the LOM plots are presumably not enough to prevent the

decline of soil fertility.

Soil analysis showed a loamy-sand texture with alkaline

reaction (calcareous soil) for the apricot site, while the kiwi-

fruit soil was a sandyclay with a subalkaline pH(Table V).The

two soils were characterised by a very low content of SOC

chards soil samples

) Soil paste pH

Clay

19�5 7�6419�4 7�7915�4 7�7539�8 7�67

25�5 8�1526�8 8�0928�5 8�2728�6 8�14

LAND DEGRADATION & DEVELOPMENT, 21: 132–138 (2010)

Table VI. Soil organic carbon (%) of kiwifruit and apricot orchards

SPOM LOM

Initial After 4 year Initial After 4 year

Kiwifruit0–15 cm 1�34 1�39 ns 1�24 1�28 ns15–30 cm 1�18 1�20 ns 1�15 1�26 ns30–60 cm 0�69 0�74 ns 0�71 0�79 ns60–90 cm 0�54 0�65 ns 0�50 0�55 ns

Apricot0–15 cm 1�13 1�27 ns 1�11 1�19 ns15–30 cm 1�03 1�17 ns 1�23 1�19 ns30–60 cm 0�83 0�74 ns 0�89 0�85 ns60–90 cm 0�83 0�80 ns 0�88 0�82 ns

Comparing SOC values at the beginning and at the end of experiment in the same treatment ns¼ not significant at p< 0�05 (Student’s t-test).

SOIL-PROTECTING PRACTICES IN FRUIT TREE ORCHARDS 137

typical of degraded Mediterranean soils (Table VI) (Trinchera

et al., 1999; Bastida et al., 2006). The final content of SOC was

not affected by 4 years of different treatment practices, being

very close to the initial SOC content for the two sites and

treatments (Table VI). This result is in accordance with

Franzluebbers and Arshad (1996) who reported little or no

increase in SOC in the first 2–5 years after changing to

conservation management in canola–wheat–barley cropping

system. Results also agree with the idea that response of SOC

to changed practices (i.e. residue application and no tillage)

may only be expected from a long-term (�10 years)

perspective (Al-Kaisi and Yin, 2005).

The Mediterranean area is characterised by a dry summer

with little or no precipitation (Figure 1), consequently

irrigation is typically used to compensate for inadequate

rainfall for most of cultivated plants. At the end of 4th year,

cumulative irrigation volume reached 35 411 m3 ha�1 in

kiwifruit orchard under SPOM and up to 27 600 m3 ha�1 in

the LOM one, for the apricot orchard it reached approximately

8900 (SPOM) and 6700 (LOM) m3 ha�1 (Table III)x. It appears

that SPOM practices induced higher water consumption,

however to correctly interpret the treatment effects on that

consumption, irrigation volumes may well be related to yield.

That is, the analysis of water use efficiency (amount of water

per unit of yield) reveals that SPOM induced for kiwifruit a

better resource use (i.e. 25 per cent lower water use efficiency),

while in apricot that efficiency was similar in both treatment

(125–130 m3 per ton of harvested fruit) (Table III)x. Thus, it

appears that the SPOM actions may be, at least for kiwifruit, a

practicable set of techniques able to maximise yield per unit of

irrigation water.

The yield/residues ratio could help to guide the farmer’s

decision in order to identify the better equilibrium amidst

production and adoption of practices to increase carbon

input. For kiwifruit, a ratio of 0�75 seems to be optimal for

xCorrection made here after initial publication.

Copyright # 2009 John Wiley & Sons, Ltd.

both implementation of residues retention and achievement

of 50 per cent increased yield (Table III). In the apricot

orchard, SPOM techniques induced a lower yield increase

(28 per cent), thus, the yield:residues ratio of 0�25 (Table III)

could be increased via rising yield. It is likely that the

additional inorganic nitrogen of 17 kg ha�1 y�1 needs to be

adjusted (increased) in order to promote nutrient release

from crop residues by mineralisation processes and

adequately sustains crop productivity (Gebrekidan et al.,

1999; Loveland and Webb, 2003).

CONCLUSIONS

This study focused on the critical issue of increasing SOC in

croplands through the addition of crop residues, organic

amendments and the reduction in soil disturbance. Under that

practices the mean annual carbon inputs was increased from

approximately 1�5 to 9�0 t ha�1 without significative effect on

SOC content, while yield increased by 28 and 50 per cent in

apricot and kiwifruit, respectively. It could be concluded that

the soil-protecting actions positively affect the yield (mainly

via improving the reservoir of minerals in soil in spite of a

lower mineral fertilisation rate) and increase the soil carbon

inputs that reasonably represents a prerequisite to maintain

and increase SOC pools (Reeves, 1997).

ACKNOWLEDGEMENTS

This study was financially supported by the Italian Ministry

of University and Scientific Research. Special grant BRI-

MET. Authors thank Mr. A. Mossuto (NaturaInformatica

Soc. Coop) for field assistance.x

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