Organic matter pools and nutrient cycling in different coffeeproduction systems in the Brazilian Cerrado

Eduardo Barros Marinho • Aline Lima de Oliveira • Daniel Basılio Zandonadi •

Luiz Eduardo Celino Benedito • Ronessa Bartolomeu de Souza •

Cıcero Celio de Figueiredo • Jader Galba Busato

Received: 5 February 2014 / Accepted: 7 June 2014 / Published online: 19 June 2014

� Springer Science+Business Media Dordrecht 2014

Abstract Agroforestry and organic systems have

been used to reduce the negative effects that conven-

tional coffee cultivation has on soils. In this work,13C-CPMAS-NMR, Fourier transform infrared spec-

troscopy, elemental composition, classical humus

fractionation and the soil fertility status were used to

evaluate the impact of these three systems on a Latosol

from the Brazilian Cerrado. Continuous input of tree

residues promoted changes to the soil organic matter

with increase in total organic carbon, humic acids

(HA) and light organic matter, mainly in the topsoil.

Available P and cation exchange capacity were also

increased and the acidity status decreased in the

agroforestry system. Moreover, HA from the agrofor-

estry were enriched in O-alkyl C, O-di-alkyl C and

alkyl C groups and the organic system resulted in

HA richer in carboxyl groups. The conventional

system resulted in greater aromatic and methoxyl

participation, and lower phenol groups. HA from the

agroforestry system were richer in easily degradable

structures and the chemical fractionation demon-

strated a decrease in both recalcitrant fractions,

allowing for a more conservative and sustainable

management of soil fertility. The modifications were

not as evident in the organic system, probably due to

the low organic fertilizer input.

Keywords Agroforestry � Organic cultivation �Humic acids � 13C-CPMAS-NMR spectroscopy

Introduction

Coffee is one of the most widely consumed food

products in the world and Brazil is the main producer

E. B. Marinho � L. E. C. Benedito � C. C. de Figueiredo �J. G. Busato (&)

Faculdade de Agronomia e Veterinaria, Universidade de

Brasılia (UnB), Campus Universitario Darcy Ribeiro -

Asa Norte, Caixa Postal 4508, Brasılia,

DF CEP 70910-970, Brazil

e-mail: jaderbusato@unb.br

E. B. Marinho

e-mail: e_barros.m@hotmail.com

L. E. C. Benedito

e-mail: leduardo420@gmail.com

C. C. de Figueiredo

e-mail: cicero@unb.br

A. L. de Oliveira

Instituto de Quımica, Universidade de Brasılia (UnB),

Campus Universitario Darcy Ribeiro - Asa Norte,

Brasılia, DF CEP 70910-970, Brazil

e-mail: aline.alo@gmail.com

D. B. Zandonadi � R. B. de Souza

Empresa Brasileira de Pesquisa Agropecuaria

(EMBRAPA), Centro Nacional de Pesquisa de Hortalicas

(CNPH), Brasılia, DF CEP 70359-970, Brazil

e-mail: daniel.zandonadi@embrapa.br

R. B. de Souza

e-mail: ronessa.souza@embrapa.br

123

Agroforest Syst (2014) 88:767–778

DOI 10.1007/s10457-014-9723-4

and exporter of green coffee, accounting for approx-

imately 35 % of the global production (Monteiro and

Farah 2012). The coffee farms are responsible for

millions of jobs and about 7 % of all Brazilian

agribusiness exports in 2012 were due the coffee

activity. However, besides its economic and social

importance, coffee cultivation strongly changes agro-

ecosystem characteristics. The loss of soil organic

matter (SOM) and decrease in nutrients levels due to

soil disturbance and runoff in conventional systems

favor the impoverishment of highly weathered soils.

Also, mineral nitrogen fertilizer inputs increase soil

acidity and enhance greenhouse gas emissions as N2O,

which has greater global warming potential than CO2

(Stehfest and Bouwman 2006; Chu et al. 2007).

Many practices have been proposed to reduce the

negative effects of coffee cultivation. Agroforestry

systems are structurally diverse compared to mono-

cropping and frequently improve the use of natural

resources by both temporally and spatially accessing

different sources of light, water and nutrients (Moreno

and Obrador 2007). Introduction of trees in agrofor-

estry systems enhances the potential energy as

biomass and results in a larger carbon stock in soils,

favoring nutrient cycling and plant growth (Khanna

1997; Hergoualc’h et al. 2012). Furthermore, trees

decrease water runoff, protecting the soil against

erosion (Cannavo et al. 2011). Organic production

systems also have been used to restore the soil quality.

Organic farming avoids the use of synthetic high

soluble fertilizers and emphasizes organic inputs as

nutrients source (Araujo et al. 2008). In Brazil

approximately 800,000 hectares are occupied by

organic crops (Willer et al. 2008), but there is a clear

increasing trend to support both great national and

international market demands.

Besides total carbon stocks and nutrient status of

soil, SOM chemical compartments are changed when

agroforestry or organic managements are established

(Aranda et al. 2011; Benbi et al. 2012; Guimaraes et al.

2013). Humic substances (HS) are the major compo-

nents of stabilized SOM and the most widespread

natural products found on the Earth’s surface. Changes

in the distribution, functionality and molecular com-

position of HS have been successfully used to assess

the impact of management on agricultural environ-

ments (Canellas et al. 2010). Humus fractionation by

chemical procedures and non-destructive spectro-

scopic techiques such as Fourier Transform Infrared

Spectroscopy (FT-IR) and cross-polarization magic-

angle-spinning nuclear magnetic resonance (13C-

CPMAS-NMR) are useful methods for the character-

ization of the HS, enabling increased knowledge on

the influence of crops on soil quality.

Based on these facts, this study was carried out to

determine the influence of agroforestry and organic

coffee systems, in comparison to conventional system,

on nutrient levels, HS content and characteristics in a

Latosol from the Brazilian Cerrado. The hypothesis

evaluated was that the combined use of tree species

and crops, or the adoption of organic crop production,

improved soil quality by increased nutrients and HS

due to a higher and efficient cycling when compared

with the conventional system.

Materials and methods

Site characterization and experimental design

The Brazilian Cerrado is the most extensive area of

savanna-type vegetation in South America, originally

covering about 2,000,000 km2. The major areas of

Cerrado are located on the Central Brazilian Plateau,

presenting annual rainfall between 1,100 and

1,600 mm, concentrated in the months of October to

April. Long-term mean temperatures of the site range

between 22 and 24 �C (Buol 2009). An experiment

involving the cultivation of coffee in agroforestry,

organic and conventional systems was established in

2007 at the Centro Nacional de Pesquisas de Hortalicas

(Embrapa Hortalicas) farm, located at 15�560700S and

48�80900W, 997 m elevation, in Brasilia—DF, Brazil

(Fig. 1). The agroforestry system consisted of planta-

tions of Gliricidia sepium (Jacq.) Steud in close

association with coffee plants (Coffea arabica L). The

organic system consisted of cultivation that received

only fertilizer permitted for organic production. Both

the agroforestry and organic systems received organic

composts at planting produced from castor meal

(300 g plant-1), lime (2 ton ha-1) and magnesium

thermophosphate (500 g plant-1). After planting, the

coffee plants received an organic fertilizer every

6 months based on cattle and chicken manure and

castor meal at the rate of 300 g plant-1. No pesticides or

chemical weed control were used at these sites. To

conventional system, lime (2 ton ha-1) and cattle

manure (5 L plant-1) were applied at planting. During

768 Agroforest Syst (2014) 88:767–778

123

the first year, 170, 100 and 300 g plant-1 of N, P2O5 and

K2O, respectively, were applied as mineral soluble

fertilizers. After the second year, mineral fertilization

consisted of 60 g plant-1 of P2O5, 80 g plant-1 of both

N and K2O per year, again using soluble sources.

Mechanical and chemical weed controls were per-

formed and as well chemical pesticides were occasion-

ally used.

Soil samples

Soil was classified as Dystrophic Red–Yellow Latosol

according to the Brazilian taxonomy system (Embrapa

2006), corresponding to a Typic Haplustox according

to the US soil taxonomy system (Soil Survey Staff

2010). In September 2012, each coffee production

system was divided into three plots of approximately

100 m2. In each plot, twenty soil sub-samples were

randomly collected to obtain a composite soil sample.

Three sampling depths were considered: 0–0.05,

0.05–0.10 and 0.10–0.20 m.

Laboratory analysis

Chemical and physical properties

The soil samples (three replicates for each system) were

transported to the laboratory in plastic bags, air dried,

sieved through a 2-mm screen and stored prior to

analysis according to Embrapa (1997). The pH was

measured in water (soil:solution relationship equal to

1:2.5); P and K? were extracted by Mehlich–1 solution;

Ca2?, Mg2? and Al3? were extracted with KCl

1 mol L-1. Total organic carbon (TOC) was deter-

mined by the modified Walkley–Black procedures

(Yeomans and Bremner 1988). Mineral particle-size

distribution was analyzed using the pipette method

(Embrapa 1997). Prior to start the experiment, the soil

presented the following chemical characteristics: 5.2 of

pH H2O; 5.1 mg dm-3 of P; 30.0 mmolc dm-3 of Al3?,

28.0 mmolc dm-3 of Ca2? ? Mg2?, 2,4 mmolc dm-3

of K?, 80.5 mmolc dm-3 of total acidity and

29.8 g dm-3 of organic matter.

Fig. 1 Location of sampling sites in agroforestry, organic and conventional coffee systems in the Brazilian Cerrado: (1) organic

system; (2) agroforestry system; (3) conventional system

Agroforest Syst (2014) 88:767–778 769

123

Organic matter fractionation

Soil samples were pre-treated with a 2 mol L-1

orthophosphoric acid solution which separated the

light organic matter (LOM) through density and also

solubilized the free fulvic acids (FFA) fractions.

Thereafter, a 0.1 mol L-1 NaOH solution was added

to residual soils (1:20, v:v), which solubilized the

fulvic acids (FA) and humic acids (HA). The insoluble

solid residue resulting from the fractioning process

was called as humins (HUM). HA were separated from

the FA through centrifugation after precipitation in

acid medium using concentrated H2SO4 to pH 1–1.5.

The carbon content of FFA, FA, HA and HUM was

determined according to Yeomans and Bremner

(1988). Light organic matter was determined using

an analytical balance.

Humic acids extraction

Soluble humic substances were extracted from the top

soil samples (0–0.05 m) by adding 200 mL of a

0.1 mol L-1 NaOH solution to 10 g soil samples,

followed by 16 h of agitation at room temperature

under N2 atmosphere. The dark colored supernatant

solution was separated from the residual fraction by

centrifugation (3,000g, 30 min). The insoluble residue

was re-suspended in 200 mL of 0.1 mol L-1 NaOH

and shaken for 4 h. Then, the solution was centrifuged

again and the previously collected supernatant was

added. This procedure was repeated until a clear

solution was obtained. The extracted alkaline solution

was acidified to pH 1.0–1.5 with concentrated H2SO4

and the HA was separated from the FA by centrifu-

gation at (5,000g, 15 min). The HA was treated with

100 mL of a dilute HF-HCl solution [5 mL HCl (36 %

m/v) ? 5 mL HF (48 % m/v)] and agitated overnight.

After centrifugation (5,000g, 15 min), the HA was

repeatedly washed with deionized water, dialyzed

against deionized water using a 12–14 kDa-cutoff

membrane (Thomas Scientific, Inc) and freeze-dried.

13C-CPMAS-NMR spectroscopy and elemental

composition

Humic acids extracted from the top soils (0–0.05 m)

were characterized by solid state carbon nuclear

magnetic resonance (13C-CPMAS-NMR) using a

Varian Mercury 300 at 75.452 MHz. Samples of the

HA were packed in zirconia rotors with Kel-F caps and

spun at 13 ± 1 kHz. To account for possible inhomo-

geneity of the Hartmann–Hahn condition at high rotor

spin rates, a 1H ramp sequence was applied in CP

experiments during a contact time (CT) of 1 ms.

Experiments were conducted at an acquisition time of

20 ms and a recycle delay of 2.0 s. The ACD/NMR

processor software was used to collect and elaborate

the spectra. The areas for different 13C resonances

were assigned into six integrating regions: 0–46 ppm

(aliphatic C; alkyl), 47–66 ppm (methoxyl C; meth-

oxyl/N-alkyl), 67–111 ppm (oxidized and/or carbo-

hydrate C; O-alkyl; anomeric C; di-O-alkyl),

112–141 ppm (unsubstituted and alkyl-substituted

aromatic C; aryl), 142–164 ppm (oxygen substituted

aromatic C from lignin and nonhydrolyzable tannins;

phenolic, O-aryl) and 165–188 ppm (aliphatic and

aromatic carboxyl C, C in amidic groups; carboxyl/

amide). Elemental composition of the HA was deter-

mined using a Perkin Elmer 2400 Series II.

Fourier Transform Infrared Spectroscopy

Fourier Transform Infrared Spectroscopy spectra of

HA were recorded on KBr pellets in the

400–4000 cm-1 wave number, with a 4 cm-1 resolu-

tion and 16 scans for each sample using a Varian 640

spectrophotometer. A mixture of 1 mg HA and

100 mg KBr was pressed to obtain the KBr pellets.

The spectra subtraction procedure was used to infer

the H2O and CO2 contaminations.

Statistical analysis

Changes in the carbon pools and soil fertility were

analyzed according to a complete randomized design.

The coffee systems and sampling depths were con-

sidered as primary and secondary effects, respectively.

Results were submitted to variance analysis and the

means were compared via the Tukey test (p \ 0.05).

The data of all variables together was subjected to

principal component analysis (PCA), based on linear

combinations of the original variables on the inde-

pendent orthogonal axes. This analysis was performed

for distinction of the different coffee production

systems, considering all the attributes together

(TOC, LOM, CFFA, CHA, CFA, CHUM, pH, Al3?,

H ? Al?3, Ca2? ? Mg2?, K?, effective CEC, CEC

(pH 7.0), SB, P, V and m). Statistical analyses were

770 Agroforest Syst (2014) 88:767–778

123

performed using the software XLSTAT 2011 (Addin-

soft 2011).

Results and discussion

Chemical properties of the soils varied significantly

among the coffee productions systems (Table 1). In

the 0–0.05 m layer, controlled soil acidity was

observed when the agroforestry or organic systems

were implanted. The soil exchange complex under the

conventional system was saturated with Al3? (mean of

15.1 % for the three depths), indicating the absence of

a residual effect from the lime after 5 years of coffee

planting. Low pH in the conventional system was

presumably due to the high doses of nitrogenous

fertilizers in the ammoniacal form. Conversion of

ammonium to nitrate in soils, as well the continued

uptake of NH4? by plants, are followed by the release

of H? ions, increasing the acidity and decreasing the

base reserves (Middleton and Smith 1979). Moreover,

the conventional system showed the lowest values for

pH, sum of bases, base saturation and (Ca2? ? Mg2?),

whereas the agroforestry and organic systems, which

did not receive mineral fertilizer applications, pre-

sented an exchange complex occupied by cations with

alkaline character and low acidity index, mainly in the

top soil. The lowest values of Al3? and H ? Al3? in

conservation tillage systems, especially under organic

management, may be the result of Al3? complexing by

low molecular weight organic acids in soils (van Hees

et al. 2001).

The organic system was particularly effective in

neutralizing acidity even in the deepest soil layer. On

the other hand, control of acidity by the agroforestry

system occurred only in the two shallowest samples

(0–0.05 and 0.05–0.10 m) and similar values to those

in the conventional system were observed at increased

depths. In forest systems, the action of low weight

molecular organic acids on aluminium complexing is

higher in the surface soil layers, decreasing with depth

(van Hees et al. 2001). Increase in soil acidity was also

observed in areas covered with tree-legumes when soil

samples were obtained at depths deeper than 0.10 m

(Schiavo et al. 2009). This behavior can be associated

with biological nitrogen fixation since when main-

taining the intracellular pH, and making the fixation

process effective, the legume species perform H?

extrusion with consequent rhizosphere acidificationTa

ble

1C

hem

ical

attr

ibu

tes

of

soil

fert

ilit

yo

nd

iffe

ren

tsy

stem

so

fco

ffee

pro

du

ctio

nin

the

Bra

zili

anC

erra

do

Cro

p

syst

em

Dep

th

(m)

pH

(H2O

)

Al3

?

(mm

ol c

dm

-3)

(H?

Al)

(mm

ol c

dm

-3)

Ca2

??

Mg

2?

(mm

ol c

dm

-3)

K?

(mm

ol c

dm

-3)

Eff

ecti

ve

CE

C

(mm

ol c

dm

-3)

CE

C(p

H7.0

)

(mm

ol c

dm

-3)

SB

(mm

ol c

dm

-3)

P (mg

dm

-3)

V(%

)m

(%)

San

d

(gdm

-3)

Sil

t

(gdm

-3)

Cla

y

(gdm

-3)

Conven

tional

0–0.0

55.3

c4.5

a80.5

a18.5

c5.9

b28.9

c104.8

b24.4

c18.0

b23.2

c15.6

a637.4

100.5

262.1

Org

anic

6.4

a0.0

c47.9

c42.0

b6.6

a48.6

b96.4

c48.6

b15.0

c50.4

a0.0

c612.9

105.9

281.2

Agro

fore

stry

6.0

b0.5

b59.0

b50.5

a3.5

c54.5

a113.0

a54.0

a22.9

a47.8

b0.9

b595.6

118.2

286.2

Conven

tional

0.0

5–0.1

05.3

c4.0

a78.4

a18.8

c5.6

a28.3

c102.7

a24.3

c17.6

a23.7

c14.1

a615.6

113.2

271.2

Org

anic

6.2

a0.0

c48.3

c40.0

a2.3

c42.3

a90.5

b42.3

a7.7

c46.7

a0.0

c602.0

110.9

287.1

Agro

fore

stry

5.7

b1.0

b65.6

b33.3

b3.4

b37.7

b102.2

a36.7

b12.0

b35.9

b2.6

b616.5

117.3

262.2

Conven

tional

0.1

0–0.2

05.4

b4.0

a76.3

a17.3

b4.4

a25.7

a98.0

a21.7

b9.4

a22.1

b15.6

b639.7

109.1

251.2

Org

anic

6.0

a0.5

b49.1

c25.0

a1.9

b27.4

a76.0

c26.9

a5.7

b35.5

a1.8

c590.2

92.7

317.1

Agro

fore

stry

5.5

b4.3

a68.1

b13.5

c1.6

c19.8

b83.1

b15.1

c2.6

c18.2

c23.0

a599.7

109.7

291.2

Sum

of

bas

es(S

B)

=C

a2?

?M

g2?

?K

?;

Eff

ecti

ve

cati

on

exch

ange

capac

ity

=S

B?

Al3

?;

Cat

ion

exch

ange

capac

ity

atpH

7.0

(CE

Cp

H7

.0)

=S

B?

(H?

Al3

?);

Bas

esa

tura

tion

(V)

=100

9S

B/T

;A

lum

inum

satu

rati

on

(m)

=100

9A

l3?

/t.

For

each

layer

,av

erag

esfo

llow

edby

the

sam

ele

tter

inth

eco

lum

nar

enot

stat

isti

call

ydif

fere

nt

(Tukey

test

,p

\0.0

5)

Agroforest Syst (2014) 88:767–778 771

123

(Marschner and Romheld 1983). Additionally, in

samples obtained from the agroforestry system at

0.05–0.10 and 0.10–0.20 m, there was decrease in the

Ca2? ? Mg2? content, probably due to absorption by

the tree which allowed for an increased soil acidity

index. The pH values of 6.4 and 6.0 for the organic and

agroforestry systems in the 0–0.10 m samples, respec-

tively, justify the absence or low level of exchangeable

Al3? in these managements (Table 1).

Available P was significantly increased in the

agroforestry system compared to the organic and

conventional systems in the top soil (Table 1). Content

of available P depends on soil management and

cropping systems, where accumulation of SOM usu-

ally results in higher levels of available P (Cardoso

et al. 2003; Busato et al. 2005; Canellas et al. 2010).

The turnover of P forms accumulated in vegetal

biomass produced in higher amounts by arborous

legume species contributed to these increased P levels.

Degraded soils re-planted with Acacia mangium also

increased the available P in a relatively short time

period (3 years) due a combined effect of nutrient

cycling and reduced P fixation resultant of the higher

SOM content (Schiavo et al. 2009). However, the

agroforestry system showed a marked decrease of P in

the samples obtained at 0.10–0.20 m. The complex

system involving trees and coffee plants influenced the

dynamics of P through the conversion of a portion of

the inorganic P into organic forms, mainly in deeper

layers (Cardoso et al. 2003). It was possible that part of

the inorganic P present in agroforestry soils was

converted to organic forms that are not reached by the

extractor used in the available P analysis (Nelson et al.

1953). Levels of organic P forms increased consider-

ably in agricultural soils when managements based on

preservation of SOM are adopted (Busato et al. 2005).

Under these conditions, diester organic phosphates

can be protected against microbial degradation in the

hydrophobic domain of SOM (Canellas et al. 2010),

forming an important reservoir for P in soils.

Total organic carbon was about 15 % higher in the

0–0.05 m layer when tree-legumes were cultivated

together with coffee plants (Table 2). Conservation

practices using leguminous cover crops and inputs of

organic amendments improve the plant biomass

production by increasing the quantities of residues

added to the soil (Guimaraes et al. 2013). The presence

of trees promoted frequent input of plant tissues,

mimicking natural systems by increasing residue

returns and minimizing C removal. In the Brazilian

Cerrado, however, carbon mineralization is particu-

larly fast due to the high temperature, rainfall and

microbial activity (Kaschuk et al. 2010). Therefore,

only managements with constant input of organic

residues enable accumulation and increase in the TOC.

The volume of compounds applied in the organic

system was not sufficient to alter the TOC, resulting in

a value similar to that observed in the conventional

system. Furthermore, no differences in the TOC were

observed between the three systems in the deeper

layers. The results are in agreement to those of

Guimaraes et al. (2013), who reported greater SOM in

the upper layer of cultivated soils using conservation

practices when compared with conventional systems,

although there was no difference for depths below

0.10 m. The absence of soil disturbance, natural

mulching and the relatively short time of agroforestry

implementation may have resulted in accumulation of

SOM on the soil surface, retaining these residues

isolated from the rest of the soil profile.

Although differences in the SOM content were

observed only in the upper layer, adoption of both

organic and agroforestry systems greatly affected the

carbon pools distribution even in the deeper layers

(Table 2; Fig. 2). In the 0–0.05 m layer, the agrofor-

estry system showed the highest LOM content, which

represented 20 % of all fractions (Fig. 2). The

conventional system showed only 5 % of LOM and

most of the organic matter (77 %) was related to the

most recalcitrant carbon form (HUM). The organic

system had 38 % more alkali-soluble forms

(HA ? FA) than the other management systems.

Increase in the LOM and soluble alkaline forms in

the agroforestry and organic systems, respectively,

were followed by decreases in the HUM fractions,

showing conversion among carbon forms. A similar

result was observed for the 0.05–0.10 m depth in

agroforestry systems, with higher LOM content and

decrease in the HUM fraction when compared to the

conventional system (Table 2). Furthermore, a slight

increase in the FFA fraction was observed. No

alterations were noticed between organic and conven-

tional systems at this depth. Even in the samples

obtained for the 0.10–0.20 m depth, the agroforestry

system showed a higher LOM fraction and lower value

for HUM. Alkali-soluble forms represented 15 % of

total carbon in the agroforestry system, while both

organic and conventional systems presented 10 and

772 Agroforest Syst (2014) 88:767–778

123

6 %, respectively. No LOM fraction was detected in

the conventional system at the deepest sampled layer.

Two principal components (PC1 and PC2) were

generated (Fig. 3). These components were created as

tools to discriminate the effects of the different coffee

production systems, considering the organic matter

fractions (TOC, LOM, CFFA, CHA, CFA and CHUM) and

chemical characteristics (pH, Al3?, H ? Al3?,

Ca2? ? Mg2?, K?, effective CEC, CEC (pH 7.0), SB,

P, V and m) together for the layers of 0–0.05 m

(Fig. 3a), 0.05–0.10 m (Fig. 3b) and 0.10–0.20 m

(Fig. 3c). The distribution of selected variables showed

cumulative variance of 87.3, 90.8 and 87.6 % for the

sum of the principal components PC1 and PC2 in the

layers of 0–0.05, 0.05–0.10 and 0.10–0.20 m, respec-

tively. For all layers, the PC1 and PC2 axes separated the

three systems: conventional, organic and agroforestry.

This distinction indicates that the managements adopted

for coffee production in weathered Latosols with

different inputs of organic material changes the chem-

ical composition, leaving a distinct soil profile as a

function of agricultural management.

Despite this general pattern of distinction, accord-

ing to the PC1 axis which is responsible for the largest

percentage of explained variance in the 0–0.05 m

layer, it may be possible to observe that conservation

systems (organic and agroforestry) differed from the

conventional system, influenced by greater accumu-

lation of organic matter fractions and cation exchange

complexes and reduction of acidity components in

conservation tillage systems. In the 0.05–0.10 m layer,

there was clear distinction between organic and

conventional systems, with the agroforestry system

presenting intermediate behavior. In this layer and also

in the 0–0.05 m layer, the organic system generally

higher levels of carbon in fractions of humified

organic matter, reduction of acidity components, and

increase in the sum of bases and exchange complexes.

In the 0.10–0.20 m layer, the three systems showed

distinct patterns. This differentiation was influenced

by the accumulation of nutrients derived from mineral

fertilizers in the conventional system by reducing the

acidity components promoted by the organic system,

as well as by increasing the acidity in the agroforestry

system, despite its high capacity to accumulate LOM

in that layer (Tables 1, 2).

Humic acids content also varied greatly among

systems. In the 0–0.10 m layer, mean HA concentra-

tions were 1.3, 1.8 and 1.5 g kg-1, respectively, for

the conventional, organic and agroforestry systems

(Table 2). Both organic and agroforestry systems were

38 and 19 % richer in HA content, respectively, as

compared with the conventional system. Elemental

composition and atomic ratios of the HA are listed in

Table 3. The C content of the HA varied from 425.0 to

481.9 g kg-1 and only slight modifications were

observed for N and H contents among the manage-

ments (from 37.3 to 40.1 and 42.6 to 44.9 g kg-1,

respectively, for N and H). A high C/N ratio is

considered to indicate a high stability of humus and

large degree of condensed structures (Stevenson

1994). Therefore, organic and conventional systems

presented HA traditionally interpreted as humic

material with an advanced humification stage.

Table 2 Total organic carbon (TOC) and carbon content in the

light organic matter (LOM), free fulvic acids (FFA), fulvic

acids (FA), humic acids (HA), humins (HUM) and humic

acids:fulvic acids ratio (CHA/CFA) in different systems of

coffee production from Brazilian Cerrado

Crop system Depth

(m)

TOC

(g kg-1)

LOM

(g kg-1)

CFFA

(g kg-1)

CHA

(g kg-1)

CFA

(g kg-1)

CHUM

(g kg-1)

CHA/

CFA

Conventional 0–0.05 23.0 b 0.8 b 0.6 b 1.3 b 0.7 b 11.7 b 1.9

Organic 22.7 b 1.5 b 1.1 a 1.8 a 1.7 a 13.8 a 1.1

Agroforestry 26.1 a 3.8 a 0.9 ab 1.5 ab 0.9 b 11.5 b 1.7

Conventional 0.05–0.10 22.9 a 0.4 b 1.1 b 1.4 a 1.7 ab 12.0 b 0.8

Organic 20.2 b 1.0 b 1.3 a 2.0 a 2.2 a 20.0 a 0.9

Agroforestry 21.9 ab 1.9 a 1.0 b 1.0 b 1.4 b 10.0 b 0.7

Conventional 0.10–0.20 21.8 a 0.0 c 0.9 b 0.6 a 0.3 b 12.1 b 2.0

Organic 19.4 b 0.5 b 0.9 ab 0.9 a 0.8 a 13.9 a 1.1

Agroforestry 19.4 b 0.9 a 1.2 a 1.5 a 1.2 a 11.5 b 1.3

For each layer, averages followed by the same letter in the column are not statistically different (Tukey test, p \ 0.05)

Agroforest Syst (2014) 88:767–778 773

123

The changes, however, were not restricted to the

amount of HA or content of C in this humic fraction,

but also the structural composition, resulting in

different spectroscopic signature when the HA from

the topsoil were analyzed by 13C-CPMAS-NMR

(Fig. 4; Table 3). HA from the agroforestry system

were enriched in O-alkyl C and O-di-alkyl C

(67–111 ppm), as well in alkyl C groups

(0–46 ppm). The conventional system resulted in

HA with greater aromatics (112–141 ppm and me-

thoxyls (47–66 ppm) and lesser participation of phe-

nols (142–164 ppm); the organic system was enriched

with HA in carboxyl groups (165–188 ppm). In the

aliphatic C region, a sharp peak centered at 30 ppm,

assigned to methylene C from waxes, lipids, cutin and

suberin polymers (Quideau et al. 2000; Keeler et al.

2006), was observed in the HA from the agroforestry

Fig. 2 Percent distribution of humidified fractions of the

organic matter from soils in 0–0.05 m (a), 0.05–0.010 m

(b) and 0.10–0.20 m (c). 100 % = FFA ? FA ? HA ?

HUM ? LOM, respectively representing the carbon content

present in the free fulvic acids, fulvic acids, humic acids, humins

and low organic matter

Fig. 3 Ordination diagram derived from the principal compo-

nent analysis of the scores of treatments under different coffee

production systems: a 0.00–0.05 m, b 0.05–0.10 m,

c 0.10–0.20 m

774 Agroforest Syst (2014) 88:767–778

123

and organic systems. These systems also showed a

signal at 47 ppm, attributed to methylene or methine C

groups in amino acids residues (Almendros et al.

2000). In the conventional system, the peak at

30 ppm was decreased and widened, typical of

humic material with a greater chemical stability.

Agroforestry exhibited various signals between 53

and 111 ppm, the region of readily degradable

aliphatic groups. On the other hand, only signals

at 56 and 74 ppm were observed in the organic

system. In turn, the conventional system showed

extended signals between 52–57 ppm, 68–74 ppm

and 107–111 ppm, typical for more humified humic

material (Preston et al. 1994). This may be a result

of the absence of new inputs of organic materials in

the conventional system, which preserved only

recalcitrant structures in HA.

Stabilized HA are usually enriched in paraffinic

structures resistant to degradation such as cutin and

suberin (C-alkyl; 0–46 ppm) and this spectral region

was slightly increased in the agroforestry system,

which could be associated with the chemical nature of

residues from Gliricidia. Extended signals between

124 and 145 ppm observed in the organic and

conventional systems are characteristic of aromatic

C-transformed and recalcitrant structures. Instead of

an extended signal, the agroforestry system showed

multiple peaks in that region (126, 132, 135, 141 and

145 ppm). Modifications of the aromatic lignin rings

decreased the signal of aromatic groups (112–

120 ppm) in the organic system and promoted the

presence of a peak near 132 ppm. All managements

presented a signal near 75 ppm, assigned to C-car-

boxyl derived polypeptides (Keeler et al. 2006). The

spectra of organic and agroforestry management

systems, however, showed an additional signal at

181 ppm, assigned to the C-carbonyl group.

Similarities between HA from the three different

managements were observed in the FT-IR spectra

(Fig. 5), especially in the regions of 3,500, 2,950,

2,800, 1,650 and 1,450 cm-1 and only slight differ-

ences were detected in the regions of 1,250 and

1,000 cm-1. The different absorption bands were

identified according to Colthup et al. (1964), Bloom

and Leenheer (1989) and Stevenson (1994). Intense

and broad band absorption around 3,500 cm-1 due to

OH stretching vibrations and NH was observed in all

managements. Absorption near to 2,950 cm-1 was

due to stretching vibrations of CH bonds (CH3

aliphatic) and that near 2,800 cm-1 can be associated

with aldehydes. Absorption at 1,650 cm-1 is due to

amides and near 1,450 cm-1 may be attributed to

deformation vibrations of aliphatic CH (CH2 and

CH3). Broad bands at 1,250 cm-1, associated with the

presence of CO carboxylic groups, ether or phenol,

were slightly more intense in the organic and conven-

tional systems. Finally, absorption near 1,000 cm-1,

intense in the agroforestry system, was due to

stretching of C–O from polysaccharides.

Conclusions

The adoption of agroforestry promoted changes in the

soil that resulted in a chemical environment more

favorable to coffee plant development, i.e., less acid

environment, more available cations and P. The

organic system decreased the effects of acidity typical

of Latosol in the Cerrado, generating a favorable

environment for proper development of coffee plants.

Table 3 Elemental

composition and 13C-

CPMAS-NMR integrated

area of humic acids in

topsoil (0–0.05 m)

extracted from different

coffee production systems

Elemental composition (g kg-1) Conventional Organic Agroforestry

Carbon 464.6 481.9 425.0

Hydrogen 42.6 44.9 43.1

Nitrogen 38.5 40.1 37.3

C/N ratio 12.1 12.0 11.413C-CPMAS-NMR integrated area (%)

0–46 ppm (Alkyls) 23.6 23.6 24.3

47–66 ppm (Methoxyls) 16.6 14.7 14.5

67–111 ppm (Carbohydrates and sugars) 23.2 23.4 25.4

112–141 ppm (Aromatics) 18.6 16.6 16.0

142–164 ppm (Phenols) 7.3 8.2 8.9

165–188 ppm (Carboxyls) 10.7 13.6 11.0

Agroforest Syst (2014) 88:767–778 775

123

Fig. 4 CPMAS 13C-NMR

spectra of humic acids

isolated from a Latosol

under different coffee

production systems:

a conventional, b organic

and c agroforestry systems

776 Agroforest Syst (2014) 88:767–778

123

However, effects of changes promoted by this system

on other soil characteristics were not so evident,

probably due to the lower organic fertilizer input,

suggesting that for weathered Latosol from the

Brazilian Cerrado the incorporation of organic mate-

rials must be constant to alter the structural properties

of the SOM. Although it is very well documented that

the HA fraction is not, quantitatively, the major

portion of humic material in soils, this fraction can be

successfully used to describe the status of soil quality

according to the management to which they are

submitted. The 13C-CPMAS-NMR showed that HA

from the agroforestry system was richer in easily

degradable structures, and chemical fractionation

showed a decrease in both recalcitrant fractions and

accumulations of other less humified fractions.

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