Quantitative and qualitative changes of humus in whole soils and their particle size fractions as influenced by different levels of compost application

doi:10.4236/as.2011.21001

Paper Menu >>

Journal Menu >>

Vol.2, No.1, 1-8 (2011) Agricultural Sciences

doi:10.4236/as.2011.21001

Quantitative and qualitative changes of humus in whole

soils and their particle size fractions as influenced by

different levels of compost application

Thu Ha Nguyen, Haruo Shindo*

Faculty of Agriculture, Yamaguchi University, Yamaguchi, Japan; *Corresponding Author: shindo@yamaguchi-u.ac.jp

Received 11 November 2010; revised 24 December 2010; accepted 7 January 2011

ABSTRACT

Effect of long-term application (ca. 30 years) of

compost at different levels on humus composi-

tion of whole soils and their particle size frac-

tions in a field subjected mainly to double

cropping (barley and paddy rice) was investi-

gated. Soil samples were collected from three

plots of different types of management: (a) F

plot, only chemical fertilizers containing N, P

and K were applied; (b) F+LC plot, both chemi-

cal fertilizers and a low level of compost were

applied; (c) F+HC plot, both chemical fertilizers

and a high level of compost were applied (the

amount of compost applied in the F+HC plot

was three times larger than that applied in the

F+LC plot). Each soil sample was divided into

coarse sand- (CSA), medium sand-(MSA) and

fine sand-(FSA) sized aggregate, silt-sized ag-

gregate (SIA) and clay-sized aggregate (CLA)

fractions by wet-sieving and sedimentation. In

addition, the CSA and MSA fractions were sub-

divided into “mineral particles” (MP) and “de-

cayed plants” (DP) by a density fractionation.

Humus composition was influenced depending

upon the level of compost applied. The applica-

tion induced an increase in the amounts of total

humus (TH), humic acid (HA) and fulvic acid (FA)

in the whole soil and many size fractions, par-

ticularly, SIA fraction. The increase was re-

markable in the F+HC plot. In the CSA and MSA

fractions, the amounts of TH, HA and FA were

much larger in the CSA- and MSA-DP fractions

than in the CSA- and MSA-MP fractions. The

amounts of TH, HA and FA in the SIA fraction

were larger than those in the CLA fraction for

the F+HC and F+LC plots, and the reverse was

true for the F plot. On the other hand, the de-

grees of humification of humic acids in whole

soils and many size fractions, particularly SIA

fraction, decrease d by com post appli cation. The

decrease w as markedly in the F+HC plot. These

findings suggest that the SIA fraction play an

important role in the quantitative and qualitative

changes of humus, including HA and FA, as in-

fluenced by a long-term compost application.

Keywords: Paddy and Upland Fields; Straw-Cow

Dung Compost; Humic and Fulvic Acids;

Humification

1. INTRODUCTION

A variety of organic amendments such as compost,

farmyard manure, plant residues, food processing

wastes and sewage sludge is applied to various agri-

culture soils. Many researchers have reported beneficial

effects of these amendments on the physical, chemical

and biological properties, and fertility of soils in upland

and paddy fields. However, the role of the amendments

in the soils of double cropped fields (upland and paddy

crops) has received little attention. Thus, the authors

began to investigate the effect of continuous compost

application on various properties of soils in a field

subjected to long-term double cropping (paddy rice and

barley). The results obtained are summarized as follows:

Compost application increased (1) the activities of or-

ganic C, N and P decomposing enzymes, (2) the micro-

bial biomass N content and the hyphal length, (3) the

degree of water-stable macroaggregation (>0.25 mm)

and (4) the contents of total humus (TH) including hu-

mic (HA) and fulvic (FA) acids, organic C, total N,

hydrolysable carbohydrates and active Al [1-3].

Humus is one of the most important constituents of

soils and it affects various soil properties as well as

global C cycle. Regarding the effects of organic amend-

ments on humus composition, we can find some papers.

For examples, Roppongi et al. [4] reported that the in-

T. H. Nguyen et al. / Agricultural Sciences 2 (2011) 1-8

corporation of compost into an alluvial soil induced an

increase in the amounts of TH, HA and FA and a de-

crease of humification degree of humic acids (HAs).

Similar results were obtained even when cattle manure

was applied to an Ando soil or a Yellow soil [5,6].

When organic amendments were applied to soils, the

sizes of the amendments become smaller and the

amounts of mineral particles adhering and/or being

associated with them increase with the progression of

transformation and degradation by abiotic and biotic

reactions. Although these processes are very compli-

cated, the amendments-derived organic matter may be

distributed into soil fractions with different particle

sizes under the soil conditions. Organic matter of recent

plant origin in soils is considered to be preferentially

recovered in the sand-sized fraction, whereas more

microbially processed material can be found in the

silt-sized and clay-sized fractions [7]. Accordingly,

particle size fractionation of soil may provide an effec-

tive approach to clarify the fate and behavior of organic

matter in soil ecosystem. Leinweber and Reuter [8]

found that compost had clearly greater effects than

fresh farmyard manure and straw plus chemical fertil-

izers for the enrichment of organic C and N in the par-

ticle size fractions. Aoyama and Kumakura [5] divided

manure-treated soil into two fractions, particulate or-

ganic matter (>53 µm) and mineral-associated organic

matter (<53 µm) fractions. They found that manure

application increased significantly the amount of par-

ticulate organic matter, while it did not affect the

amount of mineral-associated organic matter. Further-

more, the analysis of the HAs revealed that manure

application led to a decrease in the degree of humifica-

tion and an accumulation of high molecular weight

components. However, the effects of amendments on

humus composition in various particle size fractions of

soils and the relationship between the amount of

amendment and humus composition need to be further

studied. The objective of the present study was to in-

vestigate the effects of different levels of compost on

the quantitative and qualitative changes of humus in

whole soils and various particle size fractions, using

soil samples which were taken from three plots (only

chemical fertilizer, chemical fertilizer plus a low level

of compost and chemical fertilizer plus a high level of

compost plots) in the field described above.

2. MATERIALS AND METHODS

2.1. Field Experiment

The field experiments with different types of man-

agement were established in 1975 at Yamaguchi Prefec-

ture Agricultural Experimental Station, Yamaguchi, Ja-

pan. The soil at this site was classified as Gray Lowland

soil. Three plots (200 m2 each) of the field experiments

were selected: (a) F plot, only chemical fertilizers con-

taining N, P, and K were applied; (b) F+LC plot, both

chemical fertilizers and a low level of compost were

applied; (c) F+HC plot, both chemical fertilizers and a

high level of compost were applied (the amount of

compost applied in the F+HC plot was three times larger

than that applied in the F+LC plot). Ta bl e 1 shows the

amounts of fertilizer and compost applied in the soils of

three different plots. The same plots were used as paddy

fields for rice in summer and as upland fields for barley

in winter until June 2001. The application rate of N,

P2O5 and K2O for each crop was 100 kg ha-1. After har-

vest (June and November), rice straw-cow dung compost

was applied at two different levels of 5 and 15 Mg ha-1.

However, since June 2001, these plots were used only as

paddy fields and the amounts of fertilizer and compost

applied were reduced by half. In April 2007, to obtain an

average soil sample in each plot, soils were taken from

the plow layer (0-15 cm) of five sites across each of the

three plots and mixed well. The soils were air-dried,

gently crushed and then passed through a 2-mm mesh

sieve. These sieved samples were used for analytical

determinations and particle size fractionation.

2.2. Particle Size Fractionation

Particle size fractionation of the soils was conducted

by the physical fractionation method described in Tanaka

and Shindo [9]. Soil-water suspension was divided into

coarse sand-sized aggregate (212-2,000 μm, CSA) and

medium sand-sized aggregate (53-212 μm, MSA) frac-

tions successively, using a 212 and 53 μm mesh sieve.

Clay-sized aggregate (>2 µm, CLA) and silt-sized ag-

gregate (2-20 µm, SIA) fractions in the suspension

which passed through the sieves were collected succes-

sively by repeating dispersion and sedimentation, and

then concentrated. After removal of the CLA and SIA

fractions, the remained particle was recovered as fine-

sand aggregate fraction (20-53 µm, FSA). Furthermore,

the CSA and MSA fractions were subdivided into “de-

Table 1. Amounts of fertilizers and compost applied in three

different plots.

N P2O5 K

2O Compost

Plot

(kg ha-1) (Mg ha-1)

Fa 100 100 100 0

F+LCb 100 100 100 5

F+HCc 100 100 100 15

a. only chemical fertilizers containing N, P and K were applied; b. chemical

fertilizers plus a low level of compost were applied; c. chemical fertilizers

plus a high level of compost were applied.

T. H. Nguyen et al. / Agricultural Sciences 2 (2011) 1-8

cayed plants” (DP) and “mineral particles” (MP) by a

density fractionation (decantation) in water. All the frac-

tions obtained were freeze-dried, weighed and then used

for the determination of humus composition.

2.3. Humus Composition

Humus composition was analyzed according to the

method described in Kumada [10]. Humus was extracted

with a mixture of 0.1 mol L-1 NaOH + 0.05 mol L-1

Na4P2O7 (1:1). Then, the extract was separated into HA

and FA by addition of H2SO4. The amounts of TH, HA

and FA were determined by the KMnO4 oxidation me-

thod. In the present study, 1 mL of 0.02 mol L-1 KMnO4

consumed was calculated as corresponding to 0.48 mg C

[11]. The degree of humification (darkening) of HA was

determined using color coefficient (∆ log K) and relative

color intensity (RF) values, where the ∆ log K is the lo-

garithm of the ratio of the absorbance of HA at 400 nm

to that at 600 nm; the RF represents the absorbance of

humic acid at 600 nm multiplied by 1,000 and then di-

vided by the number of milliliters of 0.02 mol L-1

KMnO4 consumed by 30 mL of HA solution. Humus

composition was analyzed in duplicate at least and the

average values obtained were given.

3. RESULTS AND DIS CUSSION

3.1. Distribution of Mass Weight in Particle

Size Fractions

The recoveries of mass weight by the physical frac-

tionation used were 97.0 for the F plot, 96.0 for the

F+LC plot and 100.9% for the F+HC plot. Thus, the

percentage distribution of mass weight in the particle

size fractions was corrected to a total of 100% (Table 2).

The percentage distribution of mass weight in each par-

ticle size fraction ranged from 11.9 to 32.2% in the F

plot, from 10.9 to 36.2% in the F+LC plot and from 9.3

to 34.0% in the F+HC. In all plots, the distribution val-

ues increased in the order of CLA < FSA < MSA < SIA

< CSA fractions. These results indicate that in the field

experiments, the distribution of mass weight was not

greatly affected by compost application. As expected, in

the CSA and MSA fractions, the distribution values of

the MP were much higher than those of the DP.

It is well known that the digestion of soil samples by

hot H2O2 can decompose soil organic matter. Compari-

son of percentage distribution of mass weight in the par-

ticle size fractions before and after H2O2 treatment re-

vealed that the distribution values in the 2-20 and

210-2,000 µm fractions were higher in the former sys-

tem than in the latter system, and the reverse was true for

the <2 and 20-210 µm fractions (data was not shown).

These findings indicate that highly recalcitrant organic-

inorganic complexes, which are resistant to water-sieving,

exist in the soils studied. Thus, in the present study, par-

ticle size fractions obtained were designated as aggre-

gate fractions.

The aggregation of soil particles may be promoted

when paddy field is changed to upland field.

3.2. Humus Composition of Whole Soils

The humus composition of whole soils in the F, F+LC

and F+HC plots is shown in Table 3. The amounts of the

TH, HA and FA in the whole soils ranged from 13.9 to

26.0, from 4.65 to 11.6 and from 4.02 to 6.76 g C kg-1,

Table 2. Percentage distribution (%) of mass weight in particle size fractions.

CSAb MSAc FSAd SIAe CLAf Total

Plota MPg DPg Sum MP DP Sum

F 31.1 1.1 32.2 19.7 0.9 20.6 14.1 21.3 11.9 100

F+LC 33.2 3.0 36.2 15.1 1.5 16.6 13.4 23.0 10.9 100

F+HC 32.7 1.3 34.0 17.1 1.7 18.8 12.6 25.3 9.3 100

a. see Table 1, b. coarse sand-sized aggregate (212-2,000 µm) fraction, c. medium sand-sized aggregate (53-212 µm) fraction, d. fine

sand-sized aggregate (20-53 µm) fraction, e. silt-sized aggregate (2-20 µm) fraction, f. clay-sized aggregate (< 2 µm) fraction, g. MP and

DP stand for “Mineral particles” and “Decayed plants”, respectively.

Table 3. Humus composition of whole soils.

Total humus Humic acid Fulvic acid

Plota

(g C kg-1 whole soil) Amount

(g C kg-1 whole soil)∆ log Kb RFc Typed(g C kg-1 whole soil)

F 13.9 4.65 0.696 40 B 4.02

F+LC 17.6 7.04 0.738 36 Rp 4.91

F+HC 26.0 11.6 0.807 28 Rp 6.76

a. see Tabl e 1, b. the logarithm of the ratio of the absorbance of humic acid at 400 nm to that at 600 nm, c. the absorbance of humic acid at

600 nm multiplied by 1,000 and then divided by the number of milliliters of 0.02 mol L-1 KMnO4 consumed by 30 mL of humic acid solu-

tion, d. classification diagram by Kumada [10].

T. H. Nguyen et al. / Agricultural Sciences 2 (2011) 1-8

respectively, and these amounts were in the order of F <

F + LC < F + HC plots. The amounts of FA and HA in

the F + HC plot were 1.4 and 1.6 times larger than those

in the F + LC plot, respectively. In the F + LC and espe-

cially F + HC plot, the amount of HA was much larger

than that of FA.

According to Kumada [10], the degrees of humifica-

tion of soil HAs become higher as ∆ log K value de-

creases and RF value increases. In the present study, the

∆ log K values of the HAs increased from 0.696 for the

F plot to 0.807 for the F + HC plot. In contrast, the RF

values of the HAs decreased from 40 for the F plot to 28

for the F + HC plot. The HAs in the F, F + LC and F +

HC plots belonged to Types B, Rp and Rp, respectively

[10], and the degree of humification of the HA was the

lowest in the F + HC plot.

In the present study, by continuous compost applica-

tion, the amounts of TH, HA and FA increased and the

humification degrees of the HAs decreased. The increase

and decrease occurred markedly in the F + HC plot. The

reasons are proposed as follows: (1) the growth of crops

is promoted to a larger extent in the F + HC plot than in

the F + LC and F plots, because larger amount of com-

post was applied in the former plot. Consequently, larger

amounts of plant residues such as roots and stubbles,

which can be transformed to humus, remain in the F +

HC plot than in the other plots. (2) The degrees of humi-

fication of the HAs in the compost as well as in fresh

plant residues are very low [10]. (3) Part of indigenous

soil HA with a high degree of humification is decom-

posed by microorganisms, due to priming effect [12].

The decomposition is accelerated to a larger degree in

the F + HC plot than in the other plots.

3.3. Humus Composition of Particle Size

Fractions

In the present study, the amounts of the TH (Table 4),

HA (Table 5) and FA (Table 6) in the particle size frac-

tions were expressed as g C kg-1 fraction and as g C kg-1

whole soil. Furthermore, percentage distribution of the

TH, HA and FA in each size fraction were calculated and

shown in Figures 1-3.

The amount of the TH per fraction (g C kg-1 fraction,

Ta bl e 4 ) ranged from 1.00 to 246 in the F, from 1.68 to

154 in the F + LC and from 1.13 to 222 in the F + HC

plots. In all plots, the amount of the TH in the CLA frac-

tion exceeded that in the SIA or FSA fraction. The amounts

of the TH in the CSA- and MSA-DP fractions were

Table 4. Amount of total humus (TH) in particle size fractions.

Fb F+LCb F+HCb F F+LC F+HC

Particle size

fractiona (g C kg-1 fraction) (g C kg-1 whole soil)

CSA MP 1.28 1.68 3.17 0.398 0.558 1.04

DP 246 154 222 2.71 4.62 2.89

MSA MP 1.00 N.Dc 1.13 0.198 N.D 0.192

DP 187 140 185 1.68 2.10 3.15

FSA 1.52 2.46 3.72 0.214 0.330 0.469

SIA 18.3 27.1 27.9 3.90 6.23 7.06

CLA 39.9 46.1 60.2 4.75 5.02 5.61

Total 13.9 18.9 20.4

a. see Table 2; b. see Table 1; c. not determined.

Table 5. Amounts of humic acids (HAs) in particle size fractions.

Fb F+LCb F+HCb F F+LC F+HC

Particle size

fractiona (g C kg-1 fraction) (g C kg-1 whole soil)

CSA MP

N.A.c N.A. N.A. N.A. N.A. N.A.

111 70.7 118 1.22 2.21 1.53

MSA MP

N.A. N.A. N.A. N.A. N.A. N.A.

61.4 126 112 0.553 1.89 1.90

FSA

N.A. N.A. N.A. N.A. N.A. N.A.

SIA

7.71 11.9 21.3 1.64 2.74 5.39

CLA

14.8 15.0 26.7 1.76 1.64 2.48

Total

5.17 8.48 11.3

a. see Table 2; b. see Table 1; c. not applicable because the amount of humic acid is very small.

T. H. Nguyen et al. / Agricultural Sciences 2 (2011) 1-8

Table 6. Amounts of fulvic acids (FAs) in particle size fractions.

b F+LCb F+HCb F F+LC F+HC

Particle size

fractiona (g C kg-1 fraction) (g C kg-1 whole soil)

CSA MP N.A.c N.A. N.A. N.A. N.A. N.A.

DP 73.6 48.3 55.7 0.810 1.450 0.724

MSA MP N.A. N.A. N.A. N.A. N.A. N.A.

DP 17.6 28.2 42.8 0.158 0.423 0.728

FSA N.A. N.A. N.A. N.A. N.A. N.A.

SIA 5.32 8.68 11.5 1.13 2.00 2.91

CLA 17.2 18.9 22.6 2.05 2.06 2.10

Total 4.15 5.93 6.46

a. see Table 2; b. see Table 1; c. not applicable because the amount of fulvic acid is very small.

100

FF+LC F+HC

Percentage distributi on (%)

CS A-MP

CS A-DP

MSA-MP

MSA-DP

FSA

SIA

CL A

Figure 1. Percentage distribution of total humus (TH) in

particle size fractions. See Table 1 for F, F + LC and F + HC.

See Table 2 for CSA, MSA, FSA, SIA, CLA, MP and DP.

100

FF+LCF+HC

Percentage distributi on (%)

CS A-DP

MSA-DP

SIA

CL A

Figure 2. Percentage distribution of humic acids (HAs) in

particle size fractions. See Table 1 for F, F + LC and F +

HC. See Table 2 for CSA, MSA, SIA, CLA and DP.

about 70-190 times larger than those in the CSA- and

MSA-MP fractions.When the amount of the TH was

calculated as g C kg-1whole soil (Tab le 4), the amount

reached 4.75 for the F, 6.23 for the F + LC and 7.06 for

the F + HC plots. In almost fractions, the amount of the

TH was in the order of F < F + LC < F + HC plots. Fur-

thermore, in the F + LC and especially F+HC plots,

100

FF+LCF+HC

Percentage distribution (%)

CSA-DP

MSA-DP

SIA

CLA

Figure 3. Percentage distribution of fulvic acids (FAs)

in particle size fractions. See Table 1 for F, F + LC and

F + HC. See Table 2 for CSA, MSA, SIA, CLA and DP.

the amount of the TH in the SIA fraction exceeded that

in the CLA fraction, while the reverse was true for the F

plot.

Percentage distribution of the TH in each fraction

(Figure 1) ranged from 1.43 to 34.4 for the F, from 1.75

to 33.0 for the F + LC and from 1.19 to 34.6% for the F

+ HC plots. In all plots, about 60% of the TH was occu-

pied by the SIA and CLA fractions, and the other 30%

existed in the CSA- and MSA-DP fractions. In the F +

LC and F + HC plots, the distribution value was higher

in the SIA fraction (33.0 and 34.6%) than in the CLA

fraction (26.6 and 27.4%), while the reverse was true for

the F plot (28.2 and 34.4%).

Aoyama [13] and Aoyama and Kumakura [5] found

that soil organic C accumulated to a larger amount in the

fraction of larger than 53 µm than in the fraction of less

than 53 µm, when manure (160 and 320 Mg ha-1 y-1) was

applied continuously to Kuriyagawa Ando soil for 20

years. A similar result was obtained for Hirosaki Ando

soil [14]. However, in the case of a Gray Lowland soil of

present study, the amount of the TH accumulated was

larger in the SIA and CLA fractions of less than 20 µm

than in the other fractions. In the study, compost was

applied at the level of 30 Mg ha-1 y-1 or less for about 30

T. H. Nguyen et al. / Agricultural Sciences 2 (2011) 1-8

years. Furthermore, in Fujisaka Ando soil where com-

post was incorporated continuously at the level of 11 and

34 Mg ha-1 y

-1 for 43 years, the distribution pattern of

soilorganic C in size fractions was similar to that in the

present study [13]. Accordingly, it is assumed that parti-

cle size fraction, which can accumulate a large amount

of organic matter after the application of organic amend-

ments, changes depending upon annual application

amount.

The amount of the HA per fraction (g C kg-1 fraction,

Table 5), except for the CSA- and MSA-MP fractions

and the FSA fraction (not calculated because the amount

of HA was very small), ranged from 7.71 to 111 for the F,

from 11.9 to 126 for the F + LC and from 21.3 to 118 for

the F + HC plots. In all plots, the amount of the HA in

the CLA fraction exceeded that in the SIA fraction. As

expected, the amounts of the HAs in the CSA- and

MSA-DP fractions were very large.

The amount of the HA per whole soil (g C kg-1 whole

soil, Table 5) reached 1.76 for the F, 2.74 for the F + LC

and 5.39 for the F + HC plots. In almost fractions, the

amount of the HA was the highest in the F + HC, fol-

lowed by the F + LC and F plots. Furthermore, in the F +

LC and especially F + HC plots, the amount of the HA

was larger in the SIA fraction than in the CLA fraction

and CSA- and MSA-DP fractions. In contrast, in the F

plot, the amount of HA was larger in the CLA fraction

than in the SIA fraction and CSA- and MSA-DP frac-

tions.

Percentage distribution of the HA in each fraction

(Figure 2) varied from 10.7 to 34.0 for the F, from 19.5

to 32.7 for the F+LC and from 13.5 to 47.7% for the

F+HC plots. The distribution value was higher in the

SIA fraction (32.7 and 47.7%) than in the CLA fraction

(19.5 and 21.9%) for the F+LC and F+HC plots and the

reverse was true for the F plot (31.7 and 34.0%). In the

CSA- and MSA-DP fractions, the distribution value

ranged from 10.7 to 25.3%.

The amount of the FA per fraction (g C kg-1 fraction,

Table 6), except for the CSA- and MSA-MP fractions

and the FSA fraction (not calculated because the amount

of FA was very small), varied from 5.32 to 73.6 for the F,

from 8.68 to 48.3 for the F + LC and from 11.5 to 55.7

for the F + HC plots. In all plots, the amount of the FA in

the CLA fraction exceeded that in the SIA fraction. The

amounts of the FAs in the CSA- and MSA-DP fractions

of three plots varied from 17.6 to 73.6.

The maximum amount of the FA per whole soil (g C

kg-1 whole soil, Table 6) was 2.05 for the F, 2.06 for the

F + LC and 2.91 for the F + HC plots. In almost frac-

tions, the amount of the FA was in the order of F < F +

LC < F + HC plots. In the F + HC plot, the amount of

the FA was larger in the SIA fraction than in the CLA

fraction, while the reverse was true for the F and F + LC

plots.

Percentage distribution of the FA in each fraction

(Figure 3) varied from 3.51 to 59.1 for the F, from 8.62

to 42.0 for the F + LC and from 2.58 to 49.4% for the F

+ HC plots. In the F + HC plot, the distribution value of

the FA was larger in the SIA fraction (49.4%) than in the

CLA fraction (35.7%), while the reverse was true for the

F (32.8 and 59.1%) and F + LC (40.5 and 42.0%) plots.

As shown in Figures 1-3, it is clear that CSA- and

MSA-DP fractions contribute to the accumulation of

humus, although the percentage distribution of TH, HA

and FA in both DP fractions were smaller than that in the

SIA and CLA fractions in most cases. Comparison of the

distribution values of TH, HA and FA between the SIA

and CLA fractions indicated that the values in the SIA

fraction were mostly higher than those in the CLA frac-

tion for the F + HC and F + LC plots and the reverse was

true for the F plot. In the physical fractionation of the

present study, after the CLA fraction was collected by

sedimentation, the SIA and then FSA fractions were ob-

tained. Since the quantitative distribution of TH, HA and

FA in the FSA fraction was very small (Figures 1-3)

compared to the SIA and CLA fractions, it is reasonable

to consider that free (not connected with minerals, a low

density) and fine decayed plants are recovered in the

CLA fraction. Accordingly, in most cases of the F + HC

and F + LC plots, higher distribution values of TH, HA

and FA in the SIA fraction compared to the CLA fraction

may be because organic matter including decayed plants

were connected to the minerals (including aggregated

clay-sized minerals) in the SIA fraction and preserved

there as stable aggregates. The distribution values of TH,

HA and FA in the SIA fraction were higher in the F +

HC plot than in the F + LC plot, indicating that stable

aggregates might be produced to a larger extent in the

former plot compared to the latter plot.

According to Kumada [10], the degrees of humifica-

tion (darkening) of HAs become higher as ∆ log K value

decreases and RF value increases. The ∆ log K and RF

values and types of HAs obtained from the CSA-DP,

MSA-DP, SIA and CLA fractions of three plots were

investigated (Figure 4). The analysis of HA was not

conducted for the CSA-MP, MSA-MP and FSA fractions,

because the amount of HA was very small. The RF val-

ues ranged from 14 to 52 for the F plot, from 18 to 51

for the F + LC plot and from 15 to 37 for the F + HC

plot, and increased with decreasing particle size in these

plots. On the other hand, the ∆ log K values varied from

0.638 to 0.940 for the F plot, from 0.667 to 0.867 for the

F + LC plot and from 0.719 to 0.939 for the F + HC plot,

and decreased with decreasing particle size in the plots.

From the ∆ log K and RF values, the types of HAs were

examined [9]. The HAs in the CSA- and MSA-DP frac-

T. H. Nguyen et al. / Agricultural Sciences 2 (2011) 1-8

0.60.70.80.91.01.1

∆ log K

F+HC

CLA

F+HC

SIA

F+HC

MSA-DP

F+HC

CSA-DP

F+LC, CLA

F+LC

SIA

F+LC

MSA-DP

F+LC

CSA-DP

MS A-DP

F, SI

CLA

CSA-DP

Figure 4. RF and ∆ log K values of humic acids in particle

size fractions. See Table 1 for F, F + LC and F + HC. See

Table 2 for CSA, MSA, SIA, CLA and DP. Rp, B and P in

the figure indicate the types of humic acids.

tions of the F, F + LC and F + HC plots belonged to

Type Rp with a low degree of humification (Figure 4),

and the HAs in the SIA fractions of the F + LC and F +

HC plots and the HA in the CLA fraction of the F + HC

plot belonged to Type Rp. On the other hand, the HAs in

the SIA and CLA fractions of the F plot and in the CLA

fraction of the F + LC plot were Type B with a medium

degree of humification. Larger amount of compost ap-

plication decreased remarkably the humification degree

of HA.

Since the sum of the percentage distribution of HA in

the SIA and CLA fractions of three plots was between

52.2 and 69.6% (Figure 2), these fractions affected

largely on the amount and type of the HAs in the whole

soils (Table 3 and Figure 4).

4. CONCLUSION

Continuous compost application to the field subjected

to long-term double cropping (ca. 30 years) affected the

quantitative and qualitative changes of humus depending

upon the application amount. The application at a high

level (F + HC plot) increased remarkably the amounts of

TH, HA and FA in the whole soil and many particle size

fractions, particularly, SIA fraction. On the other hand,

the degree of humification of HA decreased markedly by

the application. The changes at a low level (F + LC)

were limited. The SIA fraction merit close attention as an

important reservoir of soil organic C, including HA and FA.

5. ACKNOWLEDGEMENTS

The authors are grateful to the members of the Soil Fertility and

Conservation Division, Yamaguchi Prefecture Experimental Station,

Yamaguchi, Japan for supplying the soil samples.

REFERENCES

[1] Shindo, H. and Shojaku, M. (1999) Effect of continuous

compost application on the activities of various enzymes

in soil of double cropping fields. Japanese Journal of

Soil Science and Plant Nutrition, in Japanese, 70, 66-69.

[2] Imbrahim, S.M. and Shindo, H. (1999) Effect of continu-

ous compost application on water-stable soil macro-

aggregation in a field subjected to double cropping. Soil

Science and Plant Nutrition, 45, 1003-1007.

[3] Shindo, H., Hirahara, O., Yoshida, M. and Yamamoto, A.

(2006) Effect of continuous compost application on

humus composition and nitrogen fertility of soils in a

field subjected to double cropping. Biology and Fertility

of Soils, 42, 437-442. doi:10.1007/s00374-006-0088-3

[4] Roppongi, K., Ishigami, T. and Takeda, M. (1994) Effects

of continuous application of rice straw compost on

humus forms of alluvial upland soil. Japanese Journal of

Soil Science and Plant Nutrition, in Japanese, 65, 426-

431.

[5] Aoyama, M. and Kumakura, N. (2001) Quantitative and

qualitative changes of organic matter in an Ando soil

induced by mineral fertilizer and cattle manure appli-

cations for 20 years. Soil Science and Plant Nutrition, 47,

241-252.

[6] Watanabe, A., Kawasaki, S., Kitamura, S. and Yoshida,

S. (2007) Temporal changes in humic acids in cultivated

soils with continuous manure application. Soil Science

and Plant Nutrition, 53, 535-544.

doi:10.1111/j.1747-0765.2007.00170.x

[7] Cheshire, M.V. and Mundie, C.M. (1981) The distri-

bution of labelled sugars in soil particle size fractions as

a means of distinguishing plant and microbial carbo-

hydrate residues. Journal of Soil Science, 32, 605-618.

doi:10.1111/j.1365-2389.1981.tb01733.x

[8] Leinweber, P. and Reuter, G. (1992) The influence of

different fertilization practices on concentrations of organic

carbon and total nitrogen in particle-size fractions during

34 years of a soil formation experiment in loamy marl.

Biology and Fertility of Soils, 13, 119-124.

doi:10.1007/BF00337346

[9] Tanaka, M. and Shindo, H. (2009) Effect of continuous

compost application on carbon and nitrogen contents of

whole soils and their particle size fractions in a field

subjected mainly to double cropping. In: Composting,

Processing, Materials and Approaches, Pereira, J.C.

and Bolin, J.L., Eds., Nova Science Publishers, New

York, 187-197.

[10] Kumada, K. (l987) Chemistry of soil organic matter.

Japan Scientific Societies Press, Tokyo.

[11] Ikeya, K. and Watanabe, A. (2003) Direct expression of

an index for the degree of humification of humic acids

using organic carbon concentration. Soil Science and

Plant Nutrition, 49, 47-53.

[12] Stevenson, F.J. (1982) Humus chemistry. John Wiley &

Sons, New York.

[13] Aoyama, M. (1992) Accumulated organic matter and its

nitrogen mineralization in soil particle size fractions with

long-term application of farmyard manure or compost.

T. H. Nguyen et al. / Agricultural Sciences 2 (2011) 1-8

Japanese Journal of Soil Science and Plant Nutrition, in

Japanese, 63, 161-168.

[14] Aoyama, M. and Taninai, Y. (1992) Organic matter and

its mineralization in particle size and aggregate size

fractions of soils with four-year application of farmyard

manure. Japanese Journal of Soil Science and Plant

Nutrition, in Japanese, 63, 571-580.