Vol.2, No.3, 213-219 (2011)
doi:10.4236/as.2011.23030
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
Agricultural Scienc es
Effects of different levels of compost application on
amounts and distribution of organic nitrogen forms in
soil particle size fractions subjected mainly to double
cropping
Thu Ha Nguyen, Haruo Shindo*
Faculty of Agriculture, Yamaguchi University, Yamaguchi, Japan; *Corresponding Author: shindo@yamaguchi-u.ac.jp
Received 24 May 2011; revised 24 June 2011; accepted 25 July 2011.
ABSTRACT
Effects of different levels of compost applica-
tion on the amount s and percentage distributio n
of organic N forms in whole soils and particle
size fractions were investigated. Soil samples
were collected from three plots: a) F, only
chemical fertilizers; b) F + LC, chemical fertiliz-
ers plus low level of compost; (c) F + HC, chemi-
cal fertilizers plus high level of compost. Each
soil sample was divided into five fractions:
coarse sand-sized aggregate (CSA), medium
sand-sized aggregate (MSA), fine sand-sized
aggregate (FSA), silt-sized aggregate (SIA) and
clay-sized aggregate (CLA) fractions. The sand
fractions were subdivided into decayed plants
(DP) and mineral particles (MP). The amounts of
total N and different organic N forms in the
whole soils as well as size fractions generally
increased with increasing the amount of com-
post. In the whole soils, percentage distribution
of non-hydrolysable-N and amino sugar-N in-
creased by compost application while the dis-
tribution values of the hydrolysable ammonium-
N and uniden tified-N decreased. The application
did not affect the distribution degree of amino
acid-N. In the size fractions, the distribution
values of most organic N forms increased in the
CSA-DP, MSA-DP and FSA-DP fractions by
compost ap plicat ion. In the CLA fractions, the a -
mounts and percentage distribution of organic
N forms were the highest, although the applica-
tion caused decreases in their distribution val-
ues. These findings indicate that the CLA frac-
tion merit close attention as an important res-
ervoir of various organic N.
Keywords: Compost Application; Upland and
Paddy Fields; Soil Organic N Forms; Size Fractions
1. INTRODUCTION
In the surface layer of most soils, over 90% of N
occurs in organic forms [1]. The forms of soil organic N
can be divided into two broad categories: 1) organic
residues and 2) soil organic matter or humus [2]. All
these materials play key roles in terms of maintaining or
improving soil fertility and plant nutrition through the
direct and indirect effects on microbial activity and
nutrient availability.
Application of organic fertilizer has received great
attention from agriculturists and environmentalists be-
cause of directly and indirectly effects on crop growth
and yield as well as soil properties. Organic amendments
may affect the amounts and percentage distribution of
organic N forms in whole soils and their particle size
fractions. Results of 15N studies clearly demonstrated
that from 20% to 40% of the fertilizer N (inorganic N)
added to agricultural soils was incorporated into organic
forms during the first growing season [2]. Hassink [3]
suggested that N associated with particle size fraction of
less than 20 µm were better protected against decom-
position. A number of authors have studied the influence
of different types of organic fertilizer on the amounts
and properties of N in the particle size fractions. For
example, Schulten and Leinweber [4] reported that the
amounts of N compounds increased with decreasing
particle size and that the fine- and medium-clay and the
fine- and medium-silt fractions of farmyard manure soil
were enriched in amino-N and amide-N. Leinweber and
Reuter [5] pointed out that N concentration was
generally highest in the clay fraction, followed by the silt
and sand fractions. The N content of the soil particles
from 250 to 2000 μm was reported to be greater with
increased management intensity [6]. According to Xu et
T. H. Nguyen et al. / Agricultural Science 2 (2 011) 213-219
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
214
al. [7], in the plot received mineral fertilizer plus organic
manure, most of the N remaining was transferred into
amino sugar-N in every size fractions studied and amino
acid-N in the size fraction of larger than 2 µm. Tanaka
and Shindo [8] found that long-term compost application
increased the amount of N to a larger degree in the silt-
sized aggregate fraction than in the other size fractions.
On the other hand, several authors have observed the
effects of different levels of organic amendments on soil
properties and fertilities. For example, soil organic matter
content, total N content and soil microbial population
increased with increasing the rate of compost application
[9-11]. Angers and N’Dayegamiye [12] presented evi-
dences that bi-annual application of 40 and 80 Mg·ha-1
increased N contents of whole soil and all particle size
fractions studied. However, the effects of amendments
on the contents and distribution of forms of organic N in
particle size fractions of soils and the relationship be-
tween the amounts of amendment and organic N forms
have received little attention. The objective of present
study was to assess the influences of different levels of
compost application on the amounts and distribution of
several organic N forms in whole soils and their particle
size fractions of mainly double cropped fields (paddy
rice and barley). This is the first report on the relation-
ships among the organic N groups, soil particle size
fractions of double cropped fields and levels of compost
applied.
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 (FAO-UNESCO: Eutric Fluvisol). For the field ex-
periments, we selected three plots (200 m2 each): a) F
plot, only chemical fertilizers containing N, P and K
were applied; b) F + LC plot, chemical fertilizers plus a
low level of compost (5 Mg·ha–1) were applied; c) F +
HC plot, chemical fertilizers plus a high level of com-
post (15 Mg·ha–1) were applied. The same plots were
used as paddy fields for rice in summer and as upland
fields for barley in winter until June 2001. The applica-
tion rate of N, P2O5 and K2O for each crop was 100
kg·ha–1. After harvest (June and November), rice straw-
cow dung compost was applied as described above.
However, since June 2001, these plots were used only as
paddy fields and the amounts of chemical fertilizers and
compost applied were reduced by half. In October 2008,
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 physical fractionation.
2.2. Particle Size Fractions
The size fractionation of soil samples was conducted
by physical fractionation described in Tanaka and
Shindo [8], except that the particle size fraction of 20 -
53 μm was recovered by sieving. Firstly, the samples
were divided into five particle size fractions, namely
coarse sand-sized aggregate (212 - 2000 μm, CSA), me-
dium sand-sized aggregate (53 - 212 μm, MSA), fine
sand-sized aggregate (20 - 53 μm, FSA), silt-sized ag-
gregate (2 - 20 μm, SIA) and clay-sized aggregate (<2
μm, CLA) fractions. Three sand-sized fractions were
separated by sieving and then silt-sized and clay-sized
fractions were separated by sedimentation. Secondly, the
CSA, MSA and FSA fractions were subdivided into
“mineral particles” (MP) and “decayed plants” (DP) by a
density fractionation (decantation) in water.
All the fractions including DP and MP were freeze-
ried and weighed. d
2.3. Organic N Forms
Organic N composition was analysed according to the
method described in Yonebayashi and Hattori [13], who
partly modified the N fractionation method proposed by
Bremner [14]. It was considered that the improved
method is suitable for establishing the origin of soil or-
ganic N fractions, especially in case of tropical soils.
Soil sample containing about 10 mg N was hydrolysed
with 20 mL of 6 mol·L–1 HCl and octyl alcohol for 24
hours at 150˚C. The hydrolysate obtained was made up
to a volume of 100 mL after filtering under suction and
neutralizing (pH from 6.4 to 6.6) by NaOH. A scheme
for the fractional determination of soil organic N is
shown in Figure 1.
The amount of hydrolysable ammonium-N (HAN) (a)
was estimated by distilling the hydrolysate with MgO.
Figure 1. Scheme for the fractional determination of soil or-
ganic N.
T. H. Nguyen et al. / Agricultural Science 2 (2 011) 213-219
Copyright © 2011 SciRes. http://www.scirp.org/journal/AS/
215215
The sum amount (b) of the HAN and amino sugar-N
(ASN) was determined by distilling the hydrolysate with
phosphate-borate (PB) buffer. The amount of the ASN
was calculated by subtraction of (a) from (b).
In the determination of amino acid-N (AAN) (c), the
hydrolysate was heated at 100˚C in the presence of 0.5
mol·L –1 NaOH and ninhydrin powder and then distilled
with PB buffer.
Openly accessible at
Total hydrolysable-N (d) and total N (e) were deter-
mined by Kjeldahl procedure recommended by Bremner
and Mulvaney [15]. The unidentified-N (HUN) and non-
hydrolysable-N (NHN) contents were calculated as fol-
lowing formulations:
HUN = (d) – (c) – (b).
NHN = (e) – (d).
Amounts of different organic N forms were analysed
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
In the physical fractionation of soil samples, the re-
coveries of mass weight ranged from 99.5% to 101% in
all plots. The percentage distribution of mass weight in
the particle size fractions was corrected to a total of
100% (Table 1). In all the plots, the distribution of mass
weight in the particle size fractions was generally in the
order of CLA < FSA < SIA < MSA < CSA. As expected,
in the CSA, MSA and FSA fractions of all plots, the dis-
tribution values of MP were much larger than those of
DP. The particle size fractions obtained were designated
as aggregate fractions because percentage distribution of
mass weight in particle size fractions differed before and
after H2O2 treatment of soils [16].
3.2. Total N
The amounts and percentage distribution of total N in
the particle size fractions are presented in Figures 2 and
3. In all size fractions, the amount of total N (mg·kg–1
soil) was higher in the F + LC and particularly F + HC
plot than in the F plot (Figure 2). These results were in
line with findings obtained by some authors that N con-
centration in the particle size fractions increased with
increasing levels of organic amendments application
[8,11,17,18].
Xu et al. [7] described that organic amendments ap-
plication did not change the order of N content of parti-
cle size fractions studied. The same results were ob-
tained in this study. In the F+HC plot, the amount of
total N was in order of CSA-MP, MSA-MP < FSA-MP <
Figure 2. Amounts of total N in particle size fractions.
See Ta b l e 1 for F, F + LC and F + HC. See Figure 1
for CSA, MSA, FSA, SIA, CLA, MP and DP.
Figure 3. Percentage distribution of total N in particle size
fractions. See Table 1 for F, F + LC and F + HC. See Figure 1
for CSA, MSA, FSA, SIA, CLA, MP and DP.
Table 1. Percentage distribution (%) of mass weight in particle size fractions.
CSAd MSAe FSAf
MPi DPj Sum MP DP Sum MP DP Sum SIAg CLAh Total
Plot (%)
Fa 30.9 0.77 31.7 20.0 0.95 21.0 16.3 1.14 17.4 18.7 11.2 100
F+LCb 30.1 1.28 31.4 20.4 1.56 22.0 16.1 2.05 18.2 18.8 9.60 100
F+HCc 32.6 1.73 34.3 20.4 2.40 22.8 14.2 3.24 17.4 17.0 8.49 100
a. only chemical fertilizers were applied; b. chemical fertilizers plus low level of compost (5 Mg·ha–1) were applied; c. chemical fertilizers plus high level of
compost (15 Mg·ha–1) were applied; d. coarse sand-sized aggregate fraction; e. medium sand-sized aggregate fraction; f. fine sand-sized aggregate fraction; g.
silt-sized aggregate fraction; h. clay-sized aggregate fraction; i. mineral particles; j. decayed plants.
T. H. Nguyen et al. / Agricultural Science 2 (2 011) 213-219
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
216
CSA-DP < FSA-DP < MSA-DP < SIA < CLA fractions.
Similar orders were found in the F and F + LC plots.
In all the plots, the percentage distribution of N was
greater in the SIA and CLA fractions, ranging from
23.3% to 46.0%, than in the other fractions, ranging
from 1.96% to 14.9% (Figure 3). As pointed out by Ta-
naka and Shindo [8], in the CLA fraction, distribution
value of total N was in the order of F + HC < F + LC < F
plots. Furthermore, in all the plots, the distribution of N
was the highest in the CLA fractions. These findings
were in agreement with results reported by Leinweber
and Reuter [5] and Xu et al. [7] that clay-sized fraction
contained highest N.
3.3. Organic N Forms in Whole Soils
In the reviews on soil organic N, Kelley and Steven-
son [2] and Schulten and Schnitzer [19] summarized that
the HAN originated from indigenous fixed NH4
+ plus
some fractions from the breakdown of hydroxyl amino
acids and other amino acids, amino sugars, amides and
the deamination of purines and pyrimidines. Amino ac-
ids occur in soils in the form of proteins and peptides
closely associated with and protected by humic materials
and inorganic soil constituents such as clay minerals and
hydrous oxides of Fe and Al [19]. Amino sugars appear
as structural components of a broad group of substances
called macropolysacharides. Some amino sugars exist as
chitin and others are polysaccharides that are not chitin
[1]. One-fourth to one-half of the HUN in soils has been
reported to occur as the non-α-amino acid-N such as
arginine, tryptophan, lysine and proline [20]. Kelley and
Stevenson [2] described that part of the NHN might oc-
cur as structural components of humic substances and in
the form of N-phenyl amino acids resulting from the
bonding between amino groups and aromatic rings.
The amounts and percentage distribution of organic N
forms in the whole soils are given in Figures 4 and 5.
The amount of the HAN was higher in the F + LC, espe-
cially F + HC plots than in the F plot. However, the dis-
tribution value of the HAN was in the order of F + HC <
F + LC < F plot. Similar results were found for the HUN.
The amounts of the AAN in the F + LC and F + HC
plots were 1.3 and 1.8 times higher than those in the F
plot, respectively and the distribution value was not in-
fluenced by compost application. The amounts and dis-
tribution degrees of the ASN and NHN substantially in-
creased at high level of compost application. The in-
crease of the NHN may be because N derived from
chemical fertilizers, compost and plant residues were
transferred into resistant organic forms as suggested by
Olson and Swallow [21] and Kelley and Stevenson [22].
These findings were similar to the results reported by Xu
et al. [7], except that the amount of the HAN decreased
by organic amendments application.
Figure 4. Amounts of organic N forms in whole soils. See
Table 1 for F, F + LC and F + HC. See Figure 1 for HAN,
AAN, ASN, HUN and NHN.
Figure 5. Percentage distribution of organic N forms in whole
soils. See Table 1 for F, F + LC and F + HC. See Figure 1 for
HAN, AAN, ASN, HUN and NHN.
3.4. Organic N Forms in Particle Size
Fractions.
The amounts (mg·kg–1 soil) and percentage distribu-
tion of organic N forms in the particle size fractions are
presented in Tabl e s 2 and 3. It is noteworthy that in all
three plots, the CLA and SIA fractions enriched most
organic N forms. Their amounts and distribution values
were the highest in the CLA fraction, generally followed
by the SIA fraction. As expected, the content and distri-
bution degree of organic N forms in the CSA-DP, MSA-
DP and FSA-DP fractions were higher than those in the
CSA-MP, MSA-MP and FSA-MP fractions. These re-
sults were in accordance with data published by several
authors that finer fractions contain larger amounts of N
than coarser fractions [1,3,5].
The amounts of the HAN, AAN, ASN and HUN in the
particle size factions generally increased with increasing
levels of compost application. Such a relationship was
not found for the NHN. The effects of compost applica-
tion on percentage distribution of organic N forms are
ummarized as follows (Table 3): 1) The distribution s
T. H. Nguyen et al. / Agricultural Science 2 (2 011) 213-219
Copyright © 2011 SciRes. Openly accessible at http://www.scirp.org/journal/AS/
217217
Table 2. Amounts of organic N forms in particle size fractions.
Forms of organic Nc
ASN HUN
Plota Particle size
fractionsb HAN AAN (mg·kg1 soil) NHN
CSA MP 10.8 9.62 1.52 7.83 1.45
DP 19.7 37.4 4.76 38.1 3.66
MSA MP 9.30 11.3 3.08 7.20 9.88
DP 23.6 39.4 9.38 48.4 14.0
FSA MP 10.7 15.3 2.51 5.74 13.2
DP 26.0 33.8 2.87 28.5 6.37
SIA 111 106 7.93 155 12.4
F
CLA 152 153 55.1 158 202
CSA MP 15.0 14.3 2.01 11.4 18.6
DP 30.9 40.8 11.3 80.3 26.8
MSA MP 14.9 16.5 3.67 36.1 14.7
DP 41.6 65.7 12.9 83.5 25.8
FSA MP 14.8 22.5 2.57 33.5 4.67
DP 48.0 62.1 8.62 82.4 19.0
SIA 131 147 11.3 197 12.8
F + LC
CLA 196 192 49.8 261 79.1
CSA MP 21.3 18.2 3.91 9.86 4.43
DP 77.2 72.3 15.9 130 68.6
MSA MP 16.0 14.8 4.64 7.50 15.0
DP 80.5 116 18.6 136 83.5
FSA MP 20.1 18.4 3.97 14.5 6.53
DP 95.4 98.2 15.9 136 25.0
SIA 195 197 25.5 249 19.4
F + HC
CLA 212 224 59.8 266 126
a and b. see Table 1; c. see Figure 1.
Table 3. Percentage distribution of organic forms of N in particle size fractions.
Forms of organic Nc
HAN AAN ASN HUN NHN
Plota Particle size
fractionsb (%)
CSA MP 2.98 2.37 1.74 1.72 0.55
DP 5.42 9.22 5.46 8.36 1.39
MSA MP 2.56 2.80 3.53 1.58 3.76
DP 6.50 9.72 10.8 10.6 5.32
FSA MP 2.93 3.77 2.87 2.46 5.01
DP 7.15 8.32 3.30 6.27 2.43
SIA 30.5 26.0 9.10 34.2 4.74
CLA 41.9 37.7 63.2 34.8 76.8
F
Sum 100 100 100 100 100
CSA MP 3.04 2.55 1.97 1.45 9.25
DP 6.28 7.27 11.0 10.2 13.3
MSA MP 3.03 2.94 3.60 4.60 7.29
DP 8.45 11.7 12.6 10.6 12.8
FSA MP 3.01 4.01 2.52 4.27 2.32
DP 9.74 11.0 8.44 10.5 9.43
SIA 26.6 26.3 11.0 25.1 6.34
CLA 39.9 34.2 48.8 33.2 39.3
F + LC
Sum 100 100 100 100
100
CSA MP 2.96 2.39 2.63 1.03 1.27
DP 10.8 9.54 10.8 13.5 19.7
MSA MP 2.23 1.95 3.13 0.78 4.31
DP 11.2 15.3 12.6 14.2 30.0
FSA MP 2.81 2.43 2.68 1.51 1.88
DP 13.3 12.9 10.7 14.1 7.19
SIA 27.2 26.0 17.2 26.2 5.57
CLA 29.5 29.5 40.3 27.7 36.1
F + HC
Sum 100 100 100 100 100
a and b. see Table 1; c. see Figure 1.
T. H. Nguyen et al. / Agricultural Science 2 (2 011) 213-219
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218
degrees of organic N forms in the CSA-DP, MSA-DP
and FSA-DP fractions tended to increase while those in
the CSA-MP, MSA-MP and FSA-MP fractions were less
affected. 2) In the SIA fraction, the distribution value of
the ASN increased while that of the HAN or HUN de-
clined. The values of the AAN and NHN in the SIA frac-
tion were not greatly affected. 3) In the CLA fraction,
the distribution of all organic N forms remarkably re-
duced. 4) These effects were markedly in the soil re-
ceived high level of compost.
As presented in the Tables 2 and 3, all organic N
forms dominated in the CLA fraction. It is likely that the
adsorption of organic N compounds by clay minerals
protects the proteins and other nitrogenous compounds
from decomposition by microorganisms or by proteinase
enzymes. Some organic N may be also entrapped within
the lattice structures of clay minerals [1]. These proc-
esses resulted in larger amounts of organic N in the CLA
fraction than in the other fractions.
Among the organic N forms, large proportions were
recovered as the AAN and HAN in every particle size
fractions. The proportion of the HUN was generally
higher than that of the ASN or NHN. In all size fractions,
no consistent relationship was found between the per-
centage distribution of organic N forms and the amount
of compost applied.
4. CONCLUSIONS
In the whole soils and many particle size fractions, the
amounts of total N and different organic N forms gener-
ally increased with increasing the amount of compost
applied. In the whole soil, the percentage distribution of
the NHN markedly increased by compost application,
particularly in the plot received a high level of compost
(F+HC). In the size fractions, the distribution values of
most organic N forms increased in the CSA-DP, MSA-
DP and FSA-DP fractions by compost application. The
amounts and percentage distribution of organic N forms
were the highest in the CLA fractions, although the
compost application caused decreases in their distribu-
tion values. The findings obtained in the present study
indicate that the CLA fraction merit close attention as an
important reservoir of various organic N.
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.
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