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

doi:10.4236/as.2011.23030

Paper Menu >>

Journal Menu >>

Vol.2, No.3, 213-219 (2011)

doi:10.4236/as.2011.23030

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: [email protected]

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

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

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

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

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·kg–1 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

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

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

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.

REFERENCES

[1] Stevenson, F.J. (1982) Humus chemistry. John Wiley and

Sons, New York.

[2] Kelley, K.R. and Stevenson, F.J. (1995) Forms and nature

of organic N in soil. Fertilizer Research, 42, 1-11.

doi:10.1007/BF00750495

[3] Hassink, J. (1997) The capacity of soils to preserve or-

ganic C and N by their association with clay and silt par-

ticles. Plant and Soil, 191, 77-87.

doi:10.1023/A:1004213929699

[4] Schulten, H.R. and Leinweber, P. (1991) Influence of

long-term fertilization with farmyard manure on soil or-

ganic matter: Characteristics of particle-size fractions.

Biology and Fertility of Soils, 12, 81-88.

doi:10.1007/BF00341480

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

different fertilization practices on concentrations of or-

ganic 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

[6] Dubeux Jr., J.C.B., Sollenberger, L.E., Comerford, N.B.,

Scholberg, J.M., Ruggieri, A.C., Vendramini, J.M.B., In-

terrante, S.M. and Portier, K.M. (2006) Management in-

tensity affects density fractions of soil organic matter

from grazed bahiagrass swards. Soil Biology and Bio-

chemistry, 38, 2705-2711.

doi:10.1016/j.soilbio.2006.04.021

[7] Xu, Y.C., Shen, Q.R. and Ran, W. (2003) Content and

distribution of forms of organic N in soil and particle size

factions after long-term fertilization. Chemosphere, 50,

739-745. doi:10.1016/S0045-6535(02)00214-X

[8] 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: Pereira, J.C. and

Bolin, J.L., Eds., Composting: Processing, Materials and

Approaches, Nova Science Publishers, New York, 187-

197.

[9] Chang, E.-H., Chung, R.-S. and Tsai, Y.-H. (2007) Effect

of different application rates of organic fertilizer on soil

enzyme activity and microbial population. Soil Science

and Plant Nutrition, 53, 132-140.

doi:10.1111/j.1747-0765.2007.00122.x

[10] Sommerfeldt, T.G., Chang, C. and Entz, T. (1988)

Long-term annual manure applications increase soil or-

ganic matter and nitrogen, and decrease carbon to nitro-

gen ratio. Soil Science Society of America Journal, 52,

1668-1672.

doi:10.2136/sssaj1988.03615995005200060030x

[11] Sodhi, G.P.S., Beri, V. and Benbi, D.K. (2009) Soil ag-

gregation and distribution of carbon and nitrogen in dif-

ferent fractions under long-term application of compost

in rice-wheat system. Soil & Tillage Research, 103, 412-

418. doi:10.1016/j.still.2008.12.005

[12] Angers, D.A. and N’Dayegamiye, A. (1991) Effects of

manure application on carbon, nitrogen and carbohydrate

contents of a silt loam and its particle-size fractions. Bi-

ology and Fertility of Soils, 11, 79-82.

doi:10.1007/BF00335840

[13] Yonebayashi, K. and Hattori, T. (1980) Improvements in

the method for fractional determination of soil organic

nitrogen. Soil Science and Plant Nutrition, 26, 469-481.

[14] Bremner, J.M. (1965) Organic forms of nitrogen. In:

Black, C.A., et al., Eds., Method of soil analysis. Part II,

T. H. Nguyen et al. / Agricultural Science 2 (2 011) 213-219

219219

American Society of Agronomy, Madison, 1238-1255.

[15] Bremner, J.M. and Mulvaney, C.S. (1982) Nitrogen-Total.

In: Page, A.L., Miller, R.H. and Keeney, D.R., Eds.,

Methods of Soil Analysis. Part 2, Chemical and microbi-

ological properties, American Society of Agronomy, Soil

Science Society of America, Madison, 595-624.

[16] Nguyen, T.H. and Shindo, H. (2011) Quantitative and

qualitative changes of humus in whole soils and their

particle size fractions as influenced by different levels of

compost application. Agricultural Sciences, 2, 1-8.

doi:10.4236/as.2011.21001

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

nitrogen mineralization in soil particle size fractions with

long-term application of farmyard manure or compost.

Japanese Journal of Soil Science and Plant Nutrition, 63,

161-168.

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

its mineralization in particle size and aggregate size frac-

tions of soils with four-year application of farmyard ma-

nure. Japanese Journal of Soil Science and Plant Nutri-

tion, 63, 571-580.

[19] Schulten, H.R. and Schnitzer, M. (1998) The chemistry

of soil organic nitrogen: A Review. Biology and Fertility

of Soils, 26, 1-15. doi:10.1007/s003740050335

[20] Goh, K.M. and Edmeades, D.C. (1979) Distribution and

partial characterisation of acid hydrolysable organic ni-

trogen in six New Zealand soils. Soil Biology and Bio-

chemistry, 11, 127-132.

doi:10.1016/0038-0717(79)90088-9

[21] Olson, R.V. and Swallow, C.W. (1984) Fate of labelled

nitrogen fertilizer applied to winter wheat for five years.

Soil Science Society of America Journal, 48, 583-586.

doi:10.2136/sssaj1984.03615995004800030023x

[22] Kelley, K.R. and Stevenson, F.J. (1987) Effects of carbon

source on immobilization and chemical distribution of

fertilizer N in soil. Soil Science Society of America

Journal, 51, 946-951.

doi:10.2136/sssaj1987.03615995005100040023x