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Nitrogen Dynamics in theUppermost Part of SubmergedPaddy Soils in Temperate andTropical RegionsPrapai Chairoj a , Makoto Kimura a , Hidenori Wada a & YasuoTakai aa Faculty of Agriculture. The University of Tokyo , Bunkyo-ku, Tokyo , 113 , JapanPublished online: 30 Oct 2012.

To cite this article: Prapai Chairoj , Makoto Kimura , Hidenori Wada & Yasuo Takai(1985) Nitrogen Dynamics in the Uppermost Part of Submerged Paddy Soils inTemperate and Tropical Regions, Soil Science and Plant Nutrition, 31:2, 175-187, DOI:10.1080/00380768.1985.10557425

To link to this article: http://dx.doi.org/10.1080/00380768.1985.10557425

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Soil Sci. Plant Nutr., 31 (2), 175-187, 1985

NITROGEN DYNAMICS IN THE UPPERMOST PART OF SUBMERGED PADDY SOILS IN TEMPERATE

AND TROPICAL REGIONS

11. Effect of Segregation of Soil Particles by Puddling on the Dynamics of Submerged Sandy Soil

Prapai CHAIROJ,'" Makoto KIMURA, Hidenori W ADA, and Yasuo TAKAI

Faculty of Agriculture. The University of Tokyo. Bunkyo-ku. Tokyo. 113 Japan

Received March 29, 1984

The segregation of fine particles in the uppermost part of Thai (Surin) and Japanese (Katagiri) sandy paddy soils was studied under field and laboratory conditions.

Under laboratory conditions, the soil was puddled under shallow (1 cm) or deep (12 cm) surface water. There was a pronounced segregation of clay and silt in the uppermost part of the Surin soil when the soil was puddled under deep surface water, the extent of which was similar to that under field conditions. Remarkable segregation of these fine particles also occurred in the Katagiri soil when the soil was puddled under deep surface water, to a much larger extent than under field conditions. This difference in the sorting effect in the Katagiri soil between field and laboratory conditions may be ascribed to a higher rate of water per­colation under the former condition, while in the rainfed Surin soil no water percolation took place under field conditions compared with laboratory conditions.

Puddling under deep surface water promoted the segregation of organic matter in the uppermost part of the submerged soil. and the extent was much larger in the Katagiri soil than in the Surin soil. This sorting phenomenon enhanced the ammonification process and suppressed the nitrification-denitrification process in the early to the middle stages of incuba­tion in the Surin soil and in the early stage of incubation in the Katagiri soil. Key Words: segregation, puddling, nitrification-denitrification, submerged soil.

It has been frequently observed that the plough layer of Thai sandy paddy soil differentiates into the upper layers with a fine texture and the lower layers with a coarse texture. This differentiation is conspicuous in red-yellow podzolic soils (Ultisols) which are widely distributed in the Northeastern Plateau of Thailand. This phenom­enon may be ascribed to the segregation of fine particles in the uppermost part when the submerged plough layer is disturbed by puddling and this differentiation may affect most of the processes occurring in the plough layer, particularly in the uppermost part in which the accumulation of fine particles takes place.

• Present address: Division of Soil Science, Department of Agriculture, Bangkhen, Bangkok, Thailand.

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,176 P. CHAIROJ. M. KIMURA. H. WADA. and Y. TAKAI

In paddy soils, it has been known that the contents of organic C and organic N increase with the decrease of particle size and with the increase of clay content (CHICHE­STER, 1969; SWIFT and POSNER, 1972; YOUNG and SPYCHER, 1979) and that puddling enhances nitrogen mineralization in submerged soils (SAKANOUE and MIZUNUMA, 1962; SAKANOUE and MATSUBARA, 1967; CHICHESTER, 1969; DEI and MAEDA, 1973; YOSHINO and ONIKURA, 1980).

The present investigation is an attempt to elucidate the mechanism underlying the differentiation and the effect of the segregation of fine particles on the redox state and nitrogen transformation in submerged soil, in comparing Thai and Japanese sandy paddy soils, namely the Surin and Katagiri soils, under field and laboratory con­ditions. In the field, the differentiation of the plough layer into the upper fine and the lower coarse texture layers was investigated. In the incubation experiments, the puddled and non-puddled soils were compared under submerged conditions.

MATERIALS AND METHODS

Soil. Soil samples used in the present investigation were collected from the plough layer of a paddy field at Surin Rice Experiment Station (RES) in Northeast Thailand to which rice straw compost had been applied and from a farmer's paddy field located at Katagiri, Nagano Prefecture in Japan to which farmyard manure and inorganic fertilizers had been applied. Organic materials were applied for 6 years in the Surin soil and more than 20 years in the Katagiri soil. The wet soil samples were air-dried and passed through a 2 mm screen. Some properties of the soils are shown in Table 1.

The texture of both soils was sandy loam, and CEC and organic matter content were much higher in the Katagiri than in the Surin soil.

Incubation technique. 1) Closed submerged condition. Air-dried soil samples were respectively put in

a truncated 100 ml volume syringe, in which the depth of the soil layer was 40 mm, and submerged with surface water at the depth of 10 mm. The syringe was closed by a rubber stopper, the air was removed, and incubation was carried out at 25°C for the Katagiri soil and at 30°C for the Surin soil, respectively.

2) Open submerged condition. Three hundred and eighty grams of Surin and three hundred grams of Katagiri air-dried soil samples were put in a glass cylinder 9 or 20 cm long, the bottom of which was sealed with paraffin, and submerged with

Table 1. Properties of Surin and Katagiri soils.

Soil Plot Soil pH CEC C N Mineralizable-N texture (HaO) (meq/loo g dry soil) (%) (%) (mg/loo g dry soil)

Surin M SL 5.04 4.8 0.55 0.06 4.86 Katagiri M+F SL 6.08 8.0 1. 64 0.14 7.77

M. Rice straw compost; M+F. Rice straw compost+inorganic fertilizer.

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.Sorting Effect on N-Dinamics by Puddling 177

distilled water. The soil layer was 40 mm thick and the surface water was kept at a depth of 1 or 12 cm in the short or long cylinder. The submerged soils put in the short or long cylinder were divided into two groups for the treatments shown in the chart below.

Soil sample in the cylinder

I surface water

lcmdeep

I puddling

(p-l) I

I

I I

I non-puddling

(np-t)

kept incubated at 4°C at 25° and 30°C

I I

surface water l2cm deep

I puddling

(p-12)

I I

non-puddling (np-12)

In the first group, the soil was puddJed with a glass rod for 1 min under the surface water at a depth of 1 or 12 cm immediately after submergence to induce particle segre­gation (p-l or p-12). In the other group, no puddling was carried out for the soil under the surface water at a depth of 1 or 12 cm (np-l or np-12). One set of puddled and non-puddled soils was kept at 4°C to inhibit microbial activities until the surface water in the puddled plot became clear (soil sample at the beginning of incubation). The other set of puddled and non-puddled soils was incubated at 25°C for the Kata­giri soil and at 30°C for the Surin soil. During the incubation period, the loss of water by evaporation was compensated periodically.

Analysis. At the beginning of incubation, soil and water analyses were carried out according to the procedures described in the previous report (CHAIROl et al., 1984).

In the closed incubation experiment, the soil and the water samples were well mixed, and analyses of the moisture and NH,+-N contents (BREMNER, 1965) were per­formed.

In the open incubation experiment using the cylinder, after careful collection of the surface water, the soil column was sliced into four layers, namely 0-3. 3-6, 6-9, 9-40 mm in thickness, according to the procedure described previously (CHAIROl et al .• 1984).

Soil samples at the time of submergence (0 de.y) were analyzed for particle size distribution (WADA, 1966), organic carbon c;ontent by C.N-corder (YANACO MT, 500, YANAGIMOTO, Co .• Japan) and mineralizable N content according to the fol­lowing procedure. The air-dried ~oil sample was incubated for 4 weeks under closed submerged conditions and analyzed for NH,+-N content (BREMNER, 1965).

After a certain period of incubation, the surface water and each slice of the soil column were analyzed for NH,+-N (BREMNER, 1965), Fe(U) (KUMADA and ASAMI, 1958), NOs--N and NOa--N contents (SrRlcKLAND and PARSONS, 1968).

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178 P. CHAlROJ, M. KTMURA, H. WADA, and Y. TAKAT

RESULTS AND DISCUSSIONS

J. Particle size distribution under laboratory and field conditions Figure 1 shows the distribution of sand, silt and clay in the soi l column in the

cylinder at the beginning of su bmergence under laboratory conditions. In the Surin soi l, when the soi l sample was submerged with deep surface water and

puddled (p-12), clay and si lt particles tended to accumu late in the upper thin layer, indicating that remarkable segregation of these fine particles took place. But when the soil samples were submerged with shallow surface water and puddled (p- I), seg­regation of clay and si lt was not conspicuous. Distribution of clay and si lt in. the soi l submerged with shallow surface water and puddled (p-I) or non-puddled (np-I) was uniform throughout the soi l column . On the other hand, the contents of clay and silt in the uppermost layer and subsequent lower layers amounted to 47, 25, J 9, 8% and 34, 35, 25, 6% respectively (total clay and si lt content basis) for the soi l submerged

Surin Ka t a giri

0

3

6 n on-pudd l ed soi l

9 SW 1 cm

40 j 0

..c; 3 +J p uddled s oil 0. 6 Q)

'tl SW 1 c m ..... 9 .... 0 4 0 I/)

0

3

6 p udd l ed so il

9 SW 1 2 c m

40 0 20 40 60 80 100 0 2 0 40 60 8 0 1 0 0 ~

sand , s ilt a nd clay conte nt

~ : sand , 0: silt, E] : c l ay

Fig. I . Sand, silt , a nd clay contents in each layer of Surin a nd Katagiri paddy soils as an·ected by puddling and depth of surface water.

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Sorting Effect on N-Dinamics by Puddling 179

with deep water and puddled. These clay and silt particles showed a sharp gradient in the soil profile. Such a remarkable accumulation of clay and silt in the uppermost layer was observed also under field conditions as shown in Fig. 2.

In the Katagiri soi l, no remarkable segregation of clay and silt occurred when the soil was submerged with shallow surface water and puddled (p-I) or non-puddled (np­I), but the segregation of fine particles markedly increased when the soil was puddled in deep surface water (p-12), as shown in Fig. I. The content of clay and silt decreased with depth for p-12. As shown in Fig. 2, the segregation of clay and silt in the thin uppermost layer of the Katagiri soil also occurred in the field soil profile, but under field conditions the segregation was not as remarkable as under laboratory conditions. Comparison of the Surin soil with the Katagiri soi l showed that the degree of sorting under field conditions was much higher in the former than in the latter soil.

The accumulation of clay and silt in the uppermost layer of both soils submerged with deeper water under laboratory conditions may be caused by the sorting of dis­persed soil particles associated with the very slow precipitation in stagnant surface water after the submerged soi ls were puddled.

As shown clearly in Fig. 1, the depth of the surface water is one of the important factors controlIing sorting.

The difference in the results obtained in the sorting of soil particles between the Surin and Katagiri soils under field conditions can be attributed to the rate of water

..... ..... o III

o

10

20

30

4 0

0

Suri n

25 50 75 10 0

sa nd , si lt and . : coarse s and,

IDIDI : silt

Katagi ri

0 25 50 75 1 00

clay con t e nt ( % )

0 : fi ne sand

m. : c l ay

Fig. 2. Particle size:: distribution in Surin and Katagiri soil profiles under field conditions.

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180 P. CHAIROJ, M. KIMURA, H. WADA, and Y. TAKAI

percolation at the time of puddIing. In the Surin field, which is located in a rainfed paddy area, puddIing is performed when the ground water level rises due to rain water after the onset of the rainy season and the field is flooded with water more than 15 cm deep. On the other hand, in the Katagiri irrigated field, puddIing is carried out in a field flooded with water more than 15 cm deep, but with rapid percolation of irrigation water, since the soil permeability is high due to the coarse texture of soil and the low ground water level. Thus in the Surin field, the precipitation of fine particles takes place very slowly in stagnant deep water and sorting is pronounced in the vertical soil profile in the same way as under the laboratory conditions. In the Katagiri field, the precipitation of fine particles takes place much faster in deep water with water percolation and no remarkable sorting occurs.

2. Distribution of organic carbon and mineralizable nitrogen In Figs. 3 and 4, the amount of organic C and mineralizable N are shown for each

layer of the Surin and Katagiri submerged soils which were affected by puddling. In the Surin soil, no remarkable sorting occurred for organic C and mineralizable

N in each vertical soil profile, when the soil submerged with shallow surface water was puddled (P-l) or not puddled (np-I). However, when the Surin soil submerged with deep water was puddled (p-12), sorting was pronounced for the compounds among the upper layers and the bottom layers in the vertical profile. The results presented

u 4 I

e.. 3

2

1

puddling under water 1 cm deep'

puddling under water 12 cm deep

Surin

DOon I<atagiri

non-puddling under water 1 cm deep

Doon

O .. -u-u~~~ __ ~~~-u ______ ~~~~ __ ~

1 2 3 4 1 2 3 4

soil layers

Fig. 3. Organic carbon content in each layer of Surin and Katagiri submerged soils as affected by puddling in relation to the depth of surface water; 1: 0-3, 2: 3-6, 3: 6-9, 4: 9-40 mm.

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10

Sorting Effect on N-Dinamics by Puddling

puddling

under water 1 cm deep

puddling

under water 12 cm deep

no-puddling

under water 1 cm deep

15 ~ ! :0000

.' \-,

DODO b'I g 25 <"i ..... g' 20

z I 15

+"" ~

10

5

l<atagiri

soil layers

Fig. 4. Mineralizable N content in each layer of Surin and Katagiri submerged soils as affected by puddling in relation to the depth of surface water; 1: 0-3, 2: 3-6, 3: 6-9, 4: 9-40 mm.

181

here are in agreement with the data on the soil particle distribution described in the former chapter. These results indicate that remarkable segregation takes place not only for fine particles, such as clay and silt, but also for organic matter, such as plant debris and humic substances, in the upper layers of the Surin soil submerged with deep water and puddled.

In the Katagiri soil, no remarkable sorting occurred for organic C and mineral­izable N in each soil profile, when the soil submerged with shallow water was not pud­dIed (np-I). On the other hand, when the Katagiri soil submerged with shallow or deep water was puddled (p-1 or p-12), marked sorting occurred for those compounds among the layers of each vertical soil profile, although the degree of sorting was differ­ent between the p-1 and p-12 plots. Unlike in the Surin soil, the remarkable segrega­tion of organic matter in the uppermost layer of the Katagiri soil submerged with shallow water and puddled (p-t) may be attributed to the dissimilarity of organic matter constituents between both soils, that is, to the enrichment of easily decomposable organic matter such as plant debris associated with the prolonged application of com­post in the Katagiri field. This ,explanation may be applicable to the much higher degree of organic matter segregation in the upper layers of the p-12 plot in the Katagiri soil than in the Surin soil. This assumption is supported by the fact that the degree of sorting among the upper and bottom layers was higher for organic C and mineral­izable N than for soil particles in the Katagiri soil.

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182 P. CHAIROJ, M. KIMURA, H. WADA, and Y. TAKAI

These results reveal that puddIing resulted in the segregation of organic matter, particularly the easily decomposable organic matter including mineralizable N not only in the uppermost layer of the Surin and Katagiri soils submerged under deep water but also in the uppermost layer of the Katagiri soil submerged under shallow water.

J. Ferric reduction and ferrous oxidation in the soil incubated under open submerged condition

Figure 5 shows the Fe(U) content in each layer of the submerged soil column which was puddled under deep surface water (p-12).

Fe(U) content in the lower layers of both Surin and Katagiri soils increased slowly with a similar pattern from the early to the later stages of submergence, and was much lower than that in the upper layers.

In the Surin soil, Fe(U) content increased rapidly from the early to the middle stages of submergence, then rapidly decreased by oxidation afterwards. In the Kata­giri soil, a remarkable increase of Fe(II) content took place at the beginning of sub­mergence but the content decreased from the middle to the later stages. This finding suggests that in the Katagiri soil, ferric reduction was nearly completed due to the low content of easily reducible iron oxide and organic matter decomposition rapidly proceeded in the early stage.

The data presented here clearly reveal the following two points. First, puddling under deep surface water promoted ferric reduction in the upper layers of the Surin

600

500

:;:: 400 o UI

>0 300 ... "0 ~ 200 o o rl ...... ~ a

100

7th day 28th day

12341234 soil layers

60th day

1 2 3 4

Fig. S. Fe(II) content in each layer of Surin and Katagiri submerged soils as affected by puddling under deep surface water (12 cm); 1: 0-3, 2: 3-6,3: 6-9,4: 9-40 mm.

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Sorting Effect on N-Dinamics by Puddling 183

soil and of the Katagiri soil due to the sortings. Second, later ferrous oxidation in the upper layers of the Katagiri soi l took place much more significantly in the Surin soil . This difference in the rate of ferrous oxidation between both soi ls may be ascribed to the much faster progression of organic matter decomposition in the upper layers of the Katagiri soil compared with the Surin soil.

4. Nitrogen transformation in the soil incubated under closed and open submerged con­ditions

Figures 6 and 7 show the NH4 +-N contents in each layer of the submerged soil whjch was affected by puddling in relation to the depth of surface water.

Table 2 shows N02--N and NOa- -N contents in the surface water and in the uppermost layer of the Surin and Katagiri soi ls puddled under deep surface water.

..... ·rl

0 tIl

>, ... '0

C' 0 0 ..... ....... C' E

Z I

+ .,. J: Z

6 -

4

2

0

14

12

10

3

6

2

0

G

2

o m o c 1 2 3 4

28 th day 60 th day

puddling under

water 1 cm deep

I ~~~D I ~nnD pudd lin 9 under

water 1 2 cm deep

no-puddling undpr h'ilter I cm dee p

JIJnQ III C 1 2 3 4 C 1 2 3 4

soil l i1yers

Fig, 6. NH~+-N contents in each layer of Surin submerged soil as affected by puddling in relation to the depth of surface water ; open condition-I : 0-3, 2: 3- 6, 3 : 6-9, 4: 9-40 mm ; 0 day-O; closed condition-C.

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184 P. CHAIROJ, M. KIMURA, H. WADA, and Y. TAKAI

Table 2. Nitrate and nitrite nitrogen contents in the surface water and in the uppermost layer of Surin and Katagiri soils puddled under deep surface water (p-l2).

NO.--N (ppm) NOa--N (ppm) Soils Layer

Od· 7d 28d 60d Od 7d 28d 60d

Surin SW 0.02 0.06 0.55 0.00 0.00 0.54 UL 8.50 0.01 ND ND ND 0.00 ND ND

Katagiri SW 0.03 0.94 0.23 0.01 1. 68 0.00 UL 8.70 0.33 0.99 1. 71 ND 0.13 0.98 0.16

• d, Days after submergence; SW, Surface water; UL, Uppermost layer (0-3 mm); ND, No determina­tion.

Under a closed condition, ammonification in both Surin and Katagiri soils pro­ceeded steadily until the later period of incubation. NH, +-N formation during the incubation period was remarkably higher in the Katagiri soil than in the Surin soil. This reveals that the content of the easily decomposable organic nitrogen in the Kata­giri soil was higher than in the Surin soil. This difference may be ascribed to the longer period (about 30 years) of compost application in the Katagiri soil.

In the Surin soil submerged under an open condition, nitrogen transformation assumed two patterns, as shown in Fig. 6. First, in the p-l and np-! plots, ammoni­fication occurred in the early stage of incubation, and afterwards NH,+-N content in the surface water and upper layers decreased slightly, suggesting that the nitrification­denitrification process was pot active. Second, in the p-12 plot, ammonification pro­ceeded from the early to the middle stages and decreased moderately in the later stages of incubation. This decrease of NH, +-N content corresponded to the decrease of Fe(II) contents in the upper layers, as shown in Fig. S. These results suggest that nitrogen loss by the nitrification-denitrification process in the uppermost layer took place in the later stages when the content of easily decomposable organic matter was exhausted and a thin oxidized layer started to develop. In this regard, the progress of nitrification in the later stages provides experimental evidence for the increase of nitrate and nitrite concentration in the surface water from 28 days to 60 days, as shown in Table 2. Comparison of the puddled and non-puddled plots of the Surin soil shows that puddling gave rise to an appreciable enhancement of ammonification in the upper layers particularly under the submerged conditions when the field was covered with surface water 12 cm deep. This finding may be associated with the marked seg­regation of organic matter in the upper layers of the Surin soil by puddling under deep water.

In the Katagiri soil, similar patterns of nitrogen transformation were observed for all the plots, as shown in Fig. 7. In the upper layers, ammonification was completed in the early stage of incubation and a remarkable decrease of NH, +-N took place from the middle to the later stages. On the other hand, in the bottom layer, ammonification

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Sorting Effect on N-Dinamics by Puddling

1 0

8

6

2

o L..E::::L

12 r

rl 10 .... o tIl

Z I

8

6

2

+ <I' 0 '--..... r.:->.'-'--...awI1.-.L..U...u....u...~ ~

8

6

o _1:':'1

o C 1 2 J 4

-

28 th day 60 th day

pudd li ng unde r

wat e r 1 cm deep

p uddl ing under

wat e r 1 2 cm d e p

n -no - pudd ling under

wa t er 1 e n deep

LooQ C 1 2 J 4 C

so i 1 l a y e 1-5

185

F ig. 7. NH.+-N contents in each layer of Katagiri submerged soil as affected by puddling in relation to the depth of surface water : open condition-I : 0-3, 2: 3- 6, 3: 6-9,4: 9-40 mm ; 0 day-O; closed condition-Co

proceeded from the early to the later stages a nd no or li ttle decrease of N H4 +-N oc­curred in the later stages . The remarkable decrease of NH4 +-N in the upper layers between the middle and the later stages may be due to the foll owing mechanism. After the flu sh of ammoni6cation was completed in the upper layers at the ea rly stage, a thin oxidized layer developed in the uppermost part and afterwards nitrification sta rted . From the midd le to the later stages, nitric acid formed a t the level of the oxidized laye r was transported to deeper reduced layers and denitrified there. When the ammonium content in the uppermost part decreased by nitrification and denitrification, an upward

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186 P. CHAIROJ, M. KIMURA, H. WADA, and Y. TAKAI

movement of ammonium by diffusion took place from the lower part to the uppermost part in the upper layers. This process resulted in the decrease of NH, +-N not only in the top layer but also in the second and third layers. This assumption may be sub­stantiated by the data on nitrate and nitrite contents in the surface water and the uppermost layer, as shown in Table 2. A marked decrease in nitrate content took place in the early stage. Thereafter nitrate and nitrite contents increased remarkably in the middle stage and afterwards decreased in the later stage. Comparison of pud­dIed and non-puddled plots of the Katagiri soil revealed that puddIing gave rise to a remarkable enhancement of ammonification in the upper layers of both the p-t and p-12 plots, although the extent of enhancement varied.

These results indicate that puddling under deep surface water enhanced the am­monification process in the upper layers of the Surin and Katagiri soils and suppressed appreciably the nitrification-denitrification process in the uppermost layer of the Surin soil but only moderately that in the uppermost layer of the Katagiri soil. Thus threre was little progress in the nitrification-de nitrification process in the uppermost layer of the Surin soil whereas the process was active in the Katagiri soil.

CONCLUSION

The following conclusions were drawn on the basis of the above experiments on nitrogen transformation in the submerged soil which was affected by puddling depend­ing on the depth of the surface water.

1. PuddIing gave rise to an appreciable segregation of fine particles, such as clay and silt in the upper layers of sandy soil submerged with deep surface water under

"' laboratory conditions. The pattern of particle sorting under laboratory conditions was similar in the Surin and Katagiri soils. Under field conditions, the extent of fine particle segregation in the upper layers was appreciable in the Surin soil unlike in the Katagiri soil. This difference in the extent of soil particle sorting between the two soils is ascribed to the fact that the precipitation of soil particles takes place very slowly under stagnant water in the Surin rainfed paddy field, but much faster with the rapid water percolation in the Katagiri irrigated paddy field.

2. Puddling under deep surface water gave rise to the segregation of organic matter in the upper layers of both soils, the extent of which was much more remarkable in the Katagiri soil than in the Surin soil. Puddling under shallow surface water pro­moted the segregation of organic matter in the uppermost layer of the Katagiri soil, although no sorting of organic matter by the same treatment occurred in the Surin soil. The finding suggests that the proportion of easily dispersible organic matter induding plant debris to the total organic matter content may be much higher in the Katagiri soil than in the Surin soil.

3. Puddling under deep surface water enhanced ferric reduction after submer­gence and suppressed later ferrous oxidation in the upper layers of both soils, due to the sorting of easily decomposable organic matter and active iron oxide. The amount

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Sorting Effect on N-Dinamics by Puddling 187

of Fe(II) formed was much higher in the Surin soil than in the Katagiri soil and ferrous oxidation in the upper layers occurred earlier in the Katagiri soil than in the Surin soil.

4. PuddIing under deep or shallow surface water enhanced the process of am­monification, and suppressed the nitrification-denitrification process in the upper layers of both soils. A sequential reaction of ammonification and nitrification-denitrification took place concomitantly with that of ferric reduction and ferrous oxidation, which proceeded much faster in the Katagiri than in the Surin soil.

Thus puddIing under deep surface water resulted in the segregation of soil par­ticles and organic matter in the upper layers of both soils, whereas under shallow water puddIing promoted the segregation of organic matter only in the upper layers of the Katagiri soil. In the upper layers of sandy soils, such sortings of fine particles and organic matter result in the development of a reduced state and nitrogen mineral­ization after submergence, which in turn inhibits the process of nitrification-denitrifi­cation.

REFERENCES

BREMNER, J.M., Inorganic forms of nitrogen, In Methods of Soil Analysis (Part 2), ed. by C.A. Black et al., American Society of Agronomy, Madison, Wisconsin, 1965. pp. 1179-1237

CHAIROJ, P., UEHARA, Y., KIMURA, M., WADA, H., and TAKAI, Y., Nitrogen dynamics in the upper­most part of submerged paddy soils in temperate and tropical regions. I. Effect of long-term fertilization treatment, Soil ScI. Plant Nulr., 30, 383-396 (1984)

CHICHESTER, F.W., Nitrogen in soil organo-mineral sedimentation factions, Soil Sel., 107, 356-363 (1969)

DEI, Y. and MAEDA, K., On soil structure of plowed layer of paddy field, JARQ, 7 (2), 86-92 (1973) KUMADA, K. and ASAMI, T., A new method for determining ferrous iron in paddy soils, Soil Plant Food,

3, 187-193 (1958) SAKANOUE, Y. and MATSUBARA, K., Effect of stirring soil just after water lodging on the mineralization

of original organic nitrogen in paddy soils. Studies on harrowing paddy rice field in reference to the fertility of paddy soils (part 2), J. Sci. Soil Manure, Jpn., 38, 70-73 (1967) (in Japanese)

SAKANOUE, Y. and MIZUNUMA, Y., Effect of harrowing upon the behavior of nitrogen in well-drained paddy field with gravel layer, J. Sci. Soil Manure, Jpn., 33, 386-390 (1962) (in Japanese)

STRICKLAND, J.D.H. and PARSONS, T.R., A Practical Handbook of Sea water Analysis, Fisheries Research Board of Canada, Ottawa, 1968. pp. 71-86

SWIFT, R.S. and POSNER, A.M., The distribution and extraction of soil nitrogen as a function of soil particle size, Soil Bioi. Biochem., 4, 181-186 (1972)

WADA, K., Qualitative and quantitative determinations of clay minerals, J. Sci. Soil Manure, Jpn., 37,9-17 (1966) (in Japanese)

YOSHINO, T. and ONIKURA, Y., Evaluation of nitrogen supplying capacity of paddy soils by an incuba­tion method, I. Cent. Agrlc. Exp. Sta., 31, 73-86 (1980) (in Japanese)

YOUNG, J.L. and SPYCHER, G., Water-dispersible soil organic-mineral particles, I. Carbon and nitrogen distribution, Soil Sct. Soc. Am. J., 43, 324-328 (1979)

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