Influence of organic matter on the chemical and electrochemical properties of some flooded soils

Sod Bid. Biochem.

Vol. 9, pp. 259 to 266. Pergamon

Press

1977. Printed

in Great

Britain

INFLUENCE OF ORGANIC MATTER ON THE CHEMICAL AND ELECTROCHEMICAL PROPERTIES OF SOME FLOODED SOILS J. C. All India

KATYAL

Coordinated Rice Improvement Project, Hyderabad 500 030, A.P., India

Rajendranagar,

(Accepted 22 November 1976) influence of organic matter added in the form of gliricidia (Gliricidia sepium Steud.) leaves and rice straw on the chemical and electrochemical kinetics of three flooded soils was studied in a pot experiment. Soils after submergence differed markedly in the properties studied. With addition of organic matter not only the peaks of CO, production and maximum concentrations of water-soluble Fe’+, Mn’+ and other cations occurred earlier but their concentrations were also significantly higher as compared to controls (no organic matter addition). The high concentration of CO2 appeared to influence pH, the accumulation of cations in the soil solution, and to be chiefly responsible for the death of the rice plants. The lethal effects of CO2 and other reduction products can be avoided and nutritional gains to rice can be achieved by planting 34 weeks after the addition of quickly-decomposing organic materials. Summary-The

INTRODUCTION

and K2S04 to give 50 parts/lo’ N, P and K, respectively. In another treatment, along with inorganic fertilizers, organic matter (o.m.) was added to 8-Kg portions of each soil at rates corresponding to 20 tons of fresh leaves of Gliricidia sepium Steud. and 5 tons of chopped rice straw per 2 x lo6 kg soil. The treated soil samples were then transferred to plastic buckets of 121 capacity fitted with a soil solution sampling device (IRRI, 1964). The treatments were repeated twice. The soil in each pot was submerged and two 21-day-old healthy seedlings of Jaya rice variety were planted. Soil solutions were collected for chemical and electrochemical studies immediately after submergence and after 7, 14, 21, 28, 42, 56, 70, 84, 98 and 112 days of flooding. From each pot about 230ml soil solution was allowed to flow by gravity directly into an electrometric cell designed for the simultaneous determination of pH, redox potential (Eh) and specific conductance (IRRI, 1964). Temperatures for each determination were corrected to 25°C. Redox potentials were not corrected to any pH. To determine Mn*+, Fe2+, Zn*+, K+, Ca*+, about 50ml soil solution Mg2+, Na+ and NH:-N was collected in a test tube containing a few drops of 6N HCl (pH 2) to prevent oxidation. All cations, except NH:-N. were determined after appropriate dilutions or pretreatment in a Perkin Elmer@ atomic absorption spectrophotometer Model 290 B. NH:-N was estimated by micro-Kjeldahl distillation

When supplies of cheap inorganic fertilizers became available, green manure and other bulky organic manures fell into disuse. During the current increase of fertilizer costs the use of green manure as an alternative source of plant nutrients is under active investigation. In the context of intensive agriculture, the farmer may not be able to practise green manuring in the traditional manner. However, the use of leaves, twigs and loppings from leguminous and even nonleguminous shrubs and trees grown on field levees and wastelands supplemented with rice straw, stubble and other wastes may partially meet the nutrient requirements of rice. Because of the slow decomposition of organic matter and the production of substances such as COz, CH,, organic acids and reduction products under anaerobic conditions (Patrick and Mikkelsen, 1971) it may be of significance to know the influence of such a practice on the growth of rice. This paper describes the effect of adding gliricidia leaves (an easily decomposable material with a narrow C:N ratio) mixed with rice straw (a slow decomposing, material with a wide C:N ratio) on the chemical properties of three flooded paddy soils and their relationship to the growth of rice. MATERIALS

AND METHODS

Eight-kilogram portions of the three soils (Table 1) were mixed thoroughly with urea, superphosphate Table

1. Chemical

properties

of the soils 0.m.

Soil

Textural

Black soil Lateritic soil Red soil

Clay Loam Sandy

class

loam 259

PH

(%)

c.e.c. (m-equiv lOOg-‘)

7.8 6.4 7.5

1.3 1.5 1.1

42.0 7.5 5.0

260

.I. C.

(Bremner, 1965). P was determined by modification of Martin and Doty’s iso-butanol extraction method as described by Ponnamperuma (1955). Soil solutions were analysed for HCO; by the differential titration method of DiLallo and Albertson (1961). The partial pressure of CO, @co,) was deduced from HCO,, pH and specific conductance (Ponnamperuma et ul.. 1966b). log p,,? = 7.85 - pH + log [HCO,] (HendersonHasselbalch

modified

Where; Pco, is in atmospheres, 1-i and K is specific conductance 25°C.

solutions NO

8.0

were

near

ORGANIC

coelticlents

neutral.

bct\veen

pH and I-‘<<,> Correlation coctficient

Treatment No o.m. o.m. No o.m. 0.m. No o.m. o.m.

Black clay soil Lateritic

soil

* Significant

[HCO;] is mol mhos cm- ’ at

PH The final pH of the solutions from the three soils, irrespective of their original pH, were between 6.85 and 6.95 (Fig. 1). A pronounced decline in pH of the soil solution after flooding (IRRI, 1963; Ponnamperuma, 1965; Islam and Islam, 1973) was not confirmed in the present investigation. The sluggish behaviour of these soils may be due to their low organic matter content (Table I) and low temperatures prevalent during the investigation (mean minimum, 13-22°C and mean maximum, 33337°C). Strikingly. when the same soils were treated with o.m. the pH dropped almost by l&1.5 units during the first week of flooding. After the initial sudden drop the pH rose and attained more or less steady values after 4 weeks. Regardless of o.m. addition and original pH of the three soils. of the soil

7. Corrclatlon

Soil

equation).

The addition of o.m. had a pronounced effect on soil reduction and accumulation of products of anaerobic respiration. Within 1428 days of submergence there was an accumulation of CO,, water-soluble Fe2+, Mn2+ and other cations. So intense was the effect of CO, accumulation and other reduction products that the plants in the o.m. treated soils died within 2 weeks of submergence. In contrast, when no o.m. was added, soil reduction was very slow and Fe”. Mn2+ and other peaks of Pco,, water-soluble cations appeared only 7G84 days after flooding. Plant growth was normal except that symptoms of initial Fe chlorosis and slight P deficiency were noticeable in the red and black clay soils, respectively. The changes (mean of two replicates) in chemical and electrochemical properties of the three submerged soils as influenced by the addition of o.m. are discussed below.

pH

Table

Red soil

- 2./K

RESULTS

the final

KAI~AL

~ 0.9025 * -0.X442* -0.9.574* -0.9636* -0.x524* - 0.97(,4*

at l”‘;, level.

An appraisal of the pH kinetics after flooding (Fig. 1) and changes in the Pro, (Fig. 7) reveal that there was a highly significant negative correlation between these two characteristics (Table 2). The sharp and quick decline in pH and build up of PC”,. when o.m. was added, corroborates this relationship. Ponnamperuma (1965) related the fall in pH of flooded soils to accumulation of CO, and soil reduction and Motomura (1962) to production of organic acids. The subsequent increase in pH of the soil solution has been attributed to the reduction of Fe (Ponnamperuma. 1965; Islam and Islam, 1973). This study indicates that the nutritional gains to rice associated with a rise in pH of acid soils (suppression of possible Fe toxicity in o.m. treated lateritic soil, Fig. 5) and fall in pH of alkaline soils (alleviation of Fe chlorosis observed in rice plants grown in red soil) may be achieved within 21-28 days of incorporation of quickly decomposing organic matter. Eh The Eh dropped sharply (Fig. 2) during the first week of submergence. It was followed by an increase and then an asymptotic decrease. After 5670 days of submergence each soil attained an Eh value which was more or less constant during the remainder of the study (until I12 days). Addition of o.m. caused a steep fall in Eh in the early stages (Fig. 2) because of the accumulation of reducing substances as a result of O2 depletion (Ponnamperuma, 1972). The Eh values in general were lower with o.m. than without it.

Specific conductance (K. m mhos cm-’ at 25-C) of the soil solution of three flooded soils remained unaltered for the first 42 days of submergence. followed by a gradual increase up to 7&84 days. and a decrease thereafter when no o.m. was added (Fig. 3). In contrast o.m. addition caused a sharp rise in the specific conductance within 14 days of flooding. ORGANIC

MATTER

MATTER

‘........, I a

“. .._..__ h ~_~__ . ...

7.0

_-

~.~.~.z__..“” ;., $_ /

-_/c

.

-

,,... ._.. ._.., . .._.

0.5 0.0

k

““‘-0

28

56

84 DAYS

Fig.

I. Changes

112 AFTER

0

28

56

84

II 2

SUBMERGENCE

in the pH of the soil solution of the three ---- Lateritic soil; ‘.

submerged soils. Red soil.

~ Black

cldq

soil:

Organic matter and flooded soils 0.40

NO

ORGANIC

r

MATTER

ORGANIC

261

HATTER

030

0.00 0

28

56

84 DAYS

112 AFTER

0

56

28

112

84

SUBMERGENCE

Fig. 2. Changes in the redox potential __

(Eh) of the soil solution of the three submerged Black clay soil; -----------Lateritic soil; ............ Red soil.

r

NO

ORGANIC

r

MATTER

ORGANIC

soils

MATTER

A

,I’:\ : ‘\

L I

\

:”

.. .. . \

. . . . . . . .b<..““...

- .

I

0

28

84

56 DAYS

112

AFTER

0

.

.

.

*

28

“..., - . <‘;‘..... -;“-“..’

.

56

.

I

84

II2

SUBMERGENCE

Fig. 3. Changes in the specific conductance (K, m mhos cm- r, 25°C) of the soil solution of the three submerged soils. ~ Black clay soil; -----------Lateritic soil: Red soil.

Then there was a quick decline up to 28 days followed by an asymptotic decrease. The initial increase in conductance is due to soil reduction, accumulation of NHf, HCO; and RCOO-, solubilization of precipitated carbonates (IRRI, 1964; Ponnamperuma, 1965, 1972) and displacement of cations by Fe’+ and Mn2+. These hypotheses are supported by the similarity of curves for the kinetics of Fe’+ + Mn2+ and and specific conducCa2+ + Mg2+ + K+ + NH: tance (Fig. 4). The fall in specific conductance, after the peak, may be attributed to the reprecipitation of Fe’+ and Mn2+ and the consequent adsorption of cations to the exchange sites and decrease in Pco, (Fig. 7) and decomposition of organic acids (Ponnamperuma, 1972). The sudden initial increase in specific conductance may be one of the reasons for the death of the rice plants in the o.m. treatment. Water-soluble Fe’+ When no o.m. was added the concentration of water-soluble Fe’+ was very low (Fig. 5). Soils differed in the changes in concentration of water-soluble Fe’+ in the soil solution with time. The slightly acid lateritic soil built up the highest concentration of 82 parts/lo6 water-soluble Fe’+ 84 days after flooding. The corresponding peak of 20 parts/lo6 Fe*+ for red soil appeared after 98 days and black clay soil demonstrated an increasing water-soluble Fe’+ even after 112 days of submergence. In comparison the peaks of water-soluble Fe’+ with o.m. addition (Fig. 5) were strikingly sharp, appeared earlier and the content of water-soluble Fe2+ was significantly higher. The in-

itial exponential build-up was followed by a sharp decline up to 30 days of submergence and a slow decrease thereafter. The build-up of water-soluble Fe2+ is due to the reduction of ferric hydroxide (Ponnamperuma et al., 1967; Gotoh and Patrick, 1974) and the subsequent decrease (Ponnamperuma, 1972) may be due to precipitation of Fe’+ as Fe(OH), or Fe,O,. nH,O caused by an increase in pH (Fig. 1) following a decline in f’co, (Fig. 7). The similarity between the kinetics of water-soluble Fe2+ (and Mn2+) and other cations (Fig. 4) suggests that the former affects the concentration of the latter (IRRI. 1963; Ponnamperuma, 1965). The dynamics of water-soluble Fe2+ can be de80

LATERITIC SOIL (ORGANIC MATTER)

4.0

:‘: 60

~.:.....:.....~~~~~~.2 .........1 0

28

DAYS

AFTER

56

a4

112”

SUBMERGENCE

Fig. 4. Changes in the specific conductance (K, m mhos cm-r, 25°C) and cation concentration of the soil solution of a submerged soil.

262 3oo

1

NO ORGANIC

MATTER

- ; _ I\

I

260

220

I:

I

180-

m t

::

140.

,:G

IOO‘.

,’

60 I/ ,,---_-J

20 0

j.

/’

5. Changes

scribed by the following Lateritic soil:

in the

__,_,,,.,.... .” .......

.,.............

28

56

DAYS

Fig.

MATTER

I : - 1 I I , 1 I I 1 I 1 _I 1 ’ : I : _I \ \ _ I.. I .: ‘: : 1; ‘,.. I I ,: ‘...,. I ‘. I . I/ ‘:, L-. I: .I: ‘. .._,.‘\ --___ 1: .. ._..___. . ..\-.. ‘. .

m

0 \

ORGANIC

84

112 0

AFTER

28

56

84

water-soluble Fe’+ of the three submerged soils _____________ Lateritic soil; Red soil,

Black clay

soil;

assumes importance when considering Fe toxicity in strongly acid soils and Fe deficiency in alkaline soils.

equations:

No o.m. log Fezi = 0.6617 + 0.013t (r = 0.8321) o.m. log Fe*+ = 0.4266 + 3.0236 log t

- 1.2351 log t1 Red soil: No o.m. log Fe’+ = -0.2345 + 0.0159t (I’ = 0.9491) o.m. log Fe2’ = 0.5581 + 2.1612 log t - 0.8366 log f2 Black clay soil: No o.m. log Fe’+ = -0.4866 + 0.0153t (v = 0.9795) o.m. log Fe2+ = 0.2869 + 1.6217 log t - 0.5327 log t2 where. Fe2+ is in parts/lo” and t is days after submergence. These equations may help in predicting the watersoluble Fe” after submergence. Such prediction ‘5Or

112

SUBMERGENCE

NO

ORGANIC

DAYS

Fig. 6. Changes in the water-soluble

Water-soluhlr

rt,

MATTER

AFTER

Mn2-

The kinetics of water-soluble Mn2+ reflected the same pattern as that was observed for Fe2’ (Fig. 6). In the absence of o.m. the peaks of Mn2+ appeared 56-70 days after flooding in striking contrast to 14 days when o.m. was added. The peak Mn’+ values were more than doubled in the soil solutions of red soil and black clay soil in the presence of o.m. unlike lateritic soil where the increase was only marginal. The accumulation of water-soluble Mn2+ like Fe’+, is attributed to chemical and biological reductions (Ponnamperuma, 1965; Ponnamperuma et al.. 1969; Gotoh and Patrick, 1972). However, Mn reduction precedes that of Fe. The data from the present investigation, particularly in the absence of o.m. addition. confirm this thermodynamic sequence as sugORGANIC

MATTER

SUBMERGENCE

Mn*’ of the ____________ Lateritic soil;

three

submerged soils Red soil.

Black

clay

soil;

Organic matter and flooded soils

by the anaerobic decomposition of organic matter. This corroborates the higher Pcol obtained as a result of o.m. addition. The sharp decline in the Pco, of the lateritic soil (with and without o.m.) and red soil (with o.m. only) both of which had high concentrations of water-soluble Fe*+ and Mn*+ may be due to the formation of sparingly-soluble carbonates (LRRI, 1964). This hypothesis is supported by a slow decline in the Pco, of the black clay soil which was low in water-soluble Fe’+ and Mn*+ even in the presence of 0.m. High Pco, may increase the water-soluble Fe*+ to toxic amounts (IRRI, 1967) or H2C03 may directly poison the plant (Yamakawa and Kishigawa, 1957; Tanaka and Navasero, 1967). Rice plants died within 2 weeks of flooding in the presence of added o.m. perhaps because of the lethal concentrations of CO*. This study suggests that to avoid lethal effects of CO, the planting of rice should be delayed by 34 weeks after the addition of fresh o.m.

gested by Ponnamperuma (1965). A sharp fall in the concentration of water-soluble Mn’+ is due to its precipitation as MnCO,. The dynamics of water-soluble Mn*+ in flooded soils can be described by the following equations: Lateritic

soil:

No o.m. log Mn2+ = 4.4447 - 1.2038 log t - 0.3621 log tZ o.m. log Mn*+ = 2.2845 + 0.6141 log t - 0.7509 log t* Red soil: No o.m. log Mn*+ = 4.2601 + 6.2325 log t - 1.8062 log t2 o.m. log Mn2+ = 2.5028 - 0.883 log t Black clay soil: No o.m. log Mn2+ = 3.2406 + 4.1443 log I - 1.7051 log t* o.m. log Mn2+ = 3.128 - 2.2967 log t + 0.463 log t* where, Mn2+ is in parts/lo6 mergence.

system

CaCO,-H20Z02

and t is days after sub-

The data from these experiments show that there is build up of CO, in the soil solution of flooded soils. Pco, exerts a profound influence on the chemical equilibria in a reduced soil (IRRI, 1965). For the CaCO,-H,O-CO2 system, the following equations, illustrate the relationship between Pco,, pH, OHpotential, and the activity of Ca*+, in the soil solution have been derived (IRRI, 1965; Ponnamperuma, 1967) and their validity was tested.

P coz The Pcol increased steadily with submergence when no o.m. was added, attained a maximum value (56, 70 and 84 days after flooding for lateritic, red and black soils, respectively) and declined thereafter (Fig. 7). Soils differed in the kinetics of Pco,. The slightly acid lateritic soil high in water-soluble iron exhibited the largest Pco2 which appeared earlier, was higher, declined faster than in the low iron red and black soils. The maximum PC”, reached within 2 weeks, for all the soils, in the presence of added o.m. Not only were the Pco2 values higher, but the peaks were sharper and the decrease was more rapid as compared to the no o.m. treatment. The Pco2 levelled off between 0.14 to 0.17 atm after 14 weeks of submergence, when no o.m. was added. On the other hand more or less constant Pco, (between 0.10.25 atm) were observed within 4 weeks of flooding in the presence of 0.m. The initial rise in Pco2 after flooding is brought about by aerobic respiration (IRRI, 1964) followed

0.4 5

263

pH = 6.02 - 0.67 log Pm, 4.92 = pH + 4 log Ca*+ + 4 log Pco2. Flooded soils CaCO,-H,O-CO,

in our studies behaved system as shown below: PH = f(PcoJ

Black clay soil: No o.m. pH = 6.37 - 0.57 log Pco2 o.m. pH = 6.44 - 0.47 log Pcoz Red soil: No o.m. pH = 6.54 - 0.45 log Pco, o.m. pH = 6.38 - 0.64 log Pcoz

t L

E ;

0.35

0” :

0.25

.

/ -A8”.

O-15

,..’

-

,,’

._I

_’

0.05

-

0~00

w. .Y....’

0

,..”

_..’

,I

‘.,,

\.

.. .+

:.’

;’

:’

.

.

ZB

56

84 DAYS

.

I

0 AFTER

.

28

.

.

56

.

84

112

SUBMERGENCE

Fig. 7. Changes in the Pco, of the soil solution of the three submerged soils. __ _________ ___ Lateritic soil; Red soil,

Black clay soil;

like

a

264

.I. C. KATYAI

Lateritic

soil:

No o.m. pH = 6.40 - 0.38 log Pcoz o.m. pH = 6.30 - 0.59 log PC”,. The pH/log P,, slopes were, in general, close to the theoretical value of 0.67. But these values were closer for the red and the lateritic soils in the presence of added o.m. than in its absence. However, the intercepts were unusually high. Similar intercepts for three calcareous soils studied at IRRI were obtained (IRRT. 1965) and the high values were attributed to: (i) the presence of carbonates other than CaCO,, (ii) the presence of Ca-organic matter complexes and (iii) the long time taken to reach equilibrium. For the expression pH + ilog Ca’+ + &log Pm2 = 4.92 the following values were obtained. Black clay soil: No o.m. 5.18 k 0.02 o.m. 5.21 f 0.02 Red soil: No o.m. 5.33 k 0.03 0.m. 5.33 _t 0.03 Lateritic

soil :

No o.m. 5.00 If- 0.03 o.m. 4.95 k 0.06.

Rice grown on flooded calcareous soils low in o.m. may exhibit Fe deficiency (IRRI. 1965). In this study plants grown on red soil showed Fe chlorosis during the first few weeks of growth. The equations derived above explain that Fe deficiency can be alleviated in the cast of calcareous soils by adding o.m. to raise the Pro,. Watwsoluhle

K*

The concentration of K in the soil solution, in general, decreased during 70 days of flooding followed by an increase reaching a peak coinciding with that for maximum reduction, when no o.m. was added (Fig. 8). The increase was more for the light textured, low c.e.c. red and lateritic soils which showed higher concentrations of water soluble Fe” and Mn2+. This suggests that the increase in water-soluble K+ may be caused by the release of exchangeable K+ into the soil solution by Fe” and Mn” (IRRI. 1963; Patrick and Mikkelsen, 1971). The similarity of the peaks for Fe’+, Mn’+ and K’ when o.m. was added supports this theory. An increase in the availability of water-soluble Kt may be another advantage of the addition of organic matter. Water-.soluhlt~ Zn’+

The values for OH- potential show that the lateritic soil behaved remarkably like pure aqueous CaCO, equilibrated with C02. For the black and red soils the deviation from the constant for the OH- potential may be due to the above reasons. It is significant to note that in spite of large variations in the Pro1 caused by addition of o.m. and its (CO,) subsequent effect on pH and solubility of CaCO,, the values for OH- potential were near constant for any particular soil. The existence of any other carbonate equilibria involving MgCO,. Na,CO, and MnCO, could not be proved.

340

,

300

t

NO

ORGANIC

Water-soluble Zn’+ declined with the duration of flooding, irrespective of the soil type or o.m. addition (Table 3). The decrease was more rapid in case of the alkaline black clay soil and the red soil than the slightly acidic lateritic soil. Generally, the concentration of water-soluble Zn’+ was less than 0.05 parts/lOh after 4 weeks of flooding. Similar results were obtained in a study (Katyal, unpublished data) where 15 soils were submerged and the kinetics of Zn2+ were followed for 16 weeks. If the concentration of water-soluble Zn2+ determines the rate of Zn uptake by the plant these results

MATTER

60 40 30 20 IO

Fig. 8. Changes

in the water soluble K+ of the three submerged soils. ~~. _ _. ._ Lateritic soil: Red soil,

Black clay soil;

Organic Table

3. Kinetics

matter

and flooded

of water-soluble

265

soils

zinc in three flooded Parts

soils.

Zn’+/lOs

Weeks after submergence Soil

Treatment

0

2

4

6

8

10

12

No o.m. 0.m. No o.m. 0.m. No o.m. 0.m.

9 12 23 48 16 12

14 10 6 11 6 10

2 2 7 5 3 6

2 2 3 4 3 7

2 3 3 4 3 3

2 3 3 5 3 4

2 3 3 4 2 3

Black clay soil Lateritic

soil

Red soil

The increase in water-soluble P caused by o.m. addition (Islam and Ilahi, 1954) may be another advantage of using bulky organic manures for lowland rice.

explain the association of Zn deficiency symptoms with continuously submerged soils (Katyal and Ponnamperuma, 1974). Water-soluble P

Water-soluble NH:-N

The slight and transitory increase in water-soluble P observed after flooding in the absence of o.m. (Fig. 9) may not be due to the increased solubility of Fe, Al and Ca phosphates (Islam and Ilahi, 1954; Mitsui, 1954; Davide, 1961; IRRI, 1963) and the release of P fixed by CaCO, (Ponnamperuma, 1972) as in the o.m. treatment. The decrease in water-soluble P may be attributed to reprecipitation and resorption by soil minerals (Ponnamperuma, 1972). r

2.0

NO

ORGANIC

0

28

r

MATTER

56

84

112

DAYS

Fig. 9. Changes

The three soils showed peaks of NH:-N after 14 weeks of flooding when no o.m. was added (Fig. 10). Strikingly, these peaks appeared within 2 weeks following the addition of o.m. The accumulation of NH:-N may be because of anaerobic decomposition of organic matter. A decline in water-soluble NH:-N following the peak may be due to adsorption on soil colloids (IRRI, 1964) as well as active plant uptake.

in the water-soluble

AFTER

ORGANIC

0

28

56

112

soils. ~

.T. Red

soil:

360

84

SUBMERGENCE

P of the three submerged

____________ Lateritic

MATTER

r

ORGANIC

Black clay soil;

soil,

MATTER

0’) : :

LL 8’

:

:: :: : ’

‘1 ‘\

‘\

; : ,I;:::, ,: I

‘\

j”..... ,: L.,

‘;

I: /;

40

;;

..-

. . ..

\

,i

L,_

‘...

.. . . . . .

0

10. Changes

,_

2S

56

8:

J i’

.,._....“’

.. . . .. -

04

DAYS

Fig.

...._

\I

‘; t

. . ... .

0

:.; i,

tta

AFTER

0

2s

S6

04

112

SVBMERGENCE

in the water soluble NH,+-N of the three ____________ Lateritic soil;

submerged

soils. -

Red soil,

Black

clay

soil;

266

.I. C.

The decline might also be due to the diffusion of NH,‘-N from the reduced soil zone to the oxidized soil zone where NH:-N is converted to NO;-N. The NO;-N being formed in the oxidized soil zone may diffuse into the reduced soil zone where it is denitrified to N gaseous products which escape into the atmosphere. This investigation shows that early build up of available NH:-N in the soil solution may be attained by using easily decomposable. green manure leaves with a narrow C:N ratio. CONCLL’SIONS The use of bulky organic manures is being revived for low land rice in the regions of the developing world afflicted with acute fertilizer shortages. The results of the present investigation have shown that to make such a practice sound, it is essential to withhold planting for at least 3-4 weeks after their application. If there is no interval between applications of organic manure, in particular undecomposed residues, to a submerged soil and transplanting the crop is likely to fail mainly because of high concentrations of CO,, reduction products and the accompanying high electrical conductivity. The increase in pH of acid soils and decrease in calcareous, alkaline soils are one of the benefits of flooding rice soils. The earlier this is achieved the more advantageous this is for growing rice. The results of this study have indicated that near neutral pH can be attained within 28 days of planting by adding organic matter as compared to 70 days or more when no organic matter is added. These results also show that organic matter, besides being a direct source of major plant nutrients, may also help to increase their availability in submerged soils.

KATI AL S. and PATKI~-~~ W. H. JR. (1974) Transfornl~ltion of iron in a waterlogged soil as influenced by redox potential and pH. Pm. .%I/ Sci. SW. Am 38, 66 71. IRRI (1963) The International Rice Research Institute Annual Report. Los Banos, Philippines. TRRI (1964) The International Rice Research Institute Annual Report. Los Banos, Philippines. IRRI (1965) ‘The International Rice Research Institute Annual Report. Los Banos. Philippines. IRRI (19661 The International Rice Research Institute Annial deport. Los Banos, Philippines. IRRI (1967) The International Rice Research Institute Annual Report. Los Banos. Philippines. ISLAM M. A. and iLhHI h/I.A. (i954)Reversion of ferric iron to ferrous iron under waterlogged conditions and its relation to available phosphorus. d. txgric. Sci. 45, 1-2. ISLAND A. and ISLAMW. (1973) Chemistry of submerged soils and growth and yield of rice: I. Benefits from submergence. PI. Soil. 39, 555-565. KATYALJ. C. and POUNAMPERI:MA F. N. (1974) Zinc deficiency: A widespread nutritional disorder of rice in Agusan de1 Nortc. Philipp. Agric. 58 (3/4), 79 89. MITXI S. (1954) lrzorgur~icNutrition, Fc~rtili-_afion md Soil Amelioraricm for Lowlnnd Ricr. Yokendo Ltd., Tokyo. MOTOMUKA S. (1962) The effect of organic matters on the formation of ferrous iron in soil. Soit Sci. Plant Nufr. 8, 20-29. PATRICK W. H. JR. and MIKKELSN D. S. (1971) Plant nutrient behaviour in flooded soils. In Fertilizer TecI7120logy cmd G’se. 2nd ed. (R. A. Olson. Ed.) pp. 187-215. Am. Soil Sci. Sot. Madison. Wisconsin. PON~AMP~RLJ~A F. N. (1955)7% C~z~,i?zistr~;,f Suhm~rpd Soils in Rriation to rhr Growth crud Yield of Rice. Ph.D. thesis. Cornell University. p. 208. PUNNAMPERUMA F. N. (1965) Dynamic aspects of flooded soils and the nutrition of the rice plant. In Proceedings

GOTOH

yf the S~mposiur~z m Mineral Nutrition of the Rice Plar~t (1964) pp. 295-328. John Hopkins Press, Baltimore.

PONNAM~F~CMAF. N. (19673 A theoretical study of aqueous carbonate equilibra. Soil Sci. 103. 90..lOO. POKNAMPERUMA F. N. (1972) The chemistry of submerged soils. 4dt%.Agrorr. 24, 29-96. Ackriow(~~~cttwrfts--The autbor wishes to thank Dr. S. V. PONNAMPERUMA F. N.. MARTINEZE. and LOY 7‘. (1966a) S. Shastry (ex Project Coordinator), Dr. W. H. Freeman Influence of redox potential and partial pressure bf car(ex Joint Project Coordinator) and Dr. R. Seetharaman bon dioxide on pH values and the suspension effect of (Project Director) for encouragement and help during the flooded soils. Soii Sci. 101. 421331. course of this investigation. P~XNAMPERUMA F. N., TIANXI E. M. and Lou T. A. (1966b) Ionic strengths of the solutions of the flooded soils and other natural aqueous solutions from specific REFERENCES conductance. Soil Sci. 102, 408 413. PONNAMPEKUMA F. N.. TIAN~O E. M. and LUY T. (1967) BREMNCR J. M. (1965) Inorganic forms of nitrogen. In Redox equilibria in flooded soils: I. The iron hydroxide Methods of’soil Analysis (Fart 2): Chemical and-Microsystems. Soil Sci. 103, 374 3X2. hiolocrical Pronrrties (C. A. Black. Ed.) vv. 1179%1237. PONXAMPEKUMA F. N., Lou T. A. and TIANCO E. M. (1969) Am. ‘sot. A&n. Madison, Wisconsin. ’. Redox equilibria in flooded soils: The manganese oxide DAVIU~ J. G. (1961) The availability of phosphorus to rice systems. Soil Sri. 108, 48-57. grown under flooded conditions as evaluated by isotope TANAKA A. and NAVASER~S. A. (1967) Carbon dioxide dilution. Philipp. Agric. 45 (l/2), 48-56. and organic acids in relation to growth of rice. Soil Sri. DI LALLOR, and ALBERTSON 0. E. (1961) Volatile acids Phf Nltfr. 13. 25.-30. by direct titration. j. Mictt. Pnfltrr. Control Fed. 33. YAMAKAWA Y. and K~SHIGAWAH. (1957) On tile effect 356-765. of tcrnpe~tur~ upon the division and elongation of cells Gonm S. and PATKICICW. H. JR. (1972) Transformation in the root of the rice plant. Proc. Crop Sci. Sot. Jupatr of manganese in a waterlogged soil as affected by redox 26, 94.---95. potential and pH. Proc. Soil Sci. Sot. Am. 36. 738-742.