IRPS 2 Specific Soil Chemical Characteristics for Rice Production in Asia

8/4/2019 IRPS 2 Specific Soil Chemical Characteristics for Rice Production in Asia

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Number 2

~.inASiai EN. Ponnamperuma


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IRPS No.2, December 1976

SPECIFIC SOIL CHEMICAL CHARACTERISTICS FOR RICE PRODUCTION IN ASIAI

ABSTRACTEvaluation of both current and potential rlce lands is necessary to meet thepressing need for more rice in Asia. But because of the chemical changescaused by flooding soils, this evaluation cannot be based on criteriadeveloped for dry land crops.

The chemical benefits of flooding can diminish the need for initial andrecurrent financial inputs; but the opposite may also occur. Soils, which bydryland criteria may be placed in the unsuitable class, may shift into thesuitable class or the conditionally suitable class and vice versa.

When formerly non flooded soils are flooded, pH approaches 7 from both theacid and the alkaline sides, the electrolyte content increases, theavailability of nitrogen, phosphorus, silicon, and molybdenum increases, theavailability of zinc and copper decreases, and harmful concentrations ofiron, hydrogen sulfide, and organic reduction products may build up.

The chemical changes brought about by flooding and inherent soils prorertiescomplicate the evaluation of saline, sodic and peat soils, and soils withnutritional problems.

There is promise that some of the chemical changes with implications forevaluation of land for use in wetland rice cultivation can be predicted, atleast qualitatively, from such properties of the dry soil as pH, cationexchange capacity, exchangeable aluminum content, organic matter content,content and reactivity of the iron oxides, and content of and availability ofmacro and micro elements, considered with soil temperature and percolationrates.

lby F. N. Ponnamperuma, principal soil chemist, International Rice ResearchInstitute, Los Banos, Philippines. Submitted to the IRRI Research PaperSeries Committee, 6 October 1976.


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IRPS No.2, December 1976

SPECIFIC SOIL CHEMICAL CHARACTERISTICS FOR RICE PRODUCTION IN ASIA

Rice is the most important crop In Asia, where more than 80% of the world'srice lS grown and consumed and where pressu~e is mounting for an annualincrease of from 7 to 8 million tons in rice production to keep pace withpopulation growth. That increase can be achieved by increasing rlce yieldper hectare or by extending the area under rice cultivation. Either way soilproblems are obstacles. This paper deals with soil chemical problems andtheir implications for land evaluation for wetland rice.

In many parts of the world the new high-yield-potential rice varieties arenot doing well. Soil problems, which had gone undetected earlier because ofthe low yield potential -- and low demand on soils -- of the old varieties,and perhaps also because of their tolerance to adverse soil conditions, arenow assuming more importance. Examples are iron toxicity on acid soils;phosphorus deficiency on ultisols, oxisols, vertisols, and andepts; zincdeficiency on sodic, calcareous, peat, and waterlogged soils; iron deficiencyon high-pH soils and, regardless of pH, on aerobic soils; and manganese andaluminum toxicities on acid aerobic soils.

The extent of arable land in the densely populated countries of Asia islimited and any additional rice cultivation must move onto lands that areuncultivated largely because of soil problems such as salinity, alkalinity,strong acidity, severe nutrient deficiencies, or unknown toxicities.

To evaluate current and potential rlce lands, an understanding of thepeculiar properties of flooded soils and of the physiology of the rlce plant isnecessary because the chemical changes caused by soil submergence and thepeculiarities of the rice plant drastically alter the criteria used forevaluating land for dryland crops.


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IRPSNo. 2, ~cember 19764

The maln chemical changes in flooded soils (Ponnamperuma, 1972) that haveimplications for land evaluation for wetland rlce are

1. depletion of molecular oxygen;2. increase in pH of acid soils and decrease ln pH of calcareous and

sodic soils;3. changes in electrical conductivity;4. reduction of Fe(III) to Fe(II);5. increase in supply and availability of nitrogen;6. increase in availability of phosphorus, silicon, and molybdenum;7. decrease in availability of zinc and copper;8. generation of toxins such as organic reduction products, organic

acids, ethylene, and hydrogen sulfide.

"he extent of these changes varies with chemical and physical properties ofne soil, water regime, and temperature.

DepZetion of oxygenWithin a few hours of soil submergence, microorganisms use up the oxygenpresent in soil air and water and render the soil virtually oxygen free~xcept in a thin layer at the soil surface (Ponnamperuma, 1965). Theexhaustion of oxygen causes reduction of the soil with its attendant benefitssuch as increase in pH, elimination of aluminum and manganese toxicities,and increased availability of nutrients. Rice is able to exploit thechemical benefits of soil submergence because its roots receive oxygenthrough aerenchyma in the shoot system and lysigenous channels in the roots(van Raalte, 1941). Thus not only can rice grow in oxygen-free soils but itcan also protect its roots against anaerobic poisons by oxygen secretion.Waterlogging, a drawback for plants that need aerated soils, is an advantagefor rice.

Change ~n pHWithin a few weeks of submergence the pH of acid soils increases and the pHof sodic and calcareous soils decreases (Ponnamperuma et al., 1966). Thussubmergence causes the pH values of most acid and alkaline soils to convergebetween 6 and 7 (Fig. 1). The rate and degree of the pH changeslepcnd on


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5 1RPS No.2, December 1976

pH r-------------------------------------------------------~

57

~ __ ~~--~--~--~40

SoilNo. Texture pH O.M.% Fe % Mn %2i l clay 4. 9 2. 9 4.70 O .OR35 clay 3. 4 6. 6 2.60 0.0 J40 clay 3. 8 7. 2 o.os 0.0057 clay loam 8. 7 2. 2 0.63 0.0704 clay h.7 2.6 0.96 o.o99 clay loam 7.7 4.8 1.55 O .OR

0 2 4 6 8 10 12 14 16Weeks submerged

Fig. 1 . K ine tics o f the so lu tion pH of s ix subm erged so ils .

soil properties and temperature. Soils that have adequ~te amounts of organicmatter (>2%) and active iron (>1%) and are low in acid reserves attain a pHof about 6.5 within a few weeks of submergence. If acid soils are low Inorganic matter or in active iron, or are high in acid reserves, theymay not attain a pH more than 5 even after months of submergence (Fig. 2).Organic matter magnifies the decrease in pH of sodic and calcareous soilsthrough carbon dioxide effects. Low temperature retards pH changes in bothacid and alkaline soils (Cho and Ponnamperuma, 1971). The pH values ofsubmerged soils can be described by the equations:

pE 17.87 - pFe 2+ - 3 pH

and pH 6.1 -0.58 log PCO (acid soils)2pH 6.1 -2/3 D (calcareous soils)

s. CO2pH 7.85 - log HC03 - log PCO (sodic soils)2


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IRPS No.2, December 1976 6

pH

7.0

A

5.0

._--8./_ _ ._/:

6.0

4.0

3.0 L-_-L __ L-_----'- __ .L.__---'-__ -'---'o 2 4 6 8 10 1 2Weeks submerged

F ig . 2 . K ine tics o f pH in th ree ac id su lfa te so ils .

The stabilization of the pH of submerged soils at about 7 has severalfavorable consequences.

1. Adverse effects of low or high pH per se are minimized.2. Excess aluminum and manganese in acid soils are rendered harmless.3. Iron toxicity in acid soils is lessened.4. Availability of phosphorus, molybdenum, and silicon lS increased.5. Mineralization of organic nitrogen is favored.6. Organic acids decompose.7. Lime is unnecessary.

Thus, in evaluating land for rice production the pH of the dry soil may notbe as important as the factors that influence pH kinetics on soil submergence.

Ch ang es in e lec tric c ondu cta nceThe electrical conductivity of the soil solution after submergence increaseswith time, reaches a peak, and then decreases (Table 1). In 150 wetland ricesoils whose conductivity at 25C immediately after submergence ranged from


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7 IRPS No.2, December 1976

0.2 to 15.3 mmho/cm, the peak values ranged from 1.1 to 18.5 mmho/cm. Onlysix soils had peak values less than 2 mmho/cm. Naturally, the initialconductivities are highest in the saline soils and lowest in the leachedultisols and oxisols, but the kinetics, or the course of conductivity changes,varied markedly with the soil. The changes in conductivity were highlycorrelated with the concentration of bicarbonates, chiefly iron and manganese,in the soil solutions of acid soils and with the calcium and magnesiumbicarbonate concentration in alkaline soils.

Table 1. Initial and peak electrical conductivities (EC) of the solutions offive submerged soils.

O.M. Electrical conductivitySoil pH (%) (mmho/cm at 25C)Initial Peak lIECKalayaan clay loam 5.7 1.3 0.27 1.55 0.38Luisiana clay 4.7 2.8 0.50 2.61 2.11Maahas clay 6.6 2.0 1.37 2.47 2.10Morong clay loam 7.7 4.8 5.80 8.91 3.11Acid sulfate clay 3.6 9.5 4.95 10.30 6.65

Because most submerged soils, regardless of their initial conductivities,have conductivities exceeding 2 rnrnho/cmduring a good part of the growingseason (Ponnamperuma, 1972), are they to be regarded as saline soils asdefined by the Glossary of Soil Science Terms (Soil Science Society ofAmerica, 1975)? If the ECe(electrical conductivity of the saturation extract)of the dry soil is to be used as a criterion of salinity, what of ~oi1s thatproduce high concentrations of electrolyte after soil submergence?

The salinity hazard in flooded soils may be greater than the EC values of thesoil immediately after submergence may indicate, because soil reduction and thesolvent action of carbon dioxide release large amounts of ions into the soilsolution, but due to dilution it may be less than the ECe values may suggest.


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Reduction of Fe(III) to Fe(II)The most dramatic change that occurs when a soil is submerged and undergoesreduction is that Fe(III) oxide hydrates are reduced to Fe(II) compounds.Consequently, the soil color changes from brown to gray, and large amounts ofFe(II) enter the solution phase. The concentration of water-soluble iron,which at submergence rarely exceeds 0.1 ppm, may rise to 600 ppm within a fewweeks after flooding and then declines or reaches a plateau (Ponnamperuma,1972). In acid sulfate soils the peak values may be as high as 5,000 ppm(Ponnamperuma et al., 1972).

The rate of increase of the concentration of water-soluble iron is determinedby the organic matter content of the soil, nature and content of the Fe(III)oxide hydrates, pH of the soil, and temperature (Fig. 3 and 4). Stronglyacid soils with adequate amounts of organic matter and reactive iron oxidescan build up toxic concentrations of ferrous iron (Ponnamperuma et al., 1955;Tanaka and Yo suida, 1970; Ponnamperuma et al., 1972). These concentrationsare enhanced by the presence of salt (Fig. 5). Thus iron toxicity is commonin submerged ultisols, oxisols, and acid sulfate soils in the tropics. Itmay also occur in acid sandy soils and in peat soils low in active iron~ as inAkiochi soils. Low temperatures 20Ce), by bringing about late but high andpersistent concentrations of water-soluble ie-n, may cause lron toxicity Insoils in which, at 250 to 350C, high concentrations are shortlived (Cho andPonnaillperuma, 1971). Criteria for the iron toxicity hazard are --

1. pH of the dry soil;2. amount of reserve acidity;3. reactivity and content of Fe(III) oxide hydrates;4. soil temperature;5. salt content;6. percolation rate;7. interflow from adjacent areas.

Iron toxicity may be a hazard for wetland rice on soils for which the maindrawbacks for dryland crops are manganese and aluminum toxicities and adeficiency of the macro elements.


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IRPS No.2. December 1':1(,9

S o i l pH O.M. Te xtur e Activeno . (I:) Fe (%) I1 n (%)21 4.6 4.1 c lay l o am 2.78 0.0215 5.3 2.5 c lay l o am 0.91 0.0519 5.5 4.2 c lay l oam 2.30 0.1327 6.6 2.0 clay 1.60 0.3126 7.6 1.5 clay l o am 0.30 0.06

.~-g 420e n

180

12 0

o 2 10 12 14 168Weeks S ubm erged

F i g . 3 . K in e t ic s o f F e + + in t h e s o lu t io n s o f f i v e f lo o d e d s o i ls .

1 8


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1RPS No.2. December 1976 10

Fe++ (ppm)~------------------------~

1000 i - B..........'O~~~~~~~~~~~~~A~o

II

5000

" ..,I . ,! \I 000 f - , . ,


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lRPS No . 2. December 197611

Increase ~n supply and availability of nitrogenRice has been grown for centuries in many parts of Asia without the use ofnitrogenous manures or fertilizers. Nitrogen additions in rain water andirrigation water represent only a small part of the nitrogen removed by thecrop or lost from the soil. There must be other sources of nitrogen. Nitrogenfixation by algae and anaerobic bacteria was once regarded as one of the mainnatural sources of soil nitrogen in flooded rice fields. Now there is evidencethat aerobic bacteria living on the surface of rice roots in flooded soils fixabout 50 kg Nlha per season (Yoshida and Ancajas, 1971).

The availability of nitrogen 1n flooded soils is higher than in nonflooded,aerobic soils. Although organic matter is mineralized at a slower rate inanaerobic soils than in aerobic soils, the net amount mineralized is greaterbecause less is immobilized (Borthakur and Mazunda, 1968). Thus the A valuesof nitrogen in flooded soils are about twice as high as in nonflooded soils(Broadbent and Reyes, 197J). The availability of nitrogen in flooded soilsincreases with nitrogen content of the soil, soil pH, temperature, and previousdesiccation of the soil (Ponnamperuma, 1965).

To obtain comparable yields, less nitrogen input is required for wetland ricethan for other cereals. This observation could be considered in evaluatingland for wetland rice.

Increase in availability of phosphorus, silicon, and molybdenwnThe availability of phosphorus and silicon, whether judged by chemicalmethods or by plant uptake, increases on submerging a soil (Ponnamperuma,1972). The increase in: availability of these elements is often cited as oneof the benefits of flooding rice soils. The increase in solubility ofphosphorus, however, -is low inul tisols and oxisols(Fig. 6 and 7).

The concentration of water-solubJe molybdenum increases on flooding presumablyas a result of desorption following reduction of ferric oxides. This maybenefit nitrogen fixing algae at the surface, anaerobic bacteria in thereduced soil, and aerobic bacteria on the roots.

The phosphate input for wetland rice is less than that for other cereals.


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P Extracted by NaAc at pH 2.7 ( ppm of the dry so il)Soil O.M. Active FepH (%) Texture (%)o.9 6. 0 4 . 0 sandy loam 0. 21 4 4 .6 2 . 8 clay 2 . 11 8 5 .6 6 . 0 sandy loam 0. 321 4 .6 4. 1 clay loam 2. 82 2 5 .7 3 . 5 clay loam 0 .426 7 .6 1. 5 clay loam 0 .335 27 6 .6 2. 0 clay 1. 628 4 . 7 3 . 2 clay 2. 9

1 5

5- . _ _ _ _ _

2 _ 8 . , ' . .

30

25

20

10

4Weeks subme rg ed

F ig . 6 . K i netics of P extrac tab le in pH 2.7 N aAc in so me flooded so i I s .

2 6 8


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P (ppm)

Soil Textureno. pH O.M. (% ) Fe (% )

1 sandy loam 7.6 2.3 0.1814 clay 4.6 2.8 2.1325 sandy loam 4.8 4.4 0.1826 clay loam 7.6 1.5 0.3027 clay 6.6 2.0 1. 60


Weeks submergedF ig. 7 . K in etics of w ater-soluble phosphate in 5 submerged soils.


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Decrease in concentrations of water-soZubZe zinc and copperA decrease in concentrations of water-soluble zinc and copper ~s one of thefew disadvantages of flooding soils for rice (Tables 2 and 3). Since 1966 zincdeficiency has been recognized as a widespread nutritional disorder of rice

sodic and calcareous soils. Recent work suggests that zinc deficiency (andperhaps copper deficiency) is a serious obstacle to the growth of rice oncontinuously wet soils and peat soils (Katyal and Ponnamperuma, 1974; IRRI*,1974). The deficiencies may not be as acute for dryland crops grown on thosesoils after they are drained.

The possibility of zinc and copper deficiencies should be considered in evaluatingland for wetland rice.

Table 2. Kinetics of water-soluble z~nc In SlX submerged soils.

O.M. Weeks submergedSoil pH (%) 2 4 6Zn (ppm)

Acid sulfate soil (1) 3.4 5.6 1.90 0.28 0.14 0.10Acid sulfate soil (2) 3.6 9.5 0.65 0.48 0.42 0.32Luisiana clay 4.8 3.2 0.18 0.09 0.06 0.05Silt loam (Korea) 4.9 2.8 0.18 0.14 0.05 0.04Maahas clay 6.6 2.0 0.14 0.06 0.04 0.03Pila clay loam 7.6 1.5 0.11 0.07 0.03 0.03

Table 3. Kinetics of water-soluble copper ~n six submerged soils.

O.M. Weeks submergedSoil pH (%) 1 2 4 6Cu (ppb)

Acid sulfate soil (1) 3.4 5.6 150 100 60 40Acid sulfate soil (2) 3.6 9.5 80 80 40 30Luisiana clay 4.8 3.2 60 40 30 30Silt loam (Korea) 4.9 2.8 70 60 30 30Maahas clay 6.6 2.0 60 40 30 30Pila clay loam 7.6 1.5 60 40 30 30

"'1nterna tional Rice Research Institute


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Production of toxinsHydrogen sulfide is produced in submerged soils as a result of sulfatereduction and anaerobic decomposition of organic matter. In normal soilsit is rendered harmless by precipitation as ferrous sulfide, but in soilshigh in sulfate and organic matter and low in iron, it may harm rice plants.

Organic acids, ethylene, and organic reduction products harm rice plants.They are produced and persist in anaerobic soils (Takijima, 1963). Thetoxicity of peat soils for wetland rice may be due to hydrogen sulfide andorganic products of anaerobic metabolism. Thus a soil, which under drylandconditions may not be injurious to plants, may become toxic to rice when it lSflooded.

Implications for land evaluation for wetland r&ceThe chemical changes brought about by soil submergence may alter drasticallythe category in which a soil 1S placed on the basis of criteria for drylandsoil. Some soils may shift from suitable to unsuitable and vice versa. Thesame chemical changes, along with inherent soil properties, complicateenormously the evaluation of problem soils (Tables 4-8).

Table 4. Saline soils.Kind of soil Other growth limiting factors

Arid saline soils Alkalinity, zinc deficiency, Nand Pdeficiencies

Acid coastal saline soils Iron toxicity, phosphorus deficiency, deepwater

Neutral and alkalinecoastal saline soils

Zinc deficiency, deep water

Deltaic and estuarineacid sulfate soils

Iron toxicity, phosphorus deficiency, deepwater

Coastal histosols Nutrient deficiencies, H2S toxicity,toxicity of organic substances, deep water,Fe toxicity


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Table 5. Acid sulfate soils.Kind of soil Other growth limiting factorsCoastal soils Salinity, Fe toxicity, Nand P deficiencies,

deep waterNand P deficienciesld inland soils

Histosols Fe toxicity, H2S toxicity, nutrientdeficiencies, aeep water, salinity

Table 6. Iron-toxic soils.Kind of soil Other growth limiting factors

Acid sulfate soilsAcid oxisols and ultisols

Salinity, Nand P deficiencies, deep waterP deficiency, low base status, low Sicontent

Histosols H2S toxicity, toxicity of organicsubstances, macronutrient deficiencies, Znand Cu deficiencies, deep water

Table 7. Phosphorus deficiency 1n wetland rice.Kind of soil Other growth limiting factors

Vertisols

Strong acidity, iron toxicity, low nutrientstatus, base deficiency, salinityIron toxicity, base deficiencyZinc deficiency, iron deficiency, salinity,alkalinity

Acid sulfate soils

Acid oxisols and ultisols

Table 8. Zinc-deficient soils.Kind of soil Other growth limiting factorsSaline-sodic and sodic soils Salinity; N, P, and Fe deficiencies

P and Fe deficiencies, salinity, alkalinityK deficiencyCu deficiency?N, P, K, Si, Cu deficiencies; H2S toxicity;deep water

VertisolsCalcareous soilsWet soilsHistosols


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Much work nee ds to be do ne befor e chem ical crite ria c an be devel oped for asyst~matice valuation of land for wetland ri ce. Multiple criteria may bemor e impor tant for we tland r ice than for dryland soils.

Pr ogre ss in the de velo pment of ric e varie ties with r esistanc e to adve rse soilconditi ons will ne cessitate r evisi on of land evaluation standards.

LI TER ATUR E CI TEDBo rthakur, H. P ., and N . N. Mazunda. 1 968. Effec t of lime on nitroge n

availab ility in paddy soils. J. Indian S oil Sci. Soc. 16 :143-147 .Br oadb ent, F. E., and o . C. Reyes. 19 71. Uptake of so il and fertilize r nitrogen

by r ice in som e Phi lippine so ils. S oil S ci. 11 2:20 0-205 .Cho , D. Y., and F. N. Po nnam peruma. 19 71. Influenc e of temperature regime on

the c hemi cal kine tics o f flooded so ils and the growth o f ri ce. So il S ci.1 1 2 : 1 8 4 -1 9 4 .

International Ri ce R esearch I nstitute. 197 5. Annual r epor t for 197 4. Los Bano s,Phil ippines. 384 p.

Katyal, J. C. , and F. N. Ponnampe ruma. 1974 . Zinc deficie ncy: A widespreadnutriti onal disorder of r ice in Agusan del No rte. Phil ipp. Agr ic.58(3 & 4): 7 9-89 .

Po nnam peruma, F. N. 196 5. Dynami c aspects of flo oded soils. Pages 295-328 'L-nInter national Rice Researc h Institute, Mine ral nutriti on o f the ric eplant. Johns Hopkins P ress, Baltimore , Maryland.

Po nnam peruma, F. N. 19 72. Th e chem istr y of subme rged soils. Adv. Agro n.24:29-96.

Ponnamperum a, F. N., T. Attanandana, and G. Beye. 1972. Am elio rati on ofthree acid sulfate soils for l owland r ice. In Proc eedings of theI nternatio nal S ympo sium on Acid Sulfate Soi ls, August 1 3-20 , 19 72,Wageningen,

Ponnamper uma, F. N., R. Br adfield, and M. Pe ech. 19 55. P hysi ological diseaseof ric e attrib utabl e to iro n toxicity. Nature 1 75:26 5.

Ponnampe ruma, F. N ., Eo H. Hartine z , and T. A. leu)'.1 966. Th e influenc e ofredox po tential and the partial pressure or carb on dioxide on the pHvalues and the suspensio n effe ct o f floo ded soils. S oil Sci. 101:421-431.

Raalte, R.B. van. 1941 . On the oxygen supply of r ice r oots. Ann. Bot. Gard.Buite nzo rg, May 1 944 :1 3-3 4.

So il Sc ienc e Soci ety of Amer ica. 1 975. Glossary of so il science ter ms. So ilS c. So c. Am. , Madiso n, \oJisconsin, U. S. A.


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I R P S N o . 2 , D e c e m b e r 1 9 7 6 18

Takijima, Y. 1963. Studies on behavior of the growth inhibiting substances inpaddy soils with special reference to the occurrence of root damage inpeaty paddy fields. Bull. Natl. lnst. Agric. Sci. Jpn. Ser. B, 13:117-252.

Tanaka, A., and S. Yoshida. 1970. Nutritional disorders of the rice plant inAsia. Int. Rice Res. lnst., Tech. Bull. 10. 51 pp.

Yoshida, T., and R. R. Ancajas. 1971. Nitrogen-fixing activity in upland andflooded rice fields. Soil Sci. Soc. Am. Proc. 37(1):42-46.


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IRPS 2 Specific Soil Chemical Characteristics for Rice Production in Asia

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