chemistry of lowland rice soils and nutrient availability

This article was downloaded by: [University of Northern Colorado]On: 29 September 2014, At: 23:12Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registeredoffice: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK

Communications in Soil Science andPlant AnalysisPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/lcss20

Chemistry of Lowland Rice Soils andNutrient AvailabilityN. K. Fageria a , G. D. Carvalho a , A. B. Santos a , E. P. B. Ferreira a

& A. M. Knupp aa National Rice and Bean Research Center of EMBRAPA (EmpresaBrasileira de Pesquisa Agropecuaria), Santo Antônio de Goiás ,Goiás, BrazilPublished online: 26 Jul 2011.

To cite this article: N. K. Fageria , G. D. Carvalho , A. B. Santos , E. P. B. Ferreira & A. M. Knupp(2011) Chemistry of Lowland Rice Soils and Nutrient Availability, Communications in Soil Science andPlant Analysis, 42:16, 1913-1933, DOI: 10.1080/00103624.2011.591467

To link to this article: http://dx.doi.org/10.1080/00103624.2011.591467

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the“Content”) contained in the publications on our platform. However, Taylor & Francis,our agents, and our licensors make no representations or warranties whatsoever as tothe accuracy, completeness, or suitability for any purpose of the Content. Any opinionsand views expressed in this publication are the opinions and views of the authors,and are not the views of or endorsed by Taylor & Francis. The accuracy of the Contentshould not be relied upon and should be independently verified with primary sourcesof information. Taylor and Francis shall not be liable for any losses, actions, claims,proceedings, demands, costs, expenses, damages, and other liabilities whatsoever orhowsoever caused arising directly or indirectly in connection with, in relation to or arisingout of the use of the Content.

This article may be used for research, teaching, and private study purposes. Anysubstantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,systematic supply, or distribution in any form to anyone is expressly forbidden. Terms &Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/loi/lcss20

http://www.tandfonline.com/action/showCitFormats?doi=10.1080/00103624.2011.591467

http://dx.doi.org/10.1080/00103624.2011.591467

http://www.tandfonline.com/page/terms-and-conditions

http://www.tandfonline.com/page/terms-and-conditions

Communications in Soil Science and Plant Analysis, 42:1913–1933, 2011Copyright © Taylor & Francis Group, LLCISSN: 0010-3624 print / 1532-2416 onlineDOI: 10.1080/00103624.2011.591467

Chemistry of Lowland Rice Soils and NutrientAvailability

N. K. FAGERIA, G. D. CARVALHO, A. B. SANTOS,E. P. B. FERREIRA, AND A. M. KNUPP

National Rice and Bean Research Center of EMBRAPA (Empresa Brasileira dePesquisa Agropecuaria), Santo Antônio de Goiás, Goiás, Brazil

Rice is the staple food crop for about 50% of the world’s population. It is grown mainlyunder two ecosystems, known as upland and lowland. Lowland rice contributes about76% of the global rice production. The anaerobic soil environment created by floodirrigation of lowland rice brings several chemical changes in the rice rhizosphere thatmay influence growth and development and consequently yield. The main changes thatoccur in flooded or waterlogged rice soils are decreases in oxidation–reduction orredox potential and increases in iron (Fe2+) and manganese (Mn2+) concentrationsbecause of the reductions of Fe3+ to Fe2+ and Mn4+ to Mn2+. The pH of acidic soilsincreased and alkaline soils decreased because of flooding. Other results are the reduc-tion of nitrate (NO3

−) and nitrogen dioxide (NO2−) to dinitrogen (N2) and nitrous oxide

(N2O); reduction of sulfate (SO42−) to sulfide (S2−); reduction of carbon dioxide (CO2)

to methane (CH4); improvement in the concentration and availability of phosphorus(P), calcium (Ca), magnesium (Mg), Fe, Mn, molybdenum (Mo), and silicon (Si); anddecrease in concentration and availability of zinc (Zn), copper (Cu), and sulfur (S).Uptake of nitrogen (N) may increase if properly managed or applied in the reducedsoil layer. The chemical changes occur because of physical reactions between the soiland water and also because of biological activities of anaerobic microorganisms. Themagnitude of these chemical changes is determined by soil type, soil organic-mattercontent, soil fertility, cultivars, and microbial activities. The exclusion of oxygen (O2)from the flooded soils is accompanied by an increase of other gases (CO2, CH4, andH2), produced largely through processes of microbial respiration. The knowledge of thechemistry of lowland rice soils is important for fertility management and maximizingrice yield. This review discusses physical, biological, and chemical changes in floodedor lowland rice soils.

Keywords Denitrification, Oryza sativa L., oxidation–reduction potential, sub-merged soil

Introduction

Rice (Oryza sativa L.) is the staple food crop in the diet of about one-half of the world’spopulation (Fageria, Slaton, and Baligar 2003). It is grown mainly under two ecosystems,known as upland and lowland. Upland rice, also known as aerobic rice, is generally grownon undulated and unbunded fields and totally depends on rainfall for water requirements.

Received 20 January 2010; accepted 11 February 2011.Address correspondence to N. K. Fageria, National Rice and Bean Research Center of

EMBRAPA (Empresa Brasileira de Pesquisa Agropecuaria), Caixa Postal 179, Santo Antônio deGoiás, Goiás, CEP 75375-000, Brazil. E-mail: [email protected]

1913

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014

1914 N. K. Fageria et al.

Lowland rice, also known as irrigated rice or flooded rice, is grown on leveled lands withbunds and with irrigation facilities. Yields of lowland rice are much greater than thoseof upland rice because of the assured water supply and use of high inputs by farmers.For example, in Brazil, upland rice average yield is about 2.2 Mg ha−1, whereas low-land rice yield is more than 5 Mg ha−1. The lower yield of upland rice is associated withbiotic and abiotic stresses (Fageria 2001). Upland rice has lower yields than lowland rice,but its cost of production also is lower. Because of the lower cost and lack of irrigationfacilities, upland rice will continue to be an important component of cropping systems inSouth America, Africa, and Asia. Figures 1 and 2 show lowland and upland rice growth,respectively, in the central part of Brazil.

Under normal conditions, lowland rice fields are flooded with water about 3 to 4 weeksafter sowing. The water level of about 10 to 15 cm is maintained during the crop growthcycle and is drained before harvest. Because of flooding, lowland rice suffers less fromdisease, insects, and weeds compared to upland rice. These factors also contribute to the

Figure 1. Lowland rice crop in the state of Tocantins, central Brazil.

Figure 2. Upland rice crop grown on an Oxisol of central Brazil.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014

Chemistry of Lowland Rice 1915

greater yield of lowland rice compared to upland rice. Flooding or waterlogging eliminatesoxygen from the rhizosphere and causes changes in the soil chemical properties. Thesechemical changes are associated with physical reactions between the soil and water andalso because of biological processes set in motion as a result of excess water or oxygendeficiency (Patrick and Mahapatra 1968).

The most important change in the soil as a result of flooding is the conversion ofthe root zone of the soil from an aerobic environment to an anaerobic or near-anaerobicenvironment where oxygen is absent or limiting (Patrick and Mahapatra 1968). Oxygendeficiency or exclusion in submerged soils can occur within a day after flooding. The oxy-gen movement through the flooding water is usually much slower than the rate at whichoxygen can be reduced in the soil. This situation may result in the formation of two dis-tinctly different layers being formed in a waterlogged soil. On the top is an oxidized oraerobic surface layer where oxygen is present, with a reduced or anaerobic layer under-neath in which no free oxygen is present. Illustrated in Figure 3 is the thin oxidized layer(usually 1 to 20 mm in thickness) normally found at the interface between water and soil(Bouldin 1986). In addition, flooding also has major effects on the availability of macro-and micronutrients. Some nutrients are increased in availability to the crop, whereas oth-ers are subject to greater fixation or loss from the soil as a result of flooding (Patrick andMikkelsen 1971). The objective of this review is to discuss the chemistry of lowland orflooded rice soils, which may help in better nutrient management and consequently greateryields.

Type of Soils Used for Lowland Rice Cultivation

Lowland rice is produced on a variety of soils in different agroecological regions of theworld. Because of the heterogeneity of agroecological regions, the pedogenetic and mor-phological characteristics of soils used to grow rice also vary considerably. The soilsused for rice production worldwide are distributed over the 10 soil orders (Moormann

Figure 3. Oxidized and reduced soil layer in the submerged rice soil.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


1978; Hudnall 1991). Moormann (1978) summarized that, worldwide, rice is grown onall soil orders identified in the soil classification system (USDA 1975). Worldwide, thewide array of soils used to produce rice results in an equally diverse assortment of man-agement practices implemented for successful rice production on these soils. Murthy(1978) reported that the soils on which rice grows in India are so extraordinarily var-ied that there is hardly a type of soil, including salt-affected soils, on which it cannotbe grown with some degree of success. In Brazil, flooded rice is mainly grown on Alfisols,Vertisols, Inceptisols, Histosols, and Entisols (Moraes 1999). In Sri Lanka, rice is grown onAlfisols, Ultisols, Entisols, Inceptisols, and Histosols (Panabokke 1978). In Indonesia, themain rice soils are Entisols, Inceptisols, Vertisols, Ultisols, and Alfisols (Soepraptohardjoand Suhardjo 1978). Raymundo (1978) reported that in the Philippines the soils usedfor wetland rice production are mainly Entisols, Inceptisols, Alfisols, and Vertisols. InEurope, rice is planted on limited areas in Albania, Bulgaria, France, Greece, Hungary,Italy, Portugal, Romania, Spain, and Yugoslavia, where the predominate soil orders areInceptisols, Entisols, and Vertisols (Matsuo, Pecrot, and Riquier 1978). In the UnitedStates, rice is grown primarily on Alfisols, Inceptisols, Mollisols, and Vertisols (Flach andSlusher 1978). However, in Florida, a small hectarage of rice is produced on Histosols.Most of the soils used for rice production in the United States and some other geographicareas have properties that make them ideally suited for flood-irrigated rice. The soils arerelatively young, contain significant amounts of weatherable minerals, and have relativelyhigh base saturations despite the fact that some are in areas of high precipitation (Flach andSlusher 1978).

Soil parameters for optimum rice yields are optimum soil depth, compact subsoil hori-zon, good soil moisture retention, good internal drainage, good fertility, and a favorablesoil structure (Fageria, Slaton, and Baligar 2003a). Clayey to loamy clay texture soils areappropriate for lowland rice production. Permeable, coarse-textured soils are less suitablefor flood-irrigated rice production because they have low water- or nutrient-holding capac-ities. In Brazil, there are about 35 million ha of poorly drained soils, known locally as“Varzea,” distributed throughout the country. Generally, Varzea soils have good initial soilfertility, but after 2 to 3 years of cultivation, the fertility level is known to decline (Fageriaand Baligar 1996). Farming systems need to be developed with improved soil manage-ment technology to bring these areas under successful crop production. A sufficient supplyof nutrients is one of the key factors required to improve crop yields and maintain sus-tainable agricultural production on these soils. Flood-irrigated rice is an important cropthat needs to be included in the cropping system of these poorly drained areas during therainy seasons. During dry periods, other crops can be planted in rotation, provided there isproper drainage. These soils generally have an adequate natural water supply throughoutyear, but are acidic and require routine applications of lime if legumes are grown in rota-tion with rice. Physical and chemical properties of varzeas soils of Brazil are presented inTables 1–4. Data in these tables show that chemical and physical properties varied largelyfrom state to state and from municipality to municipality within states.

Physical, Biological, and Chemical Changes in the Flooded Soils

Omission of oxygen from the large part of soil profile causes physical, biological, andchemical changes to occur in the submerged or flooded rice soils. These changes var-ied with the type of soil, presence of microbial biomass, quality and quantity of organicmatter, cultivar planted, and level of soil fertility. In addition, these changes affect availabil-ity of essential plant nutrients and consequently plant growth and yield. Furthermore, the

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Table 1Chemical properties of varzeas (lowland) soils of some states of Brazil

Ca Mg AlMO pH P K (cmolc (cmolc (cmolc

State (g kg−1) in H2O (mg kg−1) (mg kg−1) kg−1) kg−1) kg−1)

Goiás 42 5.2 15.2 85 4.7 2.6 1.5Mato Grosso 16 5.1 6.9 68 2.5 1.4 1.3Mato Grosso

do Sul69 5.3 21.7 75 7.8 3.4 1.1

Paraná 138 4.3 36.4 84 2.6 1.8 4.4Minas Gerais 25 5.0 17.7 133 3.9 1.6 0.5Rio Grande do

Norte25 7.1 45.1 168 10.4 6.6 0.1

Piauí 10 5.6 13.6 115 10.3 6.7 0.7Maranhão 8 4.8 1.9 82 6.7 10.7 1.5Average 42 5.3 19.8 101 6.1 4.4 1.5

Source: Fageria et al. (1991, 1994, 1997).Note. Values are from the 0- to 20-cm soil depth and lowland rice is generally grown on these soils

during rainy season.

Table 2Micronutrient concentrations, cation exchange capacity (CTC), base saturation (V), and

aluminum saturation (M) of várzeas (lowland) soils of some states of Brazil

CTC V MCu Zn Fe Mn (cmolc (cmolc (cmolc

State (mg kg−1) (mg kg−1) (mg kg−1) (mg kg−1) kg−1) kg−1) kg−1)

Goiás 7.4 3.0 436 42 27 33 16Mato Grosso 1.3 1.4 263 33 12 33 32Mato Grosso

do Sul11.9 2.5 193 23 26 42 18

Paraná 6.3 1.5 65 12 52 22 29Minas Gerais 2.9 7.9 627 98 15 42 10Rio Grande do

Norte1.9 2.0 307 163 39 95 1

Piauí 3.4 3.2 382 61 30 81 3Maranhão 0.9 3.7 320 43 29 70 7Média 4.5 3.2 324 59 29 54 15



percolation rate decreases with flooding because of physical and chemical changes such asswelling, dispersion, disintegration of soil aggregates, reduction of soil pores by microbialactivity, and organic-matter decomposition, which reduces the binding effect of aggregatesand causes the soil to seal off (Wickham and Singh 1978).

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Table 3Textural analysis of várzeas (lowland) soils of some states of Brazil

State Sand (g kg−1) Silt (g kg−1) Clay (g kg−1)

Goiás 350 220 422Mato Grosso 408 282 310Mato Grosso do Sul 394 250 356Paraná 600 187 213Minas Gerais 223 184 593Rio Grande do Norte 431 308 261Piauí 301 335 364Maranhão 118 410 472Average 354 272 374



Physical Changes

As soon as soils of lowland rice are flooded, the oxygen level begins to decline. The rateof decline is very fast, and within 6 to 10 h after flooding, the O2 level drops to near zero(Patrick and Mikkelsen 1971). The rapid declines of O2 from the soil are accompanied byan increase of other gases produced through the microbial respiration. The major gases thataccumulate in the flooded soils are carbon dioxide (CO2), methane (CH4), nitrogen (N2),and hydrogen (H2). Patrick and Mikkelsen (1971) reported that the composition of thesegases may vary from 1 to 20% CO2, 10 to 95% N2, 15 to 75% CH4, and 0 to 10% H2. Thisvariation may be associated with the presence of microbial biomass, organic matter, andinorganic substances and also the cultivar planted.

Flooding may also alter the soil temperature and may disintegrate soil structure. At agiven soil moisture content, and as bulk density increases, thermal conductivity increases(Ghildyal and Tripathi 1971). As the thermal conductivity of soil particles is greater thanthat of air, increased density decreases the volume of gases and increases thermal con-tact between the soil particles. As a result, thermal conductivity increases (Ghildyal 1978).Permeability to water may be reduced by clogging the soil pores, which results from phys-ical, chemical, and biological changes. This may help to reduce percolation of water andleaching of nutrients. In the lowland rice production system, the subsoil layer is com-pacted with the help of a roller, a process known as puddling. According to the SoilScience Society of America (2008), puddling is defined as any process involving bothshearing and compactive forces that destroys natural structure and results in a conditionof greatly reduced pore space. Ghildyal (1978) defined puddling as mixing soil with waterto render it impervious. Intensive tillage by repeated plowing of a wet soil breaks downcoarse aggregates and mean particle size decreases. Soil compaction affects the water-retention characteristics, water-intake rates, and gas exchange. In compacted soil, bulkdensity, microvoids, thermal conductivity and diffusivity, and nutrient mobility increase,and macrovoids, hydraulic conductivity, and water-intake rates decrease. Medium-texturedsoils are most susceptible to compaction.

Puddling is very common in Asian rice-producing countries. Puddling, intensive wet-land cultivation, breaks the natural aggregates to finer fractions. It decreases the apparent

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014

Tabl

e4

Che

mic

alan

dte

xtur

alpr

oper

ties

ofvá

rzea

s(l

owla

nd)

soils

ofst

ate

ofR

ioG

rand

edo

Sulo

fB

razi

l

Loc

atio

n/C

a+M

gSa

ndSi

ltC

lay

mun

icip

ality

MO

(gkg−1

)pH

inH

2O

(cm

olc

kg−1

)K

(mg

kg−1

)A

l(cm

olc

kg−1

)V

(%)

M(%

)(g

kg−1

)(g

kg−1

)(g

kg−1

)

Palm

ares

205.

00.

520

0,6

1570

840

6010

0V

acac

aí11

95.

01.

320

1,7

2353

640

260

100

Pelo

tas

95.

43.

127

1,1

5224

440

360

190

Mel

eiro

84.

80.

939

2,9

973

370

280

350

Col

égio

130

4.5

18.6

234

1,2

446

240

270

490

Jund

aí32

4.4

3.9

398,

812

6720

310

670

Jaci

nto

Mac

hado

105.

510

.578

0,2

741

420

270

280

Cur

umim

405.

51.

227

3,8

773

790

130

80A

vera

ge41

5.0

5.0

612,

528

4647

024

628

4

Sour

ce:K

lam

teta

l.(1

985)

.N

ote.

Val

ues

are

from

the

0-to

20-c

mso

ilde

pth

and

low

land

rice

isge

nera

llygr

own

onth

ese

soils

duri

ngra

iny

seas

on.R

ioG

rand

edo

Sul

isth

ela

rges

tlo

wla

nd-r

ice-

prod

ucin

gst

ate

inB

razi

l.

1919

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Figure 4. Puddling is done in the lowland rice plots in the state of Para in the Amazon basin (earlierproject of Jari, funded by D. K. Ludwig), Brazil.

specific volume and hydraulic conductivity, creates an anaerobic environment, and affectsEh and pH (Ghildyal 1978). Ghildyal (1978) reported that rice root growth, nutrient uptake,and water use are favorably affected by moderate compaction of a flooded soil where thesoil strength is low. Figure 4 shows that puddling is done in the lowland rice plots beforesowing the pregerminated seeds of rice. In many Asian countries, rice is transplanted in thepuddle fields by small farmers.

Biological Changes

In waterlogged or flooded rice soils, aerobic microorganisms become quiescent or die, andfacultative and obligate anaerobic bacteria proliferate. These new microorganisms bringmany biological changes in the reduced soil environment. In the absence of oxygen, manyfacultative and obligate anaerobic bacteria oxidize organic compounds with the releaseof energy in a process called “anaerobic fermentation” (Patrick and Mikkelsen 1971).Anaerobic fermentation usually produces lactic acid as a first product. This is subsequentlyconverted to acetic, formic, and butyric acids. Among aerobic organisms, oxygen servesas the electron acceptor, but in anaerobic forms, either an organic metabolic by-product orsome inorganic substance must substitute for oxygen (Patrick and Mikkelsen 1971). In theflooded soils, organic-matter decomposition is retarded because of lower carbon assimila-tion rates of anaerobic bacteria. In a submerged soil, the facultative and obligate anaerobicorganisms utilize nitrate (NO3

−), manganese (Mn4+), iron (Fe3+), sulfate (SO42−), dis-

similation products of organic matter, CO2, and H+ ions as electron acceptors in theirrespiration, reducing NO3

− to dinitrogen (N2), Mn4+ to Mn2+, Fe3+ to Fe2+, SO42− to

sulfide (S2−), CO2 to CH4, and H+ to H2 gas (Patrick and Reddy 1978).

Chemical Changes

The most important chemical changes that occur in flooded or submerged rice soils are topH, redox potential, and ionic strength or electrical conductivity. These changes occur as aresult of oxygen depletion.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


pH. Soil pH is an important chemical property because of its influence on soil microor-ganisms and availability of nutrients to plants. It is determined by a pH meter using a glasselectrode and in a specific soil–solution ratio. Usually distilled water or 0.01 M calciumchloride (CaCl2) or 1 M potassium chloride (KCl) solution is used for soil pH determina-tion. Soil pH indicates acidity, alkalinity, or neutrality of a soil. Soil pH 7.0 is a neutralvalue. Above this pH, soils are designated as alkaline, and below this, soils are acidicin reaction. The pH of acidic soils increases and alkaline soils decreases as a result offlooding. Overall, pH of most soils tends to change toward neutral after flooding. An equi-librium pH in the range 6.5 to 7.5 is usually attained (Patrick and Reddy 1978). A majorityof oxidation–reduction reactions in flooded soils involve either consumption or produc-tion of H+/OH− ions (Ponnamperuma 1972). The increase in pH of acidic soils is mainlydetermined by reduction of Fe and Mn oxides, which consume H+ ions. These reductionprocesses are shown in the following equations:

Fe2O3 + 6H+ + 2e− ↔ 2Fe2+ + 3H2O

MnO2 + 4H+ + 2e− ↔ Mn2+ + 2H2O

The decrease in the pH of alkaline soils is associated with the microbial decomposi-tion of organic matter, which produces CO2, and the produced CO2 reacts with H2O toform carbonic acid, which dissociates into H+ and bicarbonate (HCO3

−) ions. Patrick andReddy (1978) reported that the decrease in pH of alkaline and calcareous submerged soils isassociated with sodium carbonate (Na2CO3)–H2O–CO2 and calcium carbonate (CaCO3)–H2O–CO2 systems, respectively. Figure 5 shows the change in soil pH of lowland ricecollected from four locations in the state of Rio Grande do Sul, Brazil. It can be seen fromFigure 5 that soil pH increases with flooding and stabilized around 56 days after floodingin all the soils. However, the magnitude of pH change differs from soil to soil. The pH of

Figure 5. Change in soil pH with the flooding of lowland rice. Adapted from Moraes and Freira(1974).

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


most agricultural soils is in the range of 4 to 9 (Fageria 2009). The most suitable pH forgrowth of annual crops such as soybean, corn, dry bean, and wheat in Brazilian lowlandsoils is around 6.5 (Fageria and Baligar 1999).

Oxidation–Reduction Potential

Oxidation–reduction or redox potential has significant influence on chemistry of iron andother nutrients in the submerged soils. It is the best single indicator of the degree of anaer-obiosis in the flooded soil and allows reasonable predictions to be made concerning thebehavior of several essential plant nutrients (Patrick and Mikkelsen 1971). Oxidation isthe donation and reduction is the acceptance of electrons from other substances. Oxidizingagents accept electrons from other substances and thereby reduce themselves. Reducingagents donate electrons to other substances. For example, iron(II) is an electron donor ora reducing agent when it oxidized to iron(III). Hydrogen peroxide (H2O2) is an oxidizingagent when it accepts electrons from organic matter and oxidizes it to CO2 (Bohn, McNeal,and O’Connor 1979).

Oxidation–reduction potential is measured in millivolts, and symbol used for thischemical change in flooded soil is Eh. Oxidized soils have redox potentials in the rangeof +400 to +700 millivolts, whereas waterlogged soils’ redox potential is generally inthe range of −250 to −300 millivolts (Patrick and Mahapatra 1968). Important oxidation–reduction processes that occur in the waterlogged soils are presented in Table 5. Some ofthe oxidized soil components that undergo reduction after oxygen is depleted are reducedsequentially; that is, all of the oxidized components of one system will be reduced beforeany of the oxidized components of another system begin to be reduced. Others overlapduring reduction (Patrick and Reddy 1978). As the O2 depletes from the waterlogged soils,reduction processes occur in sequence. Nitrate and manganese compounds are reducedfirst, then ferric compounds are reduced to the ferrous form, and at last sulfate is reducedto sulfide. Redox potential decreased with flooding of rice soils (Figure 6).

Table 5Thermodynamic sequence of reduction processes in the submerged soils

Reaction Redox potential E07a (V)

O2 + 4H+ + 4e− ←→ 2H2O 0.812NO3

− +12H+ +10e− ←→ N2 + 6H2O 0.74MnO2 + 4H+ + 2e− ←→Mn2+ 2H2O 0.40CH3COCOOH +2H+ + 2e− ←→ CH3CHOHCOOH −0.16Fe(OH)3 + 3H+ + e− ←→ Fe2+ + 3H2O −0.19SO4

2− + 10H+ + 8e− ←→ H2S + 4H2O −0.21CO2 + 8H+ + 8e− ←→ CH4 + 2H2O −0.24N2 + 8H+ + 6e− ←→ 2NH4

+ −0.28NADP+ + 2H+ + 2e− ←→ NADPH −0.32NAD+ + 2H+ + 2e− ←→ NADH −0.332H+ + 2e− ←→ H2 −0.41Ferredoxin (ox) + e− ←→ Ferrodoxin (red) −0.43

aE0 corrected to pH 7.0.Sources: Ponnamperuma (1972); Ponnamperuma (1976), and Patrick and Reddy (1978).

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Figure 6. Influence of flooding on redox potential of some Mexican soils. Adapted from Moraesand Freira (1974).

A rapid decline in redox potential is characteristic of soils with low contents of reduc-ing Fe and Mn and high organic-matter content. Iron and Mn compounds serve as buffersagainst the development of reducing conditions in the soil (Patrick and Mahapatra 1968).The critical redox potentials for Fe reduction and consequent dissolution are between+300mV and +100 mV at pH 6 and 7, and −100 mV at pH 8, while at pH 5 appreciablereductions occur at +300 mV (Gotoh and Patrick 1976). Oxidation–reduction or potentialreduction values for oxidized and submerged soils and reduction processes are given inTable 6.

Ionic Strength

Ionic strength is defined as the measure of the electrical environment of ions in a solution.Ionic strength can be calculated by using the following formula (Fageria et al. 2008):

Ionic strength = 1/2

∑MiZ

2i

where M is the molarity of the ion, Zi is the total charge of the ion (regardless of sign), and� is a symbol meaning the “sum of.”

The concentration of ions in the soil solution is measured by electrical conductiv-ity. The ionic strength of the submerged soil increases with the release of macro- andmicronutrients in the soil solution (Patrick and Mikkelsen 1971) (Figure 7).

Nutrient Availability

Reducing conditions in flooded rice soils change concentration and forms of applied aswell as native soil nutrients. Hence, availability of essential macro- and micronutrients issignificantly influenced in the flooded rice soils.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Table 6Range of oxidation–reduction potential values in oxidized and

submerged soils and at which reduction processes occur

Soil moisture/reduction processes Redox potential (mV)

Well-oxidized soils +700 to +500Moderately reduced soils +400 to +200Reduced soils +100 to −100Highly reduced soils −100 to −300NO3

− to N2 +280 to +220Mn4+ to Mn2+ +280 to +220Fe3+ to Fe2+ +180 to +150SO4

2− to S2− −120 to −180CO2 to CH4 −200 to −280O2 to H2O +380 to +320Absence of free O2 +350

Sources: Adapted from Patrick (1966), Patrick and Reddy (1978), Marschner(1995), and Fageria et al. (2008).

Figure 7. Influence of flooding on electrical conductivity of some Mexican soils. Adapted fromMoraes and Freira (1974).

Nitrogen

Nitrogen is a key nutrient in improving growth and yield of crop plants in all agroe-cosystems. Its main role is in increasing the photosynthesis process in the plants, whichis associated with improving grain yield. Response of five lowland rice genotypes to N

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Figure 8. Responses of five lowland rice genotypes to nitrogen fertilization.Source: Fageria and Baligar (2006).

fertilization is presented in Figure 8. Nitrogen is responsible for increasing yield compo-nents such as panicles or heads in cereals and pods in legumes (Fageria 2009). It alsoimproves grain weight and reduces grain sterility. Figure 9 shows influence of N on yieldcomponents of lowland rice. Grain yield in rice is a function of panicles per unit area,number of spikelets per panicle, 1000-grain weight, and spikelet sterility or filled spikelets(Fageria 2007). Therefore, it is very important to understand the management practices thatinfluence yield components and consequently grain yield. Nitrogen application up to 210kg ha−1 influenced panicle length significantly (P < 0.01) and the relationship betweenN applied and panicle length was linear (Figure 9). The number of panicles m−2 and1000-grain weight also increased significantly and quadratically with the application ofN fertilizer. Spikelet sterility, however, decreased significantly and linearly with increas-ing N rates. Nitrogen treatment accounted for about 96% variation in panicle length, about91% variation in panicles m−2, about 75% variation in spikelet sterility, and about 73% ofvariation in 1000-grain weight. Fageria (2007) also reported that panicles per unit area,filled spikelet percentage, and 1000-grain weight were major contributors to increasedgrain yield in modern high-yielding rice varieties.

A major part of N in the flooded rice soils is lost through leaching and denitrification(Fageria and Baligar 2005). The major biological reaction involving nitrate in flooded soilis denitrification. Denitrification is the biological process in which nitrate reduces to N gasor nitrous oxide, or both. Patrick and Mikkelsen (1971) reported that denitrification lossesof 50% or more of applied N are common in flooded rice soils. Frequent fluctuations in

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Figure 9. Influence of nitrogen on number of panicles, panicle length, thousand-grain weight, andspikelet sterility of lowland rice.Source: Fageria and Baligar (2001).

moisture content of a field as a result of flooding and drainage create ideal conditions fordenitrification (Patrick and Wyatt 1964). Nitrogen converted to the nitrate form during theperiod when the soil is drained is lost through denitrification when soil is flooded. Deepplacement of N in the flooded rice reduces N lost through denitrification. Nitrate producedin the surface oxidized layer of a waterlogged soil can easily move downward by diffusionand percolate into the underlying reduced layer, where it is rapidly denitrified (Patrick andMahapatra 1968).

Even with best management practices such as adequate rate, forms, methods, and tim-ing of application, the utilization of added N is generally poorer in flooded rice soils.Fageria and Baligar (2001) and Fageria, Santos, and Cutrim (2007) studied N-recovery effi-ciency of lowland rice grown on Brazilian Inceptisols (Table 7). Average efficiency underdifferent rates was 39%, whereas average N-recovery efficiency of five genotypes was 29%.Hence, a large part of applied N is lost in soil–plant systems. Patrick and Mahapatra (1968)reported that in Japan 30 to 40% applied N is recovered by lowland rice as compared to anavailability of 50 to 60% when applied to upland crops.

In aerated soils, most of the N is in the form of NO3−because of the nitrification

process. In waterlogged soils, absence of O2 inhibits the activity of the Nitrosomonasmicroorganisms that oxidize NH4

+, and therefore N mineralization stops at the ammonium(NH4

+) form. Accumulation of NH4+ in the waterlogged soils would mean that the N is

not lost from the soil–plant system, as is the case in denitrification. This may only happenif rice fields are constantly flooded during the crop growth cycle. If availability of water isnot under farmers’ control because of lack of rainfall or storage facility, the situation maychange in the transformation and availability of N to plants. Hence, if N is applied in the

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Table 7Nitrogen recovery efficiency in lowland rice as influenced by N rate

and genotypes

N rate N recovery Lowland rice N recovery(kg ha−1) efficiency (%) genotype efficiency (%)

30 49 CNAi 8886 3760 50 CNAi 8569 2990 37 BRSGO Guará 29120 38 BRS Jaburu 26150 34 BRS Giguá 23180 33 Average 29210 32Average 39R2 0.82∗∗

Note. N recovery efficiency (%)= N uptake by plants in N fertilized plot − N uptake by plants in control treatmentQuantity of N applied∗∗Significant at the 1% probability level.

Sources: Adapted from Fageria and Baligar (2001) and Fageria et al. (2007).

reduced soil layer and the water level is maintained in the rice field constantly, N uptakemay improve in flooded rice.

Phosphorus

Phosphorus (P) plays an important role in the growth and development of crop plants.Its role is well documented in many physiological and biological processes in the plants(Fageria 2009). Phosphorus deficiency is one of the most important yield-limiting factorsin annual crops grown on highly weathered acidic soils of the tropics (Sanchez and Salinas1981; Dobermann, George, and Thevs 2002; Fageria and Barbosa Filho 2007). The P defi-ciency is associated with low natural P as well as with high P-fixation capacity of thesesoils. Added soluble P is usually rapidly adsorbed on the surfaces of Fe and aluminum(Al) oxides, which are followed by immobilization in other forms and within soil particles(Hedley, Kirk, and Santos 1994; Linquist et al. 1997). Data in Table 8 show that yield andyield components of lowland rice were significantly improved with the addition of P in aBrazilian Inceptisol.

Phosphorus availability is increased in the flooded soils because of the reduction offerric phosphate to the more soluble ferrous form and the hydrolysis of phosphate com-pounds. This may be more pronounced in acidic soils where P is immobilized by Fe andAl oxides. Similarly, P uptake in flooded alkaline soils also improves because of the libera-tion of P from Ca and calcium carbonate resulting from the decrease in pH. The formationof insoluble tricalcium phosphate is favored at a high pH.

Potassium

The influence of flooding is lesser on the chemistry of K than on the chemistry of N and P.The reducing conditions caused by flooding result in a larger fraction of the K ions beingdisplaced from the exchange complex into the soil solution. The release of a relativelylarge amount of Fe and Mn ions and production of ammonium ions result in displacement

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Table 8Dry-matter yield of shoot, panicle number, panicle length, 1000-grain weight, spikelet

sterility, and grain harvest index as influenced by phosphate treatments

Shoot dry Panicle Panicle 1000-grain Spikelet GrainP rate weight number length weight sterility harvest(kg ha−1) (kg ha−1) (m−2) (cm) (g) (%) index

0 3930.3 264.3 19.0 23.2 17.9 0.23131 7088.7 365.0 20.1 25.1 21.2 0.29262 7753.5 432.0 21.3 26.3 18.2 0.37393 7664.3 412.2 20.9 26.5 17.9 0.40524 8093.3 417.3 20.8 26.0 16.9 0.37655 7021.0 419.2 22.3 26.6 13.3 0.43F-testYear (Y) ∗∗ ∗∗ ∗∗ ∗ NS NSP rate (P) ∗∗ ∗∗ ∗∗ ∗∗ NS ∗∗Y × P NS NS NS NS NS NSCV (%) 22 10 5 5 22 17

Regression analyses were as follows:P rate (X) vs shoot dry weight (Y) = 4297.5420 + 19.0682X − 0.0229X2, R2 = 0.6250∗∗P rate (X) vs panicle number (Y) =276.1075 + 0.7040X − 0.00077X2, R2 = 0.7497∗∗P rate (X) vs panicle length (Y) = 19.3166 + 0.0059X − 0.0000031X2, R2 = 0.5632∗∗P rate (X) vs 1000 grain weight (Y) = 23.4333 + 0.0135X − 0.000014X2, R2 = 0.5944∗∗P rate (X) vs spikelet sterility (Y) = 18.5500 + 0.0104X − 0.0000027X2, R2 = 0.3845∗P rate (X) vs grain harvest index (Y) = 0.2314 + 0.00061X − 0.00000051X2,

R2 = 0.8193∗∗Shoot dry weight (X) vs grain yield (Y) = −10332.13 + 3.9319X − 0.00025X2,

R2 = 0.8654∗∗Panicle number (X) vs grain yield (Y) = −15604.45 + 87.1577X − 0.0919X2,

R2 = 0.8654∗∗Panicle length (X) vs grain yield (Y) = −122564.60 + 11227.76X − 246.516X2,

R2 = 0.7768∗∗1000 grain weight (X) vs grain yield (Y) = −30651.68 + 1822.5990X − 18.3971X2,

R2 = 0.8107∗∗Spikelet sterility (X) vs grain yield (Y) = 7529.74 − 244.5112X + 2.2283X2,

R2 = 0.1493NS

Grain harvest index (X) vs grain yield (Y) = −10743.00 + 69155.70X − 74449.30X2,R2 = 0.9440∗∗

Notes. Values are averaged across 2 years.∗, ∗∗, NSSignificant at the 5% and 1% probability levels and nonsignificant, respectively.Source: Fageria and Santos (2008).

of some of the K ions from the exchange complex to the soil solution. This may leads togreater availability of K to rice in flooded soils (Patrick and Mikkelsen 1971).

Sulfur

In flooded soils, SO42− ion is reduced to hydrogen sulfide (H2S) by anaerobic microbial

activities. Furthermore, in flooded soils, Fe3+ reduction to Fe2+ precedes SO42− reduction;

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Fe2+ will always be present in the soil solution by the time H2S is produced, so that H2Swill be converted to insoluble iron sulfide (FeS). This reaction protects microorganisms andhigher plants from the toxic effects of H2S (Patrick and Reddy 1978). Overall, availabilityof S is reduced in flooded soils due to formation of insoluble FeS.

Calcium and Magnesium

Calcium (Ca) and magnesium (Mg) deficiencies are rare in lowland rice. Rice is highlytolerant to soil acidity. Optimum soil pH for lowland rice grown on Brazilian Inceptisolwas reported to be 4.9 (Fageria and Baligar 1999). In highly acidic soils, dolomitic limecan be added to supply Ca and Mg. Only a small amount of these elements are removedin the grain, and unless the straw is removed from the field, the total removal is small.Changes in Ca and Mg concentrations are minimum in flooded soils.

Micronutrients

The Fe3+ reduces to Fe2+ and Mn4+ reduces to Mn2+; hence uptake of these elementsincreased in the flooded rice soils. The reduction processes of Fe and Mn are shown underthe section on pH changes. The greater concentration of Fe2+ (>300 mg kg−1) may betoxic to rice plants under certain conditions (Fageria 1984; Fageria et al. 2008). Sims andJohnson (1991) reported that for most crops the critical deficiency soil Fe concentrationrange was 2.5–5.0 mg kg−1 of diethylenetriaminepentaacetic acid (DTPA)–extractable Febut is also influenced by soil pH. In both field and pot experiments, the degree of bronz-ing in a given variety showed a highly significant correlation (r = 0.90∗∗) with yield(Breemen and Moormann 1978). Iron toxicity in rice plants, as indicated by bronzing ofleaves, was reported when soluble Fe in the soil solution was more than 300–500 mgkg−1 (Ponnamperuma, Bradfield, and Peech 1955; Tanaka, Loe, and Navasero 1966) byDTPA extracting solution. However, Breemen and Moormann (1978) reported that bronz-ing symptoms appear generally when Fe concentrations in the soil solution are in the rangeof 300–400 mg kg−1 by DTPA extracting solution. Barbosa Filho, Fageria, and Stone(1983) reported that Fe toxicity in lowland rice occurred when Mehlich 1 extracting Fein the soil was in the range of 420 to 730 mg kg−1. This means that Fe toxicity level in thesoil is also dependent on the extracting solution used to extract the Fe from the soil. Valuesfor the Mehlich 1 extracting solution are greater than for the DTPA solution.

Iron toxicity in lowland rice has been reported in South America, Asia, and Africa(Sahu 1968; Barbosa Filho, Fageria, and Stone 1983; Fageria 1984; Fageria and Rabelo1987; Fageria, Slaton, and Baligar 2003; Fageria, Stone, and Santos 2003; Sahrawat 2004).Metal toxicity in crop plants can be expressed in two ways. One is when metal is absorbedin greater amounts and becomes lethal to the plant cells. This is known as direct toxicityof metals. Another metal toxicity is associated with inhibition of uptake and utilizationof essential nutrients by plants. This is known as indirect metal toxicity. Indirect toxicitycreates nutrient imbalance in plants. This type of Fe toxicity is more common in lowlandrice than direct toxicity (Fageria, Baligar, and Wright 1990; Fageria, Baligar, and Clark2006). The most important nutrient deficiencies observed in irrigated or flooded rice inBrazil are P, K, and Zn (Barbosa Filho, Fageria, and Stone 1983). The yield reductionof rice cultivars due to Fe toxicity depends on tolerance or susceptibility of cultivars totoxicity. Ikehashi and Ponnamperuma (1978) reported that reduction of the yield on an Fetoxic soil ranged from a mean of 29% for five moderately tolerant lines to a mean of 74%for five susceptible lines.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Zinc and copper (Cu) concentrations generally decreased after flooding rice soils. Thedecrease in concentration with the flooding may be associated with increase in soil pHafter flooding. Little is known about the behavior of B and Mo in the submerged soils.Boron concentration seems to remain more or less constant after submergence of rice soils(Ponnamperuma 1975). Molybdenum concentration in rice soils was found to increase aftersubmergence (Ponnamperuma 1975), possibly because of the increased pH. In floodedsoils, Si generally tends to increase after submergence. This increase is probably due tothe release of adsorbed and occluded Si from oxyhydroxides of Fe and Al as well as to theeffect of the increased pH resulting from submergence. Decompositing rice straw with itshigh silica content may also contribute to the increased Si content of the soil solution offlooded soils (Patrick and Reddy 1978).

Conclusions

Rice is mainly produced under upland and lowland ecosystems. Lowland ecosystem con-tributes the most rice production worldwide. Lowland rice is also known as flooded orsubmerged rice. Direct-seeded lowland rice fields are generally flooded about 3 to 4 weeksafter sowing and remain flooded throughout the growing season; water is drained at har-vest. Because of flooding, chemistry of lowland rice soils changes, which affect physical,chemical, and biological properties and consequently rice yields. The most significantchemical changes are increase in the pH of acidic soils and decrease in the pH of alkalinesoils, reduction in the redox potential, and increase in the electrical conductivity or ionicstrength. The magnitude of change of these chemical processes depend on soil type, micro-bial biomass, soil organic-matter content, and rice cultivar or genotype planted. All thesechanges influence availability of essential plant nutrients. Availability of essential nutrientsis significantly influenced by flooding the rice soils. Availability of P, K, Si, Fe, Mn, andMo increased in flooded soils, and availability of S, Zn, and Cu decreased. Availability ofN depends on its proper management. If applied in the reduced soil zone, its uptake mayimprove as a result of fewer losses by denitrification. Both nitrate and ammonium ions canbe assimilated by the rice plant, but better stability of the ammonium form in flooded soilsmakes it the superior form of N for lowland rice. In addition, the ammonium (NH4

+) formof N requires less energy for absorption by plants compared to the nitrate (NO3

−) form ofN. In addition, Al toxicity is decreased in flooded acidic soils because of the increase insoil pH. Flooding also favors microbial processes that release essential nutrients for plantgrowth.

References

Barbosa Filho, M. P., N. K. Fageria, and L. F. Stone. 1983. Water management and liming in relationto grain yield and iron toxicity. Pesquisa Agropecuaria Brasileira 18:903–910.

Bohn, H. L., B. L. McNeal, and G. A. O’Connor. 1979. Soil chemistry. New York: John Wiley &Sons.

Bouldin, D. R. 1986. The chemistry and biology of flooded soils in relations to the nitrogen economyin rice fields. Fertilizer Research 9:1–14.

Breemen, N. V., and F. R. Moormann. 1978. Iron-toxic soils. In Soils and rice, 781–800. Los Bãnos,Philippines: IRRI.

Dobermann, A., T. George, and N. Thevs. 2002. Phosphorus fertilizer effects on soil phosphoruspools in acid upland soils. Soil Science Society of America Journal 66:652–660.

Fageria, N. K. 1984. Fertilization and mineral nutrition of rice. Goiânia, Brazil: EMBRAPA-CNPAF.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Fageria, N. K. 2001. Nutrient management for improving upland rice productivity and sustainability.Communications in Soil Science and Plant Analysis 32:2603–2629.

Fageria, N. K. 2007. Yield physiology of rice. Journal of Plant Nutrition 30:843–879.Fageria, N. K. 2009. The use of nutrients in crop plants. Boca Raton, Fl.: CRC Press.Fageria, N. K., and V. C. Baligar. 1996. Response of lowland rice and common bean grown in rotation

to soil fertility levels on a varzea soil. Fertilizer Research 45:13–20.Fageria, N. K., and V. C. Baligar. 1999. Growth and nutrient concentrations of common bean, low-

land rice, corn, soybean, and wheat at different soil pH on an Inceptisol. Journal of PlantNutrition 22:1495–1507.

Fageria, N. K., and V. C. Baligar. 2001. Lowland rice response to nitrogen fertilization.Communications in Soil Science and Plant Analysis 32:1405–1429.

Fageria, N. K., and V. C. Baligar. 2005. Enhancing nitrogen use efficiency in crop plants. Advancesin Agronomy 88:97–185.

Fageria, N. K., and V. C. Baligar. 2006. Nutrient efficient plants in improving crop yields in thetwenty-first century. Paper presented at the 18th World Soil Science Congress, July 9–15,Philadelphia, Penn.

Fageria, N. K., V. C. Baligar, and R. B. Clark. 2006. Physiology of crop production. New York:Haworth Press.

Fageria, N. K., V. C. Baligar, and R. J. Wright. 1990. Iron nutrition of plants: An overview onthe chemistry and physiology of its deficiency and toxicity. Pesquisa Agropecuaria Brasileira25:553–570.

Fageria, N. K., and M. P. Barbosa Filho. 2007. Dry-matter and grain yield, nutrient uptake, and phos-phorus use efficiency of lowland rice as influenced by phosphorus fertilization. Communicationsin Soil Science and Plant Analysis 38:1289–1297.

Fageria, N. K., M. P. Barbosa Filho, and F. J. P. Zimmermann. 1994. Chemical and physicalcharacterization of varzea soils of some states of Brazil. Pesquisa Agropecuaria Brasileira29:267–274.

Fageria, N. K., and N. A. Rabelo. 1987. Tolerance of rice cultivars to iron toxicity. Journal of PlantNutrition 10:653–661.

Fageria, N. K., and A. B. Santos. 2008. Lowland rice response to thermophosphate fertilization.Communications in Soil Science and Plant Analysis 39:873–889.

Fageria, N. K., A. B. Santos, M. P. Barbosa Filho, and C. M. Guimarães. 2008. Iron toxicity inlowland rice. Journal of Plant Nutrition 31:1676–1697.

Fageria, N. K., A. B. Santos, and V. A. Cutrim. 2007. Yield and nitrogen use efficiency of lowlandrice genotypes as influenced by nitrogen fertilization. Pesquisa Agropecuaria Brasileira 42:1029–1034.

Fageria, N. K., A. B. Santos, I. D. G. Lins, and S. L. Camargo. 1997. Characterization of fertilityand particle size of varzea soils of Mato Grosso and Mato Grosso do Sul States of Brazil.Communications in Soil Science and Plant Analysis 28:37–47.

Fageria, N. K., N. A. Slaton, and V. C. Baligar. 2003. Nutrient management for improving lowlandrice productivity and sustainability. Advances in Agronomy 80:63–152.

Fageria, N. K., L. F. Stone, and A. B. Santos. 2003. Fertility management of irrigated rice. SantoAntônio de Goiás, Goiás, Brazil: Embrapa Arroz e Feijão.

Fageria, N. K., R. J. Wright, V. C. Baligar, and C. M. Sousa. 1991. Characterization of physical andchemical properties of Varzea soils of Goias State of Brazil. Communications in Soil Scienceand Plant Analysis 22:1631–1646.

Flach, K. W., and D. F. Slusher. 1978. Soils used for rice culture in the United States. In Soils andrice, 199–215. Los Banos, Philippines: IRRI.

Ghildyal, B. P. 1978. Effects of compaction and puddling on soil physical properties and rice growth.In Soils and rice, 317–336. Los Banos, Philippines: IRRI.

Ghildyal, B. P., and R. P. Tripathi. 1971. Effect of varying bulk densities on the thermal characteristicsof lateritic sandy clay loam soil. Journal of Indian Society of Soil Science 19:5–10.

Gotoh, S., and W. H. Patrick Jr. 1976. Transformation of iron in a waterlogged soil as influenced byredox potential and pH. Soil Science Society of America Proceedings 38:66–71.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Hedley, M. J., G. J. D. Kirk, and M. B. Santos. 1994. Phosphorus efficiency and the forms of soilphosphorus utilized by upland rice cultivars. Plant and Soil 158:53–62.

Hudnall, W. H. 1991. Taxonomy of acid rice growing soils of the tropics. In Rice production on acidsoils of the Tropics, ed. P. Deturck and F. N. Ponnamperuma, 3–8. Kandy, Sri Lanka: Instituteof Fundamental Studies.

Ikehashi, H., and F. N. Ponnamperuma. 1978. Varietal tolerance of rice for adverse soils. In Soils andrice, 801–825. Los Baños, Philippines: IRRI.

Klamt, E., N. Kampf, and P. Schneider. 1985. Varzea soils of state of Rio Grande do Sul (Faculty ofAgronomy, Department of Soils, Technical Bulletin 4). Porto Alegre, Brazil: Federal Universityof Rio Grande do Sul.

Linquist, B. A., P. W. Singleton, R. S. Yost, and K. G. Cassman. 1997. Aggregate size effects onthe sorption and release of phosphorus in an Ultisol. Soil Science Society of America Journal61:160–166.

Marschner, H. 1995. Mineral nutrition of higher plants, 2nd edition. New York: Academic Press.Matsuo, H., A. J. Pecrot, and J. Riquier. 1978. Rice soils of Europe. In Soils and rice, 191–198. Los

Banos, Philippines: IRRI.Moraes, J. F. V. 1999. Soils. In Rice culture in Brazil, ed. N. R. A. Vieira, A. B. Santos, and E. P.

Santana, 88–115. Santo Antônio de Goiás, Brazil: Embrapa Arroz e Feijão.Moraes, J. F. V., and C. J. S. Freira. 1974. Influence of flooding water depth on growth and yield of

rice. Pesquisa Agropecuaria Brasileira 9:45–48.Moormann, F. R. 1978. Morphology and classification of soils on which rice is grown. In Soils and

rice, 255–272. Los Banos, Philippines: IRRI.Murthy, R. S. 1978. Rice soils of India. In Soils and rice, 3–17. Los Banos, Philippines: IRRI.Panabokke, C. R. 1978. Rice soils of Sri Lanka. In Soils and rice, 19–33. Los Banos, Philippines:

IRRI.Patrick Jr., W. H. 1966. Apparatus for controlling the oxidation–reduction potential of waterlogged

soils. Nature 212:1278–1279.Patrick Jr., W. H., and I. C. Mahapatra. 1968. Transformation and availability to rice of nitrogen and

phosphorus in waterlogged soils. Advances in Agronomy 20:323–356.Patrick Jr., W. H., and D. S. Mikkelsen. 1971. Plant nutrient behavior in flooded soil. In Fertilizer

technology and use, 2nd ed., ed. R. A. Olson, 187–215. Madison, Wisc.: Soil Science Societyof America.

Patrick Jr., W. H., and C. N. Reddy. 1978. Chemical changes in rice soils. In Soils and rice, 361–379.Los Banos, Philippines: IRRI.

Patrick Jr., W. H., and R. Wyatt. 1964. Soil nitrogen loss as a result of alternate submergence anddrying. Soil Science Society of America 28:647–653.

Ponnamperuma, F. N. 1972. The chemistry of submerged soils. Advances in Agronomy 24:29–96.Ponnamperuma, F. N. 1975. Micronutrient limitations in acid tropical rice soils. In Soil management

in Tropical America, ed. E. Bornemisza and A. Alvarado, 330–347. Raleigh: North CarolinaState University.

Ponnamperuma, F. N. 1976. Physicochemical properties of submerged soils in relation to fertility. InThe fertility of paddy soils and fertilizer application for rice, 1–27. Taipei City, Taiwan: Foodand Fertilizer Technology Center.

Ponnamperuma, F. N., R. Bradfield, and M. Peech. 1955. Physiological disease of rice attributable toiron toxicity. Nature 175:265.

Raymundo, M. E. 1978. Rice soils of the Philippines. In Soils and rice, 115–133. Los Banos,Philippines: IRRI.

Sahrawat, K. L. 2004. Iron toxicity in wetland rice and its role of other nutrients. Journal of PlantNutrition 27:1471–1504.

Sahu, B. N. 1968. Bronzing disease of rice in Orissa as influenced by soil types and manuring andits control. Journal of Indian Society of Soil Science 16:41–54.

Sanchez, P. A., and J. G. Salinas. 1981. Low input technology for managing Oxisols and Ultisols intropical America. Advances in Agronomy 34:279–406.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014


Sims, J. T., and G. V. Johnson. 1991. Micronutrient soil tests. In Micronutrient in agriculture, ed. J. J.Mortvedt, F. R. Fox, L. M. Shuman, and R. M. Welch, 427–476. Madison, Wisc.: Soil ScienceSociety of America.

Soepraptohardjo, M., and H. Suhardjo. 1978. Rice soils of Indonesis. In Soils and rice, 99–113. LosBanos, Philippines: IRRI.

Soil Science Society of America. 2008. Glossary of soil science terms. Madison, Wisc.: Soil ScienceSociety of America.

Tanaka, A., R. Loe, and S. A. Navasero. 1966. Some mechanisms involved in the development ofiron toxicity symptoms in the rice plant. Soil Science Plant Nutrition 12:32–38.

USDA (United States Department of Agriculture). 1975. Soil taxonomy: A basic system of soilclassification for making and interpreting soil surveys (USDA Agricultural Handbook 436).Washington, D.C.: U.S. Government Printing Office.

Wickham, T. H., and V. P. Singh. 1978. Water movement through wet soils. In Soils and rice, 337–358. Los Banos, Philippines: IRRI.

Dow

nloa

ded

by [

Uni

vers

ity o

f N

orth

ern

Col

orad

o] a

t 23:

12 2

9 Se

ptem

ber

2014

chemistry of lowland rice soils and nutrient availability

Documents