Advances in agronomy volume 25

ADVANCES IN

AGRONOMY
VOLUME 25


CONTRIBUTORS TO THIS VOLUME

K. BAEUMER
W. A. P. BAKERMANS

C. BLOOMFIELD
J. K. COULTER
A. E. FOSTER

R. F. HARRIS
T. K. HODGES

E. A. HOLLOWELL
W. E. KNIGHT
G. A. PETERSON

MOSHEJ. PINTHUS
J. R. QUINBY
J. C. RYDEN

J. K. SYERS


ADVANCES IN

AGRONOMY
Prepared under the Auspices of the
AMERICAN
SOCIETY

AGRONOMY

OF

VOLUME 25

Edited by N. C. BRADY
International Rice Research Institute
Manila, Philippines
ADVISORY BOARD

D. G . BAKER

H. M. LAUDE

G. R. DUTT
G . W. KUNZE

M. A. MASSENGALE

D. E. WEIBEL

1973

ACADEMIC PRESS

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CONTENTS
CONTRIBUTORS
TO VOLUME25 . . . . . . . . . . . . . . . . . . . . . , . . . . . . , . . . . . . . . . . . .

ix

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

xi

PHOSPHORUS IN RUNOFF AND STREAMS

J. C. RYDEN,J. K. SYERS,AND R. F. HARRIS

I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1

11. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111. Factors Affecting the Dynamics of Phosphorus in Runoff and Streams . .

2

.

IV. Phosphorus Loads in Runoff and Streams . . . . . . . . . . . . . . . . . . . . . . . . . . .

V. Impact of Phosphorus Carried in Streams on Standing Waters . . . . . . . . .
VI. Present Status and Outlook . . . , . , . . . . . . . . , . . , . . . . . , . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

20
37
38
41

CRIMSON CLOVER

W. E. KNIGHTAND E. A. HOLLOWELL

I.
11.
111.

...............................................

Morphology . . . . . . . . . . . . . . . . . . .
.................
. . . . ... .. .. .. ..
Physiology . , . . . . . . . . . . . . . , . . .
Culture . . . . . . .
... . . .. .
...............
..
Utilization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IV.
V.
VI.
VII.
VIII. Conclusions

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

48
50
52

57
65
68

....................................

. . . . .. . . . . . .. . .. . . .

........................
...............................................

12
73

ZERO-TILLAGE

K. BAEUMERAND W. A. P. BAKERMANS

1. Introduction: The Concept of Zero-Tillage

. . . . . . . . . . . . . . . . . ... . . . . . .

11. Comparison of Environmental Conditions in Tilled and Untilled Soils . . .
111. Effects of Zero-Tillage on Plant Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . .

IV. Crop Husbandry . . . . . , . . . . . , . . . , . . . . . . . . . , . . . . , . . . . . . . . . . . . . . . . .
V. Evaluation of Zero-Tillage in Farming Systems . . . . . . . . . . . . . . . . . . . . . .
VI. Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V

78
80
95
103
113
119
120


vi

CONTENTS

THE GENETIC CONTROL OF FLOWERING AND GROWTH IN SORGHUM

J. R. QUINBY

................

I.
11.
111. The Floral Stimulus

IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
XII.

..

Implications to Plant Breeding
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

160

ION ABSORPTION BY PLANT ROOTS

T. K. HOLXES
I. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Overview of Nutrient Absorption by Roots . . . . . . . . . . . . . . . . . . . . . . . . .
Energy-Dependent and Active Ion Transport . . . . . . . . . . . . . . . . . . . . . . .
Kinetics and Selectivity of Ion Absorption . . . . . . . . . . . .

.........
Energetics of Ion Transport . . . . . . . . . . . . . . . . . . . . . . . .
Proposed Model for Ion Absorption by Roots . . . . . . . . . . . . . . . . . . . . . .
Summary . . . . . . . . . . . . . . .
...................................
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

11.
111.
IV.
V.
VI.
VII.

163
164
167
180

198
201
202

LODGING IN WHEAT, AND OATS: THE PHENOMENON,
ITS CAUSES, AND PREVENTIVE MEASURES

MOSHEJ. PINTHUS
I.
11.
111.

IV.
V.
VI.
VII.
VIII.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Description and Causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Effects of Lodging on Crop Development and Yield . . . . . . . . . . . . . . . .
Plant Characters Associated with Lodging . . . . . . . . . . . . . . . . . . . . . . . . .
Environmental and Agronomic Factors Affecting Lodging . . . . . . . . . . .
Prevention of Lodging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Breeding for Lodging Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Increased Exploitation of Yield-Promoting Factors Due to the
Prevention of Lodging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References ...................................................

210
21 1
217
223
23 1
23 8
246
254
256


vii

CONTENTS

GENESIS AND MANAGEMENT

OF ACID SULFATE SOILS

C. BLOOMFIELDAND J. K. COULTER

I. Introduction . . . . . . . . . . . . . . . . . . . .
.....................
11. The Formation of Sulfides . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
111. Oxidation of Sulfides . . . . . . . . . .
...........
IV. Mining and Corrosion Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V. Classification and Mapping . . . . . .
..............
VI. Conditions for Plant Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
VII. Management for Agriculture
.........
VIII. Analysis of Pyritic Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IX. Conclusions . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

266
267
278
290
292
296
3 08

3 15
318
319

MALTING BARLEY I N THE UNITED STATES
G. A. PETERSON
AND A. E. FOSTER

I.
11.
111.

IV.
V.
VI.
VII.
VIII.
IX.
X.
XI.
XII.

Classification of Cultivated Barleys of the United States

Quality Testing P
Barley Varieties
XI11. Malting Barley Pr
References . .

cceptable Malting

..............................
.........................

364
375

AUTHORINDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
SUBJECTINDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

379
398


This Page Intentionally Left Blank


CONTRIBUTORS TO VOLUME 25
Numbers in parentheses indicate the pages on which the authors' contributions begin.

K. BAEUMER(77), Faculty of Agriculture, University of Goettingen,
Goettingen, Federal Republic of Germany
W. A. P. BAKERMANS
(77), Institute for Biological and Chemical Research
of Field Crops and Herbage, Wageningen, The Netherlands
C. BLOOMFIELD
(265 ) , Rothamsted Experimental Station, Harpenden,
Herts, England
J. K. COULTER( 2 6 5 ) , Rothamsted Experimental Station, Harpenden,
Herts, England

A. E. FOSTER(327), Department of Agronomy, North Dakota State
University, Fargo, North Dakota
R. F. HARRIS( 1 ) , Department of Soil Science, University of Wisconsin,
Madison, Wisconsin
T. K . HODGES(163), Department of Botany and Plant Pathology, Purdue
University, Lafayette, Indiana
E. A. HOLLOWELL
(47), W.S. Department of Agriculture, Beltsville,
Maryland
W. E. KNIGHT (47), U.S. Department of Agriculture, Mississippi State,
Mississippi
0.A. PETERSON
(327), Department of Agronomy, North Dakota State
University, Fargo, North Dakota
MOSHEJ. PINTHUS(209), The Hebrew University of Jerusalem, Faculty
of Agriculture, Rehovot, Israel
J. R. QUINBY ( 125 ) , Pioneer Hi-Bred Company, Plainview, Texas
J. C. RYDEN(1 ), Department of Soil Science, University of Wisconsin,
Madison, Wisconsin"
J. K. SYERS( I ) , Department of Soil Science, University of Wisconsin,
Madison, Wisconsin"

* Present address: Department of Soil Science, Massey University, Palmerston
North, New Zealand.
ix


This Page Intentionally Left Blank

PREFACE

Dramatic reductions during the past two years in the world food supply
have jolted a complacent world into the realization that the food-population
race remains unquestionably the most critical problem facing mankind.
Population growth continues at alarming rates in those countries where
food supplies are already inadequate. Food shortages are plaguing not only
the poor countries where hunger, malnutrition, and starvation are a way
of life, but have now reached the more affluent nations. Even the United
States which for a generation has sought through public programs to limit
crop production is now concentrating on programs to increase food supply.
Once again tillers of the soil, and the crops and animals which supply
our food have high national priorities. In this time of international concern
over food supply, reviews of scientific advancement such as those contained in this volume are most reassuring.
Papers contained in this volume are concrete evidence of the contribution
of crop and soil scientists to mankind’s efforts to feed himself. Four of the
papers deal with crops. One is concerned with research on crimson clover,
a legume grown in the southern part of the United States and a plant
which is most important to a growing animal industry in this area. Remarkable progress is reported on knowledge gained from the breeding of
sorghum, a plant which is rapidly becoming a major crop in the semi-arid
regions throughout the world. Factors affecting the lodging of small grains
is the subject of one review. Recent advances in research on malting
barley, a crop of expanded acreage and of increasing quality expectations
is the subject of the fourth crops article.
The reviews of advances in soil science are certainly not unrelated to
crop production. The mechanisms of ion absorption by plant roots are
the subject of one review. Plant root growth is one of the phenomena
considered in the critical analysis of the practice of zero-tillage made by
scientists who have devoted much of their research efforts to this cultural
practice. Phosphorus accumulation in streams and lakes fed by runoff

from agricultural lands is the subject of another review. The need to prevent
environmental contamination from agricultural chemicals is considered.
The genesis and management of acid sulfate soils, which occupy millions
of acres of coastal areas in warm and hot humid climates are discussed.
These soils are important especially to the rice growing areas of the world.
The international focus of this journal is maintained not only by the
nature of the subjects covered but by the selection of authors to write the
reviews. Food production is truly an international problem to which crop
and soil scientists throughout the world are addressing their attention.

N. C . BRADY
xi


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PHOSPHORUS IN RUNOFF AND STREAMS
J. C. Ryden,' J. K. Syers,' and R. F. Harris
Department of Soil Science, University of Wisconsin,
Madison, Wisconsin

I. Introduction
11. Terminology

.....................................................
.
......................
.............................

......................

B. Forms of
111. Factors Affecting

in Runoff and Streams

......................

B. Chemical Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IV. Phosphorus Loads in Runoff and Streams .
A. Influence of Point Sources on Phosphorus in Streams . . .
B. Runoff from Forest Watersheds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
C. Runoff from Agricultural Watersheds
D. Runoff from Land Associated with Ani
E. Urban Runoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
V. Impact of Phosphorus Carried in Streams on Standing Waters . . . . . .
VI. Prcsent Status and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

I.

1
2
2
4
4
4

7

20.
21
22
25
32
33
37
38
41

Introduction

Increasing evidence suggests that phosphorus ( P ) in surface waters is
a primary factor controlling the eutrophication of water supplies (Ohle,
1953; Mackenthun, 1965; Stewart and Rohlich, 1967; Vollenweider,
1968; Lee, 1970). Assessment of the relative contribution of the different
sources of P to surface waters (Fig. 1 ) is of critical importance for implementation of control measures to prevent or reverse P-induced eutrophication. Although the importance of runoff and streams as major sources of
P to standing waters is well recognized, little attempt has been made to
differentiate between and quantify the P forms in runoff and streams which
are of potential importance with respect to their impact on the biological
productivity of standing waters. Furthermore, little emphasis has been
placed on the reactions that may occur between dissolved inorganic P and
Present address: Department of Soil Science, Massey University, Palmerston

North, New Zealand.
1


2

J. C. RYDEN, J. K. SYERS, AND R. F. HARRIS

the solid phases with which it is in contact in runoff and streams, as
pointed out by Taylor ( 1967) and Biggar and Corey (1969).
Critical concentration limits have been suggested for P in surface waters
which, if exceeded, will lead to excessive biological productivity (Sawyer,
1947; Mackenthun, 1968). In this review, however, rather than emphasizing critical concentrations, P in runoff and streams will be discussed
mainly from the standpoint that any P load constitutes a potential increase
in the P fertility of surface waters.

II.

Terminology

A. HYDROLOGY
AND PHOSPHORUS
SOURCES
This review will use essentially the definitions proposed by Langbein
and Iseri ( 1960).
Watershed (drainage basin; catchment area). A part of the surface of
the earth that is occupied by a drainage system, which consists of a surface
stream, or a body of standing (impounded) surface water, together with
all tributary surface streams and bodies of standing surface water.
Stream. A general term for a body of flowing water. In hydrology the
term is usually applied to the water flowing in a natural channel.
Stream flow. The discharge (of water) that occurs in a natural channel.
Runoff.That part of precipitation that falls on land and ultimately appears in surface streams and lakes. Runoff may be classified further according to its source.
Surface runoff (overland flow). That part of rainwater or snowmelt
which flows over the land surface to stream channels. Surface runoff may
also enter standing waters directly or be consolidated into artificial channels, e.g., storm sewers in urban areas (urban runoff), before entering a

stream or body of standing water.
Subsurface runoff (storm seepage). That part of precipitation which infiltrates the surface soil and moves toward streams as ephemeral, shallow,
perched groundwater above the main groundwater level. In many agricultural areas subsurface runoff may be intercepted by artificial drainage systems, e.g., tile drains, accelerating its movement to streams.
Groundwater run08 (base runoff). That part of precipitation that has
passed into the ground, has become ground water, and is subsequently
discharged into a stream channel or lake as spring or seepage water.
In addition to runoff, the other potential contributors to streams and
standing waters are precipitation incident on the water surface and industrial and sewage effluents (Fig. 1 ) .


PHOSPHORUS IN RUNOFF AND STREAMS

3

McCarty (1967) and Vollenweider ( 1968) have made a useful division
of sources of P to surface waters based on the ease of quantification.
Point sources enter at discrete and identifiable locations and are therefore amenable to direct quantification and measurement of their impact
on the receiving water. Major point sources include effluents from indus-

FIG. 1. Schematic representation of the relationships between phosphorus sources
and runoff, streams, and standing waters.

trial and sewage-treatment plants (Fig. 1) . Diffuse .wurces may be defined
as those which at present can be only partially estimated on a quantitative
basis and which are probably amenable only to attenuation rather than
to elimination. Diffuse sources require the most investigative attention.
Vollenweider ( 1968) further divided diffuse sources into:
1. Natural sources such as eolian loading, and eroded material from
virgin lands, mountains and forests.
2. Artificial or semiartificial sources which are directly related to human

activities, such as fertilizers, eroded soil materials from agricultural and
urban areas, and wastes from intensive animal rearing operations.
The loads of P imparted to runoff and streams from natural diffuse
sources provide a datum line against which the magnitude of P loads from
artificial sources may be compared.


4

J. C. RYDEN, J. K.

SYERS, AND

R. F. HARRIS

B. FORMS
OF PHOSPHORUS

In natural systems, P occurs as the orthophosphate anion (Pod3-)which
may exist in a purely inorganic form (H2P0,- and HP0,2-) or be incorporated into an organic species (organic P ) . Under certain circumstances
inorganic orthophosphate may exist as a poly- or condensed phosphate.
A secondary distinction is made between particulate and dissolved forms
of P, the split conventionally being made at 0.45 pm.
Other terminology used is as follows:
Total P . All forms of P in a runoff or stream sample (dissolved and
particulates in suspension) as measured by an acid-oxidation treatment
(e.g., acid ammonium persulfate).
Dissolved inorganic P . P in the filtrate after 0.45 pm separation determined by an analytical procedure for inorganic orthophosphate.
Organic P . P that may be determined within the dissolved and particulate fractions by the difference between total P and inorganic P.
Ill.

Factors Affecting the Dynamics of Phosphorus in Runoff and Streams

Before evaluating the magnitude of various P sources in terms of the
loads of P in runoff and streams, and the extent to which previous studies
of P loadings enable an adequate definition of P sources, it is important
to understand the physical and chemical factors affecting the dynamics of
P in runoff and streams. These factors determine not only the movement
of P into runoff and streams, but also its distribution between the aqueous
and particulate phases.
A.

PHYSICALFACTORS

All terrestrially derived diffuse sources of P are associated with the
movement of water in contact with a solid phase. The solid phase may
be stationary with respect to water flow, or may move in the flow at some
speed equal to or less than the flow. Precipitation disposed of as subsurface
or groundwater runoff is primarily in contact with a stationary solid phase,
namely the soil profile and, in the case of groundwater runoff, possibly
the bedrock. Consequently, the amounts and concentrations of P carried
in subsurface and groundwater runoff will be influenced by the time of
contact with any component in the soil profile capable of interacting with
dissolved P in the percolating water and by the concentration of dissolved
P that the soil components maintain in the soil solution. Time of contact
between the percolating solution and any soil component will in turn depend on the rates of infiltration and percolation into and through the soil.


PHOSPHORUS IN RUNOFF AND STREAMS

5

Some of the theories developed to describe water movcment in soils can
be applied to evaluate the potential loss of P from various soil types as
a result of subsurface runoff. Gardner (1965) developed equations to describe the movement of nitrate in the soil profile due to leaching. The
chemical interactions that occur between dissolved inorganic P and soil
components (discussed later), when water percolates through the soil,
must also be taken into consideration. Inclusion of a term in the equations
developed by Gardner (1965) to describe the relationship between P in
particulate and aqueous phases is therefore necessary. This could take the
form of a linear adsorption isotherm relevant to the concentrations of dissolved inorganic P maintained in the solution of a particular soil. Biggar
and Corey (1969) have also reviewed the literature on infiltration and
percolation of water in agricultural soils as it pertains to nutrient
movement.
The movement of solid phase material in contact with natural waters
occurs during surface runoff and in streams. The amounts of solid material
capable of entering surface runoff will depend on the intensity of rainfall,
physical and chemical attachment between various solid components, and
the amounts and energy of runoff waters (Guy, 1970). It is the energy
of surface runoff or stream water, however, that governs the amounts of
a specific size fraction of particulate materials which will remain in suspension during water flow.
The primary source of particulate material to surface runoff and streams
is eroding soil (Guy and Ferguson, 1970), although in urban areas with
little ongoing development, particulates may be dominated by specifically
urban detrital material (e.g., street litter and dust) and organics derived
from urban vegetation.
The total on-site losses of soil due to sheet and rill erosion are not necessarily delivered to streams. The amount of sediment that travels from a
point of erosion to another point in the watershed is termed the sediment
yield (Johnson and Moldenhauer, 1970). Consequently the Universal Soil
Loss Equation used to predict field soil losses on an average annual basis

(Wischmeier and Smith, 1965) must be corrected when used to predict
sediment loads in streams because deposition of particulates may occur
on the land surface as a result of slope variations before surface runoff
reaches a stream. It is for this reason that estimates of soil loss in surface
runoff from sites within a particular watershed cannot be translated into
total P losses through a knowledge of the total P content of the soil, if
the P loss is to be related to P enrichment of surface waters.
An associated complication arises from the fact that soil P is primarily
associated with the solid phase. As soil erosion is a selective process with
respect to particle size, selectivity has been observed for P loss in surface


6

J. C. RYDEN, J. K. SYERS, AND R. F. HARRIS

runoff. The extent of the selectivity depends on the particle sizes with
which most of the soil P is associated. This observation has led to the
concept of enrichment ratios (ER) , which for P are calculated as the ratio
of the concentration of P in the particulate phase of surface runoff to the
concentration of P in the source of the particulate phase. This effect was
first considered by Rogers (1941), who observed ER values of 1.3 for
total P and 3.3 for “0.002 N H,SO, extractable” P for a silt loam situated
on a 20-25% slope. Other values range from 1.5 to 3.1 for total P
(Knoblauch et al., 1942; Neal, 1944; Stoltenberg and White, 1953),
whereas Massey and Jackson (1952) observed values between 1.9 and
2.2 for “water-soluble plus pH 3 extractable” P for silt loams in Wisconsin.
The selective nature of surface runoff with respect to P is due to selective
removal of fine soil particulates as a result of the energy limitations of
runoff and the fact that a large percentage of total soil P is frequently

associated with clay-sized material (Scarseth and Chandler, 1938; Williams
and Saunders, 1956; Syers et al., 1969). Greater selectivity of fines and
consequently particulate P will occur as the energy of surface runoff decreases. Stoltenberg and White (1953) observed that as precipitation disposed of through surface runoff decreased from 70 mm to 0.25 mm per
hour, the clay content of eroded material from a soil with a clay content
of 16-18% increased from 25% to 60%. This has obvious implications
in relation to the nature of the sediment load carried by a stream and the
interactions of P between the solid and aqueous phases, particularly during
periods of surface runoff. It should be pointed out, however, that although
the P content of the sediment load may increase as surface runoff diminishes, as may be predicted from the work of Stoltenberg and White
(1953), the total P load may not change, or may even decrease, owing
to lower sediment loads.
The particulate material carried in streams may be divided into bed load
and wash or suspended load. The bed load, which may also have a contribution from existing stream sediment, is that which moves along or close
to the stream bed, whereas the wash load is maintained in the flow by
turbulence (Johnson and Moldenhauer, 1970). By inference from the selectivity of surface runoff for fine soil particulates, the wash load will be
high during surface runoff events. Furthermore, Johnson and Moldenhauer
(1970) suggested that the wash load travels at about the same velocity
as the water with which it is in contact. Consequently, P associated with
the clay- and silt-sized particulates constituting the wash load will move
between any two points in the stream profile at the same speed as the
ambient dissolved forms of P.
Increased turbulence in streams during high flow, or arising from an
increasing gradient, will tend to maintain in suspension particle sizes more


PHOSPHORUS IN RUNOFF AND STREAMS

7

characteristic of the bed load, and may even resuspend existing stream

bed sediment. In a study of total P loads in the Pigeon River, North Carolina, Keup (1968) noted that an increase in gradient from 2.81 to 4.35
m/km, over which no tributaries entered the main stream, resulted in a
90.8 kg/day increase in the total P load carried.
It appears that in the majority of cases a large proportion of particulate
P in streams arises from soil erosion. Phosphorus may be stored in stream
bed sediments, but unless the stream is actively aggrading, the amount of
P stored will be less than the inflow (Keup, 1968). That which is stored
is liable to resuspension and transport owing to turbulence during periods
of high flow.

B. CHEMICAL
FACTORS
1 . Nature of Soil P
Soil P may be divided into two broad categories: inorganic P, namely,
that associated with soil mineral particles; and organic P, which forms an
integral part of the soil organic matter fraction.
a. Inorganic P . O n the basis of solubility product criteria, it has been
postulated that discrete phase crystalline Fe and A1 phosphates exist in
noncalcareous soils (Kittrick and Jackson, 1956; Hemwall, 1957; Chakravart and Talibudeen, 1962). The general occurrence of discrete Fe and
A1 phosphates seems doubtful on the basis of the ion product data presented by Bache (1964) and the experimental observations of Hsu
(1964). It is now generally accepted that secondary inorganic P in many
soils exists primarily in association with oxides and hydrous oxides of Fe
and Al, as surface-bound forms or within the matrices of such components.
However, that discrete Fe and A1 phosphates are formed as temporary
phases in the vicinity of phosphate fertilizer particles due to conditions
of localized high acidity and P concentration is well established (Lindsay
and Stephenson, 1959; Huffman, 1969). Such compounds will not be
stable as the dissolved inorganic P concentration in the soil solution or
aqueous portion of other soil-water ecosystems decreases.
The calcium phosphate mineral, apatite (Shipp and Matelski, 1960) and

calcic fertilizer-soil reaction products (Huffman, 1969) have been identified in soils. The amounts of apatite are appreciable only in weakly
weathered soils (Williams et al., 1969), as predicted by the weathering
indices of Jackson ( 1969). Calcic fertilizer-sail reaction products may be
present in neutral and calcareous surface soil horizons, and their importance in maintaining high concentrations of dissolved inorganic P in
soil-water ecosystems should not be overlooked.


8

J. C. RYDEN, J. K. SYERS, AND R. F. HARRIS

Consequently three basic forms of inorganic P may exist in unfertilized
soils (Syers and Walker, 1969; Williams and Walker, 1969): apatite,
which is a discrete phase P compound; P sorbed on the surfaces of Fe,
Al, and Ca soil components (nonoccluded); and P present within the
matrices of Fe and A1 components (occluded). In fertilized soils, a variety
of P fertilizer-soil reaction products may exist as transient phases. As the
solubility product of pure apatite in water is low (0.03 pg per milliliter
at pH 7, Stumm, 1964) and the P held within the matrices of Fe and
A1 components is virtually chemically immobile, except under reducing
conditions in the case of Fe, major emphasis should be directed toward
the reactions involving P in solution and that sorbed on the surfaces of
Fe, Al, and Ca components as well as the release of P due to dissolution
of fertilizer-soil reaction products.
b. Organic P. Elucidation of the composition of soil organic P is restricted by lack of extractants capable of removing organic P from soils
in a relatively unaltered form and by the inadequacy of current methods
for mildly degrading extracted organic P-organic matter complexes. Existing data indicate that most of the organic P in soils is associated, in an
ill-defined manner, with the humic and fulvic acid complex of soil organic
matter (Anderson, 1967). Of the specific forms of organic P that have
been identified in soils, inositol phosphates are present in largest relative

amounts, comprising up to 60% of the total organic P (Anderson, 1967;
Cosgrove, 1967; McKercher, 1969). Other specific organic P compounds
are present in soil in much lower quantities: nucleic acids account for
5-lo%, and other phosphate esters, such as phospholipids, sugar phosphates, and phosphoproteins, for less than 1-2% (McKercher, 1969).
2. Sorption of Dissolved P by Soils
Whenever water containing a particular concentration of dissolved P
comes into contact with soil material, there is a possibility for sorption,
desorption, or dissolution reactions to take place. The types of reactions
are the same regardless of whether they occur under conditions existing
in the soil profile, surface runoff, or streams. Although in some cases biological assimilation may initially affect the distribution of P between dissolved and particulate phases of soil-water systems, the distribution of P
between these phases will be determined by the nature of the inorganic
particulates and the concentrations of dissolved P in solution (Keup, 1968;
McKee et al., 1970; Ryden et al., 1972b).
a. Inorganic P. It has been demonstrated that the uptake or sorption
of P from solution by soils is significantly related to the presence of shortrange order (amorphous) oxides and hydrous oxides of Fe and A1 (Williams et al., 1958; Gorbunov et al., 1961; Bromfield, 1965; Hsu, 1964;
Saunders, 1965; Syers et al., 1971). Furthermore, “pure” oxides and hy-


PHOSPHORUS IN RUNOFF AND STREAMS

9

drous oxides of Fe and Al, and short-range order aluminosilicates have
also been shown to be particularly effective in the sorption of inorganic
P from solution (Gastuche et al., 1963; Muljadi et al., 1966; Hingston
et al., 1969). The sorption of inorganic P by Fe and A1 oxides and hydrous
oxides is known to be rapid, as is the sorption of P by soils. Furthermore,
short-range order Fe and A1 oxides and hydrous oxides are ubiquitous in
soils (Hsu, 1964), their relative amounts depending on parent material,
climatic and drainage conditions, and occur mainly as coatings on other

soil components. Shen and Rich (1962) and Jackson (1963) have noted
the occurrence of A1 hydroxypolymers and Dion (1944), and Roth et al.
( 1969) have reported the presence of F e oxide and hydrous oxide coatings
on clay mineral surfaces. Such coatings, in conjunction with the greater
surface area of the clay fraction compared to that of the other particle-size
fractions in a soil, explain the observation of Scarseth and Chandler (1938)
that up to 50% of the total P in soils may be associated with the
the clay fraction, as well as the enrichment ratio effect for P as a result
of soil erosion.
Attempts have been made to correlate P sorption with the clay content
of soils (Williams et al., 1958). Correlations between P sorption and clay
content after removal of Fe and A1 oxides and hydrous oxides often have
been poor. Better correlations may be expected if P sorption is related
to the content of water-dispersed clay. The sorption of P by water-dispersed clay and silt of soils has obvious implications to reactions occurring
between dissolved and particulate P in surface runoff and streams.
Sorption of inorganic P by CaC03 has also been demonstrated (Cole
et al., 1953). The nature of the surfaces of calcite in calcareous soils may
be very different from those of pure calcite (Buehrer and Williams, 1936;
Lahav and Bolt, 1963; Syers et al., 1972).
The sorption of dissolved inorganic P by soils may be described by sorption isotherms similar to that shown in Fig. 2. Numerous workers have
also shown that sorption may be described by some of the adsorption isotherms developed to describe gas adsorption by solids (Russell and Prescott, 1916; Olsen and Watanabe, 1957; Rennie and McKercher, 1959;
Syers et al., 1973). Similar observations have been made for the sorption
of inorganic P by soil components such as kaolinite and short-range order
Fe and A1 oxides and hydrous oxides (Gastuche et al., 1963; Muljadi et
al., 1966; Kafkafi et al., 1967). Although these studies have been useful
in describing relationships between various soils and soil components with
respect to their P sorption capacities, they have provided little information
regarding P sorption behavior from solutions containing the low dissolved
inorganic P concentrations characteristic of most soil-water ecosystems,
largely because of the high levels of added P used (Ryden et al., 1972b).

Furthermore, Syers et al. (1973) obtained two linear Langmuir relation-


10

J. C. RYDEN, J. K. SYERS, AND R. F. HARRIS

sorbed ( f )

APon
sol I

released (3

FIG.2. Typical isotherm for the sorption of added inorganic phosphorus by
a soil. E = equilibrium P concentration. (From White and Beckett, 1964.)

ships which intersected at equilibrium P concentrations varying from 1.5
to 3.2 pg P/ml, for three contrasting soils-an observation that probably
invalidates interpretations of P sorption made from many previous studies
where high levels of added P were used.
The study of White and Beckett (1964), conducted at initial dissolved
inorganic P concentrations, comparable to those existing in soil-water ecosystems, provides a useful basis for understanding the interactions between
aqueous and particulate phases of P in runoff and streams. Figure 2 illustrates the principle of the approach used. White and Beckett (1964) defined the intersection of the P sorption isotherm and the abscissa, the
“equilibrium phosphate potential” ( 5 p C a pH,PO,) , abbreviated to
“equilibrium P concentration” by Taylor and Kunishi ( 1971) . The intersection is equivalent to the inorganic P concentration in the ambient aqueous phase when there is no net sorption or release of P, i.e., AP = 0. This
is a point of reference which provides a predictive estimation of sorption
or release of P should the P concentration in solution change. Furthermore,
the average slope of the sorption curve over a given final P concentration
range provides information on the ability of the soil to maintain the P

concentration at the equilibrium P concentration. The steeper the slope,
the closer will the final P concentration be to the equilibrium P concentration. The slope of the curve, although not related to total P sorbed, is
related to the extent to which that soil may sorb P over the concentration
range considered. The potential of this approach in predicting the chemical
mobility of P in soil-water systems is clearly evident and has been used
with regard to streams by Taylor and Kunishi (1971) and Ryden et al.
(1972a,b) for rural and urban soils, respectively.
The desorption of sorbed P from soils is not as simple as may be inferred from the sorption-release relationships obtained by White and

+


PHOSPHORUS I N RUNOFF AND STREAMS

11

Beckett (1964). In fact very few studies have been reported regarding
the desorption of sorbed P, and those reported by Syers et al. (1970)
and Ryden et al. (1972a), involved desorption following sorption of P
from solutions containing P concentrations in excess of those commonly
found in soil-water ecosystems.
In studies involving the sorption of P by kaolinite from solutions containing realistic inorganic P concentrations, Kafkafi et al. (1967) observed
that initially all the sorbed P was isotopically exchangeable. During a subsequent washing or desorption step, however, a portion of the sorbed P
became nonexchangeable, or “fixed,” this portion being dependent upon
the amount of P sorbed, the number of washings, and the nature of the
previous P sorption cycle. Sorption of P was represented by either onestep sorption from a range of solutions of different initial P concentration
or by successive additions of small amounts of dissolved inorganic P. Both
these types of P sorption, as well as an effect analogous to washing, could
occur in soil-water ecosystems.
6. Organic P . Although the mechanisms involved in the retention of

organic P by soils have not been established fully, there is evidence that
inositol hexaphosphate, and possibly other organic P compounds, are retained by a precipitation rather than a sorption reaction. Nevertheless, removal of dissolved organic P from solution appears to be a rapid process.
Pinck et al. (1941 ) reported that many commonly occurring water-soluble
organic phosphates, e.g., salts of glycerophosphate, hexose diphosphate,
and nucleic acids, become nonextractable with water at almost the same
rate and as completely as dissolved inorganic P.
The retention of water-soluble organic P by sorption reactions may
occur by at least two basically different mechanisms (Sommers et al.,
1972). Goring and Bartholomew (1950) observed that removal of “free
iron oxides” considerably reduced the amount of fructose 1,6-diphosphate
sorbed by subsoil material, suggesting that the sorption of organic P may
occur through orthophosphate groups by a similar mechanism to that for
inorganic P. It is also possible that organic P can be retained by interaction
of the organic moiety of the phosphate ester with inorganic soil components. For example, nucleic acids and nucleotides are protonated at pH
5 (Jordan, 1955) and could consequently be retained on clay surfaces
by displacement of exchangeable cations. Furthermore, physical adsorption, also through the organic portion of the molecule, is possible, particularly if the molecular weight of the compound is high, as suggested by
Greenland (1965). In such cases retention is weak and is accomplished
by van der Waals and ion-dipole forces. Greaves and Wilson (1969) have
implicated physical adsorption in the retention of nucleic acids by montmorillonite. It is also possible that retention occurs indirectly through other


12

J. C . RYDEN, J. K. SYERS, AND R. F. HARRIS

soil organic compounds such as fulvic and humic acids after interaction
of organic phosphates with these species (Martin, 1964).
The desorption of sorbed organic P has not been extensively studied.
The hypothesis that inorganic P added to soils displaces sorbed organic
P to solution (Latterell et al., 1971) was not supported by the data presented by Wier and Black (1968). Although organic P may be leached

from soils, it appears that a large proportion of that removed may not
be in a dissolved form. After incubating sucrose with ammonium nitrate
in the upper portion of a calcareous soil, Hanapel et al. (1964) found
that most of the organic P removed by leaching was present in a particulate
rather than a dissolved form.
3. Chemical Aspects of P in Subsurface and Groundwater Runoig
Losses of P in subsurface and groundwater runoff have been considered
minimal in the past, but, as will be discussed later, such losses can amount
to a significant proportion of losses from agricultural land, and possibly
a major proportion from forest lands. The supposition that P losses in subsurface and groundwater runoff are low probably stems from the concept
of P immobility based on the P sorption properties of soils using added
inorganic P concentrations far in excess of those normally present in the
soil solution.
It is of interest to note that many of the reported mean concentrations
of dissolved inorganic P in subsurface runoff are within the range of values
expected to be maintained in the soil solution. Pierre and Parker (1927)
reported values ranging from 0.020 to 0.350 pg P/ml, with an average
of 0.090 pg/ml, for several surface soils from the southern and midwestern
states of the United States. These workers also noted that dissolved inorganic P concentrations could be maintained at a fairly constant level. Barber et al. (1963) reported similar values for the upper 15 cm of 87 soils
from the midwestern United States, with an average of 0.180 pg of P per
milliliter; the frequency distribution of the values obtained, however, suggested a mode of between 0.040 and 0.060 pg of P per milliliter.
As water percolates through the soil profile, there tends to be a “chemical sieving” of dissolved inorganic P (Black, 1970). This arises as a result
of the sorption of inorganic P by soil components. The low concentrations
of P found in groundwater runoff, which has experienced the maximum
effects of deep percolation with concomitant increase of contact with
P-deficient particulates of the subsoil, are undoubtedly a direct result of
the chemical sieving effect. The principle of this effect is illustrated by
other data presented by Barber et al. (1963). For the same 87 soils mentioned previously, the average dissolved inorganic P concentration at a
depth of 46-61 cm was 0.089 pg/ml, less than half that for the upper