NORTH CENTRAL REGIONAL PUBLICATION NO. 1
of the Agricultural Extension Services
I SPECIAL REPORT NO. 15
Agricultural Extension Service-Iowa State College
Ames, Iowa-November, 1955
AGRICULTURAL EXTENSION SERVICES OF
Illinois Indiana Iowa Kansas Michigan Minnesota
Missouri Nebraska North Dakota Ohio South Dakota Wisconsin
Farm Foundation and United States Department of Agriculture, cooperating.
The basic framework for this report is the result of the group efforts
of the Subcommittee for the Study of the Diffusion of Farm Practices;
an adjunct of the North Central Rural Sociology Committee which is
sponsored by the Farm Foundation, Chicago, Ill.
The original draft was integrated by George M. Beal and Joe M.
Bohlen of Iowa State College as a flannel-graph presentation entitled
"The Diffusion Process."
Associate Director Marvin A. Anderson of the Iowa State College
Agricultural Extension Service made several valuable suggestions and
was instrumental in hastening the completion of this publication.
The report has been approved by the North Central Rural Sociology
Committee composed of:
C. L. FOLSE, UNIVERSITY OF ILLINOIS
WARD W. BAUDER, UNIVERSITY OF ILLINOIS
GEORGE M. BEAL, IOWA STATE COLLEGE
JOE M. BOHLEN, IOWA STATE COLLEGE
C. R. JACCARD, KANSAS STATE COLLEGE
RANDALL C. HILL, KANSAS STATE COLLEGE
F. D. FARRELL, KANSAS STATE COLLEGE
A. LEE COLEMAN, UNIVERSITY OF KENTUCKY
HOWARD W. BEERS, UNIVERSITY OF KENTUCKY
CHARLES P. LOOmIS, MICHIGAN STATE UNIVERSITY
GLENN TAGGART, MICHIGAN STATE UNIVERSITY
ROY G. FRANCIS, UNIVERSITY OF MINNESOTA
C. E. LIVELY, UNIVERSITY OF MISSOURI
DON KANEL, UNIVERSITY OF NEBRASKA
HAROLD CAPENER, OHIO STATE UNIVERSITY
WADE H. ANDREWS, OHIO STATE UNIVERSITY
J. E. LOSEY, PURDUE UNIVERSITY
HOWARD SAUER. SOUTH DAKOTA STATE COLLEGE
ROBERT M. DIMIT, SOUTH DAKOTA STATE COLLEGE
A. F. WILEDEN. UNIVERSITY OF WISCONSIN
WILLIAM H. SEWELL, UNIVERSITY OF WISCONSIN
Consultants from the U. S. Department of Agriculture are:
MARGARET JARMAN HAGOOD
E. J. NEIDERFRANK
Advisers to the committee representing the land-grant colleges in
the North Central Region are:
MARVIN A. ANDERSON, IOWA STATE COLLEGE
A. M. EBERLE, SOUTH DAKOTA STATE COLLEGE
L. L. RUMMELL, OHIO STATE UNIVERSITY
The subcommittee accepts full responsibility for this report.
Subcommittee for the Study of Diffusion of Farm Practices
A. LEE COLEMAN, UNIVERSITY OF KENTUCKY
ROBERT M. DIMIT, SOUTH DAKOTA STATE COLLEGE
HERBERT F. LIONBERGER, UNIVERSITY OF MISSOURI
PAUL A. MILLER, MICHIGAN STATE UNIVERSITY
EUGENE A. WILKENING, UNIVERSITY OF WISCONSIN
JQE M. BOHLEN, Chairman, IOWA STATE COLLEGE
How Farm People Accept New Ideas
Some farmers will try any new idea that
comes along, while others will accept an idea
only after it is proven in their neighborhood.
A major concern of agricultural leaders is that
of narrowing the time gap between the early
and late adoptions of recommended practices.
Some new ideas and practices are accepted
quickly and with little apparent effort, while
others are accepted only after years of effort
on the part of agencies and leaders working
with rural people.
This lag between what is known and what
is done by most farmers has been the focus
of considerable research in recent years by rural
sociologists and others. Some aspects of the
problem have been more adequately studied
than others. Many of the studies are explora-
tory, resulting in only tentative findings. De-
spite the many gaps in our present knowledge,
there is a need for bringing together and in-
terpreting the results of the various studies
for use by agricultural leaders and agencies.
The major purpose of this publication is to
show the process by which ideas become ac-
cepted. This diffusion process will be dis-
cussed from three points of view:
1. The stages through which an individual goes
from the time he first learns of an idea until
he adopts it, and the media which are most
effective at these various stages.
2. Some situational and group influences af-
3. Some of the characteristics of farm people
as they relate to rate of adoption.
Stages in the Process of Acceptance
The acceptance of a new idea is a complex
process involving a sequence of thoughts and
actions. Usually decisions are made after
multiple contacts with various communication
channels. These contacts are made over a
period of time. For instance, the average time
span from awareness to adoption of hybrid seed
corn in Iowa was 7 years. Adoption of most
other hybrid seeds has come more rapidly.
Changes which involve new skills or techniques
usually require longer periods of time. How-
ever, once an idea has been introduced and the
process initiated in any given community, some
people can be found at all stages in the process
of acceptance. This process may be broken
down into five stages as follows:
1. AWARENESS: At this stage the individual
learns of the existence of the idea or prac-
tice but has little knowledge about it.
2. INTEREST: At this stage the individual
develops interest in the idea. He seeks more
3. 4. 5.
information about it and considers its general
3. EVALUATION: At this stage the individual
makes mental application of the idea and
weighs its merits for his own situation. He
obtains more information about the idea and
decides whether or not to try it.
4. TRIAL: At this stage the individual actu-
ally applies the idea or practice-usually on
a small scale. He is interested in how to
apply the practice; in amounts, time and con-
ditions for application.
5. ADOPTION: This is the stage of acceptance
leading to continued use.
An integral part of the acceptance process
is the communication of information at these
various stages. Information is communicated
through various channels which may be gener-
ally classified as follows:
1. Mass communications media (newspapers,
magazines, radio, TV and circular letters)
2. Neighbors and friends
3. Salesmen and commercial dealers
4. Direct contacts with agricultural agencies
(professional workers in Extension, Soil
Conservation Service, Agricultural Conser-
vation Program and Vocational Agriculture)
THE DIFFUSION PROCESS
In the Awareness Stage
At this stage the individual knows little about
the new idea beyond the fact that it exists.
More people become aware of new ideas from
mass communications media than from other
sources. This is supported by studies in differ-
ent parts of the country. Some studies, such as
that of hybrid corn in Iowa, indicate that sales-
men are important in creating awareness of new
ideas which involve the use of a commercial
product. Neighbors and friends are important
creators of awareness of new ideas among the
lower socio-economic groups.
Some studies reveal that government agencies
such as the Extension Service and other agen-
cies are the second most important contact for
informing people of the existence of an idea.
It is at the AWARENESS stage that the
mass media devices have their greatest impact.
The evidence is that for the majority, mass
media become less important as sources of in-
formation after the individual has become aware
of the idea.
In the Interest Stage
At this stage, the individual obtains general
information about the idea. Mass media still
play an important role in providing this type
of information. They provide information
which is timely and readily available from a
wide range of sources. Many rely upon agri-
cultural agencies at this stage while others rely
upon neighbors and friends. Agencies can pro-
vide results of experiment station research.
\ Farmers with outside contacts are also im-
portant in stimulating interest in new ideas and
practices. The channels of communication which
can provide general information which rural
Aware# people will accept as valid are the most in-
Sfluential at this stage.
In the Evaluation Stage
In this stage the potential adopter evaluates
the new idea in terms of his own situation. He
weighs its economic aspects in terms of land,
labor, capital and net returns. He also ap-
praises it in relation to values other than eco-
nomic-i.e., his personal preference in enter-
prises and activities, family resources, family
goals and interests, and its effect upon his re-
lationships with his neighbors and friends.
The data available indicate that as people
are evaluating an idea for their own use. they
usually consult with neighbors _and friends
whose opinions they respect.
The earlier adopters tend to depend upon
agricultural agencies during this stage. Farm
people, in general, go to sources of information
which they consider to be dependable for in-
formation at this stage. This usually means
that the sources are ones with which the
farmer has personal contact, i.e. his neighbors
and friends. These sources have demonstrated
ability to consider new ideas in terms of the
local situation. The reasons for the apparent
lack of importance of mass media and sales-
men at this and later stages of the adoption
process are: (a) The information provided
through these channels is too general; (b) the
potential adopters mistrust some mass media
information because they feel that the infor-
mation is tempered by the business interests
of those who are in control of them.
In the Trial Stage
This is the stage where farm people preparing
Sto try out the new idea are primarily concerned
with getting information on how to do it and
When to do it. Where possible, the new idea
or technique is tried on a small scale, i.e., one
bushel of hybrid seed corn was planted the first
year; commercial fertilizers were used on small
plots, etc. At this stage agricultural agencies
become more important along with neighbors
and friends, who continue to be important
sources of information. Two-way information
is usually needed to obtain the detailed infor-
mation on how and when the new technique is
to be applied. Some techniques require technical
"know-how" which the average individual does
Salesmen are important providers of infor-
mation at this stage when a commercial prod-
uct is involved.
Mass media have been relatively unimportant
as information sources at this stage.
In the Adoption Stage
This is the stage at which the idea has been
completely accepted. The individual is satisfied
with its use under existing conditions. The
greatest single influence in continued use of
any idea is the individual's personal satisfac-
tion with early trials. Continued use also de-
pends upon the individual's success with the
practice under varying conditions.
There is some evidence to indicate that
adopters seek information to interpret results
in relation to their own situation. This is
most likely to be provided by neighbors and
friends and agricultural agencies.
An understanding of failures of new prac-
tices is as important as interpretation of suc-
cesses. For example, hybrid seed corn use
is sometimes discontinued because individuals
have used strains unadapted to their climate
and soil conditions and have had results that
Diffusion Process Varies With Types
There is a wide variation in the types of
changes in farming. They are of a qualitative
as well as a quantitative nature. An example
of a qualitative change would be a change
from non-use to the use of commercial ferti-
lizer. An example of a quantitative change
would be the variation in the amounts of ferti-
lizer applied. For some changes, however, the
distinction between a quantitative and a quali-
tative change is not always clear-i.e., a change
from low analysis to high analysis fertilizer.
The content of changes includes: (a) the
change in the amount of human effort required,
(b) the change in amount of capital or physical
materials required, (c) the change in manipu-
lative skills and (d) the change in management
ability required for maximum benefits from
the new idea. Taking these elements into
consideration, changes in farm practices may
be classified as follows:
1. Change in materials or equipment only, with-
out a change in techniques or operations (e.g.,
new variety of seed).
2. Change in existing operations with or with-
out a change in materials or equipment (e.g.,
change in rotation of crops).
3. Change involving new techniques or oper-
ations (e.g., contour cropping).
4. Change in total enterprise (e.g., from crop
to livestock farming).
Such a classification of changes is helpful in
determining the role of various communicating
agents in implementing change. For example,
the one-way communication of the mass media
may be sufficient to initiate a change in a seed
variety, while a combination of media including
two-way personal communication may be neces-
sary to implement a change from straight-row
to contour farming.
The relative advantage of the new as com-
pared with the old way of doing things is an-
other condition affecting its acceptance. In eco-
nomic terms this is the comparison of output
per unit of input-the relative efficiency of the
new items. The greater the efficiency of the
new technology in producing returns, not only
in the form of economic goods but also in other
forms of satisfaction, the greater its rate of
Another aspect of new practices affecting
their rate of acceptance is the relative ease
with which they can be demonstrated and com-
municated. For example, the ease with which
an advantage of hybrid corn over open-polli-
nated varieties can be demonstrated no doubt
has influenced its rapid acceptance. On the
other hand, the difficulty of demonstrating the
advantage of strip-cropping or new crop rota-
tions has made for slower acceptance of these
Some Personal and Social Character-
istics Related to Adoption
The adoption of farm practices is influenced
by social and psychological as well as economic
factors. Community standards and social re-
lationships provide the general framework
wherein the process of change occurs. Indi-
vidual differences help to explain variations in
adoption of practices within the community.
Group and Community Variations
In some groups and communities people place
a higher value upon material gains and money
Prestige. is a factor in the adoption
Ideas and techniques.
than they do in others. In some, changes in
farming are encouraged and expected. Prestige
is attached to the adoption of new ideas and
techniques. In others, more value is placed
upon tradition'and little freedom is allowed the
individual to deviate from the group's pattern
in adopting innovations.
If the adoption of new practices goes con-
trary to the established customs and traditions
of the people, the innovator may be ridiculed
or lose prestige.
The extent to which changes are adopted de-
pends upon the values and expectations of the
group and upon the extent to which the in-
dividual is expected to conform. Where there
is great emphasis on maintaining family tradi-
tions and values rooted in the past, change
occurs more slowly. On the other hand, where
emphasis is upon individualism and personal
success, change occurs more rapidly.
The acceptance of change is also influenced
by the nature of leadership and control in the
group or community. In one community, none
would agree to go along with a program to
eradicate brucellosis in dairy herds until one
man in the community was sold on the idea.
Once sold, he influenced all farmers in the com-
munity to go along with it. In this situation,
change was brought about by working through
the leader of the group. In most communities,
no single leader has such influence. Whenever
there are leaders that the people look to, it is
important to identify and use them. The in-
fluence of informal leaders is likely to be
greater where neighbor, community and kin-
ship ties are the strongest.
The extent and nature of social contact with-
in the community is important in the diffusion
of- new ideas and techniques. The presence of
organizations whose objectives include the pro-
Ideas through bulletins, farm magazines and
motion of changes will aid directly and in-
directly in the diffusion process. On the other
hand, where social contacts are primarily
through kinship, visiting and other informal
activities, there may be greater resistance to
change. The introduction of change may dis-
rupt these relationships. For example, the use
of modern machinery makes the work-exchange
group less essential. Hence, the nature of the
social contacts in a community is an important
factor in the process of change.
The degree to which social contacts are con-
fined to the immediate locality is a factor. The
broader one's social orientation, the more likely
he is to accept new ideas. Only a few indi-
viduals may have such outside contacts, but they
may be in a position to influence their neighbors.
Local orientation on the part of the majority is
not necessarily a limiting factor in the diffusion
of new ideas so long as a few leaders have out-
Neighborhoods and clique groups facilitate ex-
change of farm information among their mem-
bers. There is evidence that social cliques
serve as barriers to the spread of information
outside themselves. Members of neighborhoods
and cliques rely more upon other members for
information and advice in the adoption of farm
practices than they do upon outsiders. This
is due to the high degree of identification that
prevails among intimate associates.
If information is from persons who are al-
ready well informed on the new practices,
changes will take place more rapidly than if
information is sought from friends regardless
of how well informed they may be.
The social distances associated with wide
status differences are also a factor in the dif-
fusion of farm information through inter-
personal channels. For example, tenant farmers
in some areas of the country do not get ideas
from the large farm owners because of their
lack of contact. Also small-scale farmers may
fail to communicate with large-scale farmers.
Rigid class structure impairs interclass com-
munication of ideas.
Individual and Family Variations
Decision making is influenced by the aspir-
ations and capabilities of farm families. In-
dividual member and family aspirations are re-
flected in their goals, values and means of
achievement. Their capabilities include general
farm knowledge and managerial skills of the
operator and his family. These are related to
such things as age, formal education, socio-
economic status and social contacts.
SThe more education an individual has, the
pore likely he ia to adopt new farm practices.
Chose with high school training, and above,
tend to adopt new practices earlier than those
who have had less formal schooling.
/ Young operators tend to be more aware of
and more favorable toward new ideas and
practices, but-are not always in a position to
Sput their ideas into operation. This may be
due to lack of available capital or land or lack
of freedom to make decisions.
Participation in general farm organizations
and farmer cooperatives is associated with early
adoption of new farm practices. Favorable
attitudes of farm families toward extension
/ and other educational agencies is positively re-
lated to acceptance of farm practices.
Farmers who have children (in 4-H clubs ..
vocational agriculture tend to adopt more ap-
proved practices than others. Participation in
the .adult extension programs is positively re-
lated to adoption of practices. Likewise, the-
number of contacts which individuals have with
new ideas through bulletins, farm magazines J/
and newspapers is positively related to early"
adoption of practices.
Individual and family goals and values af-
fect the decisions to adopt or reject new farm
practices by providing motivation for individual
and family action. For example, the high value
placed on, security, as reflected in owning land
debt-free and being reluctant to use borrowed
capital, is negatively related to adoption of new
practices. People who rate this value highly
prefer to use money for paying off debt on their
farms. Also new practices involve risks which
people who place a high value on security are
reluctant to take.
High values upon individual achievements
and satisfactions are positively associated with
adoption of new ideas and practices. These
achievements and satisfactions include formal
education for family members, modern living
conveniences and family recreation.
Attitudes pertaining to the participation of
family members in decision making and in the
operation of the farm are associated with ac- j
ceptance of changes in farming. For example,
farmers who have sons over 12 years of age
who encourage the adoption of new practices
are among the earlier adopters. Those farm
families having equitable arrangements for
Community Adoption Leader
sharing farm income and ownership between\
father and sons tend to be earlier adopters a
than families in which the father retains control u
of the farm. i
Sequence of Influences in the Adoption t
of Practices a
From the time a new idea is formed until it c
is generally accepted, multiple influences are at o
work. These include the various means of com- o
municating ideas which have been discussed a
earlier in this report. P
The relative importance of these means varies o
with stages in the process of acceptance dis-
cussed above. Also earlier and later adopters
rely upon different channels of communication
particularly at the evaluation and trial stages.
As shown on page 10, people may be classified b
into categories according to the sequence in
which they adopt new practices: innovators,
community adoption leaders, local adoption
leaders, later adopters and nonadopters.
Innovators are the first to adopt new ideas. p
They are independent in their thinking and s
have a wider range of contacts. They are t
known as "experimenters" and "people who are a
always trying out new things." They are le
seldom named as persons to go to for advice on o:
farming. They are not necessarily adoption g
leaders in their neighborhoods and communities. o
Such persons may not be present in every com- p
Community adoption leaders are not the very 1e
first to try new ideas, but are among the first r
o use approved practices in their community
areas. They are not the persons who test the
tried ideas but they are quickest to use tried
ideas in their own situation.
The community adoption leaders are usually
he larger and more commercial farmers in their
reas. They have direct contacts with agri-
ultural agencies and may be the leaders in farm
organizations. They tend to have a higher level
f education and read more bulletins, magazines
nd newspapers than do the average. They
participate more than the majority in formal
organizations and have wider social contacts.
Local adoption leaders. These are the people
o whom the majority look for information
nd ideas in their farming operations. They
re not necessarily innovators or early adopters.
ut they do adopt ideas sooner than the majority
rho look to them for information. They have
formation contacts with agricultural agencies
nd other farmers outside their immediate lo-
alities who have tried the ideas. In their
personal and social characteristics they are
similar to the majority, but they are expected
o take the initiative within their groups. They
re sometimes called informal leaders. Their
!adership position is maintained on the basis
f being "sound" and showing ability to use
ood judgment. One remains an informal leader
nly so long as he is considered by others to
ossess these attributes.
These local adoption leaders or informal
waders are important links in the chain of com-
lunication. Studies show that these informal
Local Adoption Leader
leaders are identified by the majority of farm
people as neighbors and friends rather than as
"leaders," because that's what they are to these
people. They are not thought of as leaders by
their associates. Their leadership is not estab-
lished by election-it's established by actions
which have won the respect of their associates.
These informal leaders are not necessarily the
open seekers of offices in formal organizations.
They are not necessarily the volunteer leaders
who recommend themselves to the county agent
or the vocational agriculture teacher for serv-
ice. Their leadership is oriented toward their
following rather than toward those whom they
may consider to be "leaders."
Later adopters are the majority of the people
in the community who adopt new ideas. This
group depends primarily on the local adoption
leaders for information and ideas, although
some have contacts with agricultural agencies
and become aware of ideas through mass media.
The later adopters have less education, partici-
pate less in community affairs and are older
ththan those who adot ideas earlier. There are
some to whom a practice might apply who never
adopt it. They have even less education and
social contacts than the later adopters.
In any community, there are always some to
whom the practice does not apply and for
whom these generalizations do not hold true.
CHART 1. SEQUENCE OF INFLUENCES IN THE ADOPTION OF PRACTICES WITHIN A GIVEN AREA
Wide range of
a. College and
b. Farm papers
b. Other sources.
c. Mass media
*-~~~~~~~~~ -;-.-;---- ?-
* : *
SUMMARY AND APPLICATION
People go through several stages in learning
about and in adopting new ideas. These stages
may be classified as: awareness, interest, evalu-
ation, trial and adoption. Mass media make
their greatest impact in the awareness and in
the interest stages. Neighbors and friends are
most important as sources of information in the
evaluation stage. In the trial stage agricul-
tural agencies and neighbors and friends are
important. Dealers and salesmen are important
as sources of information in this stage when
commercial products are involved. There are
also variations in the types of communication
used according to the nature of the change.
Variations in rates are influenced by indi-
vidual, group and community factors. These
i. .:;.i j~* .:...:J~:~EL~~!L~;11jsE~i~FRa~bJt'. ~'I
condition the decisions of farm operators in
considering new ideas and practices.
The adoption of a new idea follows a sequence
of influences from the time an idea is formed
until it becomes generally accepted. In this
diffusion process people may be classified into
types based upon the sequence in which they
accept new ideas and practices as follows: in-
novators, community adoption leaders, local
adoption leaders and later adopters.
One of the functions of leaders among farm
people is to diffuse new ideas and practices. It
is their task to expedite the process of getting
ideas from their sources of origin to those who
can use them.
To be effective in this process one must know
what techniques to use at the different stages
and how to mobilize them effectively.
He must also know in which stages in the
diffusion process the people are. For example,
it would be a waste of energy to devote edu-
cational efforts to instruct people how to do
something-information pertinent to the trial
stage-when the majority of them are at the
stage of needing data about what the idea is-
i.e., at the interest stage.
In order to be most effective, an agricultural
leader must know how to use all of the com-
munications channels available to him. For
example, the informal leaders have contacts
and influence with people which no other
channels can provide. The most effective use
of the informal leader requires that one work
with him on an informal basis. Giving the in-
formal leader public recognition may jeopardize
his position of leadership and thereby the in-
fluence which makes him an important resource
in extension and other programs.
In order to be effective as an educational
worker one must understand:
a. The nature of the acceptance process.
b. The values and aspirations of the people with
whom he must work.
c. The formal and informal group relationships
within his area.
d. The availability and most appropriate use of
e. The sequence and interrelationships of in-
fluences in acceptance of new ideas.
In addition to knowing how to use the various
channels of communication in bringing about
adoption of practices, educators must be sensi-
tive to the customs, values and aspirations of
the people with whom they work. Changes are
accepted when they support these values and
aspirations. Hence it is important to show how
and to what extent they do so. For those most
concerned with the security obtained by own-
ing their farms free of debt, one can show
how the adoption of improved practices will
contribute toward this end. For those placing
a high value upon material conveniences, one
can show how the adoption of improved methods
of farming will help obtain these conveniences.
Finally, the person attempting to speed up the
process of acceptance of new ideas and practices
must be aware of the total process and the se-
quence of influences at different points in this
process. It is necessary to intermesh the im-
personal with the personal and the technical
with the nontechnical. In this sense the in-
fluencing of change is an art which requires
sensitivity to the many phases of the accept-
ance process; it also requires the ability to
make most effective use of the various means
of influencing acceptance.
A representative sample of literature in this field follows:
Lionberger, Herbert F., "The Diffusion of Farm and Home Information as
an Area of Sociological Research," Rural Sociology, Vol. 17, No. 2, June
1952, pp. 132-144.
Lionberger, Herbert F., Sources and Use of Farm and Home Information by
Low-Income Farmers in Missouri, University of Missouri Agricultural
Experiment Station, Research Bulletin 472, April 1951.
March, C. Paul, and A. Lee Coleman, "The Relation of Kinship, Exchanging
Work, and Visiting to the Adoption of Recommended Farm Practices,"
Rural Sociology, Vol. 19, September 1954.
March, C. Paul, and A. Lee Coleman, "Farmers' Practice-Adoption Rates in
Relation to Adoption Rates of 'Leaders'," Rural Sociology, Vol. 19, No. 2,
pp. 180-183, June 1954 (research note).
Ryan, Bryce, and Neal Gross, "The Diffusion of Hybrid Seed Corn in Two
Iowa Communities," Rural Sociology, 8:15-24, March 1943.
Wilkening, E. A., Acceptance of Improved Farm Practices in Three Coastal
Plain Counties, North Carolina Agricultural Experiment Station, Tech-
nical Bulletin 98, May 1952.
Wilkening, E. A., Adoption of Improved Farm Practices as Related to Fam-
ily Factors, University of Wisconsin Agricultural Experiment Station,
Research Bulletin 183, December 1953.
A bibliography containing over 110 references to work in this field is
Dr. Joe M. Bohlen
203 Ag. Annex
Iowa State College
Cooperative Extension Work in Agriculture and Home Economics, Iowa State College of Agriculture and Mechanic Arts
and the United States Department of Agriculture cooperating. Extension Service, Floyd Andre, director, Ames, Iowa. Dis-
tributed in furtherance of the Acts of Congress of May 8 and June 30, 1914.