A Half Century of Agricultural Meteorology

William E. Reifsnyder, Yale University, New Haven, Connecticut, USA

Zusammenfassung

Abstract
Developments in agricultural meteorology, especially in North America, in the past half century are reviewed. The explosion of interest in meteorology following the Second World War produced considerable scientific activity in the file of agricultural meteorology. Work by Thornthwaite, Penman, Budyko and others stimulated research on crop evapotranspiration. Earlier work by I. S. Bowen on the ratio of the transfer of heat to the transfer of moisture through the boundary layer was rediscovered by micrometeorologists and applied to the measurement and analysis of energy fluxes above crops. Frederick Brooks applied these and other concepts to problems of crop growth in California.
The sixties and seventies saw attempts to model heat flux and microclimate in plant stands on physical/mathematical basis. These works stemmed largely from Raschke’s earlier work on the energy balance of single leaves. Current research on the effects of free-air carbon dioxide enrichment of the atmosphere on growth and carbon relations in various vegetative complexes has shown that although relationships are not simple, many of the crops studied have shown increased growth and water-use efficiency.
The interest and activities of the Commission for Agricultural Meteorology of the World Meteorological Organization have had major effect on the application of agrometeorology to agricultural production and protection throughout the world. The post-war period also saw the establishment of a journal specifically oriented to agricultural meteorology—Agricultural Meteorology, now Agricultural and Forest Meteorology. The twenty-three conferences on agricultural and forest meteorology sponsored by the American Meteorological Society since WWII have had a profound effect on the development of the field.
1. Introduction
The roots of agricultural meteorology are lost in antiquity. Farmers planting grape vines on terraced slopes in northern European latitudes quickly found that south-facing vineyards succeeded where others failed. Much later, scientists showed that the more-direct sunshine on such slopes produced favorable temperature conditions for growth and maturity of the grapes.
Probably the first published record of a numerical relationship between a meteorological measurement and crop growth was that of René Réamur who developed a thermometer scale and subsequently studied the relationship between temperature and crop growth. In 1735, he published the results of his studies on what came to be known as Réamur’s thermal constant, now known as the “heat unit” (Réamur 1735). Progress came slowly and it was not until 1920 that J. W. Smith published the first text, entitled “Agricultural Meteorology.”
However, it was not until 1948 that several seminal papers appeared and at least one major event occurred. Perhaps we can thus date the emergence of scientific agricultural meteorology to that time, just a half-century ago.
It was at this time that I first became aware of the interaction between agriculture (in its broadest sense) and meteorology. Prior to the Second World War, I had studied forestry and biology. I studied meteorology at New York University as an aviation cadet and subsequently became involved in lightning detection technology. After the war, I and others retained our interest in meteorology, often ending up as teachers of one aspect or another of the atmospheric sciences. I could see the close connection between my earlier studies in forestry and what I had learned as a meteorologist; and determined that I would pursue a career combining the two fields. What follows in this short survey is my view of how the field of agricultural meteorology developed during the subsequent half-century. It is highly idiosyncratic and represents very much the trends and events that influenced me and which I, to some extent, helped develop. Others would emphasize a different set of scientific and practical developments. But this is the way I saw things.
Shortly after the end of World War II, academic and commercial activity in all phases of atmospheric science was stimulated by the flood of war-trained meteorologists, many of whom elected to stay in the field. (My own wartime class at New York University included David Atlas, Louis Battan, and Vaughn Havens.) Some of those who obtained basic meteorology during the war—whether as soldiers or civilians--decided to branch out into fields such as agricultural meteorology, not specifically a part of their wartime training. Others, perhaps stimulated by the wartime importance of weather forecasts for military operations, studied atmospheric science as civilians. This post-war cadre included Paul Waggoner, Vaughn Havens, Wayne Decker, Gerry Barger, Bob Shaw, Bob Dale, Norman Rosenberg, James Newman, and Champ Tanner, among others.
Many of the veterans went back to school, courtesy of the “GI Bill”, and obtained advanced degrees in some branch of agriculture and/or atmospheric science. And many of these went on to establish departments or programs in agricultural meteorology. Others taught specialized courses, frequently in agronomy departments, more rarely in meteorology departments. And many found their way into federally-supported agricultural experiment stations, mostly located at state universities.
A substantial number ended up at what was then Iowa State College. This group included Bob Shaw, Wayne Decker, Gerry Barger and Paul Waggoner, a veritable “Who’s Who” of post-war agricultural meteorologists (Fig. 1). (It would be an interesting exercise to develop an academic genealogy of agricultural meteorologists. I suspect that most of the current crop of agricultural meteorologists can trace their academic lineage to one or another of this group). Other departments that still have active programs include the Department of Agricultural Meteorology at the University of Nebraska-Lincoln; the Department of Atmospheric Science at the University of Missouri; the Department of Meteorology and Oceanography at Rutgers University; the Department of Soil Science at the University of Wisconsin--Madison; and the Department of Land Resource Science at Guelph University.

2. Seminal events in the past half century
Science proceeds in an unsteady manner. Certain seminal developments spur a burst of activity. Scientists utilize these developments to push the science (and practice) forward at a relatively steady pace until another seminal event takes place. This is not a purely linear process: there are often several tracks occupied at the same time, with much cross-fertilization. I have identified a half-dozen or so of these events which seem to me to be crucial in pushing the field forward. They are ones that have been especially important to me in my career; others may have a slightly different list. It is selective and I apologize to those who may feel slighted by my selection

2.1 The Immediate Post-War Period
C. W. Thornthwaite, a physical geographer, had long been interested in the relationships between climate and agriculture. He had apparently been impressed with an article by John Leighly rather blandly entitled, “A note on evaporation” (Leighly 1937) in which Leighly analyzed the ecological significance of evaporation. In 1948, Thornthwaite published the paper that defined potential evapotranspiration, a seminal concept that guided much of the research in agricultural meteorology for several decades, indeed up to the present time. He supposed that evaporation from an area fully covered by plants was dependent only on meteorological conditions and not on soil types or albedo, so long as the soil was well-watered. The important meteorological conditions were those related to the source of energy for evaporation; he used day length and mean air temperature as surrogates for the more fundamental but generally not measured net radiation.
The invention of the aspirated flat-plate radiometer in 1949 (Gier and Dunkle, 1951; later manufactured by Beckman & Whitley, Inc.) which measured the net all-wave hemispherical radiation balance, led to an explosion of interest and research in the physical significance of the radiation balance for the evapotranspiration of field crops.
The same year that Thornthwaite published his article on potential evapotranspiration, Howard Penman, a physicist working at Rothamsted in England, published his influential paper, “Natural evaporation from open water, bare soil and grass” (Penman 1948). Penman recognized the importance of the vapor pressure gradient between the evaporating surface and the air above it; and included this factor as an explicit function of wind, temperature and moisture content of the air in addition to net radiation. It is impossible to overestimate the influence of this paper. The approach is still used today in the so-called “big leaf” approximation, as elaborated primarily by John Monteith (Monteith 1972, p. 197) who worked with and ultimately succeeded Penman at Rothamsted. Monteith’s main contribution was the inclusion of various resistances to vapor movement from the cell space to the free air above a vegetative canopy. Indeed, this methodology is universally referred to as the “Penman-Monteith method.”
At the same time that Thornthwaite and Penman published their papers, M. I. Budyko came out with a paper summarizing his work in Russia (Budyko 1948, as quoted in Thornthwaite 1965). Although his interest was primarily in global heat balance, his approach bears much similarity to those of Penman and Thornthwaite. His equations include explicit formulations for wind speed, net radiation and vapor pressure gradient. All of these methods treat conditions as essentially one-dimensional: heat transfer at a horizontally-uniform surface.
An earlier development that went unrecognized for many years was the so-called Bowen ratio. This was originally proposed by Schmidt (1915) as the ratio of heat transfer by conduction through the laminar boundary layer to that by evaporation and diffusion through the same layer. Ira S. Bowen (an astrophysicist!) elaborated the relationships in his doctoral dissertation at the California Institute of Technology (Bowen 1926a, 1926b)1. Perhaps because most of the subsequent application of this ratio was to the problem of evaporation from the oceans, it did not appear in the literature of agricultural meteorology until after the war. I believe that the first such use was by Heinz Lettau, although I cannot locate the appropriate reference. I believe that it was Lettau who pointed out that the Bowen ratio could be applied to the diffusion of moisture and heat in the turbulent air layers near the earth’s surface. At any rate, much early work in agricultural meteorology was devoted to ascertaining by theory and measurement the appropriate values of the Bowen ratio.
Most of this post-war work was by meteorologists and physical geographers and dealt primarily with evaporation and energy balance. But for practical agriculture, a missing link was specific information on what plants required from their atmospheric milieu. An important effort to provide this was started by Fritz Went at the California Institute of Technology in 1949. In that year he started building his “phytotron,” a series of growth chambers and greenhouses in which he could control light, temperature and moisture (Went, 1950, 1957). He could program these rooms to mimic to a considerable degree the diurnal cycles of weather to which a plant growing in the natural environment would be exposed. His success with these growth chambers led to a proliferation of similar installations until now just about every botany department and agricultural experiment station has a group of chambers with increasingly sophisticated environmental controls.
On the application side, Frederick Brooks, an agricultural engineer at the University of California, Davis, produced a manual that combined theoretical considerations of energy balance with practical applications that could be used by farmers and horticulturists. He brought to this task the practical bent of an engineer; and his book (which he characterized in the preface as an “unfinished treatise”) had great influence on those who were fortunate enough to obtain a copy (Brooks, 1957). Unfortunately, it was published locally and did not receive the distribution that it deserved. 2

2.2 The Decades of Sixties and Seventies
As in any applied science, the development of agricultural meteorology has followed along two intersecting paths. One group of scientists has been primarily interested in basic science: how do things work? The other group has been interested in how this knowledge can be applied to the problems of growing plants and husbanding animals. It is my impression that in the past half-century, most of the reported research has been in the science rather than in the application. But this may hide the importance of application to the farmer and horticulturist: the work of agricultural extension personnel rarely gets reported in print. Clearly, the recent trend has been toward the science.
The concept of the energy budget of the earth’s surface and of the plants, animals and humans inhabiting that surface has been around a long time. Geiger (1965, p. 234) quotes Albrecht’s analysis of measurements of the heat budget in Potsdam made in 1903. Only a few other measurements of surface energy balance were published in the pre-WWII period (Geiger, op cit., Table 59).
Raschke’s (1956a, 1956b) studies of the heat balance of individual leaves laid the groundwork for many later studies of the energy balance of leaves and canopies. Paul Waggoner, building on this work and that of J. R. Philip (1964), hypothesized that it should be possible to reconstruct temperature and moisture profiles in a plant canopy given upper and lower boundary conditions and within-canopy parameters such as the vertical distribution of vegetation. He used an electrical analogy, dividing the canopy into layers to facilitate computation (Waggoner and Reifsnyder, 1968). George Furnival, a statistician at Yale, simplified the algebraic solution and made calculation easy using the computers available at the time (Furnival, Waggoner and Reifsnyder, 1975).
Monteith, utilizing theory and observations from plant, animal and human environmental research, developed a unified engineering approach to energy budgets in the natural world (Monteith, 1973). His book, and a subsequent revision (Monteith and Unsworth 1990) are the appropriate starting points for anyone interested in the physics underlying energy transfer in the biological world. David Gates (1980) used these same principles to develop a biophysical approach to ecological problems.
The U. S. National Science Foundation sponsored the translation and publication of several East European textbooks in the early sixties. These translations brought to the attention of western agrometeorologists the extensive Russian and Polish literature. The first of these, Agrometeorology, by G. Z. Ventskevich, was a translation of the 1958 edition of a book first published in 1952 (Ventskevich, 1958). Although it presented a brief summary of the fundamentals of microclimatology, it was primarily oriented toward practical problems of agriculture. It relied exclusively on Russian research. A subsequent text, Agricultural meteorology, by V. I. Ventskevich (1960), was devoted mostly to the micrometeorology, although it included a few applications to practical agrometeorology. Curiously, the text contains very few references to the agricultural meteorology literature.
A third product of the National Science Foundation effort was the publication of the translation of a Polish text, Agricultural meteorology, outline of agrometeorological problems (Molga, 1958). It relied heavily on Russian, Polish and German research. Much of the basic microclimate was adapted from Rudolf Geiger’s works in Germany. Taken together, these three books give the reader an excellent overview of the state of agricultural meteorology in Europe in the decade after World War II.
The first—and still only—comprehensive text in English was prepared by Jen-Yu Wang at the University of Wisconsin (Wang, 1963). Nearly half of the book covers basic micrometeorology and microclimatology; the remainder is devoted to agricultural applications. It is a monumental work that quotes more than one thousand authors. It is a basic work that anyone wishing to gain an understanding of the flavor of agricultural meteorology in the early sixties will find indispensable.
Airborne transport of plant pathogens had long been implicated in the long-range spread of diseases of agricultural crops. Plant pathologists speculated that such disease spread was possible, even common, but most of the evidence for such transport was anecdotal. Field-to-field inoculation is relatively easy to demonstrate, but the question remained as to whether a disease inoculum could be transported many miles and remain viable enough to infect an agricultural crop.
During the war, meteorologists had begun to apply turbulent diffusion theory to the problem of evaluating the dispersion of poison gas. An important corollary study was the backward analysis of the trajectories of balloon-borne incendiary devices found along the Pacific coast early in World War II. Where were the balloons launched? The analysis indicated that the balloons almost certainly originated in Japan and not from submarines off the Pacific coast (Jacobs, 1947).
To my knowledge, the first attempt to quantify and integrate these meteorological concepts with the problem of disease spread was made by Waggoner and Horsfall in the development of a computer simulation of the short-range spread and subsequent development of early blight of potato (Waggoner and Horsfall, 1957). They isolated each step of the process from the development of the sporangia to the release of the spores, their transport and dilution by the wind to the settling on the target host and their subsequent germination. Each step of the process was quantified and expressed in processes that could be simulated in the computers available at the time. It was an important step. Subsequently, Don Aylor, also working at the Connecticut Agricultural Experiment Station in New Haven, quantified the role of long-range transport of disease spores. In an important essay, he built a framework for analyzing the entire process from the growth and release of the spores from their source, to their transport, their turbulent diffusion, their survival en route and the deposition to a distant canopy at a time and in sufficient quantity to produce clinical disease (Aylor, 1986). It was real biometeorology, for each step in the process involves complex interactions of biology and meteorology.

2.3 Recent developments
As indicated above, much of our knowledge of how plants respond to environmental conditions has been the result of experiments conducted in growth chambers. But there are obvious limitations to growing plants indoors. In the first place, a suitable light environment is difficult if not impossible to obtain in a chamber environment: intensity, spectral quality, simulation of the diurnal cycle are only a few. And the control of ventilation and carbon dioxide and water vapor exchange add to the difficulties. So experimenters went outdoors, built open-top chambers framed in transparent plastic in which natural sunlight would provide the driving source; other experimental parameters such as moisture supply, carbon dioxide, even rainfall, could be more-or-less controlled. But the plastic walls disrupted natural ventilation and prevented realistic gas exchange and leaf temperature.
More recently, scientists in various parts of the world—stimulated by pioneering work by the U. S. Department of Energy—have developed so-called free-air carbon dioxide exchange (FACE) experiments in which plants are grown in agricultural fields in unconfined plots subjected to elevated carbon dioxide concentrations introduced through a piping system (Hendrey, 1993; Dugas and Pinter, 1994). This work was initiated largely in response to concerns over the direct effects of increasing atmospheric carbon dioxide concentrations in the atmosphere from anthropogenic sources. The first proposal for such a free-air experiment was put forth by L. H. Allen, Jr., in 1979 (Allen, 1979). Subsequent discussions between Allen and a number of scientists (including H. Z. Enoch, D. N. Baker, S. B. Idso and myself, among others) led to a feasibility study funded by the U. S. Department of Energy (Allen and Beladi, 1990). The techniques developed have been so successful that researchers in many parts of the world have applied them to their local conditions. There is even a current program for monitoring the response of a mature loblolly pine plantation (Hendrey et al, 1998). Although the relationships vary with the specific plant and the level of CO2, most of the studied crops have shown increased growth and increased water use efficiency (Hendrey, op. cit.)
The characterization of air flow within plant canopies has puzzled scientists for many years. The classic explanation was that air near the ground was dragged along by the air flow above, following a logarithmic law, approaching zero as the ground surface is approached. With a dense plant canopy, the apparent surface is displaced upward, leading to the concept of a “zero plane displacement.” A further parameter, the roughness length, appears in the equation for windspeed as a function of height above a plant canopy (Monteith, op. cit. p. 88). Within the canopy, wind speeds tend to be low and somewhat irregular.
In a forest stand with a distinct crown region and relatively open trunk space, wind profiles show a pattern that has perplexed observers for many decades: measured wind speed appears to increase in the trunk region. The explanation given above, which assumes that the air at ever lower levels is dragged along by the air above it, clearly breaks down. Roger Shaw (1985) proposed a scheme for characterizing the complicated vertical exchanges of momentum that occur in an irregular canopy. His scheme accounts for the upward transfer of momentum, counter to the downward transfer implied by time-averaged gradients.
Air flow and energy exchanges at and near the surface of the earth have frequently been considered to be disconnected from “free-air” conditions at the top of the planetary boundary layer. The canopy model of Waggoner and Reifsnyder, referred to above, considers conditions at soil level and at the top of the canopy as boundary conditions. A major theoretical contribution to the connection was made by Jarvis and McNaughton (1986). Early models of the global climate tended to ignore vegetative processes at the erath’s surface. With the Jarvis-McNaughton model and many subsequent developments, climatic modelers are increasingly aware of the importance of such surface processes. It should be noted that the major driving force for the so-called enhanced greenhouse effect is the radiation balance at the earth’s surface. It is this that drives climate change, not that climate change (as modelled by GCMs) modifies the surface climate. This distinction seems frequently to be confused in the minds of many.

3. Activities of the American Meteorological Society
Most of the post-war group of agricultural meteorologists were associated with academic departments of meteorology or agronomy, or with government agencies. The first formal meeting of this group was organized in 1957 by Verner Suomi and Gerry Barger and was held in May of that year at the University of Wisconsin. It was billed as the “First Workshop on Agricultural Meteorology” and included a total of ten papers. This first conference on agricultural meteorology was sponsored by the Department of Meteorology at the University of Wisconsin, and the American Meteorological Society.
The roster of participants does indeed include the names of individuals who were instrumental in developing the field in those post-war years: in addition to Suomi and Barger, the list includes James Newman, A. G. Norman, Paul Miller, Robert Holmes and George Robertson of Canada, Russell Hamon, Ed Lemon, Bob Shaw, Joe Caprio, Champ Tanner, and Paul Waggoner and myself. Reflecting the interest in evapotranspiration stimulated by Thornthwaite, four of the papers plus a discussion session on measurement techniques were devoted to that subject.
Paul Waggoner, then a young plant pathologist recently hired by the Connecticut Agricultural Experiment Station, and I, a new assistant professor at the Yale School of Forestry, organized the second conference, held in New Haven in October 1958. Vaughn Havens, at Rutgers, was program chairman. Twenty-three papers were presented, including a session on forest meteorology. As I recall, we had about ninety registrants. Again, the main emphasis of the papers was on evapotranspiration, an emphasis that was to last for many years. Heinz Lettau was our banquet speaker. (It is interesting to note that a registration fee of two dollars was charged!)
At the time of the Second Conference, Gerry Barger, Assistant Director of the National Weather Records Center in Asheville, North Carolina, was also chairman of the AMS Committee on Agricultural Meteorology. From that time until his untimely death in 1980, Gerry was a visible and active advocate for agricultural meteorology. More than anyone else, Barger kept the field alive in those early days through his enthusiasm and persistence.
During a portion of his tenure as chairman of the AMS committee, I was privileged to be a member. I remember long discussions (arguments?) with Gerry over where forest meteorology fit into the scheme of our science. He adamantly maintained that forest meteorology was part of agricultural meteorology (just as the Forest Service is part of the U. S. Department of Agriculture) and so needed no special recognition. It was not until the early 1970s that “forest meteorology” was formally recognized as coeval with agricultural meteorology and the name of the AMS committee was changed to include it.
The most recent meeting, the 23rd Conference on Agricultural and Forest Meteorology, held in Albuquerque, New Mexico, in November 1998, was the largest ever, with 150 authors representing 18 countries. Some 300 registrants attended the conference which was held in conjunction with the 13th Conference on Biometeorology and Aerobiology and the 2d Urban Environment Symposium.



  1. The Role of the World Meteorological Organization.
The predecessor of the World Meteorological Organization (WMO), the non-governmental International Meteorological Organization (IMO), was formed in 1878 at Utrecht, The Netherlands (Blanc and Smith, 1964). This informal organization occupied itself with exchange of information and publications and devoted much of its efforts to obtain recognition for meteorological services by the members’ governments. The IMO Commission for Agricultural Meteorology, ninth in a series of technical commissions, was established in 1913. Although the work of the IMO was disrupted by the intervention of two world wars, it continued to grow. In 1950, after much bureaucratic maneuvering, IMO succeeded in having its plans for conversion to a United nations activity accepted; and in 1951 all of its functions were transferred to the newly formed World Meteorological Organization (WMO). The First Congress of WMO, held in Paris in 1951, created successor bodies to the IMO technical commissions, among which was the Commission for Agricultural Meteorology (CAgM).
In 1962, terms of reference for CAgM were revised and expanded by WMO. These terms of reference (quoted in full in Blanc and Smith, op. cit.) included keeping abreast of and promoting relevant scientific and practical developments; standardizing methods and procedures; formulating agricultural meteorology requirements; studying questions of the interaction of weather and the biological milieu; developing instrumentation; promoting biological observations; providing meteorological advice to agriculturists, in particular unfavorable influences, combating of pests and diseases, among other specific activities. The Commission accomplishes these goals largely through the activities of ad hoc working groups and consultants. Primary emphasis has been on the providing of useful technical information to member governments; however, much of the information finds its way into various technical publications of WMO, available to anyone for a price.

5. Agricultural and Forest Meteorology, an International Journal
The first goal of CAgM as listed in the 1962 terms of reference was to “…promote meteorological developments in relation to agricultural meteorology both in scientific and practical fields…” That same year, Elsevier Publishing Company in Amsterdam initiated a survey of agricultural meteorologists to assess the need for a specialized journal in their field. Eighty two percent of the individuals who responded expressed support for the proposal (Anonymous, 1964). Lionel Smith, then President of CAgM, and Milton Blanc, then at Arizona State University, enthusiastically pursued the idea. They assembled an informal group of “founding editors” that included C. C. Wallén, P. M. Austin Bourke, F. Schnelle and M. Gilead. At first, the journal—called Agricultural Meteorolog--was edited by a troika of regional editors (Wallén, Gilead and James E. Newman). They assembled an international editorial board that included scientists from every continent. The first issue appeared in March 1964.3 At various times during the next ten years, Tom Denmead and James Newman also served as regional editors.
Although this system worked reasonably well, Elsevier decided in 1974 that the journal should have an editor-in-chief; and Newman was so appointed. After his retirement as editor-in-chief in 1976, Tom Denmead, Lionel P. Smith and I took over as an editorial troika again. This arrangement lasted until 1985, when I was appointed editor-in-chief. More recently, Don Aylor and K. T. Paw U have served terms as editor-in-chief. At my urging, the name of the journal was changed to Agricultural and Forest Meteorology in 1984, the year before I took over as editor-in-chief.
For the 50th volume, published in 1991, I assembled a complete bibliography of the articles published in the journal (Reifsnyder, 1991). The entries total more than 1500, representing work by about the same number of authors. The pace of publishing has picked up since that time. In the nine years from 1991 to date, the number of pages is approximately two thirds of the total in the previous twenty-seven years, a three-fold increase.
A recent survey of the trends in atmospheric science journals—which included Agricultural and Forest Meteorology—sheds interesting light on the developing quality and quantity of scientific publishing in the period from 1965 to 1995 (Geerts 1999). Analysis of the publication record of AFM showed that in 1965, 20% of first authors were from the US, 20% from Europe and 17% from Africa, with other countries showing smaller percentages. By 1980, the US remained number one, with 27%, but Australia and New Zealand ranked second, with 20%; and the UK kept its 20%. By 1995, the ranking was: Europe (40%), UK (20%) and the US in third place with 17%. This decline in US contributions probably reflected the decline in US Federal R&D funding after 1988.
Throughout the period, the number of authors, number of pages per article and the number of figures per article also increased, doubling for authors, with smaller increases for the other categories. However, the total number of pages published in AFM remained nearly constant for the five-year period 1990-1994, at about 1500 pages per year.
The definition of “agricultural meteorology” has changed significantly during the past half century. By definition, it is an applied field with both “scientific” and “practical” components. Although mostly plant-oriented, it has always had a strong animal component. It is my impression that the trend has been away from the practical and away from the animal and very much toward theoretical plant science. A perhaps unrepresentative and brief survey of the literature bears this out. The first volume of Agricultural Meteorology had twenty-one articles, about half plant science, a quarter animal science and a quarter practical, with one article on forest meteorology. The most recent volume, published in 1999, had essentially the same number of articles; of which nearly three-quarters could be characterized as plant science, one-quarter forest meteorology, no animal science articles and only two that could be characterized as practical agrometeorology. Although characterizing articles as “scientific” or “practical” is somewhat arbitrary, the trends are clear. In the past decade, the journal has also published a substantial number of articles relating agricultural meteorology to global change, consistent with the tremendous increase in interest in this field.

  1. Textbooks and monographs.
To a considerable extent, the progress of a field can be measured by the number and quality of the textbooks it spawns. Agricultural meteorology has seen no dearth of such publications. Many of these have been discussed above. The closest thing to an up-to-date text is Norman Rosenberg’s Microclimate, the biological environment (Rosenberg, Blad and Verma, 1983). The Handbook of Agricultural Meteorology, a compilation of articles edited by John Griffiths (1994), contains a wealth of useful information, but like most handbooks, lacks the integration of a single-author text. A true text, one that does for agricultural meteorology what Snedecor’s Statistical methods applied to experiments in agriculture and biology (1938 and subsequent editions) did for agricultural statistics, is desperately needed. How many of us cut our statistical teeth on Snedecor’s pig gains?
Barger and his AMS committee were instrumental in the authoring and publication of an AMS monograph on agricultural meteorology (Waggoner et al, 1965). First proposed in 1960, its appearance in 1965 signalled the growing maturity of the field and the application of mathematical and physical principles to the problems of practical agricultural meteorology. The final chapter in the monograph was an analysis of the application of decision theory to the management of farms by James McQuigg (1965). McQuigg’s work on melding microeconomics and farm management had great influence on researchers and practitioners alike.



  1. Concluding remarks.
Whither agricultural meteorology in the next half-century? Decker (1994) in a recent review of the history of agricultural meteorology and a projection of needs for the next century took a rather pessimistic view. At present, there is only one university with a department of agricultural meteorology—the University of Nebraska. Perhaps because agricultural meteorology is generally taught in departments of atmospheric science (at least in American universities), most graduates in recent years have entered careers in basic research rather than applied agrometeorology. Hollinger (1994) points out that the retiring post-war group of agricultural meteorologists is not being replaced. Decker (op. cit.) attributes the declining interest in practical agricultural meteorology to two factors: first, farmers accept the weather as a given that must be accepted as a risk of production; and second, (in the US) responsibility for agriculture and meteorology is split between two federal agencies: agriculture in the Department of Agriculture, and meteorology in the National Weather Service. Thus there is no “lead” agency that understands and accepts the importance of the interdisciplinary field. Accordingly, in an era of shrinking budgets, such programs tend to be diminished or eliminated. (It might be said that a similar situation exists in our institutions of higher learning).
A more optimistic assessment is given by Changnon and Kunkel (1999). They state that “the use of climate data and information in agriculture, water resources, and other weather-sensitive sectors has grown dramatically in the past 20 years…” They attribute this increase is due to eight factors, most of which are related to the dramatic increase in the sophistication and availability of climatic information. Much of this increased use has resulted from the widespread availability of the personal computer and Internet accessibility, even (perhaps especially) at the farm level. They describe a successful program at the University of Wisconsin to develop and disseminate applications that “serve agricultural needs for real-time information …based on the use of satellite and conventional weather data, coupled with forecast models and climate data, to help schedule irrigation, to plan for plant disease treatments, and to employ frost protection.”
The Wisconsin Program, described in detail by Diak et al (1998), is based primarily on the ease of accessing the satellite and surface data that are required for routine use by agricultural applications. However, Diak et al lament that “slow adoption of new decision support tools within agriculture is a general area of concern.” One of the operational products—daily irrigation needs based on satellite data—available on their Web site has experienced a “steady and significant rise in the number of daily Web hits from Internet providers known to service Wisconsin cranberry growing regions.”
Such efforts are not confined to the United States. A recent international workshop on the application of meteorology to agroforestry in the area of systems planning and management (Reifsnyder and Darnhofer, 1989) detailed numerous examples of such application. Many other examples appear in the publications of WMO, such as a monograph on operational crop protection (Working Group on Agrometeorolgocial Aspects of Operational Crop Protection, 1983).
Decker (op. cit.) states that, “The twenty-first century offers a challenge for the development of applications to risk analysis, crop and forest models, and assessments of production.” But he worries that “there is a real danger that this interdisciplinary effort will sustain a real reduction through smaller personnel pools in the research and service components dedicated to agriculture and forestry.”
I venture a few guesses only because I won’t be around to suffer the disapprobation of the pundits alive fifty years from now. If one looks back on the progress of agriculture in the past fifty years, certain trends are obvious. Plant breeding for increased crop yields has resulted in dramatic increases. Widespread irrigation has permitted substantial control over a major limiting factor in plant growth and maturation. Scientific application of fertilizer completes the triad of major technological advances to date. The practical application of agricultural meteorology has had effects secondary to these three. As noted above, there are numerous practical agrometeorological applications that have the potential for great economic benefit to agricultural producers.
But as the demand food increases with world population increase, society will attempt to squeeze ever greater yields from a diminishing agricultural land base. This will inevitably lead to increasing application of meteorological knowledge to crop and animal husbandry. I predict that there will be something of a renaissance in practical agrometeorology as the new century begins.

7. Acknowledgments
My thanks to Evelyn Mazur, Meetings Secretary of the American Meteorological Society for providing me with the history of the agricultural meteorology meetings sponsored by the Society. I enjoyed conversations with Paul Waggoner and Wayne Decker that helped jog my memory about events surrounding the early meetings and events.

8. References
Allen, L. H., Jr., 1979. Potentials for carbon dioxide enrichment. In: B. J. Barfield and J. F. Gerber (eds), Modification of aerial environment of crops. Amer. Soc. Agr. Eng., St. Joseph, Michigan. P. 500-519.
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Anschrift der Verfasser:
Dr. William E. Reifsnyder
HC81, Box 3
Questa, NM 87556 USA

email: william.reifsnyder@yale.edu



Figure caption

Photo taken circa 1948. From left to right: Wayne Decker, Ray Weygant, Robert Shaw, Gerry Barger (seated in truck), Paul Waggoner and unknown student. Photograph courtesy of Paul Waggoner.

1 The fascinating story of how Bowen, an astrophysicist, came to write his doctoral dissertation on a meteorological subject is related in a recent article by J. M. Lewis (1995).

2 Because of his background, Brooks generally utilized engineering units. I must admit that I still have trouble converting in my mind between Btu/(hr ft2), cal/(cm2 sec), langley/min, and W/m2.

3 Reflecting the broad range of disciplines encompassed by agricultural meteorology, the first three technical articles published by the journal involved animal housing, transpiration and water use of cotton; and solar radiation in a pine forest.