Table Of ContentMETEOROLOGICAL MONOGRAPHS
Volume 6 July 1965 Number 28
AGRICULTURAL METEOROLOGY
by
Paul E. Waggoner, D. M. Gates, E. K. Webb, W. R. van Wijk,
J. A. Businger, Todd V. Crawford, C. H. Hendershott,
D. N. Moss, H. D. Johnson, W. S. Chepil, W. R. Henson,
W. R. Gardner, Bohdan Slavik, C. Warren Thornthwaite,
F. Kenneth Hare and James D. McQuigg
PUBLISHED BY THE AMERICAN METEOROLOGICAL SOCIETY
4 5 B E A C 0 N ST., B 0 S T 0 N, MASS. 0 2 I 0 8
AMERICAN METEOROLOGICAL SOCIETY
PUBLICATIONS COMMISSION
Jule G. Charney, Chairman
Massachusetts Institute of Technology
Louis J. Bat tan
University of Arizona
Richard M. Goody
Harvard University
Richard J. Reed
University of Washington
Robert Jastrow, ex officio
JOURNAL OF THE ATMOSPHERIC SCIENCES
Gordon J. F. MacDonald, ex officio
JOURNAL OF THE ATMOSPHERIC SciENCES
Robert D. Elliott, ex officio
JOURNAL OF APPLIED METEOROLOGY
Donald P. Mcintyre, ex officio
JOURNAL OF APPLIED METEOROLOGY
J. Murray Mitchell, Jr., ex officio
METEOROLOGICAL MONOGRAPHS
Malcolm Rigby, ex officio
METEOROLOGICAL AND GEOASTROPHYSICAL ABSTRACTS
David M. Ludlum, ex officio
WEATHERWISE
ISBN 978-1-940033-58-7 (eBook)
DOI 10.1007/978-1-940033-58-7
jULY 1965 METEOROLOGICAL MONOGRAPHS iii
PROLOGUE
Agricultural meteorology or agricultural climatol and sometimes controlling how plants and animals
ogy is not a mere specialty of meteorologists. Rather, grow.
it is a common domain for scientists of diverse dis Three classes of scientists have contributed to agri
ciplines. This prologue will in simple language intro cultural climatology: physicists, biologists, and what
duce these scientists. Then the authors of the chapters we shall call historians. The physicist studies the com
that follow will present in the language of the special plementary operations of atmosphere, soil and the
ists the problems, methods, and solutions that exem organisms themselves that fix the temperature, wind
plify the study of agriculture and weather. Since much and moisture at a particular place and time. The bi
of agricultural meteorology deals with creation of and ologist studies the response of plant or animal to this
response to environment, this Monograph may have environment. The historian combines the established
even wider application than agriculture alone. biologic responses and past behavior of the weather
Biologists have, of course, always been aware of the and from this knowledge foresees the future. As we ex
effects of weather. For example, ecologists have asso amine the primary elements of meteorology-warmth,
ciated certain communities of plants with particular wind and water-we shall be reviewing the work of
climatic zones on a mountain, and physiologists have these physicists, biologists and historians. We begin
associated certain rates of photosynthesis with particu with warmth or energy.
lar light intensities in a laboratory. Meteorologists, In an earthly field or wood begins much of meteor
on their part, have been well aware of organisms. In ology and especially agricultural meteorology. The
fact, the five major divisions of Koppen's classic clas climate is created, in part, by the quantity of radia
sification of climate correspond to de Candolle's five tion reaching the field or wood. But then it is modified
large plant groups. Still, the agricultural meteorology by the distribution of this energy, and the distribution
of the past two decades differs markedly from that depends upon the surface that the radiation strikes.
which went before. Is it grass or gravel, corn or pine? The study of this
Time alone has brought about some of the change. distribution is the province of the physicist.
But some of the sources of change can be identified: This physicist or micrometeorologist investigates
a systematic use of physics and employment of more the income, interception, and reflection of short-wave
refined instruments permit understanding and meas radiation from the sun and of long-wave radiation
urement of micrometeorology of the boundary where from the sky. He studies the emission of radiant energy
plants and animals actually live; air-conditioning al from soil, plants and animals. In the first chapter,
lows direct experiments in the effect of weather upon D. M. Gates treats radiant energy, its receipt and
plants and animals; use of probabilities has turned disposal.
climatology from a mere description to a foundation During a summer day, a net gain of hundreds of
for rational decision; wartime meteorologists have mi calories accrues to each square centimeter of the earth
grated into agricultural experiment stations. Thus new because the radiant loss is less than the gain. Some of
life has been breathed into the study of weather, farm, this gain, we shall see, is employed in heating the soil
and forest, and the time has come for a Monograph. and in photosynthesis. Much of it, however, is con
The function of this Monograph is to present recent sumed in heating the air and in evaporating water.
solutions to problems in environment and agriculture. This consumption is mediated by atmospheric turbu
These exemplify the contributions of several disci lence, and it determines the temperature and humidity
plines to the elevation of agricultural meteorology in of the air. These processes that determine the aerial
the last 20 years from a repository for phenomena that microclimate are the subject of E. K. Webb, who has
had no other explanation to a means of understanding written Chapter 2.
IV METEOROLOGICAL MONOGRAPHS VoL. 6, No. 28
Some of the energy reaches the soil about the plant fewest specifications of the environment we want to
roots, which then grow and collect water and nutrients. be able to estimate the state of all environmental
This energy absorbed by the soil also tempers the factors that affect the organism. The knowledge of
aerial microclimate as it is subtracted from the day processes that is provided by the first three chapters
time budget and added to the nighttime budget of the is one essential of agricultural meteorology. Knowing
atmosphere. Obviously frosts are more frequent over the response of organisms is another essential. This
peat than sand. Soil temperature shows rhythmic second is a task for biologists.
changes according to its conductivity and capacity for Since plants of field and forest are rarely sheltered,
heat. The mathematics of this phenomenon has been their survival and growth into larger plants depend
understood for some time. Application has been diffi upon weather. \Ne begin with the simpler matter of
cult, nevertheless, for not only are the soil's thermal destruction and later turn to the more complicated
properties difficult to determine, but also they vary matter of growth. Some of the most important effects
greatly and frequently as the water content changes. of environment are the influences of radiant and sen
Further, plates or barriers, that are inserted into the sible heat upon destruction and growth.
soil for the measurement of thermal flux, disturb the The elementary biology of destruction by frost is
soil and, hence, cannot measure the flux in the mass clear: when some plant becomes colder than, say, -1 C
of undisturbed soil. In Chapter 3, therefore, W. R. it is destroyed. Because this response is clear cut,
van Wijk introduces a new method of measuring the physicists have been able to analyze the cooling of the
thermal flux and properties of the soil, and he discusses plant and, hence, determine how it may be retarded.
the creation and modification of soil microclimate. Thus the analysis of frost and frost protection by J.
In these first three, primarily physical Chapters A. Businger and T.V. Crawford in the fourth Chapter
there is a remarkable lack of temperature and hu is an exemplary application of the meteorology pre
midity data. Instead the primary concern is with the sented in the first three Chapters. The biologist can
streams of energy that determine temperature and assist in solving this clearly defined problem. Also in
evaporation. This is, of course, one of the great changes Chapter 4, C. H. Hendershott gives an example of
that differentiates present from past micrometeorology how plants can be made to resist frost.
and agricultural meteorology. The biologist's task in agricultural meteorology is
Thus, on a clear, midsummer noon the income of not a simple one, particularly when he must learn how
radiation R; is 1.2 cal cm-2 min-1 from insolation and weather affects growth. He is enmeshed in two things.
0.6 from long-wave. The radiation leaving a bare soil, First are the complexities and unceasing changes of
Ro, is composed of 0.3 reflected and 0.7 emitted. Conse the weather: sun follows cloud, flood follows drought,
quently net radiation and frost follows heat in limitless combinations and
+ in rapid and random order. Then he is trammelled up
R;- Ro = 1.2 0.6 - 0.3 - 0.7
in the responses themselves: plants respond in a non
0.8 cal cm-2 min-1•
linear fashion and then store their responses according
If the bare soil were wet, evaporation E might con to their own summation method in a memory called
sume 0.5, leaving only 0.3 for warming the air A and "yield."
ground G. If, instead, the soil were dry, E would nearly In such a snare, progress has come with new analytic
disappear, and fully 0.8 would be available for A and methods. The seemingly straightforward method was
G and the creation of a warmer environment. The to accumulate, say, 30 years' experience: the yields
partition between A and G and the consequent warm and weather of 30 years. Then, with graph paper or
ing of air and soil will depend upon the relative turbu statistics, correlate one with the other:
lence of the air and conductivity and capacity of the
Biologic Response = !(Weather), orB = f(W).
soil.
Thus unlike a mere description of temperatures and This relation is immediately applicable because it sum
humidities applicable to a single place and time, marizes experience in real fields and real weather.
knowledge of energy and water exchanges provides Its disadvantages are disabling, unfortunately. It is
understanding of how environment is controlled. This empirical and cannot logically tell us anything about
understanding of control permits calculation of tem elements not directly observed. More important, since
perature and evaporation at other places and times. we generally do not know which factors affect growth
Such understanding is necessary in learning how or when they act, and since later events generally
weather affects plants and animals because weather obscure the results of earlier ones, the actual results
changes ceaselessly and cannot practically be observed will be badly scattered about the simple curve relating
everywhere that a plant or animal grows. From the responses and weather.
jULY 1965 METEOROLOGICAL MONOGRAPHS v
A means of obtaining B j(W) more precisely is variability in response to weather. With this varia
to shorten the period of observation, thus simplifiying bility to play upon, geneticists can create more resist
the specification of the environment and enabling the ant varieties or breeds to endure unfavorable climates
response to be observed unobscured by its storage or and more productive varieties to exploit favorable
by later events. Growth analysis, the frequent and climates. Now we have finished with the first major
careful measure of the plant, permits us to see the subject of our }vfonograph, heat, and turn to the sec
response to the weather of a week. This weather can ond, wind.
be described much more easily than that of a season. Wind may carry away the soil in which plants might
But even a week's weather is too complex. grow. It may also drift snow. In the 1930's a great
The instantaneous, continuous measuring of re drought demonstrated to Americans the power of
sponse (photosynthesis and transpiration) has, there weather to control the success of plants, even people
fore, been undertaken. Sometimes the plants are en and whole societies. The "black blizzards" were the
closed in transparent chambers and the disappearance most awesome sight, and the fugitives from the Dust
or appearance of a gas measured. Alternatively, the Bowl were the most pathetic victims. Now, a genera
plants stand undisturbed, and gas exchange is esti tion later, much has been learned about how wind
mated by means of turbulent transfer theory. The lifts particles of soil, how it carries and deposits the
crucial thing, however, is not the precise device. soil, and hence, how the process can be controlled.
Rather, it is the observation of field-grown examples This is the subject of W. S. Chepil, the author of
of productive species that are important to man. It is Chapter 7.
the observation of these plants in the brilliant light Wind carries parasitic insects and pathogenic fungi
of the sunlit field. that can destroy plants. As many examples of the
The results have been surprisingly different from spread of a disease across a field demonstrate, the
those observed in the botanical laboratory as D. N. obedience of the air-borne spores to the laws of tur
Moss discusses in Chapter 5. bulent transfer over short distances is precise. Un
The advantages of experiment over correlation are doubtedly many small, weak insects spread likewise.
well known. Another way around the complications But the fascinating examples are those insects that
of the field, therefore, is performing controlled experi board air currents which are blowing toward favorable
ments in air-conditioned chambers. This has achieved environments afar.
much in relating the development of, say, flowers to They exert themselves only enough to maintain
the environment. Also, as discussed in Chapter 5, anal their formation while being carried forward by the
ysis of gas uptake or photosynthesis in controlled swift mean velocity, and thus arrive together at a
experiments has revealed general relations between distant and desirable destination. In Chapter 8, W. R.
environment and growth that permit understanding of Henson and P. E. Waggoner tell of this simultaneous
diverse situations in real fields. employment of speeding air and avoidance of turbu
Animals of the farm not only are often confined and lent dispersion as well as our knowledge of short dis
sheltered, they also generate heat. These things that tance dispersion of spores.
help them endure cold, however, make them suscepti The third major subject, water, has become a prob
ble to hot weather. Thus to the energy budget given lem shared by city, farm and forest: as the city
above for the soil or a plant is added a considerable dwellers increase in number and wealth, they demand
quantity of metabolic heat that animals must dissi more water; they learn that fields consume much and
pate, sometimes in the reduced convection and evapo that wild vegetation consumes most of the earth's
ration within a building. As in the case of plants, air water.
conditioned chambers and the experiments they make In many soils there are enough pores to hold fully
possible have revolutionized the investigation of the 3 inches of rainfall in each 12 inches of soil profile.
response of animals to weather. In addition, consider Some pores are large and their contents percolate
able progress has been made in elucidating the bio downward; others are small and their contents are
chemistry or physiology of the response of animals to too tightly held to be extracted by plants. In between
heat. This response is discussed by H. D. Johnson in are enough pores, however, to retain and then release
Chapter 6. about 2 units of water. In both micrometeorology and
Most research in agriculture is useful as well as agriculture, this is the water that matters. It is the
interesting. The knowledge of the response of plants water that reaches the surface of soil and leaf between
and animals to environment is no exception. The bio rains, is evaporated, and appears in the energy budget.
chemistry of resistance may permit chemical remedies In analyzing this storage and return of rainfall, W.
for inclement climate. Even more promising is the R. Gardner reviews the laws that govern the water
Vl METEOROLOGICAL MONOGRAPHS VoL. 6, No. 28
that enters and is held within the soil pores. Recently, cloudier than another because the mean temperature,
however, it has become possible to recognize that this rainfall or cloudiness was greater. This system was not
system is in fact a dynamic one, and an important particularly helpful in agriculture, for the kind and
part of Chapter 9 is the analysis of the changing con condition of native plants and animals gave essentially
ductivity and availability of water as the reservoir the same information and a good deal more quickly
of the soil pores is emptied or as the demand of the and directly. During the past score of years, however,
plants is increased. improved knowledge of biological response and better
Although a considerable amount of water is evapo ways to estimate the probability of weather events to
rated from soils that are frequently wetted by rain, come have combined to make agricultural climat
most of the water that is removed from storage and ology a valued partner in real planning.
then evaporated passes through plants. The aqueous In symbolic terms, climatology permits the extra
content of the plant as well as its conduction is im polation of experience in this way: In earlier chapters
portant, of course, for it must have water to absorb, we saw how a biologist discovered that a biologic
to synthesize, to grow, even to survive. Thus the water response was a function of weather,
that is in plants and passes through them is both an
B = j(W).
agricultural problem in itself and a vital link in mi
crometeorology. In Chapter 10, B. Slavik describes Then, drawing on historical records, the climatologist
the injury that follows a shortage of water in the plant. estimates the probability of critical weather events
Equally important, he discusses how both linkages and and of f(W). Finally
decreases in water potential cause water to pass from
P(B) = P(f(W)).
soil, to stem, and on to leaf. Recently, the measure
ment of potential has become more practicable, per The physicist's knowledge may even permit calcula
mitting more certain location of the resistance in this tion of the weather events W for places where weather
conductor, the plant. As told by Slavik, much of this has not or cannot practically be observed. Useful
resistance is in the final link, that from leaf to air, indeed is this means of anticipating the probability
and this resistance varies many fold. Thus transpira of a biologic and agricultural success or failure in the
tion, or the evaporation from leaves, is a botanical as future or in a place known only by its weather.
well as meteorological problem. A weather forecast, translated into terms of, say,
The loss of water to the air is, of course, an integral the imminent death of a plant or animal, may be the
part of the creation of the aerial microclimate, of the eventual product of the investigation of micrometeor
energy budget, of Chapter 2. The paramount impor ology and biology that is set out in the preceding
tance of evapotranspiration in agriculture and the chapters. This forecast of catastrophe may be highly
methods of measuring and predicting it, however, profitable-or it may simply prolong the painful an
require separate treatment for this subject. ticipation. The profitability depends, of course, upon
The same great drought that inspired the investiga accuracy of the forecast, but it also depends upon the
tion of blowing soil also inspired the addition of an possibility of preventing the catastrophe and upon the
estimate of evapotranspiration to the classification of relative cost of preventative and loss. These considera
climate. Because evapotranspiration was rarely if ever tions, given in Chapter 12 by J. D. McQuigg, could
measured, C. W. Thornthwaite had to estimate it. lead to rational classification of agricultural weather
Implicit in his estimation are twin recognitions: theo forecasts and climatology into genuine remedies on the
retically the thermal environment controls evapora one hand and nostrums on the other. Just as climat
tion and practically only temperature data were at ology and forecasts are the conclusion of agricultural
hand. Since then many other empirical and theoreti meteorology, this Chapter on foreseeing the future
cal methods have been put forth. From all these concludes our Monograph.
have come methods for estimating the probability of In 1957, the desirability of a publication, such as
drought, the profitability of irrigation and the opti this Monograph, that would embrace much of agri
mum time for irrigation. In Chapter 11, Thornthwaite cultural meteorology and exemplify its progress and
and F. K. Hare put in order this myriad of methods outstanding problems was stated by the Committee
and discuss their usefulness. This chapter concludes on Agricultural Meteorology of the Agricultural Board
the treatment of three subjects, heat, wind and water. of the National Research Council. This Committee,
The mention of probability introduces the final mat first under the Chairmanship of M. H. Halstead and
ter in agricultural meteorology, foreseeing the future. then F. W. Went, continued to urge the publication
In the past, climatology was essentially restricted to and later to advise the editor.
describing one environment as warmer, wetter or The concrete suggestion of a Monograph was, how-
jULY 1965 METEOROLOGICAL MONOGRAPHS Vll
ever, made in 1960 by the Committee on Agriculture Agricultural Experiment Station, and during 1963 at
of the American Meteorological Society. This Com the Rothamsted Experimental Station, the publica
mittee, then under the chairmanship of G. L. Barger, tion has been prepared. The essential ingredient, the
designated the editor to arrange the manuscript of contributors' knowledge, is seen in their chapters.
this Monograph and submit it to the Editor of the
Monograph series for publication by the Society. With PAUL E. WAGGONER
the help of the two Committees, of officers of the The Connecticut Agricultural
Society, and of my colleagues at The Connecticut Experiment Station, New Haven
IN MEMORIAM
With deep regret, the American Meteorological Society notes the
passing of two of the authors of this Monograph, C. Warren Thornthwaite
and W. S. Chepil. Thornthwaite's chapter was completed by Prof. F.
Kenneth Hare of the University of London, and revisions of Chepil's
'
completed chapter were undertaken by Prof. N. P. Woodruff of Kansas
State University. In their memory we can only dedicate ourselves to
continuing the work they had so ably carried on.
TABLE OF CONTENTS
PROLOGUE-PAUL E. WAGGONER............................................... 111
IN MEMORIAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vu
A. HEAT, RADIANT AND SENSIBLE
CHAPTER 1. RADIANT ENERGY, ITS RECEIPT AND DISPOSAL-D. M.
GATES....................................................... 1
1. Introduction..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2. Spectral distribution of sunlight.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
3. Plants and radiation............ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Energy budget and net radiation. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Direct solar radiation... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
6. Diffuse sky radiation on clear days. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. Diffuse sky radiation on cloudy days.............. . . . . . . . . . . . . . . . . . . . . . . . . 11
8. Geographical distribution of solar radiation........ . . . . . . . . . . . . . . . . . . . . . . . . 12
9. Insolation on slopes..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
10. Twilight period. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
11. Illumination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
12. Thermal radiation...................................................... 15
13. Albedo and reflectance.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
14. Radiation instruments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
A. Solarimeters and pyrheliometers: electrical and shielded.. . . . . . . . . . . . . . . . . 22
B. Actinograph: mechanical and shielded. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
C. Radiometers: electrical and shielded. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23
D. Radiometers: electrical; ventilated .......................... ·. . . . . . . . . . 23
E. Radiometers: electrical; exposed; unventilated.. . . . . . . . . . . . . . . . . . . . . . . . . 24
15. Radiation and crops. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
CHAPTER 2. AERIAL MICROCLIMATE-E. K. WEBB. . . . . . . . . . . . . . . . . . . . . . . 27
1. Introduction........................................................... 27
2. Turbulent transfer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
A. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
B. Neutral conditions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29
C. Thermally stratified conditions... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
D. Flux of water vapor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
E. The spectrum of atmospheric turbulence. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3. Mean profiles related to transfer processes... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
A. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
B. Lapse conditions.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
C. Inversion conditions................................................. 37
4. Modification of an airmass. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38
A. Departures from steady and horizontally uniform conditions.. . . . . . . . . . . . . 38
B. Diurnal variation; nocturnal cooling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
C. Change of concentration or flux at the surface. . . . . . . . . . . . . . . . . . . . . . . . . . 41
D. Change of surface roughness. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
5. Methods of measurement and estimation.................................. 42
A. General. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
B. Heat budget method................................................. 43
C. Bulk aerodynamic method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
Vlll
jULY 1965 METEOROLOGICAL MONOGRAPHS IX
D. Combination methods .............................................. . 44
1. Method of Penman .............................................. . 44
2. Method of Mcilroy .............................................. . 45
E. Profile methods ................................................... . 45
1. Estimation of Richardson number ................................. . 46
2. Method of related profiles ........................................ . 46
3. Method of Thornthwaite and Holzman ............................. . 46
4. Method of Deacon and Swinbank .................................. . 46
5. Method of Priestley .............................................. . 47
6. Method of Webb ................................................ . 47
7. Method of Panofsky ............................................. . 49
6. Application over reservoirs and crops .................................... . 49
A. Application of methods available ..................................... . 49
1. Reservoirs ...................................................... . 49
2. Crops .......................................................... . 49
B. Practical information in the literature ................................. . 51
7. The atmosphere in relationship to plants and animals ...................... . 52
A. General ........................................................... . 52
B. Plants ............................................................ . 52
C. Animals ........................................................... . 53
CHAPTER 3. SOIL MICROCLIMATE, ITS CREATION, OBSERVATION AND
MODIFICATION-W. R. VAN WIJK............................ 59
1. Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
2. Heat flow and soil temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
3. Time courses of soil temperature. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60
4. Applications and refinements of the simple theory. . . . . . . . . . . . . . . . . . . . . . . . . . 61
5. Heat flux density..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63
6. Determination of A and C near the surface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65
7. Thermal properties of soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66
8. Comparison of different soils...... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
9. A peat and a sand soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
10. Biological consequences. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
11. Soil tern perature and plant growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
12. Average temperature and growth curve. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69
13. Microflora............................................................. 70
14. Changing soil microclimate. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
15. Application to a cornstraw mulch. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
16. Soil mulch, tillage, windscreens. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72
17. Penetration of frost..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
CHAPTER 4. PROTECTION FROM THE COLD............................ 74
Section 1. FROST PROTECTION WITH IRRIGATION-]. A. BusiNGER........ 74
1. Energy budgets of leaf and fruit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
A. Radiation.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
B. Transfer of sensible and latent heat.................................... 75
C. Determination of leaf temperature..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
D. Temperature of a spherical object. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76
2. Required energy for cold protection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
3. Protection by sprinkling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 7
A. Required sprinkling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
B. Comparison of theory with experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
C. Intermittent sprinkling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
