When "droughts, unlike rain free periods,
may not be defined from standard meteorological observations, since the
intensity and the length of the drought depends on genetic characteristics of
crops, soil water, soil fertility conditions, and meteorological
parameters," [quoting Wayne L. Decker, University of Missouri
Climatological Research Project], it will be evident that we need to recognize
the soil as a major factor in the disturbances to crops which we call
"droughts". These are in reality dry periods extending themselves to
lengths of time that bring about crop disaster. The drought then is more a performance
measured by damage to crops than by meteorological indexes.
Drought is then a time period
during which there is a serious shortage of water by rainfall for the
biological services it usually represents in crop plants. Since the water's
services to plants are exercised mainly after the rainwater has entered the
soil, then the soil, which is more than merely a water reservoir, may be
considered as influencing the effects of the shortage of stored water over an
extended rain free period through all of its services to crops beyond that of
holding a supply of water. Those many services need to be considered before we
use water shortage per se as the alibi for poor crops.
1.
The
law of continentality vs. the law of averages
The
geographic climatic setting for most of the droughts are the area between the
humid and the semi-arid soil regions. These represent mineral-rich soils in
general, since the low rainfall has not developed them excessively or removed
the calcium, and minerals of similar soil behavior, from the profile and
replaced them by hydrogen as acidity. These are the soils where agriculture
grows protein rich forages; where soils are windblown and where animals grow
more readily on what is apt to be called the prairie and the plains soils.
Droughts are
also geographically located in the midst of larger land areas where the effects
of what is called "continentality" are more pronounced. This
represents the degree to which the weather or the daily meteorological
condition varies from the climate, which is the mean or the average of the
weather for the longer time period of records considered. The larger the body
of land, i.e., the more continental the area, the more the weather or the daily
condition will vary from the climate or the average. This is "the law of
continentality" in brief. Droughts then may be more commonly what we call
"continental" manifestations. They are a variation from the mean and
the expected since climate is reported as the mean of much meteorological data.
It is in the midcontinent of the United States where droughts may be expected
more commonly.
When the
average, or mean, of weather records is used to describe the meteorological
conditions of a region – Columbia, Missouri, for example, is reported to have
an annual rainfall of 29.33 inches. For Springfield, Missouri, the same figure
is 41.42 inches. This rainfall figure which is a mean total for the year
obtained from records of nearly a half century says nothing about how high or
how low the amounts for an single year may be. Because of the continentality of
Missouri – its location a thousand miles from any seacoast – we formerly
considered that from the previous data, Columbia, Missouri, had a
continentality effect of 50%. That says that while the rainfall is reported to
be roughly 40 inches, the precipitation might vary over a range of 50%, namely,
25%, or 10 inches, below 40 and 25%, or 10 inches above 40. It might range from
a low of 30 inches to a high of 50 inches of precipitation for the different
years.
But that figure,
once established for continentality, is no longer the fact. That record of
continentality was broken in 1953 when, because of the drought of that year,
the annual rainfall was but 25.12 in place of 39.33 inches. This annual weather
in terms of a rainfall of 25.12 is 36.1% below the mean of 39.33 inches, or
that much below the climate. Hence, we may expect excess rain also of 36.1%, a
high sometime of 53.54 inches, or a continentality effect of twice 36.1, which
is 72.2%. For Springfield, Missouri, the drought of 1953 gave but 25.21 inches
of rainfall annually, or a deficiency of 39.1% to suggest a continentality
effect there of 78.2%.
If one
considers the rainfall for only the summer months - May to September, 1953
inclusive - when the effects of the extended rain free period on vegetation are
exaggerated by high temperatures, Columbia, Missouri suffered under a
continentality effect amounting to 86%. At the same time, Springfield, Missouri
suffered one amounting to 135%. This latter was a most severe disaster to an
agricultural area given largely to the dairy phase of that business with so
much dependence on grass as the crop. Thus the law of averages applied to
Missouri may leave one content with averages, but the law of continentality is
truly disturbing but highly revealing when such droughts as 1953 are
experienced in record breaking dimensions.
|
The Missouri Drought of 1953
Emphasized Continentality When the Records of the Weather are put in Contrast
to Those of Climate
|
||||||||||||
|
2. Droughts are becoming urban - no longer remaining rural
With 85% of our population
collected into urban centers, while only 15% are still rural, we would scarcely
expect the urban group to appreciate droughts, exhibiting the effects of rain
free time largely through the water shortage within the soil bringing crop
disasters and livestock troubles. But droughts as water shortage through
falling water tables and failing wells are not only rural troubles for thirsty
livestock. They are coming to be serious troubles also for urban centers and
areas of congested peoples. Where the per capita water consumption per day was
formerly a few gallons – a pail full carried from the spring – it is now
estimated at 700 gallons per day on a national scale. When this increase per
capita is coupled with the increase in population our water consumption since
"water pail days" represents an increase of several thousand percent.
This supply comes mainly from deep wells. For this the soil is the filtering,
clarifying and bacteriacidal agency in most cases which gives us clean,
health-supporting water to drink. We have taken water of this kind for granted.
We have not seen the soil's services connected therewith. Droughts are making
us become water-conscious, not only via disasters to crops as feed and
livestock as drink, but also even to the value of water as the major liquid
mineral we all drink. When eastern Kansas in 1954, following a rain free period
of serious shortage in 1953, had 26 cities critically sort of water, we have
reason to become conscious of droughts of larger significance than of such to
the rural population only.
3.
Water
shortage - a result from excessive erosion and drainage
Our urban centers are coming to
see the soils as reasons for droughts in broader meaning of that loosely used
term. We realize that we must either limit water consumption per capita, or we
must raise the level of the groundwater, i.e., the water table, by getting more water per rainfall to enter
the soil. The shortage in soil-stored water is a sequel to soil erosion. As
the surface soils become shallower they are less of a blanket to hold larger
portions of each rainfall for increased amounts of it to filter or to soak down
more deeply into the soil to raise the water table there. Every little rill of
erosion is a drainage ditch to hustle the rainfall off just that much more
rapidly and to leave that much less to enter the soil for storage there. With
erosion, too, the structure of the remaining cultivated surface soil has become
less granular and less stable. Less infiltration of water per rain is possible
for that reason.
Our
excessive drainage, increased more recently by the excessive surface runoff
bringing about erosion is now magnifying the shortage of water taken from and
given out by the soil. In the mind of the pioneer it was the surplus water and
not the water shortage against which he waged a constant struggle. He used
drainage ditches, tiles, and all possible means of getting rid of what he
considered too much water. We seem to have inherited the pioneer's animosity
for water and delight in the extra speedy drainage. Instead we now should
encourage more standing water for infiltration because we have too much
drainage for sufficient of that.
We have
apparently lifted our soils too high out of the water when now nearly every
acre is drained. Also when all-weather roads are considered a necessity almost
every section of land is encircled by such. Each roadway under concrete cover
is allowing no rainwater to enter that much soil. Also by its sloping shoulders
and parallel drainage ditches each highway is hustling off to the rivers the
rainwater falling upon acres and acres in roadways, while draining also more
quickly the arable land adjoining them. When we are bringing about all these
changes which reduce the rate and total of water infiltration into the soil
while rates of water consumption are increased to lower the supply stored, both
in the soil profile for our crops and in the water tables for our livestock and
the people of our population, is it mysterious that droughts are getting worse
and floods more disastrous? Are these new records other than man-made? Are they
coming other than by way of the soil?
We have then
been bringing our droughts as they represent shortage of supplies of water upon
ourselves. Droughts are disastrous in terms of deficiency of that liquid
mineral in the soil and of the food it grows. The more fertile, high protein
producing soils are exhibiting the more serious drought disasters. Man is thus
pushing himself off the soils which are better for nutrition. He is crowding
himself to areas of higher rainfall and to soils giving feeds and foods of
high-fattening rather than high-feeding values. He has not noticed that he was
moving himself out of quality foods by soil exploitation, since hidden hunger
is registering itself all too slowly. But now that he is crowding himself out
of drink, that will register more quickly since thirst is more speedily lethal
than hunger, droughts take on more meaning. They, too, are moving from the
country to the towns and the cities. Droughts register as disasters regardless
of whether via humans or via vegetation. Since
both routes for troubles of this nature go through the soil, they will finally
lead us to the soil as the basis of creation in terms of both drink and food.
4.
Confusion
in considering water shortage in the soil but not recognizing fertility
shortage there
In seasons of water shortage for our
crops, that shortage in the soil has too commonly been mistaken for the
shortage of plant nutrition there. When the farmers said, "The drought is
bad since the corn is fired for four or five of the lower leaves on the
stalk," they were citing a case of the plant's translocating nutrients,
especially nitrogen, from the lower, older, nearly spent leaves in order to
maintain the upper, younger, and growing leaf parts of the plant. Now that we can apply fertilizer nitrogen
along with other nutrient elements, we know that in the confusion and lack of
knowledge about plant nutrition we made so much of the drought in many cases
where it was not the direct shortage of the water as liquid for the plants, but
rather the more common shortage of nitrogen entering into protein and all it
represents in crop production.
In this case
the soil as shortage of nutrition and not of water was responsible for what was
called "drought". With a shallow horizon of surface soil to which the
fertility of the entire profile was confined and with an acid, infertile clay
horizon beneath it, the drying of that
surface layer compelled the roots to go out of the drying horizon originally
providing both fertility and water, and into the subsoil where only water but
little or no fertility was present. That shallow surface layer was dried,
not only as the result of the heat from the sun but also because the roots of
the growing crop like corn are estimated to be taking from .15 to .25 of an
inch of water by transpiration alone per day (Some folks consider .10 inch of
water transpired daily by a corn crop and define a drought for corn as rainfall
of less than one inch every ten days. This gives no consideration to the soil
concerned.). To miss recognizing the fertility shortage when emphasizing the
water shortage in the surface soil during drought is a mental behavior of long
standing. In that error of thought we
have been blaming the drought via the soil water for a "fired" crop
when it was plant starvation via that route from which also insufficient
fertility for plant nutrition was coming.
If these
fertility conditions cause the lower leaves of the corn stalk to
"fire", in the case mistaken for drought, one needs only to note the
growing tip of the corn stalk. If water shortage is responsible, then the
growing tip of the plant will not commonly be wilted since the roots going
deeper into the subsoil are delivering water to maintain the active plant tip
without its wilting. It is the wilting of the growing tip of a plant which
tells us when water is needed, a question to which most any housewife knows the
answer who cares for her house plants. Droughts
may often be a case of infertility of the soil, or one of imbalanced plant
nutrition apt to be mistaken for shortages of rainfall and for bad weather.
5.
Plants
spend most soil water to keep leaf tissue moist for gaseous interchange with
the atmosphere - this loss represents cooling effects
Should we
clarify some other confusions connected with the properties of water and its
biochemical services to plants, animals, and man, we may simultaneously clarify
more effectively our understanding of the soil's significance under what we
call "droughts". In connection with our own body comfort during times
of higher temperatures and longer rain free periods, we appreciate the help by
speedy evaporation of water from our own skin as a means of keeping us cool. It
is a fortunate property of water that a tremendous amount of heat is taken up
when water changes from its liquid form to a gas, or when it vaporizes. We can
use melting ice to cool ourselves since about 85 calories of heat are taken up
in melting one gram of solid water as ice into the liquid form at the same
temperature. But nature has been more efficient in using vaporization of water
from our skin as a means of offsetting high temperatures or heat, since about
585 calories of heat are taken up when one gram of water is vaporized from the
skin, or in the breath as discharged in the form of water vapor from the lungs.
This property of water, namely,
its high heat of vaporization, holds down, and to a considered regularity, the
temperatures of small bodies of land surrounded by water. It offsets the effect
of continentality as illustrated when Great Britain has a continentality of but
10%, or the Hawaiian Islands have almost none. Vaporization from the
surrounding water mass spends the sun's heat which would otherwise raise the
atmospheric temperature over the adjoining land were the air from there not
exchanged by air from over the
water. Soil
water vaporizing from the soil's surface is then a cooling agent of the soil
and the air above it. So is the water vaporizing from the plant's leaf
surfaces. Trees bringing up water stored much deeper in the soil to be
vaporized from the tree's leaf surface are a means of spending the heat from
the sun and thereby of cooling the atmosphere. Clearing areas of forests has
done much in bringing about wider fluctuation in temperatures, first because
trees are helpful in getting rainfall into the soil for increased storage and
less sudden fluctuation in soil temperature and moisture, and second, in
lessened fluctuations in atmospheric temperatures within considerable heights
from the soil because of their transpiration or vaporization of water from
within their leaves. As crops grow taller they ameliorate for themselves the
effects of variations in heat from the sun by means of the water evaporated
through them from the soil (A medium sized hardwood tree may lose 50 gallons of
water through its foliage in a day, reports William B. Love, Michigan State
College Specialist in municipal forestry.).
Unfortunately, crops have been
classified by means of these values into different "efficiencies with
which they use water from the soil to give us yields of crop," i.e., only
vegetative bulk. "What difference is there in the quality of crop yield
per pound of dry matter produced?" was not the question raised even when
the transpiration ratios were widely different and the final figures were an
average of them over wide ranges. Photosynthesis by the sorghum and sugar cane
piling up rapidly their photosynthetic products, namely, sugars and starches as
energy food for the plant, was emphasized. Biosynthesis, the production of the
compounds like proteins which takes place without the direct service of light
and uses some of the sugars and starches for starting compounds and for energy
sources or fuel for the synthetic processes, was not considered. The ratio of
the pounds of water transpired to the pounds of complete protein produced would
have put this thinking on a truly nutritional basis. It would let us see water
of transpiration used highly efficiently by alfalfa making a pound of very good
protein per 8,000 pounds of water transpired. This is high efficiency in
contrast to sorghum, making a pound of incomplete, or very crude, protein per
10,000 pounds of water of transpiration. Alfalfa, a quality feed producer, is
more efficient in using water for this purpose than is sorghum.
In the desert where the soil is
so dry, to cite a third case, the moisture condensing on the plants at night is
enough to moisten the soil around the plant's roots by reversing the stream of
transpiration. But this does not necessarily reverse the plants movement of
fertility, which continues to go from the soil into the plants. Desert plants
take fertility regularly even if the transpiration stream should be a diurnal
reversal of its current. As another good case, one can demonstrate plant growth
and nutrient movement into the root from the soil when the transpiration stream
is not flowing. One can demonstrate growth by putting a potted plant under a
glass bell jar into an atmosphere laden with moisture and carbon dioxide with a
humidity of 100% and no transpiration. Given plenty of carbon dioxide and
sunlight, we can have both plant growth and nutrient movement from the soil
even when the transpiration stream is at a standstill. These four cases are the
evidence that the transpiration stream is
one activity, while the movement of the nutrients is another quite independent
of it.
Among the other
plant manifestations suggesting effects of drought by high temperatures rather
than by water shortage, there is the common change in a bluegrass lawn to one
of crab grass or other species, for example, when the lawn owners persist in
keeping their lawns watered during the hot summer months. Where the lawn is
dried and the bluegrass has disappeared in going dormant, this same grass
species comes back with the break in the drought, namely, with the rain again
and the lowered temperatures. Such is not the case of the watered lawn, shifted
by that watering treatment during the heat to a crab grass flora. That flora
persists and excludes the bluegrass during the rest of the season. A Bermuda
grass lawn is undisturbed by the drought which displaces the bluegrass. Bermuda
grass stays green during both the temperature and water shortage.
The water of
transpiration from the plant's leaves demonstrates another of its vital
biochemical properties, namely, its services as a solvent of gases as well as
of salts for their ionization. Water is lost from the leaf of a plant because
the inner, moist tissue of the leaf is exposed to the atmosphere for the
exchange of the gases. Those gases are mainly carbon dioxide and oxygen. That
inner leaf surface must be kept moist since gases will not exchange through a
dry one for help to the plants in taking in carbon dioxide for photosynthesis
or oxygen for respiration. Plants lose water by transpiration according to the
meteorological conditions vaporizing that water from the leaf surface much as
water from any moist surface. The stomates of the leaf, through which gases
exchange, may be partially but not completely closed for a living plant. The
plant leaves may roll themselves for reduction in transpiration before they
wilt. But moist leaf tissue exposed for exchange of the gases must be losing
water to the atmosphere, or plants must be transpiring, if respiration and
photosynthesis are to continue to keep the plant alive under most common
conditions of the water. Only an atmosphere of humidity at 100% or one
completely saturated, eliminates transpiration. In nature, this condition does
not occur often.
6.
Plant's
transpiration ratio is not an index of efficiency of use of water: soil as
plant nutrition determines that
It was the
classic work of L.J. Briggs and H.L. Shantz [Relative Water Requirements of
Plants, Journal of Agricultural Research 3:1, 1914] that measured the water of
transpiration of crops in relation to the amount of dry weight in plant tissue
resulting as growth. The same soil was used for the many different crops under
experiment. At that time, and by many
folk today, it was believed that the kind of crop determines this relation and
little significance was given the soil as control of it. Their work gave us
many "transpiration ratios" apt to be called "water requirements"
of different crops. These values are the pounds of water transpired to the air
by the plant taking it from the soil to produce a pound of the crop's
vegetative dry weight.
Unfortunately, crops have been
classified by means of these values into different "efficiencies with
which they use water from the soil to give us yields of crop," i.e., only
vegetative bulk. "What difference is there in the quality of crop yield
per pound of dry matter produced?" was not the question raised even when
the transpiration ratios were widely different and the final figures were an
average of them over wide ranges. Photosynthesis by the sorghum and sugar cane
piling up rapidly their photosynthetic products, namely, sugars and starches as
energy food for the plant, was emphasized. Biosynthesis, the production of the
compounds like proteins which takes place without the direct service of light
and uses some of the sugars and starches for starting compounds and for energy
sources or fuel for the synthetic processes, was not considered. The ratio of
the pounds of water transpired to the pounds of complete protein produced would
have put this thinking on a truly nutritional basis. It would let us see water
of transpiration used highly efficiently by alfalfa making a pound of very good
protein per 8,000 pounds of water transpired. This is high efficiency in
contrast to sorghum, making a pound of incomplete, or very crude, protein per
10,000 pounds of water of transpiration. Alfalfa, a quality feed producer, is
more efficient in using water for this purpose than is sorghum.
But the crop
specialists interested only in vegetative mass as a service by transpired
water, remind us that sorghum uses water at a rate of 275 pounds per pound of
dry matter grown, while alfalfa transpires 850. In his mind, which has not yet
envisioned nutritional services by crops grown but clings to the criterion of
vegetative mass produced per acre as the criterion of crop yield, the sorghum
surpasses the alfalfa as the crop for droughty areas or those of lower
rainfall. According to these folks using such simple transpiration ratios as
their judgement of the crop's efficiencies in using water, low rainfall areas
would call for growing bulky crops that starve our animals and ourselves rather
than call for making the soils fertile in those low rainfall areas to use that
water more efficiently for the creation of real nutritional values. Speculation
in agricultural crops on the level of simple arithmetical thinking is more
universal than is the creation of real food value demanding our thinking in
terms of the science of physiology and all the other forms of organized
knowledge undergirding growth, protection and reproduction by the life forms
that live to feed us.
Any crop uses water inefficiently for the
possible biosynthetic services when the fertility supply in the soil represents
an imbalance for the support of the physiological processes required for the
maximum of nutrition of that crop. In that nutrition of the crop, any one
element in low supply in the soil may cause inefficient synthesis, while the
stream of water loss as transpiration runs on just the same. Elements like calcium,
magnesium, potassium, phosphorus and others held in place are soil fertilizers. Nitrogen, so mobile
and not so held, is the crop
fertilizer. Thus the confusion in this regard occasions inefficient use of the
transpiration stream under nature's control, because we fail to keep the supply of nutrients in the soil up to the
high level, and in the proper ratio, for the biosynthetic processes of the crop
functioning at high efficiency in giving us nutritional values in itself as our
food.
The
transpiration stream flows according to the meteorological conditions favoring
evaporation of water balanced against the soil's conditions representing forces
holding the water as a thinner film around the soil particles. The plant and
its open, internally exposed wet cells in the leaves are atmospherically
exposed water surfaced connecting themselves through the plant and its roots
contact with the water film around the soil particles. According as that soil
has less water and the film is thinner, the water is held there more firmly
against liquid and gaseous transfers of it to the atmosphere via the plant
which is the equilibrator of the atmosphere's taking water by evaporation from
the leaves and the soil's holding it by surface adsorption. The poor plant is merely the innocent equal
sign between the two opposing forces. Even though the plant's leaves may roll,
and stomates may nearly close, they must still permit carbon dioxide to enter and
escape, and oxygen to do likewise for the continued respiration if the plant
remains alive. It’s wet, living tissue exposed cannot prevent the water loss
any more than you can live and prevent the moisture loss in your breath by
stopping your breathing. Plants lose water under variable weather according to
the soil and meteorological conditions and not according to the plant species
or plant pedigree.
7.
Transpiration
stream of water from soil to plant vs. nutrient movement along that route
The
transpiration stream of water moving from the soil through the plant to the air
obeys the meteorological conditions of the atmosphere controlling it. The
nutrient elements move from the surface of the colloidal clay holding them to
the colloidal surface of the root according to the energy changes required to
bring that transfer about. This chemo-dynamic performance of nutrient activity
follows its set of laws and conditions, including the presence of water but not
the movement of the water. The nutrient, inorganic elements within the soil,
like the fish in the stream, are not victims of the current. They move with or
against it according to forces controlling them.
Experiments
using colloidal clay to measure more accurately the soil's stock and changes in
the nutrient cations have demonstrated that nutrient ions could go from the
plant back into the soil while the plant was increasing its mass by growth and
was having a normal transpiration stream of water flowing from the soil to the
atmosphere. As a second case, using the seed planted into moist sand, for
example, growth occurred with the transpiration stream moving water out of the
sterile sand but no fertility elements from there. It was an empty
transpiration stream then so far as nutrients hauled in by it are concerned,
but it was nevertheless a flow of water. It was a moistener of the leaf tissue
only for exchange of gases there which is the normal function of transpiration.
In the desert where the soil is
so dry, to cite a third case, the moisture condensing on the plants at night is
enough to moisten the soil around the plant's roots by reversing the stream of
transpiration. But this does not necessarily reverse the plants movement of
fertility, which continues to go from the soil into the plants. Desert plants
take fertility regularly even if the transpiration stream should be a diurnal
reversal of its current. As another good case, one can demonstrate plant growth
and nutrient movement into the root from the soil when the transpiration stream
is not flowing. One can demonstrate growth by putting a potted plant under a
glass bell jar into an atmosphere laden with moisture and carbon dioxide with a
humidity of 100% and no transpiration. Given plenty of carbon dioxide and
sunlight, we can have both plant growth and nutrient movement from the soil
even when the transpiration stream is at a standstill. These four cases are the
evidence that the transpiration stream is
one activity, while the movement of the nutrients is another quite independent
of it.
Our failure to study the plant nutrition
within the soil, and our contentment with complaints about droughts, have left
us growing bulk of plants rather than nutritional values in our agricultural
crops. Water has been the great alibi. We have believed the plant concerned
only about its drink. We have simply not seen the soil and the plant's concern
about something that is truly plant nourishment for biosynthesis by it of
proteins and higher food values. We have simply not diagnosed each specific case. We have been content
with propagandized practices by the majority of prescribers. We have been
running within the pack of humans in place of smelling out the trails of the
things of nature.
8.
Drought,
excess of temperature as well as the deficit of soil water
When the absence of water for its services in
vaporization from the soil and the vegetation as a cooling effect allows the
temperature of the air to rise high, shall we not expect the plant's processes
of life, centered in the proteins, to be disturbed by the increased heat? Those
processes are doubled in their rate of activities for every 10°C. increase in
temperature according to the Vant Hoff Law, until the protein itself may be
destroyed by it. We may well
expect many life processes to be interrupted long before the protein is
coagulated or changes are visible. Eggs incubated near 100°F. give a hatched
chick, but if they are held at a few degrees higher than that for even a short
period of time, the physiological processes are so disturbed that the normal
hatch of the healthy chicks does not result. The protein of the egg need not be
coagulated or even coddled to upset the process. Life processes in the plant
come under the same category as those within the egg. They deal with proteins
within the plant cell. They are concerned also with enzymes which encourage the
processes. These delicate catalytic combinations resembling the proteins in
many instances, fit into the same pattern of temperature requirements for
regular, normal life processes. Low
rainfall and accompanying irregular temperatures, then resulting in a drought
may be effects of the heat wave as well as of the shortage of the water.
In the ecological pattern of
plants distributed over the world starch production and its storage in the seed
occur under limited temperature ranges at certain physiological stages in the
plant's growth period. Corn grows for example in the temperate zone for high
starch output in the crop and at certain months within the year. Other seeds of
high starch delivery are seasonally located similarly. For starch producing
crops in the tropical zone those seem to be given to storage of this compound
in the roots or underground at lower temperatures. Seeds there seem to store
their reserve energy supplies as oil. Shall we not visualize the plant injury,
during a drought with the dry surface soil going to the higher temperatures, as
an effect of the excessive heat changing the physiology of the plant rather
than the effect of only a storage of water or this liquid nutrient?
Among the other
plant manifestations suggesting effects of drought by high temperatures rather
than by water shortage, there is the common change in a bluegrass lawn to one
of crab grass or other species, for example, when the lawn owners persist in
keeping their lawns watered during the hot summer months. Where the lawn is
dried and the bluegrass has disappeared in going dormant, this same grass
species comes back with the break in the drought, namely, with the rain again
and the lowered temperatures. Such is not the case of the watered lawn, shifted
by that watering treatment during the heat to a crab grass flora. That flora
persists and excludes the bluegrass during the rest of the season. A Bermuda
grass lawn is undisturbed by the drought which displaces the bluegrass. Bermuda
grass stays green during both the temperature and water shortage.
Observations
on Sanborn Field, Columbia, Missouri, under experimental soil studies since
1888, suggest that corn plants at a low level of physiological activity because
of low soil fertility were not visibly injured by either the water shortage or
the heat wave of the drought. But as more fertility, including nitrogen, raised
the levels and diversities of the plant's activities, the drought damage became
more severe. But this suggests itself as the result of the high temperature
damaging the plant parts commonly rich in nitrogen and most active in tissue
growth. The injury occurred in plant leaf parts where damages from nitrogen
deficiencies are commonly observed, but the appearance of the plant parts
injured was decidedly different than that exhibited under starvation of
nitrogen. This suggest the simple fact that vegetation doing little but the
elaboration of cellulosic mass is not subject to drought injury, but plants
elaborating compounds of much nutritional value for animals are injured by the
heat wave of the drought as well as by the soil's shortage of water.
As another
biological illustration of the drought, let us recall that the races of
pheasants introduced into the United States came from a range of conditions
quite unlike for example those in Missouri in which state the introduction of
this game bird have not been so successful. These birds lay their eggs and
incubate them too late in the season, or when the high temperatures we
experience in the early summer have an adverse effect on the hatch. With the
clutch of eggs on the ground, the soil temperatures rise too high and injure
the incubating processes guaranteeing a good hatch. For this biological
process, the "drought" damage results from the heat wave and not from
the deficit of water as drink.
As still
biological demonstration of the heat wave aspect of the drought of 1954, a
hatchery reported the death of many chicks, and of more mature chickens and
turkeys on its poultry farm during the high temperatures accompanying it.
Likewise in some of our experiments using rabbits for biological assay of the
differences in grains and forages resulting from soil treatments with different
trace elements, the first heat wave in late June and early July took over 70%
of the rabbits in one set of the feed arrangements while it took none of
another set. All the animals of these two sets were in the same room and
temperatures. This mounting of the fatalities of the one set was gradual and
persistent as the drought continued and the temperatures mounted in killing
even the replenishment of the dying stock from the adjoining surviving stock
moved to the fatal feed. When the high percentage of fatality on this dried
feed had been reached with eight deaths in one day of record heat, the assay
was terminated with a shift in ration emphasizing dried milk proteins. This
shift prohibited any further fatalities and stopped the disastrous effects by
the heat wave on these animals when considerable publicity of animal death by
drought was common.
A repeat
trial on the effects by the high temperatures on the rabbits, according to the
original ration increased to a grain mixture, duplicated the previous results.
This trial was carried on for only three weeks or until only 31% of fatalities
resulted during the succeeding heat wave. Here the deaths suggest themselves as
due to the high temperatures, but only when the poor nutrition suggests itself
as the route through which the high temperatures worked their damage. It also
casts reflection on the quality of the feed offered the public by some
hatcheries along with their baby chicks.
9.
Superficial
postmortems of crop failures blame the weather; accurate diagnoses point to the
soil as help to avert them
It is only
slowly that the factors in the agricultural production of our feeds and foods
are being tabulated and evaluated. For
too long a time has weather, especially rainfall as the supply of water for
plant growth, been the alibi for irregularities in crop yields.
"Drought" as a term including rain free periods of extended time has
now broken all past records and become a national disaster. As such it deserves
analysis of the problems it presents. Such analysis establishes the soil as a
major factor in determining the severity of the disturbances to the plant's
growth and reproductive processes by the water shortage and the high
temperatures through which the plant is injured under the composite of
conditions included in that term.
More soil
knowledge through research progress has now pointed to a better understanding
of the facts about soil water and the aspects through which some of the
injuries by drought can be mitigated. The
fertility of the soil as plant nutrition is decidedly significant in that respect.
Now that we are separating the nutrition of the plant by the soil from the
storage of water in it for the plant, the drought as water shortage is no
longer so much of an alibi. Rather drought is more a damage by deficient plant
nutrition. In soil management, which may include irrigation, the economy and
sound service to plant production demand that the supplying of the soil
fertility should be the first concern and the addition of water the second.
Analyses of
the problems of drought establish the fact that excessively high temperatures
per se as disturbers of the physiological functions of the plants, and even of
animals, are factors perhaps more lethal than the water shortage. Even when the high temperature is segregated
as a factor of damage, it is significant that this is increased by imbalanced
nutrition, or conversely, improved by proper nutrition.
Thus the
problem of drought damage moves itself into the lap of agriculture as a problem
either to be solved – at least in part – or tolerated with reduced disaster,
via the management of the soil for better nutrition of the plant and the
animals fed by means of it. In the case
of what we call "drought" we need to view them for possible
prevention or reduction of damage via the wiser management of the soils under
them.
-
Excerpted
from The Albrecht Papers – Vol. 1; 1954; [emphasis added].
No comments :
Post a Comment