276 MONTHLY WEATHER REVIEW.
The rrnp of 1910 was not raised without labor, anxiety, and loss. The loss waa doubtless more than it should have been. Whoever con- tributes to reducin the loss erfoms a work of value, we hold, not only to the fruit gmwertut to alfmankind. In past years there were certain losses due to what nlay be called natural causes, which were considered by fruit growers and fruit con- sumers as beyond the power of the rower to prevent. But of late, largely through the directive knowlesge of the ex erts of the Depart- ment of A 'culture and the ready acceptance oftheir work by the growers anfhppers. losses have been minimized or greatly decreased.
Passing over problems of loss due to high winds, or injury caused by drought on the one hand or excessive moisture on the other, also unfavorable weather at critical times, such, for example, as the warm spells during September in the apple belt of California, and all losses connected with low temperatures experienced by packed fruit while in transit, we come to one source of loss which in its way perhaps has caused greater damage than any other one condition, namely, frost. I t is quick in action, for the work of a year with its hoped-for rofita may be made valueless in a single night by frost. It is a conipyicated problem. calling for a knowled e not only of the lant and its condition hut a somewhat detailedtnowledge of the pgysics of the lower air and especiallv the method by which heat is P d , retained, or lost by plant surfaces. In many respects our know edge of these conditions is quite imperfect and we are working in the dark. Instninienta of sufficient sensitive- ness are not available, or at least have not been used, to get a complete and continuous record of the changes going on near the plant surface during cold winter nights and frosty spring mornings. Nor are the roblems connected with the condensation of the water vapor and the k k a t i o n of the frost crystals altogether simple. Indeed, the formation of what is called frost. i. e., the crystals of ice, is really preventive, heat bein given off in the solidification. Furthermore, a t a later period, wgen, under the influence of the heat of sunrise, the frost crystals melt, heat is required, and to some degree this prevents a too rapid warming up: and still further, when the frost has changed to water, there is stdl to be considered the latent heat of vaporization. Thie latter amount is, in round numbers, about 600 calories and the former quantity, or the latent heat of fusion of ice. about 80 calories. In ita efforts to devise adequate methods of protection against frost the Weather Bureau has for a period now extending over 15 years studied the problem from two viewpoints, and it can be said that a high degreeof successhaaresulted. The first phaseof the roblem naturally would be the giving of accurate warnings of inipen&n.g low tempera- ture. This is not an easy matter, and at the beginning of the frost campaign the forecaRts were somewhat uncertain. Persistent effort and constant vigilance have brought their reward, and I know it will pleaee this bod of practical men to hear that durin the winter of
190~10 in Caligrnia there waa not a single forecast of injurious frmt that waa not fully verified, and, what is still more satisfactory, there was not a single frost injurious to fruit occurring during that pericd that was not forecast. from 12 to 36 hours in advance. In other parts of the United States thie prnhlem of forecasting frost is being rapidly devel- oped and it seems likely that an equally high efficiency will be attained. The second line of action in connection with the protection of fruit frnm frost was to develo adequate ways and nieans for controlling the temperature. Takin tEe roblem broadly, two plans of action pre- sented themselves: first, t1e plant itself was to he 80 selected, bred, and developed as to offer aa far as possible the needed resistance to the low temperature; or, what is practically the same thing, to render the plant dormant and not sensitive durin6 the cold period. The other plan of action was to fight the cold and minimize exposure thereto by pro- ducin heat artificially durin the cold period. Unfer the first plan there f m been some work done in produring a
resistant stock; but in California. chiefly owin to the fact that extreme low tempemturea seldom occur and are of Aort duration, attention haa been 'ven mostly to the second method-i. e., preventing too great a f a f i n temperature and a too rapid rise in temperature after the lant tissue haa been chilled. There are a number of ways in whict this van be done, but the simplest method is to add heat to the lower air at the critical time to keep the plant and fruit, warm. This is beat done by burning fuel in various ways. either in a number of small fires, such as coal baskets, oil pots, orchard heaters, or small open 6rea. Within the last three years convenient form of orchard heaters have been devised, some burning coal and others burning oil. These are now in widespread use and have been successfully used in raising the temperature 5' or even more at critical tinies and have demonstrated their worth beyond future question. They have many
advantages, and if the expense is regarded in the light of an insurance premium the results have been moat satisfactory from a financial standpoint. Whether the actual use of fuel and combustion methods are the most economical of possible methods is an open question. It should have been stated that large fires are neither economical nor efficient, and
*
It is a constantly recurring source of danger.
FEBRUARY, 1911
the heat energy is largely misgBfied and practically wasted so far BR
the orchardist is concerned. it smaller fires, well distributed, there is leas of this heating up of all out-of-doors, as it has been called, and a more economical use of the fuel. Indeed, competition between the various makes of orchard heatera now on the market is keen in this matter of getting the best combustion and the highest efficiency. There are, however, other ways of obtaining heat, or rather utilizing natural conditions, and possibly in these will be found the ultimate frost protector of highest efficiency and lowest initial cost. aa well aa
coat of maintenance. If by any means we can conserve the heat of the afternoon hours, expending it gradually during the night hours and not at an extravagant rate, as is the case normally, we will be using the cheapest and cleanest of all fuels. One way to do this is to use a cover, trapping the earth heat and permitting a slow escape between the hours of midnight and sunrise. The plants themselves may be covered, which is an old, old method of rotecting against frost; but the labor item and the time required niiyitate against this ractice on a large wale. Long rolls of repared cloth, paper, or gurlap may be spread over the ground in t f e orchard about 3 o'clock in the afternoon. The ground under cover thus remains at a compara- tively high temperature. About midnight or some time thereafter the material may be rolled up and easily removed. It is also advisable that eand or loose earth be dusted over the cover or spread to a light depth. This is easily displaced in the process of rolling up the lengths of cover by siniply shaking these. This process secures a large amount of earth heat, 1. e.. second-hand sun heat, and sets it free at a time when the temperature is falling. In most cases the supply of heat will be sufficient to prevent critical temperatures before sunrise. I t should also be pointed out that a small amount of dirst in the lower air serves to prevent the usual rapid rate of loss by radiation. In fact, a certain amount of heat is reradiated. It is also possible. althou h as yet experimental evidence does not fully demonstrate this, t i a t slow convectional currents prevail in the lower air and the heat is thus more uniformly distributed. Another way is to employ some substance having, like water, a high specific heat and allow it to give up this heat slowly. In California experiments have been made with heated water, and there is no question about the eficienc r and cleanliness of the method. The expense haa been the chief oistacle to its widespread introduction Recent work by Weather Bureau officials in connection with 'the cranberry bogs of Wisconsin haa brought out the fact that the condi- tion of the soil with regard to what may be called cumulative low temperatures plays an important part. The ground being cold, frosts occlv in the marshes in Ma and early in June when the temperature of the air would not of itself cause frost. By cleaning, drainmg, and sanding damage by frost has been prevented. There waa found to be a close relation between daily maximum air temperature and soil temperature and also a close relation between soil temperature and the ensuing minimum. It must, however, be remarked that similar climatic conditions do not prevail in California, and other niethodR are more appropriate. If we use Rome good absorber of heat and can in any way connerve this heat, we have a longer period of comparative warmth and also can heat the lower air hy ronductioii or convection. A good radiator h e s heat rapidlv on quiet, clear nights, and the radiant heat does not warin the fruit. Finally. there is the method of mixing or Ntirring the air, which has not yet been utilized on a roninierrial scale. Frost is largely a problem of air drainage. As a result of many experiments i t is found that where there is a mixing of the air strata or where there is good ventilation there is less frost than where the air is quiet and stagnant. Every one is familiar with the fact that froRt does not occur on windy nights, which in a measure is the result of dryness, but also partly due to the fact that the layers of air are thoroughly mixed and whatever heat may exist at a moderate height above the ground is not confined to that height. Rnally. the most successful frost rotection may be a combination of the various devices now in use anaothers baaed upon the principles mentioned above.
STRAW AS PROTECTION AGAINST FROST.
By ALEXANDEB G. YCADIE.
The writer was recently appealed to for an opinion as
to whether a covering of straw would provide an effective wotection for young oats under i t a ainst injury by
and used as a cover woulcl certainly rotect. It appeared
the discoloration of the oats, which were found to be so
injured under the straw mulch. Moreover, it was found
that the straw had not been freshly spread, but remained
host. The answer was that straw sprea % over the ground
later that there was anot.her possib P e source of injury in
FEBRUARY, 19 11. MONTHLY *WEATHER REVIEW.
P
P
E
in place for quite a time. The problem therefore be-
comes a different one, for we are no lon er dealing with
late the same and also radiate it, but with a new con-
dition and practically a new top soil. Straw is an excel- lent radiator and would cool ra idly at night. More-
acquires only a partial quantity of the heat it would
receive if uncovered. rotective
4 p. m. or a little before sunset, and removed about sun-
rise or just before.
It was also pointed out that the copious de osit of frost upon the straw, claimed by one party in t R e con-
troversy to rove the existence of low temperature, did
In fact, a heavy deposit was evidence rather of much
water vapor resent near the ground or on the surface oft
the straw. estimating temperature fall by the amount of frost formed may lead to error. A rotten board, a
manure hea , or, as in this case, old straw more or less
damp absor E s moisture and holds it. If the substance
is a good radiator, there is a uick cooling and any mois-
the original soil and its capacity to absor B heat, accumu-
over, the soil beneath is screened P rom full insolation and
effect the straw should be spread daily, prefera \ ly about
not necessarr ? y measure the degree of fall in temperature.
It was pointed out that to get the best
ture near by will quickly con 1 ense on the chilled surface.
FROST ON LEAVES.
277
The moisture may come from the ground or from the substance or may be in the form of vapor in the lowest
air layer. Materials having a lower moisture content, although in proximity and similarly exposed, will show
less frost; i. e., the condensation wll be nothin like as
heavy on a gravel walk, for instance, as on an o P d.board
lyin across the walk. Tfere is needed in frost experimentation, in order to
properly explain such questions as the one proposed,
systematic records of temperature by sensitive resistance
thermometers at different heights and on different sur-
faces. Also there is needed, just as much as the tem- peratures, records of the actual amounts of water vapor
present, and these possibly could be obtained by the so-called saturation deficit recorders.
In the accompanyin )hotographs, made by Mr. 0. H.
in the frost experiments carried on at San Francisco, i t can be seen that the frost
on the upper or outermost the top grass frost does
that frost building
edge of a leaf than
Packer, who has cheer f1 u ly given his time and assistance
fJnder neat
to show both dew and frost in much greater quantity than elsewhere.
DISTRIBUTION OF FROST CRYSTALS ON LEAF.
(Photographs by 0. H. Paoker.)
278 MONTHLY WEATHER REVIEW. FEBRuAsr, 1911
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FROST ON unrroo A T SAI’I FRANCISCO, GAL.
(Photograph by 0. H. Packer.)