THE RELATION OF METEOROLOGY TO AGRICULTURE.

New Zealand Journal of Agriculture, Volume XXXIII, Issue 6, 20 December 1926, Page 381

THE RELATION OF METEOROLOGY TO AGRICULTURE.

R. B. Tennent,

N.D.D., Instructor in Agriculture, Dunedin.

LONG-TERM FORECASTS.

The greatest service that the science of meteorology could render -to agriculture would be the accurate forecasting of weather conditions for a fairly long period in advance. The value of such' long-term forecasts can be appreciated, allowing as they would an adequate opportunity for the agriculturist to alter or adjust his routine to suit the approaching weather conditions. Were such a service feasible the economic gain to the agricultural community of this Dominion would be immense. .

One realizes that, even with the existing short-term forecasts, great benefits would be obtained by agriculturists if more interest were taken and greater credence placed upon them. To-day meteorologists are in the position to render valuable assistance to farmers and collaborate with them with a view to obtaining better crops. The proper interpretation of prepared synoptic weather charts should make it possible to forecast the weather sufficiently early to enable possible injury to crops and stock to be greatly lessened. Although the day-to-day forecasts should apparently prove of value to New Zealand farmers, it has to be admitted that the shortness of the warning-period, coupled with the difficulty of obtaining prompt notice of weatherchanges in the average country district, renders such forecasts of little practical value. By long-time forecasts one does not necessarily infer predictions, say, one month ahead of the event. Such long predictions, of course, would be extremely desirable, -but in an insular country such as this, with its paucity of outlying observation stations, they may be regarded as being quite out of the question. Forecasts giving four or five days’ notice, widely and rapidly spread throughout the rural communities, and indicating on general broad lines the state of weather likely to be experienced, should be possible. The spread of radio broadcasting will doubtless assist in this respect.

SEASONAL CYCLES.

In rural New Zealand one hears in and out of season questions concerning the likelihood of a wet or dry summer, or a mild or severe winter. The farmer of to-day, carries out his work in a more or less routine manner. He sows in the spring with the full expectation and general realization of spring rains, followed by mild weather during the early summer, merging into a general dry period of midsummer, and concluded by the approaching autumn and frosty winter. Unconsciously he postulates a more or less regular season, and hopes that his crop from the time of germination will grow steadily and uninterruptedly to a successful harvest. Thus far he is thoroughly conversant with a more or less definite weather cycle, and all his plans and preparations are made in relation to that cycle. In the majority of years his anticipations are realized and his crops grow favourably, but at other times a bad season or run of seasons is experienced, which greatly offsets the previous beneficial ones.

The anticipation of such seasons would undoubtedly be of great importance, and it should be the aim of the meteorologist to ascertain if a definite cycle of good and bad seasons exists in this country. At first sight it might appear impossible to make such an examination, on account of the comparatively short period of time over which meteorological observations have been made. An interesting attempt, however, was made by Douglas, who by an examination of the annual rings of the giant sequoias of California endeavoured to establish if a definite weather cycle existed in that country. It was naturally assumed that where the annual ring-growth was comparatively great a good season had resulted, and vice- versa. Douglas examined 45 sequoias, ranging from seven hundred to two thousand years old. A correlation of growth with rainfall was recorded, this being greatest when a period of three years was taken with trees growing in dry situations, and with a period of ten years for trees in a wet situation. Already in New Zealand some preliminary work in this direction has. been carried out by Dr. L. Cockayne, in connection with ecological problems, on the beech forests of .Westland.

If sufficient statistics of the wheat-yields of Canterbury were available, these, correlated with existing rainfall records and other weather elements, might reveal some such cycle. The system hitherto generally adopted for making weather forecasts appears to have been essentially based on the statistical examination of meteorological data collected at various stations. It is interesting to note that many scientists have endeavoured to establish some connection between the variation in the frequency of sun-spots and the variations in certain terrestrial meteorological phenomena. It would appear essential, if an attempt is to be made in the distant future to correlate crop-yields with weather conditions with a view to investigating a probable cycle of seasons, that typical crop statistics should be taken in close proximity to each station from a few adjacent farms in order to reduce probable error. ‘ .

CROP PREDICTIONS. . - . A wide scope lies before meteorologists in predicting the probable yields of different crops from a knowledge of the weather conditions

of the preceding autumn. Sir Napier Shaw in 1905 asserted that the average wheat-yield of England, in five seasons out of six, could be predicted with a . certain degree of accuracy. When 39-5 bushels per acre was taken as the mean maximum yield, and a deduction of 1-25 bushels per acre made for each inch of rain which fell during the preceding autumn, a close approximation to the average wheat crop for the .year could be obtained. . It is interesting to speculate on the possibility of the meteorologist forecasting, say, the probable yield of turnips in Southland from a compilation of data- in regard to frost intensity, rainfall, &c., having correlated such data with the optimum conditions for aphides, the organisms of club-root or dry-rot and other parasites of this crop. There would appear to be no adequate reason why research on such lines should not be carried out, but it is opportune to here state that the services of a specialist in agriculture in addition to meteorology are essential. What would appear, therefore, to be necessary in New Zealand is an agricultural meteorologist. A meteorologist himself could not deal with the agricultural side of the question, neither could he cope with it from a botanical, biological, zoological, or chemical standpoint. Agricultural meteorology is a definite branch of agricultural science, but so far is unrecognized in this country. The agriculturist must indicate the direction the work has to take and point out the object aimed at. The meteorologist must use every means at his disposal to attain this object, and having apparently accomplished this the co-operation of both is essential in order to guarantee the correctness of conclusions arrived at. - ’

AGRICULTURAL ZONES.

The . agriculturist is concerned with the propagating of crops. His one aim is to understand the physiological conditions governing their growth, their reaction to environment, and their optimum growing factors. Many climatic - factors, such as rainfall, sunshine, frost, &c., have a direct .influence on the type of plant which may inhabit a particular locality. Thus we know that certain forms of vegetation will be prevalent in excessively wet districts, and that distinct vegetation will exist in arid districts. In other words, there are undoubtedly in New Zealand definite vegetation zones, which are more or less defined by climatic conditions. Just as vegetation zones exist, so do agricultural zones. Certain agricultural crops grow exceedingly well in the northern part of the Dominion but do not grow well in the south. There may be wide zones or narrow zones according to the climatic adaptability of the plants under consideration, and it is here suggested that if sufficient meteorological data were obtainable from stations situated in suitable localities, definite agricultural zones would be formed by the correlation of climatic conditions with soil surveys and crop observations. Well-equipped stations under proper supervision should be established in suitable localities to afford such information. The . distribution of stations of observation in New Zealand appears to be exceedingly unequal.' The exposure of .recording-instruments seems to follow no general rule, the instruments being sometimes placed at the top of buildings and sometimes near the ground. There is an undue proportion of stations in the cities, and towns, and these are subjected to whatever peculiar conditions exist there. ' :

It would therefore appear that the meteorologist and agriculturist should formulate a chain of stations in desirable localities and in sufficient number to provide the necessary data for the solution of many agricultural problems. Wherever recording - stations are established absolute continuity of records should be aimed at, and frequent inspections of an advisory nature should be made of each station, with a view to remedying any defective instruments and more or less standardizing the methods of observation. To be of value observations must be exact, and if a high standard of efficiency in this respect is to be obtained the meteorological staff must periodically visit the observers. Where for some reason the site of the station has to be altered, this should be done without any break occurring in the records, and the new site should certainly be in close proximity to the old one if the continuity of records over a long period is to be of value. Government experimental farms would appear to be ideal situations for well-equipped stations, on account of the staff available to carry out the recordingwork, the value of such records in experimental farming, and the permanency of the farms themselves. The equipment of such stations and tabulating of data are of great importance, and it is intended herewith to deal with a few of the most important features in this connection.

RAINFALL.

The importance of rainfall upon the growth of plants is sufficiently great to warrant the careful study of this climatic factor. It is to be remembered, however, that since rainfall is so remote from being the immediate environmental condition controlling the water-supply to plants in nature the measurement of this climatic condition must not be regarded as being of great value in regard to plant activity or distribution. The rainfall records at present taken at . the majority of stations are by means of an ordinary rain-gauge which collects any rain that may have been precipitated during the day. This method of recording rainfall loses much value from the fact that no indication is given in regard to the intensity of the fall. It would appear, therefore, that in so far as the research agriculturist is concerned greater value of records could be obtained by the installation of self-recording pluviometers. It seems, further, that a better interpretation of the possible effect of a recorded fall could be deduced by a study of the charts recording the rain which had been precipitated during the previous twenty-four hours. This would also eliminate the . arbitrary period at present in vogue—namely, 9 a.m. on one day to 9 a.m. on the following day.

EVAPORATION.

Hand-in-hand with rainfall must be considered evaporation. This climatic factor appears to be neglected, but it is inconceivable to carry out a proper study of climatic factors in relation to agriculture without giving due consideration to the rate of evaporation existing in different districts. From a rainfall point of view one district may appear to be “ wetter ” than another. That is, there would apparently, from rainfall records, be more moisture in the soil for —postulating the same water-holding capacity for the soil in both localities. If, however, the relation of rainfall to evaporation is studied for any two districts under discussion it might readily happen that the so-called “ wetter ” district

was, from the point of view of vegetation, much drier on account of the greater rate of evaporation taking place there. The rate of evaporation can quite easily and cheaply be recorded from a free surface of water, in a manner similar to that used at the Galloway Irrigation Farm in Central Otago. Unfortunately, there is no direct method of deducing the rate of evaporation of soil-moisture from the results of evaporation from a free surface of water ; but, even so, the results of observations of the latter would be of immense help in aiming at conclusions as to the adaptability or otherwise of certain plants and fungi in different localities. Further, the study of the rate of transpiration by plants would be greatly facilitated, especially in those portions of New Zealand requiring irrigation.. It seems surprising that in New Zealand so little has been done in recording evaporation-rates. To obtain data bearing on atmospheric evaporating-power it is only necessary to operate a number of atmometers of the same kind in various climatic districts, being sure that all have similar local exposure. The importance of this condition to plant and animal life, and the relative ease with which it may be measured, warrants earnest consideration being given to the future recording of this climatic feature. Were such data available the ratio of precipitation to evaporation as an index to the external-moisture relation of plants could be ascertained.

WIND.

As a climatic condition that assuredly influences the rate of transpiration from plants and of soil evaporation, and, further, from its often undesirable effect on live-stock and highly specialized crops such as fruit, average wind-velocity, with maximum velocity and duration and also directional origin, should be . recorded. Ecologists as well as agriculturists would welcome reliable information in this regard.

SOLAR RADIATION.

The importance of recording hours of sunshine and intensity need not be stressed. It is to be emphasized that the few sunshine-recorders now in this country give but little information .as to the intensity of the sunshine itself. They record the duration aspect of that range of intensities which is' called direct sunshine, and any data which have been thus collected are consequently of limited value. The intensity of impinging radiation should be recorded, and a systematic attempt to carry out such recording should be put in hand. Beyond a certain intensity sunshine may have a negative effect upon vegetable growth, in that it induces closing of the stomata and partially suspends transpiration and respiration. Probably Livingstone’s radio-atmometer may prove to be the most convenient instrument for canying out records of this nature.

TEMPERATURE.

Data of maximum and minimum temperatures are of great value in deducing the frost-free period of the year, which is of the greatest importance to agriculturists. The frost-free periods of different districts, provided sufficient recording - stations were available, would be most valuable. The average dates of occurrence of the last frost in spring and the first in autumn would furnish a valuable index to

the approximate length of a temperature season of general plantactivity. The absolute temperature maxima and minima are also ■ valuable as intensity-indices. More information, however, is desirable in regard to (i) the length of the period of high daily normals, and (2) the length of the period of low daily normals. The value of the present available information from the 9 a.m. maximum and minimum temperatures lies in the fact that one can record with a certain degree of accuracy the accumulated temperature in hour-degrees above a chosen datumline, thus indicating the probable value of such degrees to plant-develop-ment. Taking 68° F. as the critical normal daily mean temperature, and 32 0 F. also as the critical normal daily mean, one would naturally value information from an adequate number of stations in New Zealand of the length of period with normal daily mean temperature of 68° F. or above, and of the length of period with similar means of 32 0 F. or below, within, the year. ' Soil-temperatures would also be of value, but the recording of such may be regarded as impracticable on account of the difficulty of establishing a unit of measurement in view of the variation induced by the nature of the soil itself and its situation:

AIR-HUMIDITY.

The usual method of obtaining data in regard to relative airhumidity in New Zealand is by the wet- and dry-bulb thermometers. Relative air-humidity, however, is no direct indication of the absolute amount of moisture in the air, and it is the latter information that is required by agriculturists. Consideration should be given to the fact that as the temperature is lowered the capacity of the air to retain moisture is decreased ; and hence it follows, where two stations record the same average percentage of relative humidity but different mean temperatures, that station having the higher mean temperature will have the greater amount of moisture. Air-humidity is of great importance to the farmer. It not only affects the rate of transpiration from plants, but is a deciding factor in the prevalence or otherwise of various parasitic fungi affecting crops. Certain districts in New Zealand are practically free from certain • plant-diseases, and it is probably not far from the mark to infer that the relatively low humidity of the air in those districts < accounts for such freedom. Mycologists would welcome fuller records of not only the relative humidity of different districts, but also the average humidity of the day.

CONCLUSION.

In conclusion, the following thoughtful statement of Livingstone and Shove (“ The Distribution of Vegetation in the United States as related to Climatic Conditions ”) may be quoted: “ Climatological methods and climatological interpretations, as so far developed, are woefully inadequate for the solution of problems dealing with the control of plant-distribution. From the standpoint of ecology and agriculture no great progress is to be expected until much more attention is given to the devising of new methods for obtaining the climatic records and new methods of interpreting these records, and until a new point of view is reached different in many respects from that hitherto held by workers in climatology.”