CLIMATES AND MICRO-CLIMATES

New Zealand Listener, Volume 15, Issue 366, 28 June 1946, Page 16

CLIMATES AND MICRO-CLIMATES

(From a talk by DR.

I. G.

BLAIR

, broadcast by 3YA)

HAVE been told that rats in the tropics have unusually long tails; that beef-steak in Alabama is nutritively poor, while in Canada I saw farm horses wearing straw hats. These are among some of the facts of climate. Often, weather -the short-term feature of climate-is accepted merely as an _ inconvenient menace to week-end plans, while by Canterbury farmers last year it will be remembered by its devastating visitations, first as a tree-flattening gale, then as a wire-flattening snow storm, and finally | as crop-flattening hail. Nevertheless New Zealand’s climate is supposed to be the world’s most salubrious. To me personally Canada’s climate appealed more than our own and in its cycle one could note clearly its marked influence on national habit and charac-

ter. Canadians have six months of ice and snow at sub-zero temperatures, but with lambent sky and brilliant sunshine, and ‘tone-dry air. Spring there is not a lessening of rainfall and a gradual unfolding of growth. In Canada, spring arrives with a cracking and booming of ice on lake and river-with, overhead, dark lines of migratory birds winging it from the South. In a matter of days a tremendous thaw calls the nation to a new life and the snow-replenished earth receives a 90-day period of intense continental heat-no rain, no wind, so that spring-seeded corn grows 10ft. high in 90 days. You can see it move. That is a climate of extremes which has moulded a nation’s personality and character. Climate and Human Health Illnesses directly caused by climatic effects are rare, but you may be among those who have learned that it is possible to be snow-blinded in New Zea. land, to suffer frost-bite and mountain sickness in Canada, and to relapse under heat-stroke in tropic waters. But climate as expressed by rainfall, humidity, air pressure, and temperature mostly influences health by strengthening or weakening natural resistance. Here it works through diet and food. Or, on the other hand, climate encourages or inhibits the microbial causes of disease. Tropical climates cause a mental prostration, though sometimes it is more a cheerful lassitude-with which goes severe disease

of the microbial kind. It isn’t often realised, though, that in contrast cooler regions with less microbial or parasitic disease experience much greater incidence of heart disease, cancer, degenerative troubles — all associated with the violent, strenuous lives our temperate climates encourage us to lead. Crop Diseases My chief interest in climate, however, is its influence on crop diseases. Here are a few of the tendencies. Late or Irish Blight of potatoes is seasonal, but the effects of the disease have been determinants in human affairs. It can be demonstrated that the Irish famine, due to the blight of 100 years ago, initiated England’s age of economic expansionafter the repeal of the Corn Laws ostensibly for the purpose of bringing in cheap grain to feed the starving. Among other things a million Irish migrated. Now

the fungus which causes this potato disease is ever about us, but it goes hay-wire only when certain climatic factors assist. These factors are a little more precise than just "wet weather." Indeed a blight year is one of summer rainfall in excess of long term averages, coincident during that summer with short periods when mean air temperatures drop to about 50deg. F. while the crop remains wet. These factors encourage the fungus to multiply rapidly. It is important to know these climatic influences, for in -places where crop spraying has proved necessary, the time to spray can be forecast. Loose smut of wheat is unknown in the arid South Western States of the U.S.A. It is rarely severe in those parts of this country where air conditions are dry when wheat or barley is flowering-in Amuri County, for example, and Central Otago. "Too Much Wet" In recent years farmers have become convinced that there is something in the weather at the time of grass flowering which encourages ryegrass blind-seed disease. Some still say briefly "too much wet," but more precisely it can be shown that the interaction of temperature and air humidity at an earlier stage of crop development stimulates an increase of infective matter. In Southern U.S.A., or in Auckland, New Zealand, you cannot get good potato seed at all. The best (Continued on next page)

(continued from previous page) potato seed is produced in cold stofmv districts. In America, seed stocks’ come from Maine in the north-east. In Britain. Scottish seed is sought; in New Zealand, South Island lines. Why is this? Simplified, the answer is that where it is cold and windy the insect carriers of virus disease don’t thrive (they may not even exist). In the absence of these carriers virus disease or potato deterioration is so much less a major problem. Rust in cereals in North America was until a few years ago an intermittent harbinger of national calamity. In 1915 the spring-sown wheat crop in the U.S. alone amounted to 370 million bushels. In 1916 the same crop acreage produced 200 million bushels less. The decrease was attributable entirely to rust disease, initiated in epidemic form, when temperatures feil below 62deg. F. for a short period in July (North summer) when air humidity was high. We don’t know much about the socalled epidemiology of rust in New Zea-land-witness, for example, practically no rust in wheat this year; in others plenty. We grow rust susceptible varieties here. I am waiting for someone to go up in an aeroplane (as they do in North America) to make spore counts of infection in the air, in those years when westerly winds are unusually prolonged at a certain period of crop susceptibility. Australia suffers rust-little less than U.S.A. Possibly we get some of their surplus infection when the wind blows this way. Soil Climates So much for climate. You can’t do anything about it other than moan; so let’s pass on to a new concept-the micro-climate. Soil is more than "dirt"-it’s living, and the part microbes play in soil fertility processes should be understood

whether you are farmer, gardener, or vaguely philosophical. Organic matter’s the key whether you are a compost fanatic, a bio-dynamic farmer, a moonplanting backyard gardener, a soil conservationist, or just a farmer. Organic matter provides the working stimulus, the raw material. In breaking it down, microbes-the micro-population-create conditions, or supply materials, encoutaging new growth from and on the earth crust. This micro-population includes members, useful in organic matter decomposition, but detrimental in thet some of them (like two-legged forms of life) find parasitism an easy mode of existence. Soil fungi and bacteria thus often cause disease in crop plants--usually some form of root disease. Prevention of these troubles, therefore, requires ability to create soil conditions unfavourable for development of the disease producers. This means manipulating the micro-climate. Likewise, variations in the soil moisture element of micro-climate are reflected in differing disease outbreaks. High levels of moisture encourage such soil diseases as Club root, Potato scab, Pea wilt, Celery yellow, Lettuce collar rot. But when the micro-climate is dry, different groups of organisms predominate and diseases of low moisture adaptation occur such as Wheat Ball Smut, Oat and Barley covered smut. The issues have been over-simplified in some respects. But I have aimed to introduce to you some features of research studies on which extensive information on crop maladies is based. The climate above ground-the micro-climate within the soil-both influence working efficiency, health, disposition, and interrelationship of the creatures within the influence of the elements concerned. Farmers can’t do anything about climate, but many farming techniques are directly influencing soil micro-climates, with consequent results on plant growth.