PRESERVATION of health rather than prevention of disease should be the aim of those concerned with stock, pointed out the Chief Veterinary Surgeon of the Department of Agriculture in a lecture delivered before the Institute of Stock Inspectors. It might seem a fine distinction in terms, but health preservation took the matter of disease prevention further back. Disease prevention was too often not attempted until disease had appeared, whereas health preservation stressed the idea of preventing disease appearing at all. Especially was such action possible in connection with conditions due to food deficiency and malnutrition.
The speaker referred to the wide need for greater attention to questions of feeding, and the serious effect of insufficient or unsatisfactory feed on the health and productivity of stock. The veterinary officers and inspectors of the Department had been asked to consider existing conditions in this respect very seriously, and their comments had been invited. Some of these were very illuminating. On the subject of mineral deficiency as the result of continuous grazing without my attempt to replace what was taken out of the land, the report of the Stock Inspector in the Armidale district was quoted.
The writer referred to the decreased sheep-carrying capacity of pastures in that district as compared with thirty years ago, and deprecated strongly what was called "highly improving" grazing land by the general denudation of green timber. This, in his opinion, constituted the main cause of a decreased carrying capacity of land, and in the next twenty years, he considered, the fact would be generally realised and sylviculture would be adopted. The result of "ringing out" heavily timbered good sheep country was that, provided normal seasons prevailed and area was not over-stocked, the feed increased in abundance. After ten years the timber was stacked, burnt off, and the area cleared. Between fifteen and twenty years after being ringbarked, during which period the area had been continually grazed, indications of a falling off in the body of feed became evident, and the grazing capacity during normal years now commenced gradually to diminish. Only by giving the area a good spell to allow for seeding, a practice by no means general amongst graziers, could the pastures recover temporarily.
At first the country was rich in natural manurial elements acquired from decaying vegetable matter in the leaves, bark, and wood. As the area was opened up and grazed over, these elements gradually (after a period of fifteen to twenty years, perhaps longer) became consumed or removed by grasses, winds, and rains. Only in gullies, where the humus had accumulated for centuries, was their presence evident in a luxuriant growth of feed. The hills in summer produced a short shoot, which, unable to survive the heat and winds, burnt off, leaving bare slopes, because these "highly improved" ridges had lost the natural fertilising agents provided by decaying vegetable matter from the timber. His observations had proved to him that the grasses were much superior on country on which the dead timber was left to rot and thus provide a manural substance than on country where the timber had been burnt off.
One aspect of the reduced sheep-carrying capacity of pastures during the last thirty or forty years had perhaps been overlooked—he referred to the greatly improved wool-yielding capacity of the sheep, which had been advanced from about 5 lb. to perhaps double that quantity. From their knowledge of sheep and wool it was recognised that the sheep producing the modern fleece required more of an improved feed to the old type producing a 5-lb. fleece. Consequently, country which carried 1000 sheep of the old type thirty years ago was now capable of grazing only perhaps 750 of modern type. The result of the increased wool produce must be an increased demand from the soil. The manurial elements passed from the animal were incapable of compensating the soil for the mineral food extracted through grazing, and as a consequence the soil, gradually denuded of its natural fertiliser and after years of grazing, produced feed which was deficient in the more essential mineral ingredients necessary to produce or sustain healthy animal life.
To combat disease by the preservation of health or to win back a general healthy condition of our flocks was undoubtedly only to be attained by returning to the soil that which we had for years been extracting in producing wool and carcase. The era was not far distant when pastoralists in general would recognise the necessity of cultivation as the direct means of preserving the health of the stock. Messrs. Gatenby and Horsfall of the Forbes district had proved this during the 1902 drought by obtaining remarkably favorable results with sheep on cultivated areas assisted by irrigation. Messrs. H. White, of Bald Blair, and L. Dutton, of Urandangie, Guyra, had for years adopted the scheme of cultivating grazing areas. The condition of their stock and holdings should convert the most prejudiced person.
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In some districts which had been more recently developed the truth of the foregoing observations might not be recognised, commented the lecturer. Those districts were approaching or were at the peak; they were still living on the reserves of food material stored up in the soil through unknown periods of time during which the demand on the soil was practically nil. When that reserve became exhausted they would begin to go downhill, and the result would be malnutrition and ill-health in the stock. The thing was a mathematical certainty. The length of time before such a tendency was exhibited would depend on the original richness of the soil.
Now was the time to take action in districts which were not yet suffering. By doing so a vast amount of future disease would be prevented. As regards those districts which were already on the down grade, steady and constant work would be necessary to bring them back to such a level that they would satisfactorily maintain healthy stock.
Cases constantly came under notice where even alluvial soils, ordinarily rich in all plant-foods and minerals, had owing to long periods of cultivation and grazing, without any attempt to carry out manuring, become poor in certain plant foods and definitely deficient in minerals. This mineral deficiency was widely noticeable and was by no means confined to the coast. It was perhaps less apparent in many of the wheat districts than elsewhere because the manuring of crops was not without some residual value.
Every farmer is now familiar with the group of plants known as legumes (so called because their "fruit" which contains the seeds is a legume or pod). These plants are of the highest value and possess characteristics that distinguish them from all others, notably the high protein content of their seed, the excellent feeding value of their whole vegetative system, and their capacity for storing nitrogen in their roots and thereby leaving the soil actually enriched in that important item of plant-food.
In New South Wales legumes are grown for various purposes: Lucerne for hay and grazing, clovers as an important constituent of pasture mixtures, field peas, vetches, cowpeas for green fodder and hay, and also for green manuring and soil renovation, and garden peas and beans for the vegetable market and home use. Their place in our farm practice, indeed, is even larger than might be apparent at first sight, for the "herbage" that springs so abundantly on wheat lands when these are "left out," and that is so highly esteemed as pasture, consists largely of trefoils, which are as much legumes as lucerne or clover.
The secret of the value of these plants to the farmer is the possession of a source of plant-food that is not accessible to most other plants, particularly not to cereals. The practical experience of hundreds of years led farmers of past generations to believe that leguminous crops possessed some peculiar power of making succeeding crops grow better, and it was not till the last twenty-five or thirty years that this could be explained. It is now known that association with certain bacteria in the soil enables legumes to make use of the air in a way that other plants cannot.
This association is one of mutual helpfulness, of symbiosis, the bacteria requiring considerable quantities of certain kinds of food that are generously supplied in the plant juices of legumes, while the plants derive from the bacteria, in some way not yet fully understood, a supply of nitrogen that the bacteria have taken from the air and built into nitrogen compounds within their own cells. It is supposed that the nitrogen compounds thus manufactured by the bacteria are diffused through the cell walls and absorbed into the general circulation of the plants, where they are used for the building up of the protein compounds that are characteristic of the legumes in whatever form they are considered.
The presence of these bacteria is indicated by the development on the roots of the little growths now universally known as "nodules." These little swellings vary from the size of a small pea, and they may sometimes be seen by carefully digging up a plant with as many of the small roots as possible and then washing away the earth in a gentle stream of water.
There is unfortunately an impression amongst farmers that if the leguminous crop is removed from the land and the roots with their nodules remain, the soil is thereby enriched in nitrogen. It must be clearly understood that the nitrogen taken from the air by the organisms does not exist in the nodules, but is made use of and distributed throughout the plant, and that the removal of the above ground portion of the plant from the land means the removal of a large amount of nitrogen. An increase in the nitrogen content of the soil can only result from the growing of leguminous crops when they are fed off, ploughed in, or soiled to stock, and the resultant manure from the stock returned to the soil.