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ORGANIC WASTE MATTER

Plant and animal waste products contain all the essential constituents of plants, and help perform all the necessary col­lateral functions. Every garden soil will be improved by them; very light and very heavy soils cannot be rendered fertile and of good tilth without them. Their actual amount of plant food is very small in proportion to their bulk, but the amount of mineral food needed by plants is also very small, and the bulk improves the physical condition of the soil. Organic foods are rendered soluble by soil action, slowly, and over a long period.

After millenniums of soil husbandry, chemists began to in­vestigate animal tissues, plant tissues, soils, animal excreta, air, tap-water and sunlight-all factors in plant feeding. Although soil-derived food comprises so small a part of plant ash, it does not mean that any one of its component elements is unimportant. So far at least nineteen elements have been found in the tissues of a healthy rose plant. Next in order of quantity to carbon, oxygen, and hydrogen come nitrogen, potassium, sulphur, calcium, magnesium, phosphorus, iron, manganese, boron, zinc, copper, and others in merest traces, yet of vital importance. Any of these so-called "trace elements" should be added under only expert guidance; a slight excess of any one of them will kill plants. Most organic manures contain them in sufficient quantity.

Thousands of skilful gardeners rely solely on organic fer­tilizers, and their long-range results are much better than those who use only inorganic chemicals as manures, even though these men may prove, by analysis, that two or three pounds of chemicals, mixed in balanced proportions, contain as much plant food as a dray-load of animal manure or compost. After all, our forefathers had none of these compounds available, but they grew excellent crops of all kinds. Today, we can produce greater quantities of products from the land, in shorter spaces of time, by using chemical manures. We do not need, now, to allow long resting periods for the soil between crops, but these methods of intensive cultivation will ruin the soil quickly, if we do not incorporate large quantities of organic matter from time to time. This is necessary in order to maintain good physical conditions of the soil, its moisture-retaining powers, «nd its aeration. Chemical fertilizers decrease all of these pro­perties, and decrease plant resistance to disease, but, used sparingly, they are a wonderful adjunct to organic manures. In fact, many organic manures produce starvation for one or more elements, and need to be supplemented appropriately. For example, vegetable matter should never be used without the application of a rich nitrogenous manure a couple of weeks later.

With ever-decreasing available supplies of horse and cow manure, gardeners should think of green manuring. Rose plants do not grow very actively from late April to mid August, and during that time a crop of Cape barley or Algerian oats could be grown between them. It will look untidy, but will keep the surface layers of the bed from setting hard, will help to keep the beds from becoming sodden, and will retain plant foods in the surface-soil. It will also provide excellent vege­table waste matter. Legumes, such as peas, beans, or red clover could be used, for their roots go deeper into the soil and so increase aeration, but they are more subject to disease than the barley or oats. Any mulching adds organic matter.

As the presence of humus increases the amount of available plant food, the concentration of nutrients in solution in soil moisture greatly increases unless watering is increased too. For this reason plants wilt quickly in rich soil unless well watered. The moisture-holding capacity of a soil is increased by the incorporation of organic matter.

Frequently, but erroneously, it is stated that a heavy sub­soil will ensure continuous replenishment of water to lighter surface soil superimposed upon it. The suction or attraction for water is greater in the fine interstices of clay than in coarse soil. If the roots cannot penetrate sufficiently deeply, the plant will wilt despite the presence of adequate moisture near at hand-Addition of heavy loam to light surface soil will increase water-retaining powers and may even help to raise some water from more sandy lower levels. In addition, there would be better conservation of plant foods, especially potash. Adsorp­tion of dissolved mineral salts on soil particles renders the soil moisture that drains away much lower in concentration of those salts than the moisture in surface levels. Flower-pots adsorb mineral nutrients in this same way, and that is why plants send their roots towards the pot itself rather than massing them in the inner soil.

Insufficient available water-supply can be largely counter­balanced by mulching. With the exception of some of the hill and coastal areas, evaporation greatly exceeds rainfall at most times of the year in Australia.