Appendix B: Compost Making in Rhodesia
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APPENDIX B COMPOST MAKING IN RHODESIA BY J. M. MOUBRAY IN 1939, when I last wrote a few notes for An Agricultural Testament, compost making in Rhodesia was in its infancy. Now it has become general. The usual procedure now adopted is to break down the vegetable wastes by spreading them in stock-yards or pens. Here they absorb and get well mixed with the animal wastes both solid and liquid, and are then removed to the compost heaps. In this part of the country growth is very rank. When tall grass and reeds were moved straight to the compost heap, the stems took a considerable time to break down, but by being first trampled down the stems are broken and the fungi and bacteria are then able to attack both from the inside and outside at once. In the five years that have passed since 1939 little change in procedure has taken place with the exception of passing all raw material through the stock-yards. I still build the heaps some fifteen feet wide and three feet high and up to any length (Plate XII). Two turnings are sufficient and at the end of three months the breakdown is complete. In the dry weather, if the heaps are fairly moist when built, a good wetting with the hose-pipe each time the heaps are turned is sufficient (Plate XIII). Material from the outside of the heap is always turned inside. I cut a good deal more hay than I used to do and if some of this is a bit coarse or gets a wetting, it does not matter, as what the cattle do not eat goes to the compost heap. Our veldt is improving with mowing, as when the coarse grasses are kept down and in check the finer and more valuable grasses get a better chance to develop. We are learning that under conditions in many parts of Mashonaland nitrification is very rapid. Under favourable moisture conditions a green crop ploughed in leaves little visible organic matter at the end of three months. Partly for this reason, if the compost is not quite broken down when applied to land for crops like maize, we get better results. The nitrogen content of compost has been found to be quite stable. I have found the loss of nitrogen in a heap which has stood for some months in the dry weather to be negligible. Mr. van Vuren, who has done so much in the Union of South Africa for municipal compost, has found much the same to happen with him. I now spread out some of my compost in a thin layer. In the hot sun this gets quite dry in a day or two. I then grind it in a hammer mill, sack it, and it can be kept in such a manner for an indefinite period. In this way it has probably lost some 40 per cent of its moisture content and is so correspondingly richer in humus. If, instead of broadcasting rough compost, a cupful of the ground material is applied round the plant in the field for such crops as tobacco or tomatoes, a considerable economy is effected. I add ground raw rock phosphate to all my compost heaps. It is probable that some of the inorganic phosphorus is changed during the fermentation into organic forms. If this is so, and some of the best American opinion considers such a change takes place, it is all to the good, as in its organic forms phospohorus is not locked up and so made unavailable to the plant, as it does not combine with iron and alumina. As regards cost of making compost, assuming that bedding of some sort has to be provided for the stock-yards and that the work of cutting and carting such bedding is debited against the stock account, then I think most farmers in this part of the world will agree that a sum of Is. or 2s. per ton will cover the cost of compost making. That is, of course, apart from the cost of raw rock phosphate or similar material added to the heap. The effect of compost on fruits, vegetables. and field crops in Rhodesia is now so well known that further propaganda is unnecessary. A neighbouring farmer, to give one example. used it on bananas and found that in two seasons he not only doubled the size of the bananas. but doubled the numbers held in the bunch...


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