Изображения страниц

carbonate of lime be present. The amount of lime present in the samples examined has varied greatly from the merest trace to as high as 30 per cent. in some limestone soils. But, except on limestone outcrops, the soils are, as a rule, very low in this constituent. The average of all the 168 samples gives 0.81 per cent. of lime, but, as already stated, this includes several samples, consisting largely of powdered limestone. Taking 0.25 as a standard, there were 70 samples containing more than this, and 98 containing less.

The average of the 70 is 1.86, that of the 98 only 0.093 per cent. In many cases less than 0.05 per cent. of total lime was found. There can be little doubt that the application of lime in small dressings to many of our soils would be attended with a great increase in fertility.

The needs of our Transvaal soils, generally, then, are organic matter (humus), combined nitrogen, phosphates, and lime. It is of interest and importance to consider how these needs may þe supplied by the natural resources of the country. Before doing so, however, it will be advisable to briefly discuss the form in which these constituents may be applied to the soil. Organic matter, present in the very complex and indefinite form known as humus, is in the great majority of our soils, very deficient in amount. Its amount may be increased by the addition of bulky animal or vegetable matter. Stable or kraal manure, if available, is undoubtedly one of the cheapest and best manures for this purpose, especially as it also supplies small quantities of all the constituents needed by a soil. But in this Colony the quantity available in any one locality is very limited, and the cost of transport is too high to allow of its being brought from a distance. The amount of organic matter in such substances as guano and bats' guano is too small to allow of these substances having much influence directly upon the amount of humus in the soil, though they have great value as true manures. The organic matter may, however, be very greatly increased by the practice of green manuring. By growing any crop on land and plowing it in, before it seeds, a large addition of carbonaceous matter obtained by the crop from the air is added to the soil, and may greatly improve it by increasing its water-retaining powers, and in

other ways.

If the crop chosen be a leguminous one, an additional advantage is gained by the addition to the soil of the nitrogenous matter contained in the crop, which has been obtained mainly from the nitrogen of the air. In many of our soils, the micro-organisms necessary to effect this absorption of free nitrogen in the root tubercles of many leguminosa are already present, but, in any case, their presence may be insured by inoculation of the seed before sowing, with cultures of the specific organisms.

This is a plan which might with great advantage be adopted on many of our soils, but it must be remembered that the other necessary constituents, phosphates, potash, and lime, must already be present in sufficient amount to allow of a luxurious growth of the leguminous crops. or the advantage gained will be small.


may be applied in the form of complex organic compounds, such as are present in animal and vegetable matter, as already described ; in the form of ammonium compounds, or, lastly, in the form of nitrates. Organic nitrogenous substances are contained in kraal manure, guano, various oil cakes, human excreta, animal matter of all kinds, blood, offal from butchers, bones, and similar refuse. Before such substances can be utilised by plants, it is necessary, as already stated, that they undergo the process of nitrification, and therefore that the soil contain some carbonate of lime. Ammonium salts, e.g., sulphate of ammonia, have also to be nitrified before they can be absorbed into the plant. Moreover, the acid of the ammonium compound has to be combined with some base from the soil, so that with these manures, the presence of much carbonate of lime in the soil is essential.

Nitrates, on the other hand, are directly assimilated, and have not to undergo any previous change. They, however, are not retained by the soil, as are ammonium salts and most other manures, and therefore should not be applied until the plant is well rooted and can absorb them.




This may be applied in three forms.

As tricalcium phosphate, e.g., in bones.

As acid calcium phosphate, e.g., in superphosphate. 3. As tetra-calcium phosphate, e.g., in basic slag.

The first has the disadvantage of being insoluble in water, therefore difficult to distribute through the soil. It is slow in its action, as it is only absorbed by the plant after it has come into solution in the soil water by action of carbonic and other acids produced by chemical changes in the soil or plant. The second form of phosphatic manure has the advantage of being easily soluble in water, and therefore quickly distributes itself throughout the soil. It is, however, soon converted by the calcium carbonate into the first form. Nevertheless it is readily available to the plant, because of its fine state of sub-division and good distribution throughout the soil. This form of phosphatic manure can only be used successfully on soils containing a fair amount of carbonate of lime. The third form of phosphatic manure, though insoluble in water, is much more readily soluble in saline solution than the first, and, if applied in a sufficiently fine state of sub-division, is rapidly assimilated by plants. Basic slag contains free lime, in addition to its tetra-calcium phosphate, and is especially suited to soils poor in lime.

It gives excellent results on soils rich in organic matter, probably because the free lime in it promotes nitrification, while the vegetable acids resulting from the decay of the organic matter aid in the solution of the phosphoric acid.


This, which is so much needed in most of our soils, is actually useful in the form of carbonate. The best effect, however, is produced by the application of the oxide or hydroxide (quick lime or slaked lime), because these substances, being soluble in the water of the soil, are disseminated far more thoroughly than would be possible with even the most finely-divided carbonate of lime. After addition to the soil they are gradually converted by absorption of carbon dioxide into carbonate, but not until their distribution by virtue of their solubility in water has been effected. So long as the lime remains in the caustic or alkaline state, the soil is not fitted for the growth of plants. Hence lime containing much magnesia (which absorbs carbon dioxide much more slowly than lime), such as results from burning magnesian limestone, is not suited for agricultural purposes.



-COMBINED NITROGEN. A. Nitrogenous Organic Matter. As sources of this valuable substance the Colony has, like all inhabited countries, the excrements of domestic animals and of the human inhabitants, but the quantity of this material is limited, and at present inadequate to supply the needs of the soil. Kraal manure, bucket refuse from towns, waste portions of animal carcasses, and such refuse, should all be carefully utilised on the land, as they contain valuable quantities of combined nitrogen, as well as phosphates, potash and lime. Also valuable for the same reasons are the enormous cave deposits found in many limestone districts. Many of these deposits have been examined in our laboratories, and, while they have proved to be extremely variable in composition, there is no doubt that they form a valuable manurial asset. Some of the more recent deposits are very rich in nitrogen, Specimens containing as much as 9.7 per cent. of nitrogen have come under our notice, but much of the material found in the caves consists largely of fine silt, containing but little fertilising matter. Bones of animals, and excreta of wolves and other animals occur in many of the caves, and thus increase the phosphatic value of the deposits considerably and the nitrogenous value slightly.

The excrement of vultures, which occurs in considerable quantities near the nesting-places of the birds, is exceedingly rich in nitrogen. A specimen examined in our laboratories, obtained from the Orange River Colony, was found to contain about 25 per cent. of nitrogen, and to have a value, when compared with the cost of artificial manures at the coast, of about £,17 per ton.

Another product which might be utilised as a nitrogenous manure in this Colony is the locust. In the Transvaal during the past winter locusts have been only too abundant, and I would certainly recommend that farmers should endeavour to utilise them, especially as this would tend to diminish their number. Though they could probably be more profitably employed as food for pigs, poultry, etc., they have considerable value as manure. If they were collected in sacks by natives--easily done at night or in the early morning on their roosting-places-killed by being dipped into boiling water, and then dried in the sun, they could be ground in any ordinary mill. The powder thus formed, if not utilised as food, would form an exceedingly valuable manure. The product from the adult brown locust was examined recently by the writer, and was found to contain 9.5 per cent. of nitrogen, 0.28 per cent. of lime, and 1.59 per cent. of phosphoric acid. Compared with prices of artificial manures at the coast, ground locusts would thus have a fertilising value of about £7 10/- per ton.

It is true that they would probably be somewhat slow in their action as a manure, but they would undoubtedly contribute largely to the fertility of the soil to which they were applied, while the advantage to the country at large resulting from their destruction during the breeding season would be undoubted.

Still another product, possessing value as a local source of nitrogen (and other manurial substances) is the material composing ant-heaps. These are abundant enough in many districts, and when crushed afford a fine-grained soil which is much richer in nitrogen than the soil of the surrounding veld, and could be used with advantage for seed-beds for nurseries and gardens. This plan has been practised by several farmers and others in the Transvaal with great success, and it might be much more largely adopted.

A specimen of such material from an ant-heap, and another of the soil taken three feet away, near Christiana, were examined by the writer, with the following results :

Ant heap.

Veld soil. Stones retained by 3 mm sieve



[blocks in formation]

The superiority of the ant-heap material in organic matter, nitrogen, and " available" potash and phosphoric acid over the veld soil shows that it might be used with great advantage on poor soils, though, of course, it is not worth transporting any distance. Probably their fine texture and somewhat coherent character would render antheaps too close and impervious to yield a good soil by themselves, but by mixing them with a sandy soil this could readily be remedied.

B. Ammonium Salts. These, which are in Europe produced as bye-products in the distillation of coal and shale, are not made in any quantity here. Very little coal is used for gas-making, so that the amount of ammonium salts produced in the Colony must be insignificant. Moreover, in the case of many of our soils, deficient as they are in lime, these substances would not be very suitable unless a dressing of lime were previously applied.

C. Nitrates. Unfortunately few authentic cases of the occurence of nitrate deposits are known in the Transvaal. I have had several saline deposits sent from various localities for examination, in the hope that they would be found to consist largely of nitrate of soda or potash, but none have been found to be of any value.

A deposit was reported to have been discovered in the Zoutpansberg about a year ago, but I have not been able to obtain any information concerning it. I am told that many of the older farmers in the Colony speak of “saltpetre” occurring in crystals on stones in the .

” neighbourhood of pans, but I have not been able to ascertain whether the substance so called is ever really saltpetre, i.e., potassium nitrate. If such deposits do occur, it is very important, since nitrate of potash or soda would be of immense service in agriculture, provided its price were reasonable. The cost of the imported South American product is very high in this country on account of freight and transport charges.

At present, unless the farmer is willing to pay the very high prices for imported nitrate of soda or sulphate of ammonia, he must chiefly depend for nitrogenous manuring upon organic matter, kraal and stable manure, bucket refuse, carcasses of animals, bats' guano and kindred substances, or adopt the plan of enriching the soil by the growth of leguminous crops and so obtaining nitrogen from the





There are considerable quantities of bones available in the Colony. In additon to those of animals slaughtered for food, there are the bones and bodies of those which die from disease; unfortunately, these have been only too numerous in late years. Then, too, large quantities of bones occur scattered over the veld as relics of the horses, mules, and oxen which died during the war.

Bones, when reduced to fine powder, form a valuable though somewhat slow-acting manure, and might with advantage be largely employed in agriculture here.

The carcasses of animals which die from disease might, as a preventative of the spread of contagion, be burnt in a suitable furnace, and the residue would form a valuable phosphatic manure. A sample of such ash from the crematorium at the Veterinary

« ПредыдущаяПродолжить »