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DURBAN, NATAL.

By R. FERMOR RENDELL, B.A., F.R.A.S., OF THE OBSERVATORY,

DURBAN, NATAL.

[ABSTRACT.]

:

The Paper contains :-
(a) Remarks on the subject, drawing attention to its

importance and urgency. The necessity for improved
predictions is demonstrated, the only Table hitherto
available being frequently more than an hour and a
half in error. The writer has devised a method which

yields good results. (6) An ephemeris for the whole of the year 1906 is added,

giving the times of High Water at Durban, predicted

by the new method.
(c) A comparison is shown to prove the superiority of the

new method. In this comparison the following daily
particulars are given in five columns, commencing from
September ist, 1905, and including the latest records
to hand at time of writing :
(1) The predicted times of High Water given in the

Natal Directory.
(2) The predicted times calculated by my new method.
(3) The observed times supplied by the Engineer of

the Natal Harbour Works. (4) The discrepancies between the predictions in the

Natal Directory and the observations. (5) The discrepancies between my predictions and the

observations. The results show that the new method is vastly superior to the old. About half of the observed times differ by more than threequarters of an hour from the old predictions (which are sometimes too early and sometimes too late), while the majority of the new predictions are within a quarter of an hour of the observed times.

For the period of nine months, commencing September ist, 1905, the average discrepancies are 46 minutes and 14 minutes respectively. During this period 495 observed times were investigated.

The following summary indicates the nature of the results :

Old Predictions. New Predictions. Number of discrepancies over 90 minutes 27

0
45
245

I2
not over 15

68

321

By investigating a longer series of records, the writer hopes to be able to deduce still more accurate values for the quantities in his tables.

TRANSVAAL.

By HERBERT INGLE, B.Sc., F.C.S., F.I.C.
Chief Chemist, Transvaal Department of Agriculture.

Though at present the economic importance of the Transvaal depends mainly upon its mineral resources, there can be no doubt of the vital interest attached to the agricultural possibilities of the country if it is to become the permanent home of the colonist.

A factor of the utmost importance in determining these possibilities is the character and composition of the soil, for though climate, rainfall, water supply, possibility of finding a market for produce, and other circumstances, to a great extent determine the progress of agriculture as a business, these become merely insignificant considerations if the soil be not productive.

The chemical composition of the soil, though by no means the only item of importance in assessing its productiveness, is certainly a great factor in gauging its potential fertility. Unless the constituents of plant food are present in the soil in sufficient quantity, no combination of favourable circumstances as to temperature, water supply, and other features, will yield good crops.

Until recently, but few analyses of Transvaal soils had been made. The few that were available indicated that, compared with European soils, those of the Transvaal were poor in most of the important constituents of plant food, and that, judged by the experience of ordinary temperate climates, they were in urgent need of manures.

During the past three years, analyses of about 160 samples of soil from various parts of the Colony have been made in the Chemical Laboratories of the Transvaal Department of Agriculture, so that we are now in a position to speak with some degree of confidence as to the general character of our Transvaal soils, so far, at least, as their chemical composition is concerned.

In a tract of country so extensive as the Transvaal, we find, as is to be expected, considerable differences in composition among the samples, but, though here and there are to be found patches of soil rich in most manurial ingredients, the greater number of samples indicate that the soil, in general, is poor in organic nitrogenous matter, phosphates, and lime. Potash compounds, with some few exceptions, are generally sufficiently abundant. Again, speaking from the experience of European countries, most of our Transvaal soils would appear to need additions of combined nitrogen, phosphates and lime, in order to possess average fertility.

But to judge soils in tropical countries from the standpoint of the experience obtained in temperate and less sunny climates is not fair. It is found in actual practice that a soil of extreme poverty, compared with average English soil, will often, in this country, yield quite respectable crops.

This is the experience in other parts of the world, e.g., Assam, where the tea soils of great apparent poverty, nevertheless yield good

Several factors, no doubt, are influential in bringing this

crops.

1.

about. As I have stated elsewhere, these are probably the following :

The favouring influences of brilliant sunshine and high temperature upon plant growth.

2. The greater rapidity with which chemical changes probably occur in the soil. This would enable plants to obtain a sufficiency of food from a soil which, under circumstances less favourable to chemical changes, might be too poor in fertilising constituents. Organic matter in our soils very quickly decays, and no doubt the changes which render potash and phosphoric acid available, also proceed more rapidly than in cooler climates.

3. Most of our soils are of open texture and considerable depth, thus allowing of abundant root development.

4. Our rain is richer in combined nitrogen than that of cooler countries, and the rainfall being confined to the growing season, brings almost all its nitric acid and ammonia into contact with the feeding roots. In Pretoria, the total amount of combined nitrogen brought down in the rain amounts to about 7.5 lbs. per acre per annum, as against about half that quantity at Rothamsted, and, whereas in England this addition of nitrogen is distributed almost uniformly over the whole year, and a large portion is thus wasted, in this country it is confined to the summer, when the crops are in a condition to assimilate it. The absence of winter rains is also important in lessening the loss of nitrates from the soil by drainage. In Europe quite a large quantity of nitrogen is washed out of the soil into the drains, especially in autumn and winter, when the land is, for the most part, clear of crops. In this Colony no loss of this kind occurs, as in most districts the winter is absolutely rainless.

5. The dryness and low pressure of our atmosphere leads to rapid evaporation both from the leaves of plants and from the surface of the soil. The rapid transpiration of water from the leaves enables the plant to use up large quantities of the very dilute solution of its food existent in the soil, and thus to obtain a sufficiency from the soil water even when the latter is so weak that it would, in a damper climate, be incapable of providing the needed constituents in sufficient quantity. The evaporation of moisture from the surface of the soil brings up water from below, carrying with it small quantities of dissolved matter from the soil, and concentrates this dilute solution in the upper layers, so as to render it more capable of supplying the roots with plant food. The latter process sometimes goes on to an injurious extent, and sets up a brak condition of the surface soil.

But to return to the character of Transvaal soils as revealed by our analyses.

In a paper read last year before the Chemical Section of the British Association for the Advancement of Science at Johannesburg, I gave in detail the results of the analyses of nearly 100 samples of soils collected from various places in the Colony, and discussed at some length the general manurial treatment necessary to enhance their fertility. Since then some 60 to 70 additional soils have been

a

examined in our laboratories. I do not propose to give a long array of figures, but will be content to deal with averages as far as possible. In last year's paper, above referred to, will be found details of the methods employed in the analyses, and a discussion of the deductions which may be drawn from the various determinations.

It must suffice on the present occasion to point out that although plants require from the soil a large number of substances, the actual fertility generally depends upon the soil's capability of supplying a sufficiency of four materials, viz., combined nitrogen, potash compounds, phosphates, and lime. Other constituents of plants, e.g., sulphur, chlorides, iron, magnesia, etc., though indispensable, are so widely distributed that it is rare to find soils lacking in them.

For the present, then, only the four first-mentioned constituents will be considered.

COMBINED NITROGEN.

In most soils this is present almost entirely in the form of complex organic compounds, resulting from the decay of vegetable or animal matter. The organic matter, in addition to yielding supplies of nitrogen, has an important influence on the water-holding capacity of the soil.

In this state, nitrogen is not available to plants, but becomes so by processes of decomposition, resulting in the formation of ammonium compounds, nitrites, and, lastly, nitrates. It is in this form that practically all the nitrogen which the plants require is assimilated. The successive changes which lead to the formation of nitrates from complex organic nitrogenous compounds are known as nitrification, and are accomplished under the influence of at least three species of micro-organisms. In order, therefore, for a soil to be well adapted for supplying nitrogen to plants, it is necessary for it to possess a sufficient store of organic, nitrogenous matter, suitable micro-organisms, and the necessary conditions for their activity. Among the latter, some of the most important are sufficient moisture, the presence of some basic material, suitable for the formation of nitrates, and a moderately high temperature. The first and last of these are mainly dependent upon climatic conditions, the only modification which is practicable for man to introduce is by means of irrigation. The basic material most suited for the purpose is carbonate of lime, and the process of nitrification leads to a consumption of this substance.

Most of our Transvaal soils are low in lime, and the process of nitrification is probably limited in many cases by the deficiency of basic material. On the other hand, other conditions for rapid nitrification, e.g., high temperature, porosity, and, in the summer, moisture, are favourable in this country.

The amount of combined nitrogen in most of our soils is very low, compared with ordinary English soils. There are, of course, many exceptions, for soils from marshes, or “ vleis,” are often rich in organic matter, and also in nitrogen.

In an ordinary English arable soil one usually finds about 0.2 to 0.3 per cent. of nitrogen. The average of the 168 samples of Transvaal soils, examined in our Laboratories, gives 0.126 per cent. But this alone would be misleading, for, leaving out 17 soils which contained more than 0.20 per cent., the remaining 151 soils only contained an average of 0.093 per cent. of nitrogen. It is not infrequent to find 0.05, 0.03, or even 0.02 per cent. of nitrogen in samples of our soils. Soils containing so little nitrogen as, say, 0.1 per cent., would be regarded in England as hopeless unless heavily manured with nitrogenous material, but yet many such soils in this Colony are found to yield fair crops. It is probable that this is mainly due to greater rapidity of circulation of nitrogen in the warmer climate.

POTASH.

In this constituent our soils are, as a rule, fairly rich, the average amount in all the 168 samples being about 0.23 per cent. Few samples are below 0.10 per cent., while in a few cases about 1.0 per cent. was found. It is probably rare that potash manures are needed on our Transvaal soils, though a few samples have yielded results indicating that they would be benefited by additions of potash. In about 50 samples out of the 168 examined, the proportion of potash extracted by treatment with i per cent. solution of citric acid was less than 0.005 per cent., which has been proposed for English soils as the limit below which potash manures are probably needed.

PHOSPHATES.

These substances are markedly deficient in most of our soils. In England the proportion of phosphoric acid present varies greatly, but is usually about 0.10 or 0.15 per cent. In our Transvaal soils the amount rarely reaches 0.1 per cent., and is often less than 0.04, or even 0.03 per cent. The mean of all the 168 samples gives 0.06 per cent. of phosphoric acid, but this includes some exceptionally rich specimens, containing from 0.15 to 0.20 per cent. of phosphoric acid, Phosphates are as much needed on most of our soils as nitrogen and lime. In only 32 out of the whole 168 samples did the amount of "available" phosphoric acid, i.e., the quantity extracted by 7 days' treatment with i per cent. solution of citric acid, exceed o.oi per cent., which, in England, is taken as the limit, below which phosphatic manuring is considered advisable.

LIME.

The presence of lime in the form of carbonate is of great importance, not only for the effect upon nitrification already alluded to, but also for the important action it has upon the physical properties of the soil. Soils containing clay in sufficient quantity to be "heavy " and tenacious, become much more friable and porous if

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