Manurial Needs and Resources. 145 



about. As I have stated elsewhere, these are probably the follow- 

 ing :— 



1. 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 



10 



