204 HVDItOGKX lOX CONCENTKATIOX IX S.A. SOILS. 



should liki' to lay emphasis once, more on the lact that not only 

 do the usually recognised characteristic properties ot acids, sucn 

 as taste, tlepend on hydrogen ion concentration, and not on the 

 total quantity of acid present, but that it is extremely probable 

 that the influence of acidity on vegetation depends in like manner 

 on hydrogen ion concentration. 



A. Loiv Veld Soils. (1) Various samples were tested first of 

 all from virgin veld in the iSeottsville neighbourhood of Pieter- 

 maritzburg near tne Natal University College. A considerable 

 amount of preliminary work was done with these samples in 

 order to become familiar with the method. 



Taking the results obtained from testing surface Low Veld 

 soils in this neighbourhood we have found that these vary between 

 pH6"0 and pH6'9. They are, therefore, to be classed as slighth" 

 acid soils (specific acidities +10 to very nearly 1). In this area 

 shales occur near the surface and the soil is shallow. The veld 

 has been considerably disturbed and the veld grasses are mostly 

 primitive colonising species with a high proportion of ruderals. 



(2) Our expectation had been that we should find the Scotts- 

 ville soils either alkaline or at least neutral. We therefore 

 proceeded to test a more typical sample of Low Veld soil taken 

 from underneath a specimen of Acacia benthavii thorn tree 

 growing at Bisley. The pH value we found in. this case to be 7"0. 

 The soil, therefore, can be classed as neutral. 



B. High Veld Soils. (1) Samples were next tested from the 

 High Veld of the Zwartkop mountain. At altitudes of about 

 4,300 feet on the steep slopes we obtained samples which gave a 

 very acid reaction, pH4-5 — 5-0. The specific acidity is therefore 

 as high as 300, and the soil is as acid as typical Calhuia soil in 

 Europe. This somewhat surprising result at first made us 

 inclined to doubt its reliability, but a further series of tests 

 confirmed the result. 



(2) Soil from the centre of the busli on the lowe'- slopes of 

 the Zwartkop gave pH7, or a neutral reaction, another miexpected 

 rt'sult. 



(3) Two samples from tlie Dargle (higli veld) district at 

 altitudes of about 4,500 feet were obtained. The first was from 

 a slightly higher altitude, dry and somewhat clayey and gave 

 an average reaction of dH5-7. The latter was a dark coloured 

 moist soil and .gave pH5'4. These results are very much less 

 acid (specific acidity 30 + ) than those from Zwartkop. Both were 

 from forest areas. It would appear that while High Veld soils 

 are all acid, on the whole forest soils arc not so acid as open 

 grass veld soils, but the point requires much further testing. 



(4) .Samples from Signal Hill, near Maritzlmrg, were investi- 

 gated with the object of determining the influence of aspect 

 exposure. Samples from the slope facing north gave an average 

 pHo'o, from the slope facing south, an average of 6*4. The north 

 slope is open, grassy tree veld and is considerably more acid 

 (nearly ten times) than the south slope, which is a forest area 

 showing the earliest stages of forest succession. This bears out 

 the idea that the complex of factors leading to tlie development 



