(i64 Journal of the Department of Agriculture. 



Under the fiiiiiatic conditions of Witkop it is to be expected that 

 a soil containing 20 per cent, of clay will be difficult to till, provided 

 no factors are present to modify the colloidal influence of the 'ilaj-. 

 That No. 617, containing- 20.6 per cent, of clay, possesses a physical 

 structure suitable for potato culture must then be ascribed to the 

 " lightening " influence of the considerable quantities of coarse sand 

 and clay it contains and to the absence of any considerable quantity 

 of fine silt. 



IN^ow No. 618 contains 5.7 per cent, less clay than No. 617. May 

 one, therefore, conclude that it is an easier soil to work? If the pro- 

 portions of humus and coarse sand were the same as those of No. 617 

 such a conclusion would be justified, provided also that the proportion 

 of fine silt was not greater. Reference to the analysis will show that 

 these conditions are not fulfilled, that No. 618 contains less of both 

 coarse sand and humus together with a larger proportion of fine silt. 

 What No. 618 appears to gain in physical make-up in comparison 

 with No. 617 it probably more than loses in the other indicated 

 directions, a view that is supported by the permeabilities of the two 

 soils to water. No. 618 being onlv three-quarters as permeable as 

 No. 617. . . \ 



Physically considered No. 617 is therefore the better soil of the 

 two, while both should respond well to intelligent methods of tillage. 



From a chemical point of view No. 617 is superior to No. 618 in 

 iilmost every respect; but although that is so, No. 617 is by no means 

 as good as it could be — it is not, for example, so well provided with 

 phosphoric oxide as the soils of Kalkfontein and stands in need of 

 phosphatic manuring. No. 618 is very deficient in available phos- 

 jilioric oxide. 



No. 619 is a very poor soil indeed and veiy much like the zaiid- 

 biilt soil from Paardenverlies. 



The Willows : Me. Andrew de Klerk. 



The farm Willows lies to the east of Witkop. Samples Nos. 615 

 and 616 were taken here. 



The homestead is situated ou the eastern side of the stream which 

 comes down past Yaalkop from the volcanic beds about four miles 

 distant. At it are to be seen some rather young specimens of the 

 macrocarpa cypress, English gooseberry, and red currant; there are 

 also some poplars. 



Sample No. 615 repiesents a mixed sand and turf soil situated 

 on the slope at the foot of Yaalkop and facing about north. The 

 natural vegetation of this area consists of rooigras and rooi 

 platblaar grass, together with plenty of clover, which grows 

 quite tall if protected from stock The roots of the clover 

 are well covered with bacterial nodules. The data regarding 

 crops given on page 158 apply particularly to this soil. 

 Vaalkop is built up of red and white sandstones, which figure in 

 Dunn's map as Red Beds. The map shows that a dolerite dyke passes 

 through the kop. No. 616 was taken from the vlei at a point opposite 

 the homestead and over the stream leferrexl to in the foregoing para- 

 graph. Underground water is hereabouts about three feet below the 

 surface. 



