181 



Apart from the fact that the samples taken at K* represent a soil that 

 had already been under irrigation for a long period, it is plain that of 

 the five places where samples were collected K is altogether the best, 

 and that the conditions grow worse as one proceeds down the valley from 

 K to P. Taking the entire six feet depth of so^l in each case, the average 

 percentages of alkaline salts at the various spots were as follows: 



Spot. Sodium Sodium Sodium Total 



chloride. sulphate. carbonate. alkaline 



salts. 



K '062 -107 Nil. '169 



L -159 '104 -008 '271 



M '215 -122 Nil. '337 



N '215 -117 -037 -369 



P -211 -201 '087 -499 



This confirms the views of local men with regard to the alkali in the 

 soil, the opinion on the spot being practically unanimous that the lower 

 part of the valley is unfit for cultivation; the only difference between 

 one man's view and another's is that ideas vary as to the extent of the 

 unproductive area. 



It should be noted that irrigation, followed by a period of abstinence 

 from water, will tend to bring the soluble salts to the surface, and thus 

 cause the surface soils to approximate to the composition just given in the 

 above averages. In the first four feet of the soils under consideration 

 these averages are as follows : 



K '105 per cent. 



L '270 



M "288 



N -376 



P '552 



It will be seen that the soil at K is the only one which falls within 

 the limits; of safety as laid down by Professor Hilgard, in fact K is the 

 only soil which one could expect to yield a profitable return, and the fact 

 that farming has been carried on there with fair success does not, there- 

 fore, settle the matter for the entire valley. The lower layers of the soil at 

 K contain a fair proportion of gypsum (calcium sulphate), which has con- 

 verted the noxious sodium carbonate into the less harmful sulphate. 

 There is a general prevalence of carbonate of lime throughout these soils, 

 and in nearly every case a stratum of gypsum runs through the soil at 

 various levels ; this stratum appears in the fourth foot at K and M, and 

 in the second at L and at P. It is invariably accompanied by an increase 

 in the proportion of other soluble salts, including those which produce 

 brack, and although the gypsum in these layers may minimise to some ex- 

 tent the evil effects of the black brack, by converting it into sodium sul- 

 phate, it is not probable that it will do away with these effects entirely. f 



* The surface soils at K, L, M, N and P correspond respectively with Nos. 9, 

 5, 6, 7, and 8 of the Steynsburg soils in the section dealing with determinations 

 of plant food (See p. 127). 



r From the diagrams which illustrate the distribution of salts in the soil mass 

 will be seen very clearly that the soil layers in which calcium sulphate acquires 

 greater prominence are also characterised by augmented proportions of the other 

 sulphates, i.e., of magnesium and sodium. 



