MAGXKSIA I.MI'KKGXAIKJ) SOILS. 



177 



(uutieated), in spite of considerable loss from insect attack 

 (cut-worms), yielded 1,002 lbs. (five bags) of maize per acre, 

 whilst land adjoining, which received an application of 

 ten tons of kraal manure per acre, returned an average of 

 nine and a cjuarter bags of maize jjcr acre. 



Poor crojj returns on many other soils similar in com- 

 position to ]So. 307 have been reported, and, other things 

 being- equal, the chief difference between the two soils cited 

 above lies in the ratio of lime to magnesia, and, from a study 

 of the held conditions, it is inferred that the low retiu'ns 

 obtained from soils similar to jS^o. 307 have been due chiefly 

 to the presence of an excess of available magnesia over lime. 



In the course of my official duties, samples of virgin 

 soils from the Great Dyke are constantly being submitted 

 for an opinion as to the suitability of the area which thej^ 

 repiesent for arable farming, conseciuently some factor 

 regarding the lime-magnesia ratio has to be decided ujion 

 for the purpose of interpretation of analyses. From the 

 limited data gathered together by correlating the composition 

 of arable Dyke soils with the crop returns obtained therefrom, 

 it has been observed that when the ratio of lime to magnesia 

 soluble in 1 per cent, citric acid solution exceeds 1: 3 (lime 

 as 1), the tendency is to experience very poor returns of 

 luost of the common crops (maize, etc.). It must, however, 

 be pointed out that this interpretation of the figures of 

 analysis is not absolutely conclusive, although a considerable 

 amount of researcli work on the soils of the Great Dyke has 

 been accomplished. 



The Dyke soils throughout are admittedly i)0(,'rer in 

 phosphoric oxide and potash than the best soils of this 

 territory, and doubtless in building up their fertility the 

 addition of phosphatic and potassic manures will be 

 necessary, but that lack of available plant food is not the 

 cause of the low returns from at least one pyroxenite soil 

 occurring on the Great Dyke has been ])roved by the fact 

 that an attempt to grow barley under irrigation with the 

 aid of a liberal dressing* of a complete fertiliser ended in 

 complete failure. It is of interest to note that in the soil to 

 which reference is made the ratio of lime to magnesia soluble 

 in concentrated hvdrochloric acid was as follows: — 



Ratio of Lime 

 to Magnesia 

 (Lime = 1). 



1 : 15 



k 



1 : 27 



