Manurial Needs and Resources. 147 



In an ordinary English arable soil one usually finds about 0.2 to 

 0.3 per cent, of nitrogen. The average of the 168 samples of 

 Transvaal soils, examined in our Laboratories, gives 0.126 per cent. 

 But this alone would be misleading, for, leaving out 17 soils which 

 contained more than 0.20 per cent., the remaining 151 soils only 

 contained an average of 0.093 per cent, of nitrogen. It is not 

 infrequent to find 0.05, 0.03, or even 0.02 per cent, of nitrogen in 

 samples of our soils. Soils containing so little nitrogen as, say, o.i 

 per cent., would be regarded in England as hopeless unless heavily 

 manured with nitrogenous material, but yet many such soils in this 

 Colony are found to yield fair crops. It is probable that this is 

 mainly due to greater rapidity of circulation of nitrogen in the 

 warmer climate. 



Potash. 



In this constituent our soils are, as a rule, fairly rich, the 

 average amount in all the 168 samples being about 0.23 per cent. 

 Few samples are below o.io per cent., while in a few cases about i.o 

 per cent, was found. It is probably rare that potash manures are 

 needed on our Transvaal soils, though a few samples have yielded 

 results indicating that they would be benefited by additions of potash. 

 In about 50 samples out of the 168 examined, the proportion of 

 potash extracted by treatment with i per cent, solution of citric acid 

 was less than 0.005 P^"" cent., which has been proposed for English 

 soils as the limit below which potash manures are probably needed. 



Phosphates. 



These substances are markedly deficient in most of our soils. 

 In England the proportion of phosphoric acid present varies greatly, 

 but is usually about o.io or 0.15 per cent. In our Transvaal soils 

 the amount rarely reaches o.i per cent., and is often less than 0.04, 

 or even 0.03 per cent. The mean of all the 168 samples gives 0.06 

 per cent, of phosphoric acid, but this includes some exceptionally rich 

 specimens, containing from 0.15 to 0.20 per cent, of phosphoric acid. 

 Phosphates are as much needed on most of our soils as nitrogen and 

 lime. In only 32 out of the whole 168 samples did the amount of 

 " available " phosphoric acid, i.e., the quantity extracted by 7 days' 

 treatment with i per cent, solution of citric acid, exceed o.oi per 

 cent., which, in England, is taken as the limit, below which phos- 

 phatic manuring is considered advisable. 



Lime. 



The presence of lime in the form of carbonate is of great 

 importance, not only for the effect upon nitrification already alluded 

 to, but also for the important action it has upon the physical 

 properties of the soil. Soils containing clay in sufficient quantity to 

 be " heavy " and tenacious, become much more friable and porous if 



