148 Report S.A.A. Advancement of Science. 



carbonate of lime be present. The amount of lime present in the 

 samples examined has varied greatly from the merest trace to as high 

 as 30 per cent, in some limestone soils. But, except on limestone 

 outcrops, the soils are, as a rule, very low in this constituent. The 

 average of all the 168 samples gives 0.81 per cent, of lime, but, as 

 already stated, this includes several samples, consisting largely of 

 powdered limestone. Taking 0.25 as a standard, there were 70 

 samples containing more than this, and 98 containing less. 



The average of the 70 is 1.86, that of the 98 only 0.093 P^^ 

 cent. In many cases less than 0.05 per cent, of total lime was 

 found. There can be little doubt that the application of lime in 

 small dressings to many of our soils would be attended with a great 

 increase in fertility. 



The needs of our Transvaal soils, generally, then, are organic 

 matter (humus), combined nitrogen, phosphates, and lime. It is of 

 interest and importance to consider how these needs may be supplied 

 by the natural resources of the country. Before doing so, however, 

 it will be advisable to briefly discuss the form in which these 

 constituents may be applied to the soil. Organic matter, present in 

 the very complex and indefinite form known as humus, is in the great 

 majority of our soils, very deficient in amount. Its amount may be 

 increased by the addition of bulky animal or vegetable matter. 

 Stable or kraal manure, if available, is undoubtedly one of the 

 cheapest and best manures for this purpose, especially as it also 

 supplies small quantities of all the constituents needed by a soil. But 

 in this Colony the quantity available in any one locality is very 

 limited, and the cost of transport is too high to allow of its being 

 brought from a distance. The amount of organic matter in such 

 substances as guano and bats' guano is too small to allow of these 

 substances having much influence directly upon the amount of humus 

 in the soil, though they have great value as true manures. The 

 organic matter may, however, be very greatly increased by the 

 practice of ^^een manuring. By growing any crop on land and 

 plowing it in, before it seeds, a large addition of carbonaceous matter 

 obtained by the crop from the air is added to the soil, and may 

 greatly improve it by increasing its water-retaining powers, and in 

 other ways. 



If the crop chosen be a leguminous one, an additional advantage 

 is gained by the addition to the soil of the nitrogenous matter 

 contained in the crop, which has been obtained mainly from the 

 nitrogen of the air. In many of our soils, the micro-organisms 

 necessary to effect this absorption of free nitrogen in the root tubercles 

 of many leguminos(X are already present, but, in any case, their 

 presence may be insured by inoculation of the seed before sowing, 

 with cultures of the specific organisms. 



This is a plan which might with great advantage be adopted on 

 many of our soils, but it must be remembered that the other necessary 

 constituents, phosphates, potash, and lime, must alreadv be present 

 in sufficient amount to allow of a luxurious growth of the leguminous 

 crops, or the advantage gained will be small. 



