W//..S 13 



Fertility of soils. The fertility of a soil depends, said 

 LIKBIG. "on the bulk and composition of the previous crop residues, 

 and the extent to which these have been subsequently destroyed." 

 Evidently, therefore, the crop which leaves behind the largest 

 amount of roots, foliage, etc., will best maintain or increase the 

 organic capital of the soil. Fertility of soils has been summarised 

 as being dependent on the following conditions, viz. (1) a 

 sufficiency of available plant-food; (2) a suitable texture or 

 mechanical state of the soil; (3) absence of injurious compounds; 

 <4) a healthy percolative subsoil ; (5) a suitable climate, season 

 and aspect. The absence of any of these conditions will, to some 

 extent, render a soil infertile. Needless to say, one of the most 

 essential factors that control soil fertility is the amount of 

 moisture present, for on this depends the healthy action of the nitri- 

 fying bacteria. Agricultural chemists now distinguish between 

 fertility analyses and complete analyses, the latter only indicating 

 the amount of plant food present in the soil, whereas the former 

 aims at showing the proportions available to the crop a very 

 different thing. 



Sterilisation of Soils. An important fact in agricultural 

 science which has recently come to light is the beneficial effect of 

 the sun's light and heat on the surface soil. Hitherto the long 

 spells of hot dry weather which periodically occur in the tropics, 

 and during which the soil becomes extremely hard and dry, has 

 been generally deplored, and it has been commonly felt that if only 

 one could cover a fallow area with some crop that would stand the 

 drought, the ground, protected by it from the scorching sun, would 

 lose less of its moisture and be more fertile later on. Recent experi- 

 ments have shown, however, it is claimed, that sterilizing the ground 

 by intense heat restores or enhances soil fertility, the conclusion 

 arrived at being that such sterilization kills off the organisms which 

 prey on the useful bacteria in the soil, allowing the latter to increase 

 more rapidly. From this it is deducted that the fertility of the 

 soil is largely increased, and at no expense to the cultivator, since 

 most of the bacteria are engaged in the useful work of fixing 

 nitrogen from the atmosphere into a form suitable for plant-life 

 or in converting unsuitable compounds into the nitrates which 

 plarts require. 



It is thus concluded that so far from the scorching sun's 

 rays being inimical to the fertility of the soil, by killing off larger 

 organism, and enabling bacteria to grow and increase, they add 



