SOIL MAKING. 



7 



atmosphere. Thus, farm-yard manure not only itself adds to the 

 organic matter of the soil, but also ensures a further supply through 

 the agency of the clover crop. 



The organic matter, however, can only act properly if it decom- 

 poses ; undecomposed material, as already pointed out, is of no use, 

 and may even be harmful. One of the first essentials in soil making 

 is therefore to secure conditions favourable for the decomposition 

 processes, or, in other words, for the organisms that bring it about. 

 Earthworms begin the chain, bacteria carry it on : if a soil contains 

 a good stock of earthworms the conditions may reasonably be assumed 

 to be satisfactory. On the other hand, the formation of peaty layers, 

 however thin — even if only a fraction of an inch — is evidence that 

 decomposition is not proceeding normally. The soil population may 

 suffer for various reasons : there may be insufficient lime for their 

 needs, insufficient air or water, or too low a temperature. Whatever 

 the cause of the suppression of the population the result is the same 

 — a piling up of plant residues that ought to have been decomposed, 

 and consequent inconvenience for the young plants that ought to 

 grow and cannot. 



Lime is an important requisite, though perhaps it can hardly be 

 regarded as indispensable, because in many districts farmers and horti- 

 culturists have evolved schemes for managing without it. Perhaps 

 it would be more correct to say that many of the soil organisms cannot 

 tolerate acidity just as many cultivated plants cannot ; and lime 

 counteracts acidity. But the realm of Nature is very wide, and no 

 particular group of soil organisms appears to be indispensable. In 

 North Wales and in Aberdeenshire farmers do without lime on soils 

 that would be utterly condemned in the south of England, not because 

 they manage better, but because they manage differently. Potatos. 

 swedes, and oats figure largely in their programme, and these crops, 

 especially when heavily dressed with phosphates, stand less in need of 

 lime than many others. So long as there is no actual layer of peat the 

 disadvantages of a soil deficient in lime can be minimized by judicious 

 cropping. But the presence of lime in the soil allows greater freedom 

 of action, both in cropping and in cultivation, and we shall there- 

 fore continue to regard it as a prime factor in soil making. 



Another factor more nearly indispensable is sufficiency of air in 

 the soil, which in practice has to be brought about by removing excess 

 of water and preventing the formation of a compact crust on the surface. 

 A third is proper temperature, for if the soil is too cold decomposition 

 does not go on. 



Our general conclusion is, then, that the making of the soil requires 

 three conditions : the proper mineral matter, organic matter, and 

 conditions suitable for the decomposition of the organic matter. 



We now turn to the vitally important question — Can we control 

 the process of soil making ? 



The mineral matter lies outside our control : in a few special cases 

 something can be done, but not much. If soil contains too much 

 sand and is too light it can be ameliorated by the addition of clay. 



