24 JOURNAL OF THE ROYAL HORTICULTURAL SOCIETY. 



From the mechanical point of view this variation shows itself in 

 the innumerable physical differences which we encounter in soils, from 

 the very heavy clays to the lightest sands. These differences are 

 entirely due to the varying size of the particles which go to make up 

 the soil. A sand is made up almost entirely of large particles and a 

 clay of small ones, some of them so small that they cannot be measured 

 — so small that they run together to form gelatinous substances known 

 as " colloids." Between these two extremes we have the various 

 grades of loams, marls, alluvial soils, &c, which are mixtures of sand 

 and clay. The intelligent care of the soil that is here advocated is 

 conditioned in the first place by the class to which it belongs 

 mechanically — that is, whether the particular soil we are treating is a 

 heavy clay, a light sand, or one of the loams or " alluvial " soils that 

 fall between these two extremes. Fortunately many of our garden 

 and intensively cultivated soils are mixed soils, which every practical 

 horticulturist knows are the easiest to manage ; but many of our most 

 productive soils are clays, and many of our valuable early soils are 

 sands, and the management of these, while not so easy, is often most 

 profitable when done with success. 



Let us first glance at the essential points in the management of a 

 heavy clay soil. We have seen that the " heaviness " of such soils is 

 due to the fact that they contain a large proportion of very fine 

 particles, and that these particles are so fine as to form, when run 

 together, a gelatinous substance that gives them what is known as 

 their " colloidal " or adhesive properties. It is these " colloids," 

 which the potter spreads evenly throughout the bulk of his clay in 

 the process of working it, that enable him to mould it to his will, and 

 that enable the brick-maker to mould his bricks. The same thing 

 happens when we get our horses on to a heavy soil while it is still 

 wet, or when we turn up a wet furrow with too " slick " a side, or dig 

 such a soil with a spade when it is wet. In all these operations we 

 " puddle " the clay, we separate and distribute the " colloids " and 

 spread them either throughout the mass, in the case of the potter and 

 the bricks, or over a particular surface in the case of the furrow and 

 the " spit " of earth that we turn over. It will be seen that when 

 we separate and spread the " colloids " we get just the effect that as 

 cultivators of such soils we do not want. It follows therefore that 

 what we have to do is the opposite — that is, to segregate or collect them 

 and so mitigate their effect on the soil instead of aggravating it. This 

 then is the first consideration in managing a clay soil. How is it to be 

 done ? It is obvious that the aim of our management must be to unite 

 these small particles and so lighten the soil by coarsening its texture. 



The first point, as we have seen, is never to work it when it is wet. 

 Directly we see the " puddling " effect described, we should stop the 

 operation whatever it may be, remembering that by going on we 

 are only giving ourselves extra work to undo the trouble later — an 

 opportunity we may not get, in which case we may be faced with 

 " cloddy " soil throughout the summer. 



