220 THE BOOK OF NATURE STUDY 



want of water than by its excess. The weathering which a soil 

 receives by its exposure during the winter in a rough condition 

 also helps to render some of the plant food more available, but 

 these chemical actions are secondary in importance to the effect 

 upon the texture of the soil. 



When the year has turned, an early opportunity should be 

 taken to move the soil, which will have become a little set by 

 the beating of the winter's rains ; if it is sandy or a light loam 

 there need be little delay, because a day or two without rain will 

 dry it sufficiently for working, and even if it does get trampled 

 about a little, the late frosts will easily bring it into condition 

 again. But on the heavy soils and on the pure clays it is necessary 

 to wait and watch for an opportunity very carefully, because 

 one careless cultivation when the land is still wet will easily undo 

 all the good work of the winter's exposure, by tempering the clay 

 into a paste from which it has no longer a chance of recovering. 

 As soon as the east winds begin such kneaded clay will dry into 

 the toughest lumps, which no amount of cultivation will ever 

 reduce to a proper seed bed ; even though they are rolled and 

 knocked into little pieces they remain still hard and unkind. 

 But if the right moment be caught, this first spring cultivation 

 breaks up the surface soil and leaves it, still perhaps rather rough, 

 but lying loose upon the firmer unmoved land below. 



As long as the land is solid and there is a continuity between 

 the surface and the subsoil the top layer will tend to remain wet, 

 although it may be constantly losing water by evaporation. 

 Water can always rise by capillarity through compact earth in 

 which soil grain touches soil grain and the water film is con- 

 tinuous ; but after cultivation the loose earth that is left on the 

 surface is cut off from the subsoil water by its imperfect contact 

 with the firm layer below, and can therefore begin to dry. At the 

 same time as the surface soil drys it becomes warm ; as long as 

 it remains wet through its connection with the subsoil the sun's 

 rays does little towards raising its temperature, because they are 

 spent in bringing about the evaporation of the water instead of 

 turning to heat in the soil itself. But not only does the early 

 cultivation enable the surface to dry and warm, it also saves the 

 subsoil below from losing its stock of water by evaporation. The 



