82 The Control of the Soil [pt. ii 



siderable loss of plant food. A soil that is at all light or 

 porous readily loses its valuable nitrates, and although 

 the loss is not so serious on heavier loams and clays, it 

 takes place even there. The loss only goes on, however, 

 in wet weather, and if one could rely on having the 

 ground frozen hard throughout the winter it would be 

 simple enough to arrange about cultivation; one would 

 turn the ground up roughly at the beginning of the 

 winter, and leave it to the end. Unfortunately our 

 winters are variable: land turned up in autumn may 

 only occasionally get frozen, and may lie wet for long 

 periods ; it then derives very little benefit from the culti- 

 vation, and suffers considerable loss of plant food. 



It must, therefore, be arranged that the cultivation 

 effect is at a maximum, while the loss is at a minimum. 

 The general rule is that light soils may be left unculti- 

 vated until late in the winter or early spring, partly 

 because the amount of frost they require is only small, 

 partly because the loss that they would suffer in rain is 

 very large. Heavy soils, however, should be turned up 

 as early in the autumn as possible because they require 

 a large amount of frost, and suffer only little loss. The 

 rule, of course, requires intelligent application and 

 adaptation to each locality. 



The effect of winter cultivation in lightening the soil 

 is well seen in the following experiment devised by 

 Mr F. J. Gurney. Mark out a plot of groimd one rod 

 square and divide it up into square yards ; at the corner 

 of each square dig a hole 12 inches deep. Place a brick 

 at the bottom of each hole and on it stand an iron rod 

 16 inches long (and therefore projecting 8 inches above 

 the surface of the soil) and put in sufficient concrete to 

 hold the rod rigid : then fill up with earth. The plot will 



