NORFOLK V. A CROPPING ROTATION 19 



One of the chief operations of the lungs in a human 

 being is the expulsion of moisture from the system. 

 If one breathes for a few seconds on to a pane of glass, 

 the glass immediately becomes damp. Precisely the 

 same effect may be obtained by placing a cabbage under 

 a glass globe for a few minutes in the sunshine. 



A plant really obtains its nourishment from the soil 

 by absorbing through its roots, plant food dissolved in 

 the soil water. The moisture is expelled through the 

 breathing pores of the leaves and green stems, leaving 

 behind the plant food for the building up of vegetable 

 tissue. 



Now, it has been found that for every pound of dry 

 matter assimilated by a plant, 250 lb. of water are 

 expelled by the leaves. In rape, for instance, there is 

 14 per cent, of dry matter. Hence in a 25-ton crop 

 per statute acre there will be 3^ tons of dry matter. 



Since 250 parts of water are required for the 

 elaboration of one part of dry matter, it follows that 

 for the production of 3I tons of dry matter, 875 tons 

 of water are required. 



One inch of rainfall per acre is practically equal to 

 100 tons of water. Therefore, by growing during the 

 *' winter" half-year 25 tons of rape, we rid the land by 

 leaf evaporation of nearly 9 inches of rainfall. 



The root action of the rape also facilitates drainage, 

 and between this and leaf evaporation one would be 

 quite safe in saying that by cropping a field with rape 

 we rid the land of about the equivalent of 12 inches of 

 rainfall. 



It is scarcely necessary to point out, further, how 

 ridding the land, prior to the spring tillage operations, 

 of this amount of moisture, facihtates soil cultivation 

 and crop saving in a wet spring. 



So marked is this drying effect of winter crops that 

 in the districts of low rainfall if the crop is not con- 



