v] RAISING OF THE FERTILITY LIMIT 79 



and it was not till thousands of acres had been 

 wrongly drained and thousands of pounds wasted, 

 that the germ of truth underlying both sides was 

 discovered. For both -sides were partially right; 

 deep drains are needed to carry off subterranean 

 water and shallow drains to remove surface water. 

 Modern practice tends to revert to Smith's method ; 

 the drains are now commonly put 2J to 3J feet deep 

 and 15 to 30 feet apart. In one other point a change 

 has been made ; the pipes are now often 3 inches in 

 diameter instead of one or two inches as formerly. 



Where the drainage was carried out effectively 

 a most striking improvement resulted. The ground 

 lost its wet sticky character. It could be ploughed 

 earlier in the year, so that the seed could be sown 

 early, and the crops safely left growing later. As the 

 excess of water was removed air took its place ; better 

 root growth now became possible and considerable 

 increases in crop were obtained. Great improvement 

 also set in on the grass land; the reeds and rushes 

 disappeared and the grasses and clovers flourished. 

 But the change is not entirely permanent ; the drains 

 gradually become blocked up with silt, with a deposit 

 formed of oxide of iron together with organic matter, 

 and with roots of trees or plants; and considerable 

 areas of land in the country now require redraining. 



We have seen that the most generally fertile 



