CH. ix] Effects on Plant Growth 161 



Whenever land of any kind has been improved and made 

 to yield higher crops a trial should always be made to 

 see if potash is needed. 



Light sandy and moorland soils respond considerably 

 to dressings of potash, except sometimes where farm- 

 yard manure is used^. It is because of the wide occurrence 

 of these two types of soil in North Germany and of 

 moorland soils in Sweden that potash is so much used 

 in those countries ; the demand is still further increased 

 by the great quantity of sugar beet grown. Light chalky 

 soils also respond to potash. Although all three salts 

 are easily soluble they are readily precipitated in the 

 soil and only wash out with difficulty, so that the 

 drainage-water is practically free from potash. 



The main effects of potash on the plant are three. It 

 facihtates either the production or the translocation of 

 sugars and starches from the leaf ; hence its value for 

 sugar- and starch-making crops like sugar beet, man- 

 golds and potatoes. 



It stiffens the straw of cereal crops and of the grass 

 tribe generally: at Rothamsted the wheat and grass 

 crops growing on the plots deficient in potash tend to 

 become laid, especiallj^ in bad seasons. 



Further, it enables the plant to withstand adverse 

 conditions of soil, climate or disease, etc. The plants 

 well supplied with potash at Rothamsted do better in 

 bad years whether of wetness or of drought than the 

 others: they are also more resistant to rust and other 

 diseases. On the potash-starved plots the grass not only 

 becomes laid, but is also liable to attacks of the fungus 

 EpicJiloe, and in addition the seed heads are often 

 barren; the mangolds are badly attacked by the fungus 



1 See Cockle Park Bui. No 19, p. 51. 

 R. S. 11 



