30 ARTIFICIAL MANURES [CH. 



amount as in kainit ; by keeping the hedges very closely trimmed 

 and burning the trimmings one therefore obtains the double 

 benefit of small clean hedges and extra supplies of ash. Brush- 

 wood, useless fallen timber and other wastes from woods and 

 coppices yield ash containing 5 to 8 per cent, of potash and 20 to 

 40 per cent, of lime ; this sort of material can well be burnt because 

 it only harbours pests. Burnt hayricks, the waste cavings, 

 dust, etc. obtained during threshing, also yield an ash containing 

 up to 10 per cent, of potash. All these should be carefully collected. 

 The potash is in a highly available form, indeed it is so soluble 

 that a single night's rain may wash half of it away: the ash, 

 therefore, has to be collected as speedily as possible, or if it is 

 too hot to be got in before the rain comes on, it must be sheltered 

 in some way. The ash tends to absorb water from the air, so that 

 it does not keep well, and it is difficult to spread because of its 

 lightness. But both these difficulties can be overcome by mixing 

 it with superphosphate. 



Coal ashes are of no value. 



Seaweed contains a good deal of potash, and should be used 

 as much as possible ; in 1 ton of the fresh weed there is as much 

 potash as in 1J cwts of kainit. It is greatly to be regretted that 

 no satisfactory seaweed industry has yet been developed 1 . 



Farm products. All crops contain a good deal of potash, 

 especially roots, leaves and straws. Grains and seeds on the 

 other hand contain least. The amounts present are as follows: 



Size of crop per acre 

 Weight of potash 



(K 2 0) removed, 



Ibs per acre ... 400 150 110 108 54 32 12 



The animal products of the farm are very poor in potash. For 

 every hundredweight of flesh laid on, a fattening animal keeps 

 only 2 ozs of the potash present in its food. Dairy stock take a 

 bigger toll, but not very much, 1000 gallons of milk only containing 



1 See Hendrick, Journ. Ed. Agric., 1916, 22, 1095. 



