60 WEEDS OF FARM LAND 



leaves were badly burnt by both sprays, the plants as a whole 

 were not wilting or dying off. Probably a stronger solution 

 would have been more effective at this stage, but the results 

 suggest that the nickel sulphate would prove to be an effective 

 substitute for copper sulphate, though it might be necessary 

 to use it in somewhat greater concentration to hasten its 

 action. 



Potassium chloride in a 2Oto3O per cent, solution has proved 

 effective in destroying charlock, as the plants touched by the 

 liquid are completely shrivelled up. When the substance 

 can be obtained more cheaply than at present it might well 

 be given a further trial, as the potash is a most valuable 

 manure and would be beneficial in this way after the initial 

 work of weed destruction was over. The potassium chloride 

 has no bad effect on the cereals, and may be used at the rate 

 of 352 Ib. dissolved in 1092 gallons of water per acre. 1 

 Strictly speaking, this substance comes under the head of 

 manures, but as for the purpose of weed destruction it is 

 applied as a spray it is more conveniently dealt with here. 



In some places sodium bisulphate can be readily obtained 

 from the powder works at a cheap rate, and in parts of France 

 farmers have been able to get it in truck loads of 5 or 10 

 tons at the rate of 9^d. per 220 Ib. free on rail. It is a 

 most effective weed killer, resembling sulphuric acid in its 

 action, but it needs less precautions in its use. 80 gallons 

 per acre of 45 per cent, solution (i.e. 360 Ib. of bisulphate per 

 acre) are recommended for use if the fields are badly infested 

 with weeds. 2 The stuff is, however, difficult to handle, so 

 that full advantage is not taken of its availability. 



(2) Manures. The method of eradicating weeds by 

 applications of finely ground manure is not very widely used, 

 as few substances are yet known to be effective, but in recent 

 years a good deal of work has been done in this direction 

 with calcium cyanamide (lime nitrogen) and kainit. 



Calcium Cyanamide. Since the introduction of calcium 

 cyanamide as a commercial manure the Germans have been 

 using it to a considerable extent for destroying charlock and 

 wild radish. Numerous experiments have demonstrated that 

 it is quite efficient for this purpose, provided that it is applied 

 when the plants are small and while the leaves are damp. 



1 Dusserre, C. (1916), Travaux de Chimie alimentaire et d'Hygiene, VII, 

 PP. 357-358. 



2 Feuille ^information du Ministere de V Agriculture (1918), XXIII, No. 8. 



