XI.] MANURES FOR POTATOES 321 



nitrogen they require should be derived more from 

 mellow soil in high condition than from recent manure. 



(2) A good supply of phosphatic manure has been 

 shown to be important. 



(3) Potash is essential, since the potato is a starch- 

 making plant. 



(4) Manures setting up an alkaline reaction should 

 be avoided, since they facilitate the attack of Oospora 

 scabies, the fungus causing potato scab. Hence sulphate 

 of ammonia should be preferred to nitrate of soda for a 

 top dressing and superphosphate to basic slag ; lime 

 also should not be used. 



As regards the use of dung it has been repeatedly 

 shown that a better return is obtained by using 

 farmyard manure in moderate quantities of 20 

 loads per acre or so and supplemented with artificial 

 manures, than by spending all the money available for 

 manuring upon dung alone. On any but the heaviest 

 soils it is better to plough in the farmyard manure in 

 the autumn and so get the land into good heart, but on 

 the close badly working soils it is an advantage to the 

 potato plant to have the ground left a little hollow by the 

 decay of the farmyard manure ; on such soils, therefore, 

 the dung should be applied in the drills just before 

 planting. The mixture of artificials should either be 

 sown broadcast before the land is ridged up or sown 

 upon the farmyard manure in the drills before the 

 ridges are split. For ordinary cropping a mixture of 

 4 cwts. per acre of superphosphate, i cwt. of sulphate of 

 potash and i cwt. of sulphate of ammonia will be ample ; 

 when extra heavy crops are aimed at, 2 cwts. or so of a 

 good guano may be added to the mixture already 

 specified, and a further hundredweight of sulphate of 

 ammonia may be applied as a top dressing when the 

 haulm is beginning to appear. 



X 



