XI.] MANURES FOR POTATOES 319 



Supposing 20 loads of dung per acre to be available for 

 the crop, the supplementary manure should consist of 

 3 to 5 cwts. per acre of kainit (the larger quantity on 

 light soils), and 2 cwts. of fish guano or kindred fertiliser 

 if the land is in poor heart and a large yield wanted. 

 Phosphates in many cases, as at Rothamstcd, arc not 

 required when dung is used, but on soils where 

 phosphates are specially necessary, as on many of the 

 clay soils so suited to the mangold crop, it will be well 

 to add 2 cwts. of superphosphate to the mixture when- 

 ever the fish guano is omitted. The after-treatment 

 will consist in giving top dressings of a mixture of 

 equal weights of nitrate of soda and salt ; about 3 cwts. 

 of the mixture at singling time, and perhaps an equal 

 amount a few weeks later, should a specially heavy 

 yield be aimed at. 



Potatoes. — It is more than usually difficult to lay down 

 general rules for the manuring of the potato crop, so 

 varied are the tilths upon which it is grown and so 

 different are the yields that are aimed at. Potato 

 growing is largely carried out in the neighbourhood of 

 great cities where dung can be cheaply obtained ; in 

 such cases the farmer will often crop suitable land every 

 other year with potatoes, taking a cereal or a green 

 crop in the intervening years. On the other hand the 

 farmer who does not make a speciality of potatoes will 

 simply plant them on a portion of his mangold or 

 Swede land, while in good potato-growing districts 

 they will form one item in a five- or six-year rotation. 

 In the Lothians, for example, a common rotation is : — 



