PRACTICAL REMARKS 101 



The composition of the potatoes grown with sulphate of am- 

 monia, superphosphate and alkalies, is seen to be almost 

 identical with the composition of those grown with farmyard 

 manure and some superphosphate. The chemical composi- 

 tion of potatoes is by no means so greatly affected by the 

 conditions of manuring as the composition of mangel wurzel. 



That the best results as to quality are obtained from the 

 use of a well-balanced manure, may be further illustrated from 

 one of the Glasgow experiments, in which a second early variety 

 of potatoes was grown in an ordinary rotation after grass seeds. 

 Many varying proportions of sulphate of ammonia, superphos- 

 phate, and sulphate of potash, were tried. The crops obtained 

 were heavy, several exceeding 10 tons per acre. The best 

 quality of saleable potatoes was obtained from manure contain- 

 ing 2^ cwts. sulphate of ammonia, 7 cwts. superphosphate, and 

 2 cwts. sulphate of potash. When the sulphate of ammonia 

 was raised to 3^ cwts. the crop was considerably increased, but 

 the quality of the potatoes distinctly deteriorated. Professor 

 Campell, who conducted the experiments, concludes that 

 a corresponding increase of potash and superphosphate should 

 accompany any increase in the ammonia. 



4. Practical Remarks. The potato is a plant yielding 

 a small crop of high feeding quality. Being a favourite article 

 of human food it fetches a relatively high price, and its culture 

 is for this reason often extremely profitable. Its roots being 

 confined to the surface soil, it requires an abundance of 

 available plant food in its immediate vicinity if a good crop 

 is to be obtained. In order that the plant food present 

 should give a good return, it is essential that the surface soil 

 should be in a condition of fine tilth. 



The potato crop is one that especially flourishes in a 

 soil containing a considerable proportion of humus. The 

 presence of this humus ensures the possession by the soil of 

 the favourable physical condition which the potato especially 

 requires ; the humus will also increase the availability for the 

 crop of the phosphates and potash in the soil. Farmyard 

 manure has always been the favourite manure for the potato 

 crop. 



