55 



Compared with the corn crops, we see here a relatively 

 large increase from the use of mineral manures alone ; but 

 still the nitrogenous manures gave a large further increase. 

 The produce is slightly higher with ammonia salts than 

 with nitrate of soda, both in total weight and in good 

 marketable potatoes. 



The figures relating to disease are also interesting. As 

 would be expected, the proportion of diseased potatoes is 

 higher in the heavier crops grown by the use of nitrogenous 

 manures ; but it is important to notice that the crops grown 

 with nitrate were, on the average, more diseased than those 

 with ammonia salts. This, however, harmonizes with what 

 we know of the effects of the two manures on plant growth 

 generally. 



Some interesting experiments were carried out by 

 Voelcker in i68 and 1869, on the growth of potatoes in 

 rotation/ 1 ' In each year the experiment was carried out on 

 two farms. The following table gives the average results 

 per acre in each of the two years, and on the average of 

 both : 



TABLE XXXIV. 



Manures. 



1868. 1869. 



Average. 



Tons. Cwt. Lbs. Tons. Cwt. Lbs. Tons. Cwt. Lbs. 



Unmanured 4 10 33 6 11 56 5 10 100 



Superphosphate and potash 



salts 7 5 100 8 5 2 i 7 15 51 



The potash salts were in some cases crude potash salts, 

 and in others muriate of potash. Equal weights 2 cwt. 

 per acre of sulphate of ammonia and nitrate of soda were 

 used ; so that the sulphate plots received more nitrogen 

 than those dressed with nitrate. 



The average results of the two years are very similar, 

 and to a great extent repeat what we have seen in the 

 Rothamsted results. But most noticeable is the superi- 

 ority of sulphate of ammonia used with superphosphate and 

 pctash salts, not only over nitrate of soda with the same 

 minerals, but to a less extent over farmyard manure. 



The two artificial nitrogenous manures gave similar 

 results in an experiment carried out in Anglesey in 1893, 

 by the University College of North Wales, on a poor, 

 free-working soil on a clay subsoil. In this case, also, 

 equal weights of the manures were employed i cwt. per 



* " Journal of the Koyal Agricultural Society of England," 

 Vol. VI., S.S. 



