57 



With a full mineral manuring, sulphate of ammonia and 

 nitrate of soda gave practically equal results. More ex- 

 ceptional, however, is the fact that the omission of kainite 

 from the full manuring containing sulphate of ammonia 

 caused a distinct increase in the produce. Possibly a 

 lighter dressing of kainite would have given a better return 

 than either the amount applied or the total omission of 

 potash manure. 



The composition of potatoes grown with various manures 

 is chiefly important to the farmer when they are to be used 

 for feeding stock. It is, however, worth mentioning that, 

 just as we have seen with mangels, that the amount of 

 sugar produced per acre is greater by manuring with 

 ammonia salts than with nitrate of soda, when farmyard 

 manure is also applied to the crop, so with potatoes we 

 find that the chief feeding material they contain starch 

 is formed in larger quantity per acre with ammonia manures 

 than with nitrate. The amount of starch per acre per 

 annum in the crops on some of the plots at Rothamsted, 

 on the average of ten years 1876 to 1885 was as 

 follows : 



TABLE XXXVII. 



No manure 1,120 Ibs. starch 



Mineral manures 1,988 ,, 



Minerals and ammonia salts .... 3,436 ,, 



Minerals and nitrate of soda .... 3,368 



The difference between the two plots receiving nitro- 

 genous manures, though not very large 68 Ibs. of starch 

 per acre is still distinctly in favour of ammonia salts. 



Comparing all the evidence at our disposal, we may 

 safely conclude that, in practice, sulphate of ammonia will 

 prove the best nitrogenous manure for potatoes, and will 

 often give highly remunerative results. The quantity used 

 will, of course, vary according to the condition of the land 

 and the other manures employed ; but it should usually be 

 between i and 2 cwt. per acre. 



BEANS. 



This plant is a member of the natural order Leguminosse, 

 and, like other leguminous plants, has the special power 

 already noticed of obtaining the nitrogen it requires from 

 the air by means of the bacteria in the nodules on its roots. 

 As we should expect, therefore, it benefits less from the 

 application of nitrogenous manures than any of the other 

 crops we have noticed. The number of field experiments 

 with beans bearing on our subject is small, and may be 

 dealt with in few words. 



In experiments on the continuous growth of beans, Sir 

 John Lawes and Sir Henry Gilbert found that nitrate of 

 soda produced greater effect than ammonia salts, but that 

 mineral manures were more important than either in their 



- 



