39 



action, and that in the district where the experiments were 

 carried out, farmyard manure seems necessary to produce 

 a full crop of wheat. The actual increase obtained by the 

 various dressings of nitrogenous manures is, therefore, less 

 than would be usually obtained. Comparing the yields of 

 the different plots, however, we see that the limit of 

 economy was reached for autumn sowing at i cwt. per acre 

 of sulphate of ammonia ; 2 cwt. giving less corn and less 

 straw than i cwt. When half the sulphate was applied 

 in the spring, better results were obtained, as would be ex- 

 pected from what has already been said on this point. 



One point should be mentioned in connection with the 

 results obtained at Flitcham, the station not included in the 

 above table. It will be remembered that the soil here was 

 remarkably deficient in potash, so that without potash 

 manuring other artificials gave a very small return ; but 

 with potash they gave a comparatively large increase. The 

 results afford a very good example of the fact already noted, 

 that the presence of potash seems particularly important 

 if sulphate of ammonia is to produce its full effect ; for that 

 manure gave relatively worse results at Flitcham than at 

 the other two stations Whitlingham and Cawston in the 

 soils of which available potash was comparatively plentiful. 



In experiments with wheat carried out on sterile sand, 

 Pagnoul has found the same thing.* When a complete 

 manure was supplied, there was little difference in the 

 results obtained from the two manures; but if potash were 

 deficient, nitrate was twice as effective as sulphate. In a 

 second year's experiment,! he found that, while the addi- 

 tion of potash to nitrate increased the yield in the pro- 

 portion of 13 : 10, potash with sulphate increased it as 

 26 : 10. The weight of individual grains of corn was 

 increased by potash with nitrate in the proportion of 

 14 : 10, and with sulphate of ammonia in the proportion 

 of 17 : 10. 



A possible cause of the less favourable effect of sulphate 

 of ammonia when potash is deficient has been mentioned 

 already viz., the need of potash for the formation of 

 carbohydrates, and the importance of carbohydrates in 

 the plant for the formation of asparagine from the nitrogen 

 of ammonia salts, preparatory to the further formation of 

 albuminoids, &c. The nitrate of soda, also, may perhaps 

 give its better effect under these conditions, by the soda 

 of the manure taking the place of potash to some extent 

 in the plant, and so partially supplying the deficiency. 

 The evidence on this point is conflicting; but the results 

 obtained by some investigators seem to make this explana- 

 tion possible. >? ^,p^. -i*q? 



The Rothamsted wheat7experiments have already been 



* " Comptes Rendus," 111. t " Ann. Agron," 17. 



