following showed only bushel to the credit of the cake 

 manure. The succeeding clover was fed off on the land by 

 sheep ; on the cake plot the sheep received 728 Ibs. of 

 decorticated cotton-cake, and on the maize plot 728 Ibs. of 

 maize-meal. The wheat following the clover showed, on an 

 average, about 1 bushel of wheat in favour of the maize 

 plot. The richer manure thus gave, on the whole, no greater 

 crops than the poorer. 



The absence of any practical result from the excess of 

 nitrogen, known to have been applied on the cake plots, was 

 probably due to the presence in the soils of all the plots of a 

 supply of available nitrogen quite sufficient for the production 

 of crops as large as the other conditions of soil and season 

 would admit of. The swedes, in fact, averaged 17 tons, the 

 barley 46 bushels, and the wheat 41J bushels per acre, a 

 produce very good for the light land in question. 1 



It is important to remember that the utilisation of nitro- 

 genous organic manures by crops is sharply limited by 

 several conditions. The amount of nitrogen in the soil has 

 no influence on its fertility, except so far as it leads to the 

 production of nitrates ; the limitations to nitrification may 

 thus constitute an obstacle preventing the growth of bigger 

 crops. Imperfections in tillage, a deficiency or excess of 

 water in the soil, the presence of an excess of readily oxidisable 

 organic matter, or a lack of carbonate of lime, may each of 

 them effectually limit the fertility of the land, notwithstanding 

 the application of large quantities of farmyard manure. 



If the limitation is not due to an inadequate production of 

 nitrates in the soil, it may be due to an inadequate supply 

 of some of the ash constituents required by crops. The more 



1 Dr. Voelcker's remarks on this point may be quoted : " On comparing 

 the produce of the wheat and barley on these rotation plots with that obtained 

 on the adjoining permanent corn plots, highly manured every year, it was found 

 that the average produce of wheat on the maize-meal plot was higher than 

 the highest average produce, viz. 38'8 bushels, obtained, during the corre- 

 sponding years on the permanent wheat plots ; and that the average produce 

 of the barley was also nearly as high as that of the most highly manured 

 plots of the permanent barley. From this it appeared that, even with the 

 poorer maize-meal manuring, crops of wheat and barley about as heavy as 

 the land could produce were actually obtained. This being so, it would not 

 be possible for the richer cotton-cake to give more than the maximum viold 

 for the land, and, accordingly, the difference between the richer and the 

 poorer manuring could not be brought out." 



