REPORT ON PHOSPHATIC AND AMMONIACAL MANURES. 139 



extent on the soil to which it is to be applied. The chemical 

 composition of the soil varies greatly, and it would be folly to 

 suppose that So and So's "potato manure," or "wheat manure," 

 even although found to have the best proportion of phosphatic 

 and nitrogenous elements for one class of soil, should be equally 

 adapted to others. The object for which we supply all special 

 manures is either to supply the soil with some element or 

 elements in which it is deficient, or to counteract the injurious 

 predominance of some constituent in the soil. The chemical 

 composition of the soil is therefore altered by every such appli- 

 cation. What wonder, then, that farmers should find on fields 

 to which guano, or any other special manure, has been applied 

 year after year, " thas guano does not ' tell ' as it used to do." 

 We think it may be laid down as a general rule, to which there 

 may be many exceptions, " that the heavier, or, in other words, 

 the more clayey the soil, the larger should be the relative propor- 

 tion of nitrogenous to phosphatic elements in the manure, and 

 vice versa." 



The best proportions in which these substances should exist 

 in a manure, depend to a great extent, also, on the plant to which 

 it is to be applied. Some plants, such as wheat and Italian rye- 

 grass, are benefited by nitrogenous manures alone ; while the 

 produce of others, such as yellow turnips, growing on the same 

 soil, is increased only by phosphatic manures ; not that a crop 

 of turnips takes less nitrogen from the soil than does a crop of 

 wheat, for the reverse is the case. An average crop of the 

 former takes 60 lbs. nitrogen, while an average crop of the latter 

 takes only 45 lbs.;* and this leads to the remark, that the 

 analyses of plants afford no criterion to the farmer what should 

 be the most profitable proportional quantity of phosphatic and 

 nitrogenous elements to apply in the manure. 



We have found to a certain extent, " that the longer that a plant 

 takes to grow, the greater is the benefit derived from nitrogenous 

 manures ; and the shorter, the greater the benefit from phosphatic 

 manures." Whatever may be the cause, this hypothesis is, so far 

 at least, backed by practice. With the cereals, wheat is oftenest 

 grown with purely nitrogenous manures — nitrate of soda, for 

 instance ; to oats, a proportion of phosphates is added, Peruvian 

 guano being a very common manure for that crop ; to barley the 

 proportion of phosphates is increased, and it is said that if the 

 barley be sown late, the proportion of phosphates may be still 

 further profitably increased. With green and root crops the 

 same is the case ; cabbage requires the largest proportion of the 

 manure to be nitrogenous ; for mangold, the proportion of phos- 

 phates may be increased ; for swedes, still further ; while for 



* Dr Anderson, in " Transactions of Highland Society," March 1861, p. 568. 



