MANURES AND MANURING- 3? 



a heavy crop. It is more from a mechanical standpoint 

 that farmyard manure is a valuable aid to potato culture. 

 In this capacity horse dung increases the porosity and the 

 temperature of heavy soils, and so>\ or pig dung serves to 

 bind light or sandy soils together, conserve the moisture 

 in dry seasons, and, consequently, provide a congenial 

 pabulum for the surface roots. Thus, in the case of heavy 

 soils, by rendering them porous and warmer, healthy root 

 action is encouraged, and they are in a better condition 

 to receive such artificial manures, and to facilitate their 

 assimilation by the roots. Then on the lighter soils the 

 conservation of moisture, and their greater compactibility, 

 enable the artificials to be held in reserve till the roots can 

 assimilate them, instead of being washed into the subsoil. 

 All authorities are agreed, however, that it is unwise to 

 use farmyard dung too liberally. It has a tendency to pro- 

 duce over-luxuriance, and to subject a crop to disease in 

 wet seasons. It is clear, therefore, that farmyard dung 

 should only be used in moderate quantities, and for a 

 mechanical, rather than a chemical reason. 



Phosphatic Manures. Experiments have already 

 demonstrated that phosphates in som? form are absolutely 

 necessary for the successful culture of the potato; in fact, 

 all the special compound manures prepared for potatoes 

 contain superphosphate. As previously pointed out, there 

 are several forms of phosphatic manures, arid the question 

 to be decided here is, which is the best form of phosphate 

 to use. Well, on soils that are known to contain a fair 

 quantity of lime, the acid phosphates superphosphate 

 and dissolved bones are best ; while on those that contain 

 no lime, such as peats and clays, non-acid phosphates 

 basic slag, bone-meal, or Peruvian guano are more suit- 

 able. The two first act more rapidly, however, than the 

 latter. 



Potash Manures. There seems to be a difference of 

 opinion among experts as to the value of potash as a 



