MANURES. 35 



Manures of little solubility, or those for which the soil 

 has a great retentive power, may be applied to the land 

 some time before the growing period of the crop. Dif- 

 fusible manures, on the other hand, should be applied 

 only when the crop is ready to make use of them, else 

 serious loss may occur from drainage. Farmyard manure, 

 rape cake, and bones, and to some extent superphosphate 

 and potassium salts, belong to the former class ; while 

 nitrates, and all manures containing ammonia, belong to 

 the latter class. It was formerly supposed that the great 

 retentive power of fertile soils for ammonia would effectu- 

 ally prevent any loss by drainage ; we now know that 

 ammonia is speedily converted into nitrates after mixing 

 with the soil, and that these nitrates are readily washed 

 out by heavy rain. 



Following these principles, an autumn manuring for 

 wheat may consist of farmyard manure, blood, or shoddy, 

 with or without superphosphate ; but dressings of guano, 

 ammonium salts, or nitrate of sodium should be deferred 

 till the spring. The question is, however, clearly one 

 of climate, and with a dry wdnter climate ammonium 

 salts or guano may be applied with advantage in the 

 autumn. 



On soils of open texture, and little retentive power, 

 preference must often be given to manures of little solu- 

 bility, in order to diminish the loss occasioned by heavy 

 rain. Bulky organic manures, as farmyard manure or sea- 

 weed, are in such cases very suitable. 



No dressing of manure is completely taken up by the 

 crop to which it is applied, dressings larger than the 

 actual requirements of the crop must therefore be applied 

 to obtain a given result. Soluble and active manures 



D 2 



