44 THE CHEMISTEY OF THE FAKM 



Manures of little solubility, or those for which the soil 

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

 before the growing period of the crop commences. Diffu- 

 sible manures, on the other hand, should be applied only 

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

 waste may occur by drainage. Farmyard manure, sea- 

 weed, fish manure, blood, horn, wool, meat guano, 

 oilcakes, bones, and ground phosphates, and to some 

 extent superphosphate and potassium salts, belong to 

 the former class; while nitrates, and all manures con- 

 taining ammonia, belong to the latter class. It was 

 formerly supposed that the great retentive power of 

 fertile soils for ammonia would effectually prevent any 

 loss by drainage ; we know now 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 winter climate ammonium salts or 

 guano may be applied with advantage in the autumn. In 

 a wet spring loss maybe avoided by applying ammonium 

 salts, and especially nitrate of sodium, in small successive 

 dressings instead of in one application. Late applications 

 of nitrogenous manure are, however, apt to produce straw 

 rather than corn. 



On soils of open texture, and little retentive 

 power, preference must often be given to manures of 

 little solubility, in order to diminish the loss occa- 

 sioned by heavy rain; organic manures, as farmyard 



