EETUEN FOR MANURE APPLIED 69 



supply of ash constituents, the amount of nitrogen 

 recovered in the crop is seriously diminished. Other 

 nitrogenous manures generally yield a smaller return 

 than nitrate of sodium (see p. 65). 



The return from a dressing of manure is very 

 much diminished when the quantity applied is ex- 

 cessive. To obtain the largest return from the manure 

 the farmer should use sufficient manure to obtain a 

 fairly good crop, but no more. A more liberal manur- 

 ing may be profitable when the crop is fetching a 

 high price. Liberal manuring will not produce crops 

 larger than the character of the soil and season admit of. 



Most soluble and active manures produce their prin- 

 cipal effect at once, and are of little benefit to subse- 

 quent crops. Ammonium salts or nitrates usually 

 give all their effect in the first year. Sparingly soluble 

 manures, and those which must suffer decomposition 

 in the soil before they are of service to the plant, as 

 farmyard manure, bones, and Thomas' slag, will, on 

 the contrary, continue to produce an effect over many 

 years. Farmers have a prejudice in favour of the 

 latter class of manures, but it is clear that the quickest 

 return for capital invested is afforded by the former 

 class. It is evident that a small quantity of an active 

 manure will accomplish the same work as a large 

 quantity of one less active. 



At Kothamsted, where 14 tons of farmyard manure 

 were applied annually for twenty years to barley grown 

 continuously, and the manuring then ceased, about 

 thirteen years elapsed before the produce of barley 

 fell to that originally given by the unmanured land. 

 On grass land, after eight years similar manuring, the 

 hay crop took nine years to fall to its original level. 



