Food for Plants. 151) 



organic materials. They point ont that land under cul- 

 tivation is gradually being depleted of its store of nitro- 

 gen even when nitrogenous fertilizers are applied each 

 year and that the average recovery of nitrogen applied 

 m the form of hsh scrap for a period of nine years, was 

 only 36.36 per cent. 



With the same nitrogen treatment soils allowed to run 

 wild just about maintained their nitrogen content, while 

 the carbon content of these soils was slightly increased. 



The recoverv of nitrogen in the four different treat- 

 ments for the 20 years is shown l)y the curves in figure 

 1. A study of these curves shows that the high points 

 are generally reached in either the first or second year 

 of oats, and in the wheat year, while the low points occur 

 almost invariably in the corn and timothy years. It is 

 not entirely clear whether this is a seasonal variation or 

 a crop characterisic. 



It is certain, however, that the utilization of the resid- 

 ual nitrogen by the corn crop which follows the oats, 

 helps to explain the high recovery for the years when 

 oats are grown. 



Conclusions. 



In a 5-year rotation on Penn loam soil well supplied 

 with phosphoric acid, potash and lime, crop yields were 

 better maintained over a period of 20 years with nitrate 

 of soda at the rate of 320 pounds per acre than with an 

 equivalent amount of ammonium sulfate or dried blood. 

 For several years the latter gave results about on a par 

 with the nitrate, but an average of the second 10-year 

 period shows a considerable falling off with these materi- 

 als as compared with the nitrate. This is no doubt due 

 in part to the fact that the nitrate, being immediately 

 available, gives the plant an early start which tends to 

 keep it in the lead and to the further fact that in the trans- 

 formation of the ammonium salt and the organic material 

 into nitrates, there is a considerable loss of nitrogen, pos- 

 sibly as ammonia gas or gaseous nitrogen or both. The 



