No. 4.] KEEPING UP FERTILITY. 109 



slower acting materials as a rule ; or, if you decide upon 

 nitrate of soda, apply half at planting, one-fourth when the 

 crop is one-quarter grown, the balance when it is half grown. 

 As for the amount to use, until we learn how to do better, 

 ai)ply once and a half what the increase expected in the crop 

 will remove, except for legumes ; for these use but a very 

 small amount to give them a start ; force them to draw from 

 the air. 



General Rules. 



For corn, potatoes, clover, peas and beans make potash a 

 prominent constituent of the fertilizers used. For grass, 

 and in general for all crops which start into growth very 

 early in the spring, use nitrate of soda freel}-. This is 

 necessary, for the fall and winter rains wash out of the soil 

 most of its available nitrogen compounds. During warm 

 summer weather such compounds are formed hy natural 

 agencies from the organic matter in the soil, and are ready 

 in season to feed a late-growing crop like corn. For such a 

 crop, therefore, it is unnecessary under ordinary circum- 

 stances to apply a large amount of nitrogen. 



Phosphoric acid hastens the ripening of most crops, and a 

 liberal use of it may be an advantage where earliness is 

 particularly desirable. It is also, according to Wagner, 

 particularly essential for all fodder crops. 



Summary. 



The leading points that I have endeavored to bring out 

 are the following : — 



1. The productiveness of soils depends in no small 

 degree upon their physical character. 



2. To secure the conditions essential to the best effects 

 of manures and fertilizers, and to utilize in so far as practi- 

 able the natural resources of the soil, which are enormous, 

 good drainage, fall ploughing and thorough tillage are 

 essential. 



3. Soils can hold phosphoric acid and potash; they do 

 not hold soluble nicroiien. We niav wiselv endeavor to 

 accumulate a reserve of the two former, but not of the latter 

 except in the form of organic matter. 



4. The culture of suitable crops which can grow late in 



