220 BOARD OF AGRICULTURE. 



one-half (50 per cent.) of the nitrogen applied in the fertilizer is 

 recovered, ihe remainder is either lost in the drainage water, or is 

 carried down into the subsoil or held in the soil. It has been demon- 

 strated that very little if any influence is exerted by the nitrogen in 

 chemical fertilizer after the second year, and even the second 3'ear 

 this influence is very slight. AYith potash and phosphoric acid the 

 case is different, the effect of a large application being felt for many 

 years. This is explained hy the fact that nitrogen in the form 

 suitable to be used by plants is readily washed out of the soil, while 

 potash and phosphoric acid combine with the soil, and though not 

 immediatel}' available are gradually made so, and hence in time will 

 be largely recovered. 



On this point the conclusions of Lawes and Gilbert are expressed 

 as follows: '"While the soil fixes potash and phosphoric acid 

 independent of vegetation, nitric acid is only fixed by the agency of 

 vegetation." 



This being true, it follows that we must apply a suflficient excess 

 of plant food so that the roots may avail themselves of a quantity 

 equal to the excess which the full crop contains above the natural 

 capacity of the land. With nitrogen we should carefully look to see 

 just what amount may be used to advantage, for what is not 

 recovered the first year is quite likeh- to be lost ; with phosphoric 

 acid and potash this is less important since the excess above that 

 utilized b}' the plant, is retained in the soil and maj' be had by 

 future crops. 



What has thus far been said may be summarized as follows : 



First. Plants draw their nourishment from the soil and air. 



Second. The term plant food is applied to all substances which 

 help to nourish the growing plant. 



Third. From one to five per cent of the food of the plant comes 

 from the soil, the remainder coming from the atmosphere. That 

 which comes from the soil is the part that must be looked after by 

 the farmer. 



Forirth. The plaui food taken from the soil I have divided into 

 two kinds, one, abundant, and so far as the farmer is concerned 

 this requires little or no attention ; the other, deficient, or scarce in 

 an available form when soils are worn out by cropping. Deficient 

 plant food amounts to about fifty per cent., on an average, of the 

 total plant food taken from the soil (that is the total ash plus 

 nitrogen) . 



