84 Report of the Acting Director and Chemist of the 



according to the demands of special cases, maybe done by irrigating, 

 draining, deep culture, better ploughing, harrowing, hoeing, marling, 

 mucking, etc. It may often happen that the soil contains an abund- 

 ance of plant-food, most of which is still unavailable. Under such 

 circumstances an effort should be made to bring this food into an 

 available condition as rapidly as the plants can use it, and this may 

 be done by an improved system of tillage, together with the appli- 

 cation of such indirect fertilizers as have the power to make insolu- 

 ble plant-food available, to which attention has already been called. 

 It will thus be seen that it is not always so simple a matter to 

 tell when one should use commercial fertilizers. But the general 

 rule will be to use them when their use is attended with increased 

 profit coming from increased crops. 



2. What Constituents or Plant-Food are Needed. 



When it has been clearly settled that a soil needs the addition of 

 plant-food in order to grow crops more successfully, the question at 

 once presents itself as to what kinds of plant-food are required. 

 Does some form of nitrogen need to be supplied, or is it phosphoric 

 acid that is needed, or is it potash ? It may be only one, it may be 

 some two, or it may be all three of these constituents are necessary 

 to grow crops to the best advantage. How can we ascertain what 

 hind of plant-food is required f 



Analysis of Soils. — It was formerly thought that an analysis of 

 the soil would answer this question beyond doubt. But it is now 

 known not to be especially helpful except, perhaps, in a negative 

 way by making known the fact when there is little or no plant-food 

 in the soil. A chemical analysis may show an abundance of plant- 

 food in the soil, and yet this may be mostly unavailable, a fact 

 which is not readily ascertained by our methods of chemical analysis. 

 Again, there may be an abundance of nitrogen, potash and phos- 

 phoric acid compounds in the soil in an available condition, and yet 

 the soil may be unproductive from lack of humus, from need of 

 proper drainage, from lack of porosity, or from some other cause 

 which affects the mechanical or physical condition of the soil in 

 such a way as to unfit it for plant growth. Again, we may put upon 

 an acre of soil an amount of fertilizing constituents that will 

 greatly increase the crop, and yet an analysis of the soil before and 

 after the application will show no appreciable difference in the 

 quantity of plant-food present in the acre of soil. However deli- 



