25S Bueeau oe Farmers' Institutes. 



An examination of the foregoing table justifies the assertion, 

 when we consider all the conditions, that the smallest amounts of 

 plant food we can expect to use on an acre of land with any 

 satisfactory results are the following: 



Ten pounds of nitrogen. 



Fifteen pounds of available phosphoric acid. 



Twenty pounds of potash. 



To state this in another form, the foregoing amounts of nitro- 

 gen would be contained in 200 p.ounds of a fertilizer having the 

 following composition : 



Nitrogen, 5 per cent. 



Available phosphoric acid, 7£ per cent. 



Potash, 10 per cent. 



This would be regarded as a high-grade fertilizer, and on some 

 soils an application of 200 pounds an acre would be considered 

 large, while on others it Avould be entirely insufficient. The 

 above rule will probably be found fairly safe to follow in fertil- 

 izing average crops, when we know nothing at all in regard to soil 

 or crops. 



Kind of Farming. — The amount of plant food required for 

 the economical growth of plants must depend to some extent upon 

 the specific character and method of farming. In the case of 

 garden truck crops, where it is desired to secure maximum crops 

 at the earliest possible time of season, it is the practice to apply 

 amounts of plant food which would be considered excessive in 

 general farm practice. The farmer who practices an intelligent 

 form of rotation can raise crops with less expenditure for fertil- 

 izers than can the one who does not use a desirable form of ro- 

 tation. The subject of rotation of crops is of such importance 

 in connection with the use of plant food, that we will later con- 

 sider it in some of its more important applications. 



4. Ix What Forms Is It Best to Buy Plant Food? 



We have previously seen that we can obtain nitrogen in several 

 di I'm 'lint forms, such as nitrate of soda, sulphate of ammonia., 

 dried blood, tankage, fish-scrap, etc. Similarly we find in the 

 market phosphoric acid obtained from several different sources, 

 and we also find several different potash compounds. When we 

 come to use fertilizing materials as a source of plant food, we 



