86 Report of the Acting Director and Chemist op the 



obtained with ap|)lication of potash compounds. And many cases 

 require a liberal supply of all three forms of plant-food. In carrying 

 on such lield-tests, several difficulties may be met. The season may 

 frequently be sucli as to intei'fere seriously with the favorable action 

 of the fertilizing materials applied. Thus, a serious drouth may 

 counteract all other conditions and prevent a satisfactory yield. 

 The difference of mechanical condition of the soil on the same farm 

 or even in the same held may prevent a fair comparison of the action 

 of different kinds of fertilizing materials and elements. But, 

 notwithstanding such difficulties, valuable suggestions will be gained 

 from an experimental study of one's soils through the behavior of 

 the crops. 



3. In What Forms is it Best to Buy Plant-Food ? 



We have previously seen that we can obtain nitrogen in several 

 different forms, such as nitrate of soda, sulphate of ammonia, dried 

 blood, tankage, lish-scrap, etc. Similarly we find in the market 

 phosphoric acid obtained from several different sources, and we also 

 find several diffei'ent potash compounds. When we come to use 

 fertilizing materials as a source of plant-food, we must decide which 

 specific forms we shall apply. To illustrate, in applying some form 

 of niti'ogen, shall we use nitrate of soda, or sulphate of ammonia, or 

 dried blood or fish-scrap ? Shall we use as our source of phosphoric 

 acid bone-meal, dissolved bone, acid phosphate, dissolved bone-black 

 or Thomas slag ? Shall we apply muriate of potash, or sulphate of 

 potash or carbonate of potash 'i What principles are there to guide 

 us in making the best choice ? 



In deciding wliat form of material to use for plant-food, we 

 should be guided by 



(1) The availability of the plant-food, 



(2) The preference, if any, shown by different plants, and 



(3) The comparative economy possible in purchasing different 

 materials. 



Availability of Different Forms of Plant-Food. — As a rule, 

 commercial fertilizers are used for the purpose of increasing the 

 single season's crop to which i^iey are applied. Most farmers plan 

 to give to each succeeding crop by itself the plant-food it needs, and 

 to avoid supplying any one crop with more material than it can use 

 to best advantage. This is especially true of those who do not own 

 the farms which they work and who plan each years' work 



