28 EXPERIMENT STATION. [Jan. 



COMPARISO^^ OF DlFFERE^^T PlIOSniATES. 



This is the sixteenth year of the experiment, the plan and 

 oLject of which is quoted from the twenty-third annual re- 

 port : — 



Ten of the leading materials which may be used as a source of phos- 

 phoric acid have been under eomjiarison in one of our fields since 1897. 

 The different materials are applied to the separate plots in such quan- 

 tities as to furnish equal amounts of actual phosi:)horic acid to each. 

 There are three check plots to which no phosphate whatever has been 

 applied during the entire period of tlie experiment. All the plots receive 

 annually equal and liberal quantities of materials supplying nitrogen 

 and potash in highly available forms. The field has been used for a 

 large variety of crops, the succession having been as follows: corn, 

 cabbages, corn, oats and Hungarian grass (followed by rye plowed 

 under), onions, onions, corn, mixed grass and clover three years, cab- 

 bages and soy beans and potatoes. 



In view of the fact that the results of similar experiments 

 (comparison of different materials as sources of phosphoric 

 acid) in other States have not shown the marked differences 

 between the "Tound rock phosphates and the more solul)le 

 phosphates that our results show, and in view of the fact that 

 the humus content of the different soils is claimed by some 

 authorities to be the cause of the differences in the showing' of 

 the rock phosphates, it has been our aim in the treatment of 

 the field for the last few years to get as much humus into the 

 soil as possible. 



In 1911 the field was seeded in May with oats and alfalfa. 

 Two crops were harvested, one in July and one in September. 

 In 1912 the field was plowed and Japanese Buckwheat sown, 

 which was plowed under in July. In August rye was sown, 

 to be plowed under in the spring. 



