200 AGRICULTURAL EXPERIMENT STATION. [Jan. 



5. Experiments to study the Economy of using Dif- 

 ferent Commercial Sources of Phosphoric Acid 

 FOR Manurial Purposes in Farm Practice. 



Field F. 



The field selected for this purpose is 300 feet long and 

 137 feet wide, runnnig on a level from east to west. Pre- 

 vious to 1887 it was used as a meadow, which was ^vell 

 worn out at that time, yielding but a scanty crop of Eng- 

 lish hay. During the autumn of 1887 the sod was turned 

 under, and left in that state over winter. It was decided to 

 prepare the field for special experiments with phosphoric 

 acid by a systematic exhaustion of its inherent resources of 

 plant food. For this reason no manurial matter of any de- 

 scription was api)lied during the years 1887, 1888 and 1889. 



The soil, a fair sandy loam, wmis carefully prepared every 

 year l>y ploughing during the fall and in the spring, to 

 improve its mechanical condition to the full extent of exist- 

 ing circumstances. During the same period a crop Avas 

 raised every year. These crops were selected, as far as 

 practicable, with a view to exhaust the supply of phosphoric 

 acid in particular. Corn, Hungarian grass and leguminous 

 crops (cow-pea, vetch and serradella), followed each other 

 in the order stated. 



1890. — The land had been ploughed during the preceding 

 fall, and again April 19, 1890. The field was subdivided 

 subsequently into five plats of definite size, each running 

 from east to west. These plats were separated from each 

 other l)y a space eight feet wide. 



The plats and spaces between them were ploughed and 

 harrowed alike. The plats Avere fertilized at stated times ; 

 the spaces which separated them received at no time any 

 kind of manurial matter. 



The manurial material applied to each of these five plats 

 contained, in every instance, the same form and the same 

 quantity of potassium and of nitrogen, while the phosphoric 

 acid was furnished in each case in the form of a different com- 

 mercial phos|)horic-acid-containing article ; namely, phos- 

 phatic sl;ig, jSIona guano, apatite, South Carolina phosphate 



