1893.] PUBLIC DOCUMENT — No. 33. 197 



5. Field Experiments with Different Cooiercial 

 Phosphates to study the Economy of using 

 THE Cheaper Natural Phosphates or the More 

 Costly Acidulated Phosphates. 



Field F. 



The field selected for this purpose is 300 feet long and 

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

 vious to 1887 it was used as a meadow, which was well 

 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 fiekl 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 applied during the years 1887, 1888 and 1889. 



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

 year by 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 was 

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

 practicable, with a view to exhaust the supply of phos[)horic 

 acid in particular. Corn, Hungarian grass and leguminous 

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

 in the order stated. 



1890. — The field was subdivided into five })lats, running 

 from east to west, each twenty-one feet wide, with a sj)ace 

 of eight feet between adjoining plats. 



The manurial material applied to each of these five plats 

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

 (juantity of potassium and of nitrogen, while the phosphoric 

 acid was furnished in each case in the form of a dift'erent com- 

 mercial phosphoric-acid-containing article ; namely, phos- 

 phatic slag, Mona guano, Florida phosphate, South Carolina 

 phos})hate (floats) and dissolved bone-black. The market 

 cost of each of these articles controlled the quantity applied, 

 for each plat received the same money value in its particular 

 kind of phosphate. 



