422 INVESTIGATION BY CULTURE EXPERIMENTS 



phorus amounts to 42 pounds (usually in dissolved bone black). 

 On two plots (12 and 35) the phosphorus (42 pounds) is applied in 

 the form of ground bone, which also supplies 10 pounds additional 

 nitrogen. 



Farm manure (commonly called " yard manure," but sometimes 

 " barn manure," in the Pennsylvania Reports) was applied at 

 three different rates, 12, 16, and 20 tons per acre (one half for corn 

 and the other half for wheat), and in addition 12 tons were applied 

 on one of the caustic lime plots (No. 22). No analysis seems to 

 have been made of the manure, but the Pennsylvania Station has 

 at times adopted an average published by the United States De- 

 partment of Agriculture, representing one ton to contain 9.8 pounds 

 of nitrogen, 2.8 pounds of phosphorus, and 7.1 pounds of potas- 

 sium, figures that are not far from the general average of yard 

 manure (10, 3, 8). Probably the 20 tons of manure carry a third 

 more nitrogen and phosphorus, and nearly the same amount of 

 potassium, as the heaviest fertilizer application (144 Ib. N, 42 Ib. P, 

 and 166 Ib. K). 



The other applications for each four years include 640 pounds 

 of land-plaster (gypsum) , 4 tons of ground limestone, and 2 tons of 

 caustic lime, weighed as calcium oxid and applied after being water- 

 slacked. 



In addition there are five plots in each series that have received 

 no fertilizer since 1882, but one of these (No. 8) is reported to have 

 received annual applications of farm manure during the 10 years 

 previous to 1882. 



The numbering of plots and the treatment applied for one series 

 of 36 plots is the same as for every other series. By using four 

 different series, four times as much data are secured during a given 

 number of years as could be secured from one series. Thus, dur- 

 ing the 24 years (1885 to 1908), there have been 24 crops of corn, 

 24 of oats, 24 of wheat, and 24 of hay, with every different kind of 

 treatment; whereas, during 61 years, on Agdell field at Rotham- 

 sted there have been harvested only 15 crops of turnips, 15 of 

 barley, 15 of legumes, and 15 of wheat (the turnips having failed 

 one year). Of course the effect of 60 years' cropping cannot be 

 secured in 27 years, but the Pennsylvania system must give more 

 trustworthy results for the like number of years. 



