THE ROTHAMSTED EXPERIMENTS 361 



maintain the yield of wheat, unless the azotobacter or some other 

 nitrogen-fixing agency is more efficient than our present knowl- 

 edge indicates; or unless the leguminous weeds are allowed to 

 grow in sufficient quantity to furnish and maintain the nitrogen 

 balance. 



The application of commercial nitrogen does not solve the prob- 

 lem for present conditions of general farming in the United States, 

 because at reasonable average prices the addition of $21 of nitro- 

 gen has increased the average crop values by only $8.52 under the 

 only profitable system, notwithstanding the additional phosphorus 

 and potassium also supplied in the rape cake. As would be ex- 

 pected, the applied nitrogen produced a more marked effect in the 

 fallow system, which is so very exhaustive of the soil nitrogen; 

 and in this case the minerals and nitrogen produced slightly less 

 loss than the minerals alone; so that, if produce from the mineral 

 plots could be figured at prices which would show some profit, it 

 would then be profitable to add the ammonium salts and rape 

 cake. 



The question remains whether a liberal supply of decaying or- 

 ganic matter in connection with the phosphorus fertilizer would 

 not have rendered the use of potassium sulfate and other salts 

 unnecessary or unprofitable, especially since much of the potassium 

 removed in crops would be returned in the straw and leaves. 

 Since there has been a recent change on Agdell field, by which the 

 practice of pasturing off the turnips has been discontinued, 

 Director Hall is considering the plan of applying to the " fed " 

 plots, in addition to the regular fertilizers, amounts of farm 

 manure equivalent to the root crops, straw, and clover hay pro- 

 duced on those respective plots, because that would more closely 

 agree with ordinary farming practice in England. 



In passing from the Agdell rotation field to the continuous 

 wheat-growing on Broadbalk field, attention is called to the fact 

 that as an average of the third 2o-year period the unfertilized 

 plot 3 on Broadbalk produced 12.2 bushels of wheat per acre (see 

 Table 62), which at 70 cents a bushel would be worth $34.19 in 

 four years; whereas the average value of the rotation crops 

 produced on unfertilized land during four years (as an average 

 of the third 2o-year period on Agdell field) was only $33.83 in the 



