1889.] PUBLIC DOCUMENT — No. 4. 507 



A careful study of these results shows that neither phos- 

 phoric acid nor any form of nitrogen, when applied each by 

 itself, even in exceptionally large proportions, has produced 

 a material change in the annual yield, as compared with that 

 obtained on unfertilized plats. The application of potash 

 compounds alone shows in every instance a decided increase 

 in the crop. The annual yield was increased by its use 

 during the first two years to twice the amount of that pre- 

 vious to its special application. 



1888. — The original plan of the experiment has not been 

 altered materially during the past season. The principal 

 aim of our investigation has been the same as during the 

 three preceding years ; namely, to study the direction and 

 the degree of exhaustion on plant food of field "A" during 

 the progress of our investigation. 



The results of the past season (1888) confirm the conclu- 

 sion presented in our previous annual report, 1887. An 

 exceptional deficiency of the soil on available potash, pro- 

 duced by continued close rotation of grasses and corn 

 fodder, without any substantial provision for an exception- 

 ally large consumption of potash, proves still the first cause 

 of a reduced annual yield of corn fodder. 



The exhaustion on available plant food assumes, however, 

 as might be expected, a more general character as years 

 pass on. This fiict shows itself plainly in a gradual falling 

 off of the annual yield on plat 9, where a liberal amount of 

 potash as the sole fertilizing material exerted in preceding 

 years a marked beneficial influence on the annual yield. The 

 same circumstance causes evidently the lower yield upon 

 those plats (1 and 7) which received a liberal manuring with 

 potash compounds two years later, and, after a repeated 

 application of each, phosphoric acid or nitrogen had failed 

 to improve the annual yield. 



A manuring for three successive years with potash alone 

 has sufficed in our case to terminate its beneficial effect on 

 the natural productiveness of the soil, as far as the corn 

 crop is concerned. More complete manures are required to 

 restore a desirable degree of fertility of the soil. 



The result obtained on plat 6 deserves a particular notice. 

 This plat had been used, in common with the entire area 



