THE POTATO 91 



crops, ' and a part of this potential plant food can 

 be made available for the use of plants by tillage, 

 and drainage, if necessary. The experiments of 

 the Cornell station, which have now covered four 

 seasons, were planned with a view to learning 

 what superior tillage and care would do in the 

 way of unlocking the hoarded fertility of the soil 

 and increasing the yield of the crops. 



"The soil on which the potatoes were grown has 

 been continuously under crop without fertilizers 

 since the winter of 1893-94, except that cover crops 

 of rye, crimson clover, or wheat, to be turned under 

 in the spring, have as a rule been grown. But the 

 growth of these has necessarily been so small and 

 the cropping so intensive that the soil is beginning 

 to show a deficiency of humus, indicated by its 

 tendency to become hard and compact under beat- 

 ing rains; for fi in order to keep a soil permanently 

 in good physical condition, it is absolutely neces- 

 sary that organic matter be returned in some way, 

 either by green manuring or the use of barn ma- 

 nures. * 



"Notwithstanding this fact, the yields in the 

 Cornell experiments have been much above the 

 average each year. This was as true of 1898 as of 

 previous years, in spite of the additional fact that 

 the latter season was one of severe drought and the 

 soil used in the experiments 'is gravelly and porous 

 and especially subject to injurious effects from 

 drought. ' 



"It is probable that frequent and deep plowing 

 has done much to bring and keep the land pro- 

 ductive. So far as the plowing is concerned all 

 plats have received the same treatment. The land 

 has been turned from two to three times each 

 year, and the pulverizing which has resulted there- 



