EXPERIMENTS WITH POTATOES 127 



AVlien a crop is to be grown on fresbly broken sod, the best 

 results will generally be obtained by plowing in a light appli- 

 cation of stable manure, and using in the drill 8 to 10 cwt. per 

 acre of a good high-grade fertilizer similar to that used in 

 Experiment I of this Bulletin. 



Chemical Fertilizers. 



In large potato-producing sections where the supply of stable 

 manure is limited many growers are obtaining splendid results 

 from the exclusive use of chemical fertilizers, using about 1,500 

 lbs. per acre. Where the physical condition of the soil is poor 

 we should recommend plowing under a crop of clover, peas, or 

 other legumes, and the application of 12 to 15 cwt. per acre 

 of a high-grade fertilizer. In using either stable or chemical 

 manures an excess should be avoided, as it tends to produce an 

 overgrowth of vines, which excludes the air and sunlight, thus 

 favoring the conditions which invite and spread the attacks of 

 the blight. 



One hundred bushels of potatoes contain about 12.6 lbs. 

 nitrogen, 4.5 lbs. phosphoric acid, and 30 lbs. potash. 



The knowledge of the analysis of the crop is of little value to 

 the grower until he has studied his soil and learned its needs; 

 but knowing both, he will be able to apply at the lowest cost 

 the proper amount of plant food required to produce a full 

 crop. 



Preparing the Ground. 



The time for plowing will depend largely upon the nature and 

 situation of the field. If infected with quack grass or located 

 upon a slope that is liable to wash, spring plowing would be 

 preferred. If plowed in the fall, an extra amount of harrowing 

 will be necessary in order to obtain the same results as pro- 

 duced by spring plowing. Whatever the time selected for plow- 

 ing, the soil should be harrowed and pulverized in a thorough 

 manner, not being content with stirring and leveling the sur- 

 face only, but using such harrows as will work deep and leave 

 the soil in the best condition to receive the crop. 



Seed. 



Good seed is one of the essentials to success in growing this 

 crop. As the potato decreases in vitality when grown from 

 poor stock, it is best to either select carefully our own seed by 



