Barn and Field Experiments in 1917. 33 



EFFECT OF OMITTING POTASH FERTILIZATION 

 UPON THE POTATO CROP. 



Since the introduction of potash in commercial fertilizers 

 in the early seventies of the last century, many experiments 

 have been made and many treatises written showing the value 

 of potash in crop growing. The experimental data on growing 

 crops without potash are very few. 



Potatoes are the chief cash crop grown in Maine. It is of 

 first importance for the growers to have what facts are avail- 

 able relative to the likelihood of obtaining a crop in 1918 without 

 the application of potash. Foreseeing the possibility that, with 

 the continuance of the war, very little potash would be available 

 for fertilizers, the Maine Agricultural Experiment Station began 

 in 191 5, at Aroostook Farm, a series of experiments to deter- 

 mine the effect of different amounts of potash. The results 

 obtained in 191 5 were published in Bulletin 246. Those for 

 1916 were published in Bulletin 260. 



Five different mixtures were used. In each case the fer- 

 tilizers contained 5 per cent of ammonia of which one-third 

 was in the form of nitrate of soda, and 8 per cent of available 

 phosphoric acid. The potash varied as follows : On one plot 

 there was no potash. The next plot also had no potash but 

 common salt was mixed with the fertilizer at the rate of 300 

 pounds of salt per acre. The salt was used to see whether this 

 would aid in freeing potash already in the soil and not in a 

 form available for plant food. The fertilizer for the remaining 

 3 plots contained respectively 3 per cent, 5 per cent and 8 per 

 cent potash. In each case the fertilizer was applied at the time 

 of planting, at the rate of 1500 pounds per acre. Each plot 

 was slightly less than one-half acre in area. The area of each 

 plot was obtained by actual measurement and the yields are 

 based on the weighed potatoes from each plot. Norcross pota- 

 toes were used for seed. Other than in respect to potash all 

 plots were treated exactly alike. The land used for this experi- 

 ment had been in sod for 2 years. The experiment was made 

 in duplicate and is separately reported. 



