l6 MAINE AGRICULTURAL EXPERIMENT STATION. I916. 



cent, which is an amount so small that it could not be detected 

 chemically. If it were not that experience and experiment 

 have alike shown that the addition of these comparatively mi- 

 nute amounts of plant food give decisive results — often mak- 

 ing the difference between a good crop and a failure — such a 

 treatment would seem absurd. The difference in quality be- 

 tween the plant food added in the fertilizer and that carried 

 by the soil is, for the lack of a better term, called "availability." 

 The plant food of the soil is for the most part unavailable. 

 That of fertilizer is (or should be) available. The subject oi 

 soil fertility is a broad one and cannot be here discussed. It is 

 evident that these soils carry potential plant food enough for 

 hundreds of crops. The serious question for 1916 is: "How 

 much of the potash contained in the soil is or can be made 

 available for crops for the coming year?" The data are few 

 and are discussed in a circular of this Station on "Growing 

 Crops Without Potash in 19 16." The experiment reported 

 in the next section also throws some light on this question. 



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 1916 

 without the application of potash. Foreseeing the possibility 

 that the fertilizers in 1916 would contain very little, if an/, 

 potash, the Station began in 191 5 at Aroostook Farm, a series 

 of experiments to determine the effect of different amounts of 

 potash. Four different mixtures were used. In each case the 

 fertilizer contains 4 per cent of nitrogen (5 per cent of ammo- 

 nia), 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 none, on another 2 per cent, 

 on another 5 per cent, and on another 8 per cent. The plots 

 were one-half acre each and they were planted in duplicate. 



