90 Maine Agricultural Experiment Station. 1920. 



The results of the greenhouse experiments to a large ex- 

 tent confirm the field observations. Potato plants in pots con- 

 taining no commercial fertilizer and those in pots to which a 

 borax-free fertilizer was added were free from injury. No 

 plants which received fertilizer containing borax escaped injury 

 in some form or other. In general the amount of injury varied 

 with the amount of fertilizer used, but the results were not uni- 

 from in this respect. 



Except where the largest amount of borax was applied, the 

 type of injury in the greenhouse differed in some important 

 respects from that observed in the field. Killing of the tips 

 and margins of the leaves was characteristic of the greenhouse 

 potato plants. At the rate of 17.6 pounds of anhydrous borax 

 per acre the most severe leaf injury was obtained where the 

 fertilizer was mixed with the upper 6 inches of soil in the pot 

 or with the 3 inches of soil below the seed-piece and the plants 

 heavily watered. The larger applications of boron caused 

 greater root injury, more stunting of the plants and less tip and 

 marginal injury to the leaves. 



An application of fertilizer in the drill equivalent to 4.4 

 pounds anhydrous borax per acre caused severe injury to beans, 

 while broadcasting the same fertilizer, applying the equivalent 

 of 8.8 pounds anhydrous borax per acre caused no apparent 

 injury to oats, wheat and buckwheat. 



Introduction. 



The soils of New England are particularly free from sub- 

 stances which are deleterious to plant growth. Hence the ap- 

 parent presence of some poisonous salt in the fertilizer used by 

 many potato growers in Maine in the season of 1919 presented 

 an entirely new problem to the farmers and the fertilizer trade 

 and to the students of plant diseases as well. 



Certain difficulties had been experienced in the use of chem- 

 ical commercial fertilizers coincident with the partial and later 

 the total disappearance on the market of European potash as the 

 result of the war. Partly because experiments conducted by this 

 Station and partly because the experience of certain practical 

 growers had shown that on the Caribou loam, the most extensive 

 and best type of potato soil in the State, the potash content of 

 the fertilizers could be reduced materially without greatly les- 

 sening the potato crop, but more on account of the fact that 



