THE MAINE EXPERIMENT STATION. 57 



importance. Work of this character cannot well be summarized 

 in definite statements. The results are published in the annual 

 reports beginning with ii 



ACQUISITION OF ATMOSPHERIC NITROGEN — NITRAGIN. 



The acquisition of atmospheric nitrogen by plants has received 

 attention. A bibliography of the subject has been compiled and 

 the special features of soil inoculation has been studied. In 

 carefully sterilized soil several of the ' nitragin" cultures were 

 compared with each other and with tubercles from various 

 leguminous plants. The plants used in the work included red 

 clover, pea, bean, vetch and soja bean. Results: The experi- 

 ments thus far carried on do not warrant the recommendation of 

 germ cultures for leguminous crops. In very few cases did the 

 culture of the specific germ of any given species give better 

 results than did a culture of a nearly related type. 



BOX EXPERIMENTS WITH FELDSPAR AS A SOURCE OF POTASH. 



Results: Oats were able to draw from the feldspar enough 

 potash for a large crop of grain. 



BOX EXPERIMENTS WITH PHOSPHORIC ACID FROM DIFFERENT 



SOURCES. 



Phosphoric acid was supplied to iS different kinds of plants 

 in three forms, viz., (i) acid phosphatic rock; (2) finely ground 

 Florida rock; (3) roasted redonda (a native phosphate of iron 

 and aluminum). Results: Plants differ in their ability to feed 

 upon crude phosphates. In nearly every case the availability 

 proved to be in the order above given. The use of the acid rock 

 hastens the maturity of the crop. The solubility of a phosphate 

 in ammonium citrate is not always a correct measure of its actual 

 value to the plant. 



EFFECTS OF DIFFERENT FORMS OF PHOSPHORIC ACID IN CROP 



PRODUCTION. 



Results: For the first year the largest increase of crop was 

 produced by soluble phosphoric acid. For the second and third 

 years without farther addition of fertilizers, better results were 

 5 



