1906.] LIMING SOILS AND PLANTS. 99 



acids. To test this point lettuce was planted in four pots 

 eighteen inches in diameter. All of the four pots were 

 manured alike. Two of the pots received no further treatment 

 and in the absence of crops from these pots stones were sub- 

 stituted for them when the photog-raph was taken. The third 

 lot from the right was grown where an additional " half-ra- 

 tion " of sodium carbonate was used, and the better lot at the 

 left where the " full ration " of sodium carbonate was em- 

 ployed. The wonderful benefit derived from its use showed 

 that here w^as another alkaline substance, containing no 

 lime, which was exceedingly helpful. 



If slacked lime proved useful only as a plant food and in 

 floculating and thus improving the physical condition of the 

 soil, then it was to be expected (judging from experiments by 

 others) that sulphate of lime (land plaster) might be equally 

 as effective, provided an equal amount of lime in each combina- 

 tion were employed. It will be remembered that the lime in 

 sulphate of lime is already combined with a strong mineral 

 acid, oil of vitriol, and hence it cannot correct acid conditions 

 without first undergoing a change into carbonate of lime in 

 the soil. This change is so slow that it has little immediate 

 practical significance in ordinary well-drained upland soils. 



The largest two piles of beets were produced by the aid of 

 air-slacked lime and the next largest pair with sulphate of lime. 

 The results were still poorer in the case of the other two plats 

 where neither lime compound was used. Mention should be 

 made of the fact that in all of the cases a liberal manuring with 

 potash, phosphoric acid, and nitrogen had been provided. It 

 will be seen that the land plaster failed to accomplish the same 

 result as the slacked lime. 



Without going further into the details of the investigations 

 in this direction, which covered in all a period of three to four 

 years, it suffices to say that potassium, sodium, and magnesium 

 compounds which were capable of neutralizing acidity were 

 all more helpful to the soil than other compounds of the same 

 elements which could not aid in the same way. It was, there- 

 fore, concluded that the need of the soil was primarily alkaline 

 substances and that, therefore, the blue litmus paper test fur- 

 nished a probably reliable guide as to its liming requirements. 

 If this is true it is obvious that this or some equally or more 

 efficient test for acidity should be more generally applied to 

 soils. • 



