74 



With lime — as caustic lime — there was tluis a proj^resslxe 

 increase as more Jime was used, ri^ht up tt) 1 tons per acre, the 

 increase bein^ shown most the first and third years ; with chalk, 

 however, though there was a slight increase, it was a much 

 smaller one and not a rej^ularly increasing- one with the amount 

 applied. It can, therefore, be hardly maintained that lime and 

 chalk act similarly in the soil, or that it is immaterial whether one 

 or the other be used, so long- as the same amount of lime (CaO) is 

 api3lied. In the present ii-istance the soil was one notably deficient 

 in lime, and here, at all events, the caustic lime has proved 

 markedly more effective. As noted in the last report (Journal 

 R.A.S.E., 1921, pp. 290-1) this experiment raises several important 

 questions, e.g., whether lime retains its causticity longer than is 

 g-enerally believed to be the case, or whether it becomes converted 

 into silicate of lime or other forms in which it continues to have a 

 marked effect. That it does not merely become changed straig-ht- 

 way into carbonate of lime (as is generally supposed), and acts in 

 the same way as chalk, would seem to be abundantly disproved 

 by this 4 years' work. Were this the case, there is no reason 

 why the results with chalk should not have been equal to those of 

 caustic lime. As the outcome of this enquiry, I am convinced 

 that the method commonly adopted of estimating the lime require- 

 ments of a soil by determining only the amount of lime present as 

 carbonate of lime is incorrect. 



III. Tlie Injluence of Fluorides on Wheat, 1922 (2nd Year). 



The experiments of 1921 were continued for a second year, no 

 further additions being given, but wheat was again sown on 

 October 27th, 1921. 



It may be repeated here that the 1921 experiments showed a 

 decidedly stimulating influence exercised by potassium fluoride 

 used in quantity containing .05 and .1% of fluorine respectively, 

 but that with sodium fluoride a complete alteration of the condition 

 of the soil took place, this becoming hard and caked on the 

 surface, very impervious to water, and dark in colour. Further, 

 while the smaller amount of sodium fluoride (.05% fluorine) 

 affected germination and killed a number of the plants, the few 

 that survived grew most vigorously. With the higher amount 

 (.1% fluorine) though a few plants came up, they were all 

 eventually killed off. Potassium fluoride showed none of these 

 changes in the soil, nor harm to the crop. 



In the second year the germination with sodium fluoride was 

 hardly affected by the smaller amount (.05% fluorine), but was 

 markedly so with the higher quantity (.10%). Much the same 

 general results were obtained as in 1921, except that the lower 

 quantity ot sodium fluoride did not kill off the plants, but produced 

 a stimulating effect on them. The higher amount (.10% fluorine), 

 however, as in 1921, killed everything off. 



The appearances are shown in Plate II, and the comparative 

 results are given in the following table : — 



