LIME REQUIREMENT OF THE SOIL 107 



ment in the yield or quality of the hay can be secured without 

 the application of potash, and that neither lime nor phosphates nor a 

 combination of the two will suffice to maintain a permanent bottom 

 of clover. 



One other result calls for explanation. The superphosphate plot at 

 Horndon, in spite of the fact that the soil contains a small reserve 

 of calcium carbonate, has never held the same bottom of clover as 

 any of the basic phosphate plots (see Plate VII and Fig. 11). Samples 

 of soil were drawn in the autumn of 1919 from this plot, and from 

 Plot 15, which received the same dressing of superphosphate (200 Ibs. 

 P 2 6 per acre), and in addition 1 ton of lime per acre. On both samples 

 the amount of citric soluble phosphoric acid and the lime require- 

 ment were determined, the results being as follows : 



Plot 15 



Plot 13 Superphosphate 

 Superphosphate and lime 



o/ o/ 



/o /o 



Total phosphoric acid -084 -082 



Available phosphoric acid ... -0046 -0106 



Lime requirement -10 -05 



Calcium carbonate -00 -13 



The figures indicate that the inability of the clover to grow so 

 vigorously on Plot 13 as on Plot 15 is not caused by sourness alone, 

 but is mainly due to the phosphoric acid having been retained by 

 the soil in a more unavailable form than is the case on Plot 15. 



