Rothamsted Symposium on Trace Elements 22 



Illrd series (7g CaO/kg soil).— The different fertilisers did not 

 noticeably influence plant growth. The good development of the 

 plants will attract attention to the low content of calcium in the 

 leaching water. 



IVth series (24g CaO/kg soil).— In the pots with and without 

 soluble calcium salts, this series generally shows satisfactory 

 growth, but growth is noticeably reduced in comparison with 

 series 3 (the injurious factor could not be washed out entirely). 

 From liming with carbonate a decrease in growth is barely visible, 

 but it is noticeable with both the small and large quantities of 

 calcium hydrate. It may appear surprising that the boron and the 

 manganese did not increase growth. This seems to contradict 

 earlier results v\dth boron manuring. It seems possible that the 

 damage done by the calcium hydrate was too great and as a result 

 boron proved ineffective. 



In this test no relation was observed between the calcium con- 

 tent and the improvement of growth on acid soil; the same can be 

 said with regard to the injury to growth on slightly alkaline soils. 

 On the contrary, the experiment pointed to a relation between 

 the increase and reduction in growth and the pH values in the 

 soil and its water. The mustard showed an optimal growth in 

 slighdy acid or neutral soil with the pH values 5.8-7.2, corre- 

 sponding to the fH values in the soil water from 6.6-7.5. The 

 depression was noticeable at pH values in the soil from 7.4-7.7 

 and in the water from 7.7-7.8, whilst growth was noticeably 

 retarded when the pH value was higher by 0.1-0.2 pH units. 

 Thus it can be said that in our test soil the hydrogen ion concen- 

 tration is more important for regular development than the 

 concentration of calcium ions. 



Can the damaging excess, caused hy overliming, he removed!— 

 Experience shows that liming acid soil is only followed by notice- 

 able damage, if the liming is sufficient to saturate the soil and the 

 pH value rises over 7 as shown in the following outline of the 

 reaction in the limed soil. 



H 



Soil| -f ICaCOs ^ ^ Ca -f Ca(HC03)2 



H 



acid soil -\- calcium carbonate ;=^ soil saturated -f calcium bicarbonate. 

 Calcium bicarbonate is a salt with a strong base and a weak acid 



