Rothamsted Symposium on Trace Elements 90 



The amount of exchangeable manganese is affected by drying. 

 It is increased when soil samples are air-dried, and also when dried 

 soil is stored. Moreover the amount of exchangeable manganese 

 is higher in the spring and summer, and lower in the autumn and 

 winter. 



Last year 17 field experiments were performed in Judand by 

 the Agricultural Associations and the results of the experiments 

 are in fairly good agreement with the manganese values found as 

 shown in Table 16. 



It is worth remembering that the apparent disagreement, 

 which always occurs in such experiments, between the increase in 

 yield and the manganese value cannot be contributed to the chem- 

 ical method only. If both the chemical method and the field 

 method were without errors and correct, there would still exist 

 a disagreement between the results obtained, because the two 

 methods in reality determine quite different things, sc, the con- 

 tents in the soil of the plant nutrient in question and the reaction 

 of the plant towards an addition of manganese at a certain level 

 of all the other plant nutrients. 



Copper deficiency, which is the other deficiency of impor- 

 tance, like manganese deficiency, occurs in Denmark chiefly in 

 Jutland and more especially in the northern, western and middle 

 parts of this peninsula. The available copper in the soil, as de- 

 termined in Denmark, comprises only a certain salt or acid soluble 

 fraction of the copper of the soil. These definitions do not pre- 

 suppose the extracted copper being combined in the soil in a 

 sharply defined manner. It may be fixed in many different ways. 

 It has been shown here, as for manganese, that all the special soil 

 conditions and climatic conditions which as a matter of experience 

 have been connected with the occurrence and severity of the cop- 

 per deficiency of crops also act in such a way on the available 

 copper that their influence on the crop may be explained by their 

 action on the available copper of the soil. 



We have now fairly good data respecting the available and 

 total amount of copper in Danish soils, the amount of copper (as 

 well as of manganese and partly of boron) in farmyard manure, 

 in liquid manure and in different plant materials. It is impos- 

 sible for me to go into details on these points. There are, on 

 this occasion, only three facts about which I want to say a few 

 words. 



First, a copper value of the soil is used at present in Denmark 



