Rothamsted Symposium on T race Elements 96 



to be the opposite of Prof. Steenbjerg's experience with copper. 



4) Manganese deficiency is common in England on calcareous 

 alluvial soils with high water tables. On such sites the deficiency 

 is usually most pronounced on areas intermediate between water- 

 logged levels and drier levels, i.e. at points where waterlogging 

 conditions fluctuate. The treatment of marsh spot in peas by 

 spraying at blossoming time is an exception to the rule that early 

 treatment of trace element deficiencies is most effective. 



The results of Miss Heintze (Rothamsted) on the intensifi- 

 cation of marsh spot symptoms by nitrogenous manuring raises 

 the question as to whether the symptom is specific or not for Mn 

 deficiency. 



Thus at Long Ashton we have found that "hollow stem" of 

 cauliflower is not specific for boron deficiency and has been ob- 

 served even under conditions of boron toxicity. 



Dr. Mulder:- 



In the polders of Holland that were flooded during the war 

 manganese deficiency of agricultural crops occurs much more 

 frequendy after the flooding than before. These results are in 

 contrast with those of earlier observations that manganese defi- 

 ciency on drained soils occurs more severely above the drain pipes 

 where the oxidation conditions are better, than between the pipes. 



Prof. Steenhjerg:— 



It seems to me too that this is rather a difficult problem. It 

 would be expected that the manganese of the soil would be more 

 available after the flooding. If the pH value of the soil is the 

 same before and after the flooding it seems to me there is the pos- 

 sibility that a part of the most reactive manganic oxides have been 

 washed out during the flooding. Finally large amounts of sodium 

 ions have been adsorbed by the soil during the flooding; this 

 means that a cation— sodium ion— has been added in large 

 amounts, a cation which to a certain extent is able to substitute 

 potassium in plant nutrition so this may mean that the relative 

 manganese deficiency has been increased. 



Dr. Erkama:— 



In determining the optimal content of trace elements in the 

 culture medium it is often not realised that the optimal content 

 may vary considerably at different stages of growth. 



