97 Steenbjerg: Microelements from a Practical Point of View 



In my own experiments on pea in water cultures, even a slight 

 amount of copper was proved to be poisonous at the early stage of 

 growth. Although the copper requirement may be great at the 

 start, as shown, for instance, by the experiments on oats by B. 

 Rademacher,^ the normal seed of pea contains an adequate re- 

 serve of copper which completely fulfils the copper requirement 

 of the plant for a comparatively long period. Thus the pea grows 

 at first more rapidly without copper than with it. Later, however, 

 the plant not given copper was left behind, especially in regard to 

 the generative growth, by the plant supplied with copper. My 

 experiments do not, however, reveal whether the copper nutrition 

 given at a later stage of growth is less for pea as appeared to be 

 the case with oats in the experiments by Rademacher. 



The experiments carried out for the elucidation of the optimal 

 time of fertilization for different species of plants, in different 

 soils and with different substances, are of great significance even 

 in regard to the trace elements. 



Prof. Arnon:— 



I should like to take advantage of the presence of so many ex- 

 perts from the field of practical work of manganese to enquire 

 whether there was any indication that light increases the require- 

 ment for Mn as reported for grey speck of oat by Samuel and 

 Piper in Australia. 



Dr. Lohnis:— 



Question to Miss Heintze. Is there any larger development 

 of the pea plants after injection with nitrogen which might induce 

 a lower content of Mn when compared with iron-injected plants? 



Miss Heintze:— 



Contrasted plots on manganese deficient soils often show only 

 small differences in total, exchangeable or readily reducible manga- 

 nese. Significant differences were however found in the mineral- 

 isable nitrogen. Evidence that manganese deficiency may be con- 

 nected with the nitrogen metabolism of soil and plant has been 

 provided by results from injection experiments in peas in which in- 

 creased nitrogen content caused marsh spot in peas. 



^ Ober die Veranderungen des Kupfergehaltes, den Verlauf der Kup- 

 feraufnahme und den Kupferentzug beim Hafer (Bodenk. u. Pflanzener- 

 nahr. 64:80-108, 1939). 



