49 E. G. Mulder: Copper and Molybdenum 



In culture solution experiments with pea plants it was shown 

 that molybdenum is essential for the fixation of gaseous nitrogen 

 by the nodules. In these experiments the pea plants were first 

 grown in a solution to which combined nitrogen had been added. 

 Nodules were formed abundantly in both series; without molyb- 

 denum the colour of these nodules was yellow-brown in contrast 

 to the nearly pink colour in the presence of this element. Nitro- 

 gen fixation, however, was quite inadequate in the absence of 

 molybdenum. The leaves of the pea plants became yellow-green 

 due to nitrogen deficiency and the plants died in an early stage. 

 Plants with molybdenum added, harvested when colour differences 

 between the two series were shown, had more than 50% higher 

 N-content in their tissues than those without molybdenum 

 (Table 9). 



Table 9: Effect of molybdenum on the nitrogen 

 fixation by the nodules of pa plants: — 



Leaves and stems Roots 



NajMoOi-IHjO 



added Dry Dry 



weight Nitrogen Nitrogen weight Nitrogen Nitrogen 

 fig g mg % g mg % 



The fact that molybdenum has the function of a catalyst in 

 nitrogen fixation by the nodules of legumes is in good agreement 

 with the relatively high content of molybdenum found in these 

 nodules. 



In Australia and New Zealand responses to molybdenum appli- 

 cations have been obtained by Anderson, Thomas and Oertel 

 (1) with alfalfa and subterranean clover growing on acid iron- 

 stone soils. Apparently molybdenum stimulated the nitrogen 

 fixation in these plants. Although it is improbable that the occur- 

 rence of molybdenum deficiency is limited to these Australian 

 soils, so far there is no evidence that this deficiency occurs in other 

 countries. 



Addendum: — It was recently shown, by the author, that molybdenum deficiency 

 in clover may be foimd in Holland on many peat soils containing iron as well as on 

 acid, sandy soils (Landbouwk. Tijdschr. 62:311, 1950; Trans. 4. Int. Congr. Soil 

 Sci. 2:124, 1950). Similar reports came from England (particularly concerning 

 cauliflower) and from the U.S.A. (Ann. Rev. Plant Physiol. 1:1, 1950). 



