Rothamsted Symposium on Trace Elements 20 



of the major plant nutrients, but has been explained by their par- 

 tial fixation. The contents of nutritive substances in the plants 

 grown, in experiments undertaken to study this point, showed a 

 diminution only exceptionally. This very interesting fact seems 

 to contradict the theory of fixation. 



Truninger also found no close relation between quantities of 

 added lime and the boron content in plants. The analysis of 

 the plants in the experiments showed a slightly higher percentage 

 of boron. Our experiments on the influence of manuring with 

 boron and of providing the soils with lime did not show any 

 change in the boron content of oat-straw as a result of the lime 

 dressings. This fact is in agreement with the results of experi- 

 ments concerning the solubility of boron. Hasler could not find 

 any increased fixation of boron from increased lime dressings. 



In other tests added boron and boron originally present in the 

 soil showed the same solubility in limed and unlimed soils. In 

 these experiments the analysis was made after two plantings fol- 

 lowing the boron manuring and one after the liming. 



On the other hand, surprising advantages were achieved by 

 employing large quantities of phosphoric and boric acid. This 

 fact stands in obvious contrast to our findings. Before discussing 

 these differences, I should like specially to mention the root de- 

 velopment as observed on limed soils. It was described by Tru- 

 ninger. In his experiments, the roots only grew in the over-lying, 

 unlimed soils, used as the covering layer for the seed, and did not 

 grow into the soil limed to excess. From experience it is known 

 that, as a general rule, the poorer a soil is in nutrients, the better 

 the roots will develop, at least as long as the seeds continue to 

 hold a nutrient reserve. 



Without going into great detail, the experiment may be sum- 

 marized as follows: — 



1 ) Tte roots did not grow into the soil that was limed in excess. The 

 root-growth seems to be prevented by a harmful factor, a superfluity of 

 lime if you will allow me to generalise. 



2) Where the plants do not grow into the soil, no certain conclusion 

 concerning the influence of the soil nutrients upon the growth of plants 

 can be drawn from their ash composition. 



3) When a supplement of phosphoric acid or boron shows an im- 

 provement of growth and an increase of yield on overlimed soils, it may be 

 explained as follows: by employing phosphoric acid, the supplement 

 changes the soil and suppresses the damaging factor, that is, the acid 

 neutralizes the strength of the alkaline reaction; by adding boron, the roots 

 are strengthened against the injurious surplus. 



