Rothamsted Symposium on Trace Elements 26 



The Causes of Grey Speck Diseases:— Opiwiotis and results. 

 —Since the fundamental research of Hudig it has been ascer- 

 tained by innumerable experiments, that the grey speck disease 

 can be prevented by manganese sulfate. Samuel and Piper as 

 well as LuNDEGARDH tried to find the quantitative relations be- 

 tween manganese in the soil and the grey speck disease. Lunde- 

 gardh's water culture experiments and his observations in the 

 field led to the conclusion that the grey speck disease occurs 

 mostly in soils of a neutral or a slightly alkaline reaction but not 

 under slightly acid and strongly alkaline conditions. By the anal- 

 ysis of plants it was shown that the curve of the availability of 

 soil manganese shows a minimum in the neutral sphere, coincid- 

 ing with the optimum of the disease. 



Results confirming these statements were reported by Popp 

 and Maschhaupt. These authors show that the grey speck dis- 

 ease can be prevented by applying large amounts of quicklime, 

 whilst similar liming with carbonate gives unfavourable effects. 



Maschhaupt does not contribute the advantages of quick- 

 lime only to chemico-physical reaction, but he also takes partial 

 sterilization of the diseased soil in account. The same theory is 

 supported by Gerretsen after comprehensive experiments. On 

 the one hand, sterilization may control micro-organisms which 

 attack the enfeebled roots under conditions of manganese defi- 

 ciency; on the other hand, the manganese assimilation by micro- 

 organisms may be reduced as a consequence of the sterilization. 



Thus the higher availability of manganese in strongly alkaline 

 soils may be explained by the smaller biological fixation. Samuel 

 and Piper consider 12 to 14 p.p.m. manganese in the dry matter 

 of oats as a threshold value for the occurrence of grey speck 

 disease. Beside this, they assume that the Ca:K relation also in- 

 fluences the occurrence of grey speck disease decisively. 



As a result of a shortage of manganese salts for manurial pur- 

 poses, the investigation of the problem of the grey speck disease be- 

 came imperative in Switzerland, during the war. Some results 

 of our experiments, in this connection, are worth noting. 



Quicklime as well as horon may favour or prevent the occur- 

 rence of grey speck disease.— In support of the results, reported 

 above, it was found in a tentative trial, that the grey speck disease 

 occurs more severely in leached soil than in non-leached soil. 

 From this it was concluded that the disease can either be favoured 



