27 Gisiger: Deficiencies Caused by Excesses 



by boron or reduced by addition of OH-ions. In a further exper- 

 iment using boron in increasing quantities, the result was incon- 

 clusive in so far as the grey speck disease was not produced. 

 After having limed the soil, already given boron, with increasing 

 quantities of quicklime, the growth of oats proved convincingly: 



O On an add peat soil which is healthy and quite suitable for the 

 growth of cereals, the grey speck disease cannot be produced by boron 

 manuring alone in increasing quantities. 



2) By increasing quicklime dressings the soil will at first become dis- 

 eased but much greater quantities of quicklime will make it sound again. 

 For the time being, the question remains open, whether the Ca-ions and 

 their concentration have a special significance in this case. 



3) If from 6 to 50 kg of boric acid is added per hectare (20 to 160 mg 

 per pot) the grey speck disease increases in soUs on which this disease ap- 

 pears. With higher boron quantities the disease decreases and does not 

 occur, when the boron application attains 400 kgs of boric acid per hectare. 



4) The chemical analysis of oat straw shows the following: 



a) with the increasing lime quantities the manganese content first 

 decreases but shows an increase after the highest lime dose; 

 h^ of the boron dressings given, only the highest quantity, 400 kgs 

 boric acid, causes an increase of the content of manganese. The 

 smaller doses produced no changes in manganese. 



5) From 12 to 14 p.p.m. Mn, in dry matter, can be regarded as a 

 limiting value for the occurrence or non-occurrence of the grey speck 

 disease. 



The K:Ca relation and its influence on grey sfeck disease. 

 —We made many observations in the field, which proved the fun- 

 damental significance of the potassium supply. Our plants did 

 not fail in a soil with a high content of potassium. On this fact 

 we based the assumption that a high potassium supply suppresses 

 the solubility and the availability of calcium. This means, ac- 

 cording to Samuel and Piper, that the K:Ca relation would keep 

 the occurrence of the grey spot disease under control. This hy- 

 pothesis became of a practical importance, when, in spite of the 

 war, our potassium supplies remained sufficient. In field experi- 

 ments, fertilising with large quantities of potassium 300, 600 and 

 1200 kgs K20/ha produced a definitely favourable effect. To 

 prove this, an experiment was undertaken under extreme condi- 

 tions. The soil used was a mixture of marshy soil with sphagnum 

 peat, the dressing per pot consisted of 1.5 g of phosphoric acid, 

 0.7 g of nitrogen and 1.0 g of potash (see Plate 3). 



The supplementary dressings were applied in three series: 



