399 



especially the spread of the bacterial infection. These conditions are simi- 

 lar to those described as leaf curl, in which I likewise have observed decom- 

 position of the tissue by bacteria. 



It thus seems that we have before us a whole group of potato diseases, 

 with the common characteristic that the ducts turn black. This mav be 

 traced to the fact that incompletely consumed nitrogenous compounds make 

 their influence felt in an insufficient development of the carbohydrates. 



We must seek to overcome this condition to the best of our ability by 

 fulfilling the requirements for a gradual, complete ripening of the tubers 

 on the plant. 



d. Excess of Calcium and Magnesium. 



In addition to the observations on the use of lime as mentioned in 

 earlier sections, we will emphasize here first of all Orth's^ warning that it 

 should be supplied to the field in small, frequent doses rather than in one 

 heavy application. 



Of course, an excess of calchun cannot be determined exactly by defi- 

 nite figures, since the demand of each plant and each field is different. Also, 

 in adding the lime it does not depend at all on the absolute amount of cal- 

 cium supplied but on the proportion to the other nutrients of which the 

 calcium influences the solubility and capacity for transportation. Finally, 

 the weather conditions at the time the lime is applied must be considered. 



Hoffmann-, from his broad experience, has given many warnings which 

 are of utmost value practically. Calcium is injurious when used in large 

 amounts on exhausted soils. On lighter, active soils, poor in humus, during 

 dry springs, it loosens and dries the soil too much and disturbs the bacterial 

 action. If it is used in the form of marl, it must first be well decomposed 

 in the air, in order that possible injurious elements can be oxidized at the 

 right time. Calcium acts detrimentally in continued drought, and also with 

 stagnant water if it, in the form of so-called "water-lime," is mixed with a 

 good amount of silicic acid, ferric oxide and clay. In wet weather, it be- 

 comes as hard as cement. 



But even under normal conditions, calcium may be detrimental, ^^'e 

 must not forget that, together with the desired effect of decomposing organic 

 substances, containing nitrogen, and of transforming the ammonia produced 

 into calcium nitrate, ammoniacal compounds are set free. If ammonium 

 nitrate or ammonium sulfate is mixed with calcium carbonate or phosphate, 

 it produces the very soluble calcium chlorid and gypsum and ammonium 

 carbonate or phosphate. In Wagner's^ experiments (Darmstadt), the loss 

 of nitrogen, produced by the volitalization of ammonia, was observed to be 

 30 per cent, of that in a fertilization with nitrate. The same losses are pro- 

 duced very easily, if the soil is rich in calcium carbonate, if the ammonium 



1 Orth, A.. Kalk- und Mergeldiingung-. Anleitung-, im Auftrage d. Deutsch. 

 Landw.-Ges. Berlin 1896. 



2 Hoffmann, M., Diingungsversuche mit Kalk. Arb. d. D. Landw.-Ges. Part 106. 



3 Zeitschr. der Landwirtschaftskammer f. d. Prov, Schlesien. 1904, p. 1683. 



