405 



the effect on Tobacco observed by Behrens^ His experiments showed 

 that the water content of the leaves increased considerably if potassium 

 sulfate was added to stable manure and that this hastened greatly the decav 

 of the leaves which dry with difficulty in the air. This probably is con- 

 nected with the increase in turgor observed by Copeland, which is due to 

 potassium salts (Potash). Sodium salts (soda) did not show this physi- 

 ological reaction^. 



The complaint of farmers that continued potassium fertilization re- 

 duces the quality of pasture plants so that animals fed with such hay, 

 grow thin, should be considered here. Even if the statement that this ex- 

 cessive action occurs is still contestible, nevertheless it is true, that a de- 

 crease in flavor has been observed in the hay from fields repeatedly fertilized 

 with kainit, or with kainit and Thomas slag^. 



The injuries appearing in different field crops and fruit trees are gen- 

 erally the result of an unexpedient use of potassium salts, a practice often 

 followed by serious injury*. These will best be prevented by not using 

 potassium in large amounts on heavy soils, by not spreading the salt with 

 the seed, by repeated, smaller applications of potassium and (in plants 

 especially sensitive to chlorine, as, for example, potatoes) by the use of the 

 40 per cent, potassium salt, and of other purified, highly concentrated com- 

 pounds, instead of the commercial salts. 



The frequent use of potassium in small quantities is often beneficial 

 becausq the calcium in the soil water, containing carbon dioxid, will be 

 more easily leached out the more potassium salts are added to the soil, since 

 the calcium is converted by them into soluble compounds. Hoffman^ 

 recommends the use of a high per cent, commercial marl, where possible, 

 and its application in at least 5 to yj^ double centner® per acre. If the 

 soil is liable to become encrusted {"he baked"), at least 2^4 double 

 centner of quick lime should be turned under superficially in the autumn 

 and repeated possibly four years later. 



f. Excess of Phosphoric Acid. 



Injuries due to an excess of phosphoric acid are rare. They can only 

 be expected where superphosphates are used abundantly, i. e. where some 

 phosphoric acid, soluble in water, is present. The phosphoric acid of 

 Thomas slag, soluble in citric acid, is less mobile. However, even the phos- 

 phoric acid, soluble in water, passes over immediately into an insoluble 

 form since the di-phosphates of calcium, magnesium, aluminum and iron 

 formed in the soil, are dissolved only very slowly by the carbon dioxid of 



1 Behrens, J., Weitere Beitrage zur Kenntnis der Tabakspflanze. Landw. 

 Versuchsstationen 1899, p. 214. 



2 Bot. Jahresber. 1897, I, p. 72. 



3 Mittellungen d. Deutsch. Landw. -Ges. vom 11. Marz 1905. 



■i Clausen, Resultate von ObstbaumdiJng-ungen. Landwirtschaftl. Jahrblicher 

 Vol. XXXIII, p. 939. 



5 Hoffmann, M., Die Kalisalze. Anleitung. Herau.sg-. v. d. Deutsch. Landw. 

 Gesellsch. 3d ed., 1905. 



6 A double centnei' equals 220 lbs. 



