239 



and consists in the hastened decomposition of the organic elements of the 

 soil, in the combining of the free acids so injurious to plant growth, in the 

 conversion of ferrous oxid into ferric oxid, and in bringing about the ab- 

 sorption of the basic nutritive substances by the soil. The bases are held in 

 the soil as hydrated silicates and as the salts of humic acid. In the absorp- 

 tion of the bases by the humus body, these must be present combined with 

 carbon dioxid. The lime promotes the formation of carbonates. Further, 

 the mineral elements of the soil are decomposed, whereby the basic nutritive 

 substances are freed and made accessible to the plant. Every marl does not 

 suit every soil, — clay soils, where possible, must have a lime or sand marl. 



Aside from these indirect advantages, the direct effect of the use of 

 marl is shown in the addition of potassium, soluble silicic acid, magnesia 

 and phosphoric acid, which, together with hme, are present in every marl. 



A few words should be added here as to the use of piaster or gypsum. 

 Franklin's words, — "This has been plastered," are well-known. He wrote 

 this in plaster on a clover field in order to recommend to his countrymen 

 the process which had been known with great advantage by the Romans 

 (Knop, Kreislauf des Stoffes) and the Greeks. According to Knop's experi- 

 ments and those of Deherain and Liebig, a solution of plaster in soils con- 

 taining absorbed potassium, frees it in the form of sulfate, while the lime it- 

 self is precipitated. The method of spreading the plaster on clover plants 

 freshly covered with dew or rain, recommended by experience, is found to be 

 advantageous, since a solution of plaster is formed on the moist plants ; 

 dripping from them, it acts at once in the immediate vicinity of the roots. 

 It thus rapidly becomes of advantage to the bacterial flora, for Pichard's^ 

 researches and those of others show that plaster and other sulfates (potas- 

 sium and sodium) exercise a most favorable influence on the process of 

 nitrification. Plaster should be used in an unburned state and indeed for 

 clover and lupines from 2 to 5 centner per acre in the spring. 



Although the influence of calcium hydrate or carbonate, favoring de- 

 composition, was discussed above, it must still be emphasized, that, as shown 

 by Wollny's^ work, this is only of value when the substance is already de- 

 composed and contains humic acid, while the addition of calcium on unde- 

 composed organic substances rather hinders decomposition. This is especially 

 true for calcium sulfate (gypsum) which comes imder consideration as a 

 conservation material for animal manure. In a mixture of quartz sand 

 (300 g.), powdered peat (5 g.), and 60 ccm. water, Wollny^ found 



Volumes CO, in 1000 Volumes Soil air — ■ 



without the addition of gypsum with the addition of gypsum 



0.05 g. 0.1 g. 



CO, 3.194 3.029 2.713 



1 Annales agronomiques X, p. 302. 



- Wollny, E., Die Zersetzung der organischen Stoffe etc. Heidelberg, Carl 

 Winter, 1897, pp. 133 ff. 



3 Journal f. Landwirtschaft, 1886, p. 263. 



