i84 



quickly, to be sure, but, by this means, save to a greater extent the water 

 supply in the lower layers of the soil. 



The warming of field soil by insolation, its aeration when winds blow 

 over its surface and all such influences, remove the water from the upper 

 layers of the soil to a greater extent than can be restored by capillary at- 

 traction for water from the lower layers. If now, by breaking up the sur- 

 face, the interstices between its particles become considerably enlarged, the 

 capillarity is decreased and the water no longer rises into the larger in- 

 terstices of the now crumbly soil. The more c]uickly the soil is broken into 

 coarsely friable pieces by chopping, hoeing and removing the turf, the more 

 the dr}'ing out of the lower layers, where the roots are found, is delayed. 



The opposite result is obtained by rolling the field land. In this case^ 

 most of the spaces, where capillarity did not act, are rolled close together. 

 Capillarity at once becomes active and the upper surface remains moist for 

 a longer time. Under certain circumstances, however, rolling may also be 

 recommended as a means of retaining moisture in the soil. This w-ill be 

 expressly suitable for all very porous soils with a scanty water capacity and 

 an abundant subsoil moisture, since, by hardening the surface, its evaporation 

 is reduced, while the conducting of water from below is increased. In 

 heavy soils, with a high saturation capacity, rolling would naturally be di- 

 rectly injurious. 



Mulching of the Soil. 



Instead of breaking up the soil, its surface may be covered with a more 

 porous material. In this connection advantageous results can be obtained 

 even by covering the surface with sand. This changes favorably the con- 

 ditions of moisture and of warmth at the same time, for, according to 

 W'ollny's investigations", the temperature of the soil is considerably re- 

 duced by breaking it up, since the conducting of heat in the friable layer is 

 decreased by the considerable amounts of enclosed air. In the same way 

 soil provided with a sandy covering is colder in the warm seasons than un- 

 covered soil, because the light color of the surface decreases the absorption 

 of the heat rays, and the considerable amount of water held back under the 

 sand is warmed with greater difficulty. If the upper surface of the soil 

 itself dries up, its temperature must increase because the evaporation which 

 uses up heat is at once prevented. 



Breaking up the soil and covering it, therefore, modify the extremes of 

 temperature, but are also valuable in still another way. According to 

 WoUny (loc. cit. p. 337), it is shown that during the warm seasons con- 

 siderably more water from the same amount of precipitation can filter 

 through the soil when covered with sand than through uncovered soil. This 

 takes place because the soil covered with a layer of sand (even if only one 



1 Wollny in Ocsterr. landw. WochenbL 1880. p. 214.- Nessler, Bad. Landw. Corres- 

 pondenzblatt 1860, p. 230.- Wagner, P., Versuche iiber das Au.strocknen des Bodens 

 bei verschiedenen DichtiKkeitsverhaltnissen der Ackerkrume. Bericht der Ver- 

 suchsstation Darmstadt 1874, pp. 87 ff.- v. Klenze, Landw. Jahrb. 1877. 



2 Einfluss der Abtrocknung- des Bodens auf dessen Temperatur-und Feuch- 

 tigkeitsverhaltnisse. Forschungen a. d. Geb. d. Agrikulturphysik, 1880, p. 343. 



