235 



that the seeds can germinate normally. The stronger, more sturdy plants, 

 which have passed through the most critical germinative stages, are then 

 better able to combat the soil moisture, which rises capillarily higher and 

 more rapidly after the green manure has decomposed. 



Freezing. The loosening of heavy soils in winter through a suitable 

 freezing is of the greatest importance in their cultivation. If we take into 

 consideration that water, when converted into ice, expands about one- 

 eleventh of its volume, it is evident that the more closely lying soil particles 

 are forced apart by the ice crystals. Also, since rocks are covered with a 

 network of fine cracks, into which the water gradually soaks, the frost is 

 constantly decomposing them and in fact the effects are greater as the 

 freezing and thawing alternate during the winter. Naturally the rapidity of 

 the action will depend upon the composition of the soil, i. e. on its water 

 content. The smaller this is, the more c|uickly and deeply the frost can 

 penetrate. Therefore, heavy and humus soils will freeze and thaw most 

 slowly. WoUny's^ experiments show the advantage accruing to the soil 

 from the loosening action of the frost. He had two plots of land loosened 

 up in the fall and left lying in open furrows, while a third was not worked. 

 This plot and one of the two others were turned over in the spring while the 

 third was worked only superficially. It was then proved that for the various 

 plants cultivated, the yield was smaller from the plot which had not been 

 left fallow in the fall, while the largest harvest was given by the one in 

 v/hich the open furrows froze during the winter and were broken up once 

 more in the spring. 



Mulching. We now come to the advantage derived in heavy soils from 

 the covering of the friable surface with litter, after having considered earlier 

 the protection given Hght soils by such a covering. The greatest advantage 

 is that the covering substance prevents the compacting of the soil particles 

 since it takes up the force of the rain drops and, conducting the water slowly, 

 spreads it over the surface of the soil, thereby keeping the friable surface 

 more porous. In nurseries the seed also germinates more uniformly in 

 covered beds. The weeds do not grow so vigorously and can be more easily 

 and completely removed, since they root more superficially in the looser 

 soils. 



The great air variations between day and night produce a heavy for- 

 mation of dew in the porous covering material. This runs off to the benefit 

 of the underlying soil and increases its fertility. If bark is used to a depth 

 of I to I ^ inches, it furnishes a covering for the seed beds in winter and, 

 in the spring, a protection against the penetration of frost and the cracking of 

 the soil. 



Seed and seedling beds should have water given them in June or July. In 

 August the ground is harrowed and, in case the bark should then be covered 

 too deeply, the exposed soil is covered with new bark. Snares for the control 



1 Wollny, E., Ueber den Einfluss des Winterfrostes auf die Fruchtbarkeit der 

 Ackererden. Biedermann's Centralbl. 1902, p. 301. 



