— 33 -^ 



perennial plants. However between the periodically upper and the per- 

 manent lower humid layers, there usually lies the separating intermediate 

 dry layer. And in order that the roots of Perennials may reach the per- 

 manent moist layer, the intermediate dry layer should not be there, or 

 it should be also moist. Therefore l/ic norma/ cotulilion of existence for 

 perennials require that there should be a humid layer at their disposal as 

 deep as the whole leni^th of their root-system. 



The permanent humid layer. 



There is but one way of getting sid of the intermediate dry layer 

 or, which comes to the same thing, of moistening it; and that is by lea- 

 ving the field in clear black fallow. On fig. 18 the course of humidity 

 on black fallow is shown. 



Here the accumulation of water 'n the upper layer also commences 

 in autumn, as it generally does on all fields under wild or cultured plants. 

 From spring onwards the soil water percolates deeper and deeper until, 

 by auntumn, the period of sowing winter corn, the thickness of the upper 

 humid layer may become so great that the intermediate dry layer gets 

 humid through, upper and lower humid layers meeting and running 

 together. In that case the soil will contain a certain quantity of good 

 water, from the surface to the ground-water, and we get an uninterrupted 

 humid layer (fig. 18 — in September). 



In such a continuous layer, roots of perennial plants will find good 

 trxkling water in all its depth, which it will be able to penetrate whet- 

 her it be 3 or 70 feet. 



But it may happen that the water accumulated under black fallow 

 does not sink into the lower permanent humid layer during the first year 

 and that there still remain the intermediate dry layer between the humid 

 ones. With an average years precipitation the upper humid layer will 

 not be less than 100 cm. (3' •_> feet) and the lower one will commence 

 from a depth of 160 — 180 cm. as we said before. Therefore the dry 

 layer remains towards winter about 60 to 80 cm. During the winter the 

 water will percolate deeper even in a certain depth of the upper humid 

 layer freezes. If the percolation goes on only at the minimum rate — 

 10 cm. per month the upper layer will reach the lower one in the 

 course of the winter and towards the beginning of spring will form a con- 

 tinuous humid layer. In very moist years, which to tell the truth, are 

 comparatively rare here, the atmospheric residue does not accumulate in 

 large quantities in a thick layer of soil, but soaks though a very thick 

 layer of 130 to 150 cm. In such a year the soil find's itself in the same 

 state of saturation as it does under black fallow. 



