V. The yearly water regime in the root-inhabited layers 



of the soil. 



The root-inhabited layer, taking into consideration the depth penet- 

 rated by the root-system, is for certain plants like potatoes and flax equal 

 approximately to 2'/:^ feet (70 to 80 cm.) For others like sunflower and 

 beet-root about 4'/-2 feet (150 cm.). But for the majority of cereals it is 

 about 31/2 feet ( 100 — 120 cm.). On the Odessa experiment field, experiment 

 fixed the soil layer at 7 feet (200 cm.), that is, the horizon lying deeper 

 than the root-inhabited layer was also investigated. 



The observations showed that the root layer became more humid or 

 got dryer according to the time of year and the quantity of atmospheric 

 deposit. I call it the periodically humid layer. Under it, to a depth of 

 160 to 180 cm. is fonnd a layer which is almost constantly in a dry 

 condition — or only contains useless water — and which I call the interme- 

 diate dry layer. And finally, under this layer, begining from a depth of 

 160 to 180 cm. lies the permanent humid layer, containing 2 to 3" in 

 the upper and 7 to 8"/() in the lower horizon, of useful water and exten- 

 ding to the ground water. 



When the intermediate dry layer moistens and the soil becomes 

 moist from the surface to the ground -water we get an uninterrupted 

 moist layer. 



The diagrams illustrating the yearly course of soil humidity have 

 been drawn up from tables, printed in the reports of the Odessa expe- 

 riment field") 



••) In all the following diagrams the unshaded parts denote dry soil wit- 

 hout any serviceable water, but with about lO'-'/o of useless water. Soil con- 

 taining 1 to 20/0 of serviceable water is shaded a light grey colour, and 2 to 

 7'\'u dark grey. In general the presence of useful water is shown on the dia- 

 grams by grey shading of various depths; the more water, the darker the shade. 

 There are also several blended deviations from the normal course, arising out 

 of some accidental feature of the spot from which the soil sample was taken. 



