29 — 



The periodically or upper humid layer. 



Many years observation of soil humidity on the Obessa Experiment 

 field, permit the following principle deductions to be made. 



Every year, at the end of June or the begineni^ of July — and with 

 a dry spring season at the end of may — our cereal grasses consume all 

 the reserve water which has accumulated in the whole thicl^ness of the 

 root-inhabited layer (110 — 150 cm.) during autumn, winter and spring; 

 that is to say, that towards autumn no useful water remains in reserve 

 for the following year or for the subsequent culfvated plants, when grasses 

 have been grown on the soil. The submitted diagrams (10, 11, 12 and 

 13) show this clearly. Thus diagram 10 shows the early course of soil- 

 moisture sown with barley (in 1905). The accumulation of water in the 

 superficial layer commenced from november of the previous (1904) year. 

 By winter the thickness of the humid layer had attained 35 c. m. and 

 remained so the whole winter because the whole layer froze and the 

 water was in a rigid condition and consequently could not shift its posi- 

 tion. After the frost, from the end of march until the end of april the 

 water sunk downwards about 10 c. m. and the layer attained a thickness 

 of 45 cm. which constituted almost a third of the soil-layer neccessary for 

 the normal developement of the root-system of barley. As we know, from what 

 has been already said about the developement of root-systems, the roots 

 of barley reach a depth of 50 cm. 31 days after sprouting; and as the 

 barley was sown in 1905 at the begin-ng of march, its roots had already 

 penetrated the whole humid layer by the end of april. Notwithstanding, 

 the growth of the roots ceased at a depth of 45 c m., or a little deeper, 

 because the root-tips theu reached a dry layer void of serviceable water. 

 To make up for this, the barley increased the developement oi its lateral roots in 

 the upper and more humid layer. The increase in the quantity of roots is such 

 an insignificant soil layer as 50 cm., instead of a normal 110, must have 

 involved an increased expediture of water in the humid layer. In fact, by 

 the middle of may the reserve of useful water was exhausted neither a 

 light nor a dark grey shading is to be seen in the periodically humid 

 layer. The plants must have perished in the absence of rain but during, 

 the period of vegetation (81 days) there were 39 falls of rain giving 68,4 m.m., 

 out of which there were 6 useful ones of from 5 to 10 m.m. With a 

 sufficiently thick humid layer and such a plentiful supply of watery 

 deposit there should have been a good crop; but the thinness of the hu- 

 mid layer produced another effect; — the crop barely ripened by reaping 

 time (2-nd June) and was very poor -about 30 puds (98 s-t). Palpably 

 the thickness of the humid layer in spring at seed time is of final impo- 

 rtance, if there is not plentiful rain later on. And so by the middle of may 



