— 36 — 



and that the development of one pood of dry mass of the crop in bulk — 

 straw and grain requires on an average about 400 poods of water 

 (according to Haberlandt about 375) for its growth then from every mil- 

 limetre of residues we should get 1 ' ^ poods of crop, and from 150 mm. — 

 about 225 poods. Spring cereal give twice as much straw as grain (ro- 

 ughly estimated, although barley give about equal quantities ot each) 

 therefore an average crop of 225 poods schould give 75 poods of grain. 

 Such schould be the average fertility of spring cereals in our southern 

 governements if the whole of the water entering the soil is taken advan- 

 tage of. Nevertheless, the average fertility according to statistics equals 

 about 40 poods. Evidently, the cultured plants do not get the benefit of 

 the whole of the water. As the height of the crop in our southern gover- 

 nements depends exclusively on the quantity of the water in the soil, 

 the deficiency in the harvest must be attributed to the farmers bad use 

 of the soil water which was at his disposal and of which he did not take 

 full advantage. 



Let us see how the accumulation and expenditure of water goes 

 on under the various combination of farming — the various alternations or 

 rotations of crops. 



We will take the simplest cases: a three-course rotation on bare 

 fallow, a four-course rotation and a free course of cereal cultures exclu- 

 sively. From these combinations many other rotations may be termed, 

 arranging them to pit in with the diagram of the yearly course of soil 

 humidity. 



With a three-course rotation (fig. 19) — bare fallow, winter and 

 spring corn — the humid layer gets so moist during the fallow course, 

 that when the winter corn is sown its roots, which as we have already 

 seen in rye (130 cm.) are longer than spring corn, can develope to a 

 full normal length; for they do not meet the intermediate dry layer in 

 the whole of their expanse. 



Such a large reserve of water in the soil after clean bare fallow"") 

 assures the winter crop even in a dry season ""'•). 



After the bare fallow, the winter corn expends all the useful water 

 in a soil layer of 120 cm.; but below that horizon there is still a reserve 

 which sinks, by degrees, to the level of the permanent humid lower 

 layer, by the following winter. 



"") For accumulating water, green april fallow stands as high as bare fal- 

 low, if ploughed, when possible, at that period when the weeds are just com- 

 mencing their development and have not touched the reserve water. 



**) In 1899, when not a grain was gathered in a distance of 40 versts, 

 the Odessa experimental field produced 85 poods of winter wheat sown on 

 bare fallow. 



