— 38 — 



With four-course rotation (fig. 20) — bare fallow, winter corn, potatoes 

 (thorough ploughed plant) and sprind corn the distribution of water will 

 be different than with the three -course rotation which we have just 

 examined. 



In the fallow and the following winter-corn stages the distribution 

 of water, that is its accumulation and expenditure, will be similar to that 

 which we saw in the threecourse rotation. Exactly in the same way, after 

 the reaping of the winter wheat the upper humid layer appears with the 

 intermediate dry layer below it; and still lower-- the permanent humid 

 layer. But in four -course rotation potatoes follow the winter corn, not, 

 spr'ng corn. Potatoes (fig. 16) do not use up all the reserve water 

 (5 to 7^';'ii). There still remains 1, 2 or 3" n in the soU (on fig. 16 shown 

 from august by a I'ghter grey shade) after the harvest. This remaining 

 unused water forms that fund which guarantees the crop of spring corn 

 following the potatoe crop. Other thorough ploughed peants like melons 

 and flax leave the field in about the same condition of humidity. Maize 

 does not leave any serviceable water in the soil and in this respect is 

 exactly like other cereals. 



In this manner thorough ploughed plants give the spring growths 

 which follow them a clean field cleared of weeds, and leave the fields 

 in various conditions as regards soil water, and potatoes leave it in the 

 very best condition. And what is more: popatoes must be reckoned the 

 best predecessors of both winter and spring corns. Alm.ost as good in 

 that respect is flax. Under it the field gets free comparatively early, in 

 June, even earlier than when under potatoes. Then the root- system of 

 flax penetrates to a less depth than grass cereals and leaves a certain 

 water reserve. 



After potatoes follow spring corn in a four-course rotation. Having 

 received, besides the remains left from the culture of potatoes, several 

 driblets of useful water from the autumn winter and spring deposits, the 

 spring culture towards harved use up all the reserve water and leave 

 the root layer of the soil in a dry state, with only useless water, until 

 the autumn months when the formation of an upper humid layer commen- 

 ces (on fig. 20 from September). 



With tree-course rotations in the fallow stage, and with four-course 

 in the fallow and after potatoes, useful water remains a long time in 

 contact with the particles of soil in deep horizons of 80 cm. and deeper. 

 During this period processes of a chemical character go on energetically 

 through the whole thickness of the humid layer; and partly, in the su- 

 perficial layer, of a biological and bacteriological character. Mineral mat- 

 ter is transformed in entering, by ass'milation, the roots of plants. After 

 bare fallow and potatoes the process of transforming mineral matter into 



