812 EXPERIMENT STATION RECORD. 



which contain a large amount of .sokible salt;-; are unfavorable to forest 

 groM'th, particularly if the soils receive a limited supply of moisture; 

 but that as soon as these conditions are corrected and the forest vege- 

 tation has gained a foothold in the steppe on the slope of some ravine, 

 it is at once in condition to protect itself against the unfavorable 

 climatic and soil influences. It gathers the snow, moderates the winds, 

 lowers the rtuige of the temperature, prepares for itself the soil neces- 

 sar}-^ for its growth, and advances little l^y little into the neighboring- 

 steppe. The different stages in this process of transformation of 

 chernozem may be observed in progress under natural conditions and 

 may be duplicated under artificial conditions. Prof. Kostichev tilled 

 a cylindrical vessel with chernozem, covered it with a layer of leaves, 

 and maintained it in a moist condition. In three years the chernozem 

 was transformed into a gray soil with 2^ per cent of hunuis. 



The upper horizon of these soils in virgin condition is 1^ to 3 dcm. 

 in depth, gra}^, gray-cinnamon, or dark gray in color and almost struc- 

 tureless. The lower horizon, 3 to i dcm. and more in depth, is ash- 

 gray, sometimes friable, but more frequently of a crmnby structure. 

 It consists of brown-gray rounded or polyhedral aggregates mixed 

 with fine quartz and siliceous flour. An admixture of humus gives to 

 this powder an ash-gray color. Lower down the aggregates become 

 larger, the amount of the ash-gray powder decreases, and the horizon, 

 gradually assuming a brown color, merges into the subsoil. 



The parent rocks (subsoils) of the forest lands are usually weathered 

 morainic clays, diluvial clays (sometimes loess-like), leached loess, and 

 ancient sedimentary rocks — clays, marls, etc. — also weathered and 

 leached. 



The content of humus fluctuates in the upper horizon between 3 and 

 6 per cent; in the lower horizon it rapidly falls to 2 and even 1 per 

 cent. The solubility of the humus in water is greater than in the case of 

 the chernozem. The total amount of nitrogen varies from O.Ol to 0.16 

 per cent (-t to 5 per cent of the humus). The amount of zeolites does 

 not exceed 20 per cent, frequently falling as low as 10 or 12 per cent. 

 The total amount of mineral substances decomposed ])y 1 per cent 

 cold hydrochloric acid is ordinarily about one-half that found in 

 chernozem. The potash varies from 1 to 2.4 per cent, lime from 0.4 

 to 1 per cent, and phosphoric acid from 0.1 to O.l-l per cent. As high 

 as 0.28 per cent of calcium carbonate has been observed. The soils 

 are much less soluble in 10 per cent hj^drochloric acid than chernozem. 



The ash-coior(Hl powder of the lower horizon is considered to be a 

 product of the action of humus acids upon the silicates, causing the 

 separation of a part of the silica in pulverulent form. 



The mechanical composition of these soils is variable. In the forest 

 subclays of the Nijni Novgorod, Orlov, or Poltava governments the 

 amount of particles less than 0.01 mm. (20 to 25-32 per cent) was to 

 that of the larger ones (80 to Y5-68 per cent) as 1; 4, 1: 3, 1: 2. The 



