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nite. In an earlier paper (43), Hosking expressed the opinion that un- 

 identified amorphous inorganic materials with high exchange capacity 

 may influence the exchange capacities of soils more often than is gen- 

 erally supposed. 



Rubashov (6/) working chiefly with certain beet-producing cherno- 

 zems, of loess and "loesslike" origin, claims that the water-stable aggre- 

 gates (7 mm. > 0.25 mm.) present possess physico-chemical properties 

 distinctly different from the soils from which he isolated them. The 

 amount of "humus" present in the surface 8 inches was found to in- 

 crease with abundance of water-stable aggregates. It also tended to 

 increase with the coarseness of the aggregates. There was some slight 

 indication, further, that the amount of absorbed calcium may have been 

 greater in the more highly aggregated soils. Aggregates coarser than 0.25 

 mm. (macroaggregates) separated from a given soil consistently con- 

 tained more humus and absorbed calcium than those finer than 0.25 

 mm. (microaggregates) obtained from the same soil. This investigator 

 (60) reported a similar relationship for podzolized soils. Improved 

 structural quality, according to Rubashov, is associated with higher 

 content of total humus and of "structure-forming humin substances." 



The content of mobile nitrogen, acid-soluble phosphorus (Truog 

 method), and exchangeable potassium in water-stable aggregates was 

 found by Rubashov to be greater than in the soil as a whole. This 

 was interpreted as indication that the water-stable aggregates strongly 

 influence the nutritional value of a soil, as well as its physical and 

 physico-chemical properties. Although more pronounced than those of 

 the organic matter, the higher levels of these nutrients were associated 

 with, and by Rubashov attributed to, the higher content and particular 

 quality of the aggregate-forming organic matter. 



Amongst many other experiments on the significance of different 

 structural conditions in the soil, Doyarenko (see 45) determined the 

 amounts of nitrates found after six weeks in vessels of moist soil con- 

 sisting of different aggregate size classes. Increases in nitrate formation 

 paralleled increases in aggregate diameter and were attributed to the 

 greater abundance of coarse ("noncapillary") pores amongst the coarse 

 aggregates, which produced more favorable conditions for biological 

 oxidation. 



Rubashov's (6/) results with respect to organic matter appear to be 



