SOILS FERTILIZERS, 117 



these materials. The so-called silica-loving plants grew vigorously on weathered 

 dolomite rich in lime, provided the porosity of the material was similar to that 

 of the quartz soils. The so-called lime-loving plants grew badly on a calcareous 

 soil which had been rendered very porous by the addition of quartz. They grew 

 well on a siliceous soil which had been rendered compact by the addition of 

 loam and a little calcareous clay. 



It seems clear, therefore, that it is the physical and mechanical properties and 

 not the chemical properties which influence the growth and distribution of plants. 

 The difference in growth on sandy soils and on calcareous and clay soils depends 

 solely upon variations in the mechanical condition of the products resulting 

 from the weathering of various soil-forming rocks. 



Some factors influencing soil fertility, O. Schreineb and H. S. Reed ([/, 8. 

 Dept. Ayr., Bur. Soils Bui. J/O, pp. .'/(). pis. 3). — This bulletin cites previous experi- 

 ments by the Bureau of Soils and other investigators which are held to indicate 

 the presence of toxic properties in unproductive soils, manifesting themselves 

 in diminished yields of succeeding crops and in the mutually injurious effects 

 of the roots of trees and other plants, and reports experiments with wheat, oat, 

 corn, and cowpea seedlings to determine the behavior of these plants when 

 grown in fresh non-nutrient agar or iu that containing the excreta from previous 

 crops of the same plant or of other plants. 



From the facts presented in the bulletin the authors conclude that " it is 

 evident that the production of toxic excretions by the roots of plants is 

 undoubtedly a factor of importance in soil fertility. Many experiments have 

 demonstrated that the accumulation of these toxic excretions may temporarily 

 impair the fertility of certain soils. The foregoing experiments have not only 

 shown that infertility may be due to actual toxic conditions of the soil, but 

 also that the toxic conditions may arise from the growth of vegetation. The 

 data given are jvist as conclusive in showing that the infertility of the soils 

 was not due to their poverty in plant food constituents. . . . 



" In our present state of knowledge it would seem that we must regard the 

 excreta of growing roots as one of the main causes of the low yields obtained 

 in improper crop rotations. 



" In some tj'pes of soil, influenced perhaps by certain climatic environments, 

 there appear to exist conditions which are imusually favorable to the rapid 

 destruction of toxic excretions. Such soils, when planted year after year to 

 the same ci'op may not only maintain their original productive powers, but even 

 increase with continued cultivation." 



Soil improvement for tlie worn hill lands of Illinois, C. G. Hopkins and 

 J. E. Readiiimer (lUhiois Sta. Bui. 115, pp. J/Sl-^/fS). — This bulletin is a 

 report of progress in the land improvement work carried on by the station, 

 chiefly in southern Illinois. A plan of the exi)eriments and earlier results have 

 been previously noted (E. S. R., 17, p. ^(>1). 



In sunmiarizing the results with wheat (m the Vienna experiment field, taking 

 into account the total yields for the last 3 years, it is shown that untreated 

 land produced 11.8 bu. per acre, while with a leguminous crop the yield increased 

 11.5 bu., and with lime used in addition to the leguminous crop the increase in 

 yield was 34.3 bu. During this period the use of phosphorus gave a further 

 increase of only 5.G bu. per acre, and the use of potassium of 10.8 bu. It is 

 pointed out that the direct effect of the lime applied in the form of ground 

 limestone is to increase the growth of the crops for green manuring. 



In the corn tests for the last 3 years the untreated land produced 109.2 bu. 

 per acre. The u.se of a leguminous crop alone increased the yield only 0.8 bu., 

 while with the further addition of lime an increase of 50.7 bu. was secured. 



