EXPERIMENT STATION BFLLETIXS. 



G58 



go to slunv that liliii moNciiieiit Itelow the zone of root penetration is 

 slight, and in addition the fact that the force of gravity is operative 

 and also that in the Ininiid region approximately 40 to 50 per cent of 

 the rainfall passes throngh the soil, it seems logical to conclnde that 

 solubh; substances carried or formed below tlit; zone of root penetration 

 are of minor importance in crop production ; yet investigations now under 

 way may lead to dift'erent conclusions. 



EFFECT. OF TLAXT (.'IIOWTII OX TTIK SOLT'HLE SALT CONTEXT OF SOILS. 



Considerable interest has been manifested in the ability of plants to 

 lower the concentration of the soil solution. It was found by Lyon 

 and Bizzell ((») that the nitrate content of the soil un(h'r dilf(M-ent crops 

 growing on similar soil was quite variable, some crops apparently 

 having the power to stimulate nitrate production while others exerted 

 an inhibitive effect. Much work has also been done by various investiga- 

 tors on tlie water extract of soils under different conditions of cropping 

 and tillage. Recently, Hoagland (7) showed that nuder controlled 

 conditions the concentration of the soil solution varies at dilTerent ])eriods 

 of the year and is mat(U'ially affected by plant growth. So far as the 

 writers are aware, however, no data have l)een jiublished showing whether 

 or not the total concentration of the soil solution as it occurs in field 

 soils is affected by the growth of- plants. We liaxc made studies of the 

 effect of plant growth u]um the concentration of tlic soil solution in the 

 soil. 



A. culti:rf studies. 



In the first series of experiments corn was grown in test tubes con- 

 taining about 50 grams of soil. When the plants were well-rooted the 

 kernels were removed so as to make the plants dependent upon the min- 

 eral nutrients in the soil as soon as possible. After twenty days the 

 ])lants were removed, the soil screened to free it of roots, and after air 

 drying, made up to a definite water content and the freezing point de- 

 termined in the usual manner. 



The freezing point lowerings and corresponding ])arts per million of 

 soluble salts, as calculated by the formula derived by BouyoucoS (8) 

 of both the cropped and uncropped soils are shown in table 19. 



TABLE 19. — EFP^ECT OF I'LAXT GROWTH OX THE rOXCEXTKATION OF THE SOIL 

 SOLUTION. DIKATIOX OF GROWTH 20 DAYS. 



(6) Lyon. T. L.. and BizzeU. J. A. 1913. Somp Relations of Certain Higher Plant to the 

 Formation of Nitrates in Soils, Mem. X'^o. 1, Cornell Uni. As:r. Expt. Sta. 



(7) HoaRland, G. R. 1918. The Freezing Point jMothod as an Index of Variations in the 

 Soil Solution Due to Season and Crop Growth. .Tonrn. Agr. Resenrch. V. XIT. No. 6, pp. 360-39.5 



(8) Bouyoucos. G. J. and lIcCool, ]\f. M. 191 (i. Further Studies on the Freezing Point 

 Lowering of Soils. Mich. Agr. Exnt. Sta. Tech. Bui. 21, 51 p. 



