1917] SOILS FERTILIZERS. 117 



expressed from roots frozen at low temperatures were not consistent. It was 

 found necessary to take samples of vegetable material for freezing-point work 

 at the same time of day or else protect the plants from light and retard trans- 

 piration, since the freezing-point depression of the leaves was found to increase 

 from morning till noon and deci'ease again in the evening. It appeared that this 

 change was due to the products of photosynthesis, as well as to the moisture 

 content of the material which decreased from morning till noon and increased 

 again In the evening. 



" The concentration of the solution in which roots of Canada field pea and 

 wheat are grown is indicated by the freezing-point lower ings of the root 

 tissues, but on the other hand only rather wide variations are indicated by 

 the freezing-point lowerings of the tops. Changes in the concentration of the 

 soil solution induced by the addition of salts may be detected by determining 

 the freezing-point lowerings of the roots of the plants growing therein. It was 

 found that the tops of the plants are far less sensitive to changes in the con- 

 centration of the soil solution. 



" The moisture content of soils is closely correlated with the freezing-point 

 lowerings of the roots of the plants in contact with them, due in part at 

 least to changes in the concentration of the soil solution so induced, but again 

 the tops of the plants studied, under both greenhouse and field conditions, 

 prove to be far less sensitive to soil moisture changes, at least until the 

 critical water content is approached. The indications are that the soil solution 

 and the root sap of plants approach each other in concentration at or near 

 the critical (low) water content of the soil. The freezing-point lowering of 

 a given crop growing in widely different soils of high water content were 

 found to differ but slightly. On the other hand, different crops growing on 

 the same soil, «nder similar conditions, vary appreciably in this respect. The 

 field studies show that crops may be subjected to sudden and very wide 

 variations in the concentration of the soil solution during the growing season." 



Twenty-eight references to literature bearing on the subject are appended. 



Relation of the water-retaining- capacity of a soil to its hygroscopic co- 

 efficient, F. J. AiwAY and G. R. McDole ( U. S. Dept. Agr., Jour Ayr. Research, 

 9 (1917), No. 2, pp. 27-71, figs. 4). — Laboratory experiments conducted at the 

 Nebraska Experiment Station with uniform columns of soil of known hygro- 

 scopic coefhcieut and moisture content are reported. The 13 soils used ranged 

 in texture from a coarse sand to a silt loam, with hygroscopic coefficients 

 of 0.6 and 13.3, respectively. 



" Five of the loams, placed in capillary connection with the natural subsoil 

 mass, saturated with water, and allowed to stand protected from surface 

 evaporation for several months, lost water until the amount retained bore a 

 close relation to the hygroscopic coefficient, being from 2.1 to 3.1 times this 

 value, according to the particular soil. When a layer of coarse sand or gravel 

 separated the column of loam from the natural subsoil mass or interrupted it, 

 the downward movement of the water in the soil above this layer was much 

 delayed. Where the column consisted of successive 2-in. layers of loams differ- 

 ing widely in texture, the order of their arrangement exerted no influence upon 

 their final water content. 



" Soil columns 30 to 36 in. long, while protected from all loss of moisture 

 at the sides and bottom, were freely exposed to evaporation at the surface 

 for periods varying from a few weeks to half a year. The moisture content, 

 originally uniform and lying between 2 and 3 times the hygroscopic coefficient, 

 fell until it reached, at depths below the first foot, an almost constant minimum 

 with the ratio 1.9:2.2. 



