284 NATURE AND PROPERTIES OF SOILS 



they are important since they have a bearing not only on the 

 chemical and biological phenomena within the soil but also 

 on its plant relationships. 



The broadest and most general factors affecting the soil 

 solution are season and crop. Whether the soil is fallow or 

 covered with vegetation, a great seasonal influence is evident 

 on the soil and its solution. Stewart, 1 working in California 

 with extracts from thirteen soils held in large containers, 

 found notable fluctuations of nitrates, calcium, potassium, and 

 magnesium both in bare and cropped earth. The phosphates 

 did not show great variation. The soluble nutrients were 

 markedly higher in the bare soils, the differences between the 

 various types being quite noteworthy. The good soils seemed 

 to have the more concentrated soil solution, a conclusion al- 

 ready reached by a number of investigators. 2 When crops 

 were growing on these soils, the concentration of soluble nu- 

 trients not only was lower than with the fallowed areas, but 

 it was about the same in every type of soil. The inherent 

 solution capacity of the different soils was roughly indicated 

 by the crop growth. Hoagland's 3 study of the concentration 



1 Stewart, G. R., Effect of Season and Crop Growth in Modifying 

 the Soil Solution; Jour. Agr. Res., Vol. XII, No. 6, pp. 311-368, 1918. 



'Snyder, H., The Water-Soluble Plant Food of Soils; Science, N. S., 

 Vol. 19, No. 491, pp. 834-835, 1904. 



King, F. H., Investigations in Soil Management; Madison, Wis., 

 1904. 



King, F. H., Investigations in Soil Management; U. S. Dept. Agr., 

 Bur. Soils, Bui. 26, 1905. 



Mitscherlieh, E. A., Eine Chemische Bodenanalyse fur Pflanzen- 

 physiologische Forschungen; Landw. Jahrb., Bd. 36, Heft 2, S. 309-369, 

 1907. 



Lyon, T. L., and Bizzell, J. A., The Plant as an Indicator of the 

 Belative Density of the Soil Solutions; Proc. Amer. Soc. Agron., Vol. 

 IV, pp. 35-49, 1912. 



Hall, A. D., Brenchley, W. E., and Underwood, T. M., The Soil Solu- 

 tion and the Mineral Constituents of the Soil; Philosoph. Trans. Roy. 

 Soc, London, Series B, Vol. 204, pp. 179-200, 1913. 



Pantanelli, E., Bicerche Sulla Concentrazione del Liquide Circolante 

 nei Terreni Libici; Bui. Orto Bot. R,, Univ. Napoli, T. 4, pp. 371-383. 



3 Hoagland, D. R., The Freezing Point Method as an Index of Varia- 

 tions in the Soil Solution Due to Season and Crop Growth; Jour. Agr. 

 Res., Vol. XII, No. 6, pp. 369-395, 1918. 



