376 NATUEB AND PEOPEETIES OF SOILS 



vanced. Loew^^ in 1901, worked out the optimum ratio for 

 a number of different plants growing in water culture. He 

 found that both, calcium and magnesium alone were toxic and 

 it was only when the ratio of these ions fell within certain 

 limits that the toxicity disappeared. This ratio varied be- 

 tween 1 of CaO to 1 of MgO and 7 of CaO to 1 of MgO. 



The question was immediately raised as to the advisability 

 of using limestone or even burned and slaked lime, the mag- 

 nesium content of which approached in any degree the cal- 

 cium present. Recent field and laboratory tests have shown, 

 however, that magnesium salts may be applied in ordinary 

 amounts alone or with calcium compounds with impunity.^ 

 The absorptive capacity of the soil seems to take care in a 

 very effective way of any toxicity that might result from a 

 soil solution physiologically unbalanced. 



206. The fineness of limestone. — The hardness of the 

 stone, its purity, and its fineness are items of extreme im- 

 portance to the manufacturer of pulverized lime. The softer 

 the limestone, the easier the grinding and the finer the product 

 with a given expenditure of power. The higher the percent- 

 age of calcium and magnesium, the greater is the effectiveness 

 of a given quantity. The farmer, other conditions being more 

 or less equal, is especially interested in the fineness of the 

 product. It is a well-known fact that the finer the division of 

 any material, the more rapid the solution. This, however, 



^ Loew^ 0., The Physiological Bole of the Mineral Nutrients of Plants; 

 IT. S. Dept. Agr., Bur. Plant Ind., Bui. 1, p. 53, 1901. 



^ Gile, P. L.J and Age ton, C. tJ., The Significance of the Lime-Mag- 

 Tiesia Matio in Soil Analyses; Jour. Ind. and Eng. Chem., Vol. 5, pp. 



Thomas, W., and Frear, W., The Lime-Magnesia Batio in Soil Amend- 

 ments; Jour. Ind. and Eng. Chem.j Vol. 7, No. 12, pp. 1042-1044, 

 Bee. 1915. 



Lipman, 0. B., A Critique of the Hypothesis of the Lime-Magnesia 

 Matio; Plant World, Vol. 19, No. 4, pp. 83-105, Apr. 1916. 



Wyatt, F. A., Influence of Calcium and Magnesinim Compomids on 

 Plant Growth; Jour. Agr. Res., Vol. YI, No. 16, pp. 589-619; 1916. 



Stewart, B., and Wyatt, F. A., Limestone Action on Acid Soils; 111. 

 Agr. Exp. Sta.j Bt3i1. 212, 1919. 



