538 SOILS: PROPERTIES AND MANAGEMENT 



458. The lime-magnesia ratio. — The physiological 

 balancing of magnesium by calcium was first worked out 

 by Loew, 1 and the ratio in which these two cations should 

 exist in nutrient solutions in order to secure the best 

 growth of certain agricultural plants has been very satis- 

 factorily demonstrated by the experiments of many 

 investigators. The optimum ratio varies with different 

 kinds of plants, and in general the calcium must exceed 

 the magnesium in amount, but there is a limit beyond 

 which it should not be present. If calcium alone is 

 present, it acts as a toxic agent on the plant, and mag- 

 nesium acts in a similar way. It is only when the ratio 

 between these cations falls within certain limits that 

 they exert no toxic action. This ratio varies between 

 one part of calcium oxide to one part of magnesium 

 oxide, and seven parts of calcium oxide to one part of 

 magnesium oxide. 



In the soil the relations of calcium and magnesium to 

 plant growth are not so simple. It is impossible to 

 determine the actual or the relative quantities of these 

 cations that are available for absorption by the plant. 

 This is mainly because of the absorptive properties of 

 soils, by which they remove the bases from solution and 

 hold them in a somewhat difficultly soluble form. The 

 ratio of calcium to magnesium is not likely to disturb 

 crop yields in soils unless the quantity of- magnesium 

 present happens to be very large. Gile and Ageton 2 

 have found ordinarily fertile soils having ratios as high 



1 Loew, O. The Physiological Role of the Mineral Nutrients 

 of Plants. U. S. D. A., Bur. Plant Indus., Bui. 1, p. 53. 1901. 



2 Gile, P. P., and Ageton, C. U. The Significance of the 

 Lime-Magnesia Ratio in Soil Analyses. Journ. Indus, and 

 Eng. Chem., Vol. 5, pp. 33-35. 1913. 



