630 SOILS: JPEOPEMTIBS AND MANAGEMENT 



448. Substances used as catalytic fertilizers. — A 

 large number of substances have been found to act as 

 catalytic fertilizers. Among these are various salts of 

 manganese, iron, aluminium, zinc, lead, copper, nickel, 

 cobalt, uranium, boron, cerium, lanthanum, and the like. 

 These substances stimulate plant growth when used in 

 small quantities, and are toxic in large amounts. In 

 water cultures a much less quantity of any of them is 

 required to produce an injurious action on plant growth 

 than when applied to an equal volume of soil. The 

 absorptive properties of the soil and the less ready diffusi- 

 bility serve to mitigate the toxic action- 

 Different kinds of plants respond differently to the same 



concentration of any of these substances. For instance, 

 Montemartini ^ found that uranium, copper, zinc, alumin- 

 ium, and cadmium oxides retard the germination of beans 

 and accelerate the germination of maize when used in equal 

 concentrations. 



Of the various plant stimulants mentioned, manganese 

 is the only one that gives promise, at the present time, 

 of usefulness on a commercial basis, and it is the only one 

 that will receive separate treatment in this book. 



449. Manganese. -^ It seems probable that all soils 

 contain manganese, but the quantity present in some 

 soils is very small, often being less than 0.01 per cent; 

 in other soils, however, more than 1 per cent is found, 

 and Kelly ^ reports an Hawaiian soil containing 9.74 per 



^ Montemartini, L. Quoted with other experiments on this 

 subject by N. H. J. Miller, in Annual Reports on the Progress 

 of Chemistry, Vol. 10, pp. 229-230. 1914. 



2 Kelly, M. P. The Influence of Manganese on the Growth 

 of Pineapples. Jour. Indus, and Eng. Chem., Vol. 1, p. 533, 

 1909. 



