THE ANALYSIS OF VIRGIN SOILS. 355 



according to Wohltmann, in the soils of Jamaica according to Fawcett 

 and in those of Madagascar according to Miintz and Rousseaux.' 

 There, potash-percentages . over .10% seem to be high, and in Mada- 

 gascar some lands in fair production range as low as .01%. The soil- 

 extractions have however in these cases been made with a weaker aciA 

 than above specified, so that some increase of the figures (perhaps 33 

 to 50%) will have to be allowed for. But even then there can be no 

 question that a far less amount of potash, as determined by acid-ex- 

 traction, is found sufficient for crop production in the tropics ; doubtless 

 because of the very intense decomposing ( " fallowing" ) effect of the 

 continuous heat and moisture, tending also to a rapid decomposition 

 of organic matter and a proportionally rapid formation of carbonic and 

 nitric acids. Such soils are of course constantly kept in a leached con- 

 dition, as a result of the heavy and continuous rainfall. 



Phosphoric Acid. As regards the lower limit of adequacy 

 of phosphoric acid, there is a remarkable agreement in the in- 

 vestigations made everywhere. It was placed at .05% by the 

 writer as long ago as 1860, as the result of investigations made 

 in the State of Mississippi ; and the same figure has since been 

 arrived at independently by agricultural chemists in France, 

 Russia, Germany and England. The cause of this remarkable 

 agreement is undoubtedly the readiness with which the phos- 

 phates that come under consideration at all for the nutrition 

 of plants, are dissolved by almost any acid treatment likely 

 to be used in soil analysis. Almost the same agreement exists 

 in regard to the "adequacy" of .1% of P 2 O 5 ; while all soils 

 showing percentages between .1 and .05% are considered weak 

 on this side, and liable to need phosphate fertilization soon. 

 One-fourth of one per cent is an unusually high percentage 

 in most countries; .30^ and over is exceptional in non-fer- 

 ruginous soils. But as stated on a previous page, a high per- 

 centage of lime carbonate may offset a smaller percentage of 

 phosphoric acid, apparently by bringing about greater avail- 

 ability; and a similar effect seems to result from the presence 

 of a large supply of humus. 



On the other hand, very large percentages of finely divided 

 ferric hydrate may, especially in the absence of lime carbonate, 



1 La Valeur Agricole des Terres de Madagascar. Ann. de la Science Agrono 

 mique, 2'me serie, tome i, 1901. 



