THE ANALYSIS OF VIRGIN SOILS. 353 



above the recognized limit of deficiency. The two Florida 

 soils however bear only pine; they are underlaid by almost 

 clean sand at two or three feet, and are therefore quickly ex- 

 hausted. It will also be noted that their lime-percentage is 

 only about half of that of the two first-named Mississippi 

 soils, both of which bear a strong growth of deciduous timber 

 trees, grape vines, and other vegetation indicating the presence 

 of lime carbonate. 



It is noteworthy, also, that the popular classification of the 

 two Florida soils corresponds exactly with the differences in 

 the percentages of plant-food; those in the " second-class " soil 

 being uniformly lower than those in the one designated as first- 

 class. This indicates, again, that as between soils of similar 

 character and origin, the production and durability are sensibly 

 proportional to the plant-food percentages when the latter fall 

 below a certain limit; a point more fully illustrated farther on. 



In the light of the above experiment and tables, it becomes 

 pertinent to consider what are the lowest percentage limits of 

 each of the more important plant-food ingredients compatible 

 with profitable production. 



LIMITS OF ADEQUACY OF THE SEVERAL PLANT-FOODS IN VIRGIN 



SOILS. 



It is obvious that the lower limits of adequacy of the critical 

 plant-food ingredients are best ascertained in the case of virgin 

 soils containing very small amounts of some one ingredient, 

 while fairly or fully supplied with the rest. In such cases, 

 which are not at all infrequent, the use of the deficient ingre- 

 dient as a fertilizer should produce a very marked effect so 

 soon as the first flush of production (always noted in fresh 

 soil) is over. This first productiveness may, even in poor 

 lands, range from one to three years, when there is a sudden 

 decline. 



Lime a Dominant Factor. When we investigate the cases of 

 such lands, it soon becomes apparent that besides the low per- 

 centage of any one ingredient, the proportions of others pres- 

 ent require consideration. Among these, lime in the form of 

 carbonate stands foremost. Its presence exerts a dominant 

 and beneficial influence in many respects, as is readily apparent 



23 



