THE ANALYSIS OF VIRGIN SOILS. 363 



The experiment could not be carried to full completion on ac- 

 count of the overwhelming invasion of mildew ; but the figures 

 speak for themselves. Moreover, a field trial made on the 

 island with saltpeter, in pursuance of the writer's recommen- 

 dation, resulted in a luxuriant growth of the cane. 



Data for Nitrogen-adequacy. It appears from the facts 

 shown above, that for the growth of grasses a nitrogen-per- 

 centage in the humus of 1.7 is wholly inadequate, no matter 

 how much humus may be present. A percentage of 3.15 in 

 the Maui soil, No. 29. containing nearly 1 1 % of humus, gave 

 only a fair crop of sugar-cane ; on the Berkeley grass plot, with 

 3.40% and only 1.65 of total humus, the ray grass was barely 

 maintaining life. The ramie, with 4.1790 of nitrogen in the 

 soil-humus, was still doing fairly well. 



It is doubtless impossible to give one and the same absolute 

 figure for nitrogen-deficiency for all plants and soils. Where 

 the conditions of nitrification are favorable, as in the presence 

 of much of the earth carbonates, a smaller percentage may 

 suffice for the same plants that elsewhere suffer ; and it is highly 

 probable that different minima will be found for plants of dif- 

 ferent relationship and root-habits. But there is every reason 

 to believe that in the nitrogen-percentage of soil-humus, con- 

 sidered in connection with other chemical and physical condi- 

 tions and soil derivations, we have a means of ascertaining the 

 needs of plants with respect to nitrogen-fertilization, if proper 

 study be given to the subject. Broadly speaking, it appears to 

 be necessary to keep the nitrogen-percentage of soil-humus near 

 4% to insure satisfactory production. 



It having been suggested that the frequent and disastrous 

 crop failures on the noted tchernoxem or black-earth soils 

 of Russia might be due in part at least to nitrogen-depletion 

 of the humus, the writer obtained through the courtesy of 

 Prof. P. Kossovitch of St. Petersburg soil samples from the 

 center of the Black-earth region, both cultivated and unculti- 

 vated. These samples arc in appearance exactly like some of 

 the dark alluvial soils of Louisiana and California, and ap- 

 proach them very nearly in the essentials of composition, as 

 will be seen from the table below : 



