Apr. IS. i9i8 Soil Acidity as Influenced by Green Manures 



189 



to decomposition than a loose sandy soil would be, and more favorable, 

 on the other, than would be the case with a compact clay soil. 



Table XV. — Total organic matter of the green-manured soils {Series II) 



Material. 



Control soil 



Legume mixtures: 



Soybean 



Sweet clover . . 



Alfalfa 



Red clover . . . 



Hairy vetch . . 



Subaverage . 



Nonlegume mixtures: 



Rape 



Cora a 



Rye 



Redtop 



Sorrel 



Losses on 

 burning. 



Per cent. 

 4.878 



5-465 



5-541 

 5-586 

 5-740 

 5.720 



5. 611 



Subaverage . . . 

 Grand average . 



5.408 



5.620 



5-723 

 5. 698 



Excess of 

 losses by 



manures v. 



control soil. 



Per cent. 



0.587 

 .663 

 . 708 

 .826 

 .843 



733 



530 



742 



854 

 821 



5.612 



734 



5.612 



734 



Weight of 

 excess in 



2,000,000 

 pounds. 



Pounds. 



11,740 

 13-360 

 14, 160 

 16, 520 

 16, 860 



14, 660 



10, 600 



14, 840 

 17, 080 

 16,420 



14, 680 



14, 670 



Loss of added orsranic 

 matter by fermentation. 



Weight. Per cent. 



Pounds. 



17,476 

 23, 504 

 22,388 

 20, 580 

 20,356 



20, 861 



21,532 



23,320 

 20, 516 

 19,652 



21,255 



59. 82 



63-33 

 61. 25 



55-47 

 54-70 



58. 73 



67. 01 



61. II 



54-57 

 54-48 



59- 15 



21,036 



58.92 



» Sample lost. 



There was no appreciable difference in the proportion of loss of the 

 organic matter of the groups of legumes and nonlegumes, respectively, 

 and both suffered greater loss than stable manure, which had doubtless 

 been considerably changed by fermentation before application. 



There was, however, a good deal of difference in the degree of loss 

 exhibited by individual materials. The figure for red clover is surpris- 

 ingly low, and those for rye and timothy are much below the average. 



We may question whether there is any direct relation between the 

 amount of total residual humus and the limestone requirement at the 

 end of the nine months period. We are at once confronted by the fact 

 that where alfalfa, red clover, hairy vetch, rye, timothy, redtop, and 

 sorrel were added to the soil, its limestone requirement was less than that 

 of the untreated soil, and yet in each of these cases there was a large 

 residue in the soil of organic matter from the green manures. We may, 

 therefore, not regard the organic residues as active, as a whole, to cause 

 the observed acidity. When we consider the variety of organic matters 

 originally present, and the differences in the mutual proportions they 

 originally bore to one another, it would at once appear highly improbable 

 that the residues from their fermentation would have like acid effects 

 for equal units by weights. 



