Apr. IS. i9i8 Soil Acidity as Influenced by Green Manures 183 



increases occurred during these two periods, is also illustrative of the lack 

 of correspondence between the degrees of soil acidity, or limestone re- 

 quirement, and of nitrification in these experiments. 



While, therefore, nitric nitrogen is contributory to the effect in all soil 

 acidity, it is by no means the chief factor producing that effect in these 

 cases. 



In passing, we may note several other points upon which these experi- 

 ments throw some light. The average legume yielded in nine months 

 more nitrates than the average nonlegume green manure, and both gave 

 more than stable manure, but less than poultry manure. At the top of 

 the list, exclusive of poultry manure, are red clover, wheat, and rape; 

 at the bottom, soybeans, timothy, and redtop. Among the nonlegumes, 

 wheat and rape held the most nitrogen and had potentially the most 

 alkaline mineral matter, but red clover had, among the legumes, the 

 least nitrogen and by no means the most alkaline ash. These properties 

 were therefore not the factors that determined the respective rates and 

 degrees of nitrification. 



On comparing the manurial mixtures -with the control soil, it appears 

 that at the end of the first month, there was, on the average, little 

 difference between the manured and unmanured soils; but the departures 

 from the average are relatively numerous. The red-clover mixture had 

 less nitrates than the control soil until after the third month, but greatly 

 exceeded it thereafter; and the timothy, redtop, and sorrel mixture did 

 not catch up to the untreated soil for about five months, and thereafter 

 differed little from it; in all other cases than the last three named, how- 

 ever, the manured soils surpassed the control soil in nitrate accumula- 

 tion. 



These "Cases are simply cumulative with the other laboratory and field 

 studies previously made upon these quite highly acid or lime-requiring 

 soils from plot 32, as to the fact that their acid properties do not prevent 

 a fairly vigorous nitrification. With respect to this point, the accumu- 

 lation of nitrates in the wheat mixture during the last four months of 

 the experiment, when its limestone requirement was upward of 7,000 

 pounds to the acre 7 inches is to be especially noted. 



SERIES II: AIR-DRIED GREEN MANURES 



For Series II the same leguminous plant material except Canada field 

 peas was used as in Series I, but mixed air-dry instead of fresh with the 

 soil; of the nonlegumes only five materials were used in the air-dry 

 state — namely, rape, corn, rye, redtop, and sorrel. Aside from the air 

 drying of the green manures, the experiments of Series II were like those 

 of Series I, except that the limestone requirements and nitric nitrogen 

 were not determined at the 4- week and 5 -month periods. 



The results of the several determinations made are given in Tables 

 VIII to XI. 



