Apr. IS, i9i8 Soil Acidity as Influenced by Green Manures 195 



to sixth months, followed in the average case by but a small decrease 

 during the eighth and ninth months! In 7 out of the 14 mixtures with 

 fresh green manures a slight depression of the limestone requirement 

 appeared at the end of the third month, and in but one of the remaining 

 cases was there an important increase during this time. 



(10) In the average case, though with a number of exceptions, the soil 

 alone had a greater limestone requirement than its fresh green manure 

 mixture up to the end of the third month, but from the end of the fifth 

 month until the end of the experiment these mixtures on the average had 

 the higher requirement. 



(11) The course of the limestone requirement varies, however, quite 

 differently in the several individual cases. With red clover it dropped to 

 nothing by the end of the third month, and then jumped within the next 

 two months to nearly 5,000 pounds, the greatest and most abrupt change 

 appearing in these records. The highest individual limestone require- 

 ment was that of wheat at the end of the fifth month — namely, 7,594 

 pounds. The sorrel mixture was the only one that did not at some time 

 exceed the soil in its limestone requirement. 



(12) Among the individual green manures the highest limestone 

 requirements on the average throughout the experiment were those of 

 corn among the nonlegumes and of sweet clover among the legumes; the 

 lowest, those of sorrel and red clover in these respective subgroups. 



(13) In the average case these mixtures held at the end of the second 

 week about as much nitric nitrogen as the soil ; but thereafter the increase 

 was continuous to the end of the experiment, when these mixtures held 

 more than twice as much of this constitutent as the soil alone. In indi- 

 vidual mixtures there were fluctuations in the quantity rather than a 

 steady increase. 



(14) The averages throughout the season show that the rape, wheat, 

 and red clover mixtures had the most nitrates, while the timothy, redtop, 

 and sorrel mixtures had less than the soil alone. 



(15) In all these cases, as in that of the stable manure mixture, nitri- 

 fication alone was absolutely insufficient to account for the observed 

 developments of the limestone requirement. 



(16) Although the green manured soil had an average limestone 

 requirement much greater than that of the untreated soil, there w^as a 

 quite strong nitrification in the presence of the green manures. In other 

 words, here, as in the field, the acidity developed has not prevented fairly 

 vigorous nitrate formation. 



IV. — THE soil, WITH ADDED AIR-DRY GREEN MANURES 



(17) All the fermentative changes followed the same direction dis- 

 played by the mixtures with fresh green manures. The depression of the 

 limestone requirement in the early weeks was less pronounced, the gain 

 steadier but more delayed thereafter. The nitrification also progressed 

 more slowly, and apparently had not reached its highest accumulation of 



