112 



acid remained nearly constant and the increase of nitrogen was almost 

 wholly in the form of ammonia. In other words, nitrification was active 

 in the moist but not in the dry soils. 



Taking the results of all the groups together, there seemed to be 

 rather more gain of nitrogen with calcareous than with non-calcareous 

 soils, but the difference was neither regular nor pronounced. The fol- 

 lowing are the author's conclusions : 



From these investigations it follows that arable soils absorb atmos- 

 pheric ammonia, whether they are devoid of vegetation, calcareous, 

 acid or neutral, dry or wet. The (luantities of nitrogen thus gained 

 are too important to be neglected. 



The absor])tion of ammonia by the soil is dependent upon the difler- 

 ence of tension of the ammonia in air and soil. The absorption, there- 

 fore, attains its greatest intensity when the tension in the soil is zero. 

 This condition is realized when the soil is moist and when nitrification 

 causes ammonia to disappear as rapidly as it is absorbed. ^Vhen the 

 soil is dry nitrification stops, the laiger jiart of the ammonia absoibed 

 retains its form, and increasing in amount etfects a tension in the soil. 

 The absorption, therefore, conslanlly diminishes. Thus moisture in 

 the soil favors the fixation of animoniii, and dryness retards it. 



Absorption depends essentially on the renewal of air at the surface of 

 the soil. It is therefore not a matter of indiflerence whether the sur- 

 face of a field is free from vegetation or is covered by the residue of 

 croi>s or by spontaneous vegetation. — f\V. O. A.] 



Green crops as nitrogenous manures, A. Miintz [Conipt. mid., 110 

 (181M)), }>. DTl'). — I'or grei'M manuring leguminous plants are generally 

 selected. Their value for this purj)0se is due to their power of gather- 

 ing nitrogen especially from the air. The author considers that their 

 ett'ectiveness when plowed under as green manure will be proportioned 

 to the rapidity with which their nitrogen is changed to nitric acid. To 

 get light upon the subject, he compared the rapidity of nitrification of 

 green lupines with that of dried blood, which is one of the most active 

 nitrogenous fertilizers, and of sulphate of ammonia, which undtrgoes 

 especially rai>id nitrification, in a series of experiments in which each 

 of the substances was added to a light calcareous soil and to a heavy 

 clay soil only slightly calcareous. For each experiment enough of the 

 nitrogenous material was added to furnish one gram of nitrogen for a 

 kg. of soil. The accompanying tabular statement shows the amount of 

 nitric acid formed: 



Fertiliziug materials supplyiiif; 1 uram of nitrogen. 



r :„!,* „„!„„»„ Ilcavv cl.iv 



Green Juplne 



Dricil lilood 



Sulphate nf ammonia 



Milliqratn. 

 183 

 1G1 

 2S& 



iliUigram. 



86.0 

 S I. 

 5. 1 



