I414 SOIL PHYSICS, CHEMISTRY AND MICROBIOLOGY 



than the osmotic pressure of the root hairs of many kinds of plants, as shown 

 by Hannig and others. 



6) The wilting of plants at the wilting coefficient of the soD cannot 

 be due to lack of moisture in the soil, nor to lack of a gradient of forces 

 tending to move water toward the plant. 



7) The view is held, therefoie, that the wilting at this critical soil moist- 

 ure content must be due to the increasing slowness of water movement 

 from soil particle to soil particle, and from these to the root hairs, the rate 

 of movement falling below that necessary to maintain turgidity of the 

 cells of the aerial parts, even under conditions of low transpiration. 



1060 - The Treatment of Peat Beds to Prevent Loss of Nitrogen Due to Bacterial Ac- 

 tivity (Germany). — Arnd, T. in LandwirtschaftUche J ahrbucher. Vol. 49, No. 2, pp. 191- 

 213. Berlin, March 25, 191 6. 



At the Bremen station for peat investigations, experiments were car- 

 ried out to determine whether denitrification and the decomposition of 

 nitrates in peat beds could be prevented. The problem was attacked by 

 two methods : (i) soil conditions were made such as to encourage nitrifi- 

 cation and processes favourable to plant growth ; and (2) the reduction of 

 nitrates was inhibited by the use of germicides. B}^ the first method 

 denitrifying organisms alone were affected while by the second method 

 the destruction of both denitrifiers and nitrate reducers was involved. 



1st. method. — The soil used was from a well rotted peat bed, crumbly 

 and rich in bacteria. On analysis it proved to contain fair quantities of 

 ammonia and traces of nitrates, but no nitrites. The sample was put 

 through the 3mni. sieve and mixed with pure calcium carbonate at the 

 rate of 0.3 gm. of carbonate to 40 gms. of soil (these proportions having 

 previously been shown to produce maximum nitrogen losses). The soil 

 was watered to bring it up to its original water content and placed in glass 

 vessels in layers 0.8 cm., 3 cms., and 9 cms., thick ; 0.5 gm. of dry nitrate 

 was added to each vessel which was then plugged with cotton wool and 

 incubated for a fortnight at 28° C. The amount of denitrification which 

 had taken place was then determined. 



The results showed conclusively that denitrification varies with the 

 depth of the soil layer in the vessels, i. e. with the amount of oxida- 

 tion which can take place. In other words, the greater the relative sur- 

 face exposed to the air, the more are the oxygen needs of the soU bacteria 

 satisfied and the smaller the loss of nitrogen and the reduction of nitrates. 

 The mean total loss of nitrogen for the three layers 9 cm., 3 cm., and 0.8 

 cm. were 17.8 mgms., 2.1 mgms, and 3.8 mgms. respectively. Where the soil 

 was very loosely packed, no denitrification took place, but in other cases even 

 thin layers of less than i cm. thickness showed losses of nitrogen, and it 

 may be concluded that under field conditions where the soil could never 

 have such a large surface exposed as in these experiments, denitrification 

 could never be completely prevented. 



In practice, therefore, tillage and drainage of peat soils may be al- 

 ways recommended in order to minimise denitrification, but some losses 

 must always be expected from that cause. 



