^IS EXPEllIMENT STATlOisT KliCOllt). [Vol. 43 



tion apparatus are described and illustrated wliich, on test with heavy loam, 

 heavy clay, light sand, heavily fertilized tomato-liouse soils, and calcareous 

 soil, showed that ammonia can be recovered from soil with an efficiency of 

 from 9S.5 to 99.5 per cent in six hours in the apparatus. For most purposes it 

 was sufficient to aerate the soil for three hours. 



Highly fertilized glasshouse soils underwent partial decomposition in the 

 cold with magnesia. In sucli cases it is stated that the soil should be aerated 

 with magnesia and strong sodium chlorid solution for a definite time, say tliree 

 hours. Tlie complete recovery of added ammonia from a calcareous soil was 

 difficult unless the soil was finely ground. 



Soil reaction, A. Demolon {Rev. Sci. [Paris], 58 {1920), No. 6, pp. 173-177).^ 

 This is a review of literature on tlie cause, nature, and determination of soil 

 acidity, talcing up both chemical and physical methods of determination and 

 calling particular attention to the bacteriological meihod of studying soil 

 acidity by means of the presence of Azotobacter. Works on the influence of 

 acidity on fertilizers and vegetation and the correction of acidity by liming are 

 also reviewed. 



The effect of aeration and other factors on the lime requirement of a 

 muck soil, S. S. Walker {Soil Sci., 9 {1920), No. 1, pp. 77-Si).— Experiments 

 conducted at the Louisiana Exjjeriment Stations are reported in which a typical 

 black muck soil was treated in various ways in order to study the effect of 

 aeration and other factors on the lime requirement, as determined by the John- 

 son method. 



It was found that the lime requirement of this soil was increased by air- 

 drying. When the soil was kept moist and frequently stirred for a period of 

 eight months the increase of acidity was decidedly less than when it was kept 

 covered with water in a sealed jar. Soil which was tii'st neutralized with cal- 

 cium carbonate and then kept for a period of eight months, under either 

 aerobic or anaerobic conditions, developed a great deal more acidity than did 

 unneutralized soil under the same conditions. This is explained by the law 

 of mass action. The lime requirement of all samples stored in a moist condition 

 was increased, but the air-dried sample decreased in acidity during storage. It 

 was emphasized that results obtained by the Johnson and similar methods are 

 comparative rather than absolute, and that rigid conditions must be adhered to 

 in using such methods. 



The reaction of the soil as influenced by the decomposition of green 

 manures, L. P. Howard {Soil Sci., 9 {1920), No 1, pp. 27-39).— Studies of the 

 influence of green manures on the reaction of soil at the Rhode Island Experi- 

 ment Station are reported. The plan followed consisted in sampling the soils at 

 various periods during the season to follow changes in acidity and in organic ; 

 matter. 



While no conclusions seem to be warranted from the limited data obtained in 

 the experiments, it was shown that there was practically no net increase in i 

 acidity during the years 1915 and 1916, finely ground limestone having been 

 applied in 1914. In fact, there was no evidence that any acidity had resulted 

 from the use of rye as a cover crop for a quarter of a century. The legumes, ^ 

 however, during the same time considerably increased the lime requirements. 

 In the uncropped soils treated in the laboratory with an equal weight of green 

 rye as compared with clover, the rye increased the lime requirement 300 to 400 

 lbs., or about twice as much as the clover, and the increase was maintained from 

 July to December. 



The •comparative rate of decomposition of green and cured clover tops 

 in soil, A. L. Whiting and W. R. Schoonovee {Soil Set., 9 (1920), No. 2, pp. 



