20 EXPERIMENT STATION RECORD. [Vol.43 



Is usual iluriuK the pei-iod, but more is washed out in tlie following year." On 

 an avcraKe " 1 in. of rain lias for the past 25 years washed out 1 lb. of nitro- 

 gen, and for 15 years before that it washed out 1.1 lb.; only in the last 6 

 years is tliere any distinct sign of falling off." 



The effect of temperature is largely masked by that of rainfall, although the 

 data indicate a relationship between summer sunshine and the loss of nitrates 

 during the following winter, the loss tending to be higher after a hot summer 

 than after a cold one. It is noted, however, that this elfect is not a simple 

 one because a hot summer is usually also a dry one. 



Tlie recorded data for chlorin show a very close agreement between the 

 amount in the rain water and that recovered in the drainage water. The amount 

 of chlorin in the rain water during the 27 years of observation was 441.5 lbs. per 

 acre, the amount in the drainage water being 441. .53 lbs. for the 20-in. drain 

 gauge. 455.8 lbs. for the 40-in. gauge, and 447.58 lbs. for the 60-in. gauge. 



The relations existing between the soil and its water content, B. A. Keen 

 {Jour. Ayr. Sci. [Enyland], 10 {1920), No. 1, pp. U~71, figs. 2).— This paper, 

 a contribution from the Rothamsted Experimental Station, summarizes a num- 

 ber of reiwrts on the subject, particularly those which are based on the so- 

 called colloidal hypothesis. The reports are discussed under the subjects of 

 (1) soil moisture in general, (2) attempts to obtain a more complete theory of 

 soil moisture i-elations, and (3) surface forces in soils and the colloidal hy- 

 pothesis. 



All the experiments discussed have a direct bearing on the soil solution con- 

 sidered as the nutrient medium for plant growth, and show that the soil and 

 the soil solution are bound together by intimate relationships and that a change 

 in the moisture content is reflected in the resulting alteration of all the com- 

 plex variables involved. " Conclusions based on an examination of soil solu- 

 tion after it has been removed from the soil can not be regardefl as necessarily 

 quantitative, and it is open to doubt whether they are always qualitative." 



The point emphasized as brought out in the experiments discussed is, there- 

 fore, that in all studies of soils it is necessary to recognize that the system 

 soil+soil solution must be treated as a whole. "The relations between the 

 soil and its moisture content are exceedingly complex, and considerations of 

 surface films distributed over an inert mineral framework such as sand grains, 

 are insufficient to explain the observed facts for they give rise to a classifica- 

 tion of soil moisture into more or less arbitrary and water-tight compart- 

 ments, . . . Study of the soil from the colloidal point of view appears to be 

 the most promising way of obtaining further knowledge of these vital but intri- 

 cate relationships." 



The evaporation of water out of sanded and unsanded moor, Tacke, and 

 Densch (Mitt. Tcr. Ford. Moorkultur Dent. Reiche, 34 {1916), No. 2-i. pp. 45-i- 

 Jf63). — Several experiments extending over two years on the evaporation of 

 moisture from moor soils which had been covered with sand, as compared with 

 the evaporation from uncovered moor soils, are reported. While in some cases 

 there was marked evaporation from the sanded soils, the results indicate that, 

 in moor soils heavily saiturated with water, evaporation is prevented by a suffi- 

 cient covering with sand, and only in extraordinary cases when the sand cov- 

 ering itself becomes saturated with water will the evaporation of excess water 

 out of the sand covering induce a stronger evaporation from the moor soil. 

 Kun-off was hindered on sand-covered moor soil.s. 



The Trufast test for sour soil, PI O. Fippin {Jour. Amer. Sac. Agron., 12 

 {1920). No. 2. pp. 65-68). — A new method for meeting the dominant require- 

 ments of the problem of so-called acid or sour soils is described. 



