SOILS FERTILIZERS. 815 



in the wet, after which the weight of roots which could be washed out de- 

 creased to maturity. The greatest transpiration was in the plants producing 

 the most dry matter. In relation to dry matter produced, water was trans- 

 pired most economically with a medium degree of soil moisture but was 

 used most economically in the production of grain when the soil was kept 

 comparatively dry up to the boot stage and then kept wet until maturity. 

 The total dry matter in the plant as a whole, however, was produced most 

 economically when the soil was kept wet until the five-leaf stage and drier 

 from then until maturity. 



The percentage of nitrogen in both grain and straw was highest on the 

 driest soil and gradually decreased as the moisture increased up to 37* per 

 cent, but as the soil approached siituratiou the percentage of nitrogen in the 

 grain slightly increased. Tlie condition that gave the highest percentage of 

 nitrogen both in the grain and straw was where the moisture was low up to 

 the boot stage and high from that stage to maturity. The lowest nitrogen 

 was found where the moisture was high during all periodw. The high nitrogen 

 fertilizer always increased the nitrogen content of the crop. While the 

 percentage of nitrogen was not so great in the crop produced with complete 

 fertilizer as with no fertilizer, the total weight of nitrogen was much greater, 

 due to the larger crop. The decrease in the percentage of nitrogen from the 

 boot stage to maturity was greater in the crops on the wet soil than in those 

 on the dry soil. 



The percentage of crude ash, calcium, magnesium, potassium, and phosphoric 

 acid was lower in wheat stx-aw grown with high moisture than in that grown 

 with low moisture. 



" These experiments bring out clearly the facts that the moisture relations 

 of plants are greatly affected by the fertility of the soil, and that the effect of 

 a fertilizer is dependent on the amount of soil moisture. They emphasize also 

 the fact that fertilizer experiments, in order to be of value, must be made under 

 widely varying moisture conditions, and that exi)eriments with the use of 

 moisture by plants, in order to be conclusive, must Include a number of fer- 

 tility conditions." 



A list of references to related literature is appended. 



The evaporation of water from soil, B. A. Keen {Jour. Agr. Set. [England/], 

 6 (1914), iVo. 4, pp. Jt5G-Jfl5, figs. 8). — Studies on water evaporation from the 

 fine sand and clay soil fractions, from china clay, and from soils, with particu- 

 lar reference to the factors governing evaporation in soils, are reported and 

 the apparatus and methods used described. 



It was found that the evaporation of water from the soil fractions, from 

 china clay, and from ignited soil is a phenomenon readily explainable by the 

 known laws of evaporation and diffusion. In the soils, on the other hand, the 

 evaporation was more complex, indicating the presence of a factor which causes 

 a more intimate relation between the soil and the soil water. The removal of 

 the soluble humus from the soil by means of 2 per cent caustic soda did not 

 appreciably affect the evaporation, and ignition of the fine sand and silt made 

 no appreciable difference in the evaporation from these fractious, thus largely 

 eliminating any possible etfect of the insoluble organic matter. Destruction of 

 the colloidal ])roperties of the clay fraction completely altered the evapora- 

 tion curve, which became identical with that given by sand or silt. 



It is concluded, therefore, " that the colloidal i)roperties of the clay fraction 

 are in part, if not mainly, responsible for the characteristic shape of the evapo- 

 ration curve from soil." 



In a mathematical study of the rate of evaporation from soil (the first differ- 

 ential of the experimental curves) two factors were distinguished which oper- 



