624 EXPERIMENT STATION RECORD. 



this unknown residue are many. . . The greatest need at present in determining 

 the value of the organic nitrogenous material of peat and humus is a closer 

 knowledge of the individual suhstances actually present in such material and 

 those which may possibly be formed by natural agents in the soil." 



Biochemical relations of the phosphate ion in the soil, J. Stoklasa (Centbl. 

 Bakt. Vetc], 2. Aht., 29 {1911), No. 15-19, pp. 385-515, pis. 2; abs. in Jour. 

 Chcm. Soc. [London], 100 (1911), No. 583, II, p. J,29; ZentU. Agr. Chem., J,0 

 (1911). No. 9, pp. 511-585). — This article deals primarily with the inorganic 

 phosphates of soils and with the conditions under which they become soluble 

 in water, especially the part played by micro-organisms in the transforma- 

 tion of the phosphates. It is shown, however, that there is a considerable pro- 

 portion of organic phosphorus in fertile soils in form of phosphatids, phytins, 

 and nucleoproteids. 



The insoluble phosphates are rendered soluble and available as plant food 

 mainly by the action of carbon dioxid and organic acids produced by the micro- 

 organisms of the soil. Bacterial activity is measured by the amount of 

 carbon dioxid contained in the soil, and this varies widely with the physical 

 and chemical conditions of the soil as well as its bacterial content. 



Data are given showing the variation in rate of production of carbon dioxid 

 by different kinds of soil organisms, and from these data it is estimated that 

 under the conditions of these experiments soil organisms produced carbon 

 dioxid at the rate of 75 kg. per hectare (66.75 lbs. per acre) to a depth of 40 cm. 

 (15.76 in.) per day. besides other organic acids which dissolve phosphates and 

 furnish food for the organisms. 



The author holds that the cooperation which exists between autotrophic and 

 heteroti'ophic organisms in the soil is not entirely explained by the death of the 

 former providing the latter with assimilable carbohydrates. The autotrophic 

 organisms always contain phosphatids from w^hich the heterotrophic organisms 

 obtain phosphorus in readily assimilable form. 



The process of assimilation of phosphate by bacteria and its conversion by 

 them into organic compounds is called by the author biological absorption of 

 phosphoric acid in the soil. The intensity of this process varied greatly with 

 the bacterial content of the soil, 98 per cent of phosphoric acid anhydrid being 

 absorbed by an inoculated soil as compared with 66 per cent for an uninoculated 

 soil. The biological absorptive capacity of the soil was closely related to the 

 vegetative gi'owth, and hence may be taken as an important factor in determin- 

 ing the productivity of a soil. Of the phosphoric acid anhydrid of sterilized 

 soils from 40 to 52 per cent was absorbed as compared with from 60 to 92 per 

 <^ent for soils not sterilized. From 2 to 2.3 gm. of free nitrogen was assimilated 

 by Azotobacter per gram of phosphoric acid anhydrid. The addition of dipotas- 

 sium phosphate greatly stimulated the development of bacteria in rather unpro- 

 ductive soils, thereby increasing the nitrogen content of the soil. In addition 

 to increasing the nitrogen of the soil, appreciable quantities of easily assimilable 

 mineral plant food, as the phosphate ions, were also made available by the 

 action of the nitrogen-fixing bacteria of the soil. The amount of phosphoric 

 acid anhydrid which was changed into organic phosphorus substances was larger 

 with ammonifying bacteria than with Azotobacter. 



The author found a definite relation between the assimilation of free nitro- 

 gen and the carbon and phosphoric acid contents of the soil. With nutrient 

 solutions containing no phosphoric acid the bacterial growth was reduced to a 

 minimum and the production of dry matter reduced to a point where its deter- 

 mination was impossible. 



It thus appears that one of the principle functions of phosphorus in the soil 

 is to aid in the promotion of bacterial action. 



