1920] SOILS — FERTILIZERS. 813 



subject, eiperiments are reported, the first of which consisted of a study for 

 (wo seasons in tlie greenhouse of the relation between the carbon dioxid in 

 cropped and uncropped soil where an oats crop introduced the only variable. 

 The object of the second experiment was to determine the influence of some 

 crop other than oats in the production of carbon dioxid. A third exiDeriment on 

 the subject was also performed with millet following oats. A clay loam soil 

 inaintuiued at a constant moisture content of 30 per cent was used. 



It was found that an oats crop increased the production of carbon dioxid in 

 the soil. The increase was marked after the first month from the time of seed- 

 ing and reached a maximum just previous to or after the plants headed, after 

 which there was a gradual decline. Ivlillet produced about the same increase in 

 carbon dioxid as oats, but the production by each millet plant was approximately 

 half as much as that by each oats plant. The most marked rise in the carbon* 

 dioxid content of the soil occurred at a later period of growth in the case of 

 the millet than of the oats. 



The cropped soil maintained a higher carbon dioxid content after the crop 

 was harvested than the bare soil, which is attributed to the decomposition of 

 plant roots left in the soil. It seemed that increased plant growth was accom- 

 panied by increased carbon dioxid production, owing to the fact that a relation- 

 ship was found between the carbon dioxid produced, presumably by the crop, 

 and the water transpired. Fluctuations in the content of carbon dioxid in the 

 bare soil were accompanied by similar fluctuations in the cropped soil only 

 after the removal of the crop and before the crop had made much growth. 



There appeared to be little relationship between the temperature of the soil 

 at the time of sampling and the carbon dioxid in the cropped soil or that as- 

 sumed to be produced by the crop. In the bare soil the carbon dioxid was usu- 

 ally high during warm weather and low when the temperature decreased. 



■ Very low atmospheric pressures were usually accompanied by an increase in 

 ^ the content of carbon dioxid in the bare soil. The carbon dioxid produced, 



presumably by the plant, was about the same in soils having a high initial car- 

 bon dioxid content as in those low in carbon dioxid, indicating the probability 

 that plants and soil organisms act independently in producing carbon dioxid. 



It is concluded that the plant itself and soil organisms produce most of the 

 carbon dioxid in the soil, that the plant often produces at the period of its most 

 active growth many times as much carbon dioxid as is produced by soil organ- 

 isms, and that the excess carbon dioxid in the soil growing a crop is due to 

 respiratory activity of the plants rather than to the decay of root particles 

 from the crop growing on the soil at the time of analysis. 



A bibliography is included. 



■ Organic phosphorus content of Ohio soils, C. J. Schollenbebgeb (Sdil Sei., 



■ 10 (1920), No. 2, pp. 127-141, fig. i).— Studies conducted at the Ohio Experi- 

 H ment Station are reported on the organic phosphorus content of samples from 

 ^L 12 types of Ohio soils and the relation of this to other soil constituents. 



^B The observations made were based upon the examination of virgin and culti- 

 ^^vated samples from each soil type, using both surface and subsurface soil. The 

 average figures indicated that virgin surface samples are considerably richer 

 in total phosphorus than the corresponding cultivated samples of the same 

 type, and that virgin subsurface samples contain slightly more total phosphorus- 

 than cultivated soils at the same depth. The organic phosphorus contents of 

 the several samples from the average soil type stood in the same order as the 

 contents of total phosphorus. The organic phosphorus bore very nearly the 

 same percentage relation to the total phosphorus in cultivated soils as in virgin 

 soils at the same depths in the greater number of cases. One-third of the 



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