52 



Journal of Agricultural Research voi. xix. No. a 



Table VI. — Effect of calcium sulphate on the production of carbon dioxid at low "water 



content 



Soil 

 No. 



Treatment. 



Calcium sulphate 



No treatment 



Calcium sulphate 



No treatment 



Calcium sulphate 

 No treatment. .. ., 

 Calcium sulphate 

 No treatment. .. . 

 Calcium sulphate 

 No treatment. .. . 

 Calcium sulphate 

 No treatment .... 



Carbon dioxid produced in — 



) days. 



Mgtn. 

 3-96 

 8. 14 

 4.40 

 7.81 

 2. 64 

 8.58 

 3-30 

 5-5° 

 7. 26 

 9.90 

 6.38 

 10.78 



20 days. 



Mgm. 



3-52 

 6. 16 



3-30 

 5.06 

 2. 20 

 6.16 

 2. 64 

 3-52 



6. 16 

 7.48 

 5-72 



7. 26 



30 days. 



Mgm. 

 2.86 

 4.84 



3-3° 

 4.40 



1. 70 

 5.28 



2. 42 

 2.86 

 5.28 

 6.60 

 4. 62 

 5.28 



Total 



carbon 



dioxid 



produced. 



Mgm. 

 10.34 

 19.14 

 II. 00 



17.27 



6.54 

 20. 02 



8.36 

 11.88 

 18.70 

 23.98 

 16. 72 

 23-32 



At the high water content the production of carbon dioxid for the 

 first lo-day period was depressed slightly in four soils by the treatment 

 with sulphate, but in two soils it was stimulated. During the second 

 period three of the untreated samples of soil still showed a slightly 

 greater rate of production of carbon dioxid than the corresponding 

 treated samples, and one of the treated samples of soil produced some- 

 what more of this material than the untreated. The remaining 

 soils showed very slight differences in the production of carbon dioxid. 

 During the third period there were more variations, two untreated 

 samples producing more gas than the corresponding treated samples and 

 three treated samples showing more activity than the untreated. The 

 total production of carbon dioxid for the 30 days was greater for the 

 untreated samples in four cases and less in one, and one soil showed 

 practically no difference. 



Without exception the untreated samples maintained at low water 

 content showed a greater production of carbon dioxid for each period 

 than the corresponding treated samples. In some instances the differ- 

 ence was so small as to be negligible, while in others it was very great. 

 In every case the total production for 30 days was decidedly greater for 

 the untreated samples. 



It would appear from the data presented that the biological activities 

 do not account for the changes in the solubility of the soils when treated 

 with calcium sulphate, if the carbon-dioxid production may be taken as 

 a measure. On the whole, there was a slight depression of such activi- 

 ties, especially when the samples were maintained at the low water con- 

 tent. This is somewhat at variance with the results reported by Fred 

 and Hart,^ who found an increased production of carbon dioxid from soil 



> Fred. E. B.. and Hart. E. B. the coMPARATrvB effect of phosphates and sulphates on son, 

 BACTERIA, wis. Agr. Exp. Sta. Research Bui. 35. P. 35-66, 6 fig. 1915. 



