20 EXPERIMENT STATION RECOED. 



The author concludes that soils have a definite sulfofying power which is de- 

 terminable in the laboratory, as shown in a previous article (E. S. R.. 31, p. 

 318), and that the process of sulfofication is mainly brought about by bacterial 

 action, although a small production of sulphates in soils by chemical action is 

 considered probable. Free sulphur was oxidized much less readily in the soil 

 than the sulphids of sodium, potassium, and calcium. 



The preferred method of measuring sulfofication is to add 0.1 gm. of free 

 sulphur to 100 gm. of fresh soil, incubate for from 5 to 10 days with a moisture 

 content of 50 per cent of saturation, leach out the sulphates with water, precipi- 

 tate with barium chlorid, and determine with the sulphur photometer. 



Additions of organic matter to the soil in the form of manure and green 

 manure increased the sulfofying power up to a certain point. The optimum 

 moisture content of the soil for sulfofication was found to be 50 per cent of the 

 amount necessary for complete saturation. This is taken to indicate that 

 optimum sulfofication may occur in soils which contain the optimum moisture 

 content for crop growth. Aeration of the soil by mixing with sand up to 50 

 per cent of each increased sulfofication, beyond which point a depression oc- 

 curred. The addition of carbohydrates to the soil depressed sulfofication, the 

 greater the amount added the greater the depression. The depression also 

 varied in inverse ratio to the solubility of the carbohydrates. 



Greenhouse tests with a loam soil showed that applications of 25 tons of 

 horse manure or cow manure and 4 tons of clover hay exerted similar effects 

 on sulfofication and on the yield of timothy. "At first there was a depression 

 in sulfofication and an injury to tlie crop, but this was followed by an increase 

 both in sulfofying power and in crop yield. Calcium sulphate applied to the soil 

 at the rate of i ton per acre increased slightly tlie crop yield, but the i ton of 

 CaS which was found to bo complett'ly oxidized in a short time to the sulphate, 

 corresponding, therefore, to the addition of a larger application of the sulphate, 

 gave no increase in crop. The sulfofying power of the soil was increase<l to a 

 very large extent in both cases, the larger amount of calcium sulphate giving 

 the greater effect. The transformation of CaS into sulpliate in this particular 

 soil was shown to be very rapid and the oxidation of the sulphur in the manures 

 was only slightly less rai)id."' 



Analyses of typical Iowa soils are also reported, the results of which are 

 taken to indicate that sulphur may be lacking and that this element should 

 not be neglected in systems of permanent agriculture. 



A review of the work of others bearing on the subject is includetl. 



Sulfofication in soils, P. E. Brown and E. H. Kellogo (Proc. Iowa Acad. Set., 



21 (1914), PP- 17-22). — The .substance of this article is noted above. 



Field tests with, a toxic soil constituent: Salicylic aldehyde, O. Schreiner 

 and J. J. Skinner (Jour. Amci: Soc. Agron., 6 {1914), No. 3, pp. 108-llS, p/«. 2; 

 abs. in Chem. Abs., 9 (1915), No. 12, p. 1653).— The substance of this article has 

 been noted from another source (E. S. R., 31, p. 620). 



Soil protozoa, G. P. Koch (U. S. Dcpt. Agr., Jour. Agr. Research, 4 (1915), 

 No. 6, pp. 511-559). — Four sets of laboratory experiments on (1) methods for 

 counting protozoa, (2) protozoa of greenhouse soils. (3) protozoa of field and 

 greenhouse soils, and (4) the effect of temperature upon the development of soil 

 protozoa are reported which were conducted at tlie New Jersey Experiment 

 Station. In these experiments small ciliates were classified to include all organ- 

 isms from the smallest to and including Colpidium colpoda and the large ciliates 

 Included all forms larger than C. colpoda. 



Tests showed an improved loop method for counting protozoa, devised by the 

 author, to be more satisfactory tlian methods previously ust^l. This consists in 

 counting the living protozoa in tlio amount by weight of culture solution which 



