ANNUAL REPORT, 1947-48 19 



increased from 0.14 p. p.m. in the untreated soil to 2.5 p. p.m. in the soil treated 

 with ethylene oxide, 7.7 p. p.m. in the soil treated with formaldehyde, and 21.7 

 p.p.m. in the soil treated with chloropicrin. 



It is interestmg to note that the use of formaldehyde and chloropicrin resulted 

 in possibly toxic concentrations of manganese. These two fumigants are widely 

 used in seedbed preparation. 



Two papers entitled "Effect of volatile disinfectants on survival of microflora 

 in soil" and "The effect of sterilization of soil upon the solubility of soil copper 

 and manganese" have been submitted to Soil Science and Florists' Exchange, 

 respectively, for publication. 



Microbiological Fixation of Copper in Soil. (Charles Hurwitz.) This is a 

 continuation of work previously reported (Mass. Expt. Sta. Bui. 441, p. 15, 

 1947). In attempting to determine the form of copper whose solubility' was 

 affected by unknown components of oat straw and alfalfa meal, it was found 

 that the solubility of copper sulfide and copper phosphate, two pr-evalent forms 

 of insoluble copper salts, was not increased by the soluble components of the 

 crop residues. It is therefore inferred that the metallo-organic salts of copper, 

 and not the inorganic salts, are the forms affected. Two papers have been pub- 

 lished: "Extraction of copper from soil as affected by soluble components of 

 oat straw and alfalfa meal," Soil Science Vol. 65, No. 3, March, 1948; and "Effect 

 of decomposition of added oat straw and alfalta meal on solubility of soil copper 

 in ammonium acetate," Proceedings of the Soil Science Society of America, 1947. 



Effect of Decomposition of Plant Residues on the Solubility of Soil Manganese. 



(Charles Htirwitz.) The results, entitled ' Effect of temperature of incubation 

 of amended soil on exchangeable manganese", have been submitted to Soil 

 Science for publication. The effect of the temperature of decomposition of oat 

 straw and alfalfa meal on the solubility ot soil manganese in Merrimac sandy 

 loam was studied at 4° C, 14° C, 31° C, 37° C, and 47° C. Neither water- 

 soluble nor easily reducible soil manganese was affected, but ammonium acetate- 

 soluble manganese showed m-arked variations. Little change was observed at 

 4° C. and 14° C, but above 30° C. the ammonium acetate-soluble manganese 

 increased as a logarithmic function of the temperature of incubation. After 

 further incubation, the exchangeable manganese decreased to initial levels. 

 There was a tendency for the increase to be maintained over a longer period at 

 the higher incubation temperatures. Glucose and peptone, when added to soil 

 instead of oat straw and alfalfa meal, also increased the ammonium acetate- 

 soluble manganese, both the increase and subsequent decrease being more rapid. 

 When no organic matter was added to the soil, no increase in soluble manganese 

 was observed from 4° C. through 37° C. At 47° C. a slight but significant in- 

 crease was observed. 



These findings may prove important in the management of greenhouse and 

 seed-bed soils where steam sterilization is used. Toxic concentrations of mangan- 

 ese may result from the sterilization temperatures. Oxidation ot these toxic 

 concentrations to insoluble forms may be delayed or may not occur because of 

 the destruction of the manganese-oxidizing bacteria by heat. 



