16 MASS. EXPERIMENT STATION BULLETIN 417 



DEPARTMENT OF BACTERIOLOGY 

 Leon A. Bradley in Charge 



Nitrification in Soils Containing Plant Residues of Varying Lignin Content. 



(James E. Fuller, cooperating with the Agronomy Department.) This study 

 was conducted on a sandy loam soil, characteristic of the Connecticut Valley 

 tobacco lands in Massachusetts. The field was divided into six plots, and each 

 plot into a sufficient number of strips to permit the planting of the several cover 

 crops, which included tobacco, corn, artichoke, buckwheat, barley, rape, sudan, 

 sorghum, oats, rye, wheat, millet, and sunflower. The plots w^ere plowed as 

 follows: two plots early, after the cover crops were well up; two in mid-season, 

 after the crops were w ell developed but not hardened ; and two at the end of the 

 season, after the plant materials had matured and hardened. 



The following season tobacco was planted over the whole field. Soil samples 

 representing all of the strips on all six plots were collected early, before the tobacco 

 was planted; in mid-season: and late, after the tobacco had been harvested. 



Two series of laboratory studies were made of the nitrifying capacity of the 

 soil: one in which dried blood (1 gm. per 100 gm. soil) was mixed with the soil, 

 and a second in which ammonium sulfate (50 mgm. N per 100 gm. soil) was 

 employed. Equal quantities of these mixtures were put into glass tumblers and 

 water was added and maintained at optimum moisture content. The tumblers 

 were allowed to stand at room temperature for four weeks, and then nitrate 

 determinations were made (phenol-di-sulfonic acid method, A.O.A.C.). 



The results of the analyses failed to indicate any relationship between the 

 nitrifying capacity of the soil and the cover crops plowed under. Attempts to 

 correlate the nitrification figures with the tobacco crop yields and indices also 

 failed to show any demonstrable relationship. The only deduction that could 

 be made was a general one: that matured and hardened plant residues plowed 

 under late in the season apparently exerted a depressing effect on the nitrifying 

 capacity of the soil as compared with the effects of the residues plowed under 

 early and in mid-season. 



Bacteriological Studies of Rural Water Supplies. (James E. Fuller.) In the 

 routine bacteriological testing of rural water supplies in this laborator}', the coli- 

 form bacteria encountered are frequently' classified as intermediates of the group: 

 that is, they do not give the differential reactions of either the fecal type Escher- 

 ichia coli or of Aerobacter aerogenes which is commonly- encountered in soil. As a 

 result, the interpretation of tests is often difficult. In the present study a number 

 of these cultures have been tested by routine standard tests (lactose fermenta- 

 tion, Endo's agar, and "Imvic" reactions) over a temperature range extending 

 from 37° to 46° C. (Eijkman test for E. coli). Results indicate that a majority of 

 contaminated rural water supplies have received their contamination from sur- 

 face wash rather than from sewage. 



Relation of Chloramine-Resistant Bacteria to Milk Supplies. (James E. 

 Fuller.) Preliminary work on this project has consisted of isolating and describ- 

 ing bacteria that have resisted chloramine (chlorine-ammonia) treatment as 

 it is applied to the Amherst water supply. A number of false presumptive tests 

 have been encountered in the water since the chloramine treatment was started. 

 Results indicate that these false tests are caused by coliform bacteria that have 

 been inactivated by long absence from their natural environment, combined 

 with non-coliform bacteria. The relationship of these bacteria to milk supplies 

 will be the next phase of the stud\'. 



