97Q 



Journal of Agricultural Research 



Vol. VI, No. 24 



Table IX. — Comparison of the ranks in IQI3 and IQ14 of the bacterial numbers and 

 nitrate-forming and inoculation experiments 



CROSS-INOCULATION EXPERIMENTS 



Unfortunately, time permitted the conducting of only one experiment 

 along the line of cross-inoculation. An effort was made to make this as 

 representative as possible, both by using as the pabulum a mixture of all 

 samples collected from the respective plots during both seasons and by 

 inoculating in duplicate sterile samples, containing 60 mgm. of nitrogen as 

 cottonseed meal from every other plot. In addition, calcium carbonate 

 was added to one of the duplicates. The results are reported in Table X. 



Reading horizontally, one obtains figures representing the capacity — 

 using this term in the sense that Stevens and Withers (17) used it — of soil 

 from the different plots to support nitrification both with and without 

 the addition of calcium carbonate. It is noted that all the soils will 

 support vigorous nitrification, provided vigorous nitrifiers are added. 

 If the averages in the last column are examined, it will be noted that 

 when calcium carbonate is added differences can be noted, but they are 

 not so marked as some other results, the highest figure being 99.9 and the 

 lowest 72.7. In the absence of calcium carbonate the figures are not 

 nearly so high, and, though the differences are somewhat more marked, 

 the relative positions are not materially different from those where 

 calcium carbonate was added. Examining any vertical column, we ob- 

 tain figues representing the ability of the various soils to support the 

 nitrifying flora from any one particular soil; or inversely, the ability of 

 any particular soil to inoculate the others. This also varies materially, 

 indicating that the soil does exercise a marked influence upon nitrifica- 

 tion, some floras thriving better in one soil and other floras better in 

 others. Considering the average of the vertical columns, we obtain what 

 may be termed the "relative inoculating ability." Here we obtain our 

 greatest variation, indicating, as previously suggested, that to the flora 

 itself must be ascribed the major differences in nitrification. Here again, 

 the continuously cropped plots, wheat and corn, rank lowest when no 

 manure is added; but manure exercises a greater influence on them than 

 any other in the series. In the case of timothy, manure has not increased 

 its inoculating ability; in fact, the reverse is true, while with the rotated 

 plot the effect has not been nearly so great as with corn and wheat. 



