HISTORICAL

In 1871, when the beneficial effects of lime were still little understood, Peterson1 showed that in soils treated with lime there was a production of three to six times as much carbon dioxide as in untreated soils. While he did not venture an explanation of this increase, in the light of later experiments it is evident that it represented larger decay of organic matter.

Wollny found likewise that additions of lime increased the carbon dioxide production and he suggested measuring the gas as an indication of the decay power of the soil. That suggestion remained unnoticed for some time, but has recently been brought to light and will undoubtedly prove of much value in the future.

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Ebermayer and Hilgard, and later Hartwell and Kellogg, confirmed these results, proving conclusively that lime increased the decay of organic matter in the soil.

Chester was the first to study the effect of lime on the numbers of soil bacteria. In three experiments, using applications of 1,000, 2,000, and 4,000 pounds of lime per acre, respectively, he found that the number of organisms developing on bouillon agar increased gradually, depending on the amount of lime applied.

Further work by the same author showed the largest increase in numbers with applications of 4,000 pounds of lime, and he concluded that the favorable action of the lime on the soil organisms was not "due to any direct action of the lime but due to the more favorable reaction which the lime gave the soil."

Fabricius and v. Feilitzens and Engberdings found similar increases in bacteria due to lime while Ehrenberg10

1Landw. Vers. Sta. 13, (1871), p. 160. 2Journ. f. Landw. 34, (1886), p. 213.

3 Forsch. Agrik. Phys. (1890), XIII, p. 15.

Forsch. Agrik. Phys. (1892), p. 400.

5 Report Rhode Island, Expt. Sta. 1904-05. Report Delaware, Expt. Sta. 1901, p. 50.

Bulletin 65, Delaware, Expt. Sta.

Centbl. f. Bakt. (etc.) 2 abt., 14 (1905), p. 166. "Centbl. f. Bakt. (etc.) 2 abt., 23 (1909), p. 603. 10 Landw. Jahr. 33 (1904), p. 91.

showed that in most cases a lack of lime accounted for small numbers of organisms.

Fischer1 obtained slightly different results, showing that lime at first caused a depression in numbers of bacteria from five million to one-half million per gram of soil in seven days. Subsequently, however, there was an enormous increase to sixty-seven millions of bacteria in twenty-two days, one hundred and five millions in forty-two days, and four hundred millions in one hundred and fourteen days. The results of previous quantitative determinations then, as a whole, show the decidedly beneficial action of lime on the numbers of microorganisms in the soil.

Quite a little work has been carried out to show that lime increases ammonia production in the soil and consequently bears an important relation to fertility conditions.

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Remy showed increased ammonia production in peptone solutions where lime was added. The same authors at a later date, Ehrenberg and Wohltmann, Fischer, and Schneider, confirmed these results, Remy's peptone solution method being employed in each case. In several experiments carried out at the New Jersey Experiment Station, lime invariably increased the ammonifying power of the soils tested, whether the peptone or the gelatin solution method was employed.

The effect of lime on nitrification and the necessity for the presence of lime in the soil for the process to occur, have long been a matter of common knowledge. Peterson in 1871, in connection with his work on carbon dioxide production, found increased nitrate production where lime was applied. These results have been amply confirmed in recent years in a great many investigations."

1Landw. Jahr. 38 (1909), p. 358.

2Centbl. of Bakt. (etc.) 2 abt., 8, (1902), p. 662. Landw. Jahr. 35, Erg. IV, (1906), p. 1.

Landw. Jahr. 33, (1904), p. 15.

5Journ. Landw. 52, (1904), p. 97.

Bulletin 210, N. J. Expt. Station.

N. J. Station Report 1906, 1907 and 1908.

'Balling-Jahr. f. österr. Landw. 2, (1862), p. 39, ref. Jahres. f. Agri. Chem. 5, p. 91.

Pichard Compt. Rend. 1884, p. 1289 and 1891, p. 1445.

Hilgard-Forsch. Agrik. Phys. 1892, p. 400.

Ewell and Wiley-Journ. Am. Chem. Soc. 18, (1896), p. 478.

Polzeniusz-Zeitschr. f. d. Landw. Versuchswesen in Österreich 1898, p. 235,

ref. Biederman's Centbl. f. Agri. Chem. 28, (1899), p. 12.

Wohltmann, Fischer & Schneider, Journ. Landw. 52, (1904), p. 97.

Remy-Landw. Jahr. 35, Erg. IV, (1906), p. 1.

The effect of lime on non-symbiotic nitrogen fixation has also been the subject of considerable investigation and the conclusion has been reached that the presence of lime is absolutely essential for the growth of the non-symbiotic nitrogen fixers.' In recent times the close relation between nitrogen fixation and lime has become so clearly recognized that the presence or absence of azotobacter has been considered an indication of the lime requirement of the soil.

Ehrenberg-Landw. Jahr. 33, (1904), p. 15.

Bonâme Rap. Ann. Stat. Agron. Mauritius, 1896, p. 74, ref. Expt. Sta. Record 9, p. 73. Dumont-Comp. Rend. 125, (1897), p. 469.

Liechti & Moser Landw. Jahr. d. Schweiz 18 (1904), p. 153.

Murmann, Österr. Chemikerztg. (2) 10, (1907), p. 181. Ref. Chem. Zentralbl. (5) 11, (1907), p. 64.

Withers & Fraps-Journ. Amer. Chem. Soc. 24 (1902), No. 6, p. 528.

Stutzer Mittheilungen der Deutschen Landw. Gesell XIV, p. 96.
Fischer-Journ. f. Landw. 33 (1904), p. 102.

Krüger-Inaug. Diss. Königsberg, 1908, ref. Bot. Centbl. 114 (1910), No. 9,

p. 238.

Lipman & Brown, N. J., Expt. Sta. Rpt. 1907.

1Fischer, Centbl. f. Bakt. (etc.) 2 abt. 14 (1905), p. 73.

Heinze- Centbl. f. Bakt. (etc.) 2 abt. 14 (1905), p. 174.
Lipman-N. J. Expt. Sta. Rpt. 1904, p. 262.

Krüger-Inaug. Diss. Königsberg 1908, p. 58, ref. Bot. Centbl. 114, (1910), No. 9, p. 238.

Christensen & Larsen, Centbl. f. Bakt., (etc.) 2 abt. 29, p. 347.

II. THE OBJECT OF THE EXPERIMENTS

The object of the experiments reported in this bulletin was to determine the effects of applications of ground limestone on certain groups of soil bacteria in a typical Wisconsin Drift soil.

Some of the soils were cropped to ascertain the relative effect of lime on an ordinary crop and on the bacterial flora. Determinations were made of the numbers of bacteria in the soils by counting the colonies developing on the so-called "modified synthetic" agar in Petri dishes.

The ammonifying, nitrogen-fixing, denitrifying and nitrifying powers of the soils were tested, the latter by the beaker method and the others by the beaker method and the older solution method, in order to obtain some idea of the effects of lime on these various groups of bacteria and also to throw additional light, if possible, on the relative values of the soil and the solution methods.

An attempt was thus made to correlate the crop yield, the total number of bacteria, and the number of bacteria of certain groups, as determined by their physiological activities, when under the influence of applications of ground limestone.

III. THE PLAN OF THE EXPERIMENTS

Twenty earthenware pots, each containing thirty pounds of sieved, fresh soil, were employed in this experiment. The soil was typical of the Wisconsin Drift, being classed by the Bureau of Soils as Marshall loam. It was obtained from an experimental plot to which no lime had ever been applied; which, during the preceding five years had been continually in corn and which prior to that time had been in a general farming rotation. Applications of ground limestone were made in amounts representing one-half, one, two, and three tons per acre. Ten pots were left bare for the bacteriological work and ten were planted to oats in December, when the experiment was started. The germination of the oats was very good and as soon as they developed the

plants were thinned out to leave twenty-five per pot, that being deemed the optimum number for the size of the pots. The plan of the experiment was as follows:

The limestone was very carefully mixed with each thirty pounds of soil on a sterile oil-cloth and then the mixture replaced in the pots.

The pots were kept in the greenhouse, the temperature being fairly uniform throughout the experiment.

The soils were maintained at a uniform moisture content by weighing the pots every third day and adding water to weight. The table given in connection with the quantitative determinations shows that the moisture conditions varied very slightly from fifteen per cent at all dates of sampling.

IV. THE METHODS EMPLOYED

QUANTITATIVE METHOD

Ever since the beginning of soil bacteriological investigations attempts have been made to determine the total number of bacteria present at any time by counting the colonies developing on some convenient medium, with the view of obtaining some relation between numbers and soil fertility conditions.