The idea of ascertaining the influence of physical factors, like moisture, temperature, air, light, as well as of certain chemical substances upon the decomposition of the organic matter in the

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soil is not new. Kostytscheff, Schloesing, Wollny. Deherain, Soyka," Warington, and Boussingault experimented along those lines. While some of them tried to find out the rate of oxidation of the organic matter by determining the amount of carbon dioxide evolved under the influence of certain factors, the others did it by estimating the proportions of ammonia, nitrites and nitrates produced. The observations of the investigators named have this in common: they represent chiefly laboratory experiments in which small amounts of soil mixed with other materials were put into tubes, cylinders or other vessels and the rate of decomposition stated. Other experimenters, too, worked along similar lines though some field observations were also made.

Results secured on a small scale in the laboratory may not necessarily hold good for field conditions. It was, therefore, deemed advisable to carry out similar experiments directly in the field and all the more so since we had at our command a number of plots under a variety of conditions. The fact that not less than twenty-two plots were to be under observation rendered determinations of ammonia, nitrites and nitrates practically infeasible, and it was decided to measure the rate of oxidations taking place in the soil by the amount of carbon dioxide evolved. It is evident that the greater the decomposition of the organic matter in the soil, the richer in carbon dioxide will be the soil atmosphere and vice versa.

THE FIELD APPARATUS.

The arrangements for the daily observations, the results of which are presented in the following pages, were made as follows: In the first place each of the twenty-two plots under experiment was provided with an iron tube twelve inches long and with an inner diameter of 5% of an inch. At one end the tube was drawn out to a point. The periphery of the lower two inches of the tube was provided with twelve small holes of one-eighth of an inch diameter. Into the upper part of the tube was put a rubber stopper, a one-eighth inch glass tube, thirteen inches long, passing through stopper and all made air tight. This tube stood out above the iron tube some three inches and reached with its lower end the periphery holes of the iron tube. In order to prevent completely the outside air from coming into the tube, the space below the rubber stopper between the glass and iron tube. was in part filled out with paraffin which together with the rubber stopper held both tubes always in the same position.

2Ann. Science agron. fr. et etrang. 1887, II. Fasc. 2, p. 165. Comptes rendus., 77, 1873, p. 203; ibid., 77, 1873, p. 353. 4Journ. f. Landw. 1886, p. 232. Journ. f. Landw. 1886, p. 243. Am. agron., 13, No. 6, 1887, p. 241.

"Zeitschr. Biol., 14, 1878.

'Landw. Versuchsst., 24, 161 (1879). Comptes rendus, 86, 22.

For drawing a portion of the soil atmosphere into the tube just described, its pointed end was forced into the soil of each plot to a depth of seven inches, the upper end of the glass tube being connected by means of rubber tubing, with the Orsat apparatus. The whole arrangement can be seen from the photographs (see Figures 3 and 4) and needs no further description. By means of the pressure bottle the soil atmosphere is drawn into the Orsat apparatus, the first 100cc. being discarded in order to force the air out of the apparatus, and the next 100cc being used for analysis. By alternately raising and lowering the pressure bottle the soil atmosphere is a number of times brought into contact with the right bulb of the apparatus containing a solution of potassium hydroxide which absorbs the carbon dioxide of the atmosphere. The decrease in volume of the soil atmosphere analyzed expresses the proportion of carbon dioxide in it. Likewise the estimation of oxygen is made by bringing the atmosphere, freed from carbon dioxide, into contact with the left bulb containing an alkaline solution of pyragallol which absorbs the oxygen. Since the burette of the apparatus has a capacity of 100cc. and is graduated into cubic centimeters with divisions allowing to record one-tenth of one cc., it is evident that the readings express directly the percentage of carbon dioxide or oxygen in the soil atmosphere.

In addition to carbon dioxide and oxygen determinations which were made once a day, the temperature of the air as well as of the soil in the various plots to a depth of six inches was regularly observed. The temperature of the soil was recordedonly once a day at the time the carbon dioxide and oxygen estimations were run, while the temperature of the air was recorded three times every day, namely, at 8 a. m., 1 p. m. and 5 p. m.

In connection with the analytical data secured we must not omit to mention here that each one of the figures given in the tables for April, May, June, July and August represents the average of the observations for a whole month, with the essential restriction, however, that, as a rule, observations were not made on rainy days or on such days which immediately followed a heavy rain, because of the muddy condition of the plots which rendered observations very inconvenient. Pressing work in the laboratory, too, sometimes prevented the field observations in question. It is for these reasons that conclusions from the results presented in the following tables will have to be made cautously.

THE INFLUENCE OF MOISTURE AND TEMPERATURE.

In reviewing the data before us we can clearly see the influence of moisture and temperature upon the decomposition of soil organic matter. Thus, in June, both the soil temperature