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the pores or in the arrangement of the pore spaces, they might behave 

 quite differently in so far as diffusion, and hence aeration, is concerned. 

 One soil having 30 per cent air space porosity with interconnected 

 channels open to the atmosphere would certainly be better aerated 

 than another having the same percentage porosity but having few 

 interconnected channels. It was suggested, in fact, that measuring the 

 diffusion characteristics of a soil and evaluating porosity in terms of 

 the diffusion process rather than on a strict volume percentage basis 

 offers a most promising method of attack on the difficult problems in 

 soil aeration. 



To accomplish this and make an even more direct determination, 

 a new method of measurement was devised. This procedure has not 

 yet been described in the literature, but it appears to have considerable 

 promise and value as a research tool. Briefly, it consists of introducing 

 a large excess of carbon dioxide into a soil from a cylinder of gas (the 

 gas is introduced through a metal capillary tube arranged into a pointed 

 sampler) to sweep out soil gases from a rather large volume of the 

 soil. The amount of gas is not critical as long as an excess is used. When 

 the flow of gas has been stopped, the oxygen analyzer is attached to 

 the same tube and small samples are withdrawn as frequently as de- 

 sired. By this means it is possible to measure the rate at which oxygen 

 diffuses into the soil to dilute the carbon dioxide until normal soil 

 atmosphere concentration is approached. The results are expressed as a 

 time curve showing renewal rate for diffusion of oxygen into the soil. 

 The method is simple and direct: no foreign materials are introduced, 

 diffusion proceeds unhampered through natural soil pores at existing 

 field moisture content, the results are easily interpreted, and the samp- 

 ling site is not changed, so that measurements can be repeated at the 

 same location as often as desired throughout a whole growing season. 

 A similar procedure which uses standard 3-inch cores of soil in natural 

 structure has also been used in the laboratory. 



Even with a limited number of determinations, some interesting data 

 were obtained with the techniques described. Thus, renewal rate — the 

 time for oxygen to reach the normal concentration usually found in the 

 soil — was two hours in a freshly plowed soil and three hours in a corn 

 plot (determinations made in late fall) ; at four hours the oxygen level 



