Phynics :11 



record anything for comparative purposes, how many of these things can 

 one get reasonable measures of for reporting? I do not see why only one 

 sjjigle factor is enough to report. There is a good answer in our case, 

 for we do not have the people that can do all these determinations for 

 us. That is why I am trying to find out how many of these determinations 

 can and should a person reasonably do. 



A. I think something you could do is to determine the percentage mois- 

 ture, which is a fairly simple task. You could also report the tex- 

 ture classification of the soil, and you might also report bulk density, 

 if this is not too difficult to determine, although it might be in cer- 

 tain instances. Those simple values are probably the minimum. Then you 

 could make some inferences concerning the other factors from the data. 



Q. I am interested in Mr. Throne's statement about moisture equivalent; 

 can it be brought into terms of pF? 



A. Moisture equivalent is the percentage water in the soil that is held 

 under a certain gravitational force. Theoretically, this is related 

 to pF value which is the centim.eters of water tension which will remove 

 a certain quantity of water leaving that particular amoiint of water in 

 the soil. Thus, the centrifugal force which you exert on the soil sample 

 in order to get moisture equivalent will be equivalent to a certain num- 

 ber of centimeters of tension which is again related to field capacity. 

 It does have a value on the pF scale which is also related to a certain 

 percentage moisture. Now the percentage moisture held in the soil under 

 certain tensions, of course, is mucli less for sandy soil than for clay 

 soil. 



Comment: One thing we should remember on this field capacity thing as a 

 guide for fumigating is this: It is fine for soils that have a field 

 capacity or a moisture equivalent of somewhere below about l5 ordinarily, 

 but do not apply it for a clay soil that has a field capacity of 30. 

 There is no farmer in tho world that can take a tractor or horse out on 

 wet soil to work it up or to draw fumigation equipment. In those cases, 

 somewhere in the order of S0-7B% of the field capacity is necessar;^^ or 

 no one can work the soil and fiimigate it. 



Q. Is not determination of the soil type as important as the m.oisture 

 determination because of porositj'' factor? 



A. Of 



course, structiiral effects are also things you cannot ignore, 



Comment: Effective fumigation is probably dependent both upon porosity 

 and the moisture content in the pores. All of the fumigants that we 

 generally use are soluble in water at about 1 part per 1,000; so the 

 more water present, the more of the gas can be taken out by tliis water 

 immediately around the point of injection. Also, the water may slow 

 dovm the movement of the gas, because it has to diffuse through liquid 

 rather than air in the soil spaces. 



Q. Would not adsorption >)e more of a factor in clay than it would in 



