32 MASS. EXPERIMENT STATION BULLETIN 388 



tests with plants. This was done by varying the base exchange capacity and the 

 calcium-hydrogen ratio of the soil artificially over the range of these values 

 observed for the other soils. It was thought that this method of approach would 

 establish certain facts that might then be confirmed by using the naturally oc- 

 curring soils for similar tests. 



The basic soil used in these tests was classified as Agawam fine sandy loam. 

 It had a pH of 5.7, an exchange capacity of 7.13 M. E.* per 100 grams and an 

 exchangeable calcium content of 2.91 M. E. per 100 grams. The material added to 

 the soil to vary the base exchange capacity was electrodialyzed bentonite, an in- 

 organic colloidal material having a base exchange capacity of 73.5 M. E. per 100 

 grams. The calcium-hydrogen ratios of both the soil and the electrodialyzed 

 bentonite were adjusted to the desired values by liming with calcium hydroxide. 

 The base exchange capacity at any desired calcium-hydrogen ratio was varied 

 between the value for the soil and that for the bentonite by mixing the two con- 

 stituents. 



Pot cultures were prepared by this method which varied in reaction from pH 

 5.7 to 7.15 and in base exchange capacity from 7.13 to 13.16 M. E. per 100 grams 

 of soil. Phosphorus, potassium, magnesium, and nitrogen were kept constant 

 in the various cultures bj' adding weighed quantities of the salts of these mate- 

 rials. Duplicate series of pot cultures, with and without added boron, were 

 prepared to check the influence cf calcium level and pH on the occurrence of 

 boron deficiency — a condition often associated with "over-liming." 



Four tobacco seedlings (Kightlinger's No. 211), five weeks old, were trans- 

 planted in each culture. The cultures were watered daily with distilled water 

 and after two weeks three of the four plants of each culture were removed. The 

 remaining plants were grown for a total of eight weeks and then harvested by 

 cutting each plant ofT at the soil surface. The plants were dried at 60° C. and the 

 dry weight was recorded. The dried plants have been stored and will be analyzed 

 for potassium to see if there was any appreciable difference in the uptake of that 

 element. 



During the growing season nitrogen deficiency developed in the plants of some 

 of the cultures even though this element was added from time to time. It seems 

 quite likely that insufficient nitrogen was supplied in the cultures. From the 

 appearance of the plants there was not a lack of boron in any of the cultures or at 

 least there was enough to prevent deficiency symptoms from occurring regard- 

 less of the reaction of the soil or its calcium level. The dry weights of the plants 

 were not greatly different although there was a tendency for the dry weight to 

 decrease at any pH as the exchange capacity and the calcium level increased. 

 This observation was most pronounced at pH 5.7. Since nitrogen deficiency was 

 observed in most of the cultures it seems logical to believe that variations in 

 growth or potassium utilization due to calcium-hydrogen ratio or base exchange 

 capacity would be minimized. 



These same cultures will be used tc grow a second crop during the summer of 

 1942, with the hope of gaining more information about the influence of these 

 various factors on plant growth and the utilization of potassium by plants. 



The Relationship of Base Exchange Capacity, Exchangeable Hydrogen, and 

 Soil Reaction to the Lime Requirement of Massachusetts Soils. (Dale H. Sieling.) 

 Samples of the varit>us soils obtained for determining the relationship between 

 lime requirement and the exchange capacity and exchangeable hydrogen were 

 limed with increasing quantities of calcium carbonate. Conditions of liming 

 were established to simulate the actual conditions in the field by placing the soils 

 on top of a layer of sea sand in lacquered metal cans perforated at the bottom. 



*M. E.= milli-equivalent. 



