26 MASS. EXPERIMENT STATION BULLETIN 441 



uronic acids were present and decreased in amount as the content of pentosans 

 increased. The magnitude of the alkali lability numbers would indicate that 

 there is little difference in the chain length of the fractions obtained by use of 

 the stronger reagents. Further interpretations are not in order at this time. 



The Influence of Base Exchange Capacity and of Exchangeable Ions in Mass- 

 achusetts Soils on the Availability of Potassium. (Dale H. Slellng.) Tobacco 

 plants grown on soils of varying base exchange capacities (B.E.C.) and avail- 

 able potassium levels in 1942 were analyzed for calcium (Ca), magnesium (Mg), 

 and potassium (K). Tobacco was grown on these same soils in 1946 to further 

 exhaust the soils of cations and to determine the influence of B.E.C. on the 

 availability of these residual bases. The plants produced were anal3'zed for Ca, 

 Mg, and K. 



From 50 to 60 percent of the available K was absorbed by the growing crop 

 during the first season. The amount of K absorbed was closely proportional 

 to the K present in the soil, and not related to the available Ca or the B.E.C. 

 The dry weight production closely paralleled the K availability. In the second 

 year the plants developed severe potash-deficiency symptoms and absorbed very 

 much less K. In general, the second crop absorbed greater amounts of K from 

 those cultures of high B.E.C. 



Ca was absorbed in greater quantities from soils of high B.E.C. than from soils 

 of low B.E.C. The relative amount of Ca to total bases absorbed was greater 

 during the second year than during the first year. In all instances, an increase 

 in K uptake resulted in a decrease in Ca uptake and a greater dry weight pro- 

 duction. 



The proportion of Mg to total bases utilized decreased significantly as the 

 uptake of K increased. No significant effect on Mg uptake was shown by varia- 

 tions in the Ca level of the soil or the B.E.C. 



There was a general tendency for the total phosphorus content of the plant 

 material to decrease as the Mg/total cation ratio decreased. 



In general, cation uptake and maximum growth was associated with soils of 

 high B.E.C, and in turn less bases were lost by leaching from soils of high B.E.C. 

 Therefore agronomic practices tending to increase the B.E.C. should be practical. 

 Increase in available K in soils definitely favored the uptake of K by the plants 

 with the subsequent decrease in the uptake of Ca and Mg. Increase of Ca, on 

 the other hand, did not decrease the uptake of K but resulted in a higher total 

 base uptake. The greatest dry weight production was associated with the widest 

 K/Ca, K/Mg, and Ca/Mg ratios in the dried plant material. It therefore seems 

 reasonable to suggest that the use of fertilizers high in K should be supplemented 

 with liberal applications of Ca and Mg to prevent the Induction of deficiencies 

 of either of these elements as a result ot luxury consumption of K. 



The Fixation of Arsenic in Soils and the Influence of Arsenic Compounds on 

 the Liberation of Fixed Phosphorus in Soils. (Dale H. Slellng.) Kaolin Is a 

 widely distributed soil mineral which has been said to have ability to fix phos- 

 phates in large quantities, especially after it has been reduced to a fine state by 

 grinding or other means. It was found that kaolin could be activated to adsorb 

 large quantities of either phosphate or arsenate by ball-milling it or heating it 

 with an alkali metal hydroxide. The longer the time of ball-milling or the greater 

 the amount of alkali hydroxide used per unit of kaolin, the greater was the sorp- 

 tion capacity of the activated kaolin. 



The active constituent of ball-milled and alkali-activated kaolin could be 

 removed by extracting the materials with O.IN HCl, O.IM tartaric acid, or 10 

 percent HCl. This active constituent was believed to be a hydrous alumina such 



