34 MASS. EXPERIMENT STATION BULLETIN 388 



low, especially in the subsoils, where only 28 pounds of calcium were found per 

 acre for each 6-inch depth. The calcium level of the surface soils was higher 

 but in no case exceeded 270 pounds per acre for a 6-inch depth. 



The exchangeable magnesium ranged from an amount too small to be meas- 

 ured by the niethod employed to 43.2 pounds per 6-inch layer of an acre. It 

 might be suspected that magnesium deficiency would occur on these trees under 

 certain growing conditions, since these amounts of magnesium are considered 

 inadequate for normal plant production. 



Total and available phosphorus will be determined on the soils previously 

 collected and on those obtained in the future, to see if the addition of organic 

 matter has any mobilizing effect on phosphate. Mineral analyses will also be 

 made of the samples collected in the future to determine the influence of mulch 

 on the amount or mobilization of the various mineral nutrient elements. 



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

 on the Liberation of Fixed Phosphates. (Dale H. Sieling.) Anion fixation in 

 soils is very important from the standpoint of the decrease in availability of phos- 

 phates added as fertilizers to the soil. This study was undertaken to see whether 

 arsenates were fixed in a similar manner to phosphates and would replace fixed 

 phosphates. If the arsenic from spray residues were fixed, it would show to some 

 extent the reason why such quantities of arsenic do not depress the growth of 

 plants in soils while growth cf plants is inhibited in cultural solutions containing 

 the same amount of arsenic. The fundamentals involved in anion exchange or 

 fixation by the soil can best be studied by using pure clay fractions found naturally 

 in soils. 



Purified Kaolinite and Halloysite, clay minerals commonly found in soils, 

 have been investigated for their property to adsorb arsenates. It has been found 

 that these clay minerals, as they ordinarily exist in large deposits, do not fix 

 appreciable quantities of either phosphates or arsenates at pH 3.0. Grinding of 

 these minerals in a ball mill for a period of 20 days reduced the particle size to 

 more nearly that of soil clay particles and increased the activity of both minerals 

 in fixing arsenates and phosphates. 



Five-gram samples of these minerals were shaken continuously for 24 to 72 

 hours in stoppered bottles containing measured quantities of a normal solution 

 of either phosphoric or arsenic acid adjusted to pH 3.0 with sodium hydroxide. 

 The fixation was measured by determining the decrease in concentration of the 

 ion in the solution after removal of the clay by centrifuging. Fixation was not 

 instantaneous but followed a pattern somewhat similar to th?t reported for 

 phosphate by other workers and confirmed in these tests. Arsenate was fixed 

 in quantities practically equivalent to phosphate by the Kaolinite clay but in 

 somewhat smaller amounts than phosphate by the Halloysite; however both 

 arsenate and phosphate fixation by pulverized Halloysite exceeded the amounts 

 of these ions fixed by Kaolinite. 



Further study is being conducted to establish the relative ability of each of 

 these two negative ions to replace the other when it has been fixed by these clays. 



CONTROL SERVICE 



Philip H. Smith in Charge 



The Fertilizer, Feed, and Seed Control Laws and the Dairy Law are all ad- 

 ministered as one service. In addition, a large amount of work is done not only 

 for other departments of the institution, but also for other State institutions 

 and for citizens as well. 



