ANNUAL REPORT, 1946-47 27 



as gamma — AlOOH which is known to be present in freshly precipitated alumina 

 and to exhibit properties similar to the ball-milled kaolin. 



The alumina of ball-milled kaolin sorbed phosphate and arsenate in practically 

 equivalent amounts from the more dilute solutions of these ions; however, from 

 the more concentrated solutions the sorption of arsenate far exceeded that of 

 phosphate. The amount of either anion sorbed was dependent upon the reac- 

 tion of the equilibrium solution and the initial concentration of the solution. The 

 lower the pH within the range of pH 3.0 to pH 7.0, the greater the sorption; 

 and the higher the concentration at any fixed pH, the more of the anion was 

 sorbed per unit of alumina. 



Freshly precipitated hydrous alumina sorbed phosphate and arsenate in greater 

 quantities than an equivalent quantity of alumina contained in ball-milled kaolin. 

 Freshly prepared anhydrous alumina was much less active in anion sorption 

 than the alumina of ball-milled kaolin. Aged commercial "aluminum hydroxide" 

 had no anion sorption activity unless it had been activated by alkali and heat. 



Phosphates were effective in replacing sorbed arsenate from the alumina of 

 ball-milled kaolin, but the reaction was not an equivalent one. Arsenates re- 

 placed only a very small percentage of the sorbed phosphates from the alumina 

 of the ball-milled kaolin even when the concentration of the arsenate was five 

 times that of the sorbed phosphate. Therefore, the use of arsenate as an analyt- 

 ical reagent for measuring the anion sorption of soils or for determining the 

 exchangeable phosphorus in soils is not recommended. It follows also that soils 

 which have received large quantities of arsenates as a result of measures used in 

 pest control might release quantities of arsenates toxic to plants if they were 

 heavily fertilized with phosphatic materials. 



The Effect of Orchard Mulches on Plant Nutrient Elements in the So'l. (Dale 

 H. Sieling and Jacob K. Shaw.) Six mature Mcintosh apple trees whch had 

 been managed by the cultivation-complete fertilizer system from 1931 through 

 1940 were selected for this study in June 1941. Six separate plots, each with an 

 area of 1600 square feet and containing one tree at its center, were treated as 

 follows: Duplicate plots received an application of 290 pounds, 417 pounds, 350 

 pounds, and 400 pounds of dry mixed-hay mulch in 1941, 1942, 1943 ,and 1944 

 respectively; duplicate plots received a mulch of fiber glass wool 2-3 inches in 

 thickness in 1941 ; and two plots were cultivated and kept fallow. No commercial 

 fertilizer was applied to any of the plots during the six years the investigation 

 has been in operation. 



Soil samples were taken at two systematically located positions under each 

 tree before the mulch was applied. At each sampling location four samples were 

 taken at the following depths: 1-3 inches, 6-8 inches, 12-14 inches, and 22-24 

 inches. This sampling procedure was repeated in 1942, 1943, 1944, and 1947 

 from newly selected positions not far removed from those of the previous 3'ear 

 but far enough to insure the obtaining of the samples from soil which had not 

 been disturbed by previous samplings. The mulch was removed from the samp- 

 ling areas before sampling time to prevent its incorporation in the surface soil 

 samples. The samples were stored in sealed containers and were analyzed for 

 exchangeable calcium, magnesium, and potassium to find whether the mulching 

 systems employed were effecting the movement of these cations into soil. 



The hay used for mulching was analyzed for calcium, magnesium, and potas- 

 sium and was found to vary considerably from year to year. In total, 34.3 pounds 

 of calcium, 2.7 pounds of magnesium, and 21.7 pounds of potassium were added 

 as mulch to each plot of 1600 square feet or at the rate of 933 pounds, 73.4 pounds, 

 and 590 pounds of these elements per acre respectively. 



The amount of these elements added as the mulch should, when the hay was 

 mineralized, have had a significant effect upon the amounts in the upper zones of 



