As a basis for eventually evaluating the effect of charcoal, formed during forest fires, on the availability of phosphate ions in the soil, the thermodynamics of aqueous phosphate adsorption on six typical synthetic and natural charcoal materials is investigated. A standard adsorption process is defined under the justifiable assumptions that primary orthophosphate is specifically adsorbed, probably through hydrogen bonding; and that the counter-ion, K+, is nonspecifically adsorbed or oriented in the diffuse double layer. Adsorption isotherm data at 25", 35" and 45° C. and surface area measurements allow determinations of the changes in free energy, AF°e , enthalpy, AH°g and entropy, AS°e for the standard adsorption process. This process is endothermic for the four most active charcoals. The shapes of the isotherms indicate that at least two types of adsorption sites or processes are involved, at high phosphate concentrations, in all cases. The four most active charcoals show an increase in adsorptive capacity with increasing temperature, associated with large positive values of AS°e. X-ray diffraction patterns show that the four most active charcoals have graphite-like structures, whereas the other two seem to have, largely, a threedimensionally cross-linked structure. The adsorption of phosphate per unit area increases in the order soil surface, lodgepole pine, duff, B & A Code 1551, Darco S51 and Darco G60 charcoals.Theoretical interpretation of the thermodynamic data indicates that, at least for the four most active charcoals, an extensive dehydration of the phosphate and/or charcoal surface is a distinctive part of the adsorption mechanism.

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The effects of temperature, moisture, and P source during the initial soil-fertilizer reaction period on subsequent P uptake by oats were investigated in a growth chamber. Phosphorus-treated soil with moisture adjusted to four different tensions was stored at 5°, 16° and 27°C. for 1 week and for 7 weeks. Following these storage intervals, P uptake by oats was measured using a shortterm method. Uptake of P from soil treated with mono-and diammonium phosphates was greater following reaction of the fertilizer with soil at 5°C. than at either 16 or 27°C. TVo significant differences between 16° and 27° were observed. 'Contribution from the Experimental Farm, Research Branch, Canada Department of Agriculture, Swift Current, Sask. Mr. A. Dueck conducted the growth chamber operations and made the phosphorus analyses. Mr. L. Timushka translated V. P. Dadykin's paper. Presented before the Twelfth Western Phosphate Conference, March 22, 1962, at Reno, Nev. Tormerly Physical Chemist, Soil Section, Experimental Farm, Swift Current, Sask.; now Soil Scientist, Research and Development Div., The Consolidated Mining and Smelting Company of Canada Limited, Trail, B.C.; and Irrigation Agronomist, respectively.Moisture tension during the 1-week reaction period did not influence P uptake. Following the 7-week reaction period, uptake of P was favored by the 2.0-bar moisture tension treatment. It was lowest from soil reacted at 0.4 bar. Water-soluble sources such as monocalcium phosphate and mono-and diammonium phosphates were the most sensitive to differences in moisture.Availability of the sources decreased in the order monoammonium phosphate > diammonium phosphate > monocalcium phosphate > dicalcium phosphate dihydrate> anhydrous dicalcium phosphate > check.