Abstract--Aluminum-substituted hematites (Fez-xAlxO3) were synthesized from Fe-A1 coprecipitates at pH 5.5, 7.0, and in 10 -1, 10 -2, and 10 -2 M KOH at 700C. As little as 1 mole % AI suppressed goethite completely at pH 7 whereas in KOH higher AI concentrations were necessary. AI substitution as determined chemically and by XRD line shift was related to AI addition up to a maximum of 16-17 mole %. The relationship between the crystallographic ao parameter and AI substitution deviated from the Vegard rule. At low substitution crystallinity of the hematites was improved whereas higher substitution impeded crystal growth in the crystallographic z-direction as indicated by differential XRD line broadening. At still higher AI addition crystal growth was strongly retarded. The initial AI-Fe coprecipitate behaved differently from a mechanical mixture of the respective "'hydroxides" and was, therefore, considered an aluminous ferrihydrite.

A BS'I RAU 1 : l~oenmite and iepidocrocite, in th~ fu~m u~ ira,, VldL~.~ ~,t,l ~r . . . . . . . . . ]-~u •v .u, faces parallel to the constituent layers, show one predominant absorption band due to OH stretching of two-coordinated surface hydroxyl groups, which are shown to be unreactive towards phosphate. In very fine grained preparations of lepidocrocite, two other species of surface hydroxyl are detected, presumably associated with (100) and (001) faces. Marked differences in the frequencies of bulk vibrations between platy and rod shaped lepidocrocite preparations can be explained partly by their crystal morphology, and partly by degree of crystalline order.Although the surface hydroxyl groups and surface reactions of gibbsite and goethite have been shown to be accessible to infrared study (Russell et al., 1974(Russell et al., , 1975Parfitt et al., 1976Parfitt et al., , 1977Parfitt & Russell, 1977), no report of IR absorption associated with the surfaces of lepidocrocite and boehmite has appeared. These minerals can crystallize in the form of thin plates with well-developed (010) faces, on which a single species of twocoordinated OH group should predominate, and we have examined suitable crystal preparations to identify this OH vibration and to determine its reactivity towards phosphate.In the course of this work, some striking differences between the IR spectra of platy and rod-shaped lepidocrocite crystals were seen in the region of bulk Fe-O vibrations. A possible explanation is proposed. S A M P L E P R E P A R A T I O N A N D C H A R A C T E R I S T I C S BoehmiteA solution of A1C13 (0.1 M) was neutralized to pH 6 with N a H C O 3 (0.4 N) and the suspension aged for one hour. The pH was then increased to pH 8 by addition of N a O H (0.15 ~) and the suspension stored for 60 h at 160~ in a sealed container. After cooling, the solid product was washed salt free by centrifugation and kept as a suspension (~20 mg m1-1) in a sealed polythene container.

We measured fluxes of N2O, CH4 and CO2 from control and urea-nitrogen fertilized soils of a mature slash pine (Pinuselliottii var. elliottii Englem.) plantation in Alachua County, Florida. The fertilization did not affect CO2 emissions, but significantly increased the emissions of N2O and lowered the uptake of atmospheric CH4. Daily average N2O emissions from the fertilized soils were 8–600 times higher (12–74 μg N2O-N•m−2•h−1) than daily average N2O emissions from control soils (0.02–4.0 μg N2O-N•m−2•h−1). Daily average CH4 uptake by the fertilized soils were 5–20 times lower (0.001–0.007 mg CH4-C•m−2•h−1) than daily average CH4 uptake by control soils (0.015–0.035 mg CH4-C•m−2•h−1). We also measured the relative activities of the bacteria populations that were responsible for CH4 oxidation in the control and fertilized soils. Results from these measurements suggest that fertilization shifted the relative activities of the CH4 oxidizing bacteria from those dominated by methanotrophs in the control soils to those dominated by nitrifying bacteria in the surface (0–2 cm) of the fertilized soils. The shift in relative activities of these bacteria may have been responsible for the lower CH4 uptake by the fertilized soils.

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