Al Organic Matter Research Articles

Massive carbon addition to an organic-rich Andosol increased the subsoil but not the topsoil carbon stock

Abstract. Andosols are among the most carbon-rich soils, with an average of 254 Mg ha−1 organic carbon (OC) in the upper 100 cm. A current theory proposes an upper limit for OC stocks independent of increasing carbon input, because of finite binding capacities of the soil mineral phase. We tested the possible limits in OC stocks for Andosols with already large OC concentrations and stocks (212 g kg−1 in the first horizon, 301 Mg ha−1 in the upper 100 cm). The soils received large inputs of 1800 Mg OC ha−1 as sawdust within a time period of 20 years. Adjacent soils without sawdust application served as controls. We determined total OC stocks as well as the storage forms of organic matter (OM) of five horizons down to 100 cm depth. Storage forms considered were pyrogenic carbon, OM of < 1.6 g cm−3 density and with little to no interaction with the mineral phase, and strongly mineral-bonded OM forming particles of densities between 1.6 and 2.0 g cm−3 or > 2.0 g cm−3. The two fractions > 1.6 g cm−3 were also analysed for aluminium-organic matter complexes (Al–OM complexes) and imogolite-type phases using ammonium-oxalate–oxalic-acid extraction and X-ray diffraction (XRD). Pyrogenic organic carbon represented only up to 5 wt % of OC, and thus contributed little to soil OM. In the two topsoil horizons, the fraction between 1.6 and 2.0 g cm−3 had 65–86 wt % of bulk soil OC and was dominated by Al–OM complexes. In deeper horizons, the fraction > 2.0 g cm−3 contained 80–97 wt % of the bulk soil's total OC and was characterized by a mixture of Al–OM complexes and imogolite-type phases, with proportions of imogolite-type phases increasing with depth. In response to the sawdust application, only the OC stock at 25–50 cm depth increased significantly (α=0.05, 1-β=0.8). The increase was entirely due to increased OC in the two fractions > 1.6 g cm−3. However, there was no significant increase in the total OC stocks within the upper 100 cm. The results suggest that long-term large OC inputs cannot be taken up by the obviously OC-saturated topsoil but induce downward migration and gradually increasing storage of OC in subsurface soil layers. The small additional OC accumulation despite the extremely large OC input over 20 years, however, shows that long time periods of high input are needed to promote the downward movement and deep soil storage of OC.

English

Many researches have performed on gypsum application to correct high exchangeable aluminum content in acidic soils, especially in subsurface. Although, they have found increases in the exchangeable calcium and sulfur contents, exchangeable aluminum has not been decreased. The exchangeable aluminum buffering by organic matter may contribute to non-significant reduction in exchangeable acidity. The objective of this study was to evaluate the effect of mineral gypsum on the aluminum compartments of Hardsetting Ultisol and monitor the capacity of gypsum to provide exchangeable calcium and sulfur in subsurface. Increasing amounts of mineral gypsum (0, 2, 4, 6, and 8 Mg ha-1) were applied with broadcast at the field. The experimental design consisted of randomized block with four replicates. Aluminum compartments (Al-organic matter, Al-amorphous and Al-crystalline) were evaluated at 0 and 15 days after gypsum application and the exchangeable calcium and sulfur contents were evaluated at 0, 15, 64 and 90 days. The evaluations were performed in three different layers. Gypsum application increased the exchangeable calcium and sulfur contents in subsurface and did not reduce the exchangeable aluminum content. Al-organic matter in the surface layers decreased along the incubation time and application gypsum. Al-amorphous in the subsurface layers increased with the increased amounts of gypsum. Al-crystalline decreased as soil depth increased. The exchangeable aluminum buffering in surface layers was performed by Al-organic matter and, in subsurface, by Al-crystalline. Key words: Aluminum compartments, aluminum fractionation, soil acidity, soil pH, exchangeable calcium.

Poorly-crystalline components in aggregates from soils under different land use and parent material

Fe and Al compounds of low degree of crystallinity are important components for the development and conservation of soil structure in many soils. In this work, the influence of parent material and land use on the abundance of poorly-crystalline forms of Fe and Al was studied in six macroaggregate fractions from 28 soils. The soils selected are developed on two geological materials with very different composition: granites or amphibolites, and under two land uses: shrubland or agricultural. Poorly crystalline Fe and Al were extracted with oxalic acid–ammonium oxalate (inorganic and organic forms), and with pyrophosphate (organic forms). Soils developed on amphibolite were richer in organic matter and poorly-crystalline Fe and Al compounds than soils developed on granite. Agricultural soils were impoverished in organic carbon and organic-complexed Al with respect to shrubland soils, and enriched in inorganic poorly crystalline forms of Fe. The differences related to land use were more evident in the amphibolite soils. Aggregate stability, assessed by water-dispersible clay quantification, decreased in agricultural soils with respect to shrubland soils, in particular for those developed on amphibolite. This reduction of aggregate stability in agricultural soils is likely due to a combination of several processes: loss of organic matter, higher pH, and an overall loss of poorly-crystalline Fe and Al compounds, in particular Al-organic matter complexes.

Adsorption and desorption of arsenate in Louisiana rice soils

ABSTRACTAdsorption and desorption of arsenic (As) in the soil are dominant parameters that affect the mobility and bioavailability of arsenic. Batch arsenate adsorption and desorption experiments were conducted using soils collected from three Louisiana, USA, aquaculture ponds representing different crayfish farming and rice cultural practices. Arsenate adsorption behavior in the soils was investigated using Freundlich and Langmuir sorption equations. Results demonstrated that the Langmuir isotherm model was the best fit based on statistical correlation with soil properties governing adsorption, for the entire range of arsenate concentrations for all soils. Adsorption of As(V) was governed by soil physicochemical properties especially Fe and Al oxides, clay and organic matter. Desorption of As(V) was initially fast, but with increasing incubation times desorption occurred progressively slower. Chemical fractionation of arsenic in the soils showed that the most mobile fraction represented 4.74–5.18% of the total arsenic. A part of this mobile fraction could potentially be taken up by rice and enter the food chain, but would require additional research to quantify.

Review on the content, specification of selenium and its availability in soils.

As more selenium(Se)rich soil has been found, people begin to give more attention to the availability of Se for plant and humanbeings. However, current understanding for the content, specification and plant availability is not complete and accurate. By analyzing the past research on Se in soils, we believed that differences in backgrounds(soil types, climate)and hiding effect of various influential factors led to different results with regard to the relationship of soil Se with influential factors. There should be more controlled study and quantitativebased model to trace the genuine relationship between soil Se and Fe and Al oxide, p H, Eh and organic matter. For the regional Se balance within air-soil-water-plant system, air precipitation, Se volatilization and leaching should be more precisely monitored. Isotope technology(natural istotope and labelling)could be a good option for tracing transformation mechanisms of Se in soil-plant system and this would give more good scientific support for the increasing Se utilization efficiency.

Genesis of Spodic Material underneath Peat Bogs in a Danish Wetland

The chemistry of wet Spodosols (Aquods) differs from well‐drained Spodosols. Two different hypotheses have been suggested to explain the contrasting genesis of wet spodic horizons. This study attempted to determine whether Aquods at a Danish peat‐bog wetland site are a result of (i) in situ illuviation under a fluctuating water table, or (ii) degradation of a former Fe‐rich, well‐drained spodic horizon. Methods included soil surveys, wet chemical analyses, micromorphology, pollen analysis, and radiocarbon dating of soil organic matter (OM) fractions. Aquods, and soil material with spodic features, were exclusively found in sandy material at the margins of or underneath sphagnum peat bogs, whereas Inceptisols were found on well‐drained sandy deposits only. Aluminum content was very high and Fe low in spodic materials with ortstein properties. Solid‐state 13C nuclear magnetic resonance (NMR) spectra of wet sandy 2Bs horizons were dominated by alkyl C (70%) from water‐insoluble OM and were clearly distinct from NMR spectra of overlying 2Bhsm material. Pollen analysis revealed that an open forest with a thick mor layer dominated until shortly after 5000 yr BP, when sphagnum was first recorded. Radiocarbon ages of bulk soil C in the spodic horizons had mean residence times of 4500 to 4400 yr. Accordingly, the spodic B horizon was probably formed by strong in situ illuviation of Al–OM complexes before the sphagnum peat bog formation. This suggests that spodic material formation and thus strong C accumulation underneath this Danish peat bog took place for a limited period, only in susceptible parent material, and at the margins of the expanding peat bog.

Sorptive stabilization of organic matter by amorphous Al hydroxide

Amorphous Al hydroxides (am-Al(OH) 3) strongly sorb and by this means likely protect dissolved organic matter (OM) against microbial decay in soils. We carried out batch sorption experiments (pH 4.5; 40 mg organic C L −1) with OM extracted from organic horizons under a Norway spruce and a European beech forest. The stabilization of OM by sorption was analyzed by comparing the CO 2 mineralized during the incubation of sorbed and non-sorbed OM. The mineralization of OM was evaluated based in terms of (i) the availability of the am-Al(OH) 3, thus surface OM loadings, (ii) spectral properties of OM, and (iii) the presence of phosphate as a competitor for OM. This was done by varying the solid-to-solution ratio (SSR = 0.02–1.2 g L −1) during sorption. At low SSRs, hence limited am-Al(OH) 3 availability, only small portions of dissolved OM were sorbed; for OM from Oa horizons, the mineralization of the sorbed fraction exceeded that of the original dissolved OM. The likely reason is competition with phosphate for sorption sites favouring the formation of weak mineral–organic bindings and the surface accumulation of N-rich, less aromatic and less complex OM. This small fraction controlled the mineralization of sorbed OM even at higher SSRs. At higher SSRs, i.e., with am-Al(OH) 3 more available, competition of phosphate decreased and aromatic compounds were sorbed selectively, which resulted in pronounced resistance of sorbed OM against decay. The combined OC mineralization of sorbed and non-sorbed OM was 12–65% less than that of the original DOM. Sorbed OM contributed only little to the overall OC mineralization. Stabilization of OC increased in direct proportion to am-Al(OH) 3 availability, despite constant aromatic C (∼30%). The strong stabilization at higher mineral availability is primarily governed by strong Al–OM bonds formed under less competitive conditions. Due to these strong bonds and the resulting strong stabilization, the surface loading, a proxy for the mineral’s occupation by OM, was not a factor in the mineralization of sorbed OM over a wide range of C sorption (0.2–1.1 mg C m −2). This study demonstrates that sorption to am-Al(OH) 3 results in stabilization of OM. The mineral availability as well as the inorganic solution chemistry control sorptive interactions, thereby the properties of sorbed OM, and the stability of OM against microbial decay.

Heterogeneity of the inland water–land palm ecotones (morichals) in the Orinoco lowlands, South America

We analyzed the distributional pattern of species and environmental gradients across inland water–land palm ecotones (morichals) of the Orinoco lowlands to increase comprehension of the nature of ecotone heterogeneity. A total of 91 species (53 genera and 45 families) with aboveground phytomass > 0.1 g dry mass were recorded. Detrented canonical correspondence analysis (DCCA) indicated that vegetation phytomass was related strongly to soil properties, including gradients of silt (14.5–4.7%), exchangeable Al (1.05–3.10 cmole kg−1), K (0.03–0.30 cmole kg−1), Na (0.01–0.08 cmole kg−1), Mg (0.03–0.54 cmole kg−1) concentrations, pH (3.7–5.0 units), and soil organic matter. Cluster analysis allowed the definition of four types of ecotones on the basis of hydrogeomorphic processes. The first major group (1) encompassing the sites from Venezuelan lowlands (i.e., 3V, 4V, 5V, 6V, and 7V) was related to less acidic soils with high organic matter content. The second group (II) from Eastern Colombian llanos (i.e., sites 8C, 9C, 11C, 12C, 13C, 14C, and 15C) was located in acidic soils (3.9–4.5 units) with high Mg concentration. The third group (III) (i.e., sites IV and 10C) was located in soils with high Na content, whereas the fourth group (IV) (i.e., site 2V) was characterized by species growing in soils with low exchangeable aluminum. The results evidenced the interactive role of valley constraint, landforms, hydrological regime, and soil feature in structuring the plant community. Biogeographic and floristic considerations were also taken into account to explain differences in species composition.

Relationship between extractable Al and organic C in volcanic soils of Chile

In previous studies, Al extracted by acid ammonium acetate (Al a) or Na-pyrophosphate (Al p), rather than silt or clay content and climate conditions, was the most important factor that controls organic matter (OM) levels in volcanic soils. Here, the hypothesis was tested that Al a is a comparable method (as much as CuCl 2) to quantify the proportion of Al bound to OM in allophanic soils. As far as we know, there are no previous antecedents in which selective dissolution method has been compared with this extractant. Secondly, we examine the effects of (a) Al, (b) silt plus clay content (particles size 0–53 µm) and (c) clay mineralogy on the control of organic carbon (OC) level in Chilean volcanic soils. This was achieved by sampling 16 soils series (11 Andisols, one Alfisol and four Ultisols, USDA classification) including 48 soil pedons up to 0.4 m depth. Soils were analyzed for Al a, Al p, oxalate (Al o, Si o and Fe o), cold NaOH (Al n) and un-buffered salts, CuCl 2 (Al Cu), LaCl 3 (Al La) and KCl (Al k). We also measured the Al-humus as soluble C fraction after pyrophosphate extraction and the C associated to the silt plus clay fraction after sonication and gravity decantation. The statistical package (S)MATR was used to examine bivariate linear regressions among soil properties by computing the standardized major axis (SMA). Our results indicate that Al a had a good correspondence with Al p ( R 2 = 0.76) in the top soil with Al a/Al p ratio of 0.19 and both extractans presented significant and positively relationship with soil OC (R 2 > 0.62). Acid ammonium acetate was as effective as Al Cu to determine the Al–OM in allophanic soils. It is cheaper than Al Cu and Al p and 0.5 h shaking is required compared to 2 h of Al Cu and 16 h of Al p. The efficiency of the extraction was: Al n ≥ Al o > Al p > Al Cu ≥ Al a > Al La > Al k. We also found that allophane content (estimated by Al/Si ratio) was strongly correlated ( R 2 = 0.82) with the OC in the fine silt plus clay and that Al-humus together with C in the finest particles explained ( R 2 > 0.60) the largest proportion of variation of soil OC across studied soils.

Precipitation of Dissolved Organic Matter by Aluminum Stabilizes Carbon in Acidic Forest Soils

Dissolved organic matter (DOM) is often neglected as a factor in the formation of stable soil organic matter (OM). Precipitation of DOM by dissolved Al could contribute substantially to C retention in acidic forest soils; however, no information is available on the stability of precipitated OM against microbial decay. We investigated the stability of Al–OM precipitates against microbial decay as related to (i) DOM composition, (ii) Al speciation, and (iii) the dissolved Al/C ratio. We produced Al–OM precipitates by adding AlCl3 (molar Al/C ratios: 0.05–0.3) at pH values of 3.8 and 4.5 to DOM solutions derived from Oi and Oa horizons, from either beech (Fagus sylvatica L) or spruce [Picea abies (L.) Karst.] litter. Between 13 and 84% of the C was precipitated, depending on pH, Al/C ratio, and the type of DOM. Precipitates were found to be enriched in aromatic C and mostly depleted in N when compared with DOM. Only 0.5 to 7.7% of precipitated C was mineralized during 7 wk of incubation. Mineralization of Al–OM precipitates was up to 28 times less than that of the respective DOM solutions. The extent of mineralization of Al–OM precipitates formed at pH 3.8 was reduced by 50 to 75% when compared with those formed at pH 4.5. The stability of precipitates against microbial decay increased with larger aromatic C content and larger C/N ratios. Our study clearly demonstrated that a large fraction of DOM can be precipitated and is thereby substantially stabilized against microbial decay.

Dissolution of phosphate in a phosphorus-enriched ultisol as affected by microbial reduction.

Phosphorus dissolution often increases as soils become more reduced, but the mechanisms are not fully understood. The objectives of this research were to determine rates and mechanisms of P dissolution during microbial reduction of a surface soil from the North Carolina Coastal Plain. Duplicate suspensions of silt + clay fractions from a Cape Fear sandy clay loam (fine, mixed, semiactive, thermic Typic Umbraquult) were reduced in a continuously stirred redox reactor for 40 d. We studied the effects of three treatments on P dissolution: (i) 2 g dextrose kg(-1) solids added as a microbial carbon source at time 0 d; (ii) 2 g dextrose kg(-1) solids split into three additions at 0, 12, and 26 d; and (iii) no added dextrose. After 40 d of reduction, concentrations of dissolved reactive phosphorus (DRP) were similar for all treatments and increased up to sevenfold from 1.5 to 10 mg L(-1). The initial rate of reduction and dissolution of DRP was significantly greater for the 0-d treatment. A linear relationship (R(2) = 0.79) was found between DRP and dissolved organic carbon (DOC). Dissolved Fe and Al and pH increased, suggesting the formation of aqueous Fe- and Al-organic matter complexes. Separate batch experiments were performed to study the effects of increasing pH and citrate additions on PO(4) dissolution under aerobic conditions. Increasing additions of citrate increased concentrations of DRP, Fe, and Al, while increasing pH had no effect. Results indicated that increased dissolved organic matter (DOM) during soil reduction contributed to the increase in DRP, perhaps by competitive adsorption or formation of aqueous ternary DOM-Fe-PO(4) or DOM-Al-PO(4) complexes.

Compost, Limestone, and Gypsum Effects on Calcium and Aluminum Transport in Acidic Minespoil

Combining limestone (CaCO 3 ) application with compost or gypsum (CaSO 4 .2H 2 O) can substantially increase subsoil Ca and decrease subsoil Al saturation in highly weathered acidic soils because of increased Ca mobility and formation of nontoxic Al-organic matter complexes. However, little is known about the effect of these surface amendments on subsoil chemistry in acidic minespoils that are high in SO 4 . This study used small segmented laboratory columns to analyze the effect of surface incorporated compost, CaCO 3 , and gypsum on Ca and Al chemistry in the highly acidic minespoil material (pH 2.5) below the zone of incorporation. Compost did not affect subsoil Al and Ca chemistry but caused a small increase in subsoil pH. Because of the high acidity in the spoil material CaCO 3 solubility in the amended layer was high and was not increased by compost. Adding gypsum increased Ca leaching into the subsoil compared with CaCO 3 alone, but extractable Ca was higher only after extensive leaching. Increases in extractable Ca in the subsoil were strongly correlated to decreases in extractable Al and Fe, indicating cation-exchange processes. However, significant losses of Al in unamended spoil columns and the small impact of CaCO 3 and gypsum on total Al leaching indicated that Al chemistry was also influenced by a solid phase. Solubility calculations pointed to a jurbanitelike solid phase buffering Al activity in the subsoil, even after extensive leaching. Because of this buffering effect and the high acidity of the spoil material, none of the surface treatments would be expected to alleviate subsoil phytotoxicity in highly acidic minespoil material.

Compost and calcium surface treatment effects on subsoil chemistry in acidic minespoil columns.

Surface incorporation of a liming agent in combination with compost or biosolids is a proven way to revegetate acidic minespoils, but little is known about the effect of the surface amendments on subsoil chemistry. We conducted a greenhouse column experiment to investigate how different surface amendments affected plant growth and subsoil chemistry in highly acidic minespoil material. Columns were filled with shale minespoil material (pH approximately 2.5), amended with CaCO3, CaSO4 x 2H2O (gypsum), and two rates of compost, and seeded with birdsfoot trefoil (Lotus corniculatus L.) and 'Kentucky 31' tall fescue (Festuca arundinacea Schreb.). We measured leachate and plant growth over a 170-d period with extensive irrigation. Without CaCO3, plants could only grow at the high compost rate (68.8 g kg(-1)), even though the soil pH in those treatments was below 3.5, indicating the capability of natural organic matter to detoxify Al(3+) by forming Al-organic matter complexes. Compost had no effect on the subsoil. When CaCO3 or gypsum was added to the surface, extractable Ca increased in the subsoil, but there was no relevant increase in subsoil pH. Even in the first 5 cm of subsoil material, extractable Al did not decrease very much, possibly because a jurbanite-like solid phase controlled subsoil Al(3+) activities. During the reclamation of highly acidic minespoil material one should therefore not expect significant effects of the surface treatment on the untreated subsoil. A sufficient root zone would have to be achieved by incorporating the liming agent down to the desired rooting depth.

VERTICAL DISTRIBUTION OF TRACE METALS IN NATURAL SOIL HORIZONS FROM JAPAN PART 2: EFFECTS OF ORGANIC COMPONENTS IN SOIL

The association of Al, Mn, Fe, Ba, Zn, Cr, Ni, Co and Pb withsoil organic matter (SOM) was investigated in three Japanesesoils. Organically bound metals were assayed by elementalanalysis of a fraction extracted with acidified hydrogenperoxide (H2O2) and the humic acid extracted withalkaline reagent, from soil sampled at various depths of solums.A Dystric Cambisol showed higher extractability with acidifiedH2O2 for most of the metals than a Humic Andosol and an Orthic Acrisol. A Humic Andosol had more metals associated with humicacid than the other two soils.Cu showed high extractability with acidified H2O2 andalso significant association with humic acid, while Pb showedhigh extractability with acidified H2O2 but itsassociation with humic acid was relatively low among the metalsinvestigated. As humic acid is highly resistant to weathering,retention of Cu with SOM may last longer than that of Pb.The binding of metals with SOM probably has contributed to theaccumulation of some metals in organic-rich shallow horizons of soil. Such metals were Zn, Cu, Ni and Pb in a Dystric Cambisol,Cu in a Humic Andosol, and Pb and Cu in an Orthic Arisol.

Aluminium: The Need for a Re-Evaluation of Its Toxicity and Solubility in Mature Forest Stands

Aluminium (Al) is a key element in critical loadcalculations for forest. Here, we argue for re-evaluating theimportance of Al. Effects of two levels of enhanced Alconcentrations and lowered Ca:Al ratios in the soil solutionin a field manipulation experiment in a mature spruce stand(1996–1999) on tree vitality parameters were tested. Inaddition, Al solubility controls were tested. Various loads ofAl were added to forest plots by means of an irrigationsystem. Potentially toxic Al concentrations and criticalratios of Ca to inorganic Al were established. The ratio of Cato total Al was not a suitable indicator for unfavourableconditions for plant growth. No significant effects on crowncondition, tree growth and fine root production were observedafter three years of treatment. In 1999, foliar Mg content inthe highest Al addition treatment had declined significantly.This agreed with the known response to Al stress of seedlingsin nutrient solution experiments. No support was found forusing the chemical criterion Ca:Al ratio in soil solution,foliar and root tissue as an indicator for forest damage dueto acidification. Al solubility was considerably lower thanimplied by the assumption of equilibrium with gibbsite,particularly in the root zone. The gibbsite equilibrium iscommonly used in critical load models. Substitution of thegibbsite equilibrium with an Al-organic matter complexationmodel to describe Al solubility in soil water may have largeconsequences for calculation of critical loads. The resultsindicate that critical load maps for forests should bereconsidered.

Geomorphic controls on aluminium in acid soils of the Axe Creek catchment, Victoria

This study investigates the influence of terrain, including steepness and position in slope, on soil pH, extractable aluminium (Al), and organic carbon (OC) in the Axe Creek catchment, Victoria. Both soil pH and Al were determined by use of 1 : 5 soil : 0·01 M CaCl2 extracts, with Al measured colorimetrically using a modified pyrocatechol violet method. Although all soils were acidic, the Al concentration was highest on the hilltops (>10 mg/kg) and lowest at base-of-slope sites (<1 mg/kg). The concentration of Al was generally inversely related to soil pH. However, on average, a lower Al concentration was found in the top 10 cm than in the interval from 10 to 30 cm, even though the soil pH remained relatively constant throughout the top 30 cm. The lower Al concentration in the surface layer corresponded to a substantially higher level of OC near the surface, suggesting the formation of Al-organic matter complexes.

Effective energy: a concept of energy utilization applied across species

An energy system is described in which, in both single-stomached and ruminant animals, the heat increment of feeding is considered to be linearly related to five measurable quantities. For both kinds of animals three of the quantities, with their heat increments in parentheses, are urinary N (wu; kJ/g), faecal organic matter (wd; kJ/g) and positive protein retention (wp; kJ/g). In ruminants the other two, with their heat increments in parentheses, are CH4 energy (wm; kJ/kJ) and positive lipid retention (w1; kJ/g); in single-stomached animals they are positive lipid retention from feed lipid (wII; kJ/g), and positive lipid retention not from feed lipid (wI; kJ/g). Data from suitable experiments on steers, pigs and chickens were used to test the system and to estimate wu 29.2, wd 3.80, wp 36.5, wm 0.616, wI 16.4 and wII 4.4. The values for wu, wd, wm and (wI - wII) allow an energy scale, called effective energy, to be defined for both single-stomached animals and ruminants. On this energy scale the values of wp and wI, together with the heats of combustion of protein and lipid of 23.8 and 39.6 kJ/g respectively, allow the energy requirement to be expressed as (MH + 50PR + 56LR) for both kinds of animal, where PR and LR are the rates of positive protein and lipid retention (g/d), and MH is the maintenance heat production (kJ/d) which can be estimated as 0.96 of the fasting heat production. The effective energy (EE) yielded to a ruminant animal by a feed ingredient can be estimated as EE (MJ/kg organic matter) = 1.15ME - 3.84 - 4.67DCP, where ME is the metabolizable energy value (MJ/kg organic matter) and DCP is the digested crude protein content (kg/kg organic matter) with both measured at maintenance. Alternatively, EE can be estimated as EE (MJ/kg) = GE (d - 0.228) - 4.67DCP, where GE is the gross energy (MJ/kg) and d is the energy digestibility (MJ/MJ) also measured at maintenance. The EE yielded to a single-stomached animal can be estimated as EE (kJ/g) = 1.17ME - 4.2CP - 2.44, where ME (kJ/g) is measured at, or corrected to, zero N-retention and CP (g/g) is the crude protein (N x 6.25) content of the feed ingredient. The system is simpler for ruminants, and more accurate for both kinds of animal, than those now in use. As effective energy values can be tabulated for ingredients, and are additive to the extent that ME values are additive, they can be used to formulate diets using linear programming.

Genesis of podzols on coastal dunes in southern Queensland .II. Geochemistry and forms of elements as deduced from various soil extraction procedures

Distribution of total elemental C, Al, Si, Fe, Mn, P, Ti and Zr in a chronosequence of podzols spanning some 7x105 years is presented. Considerable variation in elemental composition occurred down each profile due to translocation and nonuniform banding of heavy mineral concentrations. The mobility and fate of these elements and Cr were determined by extractions with sodium pyrophosphate, ammonium oxalate (pH 3.0), dithionitelcitrate and dilute HCl. In some cases, pyrophosphate extractions gave higher values than expected when considering the ammonium oxalate values, confirming that peptization can occur with the former. Extraction data demonstrate that all elements with the exception of Mn and Zr have been mobilized from the A horizon and accumulated in the B horizon. Mn is lost from the A horizons but there is no evidence for accumulation elsewhere in the profiles, while there is no evidence for the movement or accumulation of Zr. As the profiles develop and the thickness of the A horizons increases, Al accumulates as Al-organic matter complexes in the Bh and Bhs horizons and as proto-imogolite allophane, determined by 29Si n.m.r. spectroscopy, in the Bhs and Bs horizons. Selective dissolution by using oxalate and dithionitelcitrate demonstrates accumulation of proto-imogolite in the Bhs and Bs horizons with age, and also suggests that its nature may vary within profiles. In most profiles, only a small proportion of P is extracted by oxalate or dithionitelcitrate and appears to be in the form of monazite and gorceixite. Across the chronosequence, P accumulates in the lower B horizons and is associated with Al-organic matter complexes and proto-imogolite. Iron accumulates in B horizons and, as the later stages of podzol development, such as the giant pipey podzols, are reached, many of the lower horizons contain >90% of Fe as secondary Fe oxyhydroxides. Most of the secondary Fe in the Bh and Bhs horizons is present as Al substituted goethite while, in the Bs horizons and below, ferrihydrite is the dominant mineral. There is little evidence for significant concentrations of Fe-organic matter complexes. Fe maxima occur above the Al maxima in the younger profiles and below it in the older ones. Fe is progressively lost during profile development and is depleted from humus podzols which are often the final stage of podzol genesis. Titanium is the most abundant element after Si. Extraction data strongly suggest that Ti is largely present in primary minerals such as ilmenite, rutilelanatase and pseudorutile. Evidence is presented for the presence of Ti-organic matter complexes in A horizons and Ti mobilized in this form appears to result in the formation of pedogenic anatase or rutile in the upper B horizons. The selective dissolution data for Ti and Fe suggest possible Ti-substitution for iron in goethites which appears to be common in B horizons of the freely drained profiles, although little Ti is associated with ferrihydrite.

Solubility and retention of phosphate in soils of the northwestern Canadian prairie

Phosphate solubility and sorption characteristics of 39 agricultural soils in the northwestern Canadian Prairie were studied to gain insights into the retention of fertilizer P added to soil. The soils were mostly acidic with base saturation of 59–95%. The solubility of P as determined by the equilibrium P concentration and phosphoric acid potential was low and appeared to be controlled by sorption of phosphate by soil components. The mean equilibrium solution P concentration was 0.03 mg L−1. Phosphorus concentration in saturation extracts was about one order of magnitude higher, but would have included organic and colloidal P since P analysis in these extracts was done by ICP. Sorption capacity of P as determined by Langmuir isotherm was greater for the Dark Gray and Black soils and gleysols, i.e., soils with higher amounts of organic matter, than the Gray Luvisolic and Solodic soils by about 30%. Partial correlation showed that clay content, Al-organic matter complexes (AlOM) and amorphous iron oxide (FeOX) were significantly correlated with P sorption capacity. When both topsoils and subsoils were considered, clay content was the most important soil property influencing P sorption capacity, followed by AlOM and FeOX (standard partial regression coefficients, b′, of 0.47, 0.39 and 0.38, respectively). When only topsoils were considered, AlOM and FeOX became more important than clay content in influencing P sorption (b′ = 0.47, 0.47, and 0.33, respectively). Native P, estimated by oxalate and anion-resin extractions, was associated with the hydrous iron oxides only, although soil pH also affected the resin-extractable P fraction. Key words: P retention, solubility, Luvisols, solodic soils

AL-ORGANIC MATTER ASSOCIATIONS AS CEMENTING SUBSTANCES OF OCHREOUS BROWN SOIL AGGREGATES

The resistance of soil structural units to breakdown in water, Na resin, or H resin suspension was determined kinetically for a very water-stable organic soil (ochreous brown). Aggregate stability to Na or H resin was mainly a function of the more or less hydrophobic nature of Al-organic matter associations. Soil organic matter dissolution was a good tracer of the wetting process, and our study shows that two kinds of Al-organic matter associations act as cementing substances in such very water-stable, temperate, organic soils. The first association was organic matter similar to fulvic acids but richer in polysaccharides and peptides, weakly associated with exchangeable Al. The second association was organic matter also similar to fulvic acids but much richer in oxygenated functional groups and in nitrogenous compounds, probably strongly associated with poorly-ordered hydrous Al oxides. They were disrupted by Na and H resin, respectively. In both kinetic treatments, correlations among soil disaggregation, exchanged or/and dissolved Al, and dissolved organic matter were observed and interpreted as follows: breakup of soil aggregates into smaller units (slaking) could have been caused by the pressure of entrapped air which increased as a function of the soil wettability state from water treatment to Na resin treatment and finally to H resin treatment.