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Phosphorus sorption in soils of the Mekong Delta (Vietnam) as described by the binary Langmuir equation 总被引：1，自引：0，他引：1
VO DINH QUANG VU CAO THAI TRAN THI TUONG LINH J.E. DUFEY 《European Journal of Soil Science》1996,47(1):113-123
Phosphate adsorption isotherms were determined for 20, mostly very acidic, soils from the Mekong Delta. The experimental data were well described by a binary Langmuir equation which considers two groups of sorption sites that differ in their P bonding energies. The maximum P-sorption capacities of these sites were related to the soil properties by simple linear correlation and by stepwise multiple regression. Results suggest that high energy sites are on Al-oxihydroxides or small Al-substituted Fe-oxides and, to a lesser extent, on poorly ordered Fe-oxihydroxides. On the other hand, the P-sorption capacity of low energy sites is mainly related to clay content, and it increases as pH decreases. These sites are also positively correlated with organic carbon and poorly crystalline Fe-oxihydroxides. However, as these two variables are closely correlated with each other, organic matter is likely to be considered as an indirect factor of P fixation through its association with Fe-oxihydroxides and not as an important source of P-sorption sites. The maximum sorption capacity, i.e. the sum of sorption capacities of the two groups of sites, is well described (r2= 0.88) by an equation that takes into account the four variables identified above: Al-bearing oxihydroxides, poorly ordered Fe-oxihydroxides, clay content and pH. Grouping the soils according to the orders of Soil Taxonomy, the P-sorption capacity increases in the following sequence: ultisols < entisols < inceptisols. A P concentration often considered adequate for plant nutrition is 0.2 mg P 1?1 solution, and only the high energy sites are involved in sorption at that concentration. Thus an equation including only Al- and Fe-oxihydroxides could be used to fix P norms in these soils. 相似文献
3.
《Communications in Soil Science and Plant Analysis》2012,43(3-4):313-336
Abstract Loss of soil‐water saturation may impair growth of rainfed lowland rice by restricting nutrient uptake, including the uptake of added phosphorus (P). For acidic soils, reappearance of soluble aluminum (Al) following loss of soil‐water saturation may also restrict P uptake. The aim of this study was to determine whether liming, flooding, and P additions could ameliorate the effects of loss of soil‐water saturation on P uptake and growth of rice. In the first pot experiment, two acid lowland soils from Cambodia [Kandic Plinthaqult (black clay soil) and Plinthustalf (sandy soil)] were treated with P (45 mg P kg?1 soil) either before or after flooding for 4 weeks to investigate the effect of flooding on effectiveness of P fertilizer for rice growth. After 4 weeks, soils were air dried and crushed and then wet to field capacity and upland rice was grown in them for an additional 6 weeks. Addition of P fertilizer before rather than after flooding depressed the growth of the subsequently planted upland rice. During flooding, there was an increase in both acetate‐extractable Fe and the phosphate sorption capacity of soils, and a close relationship between them (r2=0.96–0.98). When P was added before flooding, Olsen and Bray 1‐extractable P, shoot dry matter, and shoot P concentrations were depressed, indicating that flooding decreased availability of fertilizer P. A second pot experiment was conducted with three levels of lime as CaCO3 [to establish pH (CaCl2) in the oxidized soils at 4, 5, and 6] and four levels of P (0, 13, 26, and 52 mg P kg?1 soil) added to the same two acid lowland rice soils under flooded and nonflooded conditions. Under continuously flooded conditions, pH increased to over 5.6 regardless of lime treatment, and there was no response of rice dry matter to liming after 6 weeks' growth, but the addition of P increased rice dry matter substantially in both soils. In nonflooded soils, when P was not applied, shoot dry matter was depressed by up to one‐half of that in plants grown under continuously flooded conditions. Under the nonflooded conditions, rice dry matter and leaf P increased with the addition of P, but less so than in flooded soils. Leaf P concentrations and shoot dry matter responded strongly to the addition of lime. The increase in shoot dry matter of rice with lime and P application in nonflooded soil was associated with a significant decline in soluble Al in the soil and an increase in plant P uptake. The current experiments show that the loss of soil‐water saturation may be associated with the inhibition of P absorption by excess soluble Al. By contrast, flooding decreased exchangeable Al to levels below the threshold for toxicity in rice. In addition, the decreased P availability with loss of soil‐water saturation may have been associated with a greater phosphate sorption capacity of the soils during flooding and after reoxidation due to occlusion of P within ferric oxyhydroxides formed. 相似文献
4.
《Communications in Soil Science and Plant Analysis》2012,43(11-12):1842-1861
Zinc (Zn) deficiency is a persistent problem in flooded rice (Oryza sativa L.). Severe Zn deficiency causes loss of grain yield, and rice grains with low Zn content contribute to human nutritional Zn deficiencies. The objectives of this study were to evaluate the diethylenetriaminepentaacetic acid (DTPA) extraction method for use with reduced soils and to assess differences in plant availability of native and fertilizer Zn from oxidized and reduced soils. The DTPA‐extractable Zn decreased by 60% through time after flooding when the extraction was done on field‐moist soil but remained at original levels when air‐dried prior to extraction. In a pot experiment with one calcareous and one noncalcareous soil, moist‐soil DTPA‐extractable Zn and plant Zn uptake both decreased after flooding compared with the oxidized soil treatment for both soils. In the flooded treatment of the calcareous soil, both plant and soil Zn concentrations were equal to or less than critical deficiency levels even after fertilization with 50 kg Zn ha?1. We concluded that Zn availability measurements for rice at low redox potentials should be made on reduced soil rather than air‐dry soil and that applied Zn fertilizer may become unavailable to plants after flooding. 相似文献
5.
《Communications in Soil Science and Plant Analysis》2012,43(11-12):885-898
Abstract The purpose of this study was to show how phosphorus (P) desorption can bring further information to what is inferred from adsorption experiments. A simple calculation procedure is proposed to predict the P amount that would be desorbed by washing with salt solution if adsorption was completely reversible. Consequently, the interpretation of P desorption can focus on the irreversible part of adsorption. This approach is applied to samples of acid sulfate soil from Vietnam that have been submerged for different periods of time, at 20°C and 30°C, and also to samples that were reoxidized after flooding. Phosphate desorption linearly increases with P concentration in solution and exponentially decreases with increasing adsorption capacity as expressed by the Freundlich coefficient of adsorption isotherms. These two types of relationships are correctly predicted by our calculation procedure. As far as reversibility is concerned, we find that with respect to calculated desorption, the proportion of irreversible adsorption greatly differ according to treatments. In relative terms, adsorption reversibility is lowest in the reoxidized soils and highest in the wet soils incubated at 30°C. This is related to the type and crystallinity of Fe‐oxihydroxides and consequent differences in P‐bonding energies. 相似文献
6.
Effects of heating and autoclaving on sorption and desorption of phosphorus in some forest soils 总被引：1，自引：1，他引：0
A number of biological and chemical processes may affect soil phosphorus availability when forest fires occur, partly as a
result of heating. We describe here a laboratory experiment to study the effects of soil heating on changes in sorption and
desorption of P. Autoclaving was also included as an additional treatment of moist heating under pressure. Five forest soils
(two Podzols, one Arenosol, one Luvisol and one Alisol) were heated to 60°C, 120°C and 250°C or autoclaved for 30 min. They
were repeatedly extracted with Bray I and analysed for inorganic and organic P fractions. The desorbed P data were fitted
to an asymptotic exponential equation to obtain the desorption rate and capacity parameters. Podzol and Arenosol soils showed
a quick P desorption after heating, while Luvisol and Alisol soils showed a slow desorption rate. The immediate increase in
available P that occurred after heating or autoclaving originated mostly from solubilisation of microbial metabolites and
soil organic components. Autoclaving decreased P sorption capacity in all soils, but the effects of heating on P sorption
differed among soils. Except for one of the soils, the low P-fixing soils (Podzol and Arenosol) showed a decrease in P sorption
when heated to high temperatures, whereas the high P-fixing soils (Luvisol and Alisol) showed little changes after heating.
Fire intensity and soil characteristics are important factors determining short-term and long-term soil P dynamics. 相似文献
7.
Bioremediation of crude oil in salt marsh mesocosms growing Spartina alterniflora was investigated during winter and summer to determine the influence of nitrogen (N) and phosphorus (P) fertilization, flooding, and season. Fertilization with urea and ammonium (NH4 +) applied at 75 or 150 kg N ha-1 with or without P did not significantly (p = 0.05) increase oil or hydrocarbon degradation in continuously flooded mesocosms over an 82 day period during winter (temperature range of 17 to 30 °C). Phosphorus applied at 40 kg P ha-1 significantly (p = 0.05) increased oil and hydrocarbon degradation. Nitrate (NO3 -) added alone did not increase oil or hydrocarbon degradation, but when added with P, it significantly (p = 0.05) increased degradation above that for P alone. Up to 70% of applied oil and 75% of applied hydrocarbons were degraded in P supplemented treatments. Inipol, an oleophilic fertilizer containing N, P, and a dispersant, significantly increased oil and hydrocarbon degradation. During a 40 day summer experiment (temperature range of 27–42 °C), N and P fertilization did not increase oil or hydrocarbon degradation. For continuously flooded treatments, 72% of applied hydrocarbons were degraded while 51% were degraded in alternately flooded treatments. Mesocosms provided conditions suitable for quantitative recovery of oil and results indicated that N and P fertilization, flooding, and season interacted to influence oil bioremediation. Even under the most favorable conditions, more than 1 month was required for most of the oil to disappear. 相似文献
8.
Rates of solute diffusion fundamentally affect the properties of flooded soils, but the effects of flooding on solute diffusion have not previously been studied in detail. Four soils with widely differing chemical and physical properties were packed to a range of bulk densities, flooded for varying times, and the self‐diffusion of chloride through the soils measured. Diffusion impedance factors were derived from the results. In each soil the impedance factor decreased linearly with increase in bulk density, and between soils impedance factors increased with increasing clay content. The impedance factor decreased by up to 20% during the first 3–6 weeks following flooding, but with prolonged flooding it increased to at least its initial value. Concomitantly the cation exchange capacities of the soils increased by between 30 and 100%, there was reductive dissolution of soil iron, probably both structural iron in soil clays and iron oxyhydroxide coatings on clay surfaces, and subsequently there was re‐precipitation of ferrous iron, probably as mixed carbonates and hydroxides. The decreases in diffusion impedance factors were consistent with the increases in cation exchange capacity and changes in soil iron, and the subsequent increases were consistent with re‐crystallization of mixed ferrous–ferric compounds. We conclude that the effects of changes in redox on diffusion impedance will be important in some soils, although they are smaller than the effects of water content per se. 相似文献
9.
Cesar Eugenio Quintero Flavio Hernán Gutiérrez‐Boem María Befani Romina Norma Graciela Boschetti 《植物养料与土壤学杂志》2007,170(4):500-505
In the Mesopotamia region (Argentina), rice is cropped on a wide range of soil types, and the response of rice to fertilizer application has been inconsistent even in soils with very low levels of available phosphorus. Phosphorus transformations in flooded soils depend on soil characteristics that may affect phosphorus availability. This study was conducted to determine which soil characteristics were related to the changes in P fractions during soil flooding. Soils were chosen from ten sites within the Mesopotamia region that are included in five different soil orders: Oxisols, Ultisols, Alfisols, Mollisols, and Vertisols. Soil phosphorus (P) was fractionated by a modified Hedley method before and after a 45 d anaerobic‐incubation period. Changes in the inorganic P extracted with resin depended on soil pH and were related to the exchangeable‐Fe concentration of soils (extracted with EDTA). Inorganic P extracted with alkaline extractants (NaHCO3 and NaOH) increased due to soil flooding. This increase was related to the organic‐C (OC) percentage of soils (r2 = 0.62, p < 0.01), and ranged from 13 to 55 mg kg–1. Even though previous studies showed that P associated with poorly crystalline Fe played an important role in the P nutrition of flooded rice, in this study, there was no relationship between ammonium oxalate–extractable Fe and P changes in soils due to flooding. Our results suggest that in the Mesopotamia region, changes in P fractions due to soil flooding are related to soil OC, soil pH, and soluble and weakly adsorbed Fe. 相似文献
10.
As repeatedly reported, soil flooding improves the availability of P to rice. This is in contrast with an increased P sorption in paddy soils. The effects of soil flooding on the transformation of Fe oxides and the adsorption/desorption of P of two paddy soils of Zhejiang Province in Southeast‐China were studied in anaerobic incubation experiments (submerging with water in N2 atmosphere). Soil flooding significantly increased oxalate‐extractable Fe (Feox), mainly at the expense of dithionite‐soluble Fe (FeDCB), as well as oxalate‐extractable P (Pox), but decreased the ratio of Pox/Feox. Flooding largely increased both, P adsorption and the maximum P adsorption capacity. The majority of newly sorbed P in the soils was Pox, but also more newly retained P was found to be not extractable by oxalate. Flooding also changed the characteristics of P desorption in the soils. Due to a decrease of the saturation index of the P sorption capacity, P adsorbed by flooded soils was much less desorbable than that from non‐flooded soils. There are obviously significant differences in the nature of both, the Feox and Pox fractions under non‐flooded and flooded conditions. The degree of the changes in Feox, Pox, P adsorption and P desorption by flooding depended on the contents of amorphous and total Fe oxides in non‐flooded soils. Our results confirm that the adsorption and desorption behavior of P in paddy soils is largely controlled by the transformation of the Fe oxides. The reasons of the often‐reported improved P availability to rice induced by flooding, in spite of the unfavorable effect on P desorbability, are discussed. 相似文献
11.
Adil Mihoub Mustapha Daddi Bouhoun Mohamed Lakhdar Saker 《Communications in Soil Science and Plant Analysis》2016,47(16):1920-1929
Crop response to the phosphorus (P) application is often erratic in most soil types in the world. In Algeria, there is no information on the P behavior in calcareous soils. The purposes of this work were to investigate the degree of P fixing capacity and to predict P fertilizer requirements of crops according to calcareous levels in the soil. Soil samples (at 0–30 cm depth) were collected and spiked with 0, 25 and 50% of lime (CaCO3). Phosphate sorption curves were well fitted to the Freundlich equation. Results indicated that the calcareous level was predominantly controlled the P sorption indices [sorption capacity (a), and P sorption energy (n)] to affect the estimation of external d P requirement (EPR0.2) and P fertilizer rates. The understanding of P sorption and desorption by soils and extrapolating the developed relationship between soil calcareous contents and P fertilizer rates would be quite promising and accurate approach for the economic and effective use of P fertilizers in calcareous soils of Algeria. 相似文献
12.
Samuel C. Pierce Matt T. Moore Dan Larsen S. R. Pezeshki 《Water, air, and soil pollution》2010,207(1-4):73-84
Vegetated drainages are an effective method for removal of pollutants associated with agricultural runoff. Leersia oryzoides, a plant common to agricultural ditches, may be particularly effective in remediation; however, research characterizing responses of L. oryzoides to flooding are limited. Soil reduction resulting from flooding can change availability of nutrients to plants via changes in chemical species (e.g., increasing solubility of Fe). Additionally, plant metabolic stresses resulting from reduced soils can decrease nutrient uptake and translocation. The objective of this study was to characterize belowground and aboveground nutrient allocation of L. oryzoides subjected to various soil moisture regimes. Treatments included: a well-watered and well-drained control; a continuously saturated treatment; a 48-h pulse-flood treatment; and a partially flooded treatment in which water level was maintained at 15 cm below the soil surface and flooded to the soil surface for 48 h once a week. Soil redox potential (Eh, mV) was measured periodically over the course of the 8-week experiment. At experiment termination, concentrations of Kjeldahl nitrogen, phosphorus (P), potassium (K), iron (Fe), and manganese (Mn) were measured in plant tissues. All flooded treatments demonstrated moderately reduced soil conditions (Eh < 350 mV). Plant Kjeldahl nitrogen concentrations demonstrated no treatment effect, whereas P and K concentrations decreased in aboveground portions of the plant. Belowground concentrations of P, Mn, and Fe were significantly higher in flooded plants, likely due to the increased solubility of these nutrients resulting from the reductive decomposition of metal–phosphate complexes in the soil and subsequent precipitation in the rhizosphere. These results indicate that wetland plants may indirectly affect P, Mn, and Fe concentrations in surface waters by altering local trends in soil oxidation–reduction chemistry. 相似文献
13.
A PHOSPHATE SORPTION INDEX FOR SOILS 总被引：19，自引：0，他引：19
Phosphate sorption isotherms covering a wide concentration range (10?6 to 5 × 10?3m phosphate) were determined for 42 soil samples at 20 °C by a standardized technique. The slope of a plot of the sorption, x, against the logarithm of the equilibrium solution phosphate concentration, log c, measured at c= 10?4M, proved a suitable reference index to characterize the phosphate sorbing properties of the soils. Several single-point methods were tested by statistical correlation against this reference index. Of these, the sorption, x, from one addition of 150 mg P/100 g soil gave r= 0.951, but r= 0.974 when the equilibrium concentration was also taken into account in the quotient x/log c. This quotient is therefore suggested as a simple yet adequate way of indicating a fundamental soil property, its phosphate sorption isotherm. 相似文献
14.
Cation treatment and drying‐temperature effects on nonylphenol and phenanthrene sorption to a sandy soil 
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下载免费PDF全文 Anastasia Shchegolikhina Yamuna Kunhi Mouvenchery Susanne K. Woche Jörg Bachmann Gabriele E. Schaumann Bernd Marschner 《植物养料与土壤学杂志》2014,177(2):141-149
The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na+, Ca2+, or Al3+ and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na+ led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca2+ and Al3+ decreased it. The 1H‐NMR relaxometry analyses showed that Al3+ restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca2+ or Na+. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil. 相似文献
15.
Ryoya Seto Kazuhiko Fujisao Akiko Toriumi Koki Homma Ryosuke Tajima 《Soil Science and Plant Nutrition》2013,59(6):677-685
ABSTRACTPoor response of rice to phosphorus (P) fertilization and low phytoavailability of soil P have been reported in sandy rainfed fields in northeast Thailand. In order to evaluate the effects of mild soil drying on the uptake of P by rainfed lowland rice, we carried out nutrient omission trials for nitrogen (N) and P at Ubon Ratchathani Rice Research Center under rainfed and flooded conditions. The surface soil was classified as sandy loam. To avoid severe soil drying and drought stress in the rainfed field, soil water potential at a depth of 20 cm was maintained at the field capacity (> ?20 kPa) by flush irrigation. The effects of flooding and drying on the soil properties were also evaluated in the laboratory using soils with diverse textures in and around the center. In the field experiments, the above-ground biomass of rice plants (RD6) did not respond significantly to P fertilization in the rainfed field, although it responded positively to N fertilization. Root length in the surface 10 cm under the rainfed condition was significantly smaller than that under the flooded condition due partly to the increased soil hardness upon drying, but this could not quantitatively explain the large discrepancy of P uptake observed between the rainfed and flooded conditions. Under the rainfed condition, the P uptake did not increase significantly, even when the concentration of soil Bray P was tripled by transferring the surface soil from the flooded to the rainfed field. From the laboratory experiments, it was further suggested that soil P was supplied mainly by diffusion and that the effective diffusion coefficient for P can become less than one-tenth of the value in the flooded field when the sandy soil with clay at around 10% dried to ?100 kPa. Our results suggest that the uptake of P by the rainfed lowland rice grown in sandy soil can be limited physically by mild soil drying that reduces the supply of P to roots by diffusion rather than the chemical extractability of soil P. 相似文献
16.
《Communications in Soil Science and Plant Analysis》2012,43(4):703-715
Abstract Experiments were conducted to seek a better basis for soil testing of rice paddy soils. Soils were incubated under variable conditions of simulated flooding, and then extracted with DTPA5 . The amounts of Cu, Zn, Mn and Fe extracted were sensitive to the imposed soil conditions. Good correlations between Zn extracted from simulated flooded soils and Zn uptakes by rice from flooded soils in pots, suggest that this approach to soil testing may be more useful for paddy soils than existing tests on air dried soils. 相似文献
17.
The sorption of phosphate on amorphous aluminium hydroxides was investigated using 27Al and 71P solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, following the effect of different exposures to soluble phosphate. The spectra obtained were compared with the spectrum of amorphous aluminium phosphate. Aluminium in the unreacted hydroxide had a 100% octahedral co-ordination. When dried at 200°C and exposed to soluble phosphate, very little (maximum 0.1%) amorphous aluminium hydroxide transformed to a tetrahedral co-ordination (A1 bound by oxygen bridges to four P atoms), even after 120d. The tetrahedral co-ordination exists in aluminium phosphate gel, although most of its A1 atoms exhibit an octahedral co-ordination. For the aluminium hydroxide dried at 200°C, no formation of aluminium phosphate in which aluminium is in octahedral co-ordination could be detected, not even when the aluminium hydroxide was exposed to a phosphate solution for 120 d. We concluded that the formation of aluminium phosphate is restricted to the surface of the hydroxide. Most of the phosphate which is bound to the aluminium oxide however may not have formed a ‘bulk solid’ aluminium phosphate, but is adsorbed on the internal and external surface of the oxide. The same amorphous aluminium hydroxide, dried at 70°C instead of 200°C, is converted much more rapidly to aluminium phosphate when exposed to soluble phosphate. We propose a P-induced weathering mechanism to describe P sorption on amorphous aluminium hydroxides at high P concentrations. In addition to NMR, phosphate adsorption experiments conducted on aluminium hydroxides dried at different temperatures produced evidence that the porosity of the aluminium hydroxide aggregated particles can also be a factor controlling the rate of phosphate uptake from solution, if the aggregate is stable (is not resuspended) in solution. 相似文献
18.
《Journal of plant nutrition》2013,36(4-5):623-637
Groundnuts (Arachis hypogaea L.) are frequently exposed to high temperatures in the semi-arid tropics. The objectives of the present research were: (i) to determine the response of groundnuts to different nitrogen sources; (ii) to quantify the effects of high air and soil temperatures on nodulation, dry matter production, partitioning and pod yields; and (iii) to discover whether plants dependent on symbiotic dinitrogen are more sensitive to heat stress than those dependent on inorganic nitrogen (N). Plants were grown at optimum air and ambient soil temperatures from sowing until the first flowering. Thereafter, plants were exposed to a factorial combination of two air temperatures [optimum: 28°/22°C (day/night) and high: 38°/22°C], two soil temperatures (ambient: 26°/24°C and high: 37°/30°C) and three N-sources [inoculated with Bradyrhizobium strain NC 92 (symbiotic N2); inoculated and supplied with 20 ppm inorganic N (symbiotic N2 plus 20 N); or not inoculated and supplied with 100 ppm inorganic N (inorganic N)]. At optimum air and ambient soil temperature dry matter and pod yields were greatest in plants dependent on inorganic N, intermediate in symbiotic N2 plus 20 N and least in symbiotic N2. High air or high soil temperatures significantly (P < 0.001) reduced pod yield to a similar extent and their effects were additive and without interaction. High soil, but not high air temperature, significantly (P < 0.001) reduced nodule numbers, nodule dry weight and 100 seed weight. High air and/or high soil temperature had no effect on pod yield in plants dependent on symbiotic N2 or symbiotic N2 plus 20 N, but significantly (P < 0.05) reduced pod yield in plants dependent on inorganic N. This suggest that effectively nodulated plants with small quantities of inorganic N are potentially more adaptable to hot environments than those relying on large quantities of inorganic N. 相似文献
19.
Modelling the effects of pH on phosphate sorption by soils 总被引：4，自引：0，他引：4
N. J. BARROW 《European Journal of Soil Science》1984,35(2):283-297
Samples of six soils were incubated at 60°C for 24 h with several levels of either calcium carbonate or hydrochloric acid. Phosphate sorption was then measured on sub-samples of the treated soils over 24 h at 25°C. In one set of measurements on all soils, 0.01 M calcium chloride was used as the background electrolyte. In another set, on two soils, 0.01 M sodium chloride was used. An interpolation method was used to give points on the three-dimensional surface relating the final pH of the suspensions to sorption of phosphate at specified solution concentrations of phosphate. The effects of pH on phosphate sorption differed between soils. For unfertilized soils, increases in pH up to about pH 5.5 decreased sorption. Further increases in pH decreased sorption further in one soil and increased it in three others. For fertilized soils, measured sorption increased with pH. When sodium chloride was used instead of calcium chloride, there was a more marked trend for sorption to decrease as pH increased. Differences between the soils were ascribed to differences in two soil properties. One was the rate at which the electrostatic potential in the plane of adsorption decreased as pH increased. Only small differences in the rate of change of potential were needed to reproduce the observed differences between soils. The electrostatic potential would decrease more quickly in solutions of a sodium salt than in solutions of a calcium salt and this explains the observed differences between these media. The other soil property that affected observed sorption was the release of phosphate from the soil. The amount released was largest at low pH. Consequently, for fertilized soils, measured sorption increased with pH. 相似文献
20.
Extreme flood events are predicted to have a negative impact on soil quality. Currently, there is a lack of information about the effect of agricultural practices on soil functioning and microbial processes under these events. We hypothesized that the impact of flooding on soil quality will be exacerbated when crop residues are present in the soil as they will induce more extreme anaerobicity. A spring extreme flood event (10 °C, 9 weeks) was simulated in mesocosms containing an arable sandy-loam soil low in nutrients. The main treatments were (1) with and without flooding and (2) with and without maize residue addition (8 Mg ha?1). We monitored changes in soil chemical quality indicators (e.g. pH, salinity, Fe3+, P, C, NH4 +, NO3 ? and organic N), greenhouse gas (GHG) emissions (CO2, CH4, N2O) and soil microbial community composition (PLFAs) during a prolonged flood period (9 weeks) and an 8-week “recovery” period after flooding. In comparison to the other treatments, flooding in the presence of crop residues resulted in a dramatic drop in soil redox potential. This was associated with the enhanced release of Fe and C into solution and an increase in CH4 emissions. In contrast, maize residues reduced potential nitrate losses and N2O emissions, possibly due to complete denitrification and microbial N immobilization. Both flooding and maize residues stimulated microbial growth and promoted a shift in microbial community composition. Following floodwater removal, most of the soil quality indicators returned to the levels of the control treatment within 5 weeks. After this short recovery phase, no major impact of flooding could be observed on plant growth (maize pot-grown). Overall, we conclude that both extreme flooding and management regime negatively impact upon a range of soil quality indicators (e.g. redox, GHG emissions); however, the soil showed high resilience and recovered quickly after floodwater removal. Further work is required to investigate the impact of repeated extreme flood events on soil quality and function over longer timescales. 相似文献