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1.
Phosphorus (P) cycles rapidly in lowland tropical forest soils, but the process have been proven difficult to quantify. Recently it was demonstrated that valuable data on soil P transformations can be derived from the natural abundance of stable oxygen isotopes in phosphate (δ18OP). Here, we measured the δ18OP of soils that had received long-term nutrient additions (P, nitrogen, and potassium) or litter manipulations in lowland tropical forest in Panama and performed controlled incubations of fresh soils amended with a single pulse of P. To detect whether δ18OP values measured in the incubations apply also for soils in the field, we examined the δ18OP values after rewetting dry soils. In the incubations, resin-P δ18OP values converged to ∼3.5‰ above the expected isotopic equilibrium with soil water. This contrasts with extra-tropical soils in which the δ18OP of resin-P matches the expected equilibrium with soil water. Identical above-equilibrium resin-P δ18OP values were also found in field soils that did not receive P additions or extra litter. We suggest that the 3.5‰ above-equilibrium δ18OP values reflect a steady state between microbial uptake of phosphate (which enriches the remaining phosphate with the heavier isotopologues) and the release of isotopically equilibrated cell internal phosphate back to the soil. We also found that soil nutrient status affected the microbial turnover rate because in soils that had received chronic P addition, the original δ18OP signature of the fertilizer was preserved for at least eight weeks, indicating that the off-equilibrium δ18OP values produced during microbial phosphate turnover was not imprinted in these soils. Overall, our results demonstrate that ongoing microbial turnover of phosphate mediates its biological availability in lowland tropical soils.  相似文献   

2.
用32P标记扩散池法测定了不同时间下土壤磷的扩散量,并用5种动力学模型对其拟合,结果表明土壤磷扩散过程最符合抛物线扩散方程。20%含水量下,磷扩散速率温度商Q10。为1.20左右,与扩散是一个物理过程相吻合。由阿尼乌斯公式求得的磷扩散活化能(EaD)随土壤水分增加而降低;在土壤水低吸力范围内(<105Pa水吸力)为12-34kJ/mol,平均为25kJ/mol左右,与溶液中离子扩散活化能较接近,说明低吸力下磷扩散主要在液相进行。将绝对反应速率理论移植用于磷扩散,所求出的磷扩散净活化能、活化熵变、活化焓变和活化自由能变在供试土壤中相同含水量下均呈规律性变化,且与EaD变化趋势基本一致,证明这些参数可用于表征磷扩散的能量特征。  相似文献   

3.
There is an increasing demand to develop a means to trace phosphorus (P) movement through the environment as excessive inputs of P have led to the eutrophication of many fresh water bodies. 18O labeled phosphate has been suggested as a potential tool for tracing P, and other researchers are using information from natural abundance 18O levels of phosphate to study phosphorus cycling. The objective of this research was to determine the rate of biological de-labeling of 18O in soils. This objective was achieved using a laboratory incubation study in which three silt-loam textured soils were incubated with 250 mg kg−1 P18O4-P for a period of 3, 10, 30, or 50 d. The incubations were conducted on both sterilized and unsterilized soils. Following incubation, phosphate from soils was extracted with a modified Bray extractant and analyzed using electrospray ionization mass spectrometry to determine the distribution of labeled phosphate species. The half-life of P18O4 in the non-sterile soils ranged from 15 to 22 d, while there was no observed P18O4 de-labeling in sterile soils after 50 d. A parameterized numerical model was developed which provided insight into the dynamics of the individual labeled phosphate species, including their half-lives and relative concentrations across the incubation period. The use of P18O4 may be useful in areas where use of radioisotopes of P is restricted, and P18O4 has potential to be useful to elucidate the dynamics of the P cycle in soils.  相似文献   

4.
The oxygen isotope composition of phosphate (δ18O‐PO4) has successfully been used to study the biological cycling of phosphorus (P) in seawater and marine sediments. However, only a few studies have used this approach in soils. In order to analyse δ18O‐PO4, phosphate must be extracted from the soil, purified and converted to silver phosphate (Ag3PO4). The published extraction methods, successfully applied to marine waters and sediments, lead to the precipitation of impure Ag3PO4when used with soils or organic‐rich samples. Here we present an improved purification protocol, designed for soils and other organic‐rich samples. After extraction with HCl, phosphate is purified with multiple mineral precipitations that do not require extreme pH adjustments of the solutions. We show that contaminant‐free Ag3PO4 can be produced from fertilizers and various soils with different chemical and physical characteristics. Our first isotopic results confirm that differences in P status and availability in soils are expressed in the δ18O‐PO4 signal, indicating the potential of this isotopic tracer to understand P dynamics in soil systems.  相似文献   

5.
Desert soils are infertile, and the ability to improve them by P-fertilization is limited by the solubility of phosphate. We aimed to understand the function of phosphate solubilizing bacteria and the mechanisms behind phosphate solubilization in desert soils. Vegetated and barren desert soils, mine spoil and a fertile temperate grassland loam were sampled. Bacteria and fungi were isolated and identified, and their phosphate-solubilizing abilities were measured in vitro. The release of plant available PO4, SO4, NO3 and NH4 from desert soils did not compare with that of a grassland soil. Desert soils had substantially lower solubilization than grassland, 162 and 99–121 µg PO4-P g?1 dry soil, respectively. Phosphate-solubilizing bacteria and fungi were inhabiting the soils. Si addition increased phosphate solubilization of fungi by 50%. The isolated microbes were shown, using 31P nuclear magnetic resonance (NMR) analysis, to rapidly take-up both intracellular and extracellular phosphate during the phosphate solubilizing process. Desert soil had potentially active microbial populations that are capable to solubilize inorganic phosphorus; S and Si as the limiting factors. Acidification as the main mechanism to solubilize mineral phosphate was not as evident in our desert soils as in former studies dealing more fertile soils.  相似文献   

6.
The long-term fertilization results in accumulation of phosphorus especially in the top layer of the soils. Inundation of agricultural lands leads to a switch to anaerobic soil condition, causing reduction of iron and leaching of phosphate simultaneously. From the ecological and environmental perspective, high nutrients flux especially phosphorus will increase the possibility of eutrophication in aquatic system. The fern Azolla had a good potential to adsorb phosphorus, it also has distinctive nitrogen-fixing capacity. We conducted a 10-week aquarium experiment to investigate the phosphorus release capacity from two agricultural soils in the Netherlands with different Fe and P concentrations but comparable Fe/P ratios. Besides, the research questions rose to whether Azolla could use the mobilized phosphate released from the soils for growth. We also tried to find an effective indicator to estimate the actually phosphate mobilization from sediment to water layer. Results showed that the soils with high Fe and P concentrations had higher phosphate release rate compared with the soil with low Fe and P concentrations. Pore water Fe: PO43? ratios were valid to identify P release to surface water, when the Fe: PO43? ratios less than 8 mol mol?1 substantial phosphorus mobilization occurred. The conclusions showed that the actual mobilization of phosphate is more important than the phosphorus retained in the sediments for the internal PO43? fluxes. From 10-week experimental results, we found that Azolla can reuse the phosphate retained in soils thus removed the mobilized phosphate in a moderately low surface water nutrient loading.  相似文献   

7.
After 100h reaction with Cl-resin and 300h reaction with HCO3-resin (approaching equilibrium), the concentration of anions complementary to phosphate was the critical variable affecting the transfer of P from soil to resin. Solution concentrations of H30+, Ca2+ and phosphate indicated that desorption of P by OH-, and dissolution of Ca phosphates, controlled P release from soils. P extracted by HCO3-resin was much greater than by Cl-resin from an acid soil, due to lower total anion and higher desorbing anion concentrations, but there was little difference between the two resins with a calcareous soil. HCO3-resin extracted a constant proportion of isotopically-exchangeable P from different soils whereas Cl-resin did not. Anion exchange resins provide a convenient means for producing P desorption curves for soils.  相似文献   

8.
Isotopically exchanged phosphorus is difficult to determine in soils that strongly sorb P (so that there is little P in solution) and in soils with large concentrations of colloidal P in soil suspensions. A method is proposed in which anion exchange membranes (AEM) are added to the soil suspension after an initial period of isotopic exchange with 32P‐labelled phosphate ions. Isotopically exchanged P, termed EAEM, is calculated from the ratio of labelled phosphate ions to the total phosphate ions on the membrane. The EAEM was compared with the E value measured in an aqueous soil extract (EWater extract) for 14 soils with different degrees of P sorption. The two methods gave similar results in soils with large P concentrations in an aqueous soil extract. However, EWater extract values significantly exceeded the EAEM values by up to 18‐fold when soluble P was near the determination limit (0.008 mg P l?1). In a second experiment, two Ferralsols received further P from inorganic and plant sources and were incubated for 7 days. Treatment effects on labile P were erroneous as detected by the EWater extract but were significant as detected with the AEM method. Third, EAEM values were followed in a Lixisol and a Ferralsol which received labelled phosphate ions with carrier just before the beginning of a 23‐day incubation. The approximate recovery of added inorganic P in the EAEM value suggested that this method adequately samples labile P in P‐sorbing soils. All these results showed that errors in the determination of E values for soils with very small concentrations of P in the soil solution are reduced using the proposed method.  相似文献   

9.
Studies on selenium adsorption were conducted on seleniferous and non‐seleniferous soils of north‐west India. Soils were equilibrated with graded levels of Se ranging from 1 to 100 μg ml—1 tagged with 75Se in the presence of sulphate, nitrate and phosphate ions, generally being applied to soils as inorganic fertilizers. The adsorption of Se on different soils, both in the presence and absence of competing anions, increased with increase in the level of Se added. Adsorption of Se conformed to Langmuir equation. In the absence of any competing anions, adsorption maxima of Se for different soils ranged from 270 to 461 μg g—1. The corresponding values decreased appreciably in the presence of competing anions; per cent decrease ranged from 3 to 21 at 10 μg SO4‐S ml—1, from 8 to 40 at 60 μg NO3‐N ml—1 and 32 to 56 at 15 μg H2PO4‐P ml—1. The bonding energy of Se in different soils decreased by 33 to 66 per cent in the presence of only phosphate ions. The changes in bonding energy were inconsistent in the case of nitrate and sulphate ions. At equal concentration of added P and Se, the amount of P adsorbed was 2 to 3 times the amount of Se adsorbed. With increasing concentration of Se, greater amounts of S were released in the equilibrium solution. The distribution coefficients (Kd) decreased significantly in the presence of different anions; the effect was conspicuous in the case of phosphate ions.  相似文献   

10.
《Geoderma》1994,63(1):43-52
The sorption of selenite by two allophanic soils containing high amounts of variable charge materials was studied. Selenite sorption exhibited a maximum near pH 4 and decreased, although not proportionally, with increasing pH. Only negligible amounts of selenite were sorbed above pH 7.In the two soils, the addition of selenite caused a release of sulphate (SO2−4), silicate (Si) and hydroxyl ion (OH−) and an increase in cation (Na+) adsorption. No measurable amount of phosphate (P) was released. Increase in negative charge as measured by Na+ adsorption accounted for 48 and 18% of selenite sorbed (soils 1 and 2, respectively), the rest being accounted for by release of anions. The results presented here are consistent with the widely held view that selenite and phosphate are sorbed onto variable charge surfaces by a similar mechanism (ligand exchange).  相似文献   

11.
Abstract

Both selenium (Se) and antimony (Sb) are major soil and water pollutants. Their sorption behavior in a soil–plant system was studied. Soil–soil solution distribution coefficients (K ds) for Se and Sb were measured, using a radiotracer, as an indicator of their sorption levels. Both Se and Sb behave as oxoanions (SeO2? 4, H2PO? 4 and SO2? 4) in soil; thus, the effects of concentrations of two major oxoanions (SeO2? 4 and SeO2? 3) on Se and Sb sorption were also examined. The K d values for Se for Japanese soils significantly correlated with the K d values for Sb (n = 141). The K ds of both Se and Sb similarly decreased with increasing SbO? 3 concentration. These results indicated that the sorption of Se and Sb was similarly controlled by a ligand-exchange mechanism such as phosphate sorption in soil. However, an increase in the concentration of SeO2? 3 did not decrease the K ds of Se and Sb. Furthermore, the ligand-exchangeable fractions of stable Se and Sb in major Japanese soils were determined by extraction with 0.1 mol L?1 Na2HPO4 solution. For both Se and Sb, the phosphate-extractable fractions were 10-fold higher for Se and fivefold higher for Sb than their water-soluble fractions. Although the total Se and Sb amounts in soils were the same, their ligand-exchangeable fractions were different. Approximately 0.9–12% of total Se and 0.2–1.3% of total Sb were extracted by the phosphate solution. These findings suggested that Se was more likely to be mobilized by the addition of phosphate than Sb. The effect of plant-available phosphate in the soil and the phosphate sorption capacity of soil on Se and Sb availabilities for plants were also examined using a pot experiment with soybean plants. The experimental results suggested that a high content of available phosphate and/or low phosphate sorption capacity of soil increased both Se and Sb availabilities to the plant. However, the results also suggested that the soil Se availability to the plant was higher than that of Sb even though the soil total Se and Sb amounts were the same.  相似文献   

12.
Sulphate sorption by variable charge soils   总被引：2，自引：0，他引：2  
The sorption of sulphate (SO2?4) by three variable charge soils from the Canary Islands (Spain) was studied. Sulphate sorption decreased with increasing pH. Only negligible amounts of SO2?4 were sorbed above pH 6.5. When the soils were washed with an indifferent electrolyte (0.01 M KCl), more SO2?4 was recovered than had been sorbed. This indicated a release of native SO2?4 Sulphate replaced hydroxyl ions (OH) and co-ordinated H2O molecules, as well as very small amounts of silicate (Si). No measurable amount of phosphate (P) was released. On average hydroxyl release accounted for 50% of SO2?4 sorbed, the rest being accounted for by the increase in negative charge as measured by K+ adsorption. The results presented here are consistent with the sorption of SO2?4 through a ligand exchange mechanism, but in a different plane of sorption to that of phosphate.  相似文献   

13.
Summary The influence of vesicular-arbuscular mycorrhizae on the efficiency of triple superphosphate and rock phosphate fertilizers was compared in two tropical, acid, P-fixing soils (Ivory Coast) in which the available P was labelled with 32PO inf4 sup3- . Both soils were planted with micropropagated oil palms. The growth reponses to the fertilizer applications were low unless accompanied by VAM inoculation, but both fertilizers were equally available to plants. Isotopic-dilution kinetics analyses indicated that the rock phosphate was solubilized in both soils and there was an enrichment of the labile pool of plant-available P, similar to that with superphosphate. The specific activity and the fraction of P derived from either fertilizer was similar in both mycorrhizal and non-mycorrhizal plants, showing that both absorbed P from the same labile pool of P in the fertilized soils. However, VAM inoculation increased the fertilizer utilization coefficient of plants 2.7- to 5.6-fold, depending on the soil and fertilizer. We conclude that VAM inoculation increases fertilizer efficiency, as much of rock phosphate as of superphosphate, for plants growing in acid, P-fixing soils, and the processes involved are not different for the two fertilizers.  相似文献   

14.
Abstract

Lead arsenate was extensively used to control insects in apple and plum orchards in the 1900s. Continuous use of lead arsenate resulted in elevated soil levels of lead (Pb) and arsenic (As). There are concerns that As and Pb will become solubilized upon a change in land use. In situ chemical stabilization practices, such as the use of phosphate‐phosphorus (P), have been investigated as a possible method for reducing the solubility, mobility, and potential toxicity of Pb and As in these soils. The objective of this study was to determine the effectiveness of calcium carbonate (lime), P, and iron (Fe) amendments in reducing the solubility of As and Pb in lead‐arsenate‐treated soils over time. Under controlled conditions, two orchard soils, Thurmont loam (Hapludults) and Burch loam (Haploxerolls), were amended with reagent‐grade calcium carbonate (CaCO3), iron hydroxide [Fe(OH)3], and potassium phosphate (KH2PO4) and incubated for 16 weeks at 26°C. The experimental results suggested that the inorganic P increased competitive sorption between H2PO4 ? and dihydrogen arsenate (H2AsO4 ?), resulting in greater desorption of As in both Thurmont and Burch soils. Therefore, addition of lime, potassium phosphate, and Fe to lead‐arsenate‐contaminated soils could increase the risk of loss of soluble As and Pb from surface soil and potentially increase these metal species in runoff and movement to groundwater.  相似文献   

15.
A laboratory experiment was carried out to study the influence of 100 mg phosphorus pentoxide (P2O5) kg–1 soil from various phosphate sources on ammonia losses from soils amended with urea at 200 mg nitrogen (N) kg–1 soil. Irrespective of soil type, ammonia (NH3) loss was significantly greater from untreated soil (control) than from the soil treated with phosphorus (P) sources. A maximum decrease in ammonia loss (56%) was observed by applying phosphoric acid followed by triple and single superphosphate. Ammonia losses were significantly greater from sandy clay loam than from clay. Rate of ammonia volatilization was maximum during the first week of incubation and became undetectable for both soils at 21 days after incubation. The addition of phosphate sources significantly decreased pH in the sandy clay loam, but in the clay a significant decrease was observed only with the phosphoric acid addition. Addition of phosphate fertilizers was beneficial in reducing NH3 losses from urea.  相似文献   

16.
A pot experiment was conducted to study the contribution of reactive phosphate rocks (RPRs) on the accumulation of Cd and Zn in 10 acid upland soils in Indonesia and shoots of Zea mays plants grown on these soils. Two types of RPR were used at a rate of 0.5 g (kg soil)–1: RPRL containing 4 mg Cd kg–1 and 224 mg Zn kg–1, and RPRH containing 69 mg Cd kg–1 and 745 mg Zn kg–1. Zea mays was harvested at 6 weeks after planting. The application of RPRH significantly increased the concentrations of Cd in the shoots. The application of this RPR also increased the amount of Cd which could be extracted by 0.5 M NH4‐acetate + 0.02 M EDTA pH 4.65 from the soils. More than 90% of the added Cd remained in the soil. As Zn is an essential element and the studied acid upland soils are Zn‐deficient, increased plant growth upon RPR application might be partly attributed to Zn present in the phosphate rock. However, more experiments are needed to confirm this hypothesis. The Cd and Zn concentrations and CEC of the soils were important soil factors influencing the concentrations of Cd and Zn in the shoots of maize plants grown on these soils.  相似文献   

17.
pH对磷钾铝石形成的影响   总被引：3，自引：1，他引：2  
Effects of column temperature and flow rate on separation of organic acids were studied by determining nine low-molecular-weight organic acids on reversed-phase C18 column using high performace liquid chromatography(HPLC) with a wavelength of UV(ultraviolet)214 nm and a mobile phase of 18 mmol L^-1 KH2PO4 buffer solution (pH2.1).The thermal stabiltiy of organic acids was determined by comparing the recoveries of organic acids in different temperature treatments.The relationships between column temperature,flow rate or solvent pH and retention time were analyzed.At low solvent pH,separatioin efficiency of organic acids was increased by raising the flow rate of the solvent because of lowering the retention time or organic acids.High column temperature was unfavorable for the separation of organic acids.The separating effect can be enhanced through reducing column temperature in organic acid determination due to increasing retention time.High thermal stability of organic acids with low concentrations was observed at temperature of 40℃-45℃,Sensitivity and separation effect of organic acid determination by HPLC were clearly improved by a combination of raising flow rate and lowering column temperature at low solvent pH.  相似文献   

18.
Abstract

Accurate measurement and characterization of phosphate rock dissolution are important for a better understanding of phosphorus (P) availability in soils. An incubation study was carried out on two New Zealand topsoils (0–15 cm; high P buffering capacity Craigieburn and low P buffering capacity Templeton) amended with North Carolina phosphate rock (NCPR) and water‐soluble phosphate (WSP) at 218 mg P kg?1 (equivalent to 60 kg P ha?1). Isotopic exchange kinetics was carried out after 12 h and 28 days of incubation to characterize P availability. This study showed that sensitivity of capacity factors (r1/R, n) to explain changes in E1min values was affected by the P buffering capacity of the soils. The recovery of applied P in the E pool (RecinE%) with extended incubation time was similar from the NCPR and WSP treatments (3.1–3.3%) in the Craigieburn soil compared with the Templeton soil in which RecinE% values were greater in WSP (9%) than NCPR (1.3%) treatment. The higher values of P derived from the applied P fertilizers in the E pool (PdffinE%>80%) suggested that the NCPR application in both soils would be efficient for increasing P availability to plants.  相似文献   

19.
Influence of iron content in sewage sludges on parameters of phosphate availability in arable soils The use of iron salts for the P elimination in sewage plants is widely used. But it is not clear whether the P availability in arable soils is negatively influenced by iron compounds or not. The aim of the investigations was, therefore, to study the influence of two sewage sludges with a high and a low Fe content respectively on P sorption and phosphate concentration (Pi) in the soil solution after application of CaHPO4 or sewage sludge to 5 loamy and 4 sandy soils (pot experiments and 1 silty loam (field experiment)). Soils were analyzed 1, 6, and 13 months after P application. Sludge Gö contained 12 kg P and 65 kg Fe (t DM)—1 (P : Fe = 1 : 5.4) and sludge Sh 25 kg P and 39 kg Fe (t DM)—1 (P : Fe = 1 : 1.5). The basic P application was 60 kg P ha—1 (= 30 mg P (kg soil)—1 in the pot experiment, as sludge or as CaHPO4). P uptake by maize was determined in a separate pot experiment with a loamy soil and the same P application rate. The P sorption capacity remained similar in all soils after application of sludge Sh (P : Fe = 1:1.5) compared with soils without sludge, however, after application of sludge Gö the P sorption increased by 16% (0—59%). After application of sludge Sh the mean Pi concentration increased in loamy soils by 34% and in sandy soils by 15%. On the other hand the Pi concentration decreased after applying sludge Gö by 13% and 36% as compared to the controls of the respective soils. In the field experiment the Pi concentration of plots with a high P level (50 mg lactate soluble P (kg soil)—1) was also significantly decreased after application of 10 t sludge Gö (126 kg P ha—1) in comparison with triple phosphate. One month after the application of increasing amounts of sludge Gö (5, 10, 15 t DM ha—1) both the concentration of oxalate‐soluble Fe in the soil and the P sorption were increased. The elevated relationship between these two parameters was highly significant (r2 = 0.6 — 0.97). Plant uptake of P was less after application of sludge Gö than after application of sludge Sh and much less than P uptake from CaHPO4. Sewage sludges with a P : Fe ratio of 1 : 5 should not be recommended for agricultural use, as the P availability is significantly reduced. Iron salts should not be used for conditioning of sludges.  相似文献   

20.
Effect of iron oxide on phosphate sorption by calcite and calcareous soils   总被引：3，自引：0，他引：3  
Pure calcite (AR grade CaCO3) was treated with ferrous perchlorate solution to give a surface coating of iron (Fe) oxide. Maximum sorption (xm) of phosphate (P) by the calcite increased from 18.2 to 160 mg P kg?1 as the amount of coating increased from 0.00 to 16.0 g Fe2O3, kg?1 CaCO3. Evidence for Fe oxide coatings on carbonate minerals in two Sudanese soils was obtained by optical microscopy and electron-probe microanalysis. The relative contributions of carbonate and Fe oxide minerals, and Fe oxide coatings to P sorption in these soils were calculated, based on an assumed model of oxide distribution. Separate-phase Fe oxide was the major contributor (30–40%) to P sorption in the soils; the Fe oxide coatings on carbonate minerals were only minor contributors (< 6%), and the contribution of uncoated carbonate minerals was found to be negligible (<1 %). These results suggest a very minor role for carbonate minerals, even when coated with Fe oxide, in the sorption of P by these calcareous, Sudanese soils.  相似文献   

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