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1.
To establish a national inventory of soil organic carbon (SOC) stocks and their change over time, soil was sampled in 1986, 1997 and 2009 in a Danish nation‐wide 7‐km grid and analysed for SOC content. The average SOC stock in 0–100‐cm depth soil was 142 t C ha?1, with 63, 41 and 38 t C ha?1 in the 0–25, 25–50 and 50–100 cm depths, respectively. Changes at 0–25 cm were small. During 1986–97, SOC in the 25–50‐cm layer increased in sandy soils while SOC decreased in loam soils. In the subsequent period (1997–2009), most soils showed significant losses of SOC. From 1986 to 2009, SOC at 0–100 cm decreased in loam soils and tended to increase in sandy soils. This trend is ascribed to dairy farms with grass leys being abundant on sandy soils while cereal cropping dominates on loamy soils. A statistical model including soil type, land use and management was applied separately to 0–25, 25–50 and 50–100 cm depths to pinpoint drivers for SOC change. In the 0–25 cm layer, grass leys added 0.95 t C ha?1 year?1 and autumn‐sown crops with straw incorporation added 0.40 t C ha?1 year?1. Cattle manure added 0.21 t C ha?1 year?1. Most interestingly, grass leys contributed 0.58 t C ha?1 year?1 at 25–50 cm, confirming that inventories based only on top‐soils are incomplete. We found no significant effects in 50–100 cm. Our study indicates a small annual loss of 0.2 t C ha?1 from the 0–100 cm soil layer between 1986 and 2009.  相似文献   

2.
Management effects on forms of phosphorus in soil and leaching losses   总被引：12，自引：0，他引：12  
We should know the effects of soil use and management on the contents and forms of soil phosphorus (P) and the resulting potential for leaching losses of P to prevent eutrophication of surface water. We determined P test values, amounts of sequentially extracted forms of P, P sorption capacities and degrees of P saturation in 20 differently treated soils and compared these data with leaching losses in lysimeters. One-way analyses of variance indicated that most fractions of P were significantly influenced by soil texture, land use (grassland, arable or fallow or reafforestation), mineral fertilization and intensity of soil management. Generally, sandy soils under grass and given large amounts of P fertilizer contained the most labile P and showed the largest P test values. Fallow and reafforestation led to smallest labile P fractions and relative increases of P extractable by H2SO4 and residual P. Arable soils with organic and mineral P fertilization given to crop rotations had the largest amounts of total P, labile P fractions and P test values. The mean annual concentrations of P in the lysimeter leachates varied from 0 to 0.81 mg l–1 (mean 0.16 mg l–1) and the corresponding leaching losses of P from < 0.01 to 3.2 kg ha–1 year–1 (mean 0.3 kg P ha–1 year–1). These two sets of data were correlated and a significant exponential function (R2 = 0.676) described this relation. Different soil textures, land uses and management practices resulted in similar values for P leaching losses as those for the amounts of labile P fractions. Surprisingly, larger rates of mineral P fertilizer did not necessarily result in greater leaching losses. The contents of P extracted by NaHCO3 and acid oxalate and the degrees of P saturation were positively correlated with the concentrations of P in leachates and leaching losses. As the P sorption capacity and degree of P saturation predicted leaching losses of P better than did routinely determined soil P tests, they possibly can be developed as novel P tests that meet the requirements of plant nutrition and of water protection.  相似文献   

3.
Several studies have focused on the formation and losses of dissolved organic matter in forest systems, whereas a limited number have dealt with this aspect in agricultural soils. The purpose of this study was to estimate the leaching of dissolved organic carbon (DOC) and nitrogen (DON), with focus on the period after cultivating grass-clover swards. Grass-clovers were ploughed in the spring prior to sowing cereals followed by either catch crops or bare soil. The concentrations of DOC and DON decreased with soil depth and ranged at 90-cm soil depth between 7 and 21 mg C L−1 and between 1 and 3 mg N L−1, respectively, in a sandy loam soil, and between 16 and 63 mg C L−1 and between 1 and 10 mg N L−1, respectively, in a coarse sandy soil. The resulting DOC/DON ratios were in the range between 2 and 42, with higher values in the coarse sandy soil than in the sandy loam soil. The total percolation was 218 mm in the sandy loam soil and 596–645 mm in the coarse sandy soil, which resulted in an annual leaching of 22–40 kg DOC ha−1 year−1 and 3–4 kg DON ha−1 year−1 in the sandy loam soil, and 174–310 kg DOC ha−1 year−1 and 10–31 kg DON ha−1 year−1 in the coarse sandy soil. It was shown that higher amounts of DOC were lost by leaching under the catch crops than from bare soil, that losses of DON were higher from bare soil than from soils with catch crops and that DON contributed significantly to the total N loss. Thus, DON needs to be taken into account in N-balance calculations.  相似文献   

4.
Nitrogen (N) and phosphorus (P) deficiencies are key constraints in rainfed lowland rice (Oryza sativa L.) production systems of Cambodia. Only small amounts of mineral N and P or of organic amendment are annually applied to a single crop of rainfed lowland rice by smallholder farmers. The integration of leguminous crops in the pre‐rice cropping niche can contribute to diversify the production, supply of C and N, and contribute to soil fertility improvement for the subsequent crop of rice. However, the performance of leguminous crops is restricted even more than that of rice by low available soil P. An alternative strategy involves the application of mineral P that is destined to the rice crop already to the legume. This P supply is likely to stimulate legume growth and biological N2 fixation, thus enhancing C and N inputs and recycling N and P upon legume residue incorporation. Rotation experiments were conducted in farmers' fields in 2013–2014 to assess the effects of P management on biomass accumulation and N2 fixation (δ15N) by mungbean (Vigna radiata L.) and possible carry‐over effects on rice in two contrasting representative soils (highly infertile and moderately fertile sandy Fluvisol). In the traditional system (no legume), unamended lowland rice (no N, + 10 kg P ha?1) yielded 2.8 and 4.0 t ha?1, which increased to 3.5 and 4.7 t ha?1 with the application of 25 kg ha?1 of urea‐N in the infertile and the moderately fertile soil, respectively. The integration of mungbean as a green manure contributed up to 9 kg of biologically fixed N (17% Nfda), increasing rice yields only moderately to 3.5–4.6 t ha?1. However, applying P to mungbean stimulated legume growth and enhanced the BNF contribution up to 21 kg N ha?1 (36% Nfda). Rice yields resulting from legume residue incorporation (“green manure use”–all residues returned and “grain legume use”–only stover returned) increased to 4.2 and 4.9 t ha?1 in the infertile and moderately fertile soil, respectively. The “forage legume use” (all above‐ground residues removed) provided no yield effect. In general, legume residue incorporation was more beneficial in the infertile than in the moderately fertile soil. We conclude that the inclusion of mungbean into the prevailing low‐input rainfed production systems of Cambodia can increase rice yield, provided that small amounts of P are applied to the legume. Differences in the attributes of the two major soil types in the region require a site‐specific targeting of the suggested legume and P management strategies, with largest benefits likely to accrue on infertile soils.  相似文献   

5.
The benefits of manure as a source of nutrients for plants and to improve soil quality are well-known. Monitoring of manure application is needed if environmental issues are to be prevented. In particular, the availability and accumulation of phosphorus (P) has to be subject to rigorous monitoring. This study aims to both evaluate the efficacy of the resin method in extracting inorganic labile P in soils under the long-term application of dairy liquid manure (DLM), and verify the influence of DLM on the recovery of applied P and soil legacy P. To realize our objectives, two long-term field experiments were established under a no-tillage system with annual DLM application on sandy clay loam (sandy Oxisol) and clayey (clayey Oxisol) soils. Treatment consisted of DLM applications (0, 60, 120, 180 m3 ha−1 year−1), independent of mineral fertilizer. Soil samples were taken from the 0–5, 5–10 and 10–15 cm layers after 10 years from the beginning of the trial. A single extraction with resin underestimated inorganic labile P; however, successive extractions were able to take up 43% and 26% of the total P in sandy and clayey Oxisols, respectively, whereas in a single extraction the take-up was 17% and 8% from the same soils, respectively. The resin method was more effective in extracting P from the sandy Oxisol. Thus, when interpreting soil P contents for fertilizer planning, the soil texture should be taken into account. DLM application decreased P recovered from applied P, ranging from 54% to 83% (sandy), and 43% to 67% (clayey), and substantially increased soil legacy P.  相似文献   

6.
Phosphate (PO4-P) sorption characteristics of soils and bedrock composition were determined in catchments of two mountain lakes, Ple?né Lake (PL) and ?ertovo Lake (CT), situated in the Bohemian Forest (Czech Republic). The aim was to explain higher terrestrial P export to mesotrophic PL compared to oligotrophic CT. Concentrations of Al and Fe oxides were the dominant parameters affecting soil ability to adsorb PO4-P. Depending on concentrations of Al and Fe oxides, P sorption maxima varied from 9.7 to 70.5 mmol kg?1 and from 7.4 to 121 mmol kg?1 in organic and mineral soil horizons, respectively. The catchment weighted mean PO4-P sorption capacity was 3.4 mol m?2 and 11.9 mol m?2 in the PL and CT soils, respectively. The higher PO4-P sorption capacity in the CT catchment was predominantly associated with higher pools of soil and Fe oxides. The CT bedrock (mica schist) released one order of magnitude less P than the PL bedrock (granite) within a pH range of catchment soils (pHCaCl2 of 2.5–4.5). The higher ability of PL bedrock to release P and the lower ability of PL soils to adsorb PO4-P thus contributed to the higher terrestrial P loading of this lake.  相似文献   

7.
The behaviour of P in a range of English arable soils was examined by plotting the change in resin P in the topsoil (ΔPres) at the end of a 3‐ to 5‐year period, against the P balance over the same period (fertilizer P applied minus offtake in crops, estimated from farmers’ reported yields and straw removal). Based on the assumption that values for offtake per tonne of crop yield used for UK arable crops are valid averages, 20–60% of ΔPres was explained by the balance. Applying excess P fertilizer increased Pres, and reducing P fertilizer use decreased it; typically 3–4 kg P ha?1 was required for each mg L?1ΔPres (6–8 kg ha?1 for each mg L?1 of Olsen P). About half the P balance seems to be resin extractable and this differed little between soil groups, except in cases of very low P (index 0) in which the P buffering was stronger, and on very high P soils (index 4/5) when buffering was less. However, on calcareous soils and red soils, when fertilizer was applied in accord with offtake, Pres fell by up to 4 mg L?1 year?1 (2 mg L?1 yr?1 olsen P) and to prevent this an extra 3–10 kg P ha?1 year?1 fertilizer was required. But on most non‐calcareous soils, replacing offtake maintained Pres, with perhaps slight rises on soils of low clay content or greater organic matter content. In soils under arable rotations, the apparent recovery of P from fertilizer was often around 100%, falling to 85% on Chalk soils and 75% on medium–heavy soils on limestone or Lower Chalk. The fate of the ‘missing’ P needs clarification. The case for corrections to current P fertilizer recommendations in the UK on certain soil types is discussed.  相似文献   

8.
Annual potassium (K) balances have been calculated over a 40‐year period for five field experiments located on varying parent materials (from loamy sand to clay) in south and central Sweden. Each experiment consisted of a number of K fertilizer regimes and was divided into two crop rotations, mixed arable/livestock (I) and arable only (II). Annual calculations were based on data for K inputs through manure and fertilizer, and outputs in crop removal. Plots receiving no K fertilizer showed negative K balances which ranged from 30 to 65 kg ha?1 year?1 in rotation I, compared with 10–26 kg ha?1 year?1 for rotation II. On sandy loam and clay soils, the K yield of nil K plots (rotation I) increased significantly with time during the experimental period indicating increasing release of K from soil minerals, uptake from deeper soil horizons and/or depletion of exchangeable soil K (Kex). Significant depletion of Kex in the topsoil was only found in the loamy sand indicating a K supply from internal sources in the sandy loam and clay soils. On silty clay and clay soils, a grass/clover ley K concentration of ～2% (dry weight) was maintained during the 40‐year study period on the nil K plots, but on the sandy loam, loam and loamy sand, herbage concentrations were generally less than 2% K.  相似文献   

9.
Leaching of dissolved organic matter (DOM) from pastoral soils is increasingly seen as an important but poorly understood process. This paper examined the relationship between soil chemical properties, microbial activity and the losses of dissolved organic carbon (DOC) and nitrogen (DON) through leaching from six pasture soils. These soils differed in carbon (C) (4.6–14.9%) and nitrogen (N) (0.4–1.4%) contents and in the amount of organic C and N that had accumulated or been lost in the preceding 20+ years (i.e. −5131 to +1624 kg C ha−1 year−1 and −263 to +220 kg N ha−1 year−1, respectively). The paper also examined whether between‐soil‐type differences in DOC and DON leaching was a major explanatory factor in the observed range of soil organic matter (SOM) changes in these soils. Between 280 and 1690 kg C ha−1 year−1 and 28–117 kg N ha−1 year−1 leached as DOC and DON, respectively, from the six soils in a lysimeter study, with losses being greater from two poorly drained gley soils. Losses of C and N of this magnitude, while at the upper end relative to published data, could not fully explain the losses at Rawerawe, Bruntwood and Lepperton sites reported by Schipper et al. (2007) . The study highlights the leaching of DOM as a significant pathway of loss of C and N in pasture soils that is often ignored or given little attention in predictive models and nutrient budgeting. Leaching losses of DOC and DON alone, or in combination with slightly increased respiration losses of SOM given a 0.2°C increase in the mean annual soil temperature, do not fully explain long‐term changes in the SOM observed at these sites. When soils examined in the present study were separated on the basis of drainage class, the losses of DOC by leaching were correlated with both total and hot‐water extractable C (HWC), the latter being a measure of the labile SOM fraction. Basal microbial CO2 respiration rates, which varied between 1 and 3.5 µg CO2‐C g−1 soil hour−1 in surface soils (0–75‐mm depth), was also linked to HWC and the quantities of C lost as DOC. Adoption of the HWC method as an approach that could be used as a proxy for the direct measurement of the soil organic C lost by leaching as DOC or respired needs to be examined further with a greater number of soils. In comparison, a poor relationship was found between the hot‐water extractable N (HWN) and loss of DON by leaching, despite HWN previously being shown to be a measure of the mineralizable pool of N in soils, possibly reflecting the greater competition for N than C in these soils.  相似文献   

10.
Effect of pH on the release of soil colloidal phosphorus   总被引：2，自引：0，他引：2  
  相似文献   

11.
The effects of 25 years of annual applications of P fertilizer on the accumulation and migration of soil Olsen‐P, and the effects of soil residual P on crop yields by withholding P application for the following 5 years, were evaluated in a subtropical region. Annual application of P fertilizer for 25 years to crops in summer (groundnut), winter (wheat, mustard or rapeseed) or in both seasons raised the Olsen‐P status of the plough layer (0–15 cm) from initially very low (12 kg P ha?1) to medium (18 kg P ha?1) and very high levels (40–59 kg P ha?1), depending on the amount of P surplus (amount of fertilizer applied in excess of removal by crops) (r = 0.86, P ≥ 0.01). However, only 4–9% of the applied P fertilizer accumulated as Olsen‐P to a depth of 15 cm (an increase of 2 mg kg?1per 100 kg ha?1 surplus P) in the sandy loam soil. In the following 5 years, the raising of 10 crops without P fertilizer applications decreased the accumulated Olsen‐P by only 20–30% depending upon the amount of accumulated P and crop requirements. After 29 years, 45–256 kg of residual P fertilizer had accumulated as Olsen‐P ha?1 in the uppermost 150 cm with 43–58% below 60 cm depth; this indicates enormous movement of applied P to deeper layers in this coarse textured soil with low P retention capacity for nutrients. Groundnut was more efficient in utilizing residual P than rapeseed; however, for both crops the yield advantage of residual P could be compensated for by fresh P applications. These results demonstrated little agronomic advantage above approximately 20 mg kg?1 Olsen‐P build‐up and suggested that further elevation of soil P status would only increase the risk of environmental problems associated with the loss of P from agricultural soils in this region.  相似文献   

12.
Modeling nitrate leaching during the winter halfyear from sandy arable soils under intensive cultivation Three years (1989–91) of post harvest and winter nitrogen dynamics (August to March) were simulated in 20 arable sandy soils to quantify nitrate leaching during winter time. Easily accessible soil, weather and management data were used for a simple but deterministic model. The calculated mineral N (Nmin) content and distribution in the soil (0–90 cm) were compared to more than 100 measurements from September to March each season. An overall agreement of approximately 50% between measured and simulated Nmin values was obtained. The simulation over- or underestimated the measured Nmin depending on the rainfall and temperature distribution which varied from year to year. Practically, the effect of fertilizer application was largely (60%) responsible for deviations greater than ±20 kgN ha?1 from the 1:1-line. Ignoring these instances, 80% of the simulated Nmin contents were within these “confidence limits” of ±20 kgN ha?1. Considering the nitrogen distribution in the profile, the Nmin content is underestimated in the top soil, but overestimated in the subsoil. Based on the 95% confidence intervals (measured versus simulated) the estimate was better for the lower (30–90 cm) than for the upper part of the profile (0–30 cm). It is concluded that winter leaching can be reduced from 130 kgN ha?1 (corn, winter grain) to about 10 kgN ha?1 growing winter hard forage crops. Two major processes were identified as reasons for the disagreement and are proposed for further model improvement: (1) The simulation underestimates the short term transport velocity on the basis of field capacity derived from survey data. (2) Nitrogen is mineralized quickly in sandy soils, especially after catch crops, and sometimes due to freeze-thaw effects. Furthermore, as ammonium remains in the surface, nitrification needs to be explicitly simulated.  相似文献   

13.
Abstract

The transformation of added phosphorus (P) to soil and the effect of soil properties on P transformations were investigated for 15 acid upland soils with different physicochemical properties from Indonesia. Based on oxide-related factor scores (aluminum (Al) plus 1/2 iron (Fe) (by ammonium oxalate), crystalline Al and Fe oxides, cation exchange capacity, and clay content) obtained from previous principal component analyses, soils were divided into two groups, namely Group 1 for soils with positive factor scores and Group 2 for those with negative factor scores. The amounts of soil P in different fractions were determined by: (i) resin strip in bicarbonate form in 30 mL distilled water followed by extraction with 0.5 mol L?1 HCl (resin-P inorganic (Pi) that is readily available to plant), (ii) 0.5 mol L?1 NaHCO3 extracting Pi and P organic (Po) (P which is strongly related to P uptake by plants and microbes and bound to mineral surface or precipitated Ca-P and Mg forms), (iii) 0.1 mol L?1 NaOH extracting Pi and Po (P which is more strongly held by chemisorption to Fe and Al components of soil surface) and (iv) 1 mol L?1 HCl extracting Pi (Ca-P of low solubility). The transformation of added P (300 mg P kg?1) into other fractions was studied by the recovery of P fractions after 1, 7, 30, and 90 d incubation. After 90 d incubation, most of the added P was transformed into NaOH-Pi fraction for soils of Group 1, while for soils of Group 2, it was transformed into resin-Pi, NaHCO3-Pi and NaOH-Pi fractions in comparable amounts. The equilibrium of added P transformation was reached in 30 d incubation for soils of Group 1, while for soils of Group 2 it needed a longer time. Oxide-related factor scores were positively correlated with the rate constant (k) of P transformation and the recovery of NaOH-Pi. Additionally, not only the amount of but also the type (kaolinitic) of clay were positively correlated with the k value and P accumulation into NaOH-Pi. Soils developed from andesite and volcanic ash exhibited significantly higher NaOH-Pi than soils developed from granite, volcanic sediments and sedimentary rocks. Soil properties summarized as oxides-related factor, parent material, and clay mineralogy were concluded very important in assessing P transformation and P accumulation in acid upland soils in Indonesia.  相似文献   

14.
A way to bring phosphate-saturated soils back to an environmentally safe P level is by P mining through plants. Phosphate-solubilizing bacteria (PSB) could be very useful for increasing mining efficiency over time. The goal of this research was to investigate the adaptation and performance of PSB in conditions of high total P content in soil. In the first experiment, the P-solubilizing capacity of five PSB species (three Bacillus spp. and two Pseudomonas spp.) were tested under fully controlled conditions on several growth media with different forms of insoluble phosphate (FePO4, AlPO4, or (Ca)3(PO4)2) added at different rates. The colony growth after 14 days of inoculation demonstrated that all five bacteria were able to proliferate and solubilize P on each of the tested growth media, in contradiction with the normally used technique of halo determination. In the second experiment, the same bacterial species were inoculated in pure quartz sand amended with a nutrient solution and P was added separately in an insoluble form, as Fe–P, Al–P, or Ca–P. The extractable ammonium lactate ranged from 3.2 to 6.9 and 29.0 to 40.7 mg?kg?1 sand for the insoluble Al–P and Fe–P treatments, respectively. Pseudomonas putida and Bacillus brevis performed best as PSB at high P concentration where the P is fixed with Al or Fe. In the third experiment, P. putida and B. brevis were inoculated in an acidic sandy, P-saturated soil for 4 weeks. The inoculation of the PSB gave promising results in solubilizing P.  相似文献   

15.
Abstract

Phosphate sorption isotherms were determined for 16 representative major soils developed from different parent materials on Okinawa. Phosphate sorption characteristics were satisfactorily described by the Langmuir equation, which was used to determine phosphorus (P) sorption maxima of the soils. Phosphate sorption maxima ranged from 630 to 2208 mg P kg‐1 soil (mean 1,362 mg P kg‐1). The standard P requirement (i.e., the amount of P required to attain 0.2 mg P L‐1 equilibrium solution) followed the same trend as sorption maximum (r =0.94***), with values ranging from 132 to 1,020 mg P kg‐1 soil (mean 615 mg P kg‐1). This mean value corresponds to fertilizer addition of 923 kg P ha‐1 indicating that the soils have high P fertilizer requirements. Results of simple linear regression analysis indicated that sorption maximum was significantly correlated with clay content, organic matter, oxalate iron (Fe), pyrophosphate Fe, DCB aluminum (Al), oxalate Al, and pyrophosphate Al, but not with DCB Fe, pH, or available P content. The best regression model for predicting sorption maximum was the combination of clay, organic matter, pyrophosphate Fe, and DCB Al which altogether explained 79% of the variance in sorption maximum. The equation obtained could offer a rapid estimation of P sorption in Okinawan soils.  相似文献   

16.
The steel-making slag (SMS), a by-product of steel manufacturing process with an alkaline pH (11–12) and high amount of iron (Fe) and calcium (Ca) oxides, was used to reduce arsenic (As) phytoextractability. The by-product was selected as an alternative to commercial Fe oxides, which can decrease plant uptake, but they are expensive if used as amendments of contaminated arable soils. SMS was applied at rates 0, 2, 4, and 8 Mg ha−1 to an As (1 N HCl-extractable As 25 mg kg−1) contaminated soil prepared by mixing non-contaminated soil and mine tailings and cropped to radish (Raphanus sativa L.) seeding. Calcium hydroxide (Ca(OH)2), a common liming material in Korea, was applied at the same rates for comparison. Steel-making slag more effectively suppressed radish As uptake and increased yield than Ca(OH)2 due to stronger As immobilization because it significantly increased extractable Fe concentration and decreased extractable As. The SMS-treated soil showed an apparent increase in As chemisorbed by Fe and Al oxides and hydroxides of surface soil, As associated at the Fe and Al oxides and hydroxides of internal surfaces of soil aggregates, and Ca-associated As. The steel-making slag can be a good soil amendment to suppress As phytoextractability and improve nutrient balance in As-contaminated soil.  相似文献   

17.
The objective of this study was to investigate possible ways of mobilizing residual fertilizer P as a result of local pH elevation caused by urea hydrolysis. The response of water-soluble P (Pw) and dissolved organic C (DOC) to urea hydrolysis was monitored in three cultivated soils and at two P levels for up to 127–135 d and compared with corresponding changes in soils limed with Ca(OH)2. Hydrolysis of urea was complete in 8–15d during which soil pH increased by 1–1.5 units at the maximum. Subsequently, the pH decreased to or below the original level owing to nitrification. Mobilization of soil P was enhanced substantially in parallel with the increase in pH, the peak Pw occurring simultaneously with the highest pH value. In all urea-treated soils, Pw remained at an elevated level for at least 60d. As compared to urea, elevation of soil pH with Ca(OH)2 had only a minor and inconsistent influence on Pw. In mobilization of soil P, the urea-induced increase in pH and a simultaneous production of NH4+ ions proved to be superior to liming with Ca(OH)2. It was hypothesized that when an acid soil is amended with urea, phosphate is first displaced by OH? ions, resulting in elevated solution P concentrations. A simultaneous dissolution of organic matter contributes to the persistence of high P concentration by competition for sorption sites on Fe and Al oxides, and thus retards the resorption of P.  相似文献   

18.
Mixtures of fine bauxite refining residue (red mud), waste gypsum and local sandy soil that are proposed to be used in a catchment nutrient management program, were watered in columns simulating rainfall over a period of 2 yr and the quality of the leachate determined. The major salts released were sodium sulphate, a product of red mud alkalinity neutralization by gypsum, and excess gypsum released at its solubility concentration. At an application rate of 850 t ha?1 of red mud the salts leached to groundwater (40 kg t?1 red mud) would be equivalent to salts leached by rainfall over a 20 yr period from soil without red mud application, and would pose no significant impact when applied to the sandy agricultural soils in the catchment area of an estuary. The leaching of Al, Fe, and Cd from the red mud and gypsum was negligible, while the retention of superphosphate was over 99%. Fluoride from the waste gypsum was leached rapidly and reduced to background concentration (less than 1 mg L?1) within one winter rainfall.  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.
A pot experiment was conducted to investigate the influence of phosphate (P) application on diethylene triamine pentaacetic acid (DTPA)–extractable cadmium (Cd) in soil and on growth and uptake of Cd by spinach (Spinacia oleracea L.). Two soils varying in texture were contaminated by application of five levels of Cd (NO3)2 (0, 20, 30, 40, and 60 mg Cd kg–1). Three levels of KH2PO4 (0, 12, and 24 mg P kg–1) were applied to determine immobilization of Cd by P. Spinach was grown for 60 d after seeding. Progressive contamination of soils through application of Cd affected dry‐matter yield (DMY) of spinach shoot differently in the two soils, with 67% reduction of DMY in the sandy soil and 34% in the silty‐loam soil. The application of P increased DMY of spinach from 4.53 to 6.06 g pot–1 (34%) in silty‐loam soil and from 3.54 to 5.12 g pot–1 (45%) in sandy soil. The contamination of soils increased Cd concentration in spinach shoots by 34 times in the sandy soil and 18 times in the silty‐loam soil. The application of P decreased Cd concentration in shoot. The decrease of Cd concentration was higher in the sandy soil in comparison to the silty‐loam soil. Phosphorus application enhanced DMY of spinach by decreasing Cd concentration in soil as well as in plants. The results indicate that Cd toxicity in soil can be alleviated by P application.  相似文献   

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