Nitrogen export by runoff from agricultural plots in two basins in China

Runoff and sediment yields from agricultural fields are major sources of nitrogen (N) entering lakes in China. Export of sediment and N can be impacted by soil and cropping management practices, but there is relatively little information on N leaving agricultural fields in lake basins in China. Sediment and surface runoff N from a series of field plots in two experimental lake basins were evaluated in situ under simulated rainfall conditions. Objectives of the study were to evaluate the effects of crop cover, slope, and fertilizer application on N in surface runoff and eroded soils. Sediment yields varied from 4.3 to 299.0 g m^-2, depending on management practice. Mean dissolved nitrogen (DN) and total nitrogen (TN) concentrations are 1.35 and 5.4 mg L^-1, respectively, in Lake Taihu basin, while mean DN and TN concentrations are 2.66 and 4.3 mg L^-1, respectively, in Lake Baiyangdian basin. For all experimental plots in two basins, weighted average concentrations of N for total-N, dissolved N and sediment N are 1.0-5.0 mg L^-1, much higher than 0.2 mg L^-1, indicating a problem in lake eutrophication due to high N concentration from agricultural surface runoff. The estimated mean annual export of total N was 6.0 and 14.7 kg ha^-1 yr^-1 for Baiyangdian and Taihu lake basins, respectively. The study showed that significantly more N (approximately ranging from 10 to 90 of total N) exported was associated with sediment, constituting a long-term source of potentially bioavailable N in lakes.     

Transformations of soil and manure phosphorus after surface application of manure to field plots

Transfer of phosphorus (P) from surface-applied manures to runoff is an important source of pollution, but few studies have closely monitored P dynamics in manure, soil, and runoff through time. We monitored manure and soil P over 14 to 17 months in field experiments in Texas and Pennsylvania, USA following dairy and poultry manure surface application. Manure was applied to porous fabric that enabled discrete sampling of both manure and underlying soil. Manure mass consistently decreased while manure total P was essentially constant through time. Manure water extractable P decreased rapidly for the first two months, likely due to rainfall leaching, but then maintained stable concentrations thereafter, with other forms of manure P gradually transformed to water extractable forms. Soil P from the upper 2 cm rapidly increased after manure application in association with manure leaching by rain. After 2 to 3 months, soil P peaked and either remained constant or gradually declined. Similar trends occurred at 2–5 and 5–10 cm, but with lesser magnitudes. At 10–15 cm, soil P changed little over time. In Pennsylvania, naturally occurring runoff from 0.7-m × 1.3-m plots without and without manure was also monitored. Runoff dissolved P concentrations were greatest for the first event after manure application and decreased steadily through time, but remained greater than P concentrations from control plots, and were always well related to manure water extractable P. This study reveals that management practices for water quality protection must consider the potential for manure P transformations to contribute dissolved P to runoff long after manure is applied.     

Nitrogen loss from different tillage systems and the effect on cereal grain yield

Grain yield, nitrogen (N) assimilation, ammonia (NH₃) volatilization, denitrification and fertilizer N distribution were examined in three commercially grown cereal crops; two were sown into conventionally tilled fields, while the third was direct drilled into an untilled field. The crops were top dressed with urea at establishment, tillering or ear initiation. Crop yield and N assimilation were measured in 16 m by 2.5 m plots receiving 0, 35, 70, 105, 140 or 175 kg N ha^–1. A mass balance micrometeorological technique was used to measure NH₃ volatilization, and other fertilizer N transformations and transfers were studied using¹⁵N labelled urea in microplots.On the conventionally tilled sites application of urea increased the grain yield of wheat from 3.9 to 5.5 t ha^–1, when averaged over the five application rates, three application times and two sites. There were no site or application time effects. However, on the direct drilled site, time of application had a significant effect on grain yield. When urea was applied at establishment, grain yield was not significantly increased and the mean yield (2.81 t ha^–1) was less than that obtained from treatments fertilized at tillering or ear initiation (4.09 and 4.0 t ha^–1, respectively). Much of the variation in grain yield at the no-till site could be ascribed to differences in NH₃ volatilization. At the no-till site, NH₃ losses were equivalent to 24, 12 and 1% of the N applied at establishment, tillering and ear initiation, respectively. Negligible volatilization of NH₃ occurred at the other sites. The surface soil at the no-till site had the highest urease activity and the soil was covered with alkaline ash resulting from stubble burning.Plant recovery of fertilizer N did not vary with application time on conventionally tilled sites (mean 62%). However, plant recovery of¹⁵N applied to the no-till site at establishment (35% of the applied N) was significantly less than that from plots where the application was delayed (45% at tillering and 55% at ear initiation, respectively). Leaching of N to below 300 mm depth was minimal (0 to 5% of the applied N). The calculated denitrification losses ranged from 1% to 14% of the applied N.The results show that the relative importance of NH₃ volatilization, leaching and denitrification varied with site and fertilization time. The importance of the various N loss mechanisms needs to be taken into account when N fertilization strategies are being developed.     

Improved field emission from amorphous carbon nanotubes by surface functionalization with stearic acid

Amorphous carbon nanotubes (a-CNTs) were synthesized by a simple process using ammonium chloride and ferrocene at a low temperature (∼250 °C) in open atmosphere. The as-prepared samples were oxidized by a simple acid treatment and further functionalized with stearic acid. For the confirmation of oxidation and functionalization, the pristine and the modified a-CNTs were characterized by Fourier transformed infrared spectroscopy, transmission and scanning electron microscopy. The as-prepared samples showed good field emission (FE) and the FE characteristics were significantly improved for the stearic acid functionalized samples compared to the pristine sample. The effects of inter-electrode distance on the FE properties of the functionalized samples were also studied.     

Ammonia loss from surface applied urea-acid products

Ammonia (NH₃) losses from soils occur only under alkaline conditions; therefore, adequate acidification could prevent NH₃ loss. In acid soils this alkaline condition will exist only as a micro-environment around the decomposing CO(NH₂)₂ granule. The objective of this experiment was to examine the degree of NH₃ loss reduction that occurs when acids are placed with surface applied CO(NH₂)₂. Phosphoric acid, H₂SO₄, HCl and HNO₃ were used with surface applied CO(NH₂)₂ in a laboratory experiment to examine resultant NH₃ loss under very extreme NH₃ loss conditions. Calcium and magnesium chloride salts were added to urea:phosphoric acid to compare the relative effectiveness of acid and Ca + Mg salts for control of NH₃ loss.Little depression of NH₃-N loss was found from CO(NH₂)₂ containing H₃PO₄ and H₂SO₄ when the sand contained free CaCO₃. However, when CO(NH₂)₂:H₃PO₄ (UP) mixtures were applied as 17-19-0 on neutral and acid sands, NH₃ losses were reduced. Molar ratios less than 1:1 (28-12-0, 35-7-0) resulted in NH₃ losses similar to those from CO(NH₂)₂ alone even in acid soils. The 110 g N m^–2 as 17-19-0 reduced relative NH₃-N loss and pH in acidified and neutral soils more effectively than 11 g N m^–2. Ammonia losses are determined by chemical reactions occurring under the individual CO(NH₂)₂ granules; therefore, the use of the high 110 g N m^–2 rates in this research. The 17-19-0 reduced soil pH and retarded the rate of CO(NH₂)₂ hydrolysis with consequent reduction in NH₃ loss. Ammonia loss was reduced only slightly at 11 g N m^–2 from 17-19-0 even in acid soils. Ammonia loss was reduced from 70 to 30% of applied N by applications of HNO₃ and HCl with the CO(NH₂)₂. The HNO₃ and HCl react with CaCO₃ in a calcareous soil to produce CaCl₂ and Ca(NO₃)₂ which are known to reduce NH₃ loss from surface applied CO(NH₂)₂. However, a dry product of HNO₃ · CO(NH₂)₂ is explosive and can not be used as a general fertilizer.Calcium chloride or MgCl₂ combined with CO(NH₂)₂:H₃PO₄ reduced NH₃ loss more at 110 g N m^–2 than at 11 g N m^–2. Calcium chloride reduced NH₃ loss more effectively than MgCl₂. The CaCl₂ and MgCl₂ salts were more effective than H₂SO₄ or H₃PO₄ in reducing NH₃ losses except when (e.g., 17-19-0) mixtures were added to neutral or acidic sands.Contribution from Texas Agric. Exp. Stn., Texas A & M University, College Station, TX 77843.     

Nitrate leaching from applied fertilizer is reduced by precision nitrogen management in baby corn cropping systems

In-situ field studies were conducted for three consecutive baby corn (Zea mays L.) growing seasons to quantify the amount of reactive N flowing beyond the rhizosphere while defining mitigation strategies. The N applications based on plant need were agronomically more efficient than the fixed-time blanket N applications. Average area-scaled leachate N losses in the winter season were 24 and 8% higher than the summer and spring seasons, respectively. A smaller root system at low N rate likely restricts plant N uptake and accelerates the magnitude of N leaching factor ranging from 6 to 9% in different seasons. Leachate N-flux peaks were more pronounced at early growth stages, attributed to the N supply in excess of the plant need. Residual soil mineral N varied little despite a wide range of fertilizer N rates, hence there was no evidence to support the idea that soils should be replenished for N removal by crops at fixed growth stages. Rather, N losses to the environment were greater using fixed-timing blanket N applications, which can be mitigated by a shift to N fertilization based on assessment of plant need. Use of the PAU-leaf colour chart and chlorophyll meter to guide need-based fertilizer N topdressings reduced average leachate NO₃¯-N load by 69% over blanket N use practice, while producing an average 17% higher cob yield in baby corn. Hence, the blanket N use practices should be replaced with need-based N management strategies to mitigate environmental footprints of N use in the baby corn based cropping system.

     

Measurement of nitrous oxide emissions from two rice-based cropping systems in China

A field experiment was conducted to investigate the effects of winter management and N fertilization on N₂O emission from a double rice-based cropping system. A rice field was either cropped with milk vetch (plot V) or left fallow (plot F) during the winter between rice crops. The milk vetch was incorporated in situ when the plot was prepared for rice transplanting. Then the plots V and F were divided into two sub-plots, which were then fertilized with 276 kg urea-N ha^–1 (referred to as plot VN and plot FN) or not fertilized (referred to as plot VU and plot FU). N₂O emission was measured periodically during the winter season and double rice growing seasons. The average N₂O flux was 11.0 and 18.1 g N m^–2 h^–1 for plot V and plot F, respectively, during winter season. During the early rice growing period, N₂O emission from plot VN averaged 167 g N m^–2 h^–1, which was eight- to fifteen-fold higher than that from the other three treatments (17.8, 21.0 and 10.8 g N m^–2 h^–1 for plots VU, FN, and FU, respectively). During the late rice growing period, the mean N₂O flux was 14.5, 11.1, 12.1 and 9.9 g N m^–2 h^–1 for plots VN, VU, FN and FU, respectively. The annual N₂O emission rates from green manure-double rice and fallow-double rice cropping systems were 3.6 kg N ha^–1 and 1.3 kg N ha^–1, respectively, with synthetic N fertilizer, and were 0.99 kg N ha^–1 and 1.12 kg N ha^–1, respectively, without synthetic N fertilizer. Generally, both green manure N and synthetic fertilizer N contribute to N₂O emission during double rice season.     

Microtensile bond strength of composite-to-composite repair with different surface treatments and adhesive systems

Objectives: The purpose was to investigate the effect of different surface treatments and bonding agents on the repair bond strength of different resin-based restorative materials by microtensile bond strength (μTBS) testing protocol. Materials and Methods: 24 Grandio SO(VOCO) and 24 Filtek Z250(3?M) resin composite blocks were prepared. Half of the samples (N?=?12) were diamond bur-roughened and the other half (N?=?12) were sandblasted by 50?μm aluminum oxide particles. They were further divided into four sub-groups (n?=?3) and received the following: Sub-Group1: Adper Single Bond2 (Etch&Rinse) (3?M); Sub-Group2: Clearfil SE (Self-etch) (Kuraray); Sub-Group3: Beauty Bond (HEMA-free all-in-one) (Shofu); Sub-Group4: All Bond3 (HEMA-free, hydrophobic, etch&rinse) (Bisco). The samples were repaired by Filtek Z250 to form a block. All of the resultant sub-groups combinations consisted of one of the composite type, surface treatment type, and adhesive systems. A total of 18 groups were prepared including 2 homogeneous blocks. They were thermocycled and μTBS measurements were performed. Data were statistically analyzed with Kruskall–Wallis and Mann–Whitney U tests. Results: The experimental regroups’ μTBS reached to 34.67–66.36% and 43.44–95.52% of the cohesive bond strength for Grandio SO and Z250, respectively. The pre-existing composite type is found to be statistically important. When the surface is bur-finished Grandio performed better; when air-abrasion is considered Z250 showed higher bond strength. All-in-one adhesive system produced the weakest bond strength at all parameters. Conclusion: It may be suggested that when the pre-existing composite is unknown, air-abrasion may be performed with etch&rinse or two-step self-etch adhesives.     

Influence of different manuring systems with and without biogas digestion on soil organic matter and nitrogen inputs,flows and budgets in organic cropping systems

Nitrogen (N) and carbon (C) cycles are closely linked in organic farming systems. Use of residues for biogas digestion may reduce N-losses and lead to higher farmland productivity. However, digestion is connected to large losses of organic C. It is the purpose of this paper (1) to compare farming systems based on liquid slurry and solid farmyard manure regarding the N, C and organic dry matter (ODM) inputs and flows, (2) to analyse the effect of digestion on soil N, C and ODM inputs and flows within the cropping system, (3) to assess the effects of organic manure management on biological N₂ fixation (BNF), and (4) to assess the effect of biogas digestion on the sustainability of the cropping systems in terms of N and C budgets. The BNF by clover/grass-leys was the most important single N input, followed by the BNF supplied by legume cover cropping. Growth of crops in organic farming systems is very often N limited, and not limited by the soil C inputs. However, balances of N inputs showed that the implemented organic farming systems have the potential to supply high amounts of N to meet crop N demand. The level of plant available N to non-legume main crops was much lower, in comparison to the total N inputs. Reasons were the non-synchronized timing of N mineralization and crop N demand, the high unproductive gaseous N losses and an unfocussed allocation in space and time of the circulating N within the crop rotation (e.g. allocation of immobile manures to legumes or of mobile manures to cover crops). Simultaneously, organic cropping systems very often showed large C surpluses, which may be potentially increased the N shortage due to the immobilization of N. Soil organic matter supply and soil humus balance (a balance sheet calculated from factors describing the cultivation effects on humus increasing and humus depleting crops, and organic manure application) were higher in cropping systems based on liquid slurry than in those based on solid farmyard manure (+19%). Simultaneously, soil N surplus was higher due to lower gaseous N losses (+14%). Biogas digestion of slurry had only a very slight effect on both the soil N and the soil C budget. The effect on the N budget was also slight if the liquid slurry was stored in closed repositories. Digestion of residues like slurry, crop residues and cover crops reduced in a mixed farming system the soil C supply unilaterally (approximately −33%), and increased the amounts of readily available N (approximately +70–75%). The long-term challenge for organic farming systems is to find instruments that reduce N losses to a minimum, to keep the most limiting fraction of N (ammonia-N) within the system, and to enhance the direct manuring effect of the available manures to non-legume main crops.     

Nitrous oxide emissions from paddy soil in three rice-based cropping systems in China

Rice-flooding fallow, rice-wheat, and double rice-wheat systems were adopted in pot experiment in an annual rotation to investigate the effects of cropping system on N₂O emission from rice-based cropping systems. The annual N₂O emission from the rice-wheat and the double rice-wheat cropping systems were 4.3 kg N ha^–1 and 3.9 kg N ha^–1, respectively, higher than that from rice-flooding fallow cropping system, 1.4 kg N ha^–1. The average N₂O flux was 115 and 118 g N m^–2 h^–1 for rice season in rice-wheat system and early rice season in double rice-wheat system, respectively, 68.6 and 35.3 g N m^–2 h^–1 for the late rice season in double rice-wheat system and rice season in rice-flooding fallow, respectively, and only 3.1–5.3 g N m^–2 h^–1 for winter wheat or flooding fallow season. Temporal variations of N₂O emission during rice growing seasons differed and high N₂O emission occurred when soil conditions changed from upland crop to flooded rice.     

Nitrate and phosphorus loss from agricultural land: implications for nonpoint pollution

The impact of agriculture on flood plains and surface water quality has received much attention in temperate countries in recent years. Little attention has been given to loss of nutrients and its impact on the quality of buffer zones and adjacent streams in many tropical environments due to the believe that fertilizer use is still very low compared to temperate countries. This may not be totally true especially in agricultural research stations and University experimental fields where a large amount fertilizers are used continuously for many years. This study was conducted in 2 years (Four seasons) to evaluate the accumulated effect of a long term fertilizer application of an agricultural land on an adjacent stream. Results showed that applied fertilizer significantly contributed to the high levels of nitrate and phosphorus in the stream water. Highest concentration of soil NO₃-N and P were found in 0–15, 15–30 and 30–45 cm soil depths with about 75% reduction in these amounts in the 60–75 cm depth for NO₃-N and 77% reduction at the same depth for soil available phosphorus, the topsoil constituting about 45% of the concentration of the two plant nutrients assessed. There were evident of leaching of basic cations below 15 cm soil depth as indicated in the increased soil pH. There were significantly (P < 0.05) higher soil NO₃-N and P in the dry season relative to the wet season. The long term application of fertilizers to the sandy loam soil significantly contributed to nitrate and phosphate pollution of the stream in excess of the maximum level accepted for potable water. The stream’s pH, temperature, nitrate and phosphate were significantly higher in the dry season. Correlation analyses indicated that agricultural runoffs from the topsoil contributed significantly to the pollution of the stream. There was also positive and significant correlation between the soil nitrate and soil phosphorus at different soil depths, thus indicating that the N and P might have been applied jointly as compound fertilizer and move down the slope through runoff.     

不同混合时间尺度下表面曝气系统的模拟

Macro and micromixing time represent two extreme mixing time scales, which governs the whole hydrodynamics characteristics of the surface aeration systems. With the help of experimental and numerical analysis, simulation equation governing those times scale has been presented in the present work.     

Nitrate loss from a tile-drained reclaimed marsh soil from SW Spain amended with different products

Tile drainage and soil amendments have been found to affect losses of nitrate N from agricultural soils. This work was aimed at measuring nitrate N losses in a tile-drained marsh soil from SW Spain under traditional fertilization and irrigation practices, and how these losses were influenced by the application of soil amendments. To this end, a randomised block experiment with three replications was performed during two consecutive growing seasons—2003 to 2004 with cotton and sugar beet, respectively—involving four different amendment treatments: (1) control without amendment, (2) phosphogypsum (PG), (3) manure, and (4) sugar factory refuse lime (SFRL). Flow-weighted (FW) nitrate–N concentrations in drainage water, estimated as the slope of the regression of the instantaneous nitrate–N flow as a function of drain flow rate, was decreased by PG in some drainage events in the 2003 season and in the four last events of the 2004 season when compared with control without amendment. The increased FW nitrate–N concentrations in drainage from SFRL in comparison to control in a drainage event of 2003 season, and in the four last events of 2004, can be explained by the contribution of N present in the amendment. These effects did not account for significant differences in nitrate–N loss among treatments over the whole season in 2003, when they ranged from 19.3 to 24.9 kg N ha⁻¹, accounting for 6–8% of applied N, nor in 2004, when they ranged from 4 to 6 kg N ha⁻¹, accounting for 3–4% of applied N. The decrease in mean FW nitrate–N concentration after the third drainage event in 2003 was not the consequence of the depletion of total soil nitrate–N because soil mineral N was increased on average by 205 kg N ha⁻¹ during the season. The high N extractions by sugar beet and the subsequent decrease in total soil nitrate–N can contribute to explain the decrease of mean FW nitrate–N concentrations along the 2004 season. Greater absolute nitrate–N loss in 2003 than in 2004 was explained by the lower efficiency of the furrow irrigation when compared with sprinkler irrigation. Results also revealed that traditional management of N fertilizer was inadequate: rates applied to cotton were excessive, increasing the risk of N losses not only during the cotton season, but also at the beginning of the following season.     

Intercomparison of national & IPCC methods for estimating N loss from agricultural land

The Intergovernmental Panel on Climate Change (IPCC) estimate indirect N₂O emissions from agriculture as 2.5% of nitrate leached, which is itself estimated as a proportion of manure/fertiliser inputs. However, this assumes leaching losses are linearly related to N inputs, over-simplifying a complex N loss function which depends on the interactions between over-winter rainfall, soil type, cropping, and the rate/timing of fertiliser/manure applications. Consideration of these factors would produce a more robust method for estimating N losses. Three alternatives were compared for estimating nitrate leaching and hence indirect N₂O loss in England & Wales: (i) IPCC method, (ii) IPCC method using UK-specific manure inputs, (iii) NEAP-N, a model developed for modelling N losses at a national scale. Introducing UK-specific livestock manure data into the IPCC calculation reduced the mean indirect N₂O loss from agricultural land from 19980 t N a⁻¹ using default IPCC data (method (i)) to 14335 t N a⁻¹ (method (ii)), indicating that IPCC default data are inappropriate for representing agricultural conditions in the UK. Adopting the NEAP-N method reduced the calculated indirect N₂O flux further to 8890 t N a⁻¹. The IPCC approach generated unrealistically low losses from peas/beans and ``zero' loss estimates from fallow and set-aside land due to their nil fertiliser N additions, highlighting a limitation in this method which assumes all nitrate leaching is derived from fertiliser or manure additions. NEAP-N uses spatially distributed agricultural census information to relate land use and crop type to dominant soil type and hydrologically effective rainfall (HER), as it is these factors which strongly influence nutrient loss. In contrast, IPCC methods (i) and (ii) do not take account of soil type and HER factors, and simply compute nitrate leached as a function of nitrogen applied. Furthermore, the IPCC method, which is based solely on the amount of nitrogen applied, will not characterise reductions in nitrate loss arising from changes to the timing of fertiliser and/or manure applications. This is an important component of strategies to reduce agricultural nitrate loss (e.g. Nitrate Vulnerable Zone regulations). NEAP-N predictions of nitrate leaching losses compare favourably with measurements of stream nitrate fluxes, whereas IPCC methods repeatedly overestimate measured loss two or threefold. We conclude that, for the UK, country-specific estimates using NEAP-N should be used in national greenhouse gas inventories in preference to values using the default IPCC method. This revised version was published online in August 2006 with corrections to the Cover Date.     

An assessment of N loss from agricultural fields to the environment in China

Using the 1997 IPCC Guidelines for National Greenhouse Gas Inventory Methodology, and statistical data from the China Agricultural Yearbook, we estimated that the direct N₂O emission from agricultural fields in China in 1990 was 0.282 Tg N. Based on micro-meteorological field measurement of NH₃ volatilization from agricultural fields in different regions and under different cropping systems, the total NH₃ volatilization from agricultural fields in China in 1990 was calculated to be 1.80 Tg N, which accounted for 11% of the applied synthetic fertilizer N. Ammonia volatilization from agricultural soil was related to the cropping system and the form of N fertilizer. Ammonia volatilization from paddy fields was higher than that from uplands, and NH₄HCO₃ had a higher potential of NH₃ volatilization than urea. N loss through leaching from uplands in north China accounted for 0.5–4.2% of the applied synthetic fertilizer N. In south China, the leaching of applied N and soil N from paddy fields ranged from 6.75 to 27.0 kg N ha^-1 yr^-1, while N runoff was between 2.45 and 19.0 kg N ha^-1 yr^-1.     

Diffusion through living systems: Sugar loss from sugar beets

The diffusion rate of sugar from sugar beets has been measured and interpreted in the light o the dual sorption theory; namely it has been assumed that the sugar contained in sugar beet is present as immobilized sugar inside the cells and as mobile sugar in the vascular bundles. Langmuir equilibrium is assumed to hold between these two states of sugar.The discrepancies between theory and experimental results are well within the limits of the uncertainty affecting the many physical parameters which play a role in the diffusion process and the complexity of the sugar beet's microstructure. The interpretative theory proposed might be applied just as well to the living tissues of other vegetables.     

Methane and nitrous oxide emissions from rice and maize production in diversified rice cropping systems

Nutrient Cycling in Agroecosystems - Traditional irrigated double-rice cropping systems have to cope with reduced water availability due to changes of climate and economic conditions. To quantify...     

污泥不同热处理工艺产物磷的浸出回收实验研究

针对污泥阴燃处理灰渣开展了关于磷浸出回收性能的实验研究,并与传统焚烧和热解处理工艺所产生的焚烧灰和热解焦的磷浸出回收性能进行了分析对比。结果表明,热产物中磷含量与残碳含量有关,而热处理过程中磷留存率与反应剧烈程度等因素有关。热处理会降低污泥中磷的生物有效性,尤其是焚烧。污泥阴燃灰、焚烧灰和热解焦的磷浸出过程主要受反应物浓度和产物层扩散控制,浸出时间不应超过8 h。通过硫酸浸出污泥热处理产物的方法,单位质量热产物的磷浸出量为25.72~34.42 mg/g,可将原污泥中的磷回收59.30%~84.21%。进一步对浸出工艺进行工况优选,可在保持较高污泥磷回收率的同时大幅降低硫酸单位消耗量。