Emissions of N2O and NH3, and nitrogen leaching from direct seeded rice under different tillage practices in central China

Tillage practices affect the fate of fertilizer nitrogen (N) through influencing transformations of N, but few studies have examined N₂O and NH₃ emissions, and N leaching from different rice tillage systems. Thus the objective of this study was to assess N₂O emission, NH₃ volatilization and N leaching from direct seeded rice in conventional tillage (CT) and no-tillage (NT) production systems in the subtropical region of China during the 2008 and 2009 rice growing seasons. Treatments were established following a split-plot design of a randomized complete block with tillage practices as the main plot and N fertilizer level as the sub-plot treatment, and there were four treatments: NT + no fertilizer (NT0), CT + no fertilizer (CT0), NT + compound fertilizer (NTC) and CT + compound fertilizer (CTC), respectively. Results showed that N fertilization significantly increased (p < 0.01) N₂O emissions, NH₃ volatilization and N leaching from rice fields in both years. In general, there was no significant difference in N₂O emissions and NH₃ volatilization between NT0 and CT0 in both years, while NTC had significantly higher (p < 0.05) N₂O emissions and NH₃ volatilization compared to CTC. Over the two rice growing seasons, NTC showed 32% and 47% higher N₂O emissions, and 29% and 52% higher NH₃ losses than CTC. Higher (p < 0.05) N₂O emissions from NTC than CTC were presumably due to higher soil organic C and greater denitrification. Total N and NO₃^? concentrations were higher (p < 0.05) in CTC than NTC, but larger volumes of percolation water in NTC than CTC resulted in no significant difference in leakage of total N and NO₃^?. Hence, application of N fertilizer in combination with NT appeared to be ineffective in reducing N losses from N fertilizer in paddy fields.     

Enhanced chromium recovery from tanning wastewater

A large volume of tanning wastewater was generated with a Cr³⁺ concentration of 3000–6000 mg/L. The prevailing method for Cr³⁺ recycle is NaOH precipitation, which is severely limited by the poor sedimentation of the sludge formed. Therefore, bridging cations, Ca²⁺ and Mg²⁺, and sonication were used to enhance the sedimentation of the precipitate. Microwave irradiation was employed to improve the re-dissolution of Cr-sludge for reuse. All alkalis effectively removed Cr³⁺ from the aqueous phase with a removal of higher than 99% and a recovery of ∼60%. The substitution of NaOH with CaO or MgO resulted in much less sludge and shorter sedimentation time. MgO also enhanced the purity and dewatering capability of the sludge. The best alkali was a mixture of CaO and MgO (4:1, by weight) to balance the cost and performance. COD and SS were removed in the process via sweeping by the precipitate with removal percentages of 47.6% and 86.3%, respectively. Two minutes sonication at 0.12 W/cm³ greatly accelerated the sludge sedimentation, cutting the settling time from 3 h to 1 h. Sonication did not alter the particle size or purity of the sludge. Microwave irradiation of 5 min increased the Cr recovery ratio from 60% to 80%.     

Comparing intensive,extensified and organic grassland farming in southern Germany by process life cycle assessment

To reduce the environmental burden of agriculture, suitable methods to comprehend and assess the impact on natural resources are needed. One of the methods considered is the life cycle assessment (LCA) method, which was used to assess the environmental impacts of 18 grassland farms in three different farming intensities — intensive, extensified, and organic — in the Allgäu region in southern Germany. Extensified and organic compared with intensive farms could reduce negative effects in the abiotic impact categories of energy use, global warming potential (GWP) and ground water mainly by renouncing mineral nitrogen fertilizer. Energy consumption of intensive farms was 19.1 GJ ha⁻¹ and 2.7 GJ t⁻¹ milk, of extensified and organic farms 8.7 and 5.9 GJ ha⁻¹ along with 1.3 and 1.2 GJ t⁻¹ milk, respectively. Global warming potential was 9.4, 7.0 and 6.3 CO₂-equivalents ha⁻¹ and 1.3, 1.0 and 1.3 CO₂-equivalents t⁻¹ milk for the intensive, extensified and organic farms, respectively. Acidification calculated in SO₂-equivalents was high, but the extensified (119 kg SO₂ ha⁻¹) and the organic farms (107 kg SO₂ ha⁻¹) emit a lower amount compared with the intensive farms (136 kg SO₂ ha⁻¹). Eutrophication potential computed in PO₄-equivalents was higher for intensive (54.2 kg PO₄ ha⁻¹) compared with extensified (31.2 kg PO₄ ha⁻¹) and organic farms (13.5 kg PO₄ ha⁻¹). Farmgate balances for N (80.1, 31.4 and 31.1 kg ha⁻¹) and P (5.3, 4.5 and −2.3 kg ha⁻¹) for intensive, extensified and organic farms, respectively, indicate the different impacts on ground and surface water quality. Analysing the impact categories biodiversity, landscape image and animal husbandry, organic farms had clear advantages in the indicators number of grassland species, grazing cattle, layout of farmstead and herd management, but indices in these categories showed a wide range and are partly independent of the farming system.     

Effects of surfactants on the combined toxicity of TiO2 nanoparticles and cadmium to Escherichia coli

The combined ecological toxicity of TiO₂ nanoparticles (nano-TiO₂) and heavy metals has been paid more attention. As the common pollutants in water environment, surfactants could affect the properties of nanoparticles and heavy metals, and thus further influence the combined toxicity of nano-TiO₂ and heavy metals. In this study, the effects of sodium dodecyl benzene sulfonate (SDBS) and Tween 80 on the single and combined toxicities of Cd^2 + and nano-TiO₂ to Escherichia coli (E. coli) were examined, and the underlying influence mechanism was further discussed. The results showed both SDBS and Tween 80 enhanced the toxicity of Cd^2 + to E. coli in varying degrees. The reaction of SDBS and Cd^2 + could increase the outer membrane permeability and the bioavailability of Cd, while Tween 80 itself could enhance the outer membrane permeability. The combined toxicity of nano-TiO₂ and Cd^2 + to E. coli in absence of surfactant was antagonistic because of the adsorption of Cd^2 + to nano-TiO₂ particles. However, in the presence of SDBS, both SDBS and nano-TiO₂ influenced the toxicity of Cd^2 +, and also SDBS could adsorb to nano-TiO₂ by binding to Cd^2 +. The combined toxicity was reduced at Cd^2 + lower than 4 mg/L and enhanced at Cd^2 + higher than 4 mg/L under multiple interactions. Tween 80 enhanced the combined toxicity of nano-TiO₂ and Cd^2 + by increasing the outer membrane permeability. Our study firstly elucidated the effects of surfactants on the combined toxicity of nano-TiO₂ and Cd^2 + to bacteria, and the underlying influencing mechanism was proposed.     

Reducing phosphorus in dairy diets improves farm nutrient balances and decreases the risk of nonpoint pollution of surface and ground waters

Reducing phosphorus (P) in dairy diets may result in different types of manure with different chemical composition. Application of these manures to soils may affect the soil P solubility and lead to different environmental consequences. A laboratory incubation study determined the impact of 40 dairy manures on P dynamics in two soil types, Mattapex silt loam (Aquic Hapludult) and Kalmia sandy loam (Typic Hapludult). The manures were fecal samples of lactating cows, collected from commercial dairy farms located in Northeastern and Mid-Atlantic United States, with a wide range of dietary P concentrations (from 2.9 to 5.8 g P kg⁻¹ feed dry matter, DM). Dried and ground fecal samples were mixed with surface horizon (0–15 cm) of soils at 150 kg P ha⁻¹ and the mixtures were incubated at 25 °C for 21 days. At the end of incubation, water soluble P (WS-P) and Mehlich-3 P (M3-P) in the soil–manure mixtures were substantially higher than the control (soil alone) but were lower than the soils receiving fertilizer KH₂PO₄ at 150 kg P ha⁻¹. Similarly, the relative extractability of P in soils amended with low- and high-P manures was always lower (<93%) than KH₂PO₄ suggesting that fertilizer P is more effective at increasing soil solution P in the short-term. Concentrations of WS-P or M3-P in soil–manure mixtures did not differ regardless of the source of manure (i.e. different farms and different diets). This suggests that when the same amount of P is added to soils through manure applications, the solubility or bioavailability of P in soils will be the same. However, P concentrations in feces correlate significantly with that in diets (r = 0.82^**); and when the manures were grouped into high-P diets (averaging 5.1 g P kg⁻¹) versus low-P diets (3.6 g P kg⁻¹), manure P was 40% greater in the high-P group (10.6 g kg⁻¹ DM) than the low-P group (7.6 g kg⁻¹ DM). Thus, lowering excess P in diets would reduce P excretion in manures, P accumulation in soils, improve P balance on farms, require less area for land disposal, and decrease potential for P loss to waters.     

新型铁铜铝三元复合氧化物除磷性能与机制研究

采用共沉淀法制备了一种新型铁铜铝三元复合氧化物吸附剂,系统研究了其对磷的吸附行为,并对吸附磷前后的吸附剂进行了表征.吸附实验结果表明,铁铜铝三元复合氧化物对磷具有优异的吸附去除效能,Freundlich吸附等温线模型能更好地拟合其对磷的吸附,最大吸附量为62.6 mg·g-1(pH=7.0),显著高于多数文献报道的磷吸附剂;吸附速率较快,吸附动力学更符合Elovich模型;溶液pH对磷吸附有一定影响,随着pH的升高,磷吸附量降低,离子强度则影响不大;共存阴离子对磷吸附具有抑制作用,影响的大小顺序为SiO_3~(2-)SO_4~(2-)CO_3~(2-)Cl~-,而共存阳离子Ca2+和Mg2+则对磷吸附略有促进作用.Zeta电位、红外谱图(FTIR)和X射线光电子能谱(XPS)表征分析表明,磷在铁铜铝三元复合氧化物表面发生了特性吸附,磷酸根主要通过取代复合氧化物表面的羟基形成内表面络合物而被吸附去除.溶出实验结果表明,当pH在5.0~8.5范围内,Fe~(3+)、Cu~(2+)、Al~(3+)的溶出量均较低.由此可知,铁铜铝三元复合氧化物是一种具有良好应用前景的除磷吸附剂.     

乙酸盐对废水生物脱氮除磷影响的研究

考察了乙酸盐（钠）含量对循序间歇式废水生物脱氮除磷工艺的氮、磷去除效果及污泥沉降性能的影响。试验结果表明,废水中乙酸盐（钠）含量对ＰＯ＾３－４－Ｐ,ＰＮ＾－ｘ－Ｎ的明显。随着乙酸盐（钠）浓度的增加,ＰＯ＾３－４－Ｐ及ＮＯ×－Ｎ的去除率相应提高。乙酸盐（钠）的最低起始浓度为１２５ｍｇ／Ｌ,但超过２１５ｍｇ／Ｌ后,便产生污泥膨胀现象。     

Simultaneous removal of arsenic and antimony from mining wastewater using granular TiO2: Batch and field column studies

Coexisting arsenic (As) and antimony (Sb) in mining wastewater is a common and great concern. On-site simultaneous removal of As and Sb from mining wastewater was achieved by using a reusable granular TiO₂ column in this study. To evaluate the accuracy of the scale-up procedure, As and Sb adsorption from wastewater was studied in both large (600 g TiO₂) and small columns (12 g TiO₂) based on the proportional diffusivity rapid small-scale column tests (PD-RSSCTs) design. The comparable As and Sb breakthrough curves obtained from small and large columns confirmed the accuracy of the PD-RSSCT theory in the design of large-scale columns. Meanwhile, the consistent As and Sb adsorption results from batch and column experiments suggested that TiO₂ adsorption for As and Sb can be predicted from bench-scale tests. Charge distribution multi-site complexation (CD-MUSIC) and one-dimensional transport modeling integrated in the PHREEQC program were performed to study the adsorption behaviors of As and Sb on the TiO₂ surface. Coexisting ions, such as Ca^2 +, Mg^2 +, and Si^4 +, play an important role in As and Sb adsorption, and the breakthrough curves were well simulated after considering the compound ion effects. The results from this study highlight the surface reactions of As and Sb on TiO₂ and provide a practical way for on-site remediation of industrial wastewater.     

Biogas production from maize and dairy cattle manure—Influence of biomass composition on the methane yield

There is an increasing world wide demand for energy crops and animal manures for biogas production. To meet these demands, this research project aimed at optimising anaerobic digestion of maize and dairy cattle manures. Methane production was measured for 60 days in 1 l eudiometer batch digesters at 38 °C. Manure received from dairy cows with medium milk yield that were fed a well balanced diet produced the highest specific methane yield of 166.3 Nl CH₄ kg VS⁻¹. Thirteen early to late ripening maize varieties were grown on several locations in Austria. Late ripening varieties produced more biomass than medium or early ripening varieties. On fertile locations in Austria more than 30 Mg VS ha⁻¹ can be produced. The methane yield declined as the crop approaches full ripeness. With late ripening maize varieties, yields ranged between 312 and 365 Nl CH₄ kg VS⁻¹ (milk ripeness) and 268–286 Nl CH₄ kg VS⁻¹ (full ripeness). Silaging increased the methane yield by about 25% compared to green, non-conserved maize. Maize (Zea mays L.) is optimally harvested, when the product from specific methane yield and VS yield per hectare reaches a maximum. With early to medium ripening varieties (FAO 240–390), the optimum harvesting time is at the “end of wax ripeness”. Late ripening varieties (FAO ca. 600) may be harvested later, towards “full ripeness”. Maximum methane yield per hectare from late ripening maize varieties ranged between 7100 and 9000 Nm³ CH₄ ha⁻¹. Early and medium ripening varieties yielded 5300–8500 Nm³ CH₄ ha⁻¹ when grown in favourable regions. The highest methane yield per hectare was achieved from digestion of whole maize crops. Digestion of corns only or of corn cob mix resulted in a reduction in methane yield per hectare of 70 and 43%, respectively. From the digestion experiments a multiple linear regression equation, the Methane Energy Value Model, was derived that estimates methane production from the composition of maize. It is a helpful tool to optimise biogas production from energy crops. The Methane Energy Value Model requires further validation and refinement.     

Effect of organic matter on phosphorus recovery from sewage sludge subjected to microwave hybrid pretreatment

Microwave (MW) hybrid processes are able to disrupt the flocculent structure of complex waste activated sludge, and help promote the recovery of phosphorus as struvite. In this study, to optimize struvite yield, (1) the characteristics of matter released in MW-hybrid treatments were compared, including MW, MW-acid, MW-alkali, MW-H₂O₂, and MW-H₂O₂-alkali. The results showed that selective release of carbon, nitrogen, phosphorus, Ca^2 +, and Mg^2 + achieved by sludge pretreatment using MW-hybrid processes. MW-H₂O₂ is the recommended sludge pretreatment process for phosphorus recovery in the form of struvite. The ratio of Mg^2 +:NH₄⁺-N:PO₄^3 −-P was 1.2:2.9:1 in the supernatant. (2) To clarify the effects of organic matter on struvite recovery, the composition and molecular weight distribution of organic matters were analyzed. Low molecular weight COD was found to facilitate the removal rate of NH₄⁺-N and PO₄³-P via crystallization, and the amorphous struvite crystals (< 1 kDa) from the filtered solutions had high purity. Therefore, the present study reveals the necessity of taking into consideration the interference effect of high molecular weight organic matters during struvite crystallization from sewage sludge.     

Ammonia and nitrous oxide emissions following land application of high and low nitrogen pig manures to winter wheat at three growth stages

Nitrous oxide (N₂O) and ammonia (NH₃) emissions from surface applied high (HN) and low (LN) nitrogen pig manures were measured under field conditions. Manures were band-spread to a winter wheat crop at three growth stages—mid-tillering, stem elongation and flag leaf emergence. The N₂O flux rates were measured using the static chamber technique while NH₃ volatilisation was assessed using a micrometeorological mass balance technique with passive flux samplers. The N₂O emissions were episodic in nature with flux rates observed ranging from 2.8 to 31.5 g N₂O–N ha^?1 day^?1 (P < 0.001). Higher N₂O emissions generally occurred after rainfall events. Highest N₂O losses were observed from the HN treatment with LN manure use decreasing emissions by 18% (P < 0.03). The NH₃ volatilisation rates were highest within 1 h of manure application with 95% of emissions occurring within 24 h (P < 0.001). Cumulative N loss was highest at mid-tillering as low crop canopy cover and increased wind-speeds enhanced NH₃ loss (P < 0.001). Highest emissions were measured from the HN manure (P < 0.03). Total ammoniacal N loss ranged from 6 to 11%. Crop N uptake and grain yield were unaffected by application timing or manure type. Therefore, the use of LN manures decreased gaseous emissions of N₂O and NH₃ without any adverse effects on crop performance.     

Methane,nitrous oxide and ammonia emissions during storage and after application of dairy cattle slurry and influence of slurry treatment

Slurries are a significant source of CH₄, NH₃ and N₂O emissions to the atmosphere. The research project aimed at quantifying CH₄, NH₃ and N₂O emissions from liquid manure stores and after manure application under field conditions. The influence of the manure treatment options “no treatment”, “slurry separation”, “anaerobic digestion”, “slurry aeration” and “straw cover” on the emission level was investigated. Approximately 10 m³ of differently treated slurry were stored in pilot scale slurry tanks. Emissions were followed for c. 80 days. After the storage period, slurries were applied to permanent grassland. Greenhouse gas emissions from slurry were mainly caused by methane emissions during storage and by nitrous oxide emissions after field application of manures. Mitigation of GHG emissions can be achieved by a reduction in slurry dry matter and easily degradable organic matter content. Ammonia emissions mainly occurred after field application. Untreated slurry emitted 226.8 g NH₃ m⁻³ and 92.4 kg CO₂ eq. m⁻³ (storage and field application). Slurry separation (liquid fraction and composting of the solid fraction) resulted in NH₃ losses of 402.9 g m⁻³ and GHG losses of 58.5 kg CO₂ eq. m⁻³. Anaerobic digestion was a very effective means to reduce GHG emissions. 37.9 kg CO₂ eq. m⁻³ were lost. NH₃ emissions were similar to those from untreated slurry. Covering the slurry store with a layer of chopped straw instead of a wooden cover increased NH₃ emissions to 320.4 g m⁻³ and GHG emissions to 119.7 kg CO₂ eq. m⁻³. Slurry aeration nearly doubled NH₃ emissions compared to untreated slurry. GHG emissions were reduced to 53.3 kg CO₂ eq. m⁻³.     

Antimony(V) removal from water by iron-zirconium bimetal oxide: Performance and mechanism

A Fe-Zr binary oxide adsorbent has been successfully synthesized using a co-precipitation method. It showed a better performance for antimonate (Sb(V)) removal than zirconium oxide or amorphous ferric oxide. The experimental results showed that the Fe-Zr adsorbent has a capacity of 51 mg/g at an initial Sb(V) concentration of 10 mg/L at pH 7.0. Sb(V) adsorption on the Fe-Zr bimetal oxide is normally an endothermic reaction. Most of the Sb(V) adsorption took place within 3 hr and followed a pseudo second-order rate law. Co-existing anions such as SO₄^2-, NO₃^- and Cl^- had no considerable effects on the Sb(V) removal; PO₃^4- had an inhibitory effect to some extent at high concentration; while CO_₃^2- and SiO₄^4- showed significant inhibitory effects when they existed in high concentrations. The mechanism of Sb(V) adsorption on the adsorbent was investigated using a combination of zeta potential measurements, XPS, Raman, FT-IR observations and SO₄^2- release determination. The ionic strength dependence and zeta potential measurements indicated that inner-sphere surface complexes were formed after Sb(V) adsorption. Raman and XPS observations demonstrated that both Fe-OH and Zr-OH sites at the surface of the Fe-Zr adsorbent play important roles in the Sb(V) adsorption. FT-IR characterization and SO₄^2- release determination further demonstrated that the exchange of SO₄^2- with Sb(V) also could promote the adsorption process. In conclusion, this adsorbent showed high potential for future application in Sb(V) removal from contaminated water.     

Monitoring GHG from manure stores on organic and conventional dairy farms

Organic farming methods are claimed to be more environmentally friendly than conventional methods and the EU MIDAIR project had an overall aim to compare emissions from organic dairy farming with conventional methods of milk production. Manure stores are the second largest source of methane emissions (after enteric fermentation) on European dairy farming.The aim of this project was to measure green house gas (GHG) emissions from manures in covered and uncovered slurry stores and farm yard manure (FYM) heaps. The chosen method for measuring these emissions was the tracer ratio method, using sulphur hexafluoride (SF₆) as the tracer gas, the limitations of this method prevented successful measurements being made on some of the stores and a modified method was used on the covered stores. The difference in concentration of the upwind and downwind samples and interfering sources were limiting factors. FYM emission measurements were successful only when the manure was stored indoors.Methane emissions were successfully measured over a 12 month period from the uncovered slurry stores. Emission rates from the uncovered slurry stores on the conventional farm and the organic farm ranged from 14.4 to 49.6 and from 12.4 to 42.3 g C m⁻³ d⁻¹, respectively, with the mean CH₄ emission rates of 35 and 26 g C m⁻³ d⁻¹. On both farms, nitrous oxide emissions were close to zero.Methane emissions measured from the indoor organic FYM in summer were 17.1 g C m⁻³ d⁻¹ and the nitrous oxide emission was 411 mg N m⁻³ d⁻¹.The covered slurry stores were in such close proximity to other GHG sources that the tracer ratio method was unsuitable and the air-injection method was adopted. The measured emissions from covered slurry stores of CH₄, CO₂ and NH₃ were, respectively, 14.9 g C m⁻³ d⁻¹, 12.9 g C m⁻³ d⁻¹ and 18.6 mg NH₃ m⁻² d⁻¹ of slurry in February and 12.0 g C m⁻³ d⁻¹, 9.5 g C m⁻³ d⁻¹ and 335 mg NH₃ m⁻² d⁻¹ slurry in March. No nitrous oxide production could be measured.     

Changes in soil respiration across a chronosequence of tallgrass prairie reconstructions

Close relationships among climatic factors and soil respiration (R_s) are commonly reported. However, variation in R_s across the landscape is compounded by site-specific differences that impede the development of spatially explicit models. Among factors that influence R_s, the effect of ecosystem age is poorly documented. We hypothesized that R_s increases with grassland age and tested this hypothesis in a chronosequence of tallgrass prairie reconstructions in central Iowa, U.S.A. We also assessed changes in root biomass, root ingrowth, aboveground net primary productivity (ANPP), and the strength of soil temperature and moisture in predicting R_s. We found a significant increase in total growing season R_s with prairie age (R² = 0.79), ranging from 714 g C m^?2 in the youngest reconstruction (age 4) to 939 g C m^?2 in the oldest prairie (age 12). Soil temperature was a strong predictor of intra-seasonal R_s among prairies (R² = 0.78–0.87) but mean growing season soil temperature and moisture did not relate to total R_s. The increase in R_s with age was positively correlated with root biomass (r = 0.80) and ANPP (r = 0.87) but not with root ingrowth. Our findings suggest that growing season R_s increases with tallgrass prairie age, root biomass, and ANPP during young grassland development.     

Nitrous oxide emissions from a dung heap measured by chambers and plume methods

Dung heaps provide a large, spatial and temporal variable, source of the greenhouse gas N₂O. In this paper emission rates measured by static and flow through chamber methods, which enclose only a small area of the heap, were compared with Gaussian plume and tracer ratio methods, which measure the emissions from the entire dung heap. The dung heap was a 300 m³ heap, composed of material from nearby cattle sheds. From the flow through and static chambers it was estimated that the dung heap emitted 315 and 51 g N₂ON m⁻³ day⁻¹, respectively. The spatial variability between the chambers and chamber methods was large. Standard deviations of the mean fluxes were >75% of the average flux. The smaller emissions were measured on the slopes of the heap and the larger emissions on the ridge. The plume of N₂O was measured downwind of the dung heap by (1) tunable diode laser spectroscopy and calculation of the N₂O source strength of the heap using Gaussian plume theory and (2) tracer ratio method releasing SF₆ from the heap summit and capture in Tedlar bags downwind with subsequent analysis by gas chromatography. The Gaussian plume theory calculated an average N₂O source strength of 5.3 g N₂ON m⁻³ day⁻¹ (1.4–6.7 g N₂ON m⁻³ day⁻¹). The tracer ratio method calculated a slightly larger average emission rate of 14.4 g N₂ON m⁻³ day⁻¹ (7.4–38.6 g N₂ON m⁻³ day⁻¹). Both methods were successfully validated by point release of SF₆ and N₂O, which suggests that the micrometeorological methods provided a good estimate of the source strength of the heap, whereas the few chamber measurements overestimated its source strength.     

海藻酸锆/聚N-异丙基丙烯酰胺半互穿网络凝胶球的除磷性能

利用离子交联和自由基聚合反应制备了一种海藻酸锆/聚(N-异丙基丙烯酰胺)半互穿网络凝胶球(ZA/PNIPAM),用于吸附水中的磷酸盐.考察了溶液初始pH、吸附剂投加量、初始磷酸盐浓度和共存阴离子等因素对凝胶球吸附性能的影响.结果表明:ZA/PNIPAM在pH=2时可获得较大的吸附能力;随着投加量的减少、初始磷酸盐浓度的升高,凝胶球的吸附性能逐渐增大;SO_4~(2-)对吸附性能影响较Cl~-和NO_3~-明显.准二级动力学模型和颗粒内部扩散模型可以较好地拟合动力学吸附数据,表明表面吸附和颗粒内部扩散是吸附速率的主要控制步骤.吸附等温线数据可以较好地被Freundlich模型描述,表明吸附过程为非均匀多分子层吸附.FTIR、XPS、零电荷点(pH_(pzc))的结果以及相关吸附数据揭示凝胶球吸附磷酸盐的机制为静电吸附(物理吸附)以及配位交换(化学吸附)的共同作用.经过4次循环再生后,ZA/PNIPAM吸附性能保持稳定,具有良好的重复使用性.     

Dairy farm CH4 and N2O emissions,from one square metre to the full farm scale

The greenhouse gas emissions from agricultural systems contribute significantly to the national budgets for most countries in Europe. Measurement techniques that can identify and quantify emissions are essential in order to improve the selection process of emission reduction options and to enable quantification of the effect of such options. Fast box emission measurements and mobile plume measurements were used to evaluate greenhouse gas emissions from farm sites. The box measurement technique was used to evaluate emissions from farmyard manure and several other potential source areas within the farm. Significant (up to 250 g CH₄ m⁻² day⁻¹and 0.4 g N₂O m⁻² day⁻¹) emissions from ditches close to stables on the farm site were found.Plume emission measurements from individual manure storages were performed at three sites. For a manure storage with 1200 m³ dairy slurry in Wageningen emission factors of 11 ± 5 g CH₄ m⁻³ manure day⁻¹ and 14 ± 8 mg N₂O m⁻³ manure day⁻¹ were obtained in February 2002.Mobile plume measurements were carried out during 4 days at distances between 30 and 300 m downwind of 20 different farms. Total farm emissions levels ranged from 14 to 95 kg CH₄ day⁻¹ for these sites. Expressed as emission per animal the levels were 0.7 ± 0.4 kg CH₄ animal⁻¹ day⁻¹ for conventional farms. For three farms that used straw bedding for the animals1.4 ± 0.2 kg CH₄ animal⁻¹ day⁻¹ was obtained. These factors include both respired methane and emission from manure in the stable and the outside storages.For a subset of these farms the CH₄ emission was compared with monthly averaged model emission calculations using FarmGHG. This model calculates imports, exports and flows of all products through the internal chains on the farm using daily time steps. The fit of modelled versus measured data has a slope of 0.97 but r² = 0.27. Measurements and model emission estimates agree well on average, for large farms within 30%. For small farms the differences can be up to a factor of 3. CH₄ emissions during winter seem to be underestimated.     

Methane and nitrous oxide emissions from an integrated rainfed rice–fish farming system of Eastern India

Integration of fish stocking with rice (Oryza sativa L.) cultivation promises an ecologically sound and environmentally viable management of flooded ecosystem. Rice agriculture contributes to the emission of greenhouse gases CH₄ and N₂O, but little is known on the effect of fish rearing in fields planted to rice on the emission of these two greenhouse gases. In a field study, CH₄ and N₂O fluxes were measured from a sub-humid tropical rice field of Cuttack, eastern India, as affected by integrated rice–fish farming under rainfed lowland conditions. Three Indian major carps, Catla catla H., Labeo rohita H. and Cirrhinus mrigala H., and Puntius gonionotus B. were stocked in rice fields planted to two rice cultivars in a split-plot design with no fish and fish as the main treatments and two rice varieties as sub-treatments with three replicates each. Fish rearing increased CH₄ emission from field plots planted to both the rice cultivars with 112% increase in CH₄ emission in cv. Varshadhan and 74% in case of cv. Durga. On the contrary, fish stocking reduced N₂O emission from field plots planted to both the rice varieties. Movement of fish and associated bioturbation coupled with higher dissolved organic-C and CH₄ contents, and lower dissolved oxygen could be the reasons for release of larger quantities of CH₄ from rice + fish plots, while higher dissolved oxygen content might have influenced release of more N₂O from the rice alone treatment. The total greenhouse gas emission, expressed as CO₂ equivalent global warming potential (GWP), was considerably higher from rice + fish plots with CH₄ contributing a larger share (91%) as compared to rice alone plots (78–81%). On the contrary, N₂O had a comparatively lesser contribution with 19–22% share in rice alone plots that was further reduced to 9% in rice + fish plots. However, considering the profit-loss analysis based on the market price of the produce, rice–fish system provided a net profit of $453.36 ha^?1 over rice alone system in spite of higher carbon credit compliance of a rice–fish ecosystem due to larger cumulative GWP.     

Lodging in rice can be alleviated by atmospheric CO2 enrichment

The projected increase of atmospheric CO₂ concentration [CO₂] is expected to increase yield of agricultural C₃ crops, but little is known about effects of [CO₂] on lodging that can reduce yield. This study examined the interaction between [CO₂] and nitrogen (N) fertilization on the lodging of rice (Oryza sativa L.) using free-air CO₂ enrichment (FACE) systems installed in paddy fields at Shizukuishi, Iwate, Japan (39°38′N, 140°57′E). Rice plants were grown under two levels of [CO₂] (ambient = 365 μmol mol⁻¹; elevated [CO₂] = 548 μmol mol⁻¹) and three N fertilization regimes: a single initial basal application of controlled-release urea (8 g N m⁻², CRN), split fertilization with a standard amount of ammonium sulfate (9 g N m⁻², MN), and ample N (15 g N m⁻², HN). Lodging score (six ranks at 18° intervals, with larger scores indicating greater bending), yield, and yield components were measured at maturity. The lodging score was significantly higher under HN than under CRN and MN, but lodging was alleviated by elevated [CO₂] under HN. This alleviation was associated with the shortened and thickened lower internodes, but was not associated with a change in the plant's mass moment around the culm base. A positively significant correlation between lodging score and ripening percentage indicated that ripening percentage decreased by 4.5% per one-unit increase in lodging score. These findings will be useful to develop functional algorithm that can be incorporated into mechanistic crop models to predict rice production more accurately in a changing climate and with different cultural practices.