Organic Matter Dynamics,Aggregation, and Carbon Sequestration in Mine Tailings Amended with Humic Substances

Mechanisms of macroaggregation, carbon dynamics, and carbon sequestration were investigated in degraded mine tailings. Humic substances (HSs), wheat straw, lime, and their various combinations were added to the mine tailings and then incubated at 20 °C for 24 weeks. A significant increase (up to 79%) of water‐stable macroaggregates was observed in the HS‐amended tailings after the incubation. During the macroaggregation, 20–33% sand of the mine tailings was bound by HS‐derived active carbon pool. The organic carbon concentration of the macroaggregates significantly increased in the HS‐amended mine tailings compared to the control. Mineral‐associated organic matter carbon derived from the HSs was mainly responsible for the increased concentration of macroaggregate carbon and the increased amount of macroaggregates as well. This active pool of added organic matter was sequestered in aggregates during the process of macroaggregation and thus improved the structure of the mine tailings.     

15N-Urea Efficiency in Maize as Influenced by Humic Substances and Urease Inhibitors Treatments

Urea treated with urease inhibitors (UI) in association with humic substances (HS) is expected to improve urea efficiency by reducing ammonia losses and also provide the benefits of HS such as improve nitrogen (N) recovery by plants. Ammonia volatilization (AV), ¹⁵N recovery efficiency in the soil (NRE) and ¹⁵N use efficiency (NUE) were evaluated in maize (Zea mays L.) in a greenhouse pot trial. Treatments consisted of ¹⁵N-urea treated with UI (0, 0.4% boron (B) +0.15% copper (Cu), 0.64% B, and NBPT (N-(n-butyl) thiophosphoric triamide)) and three levels of HS (0%, 0.6%, and 1.2%). A control treatment (without N) was also included. N treatments were applied at V4 (vegetative leaf stage 4) on soil surface. HS was not efficient on AV reduction, NBPT had the greatest reduction in AV, and B had higher efficiency on AV reduction than Cu. At V8 (vegetative leaf stage 8), NBPT had the greatest NUE followed by B. At VT (tassel fully emerged), NUE from urea treated with NBPT reduced when increased levels of HS, and NBPT had the greatest NRE. UI in association with HS treated-urea does not reduce AV and it does not improve NUE by maize in vegetative stages.     

Application of Humic Substances Results in Consistent Increases in Crop Yield and Nutrient Uptake

The effect of humic substances on yield and nutrient uptake of grass, maize, potato and spinach was investigated in six field experiments and two pot experiments in a high input cropping system. The humic substances originating from leonardite formations in Canada were applied as liquid solution to the soil (Humifirst liquid) or as a solid incorporated in mineral fertilizers (Humifirst incorporated). Formal meta-analysis of the results of all executed experiments showed that the application of humic substances had an overall positive effect on dry matter yield of the crops and this effect was statistically significant for Humifirst incorporated. In the case of permanent grassland, humic substances promoted mainly the production of the first grass cut, which has the highest grass quality among all cuts during the growing season. Tuber production on the potato field trial showed a high response on the application of humic substances. Total potato yield increased with 13 and 17% for Humifirst liquid and Humifirst incorporated, respectively. The effect of humic substances on maize yield was limited, probably due to the rather high nutrient status of both soils. Finally, the formal meta-analysis showed a consequent increase in nitrogen and phosphorus uptake of all studied crops as well. The effect on potassium and magnesium uptake was also mainly positive, while sodium and calcium uptake were not affected in most of the experiments.     

有机物料对盐土腐殖物质组成和结构特征的影响

通过室内培养试验研究了秸秆、秸秆堆肥、秸秆生物质炭对黄河三角洲地区盐土腐殖物质组成和结构特征的影响。结果表明,秸秆、秸秆堆肥和秸秆生物质炭主要增加了胡敏素含量,由对照的5.48 g·kg^–1分别增加至11.20 g·kg^–1、16.66 g·kg^–1和20.60 g·kg^–1。秸秆堆肥和生物质炭配施胡敏酸含量增加至1.36 g·kg^–1,秸秆处理的富里酸由培养30 d时的3.77 g·kg^–1下降至3.32 g·kg^–1。土壤胡敏素含量与土壤有机碳含量在培养30 d(R²=0.84,P <0.001,n=10)和180 d(R²=0.98,P <0.001,n=10)时均呈显著正相关关系。秸秆、秸秆堆肥、生物质炭均有利于富里酸脂族碳相对含量的增加。生物质炭有利于土壤胡敏酸芳香类物质的增加;而秸秆或秸秆堆肥进入土壤初期,尤其是秸秆堆肥更有利于胡敏酸中脂族和碳水化合物或多糖类物质的积...     

Productivity,Quality and Soil Health as Influenced by Organic,Inorganic and Biofertilizer on Field Pea in Eastern Himalaya

A field experiment was conducted during two consecutive years of 2010–2011 and 2011–2012 to study the effect of biofertilizers in conjunction with organic and inorganic sources of nutrient management on productivity, quality and soil health on field pea at ICAR RC for NEH Region, Nagaland Centre Jharnapani, Nagaland, India. The experiment was laid out in split plot design with five nutrient sources in main plots and four treatment of biofertilizers with zinc in sub plots. Results indicated that the application of 100% recommended dose of fertilizer (RDF) through inorganic + 50% recommended dose of nitrogen (RDN) through vermicompost significantly improved root nitrogen (N) content, cation exchange capacity (CEC) of roots, NA activates, seed yield (1153 and 1262 kg ha^?1), straw yield (2182 and 2332 kg ha^?1) in the year of 2010–2011 and 2011–2012, respectively. Nutrients (N, P, K, S and Zn) uptake by seed and straw, protein content, protein harvest, soil organic carbon (SOC), available N, P, K, S, Zn and economics significantly higher with 100% RDF through inorganic + 50% RDN through vermicompost during both the years. Seed inoculation with biofertilizers along with 5 kg Zn ha^?1 markedly enhanced the root N content, CEC of roots, nitrogenase activities (NA), seed yield (1080 and 1193 kg ha^?1), straw yield (1978 and 2128 kg ha^?1), nutrients [N, phosphorus (P), potassium (K), sulfur (S) and zinc (Zn)] uptake, soil organic carbon (SOC) (%), and available N, P, K, S, and Zn of pea in both the years, respectively. These sources also give more income and benefit cost ratio per rupees invested.     

Enhanced Heavy Metal Phytoextraction from Marine Dredged Sediments Comparing Conventional Chelating Agents (Citric Acid and EDTA) with Humic Substances

Metal (Cu, Mn, Ni, Zn, Fe) concentrations in marine sediment and zooplankton were investigated in Izmir Bay of the Eastern Aegean Sea, Turkey. The study aimed to assess the levels of metal in different environmental compartments of the Izmir Bay. Metal concentrations in the sediment (dry weight) ranged between 4.26–70.8 μg g^?1 for Cu, 233–923 μg g^?1 for Mn, 14.9–127 μg g^?1 for Ni, 25.6–295 μg g^?1 for Zn, 12,404–76,899 μg g^?1 for Fe and 38,226–91,532 μg g^?1 for Al in the Izmir Bay. Maximum metal concentrations in zooplankton were observed during summer season in the inner bay. Significant relationships existed between the concentrations of certain metals (Al, Fe, Mn and Ni) in sediment, suggesting similar sources and/or similar geochemical processes controlling such metals. Higher concentrations of Cu, Zn and percent organic matter contents were found in the middle-inner bays sediments. Based on the correlation matrix obtained for metal data, organic matter was found to be the dominant factor controlling Cu and Zn distributions in the sediment. In general, mean Cu and Zn levels in the bay were above background concentrations in Mediterranean sediments. Zooplankton metal concentrations were similar to sediment distributions.     

Changes in the Content,Composition, and Properties of Humic Substances in Particle-Size Fractions of Soddy-Podzolic Soils under the Impact of Long-Term Drainage

Specific features of the transformation of humic substances in particle-size fractions of drained soddy-podzolic soils were studied on a field (12 ha) of the Experimental and Educational Center of Lomonosov Moscow State University in Moscow oblast. The field had a clearly pronounced microtopography. Surface-gleyed soddy-podzolic soils (Albic Stagnic Glossic Retisols (Loamic, Aric, Ochric)) of microdepressions with excessive surface moistening and nongleyed soddy-podzolic soils (Albic Glossic Retisols (Loamic, Aric, Ochric)) of elevated positions were examined. These soils were studied before the field drainage and during 25 years after drainage works in the periods differing in conditions of humification and with due account for not only drainage works but also other factors, such as topography and agrotechnology and their joint action. The specificity of transformation of humic substances in the soils and their particle-size fractions was analyzed in the basis of data on the organic carbon content, group and fractional composition of humus, the intensity of individual stages of humification (the neoformation of humic acids and the formation of humates), and the optical density of the fractions of humic acids. The results of the study of these properties in the fine soil fractions (<50 μm) made it possible to assess the response of the clay (<1 μm) and silt (1–5, 5–10, 10–50 μm) fractions to changes in the ecological situation and the role of separate particle-size fractions in the degradation of humus under adverse impacts. Overall, a clear tendency toward worsening of the humus quality was observed in both soils during the 25-year-long period, which is related to the long-term (20 years) agricultural use of the reclaimed field without application of agrochemicals. The features of humus degradation were mainly manifested in the finest (<10 μm) fractions with a general decrease in the humus content, slowing down of the formation of humic acids and humates, and considerable loss of humic acids, including their agronomically valuable fractions HA1 and HA2. The degradation of humus quality in the clay fraction was largely due to the impact of the reclamation (drainage) factor; the degradation of humus quality in the fine and medium silt fractions was mainly due to the negative changes in the agricultural background. Among negative consequences of the worsening humus quality, the lowering of soil fertility, ecological sustainability, and productivity of agrocenoses should be noted.     

金属离子在铁(氢)氧化物与腐殖质微界面上的吸附机理和模型研究进展

铁(氢)氧化物和腐殖质是广泛分布在土壤中的重要天然活性物质,因其具有较大的比表面积并且铁(氢)氧化物表面的-OH与腐殖质表面的-COOH、-OH等活性官能团可通过静电作用、配体交换等多种机制对重金属离子产生较强吸附,从而影响重金属离子在环境中的迁移、转化和生物效应。深入了解重金属离子在铁(氢)氧化物-腐殖质复合体微界面相互作用的分子机理,对于阐明重金属离子在环境中的迁移、转化过程具有重要意义。本文综述了金属离子在铁(氢)氧化物与腐殖质上吸附机理和模型的研究进展,为重金属污染土壤的风险评估和控制提供理论依据。     

Interaction Study Between Humin and Phosphate: Possible Environmental Remediation for Domestic Wastewater

The increase in demand for food due to the rapid population growth in recent years has raised the use of fertilizers, particularly phosphate salts. This fact has contributed to the excess amount of phosphorus species in aquatic systems. This is due to the leaching of these species present in the fertilizers applied to the soil to aquatic environments and may lead to eutrophication in these environments. Substances capable of interacting with the phosphate in the aquatic environment are promising for the reduction on the environmental impact. The humin, an insoluble fraction of humic material, has potential for phosphate retention, behaving like a chelating resin. Thus, the purpose of this research was to study the interaction between humin and phosphate. The equilibrium time between humin and phosphate was 15 min, where hydrogenionic potential (pH) 4.0 was the most effective in the interaction process. In this pH, the humin retained 33% of phosphate added. The complexing capacity of the humin-phosphate system was 11.53 mg g^?1. The adsorption studies indicated that the system follows a kinetic pseudo-second-order model. The Freundlich model was the most suitable to describe the phosphate adsorption process in humin. To evaluate the humin application in real systems, humin was added to the domestic wastewater. Sixteen percent of the total phosphate was adsorbed by the humin. Based on these results, humin has the potential to phosphate retention in domestic wastewater and could be used as a chelating resin minimizing environmental impact.     

Humic substances: Structure,function and benefits for agroecosystems—a review

The increasing global demand for food production, often causing excessive use of chemical fertilizers, has led to the deterioration of soil health. Immediate action is required to restore soil health in a sustainable manner. This review advocates switching to use of organic matter(manure and compost) that contains vital nutrients for plant growth and helps restore soil health. Humic substances(HSs), derived from degraded plant remains and found ubiquitously in nature,are an important source of o...     

Environmental Impacts of Chemicals for Snow and Ice Control: State of the Knowledge

As chemicals are widely used for snow and ice control of highway and airfield pavements or aircrafts, recent years have seen increased concerns over their potentially detrimental effects on the surrounding environment. The abrasives used for winter operations on pavements are also a cause of environmental concerns. After some background information, this paper presents a review of the environmental impacts of chemicals used for snow and ice control, including those on: surface, ground, and drinking waters; soil; flora; and fauna. The paper provides a state-of-the-art survey of published work (with a focus on those in the last two decades) and examines mainly the impacts of abrasives, chlorides, acetates and formates, urea, glycols, and agro-based deicers. Finally, we conclude with a brief discussion of public perception of such impacts and best management practices (BMPs) to mitigate them.     

微塑料污染对土壤环境质量和微生物生态学特性的影响研究进展

微塑料这一新兴污染物已成为全球性普遍关注的重要环境问题,近年来,土壤微塑料污染也越来越受到重视。本文从土壤环境质量和微生物生态学特性的角度,综述了近几年国内外土壤微塑料污染的相关研究进展,主要包括以下几个方面:（1）微塑料对土壤物理性质和养分有效性的影响;（2）微塑料对土壤污染物的吸附和解吸作用;（3）微塑料对土壤酶活性、微生物群落结构和抗生素抗性基因的影响;（4）“微塑料圈”中微生物的群落结构及其与土壤中微生物的生态位分异特征。最后针对土壤微塑料的重点研究方向提出展望,为今后土壤微塑料污染的研究提供了科学思路。     

Nitrogen Mineralization Potential as Influenced by Microbial Biomass,Cotton Residues and Temperature

Integrating information on nitrogen (N) mineralization potentials into a fertilization plan could lead to improved N use efficiency. A controlled incubation mineralization study examined microbial biomass dynamics and N mineralization rates for two soils receiving 56 and 168 kg N ha^?1 in a Panoche clay loam (Typic Haplocambid) and a Wasco sandy loam (Typic Torriorthent), incubated with and without cotton (Gossypium hirsutum L.) residues at 10 and 25°C for 203 days. Microbial biomass activity determined from mineralized carbon dioxide (CO₂) was higher in the sandy loam than in clay loam independent of incubation temperature, cotton residue addition and N treatment. In the absence of added cotton residue, N mineralization rates were higher in the sandy loam. Residue additions increased N immobilization in both soils, but were greater in clay loam. Microbial biomass and mineralization were significantly affected by soil type, residue addition and temperature but not by N level.     

Gully erosion: Impacts, factors and control

Gully erosion attracts increasing attention from scientists as reflected by two recent international meetings [Poesen and Valentin (Eds.), Catena 50 (2–4), 87–564; Li et al., 2004. Gully Erosion Under Global Change. Sichuan Science Technology Press, Chengu, China, 354 pp.]. This growing interest is associated with the increasing concern over off-site impacts caused by soil erosion at larger spatial scales than the cultivated plots. The objective of this paper is to review recent studies on impacts, factors and control of gully erosion and update the review on ‘gully erosion and environmental change: importance and research needs’ [Poesen et al., 2003. Catena 50 (2–4), 91–134.]. For the farmers, the development of gullies leads to a loss of crop yields and available land as well as an increase of workload (i.e. labour necessary to cultivate the land). Gullies can also change the mosaic patterns between fallow and cultivated fields, enhancing hillslope erosion in a feedback loop. In addition, gullies tend to enhance drainage and accelerate aridification processes in the semi-arid zones. Fingerprinting the origin of sediments within catchments to determine the relative contributions of potential sediment sources has become essential to identify sources of potential pollution and to develop management strategies to combat soil erosion. In this respect, tracers such as carbon, nitrogen, the nuclear bomb-derived radionuclide 137 Cs, magnetics and the strontium isotopic ratio are increasingly used to fingerprint sediment. Recent studies conducted in Australia, China, Ethiopia and USA showed that the major part of the sediment in reservoirs might have come from gully erosion.Gullies not only occur in marly badlands and mountainous or hilly regions but also more globally in soils subjected to soil crusting such as loess (European belt, Chinese Loess Plateau, North America) and sandy soils (Sahelian zone, north-east Thailand) or in soils prone to piping and tunnelling such as dispersive soils. Most of the time, the gullying processes are triggered by inappropriate cultivation and irrigation systems, overgrazing, log haulage tracks, road building and urbanization. As exemplified by recent examples from all over the world, land use change is expected to have a greater impact on gully erosion than climate change. Yet, reconstructions of historical causes of gully erosion, using high-resolution stratigraphy, archaeological dating of pottery and ¹⁴C dating of wood and charcoal, show that the main gully erosion periods identified in Europe correspond to a combination not only of deforestation and overuse of the land but also to periods with high frequency of extreme rainfall events.Many techniques have proved to be effective for gully prevention and control, including vegetation cover, zero or reduced tillage, stone bunds, exclosures, terracing and check dams. However, these techniques are rarely adopted by farmers in the long run and at a larger spatial scale because their introduction is rarely associated with a rapid benefit for the farmers in terms of an increase in land or labour productivity and is often contingent upon incentives.     

Amending Soil with Sludge,Manure, Humic Acid,Orthophosphate and Phytic Acid: Effects on Infiltration,Runoff and Sediment Loss

Application of organic wastes to cultivated lands can replace mineral fertilizers but may also alter soil physical properties and enhance pollution potential. The objective of this study was to investigate the effects of biosolids [composted manure (MC) and activated sludge (AS)] and specific biosolid component [orthophosphate (OP), phytic acid (PA) and humic acid (HA)] application on soils differing in texture [loamy‐sand (Ramat‐HaKovesh, RH), loam (Gilat, GL) and clay (Bet‐Dagan, BD)], infiltration rate, runoff volume and soil sediment loss. The soils were packed in erosion boxes (400 × 200 × 40 mm) and subjected to six consecutive simulated rainstorms, each of 186 mm deionized water. The results showed that runoff volume and sediment loss from untreated soils increased with increasing clay contents. In treated soils, the response to AS application differed from the response to other amendments; in the BD clay and GL loam, it was the only amendment that caused a decrease in sediment removed by runoff. In the RH loamy‐sand, all amendments reduced the final infiltration rate, but only AS and HA increased the measured runoff. It is proposed that the difference in the response of the soils to the amendments is associated with the soil's ability to attenuate changes in the negative charge on the clay edges following the increase in the specific adsorption of charged anions, thus controlling clay swelling and maintaining aggregate integrity. The effects of amending soils with a source of organic matter in order to control runoff and soil erosion are not straight forward and depend on soil and amendment properties. Copyright © 2015 John Wiley & Sons, Ltd.     

秸秆发电和气化残余物作为肥料在水稻生产上的应用研究

秸秆发电和气化残余物(下称草木灰),其含有丰富的大量和中微量元素,如K、Ca、P、Mg、Si、Cu、Zn、B等,其中钾含量尤为丰富。而水稻是一种喜钾和硅的作物。将草木灰作为钾肥应用于水稻的生产上,一方面可节约生产成本,另一方面还可以改善大米的品质;但草木灰同时还含有重金属元素,过量的施入势必会带来土壤环境的恶化,本文通过分析土壤中和大米中重金属含量的变化,得出本试验中草木灰的施入不会引起环境的恶化;从生产成本和水稻产量与品质上综合考虑得出处理木灰1 50%替代化学钾肥和草木灰2 75%替代化学钾肥是最佳施肥处理。     

Uncomposted Sheep and Cow Manures as a Source of Commercial Humic Amendments: An Exploratory Study

Liquid humic amendments are widely used in many countries as an enhancer of crop production (particularly root growth). While leonardite is the main substrate for obtaining these products, there is growing concern about obtaining them from plant-derived residual materials, rich in lignin and polyphenolics, thus making possible a residue valorization. Composting is a necessary step for converting these residues into a source of humic substances. In arid countries, obtaining humic products from sources other than leonardite faces two main challenges: (i) often such countries are devoid of forested areas or tree crops capable of supplying lignin-rich residues in large amounts and (ii) water is scarce (or very expensive if obtained by desalination) and therefore composting on an industrial scale is very difficult. Thus it is essential to find alternative sources capable of yielding humic or humic-like compounds without any previous composting. Here we present the main results obtained using sheep and cow manure, two materials widely available in the Kingdom of Saudi Arabia (KSA). Both were extracted using potassium hydroxide (KOH) at a variety of concentrations (from 0.25 to 2 M), times (from 20 to 120 min), temperatures (from 100 to 150 °C), and pressures. Sheep manure, much easier to extract than cow manure, appears the more promising as a source of commercial humic amendments. No lengthy extraction times are needed to obtain alkaline extracts; 20 min yields only slightly less humic-like matter than 2 h. The relative abundance of humic-like substances in the extract tends to decrease with time, but some optical indicators of humification (E₄/E₆ ratio, absorption at 280 nm, ratios of absorption at 253/203 and 253/220 nm) tend to increase. Polysaccharides, the dominant form of organic matter in the original manure, strongly resist alkaline extraction: their prior hydrolysis may be necessary to increase the yields of humic-like matter from the studied manures.     

施用腐植酸对夏玉米产量、氮素吸收及氮肥利用率的影响

为了探究腐植酸与无机肥料配施对夏玉米产量、氮素吸收及氮肥利用率的影响,于2014年始在河南省南阳市卧龙区英庄镇开展田间定位试验,共设置单施磷钾肥、常规施肥、常规施肥+3 000kg·hm~(-2)腐植酸、常规施肥减氮15%+3 000 kg·hm~(-2)腐植酸、常规施肥减氮30%+3 000 kg·hm~(-2)腐植酸等5个处理,分析不同氮肥运筹下夏玉米产量和氮肥利用的特征。结果表明,施用腐植酸可以有效改善夏玉米的农艺性状,提高夏玉米的产量,促进植株对氮素的累积和提高氮肥的利用率。其中,以常规施肥减氮15%+腐植酸处理效果最佳,与常规施肥相比,产量增加8.68%~12.96%,籽粒氮含量、籽粒氮累积量、地上部总氮累积量分别增加2.83%~3.92%、11.75%~19.74%、8.83%~19.41%,氮肥利用率增加52.00%~116.55%。因此,常规施肥减氮15%+3 000 kg·hm~(-2)腐植酸是本研究区域最佳的施肥模式,对实现现代农业生产的高产高效、资源节约和生态环境保护具有重要意义,是值得推荐的肥料运筹方式。     

淮河流域氮肥农药施用的合理性及其环境影响

根据1990—2008年统计数据和相关参数,通过估算农田系统氮素平衡和农药施用水平来分析淮河流域中下游典型区氮肥农药施用的合理性及其对环境的影响。结果表明,淮河流域研究区N素盈余量和农药施用量呈增加趋势,1990—2008年按耕地平均,N素盈余量由227kg·hm^-2增加到453kg·hm^-2,农药使用量从7.43kg·hm^-2增加到22.63kg·hm^-2。从空间差异来看,在研究区的8个县中,6个县耕地N素盈余量在400kg·hm^-2以上,2个县耕地氮素盈余量超过600kg·hm^-2;5个县农药使用量在20.00kg·hm^-2以上,2个县农药使用量超过30.00kg·hm^-2。8个县中N素盈余量和农药施用量最高的分别是最低的2.54倍和5.29倍。综合潜在风险分级结果为：沈丘、淮滨、凤台、寿县属于高风险区,五河、霍邱、颍上属于中等风险区,临泉属于较低风险区。可见,该地区氮肥和农药施用量大,且分布不平衡。     

Complexation Study of Humic Acids Extracted from Forest and Sahara Soils with Zinc (II) and Cadmium (II) by Differential Pulse Anodic Stripping Voltammetry (DPASV) and Conductimetric Methods

Safranin was used as a model reactive dye for biosorption studies onto various forms of chemically modified biomass of Aspergillus wentii. The experimental equilibrium data was analyzed by various single-, two-, three-, four-, and five-parameter isotherms to understand the biosorption process. Biosorption isotherms modeling shows that the interaction of safranin with A. wentii surface is localized monolayer sorption. Results show that in general the accuracy of models to fit experimental data improves with the degree of freedom. The interaction among adsorbed molecules is repulsive having no association between them and sorption is carried out on energetically different sites and is an endothermic process. The five-parameter Fritz?CSchluender model gives the most accurate fit with high regression coefficients (0.9902?C0.9941), low standard errors (0.0389?C0.0758), and sum of squares error (0.0075?C0.0230) values to all experimental data in comparison to other models. The results disclose that the sorption isotherm models fitted the experimental data in the order: Fritz?CSchluender (five-parameter) > Langmuir > Khan > Fritz?CSchluender (four-parameter) > Temkin. This systematic evaluation of the more important equilibrium isotherm models provided the general basis for making a preliminary selection of an effective model for a given application.