Biochar-induced soil phosphate sorption and availability depend on soil properties: a microcosm study

Journal of Soils and Sediments - The effects of soil properties on biochar-induced soil phosphate sorption and availability are not well investigated. An alkaline biochar-induced soil phosphate...     

The effects of phosphate on zinc sorption by a soil

Zinc sorption curves were obtained after treatment of a soil with several rates of phosphate and with two rates of lime. The lime permitted evaluation of the effects of phosphate on Zn sorption via its effects on pH. The phosphate was either incubated with the soil at a high temperature before reaction with Zn or was supplied at the same time as the Zn. This produced treatments with similar concentration of phosphate in solution but different amounts of sorbed phosphate.
Two distinct effects of phosphate addition on Zn sorption were detected. One arose from effects of phosphate on pH. This effect could be large and could either increase or decrease Zn sorption depending on the direction of the pH effect. A second effect was correlated with the amount of sorbed phosphate and was assumed to operate through the effects of phosphate on charge. The effects were small at low levels of Zn but larger at higher levels. This suggested that Zn and phosphate were sorbed at opposite ends of a spectrum of electrostatic potentials and overlap only occurred when the level of application was high. A third possible effect, due to reaction of the soil with zinc phosphate complexes in solution, was not proved.     

A statistical study of seven curves for describing the sorption of phosphate by soil

Seven mathematical models, which have been advanced for describing phosphate sorption by soils, are studied here with respect to their statistical behaviour in estimation. These seven non-linear regression models include the Langmuir equation and two extensions of it, the Freundlich equation and two extensions of it, and Gunary's equation. Measures of non-linear behaviour, such as the Bates & Watts (1980) curvature measure of intrinsic non-linearity and the Lowry & Morton (1983) asymmetry measure of non-linearity, were calculated for each model in combination with each of six data sets. It was found that the Freundlich equation and the extension of it proposed by Sibbesen behaved best, with Gunary's equation also having acceptable statistical properties, whereas the Langmuir equation and its extensions behaved worse, exhibiting properties which indicate that the estimators of their parameters would be severely biased and non-normal in distribution. It is believed that similar conclusions may apply to other processes involving surface adsorption.     

Refining soil survey information for a Dutch soil series using land use history

Abstract. Differences in land-use history within soil series, although not influencing soil classification, lead to variability of non-diagnostic soil properties in soil databases. Regional studies that use soil databases are confronted with this considerable variability. This has, for example, been reported in regional studies focused on nitrate leaching from agricultural land. Such findings have a direct impact on regional assessments of nitrate leaching from dairy farms on sandy soils, a major environmental issue in the Netherlands. There is thus a need to deal with this variability in soil properties.
We were able to relate soil organic nitrogen, soil organic carbon and its dynamics to land use history for a Dutch sandy soil series. Within one soil series, three different land use histories were identified: old grassland, reseeded grassland and grassland converted from continuous cropping with silage maize. The addition of landscape characteristics significantly improved the regression models based on land-use only. Once established for any given soil series, such relationships can significantly improve soil survey input into dynamic models of soil behaviour such as regional nitrate leaching studies.     

垃圾堆肥对难溶性磷转化及土壤磷素吸附特性影响

在城市生活垃圾进行工厂化堆肥过程中,加入难溶性磷矿粉,探讨堆肥对难溶性磷的转化能力及堆肥产品培肥后对土壤磷素吸附特性的影响。结果表明,加入磷矿粉可使堆肥中活性有机磷、中等活性有机磷、中稳性有机磷、高稳性有机磷及速效磷含量均有不同程度的提高,与对照相比分别增加212.69%、80.36%、61.21%、62.74%、157.89%。通过电镜观察表明,堆肥后磷矿粉典型的矿物特征消失,表面呈蜂窝状。将堆肥后的产品进行培肥试验表明,富磷垃圾肥处理可明显改善土壤磷素的吸附特性,与施化肥相比,最大吸附量(Q_m)下降8.76%,最大缓冲容量(Q_m·K)下降13.58%,而磷素的吸附饱和度(DPS)、零净吸附浓度磷(EPC₀)则呈不同程度的增加,幅度依次为98.52%、7.13%。试验结果显示,通过堆肥生产富磷垃圾肥可为解决中国磷素资源缺乏、化学磷肥利用率低等问题提供一条生物学途径。     

Factors affecting phosphate sorption along a Mediterranean, dolomitic soil and vegetation chronosequence

Phosphate sorption by calcareous soils has been studied mainly on heavily fertilized agricultural soils and soils with calcite as the main carbonate mineral. We examined factors affecting phosphate adsorption in the soils of a semi-arid, mediterranean, dolomitic, soil and vegetation chrono-sequence in southeastern Spain. The youngest soils are highly eroded, Sandy Regosols (Typic Xerorthents) under gorse-scrubland vegetation. These have small P sorption capacities, large Mg-Ca carbonate contents but small amounts of Fe and Al oxides. Small total P (HNO₃/HClO₄ digestion) concentrations (30–130 μg P g^?1), of which up to 90% is Ca-bound (HCl-extractable), are typical of these young soils. P sorption markedly increased when Ca²⁺ was added to the solution. The fractionation of previously sorbed P indicates that the fate of most of this extra-sorbed P is the labile-P fraction sorbed on to (carbonate) surfaces and the apatite-like fraction (NaHCO₃-extractable and HCl-extractable fractions). At the other extreme, older more-intensively weathered, sandy-clay-loam rendzinas (Entic Haploxerolls), supporting dense mature garrigue, have a much greater P adsorption capacity and larger clay and Fe and Al oxide concentrations. They have more total P (ca 400 μg P g^?1), much of it in occluded form (residual fraction). These soils show no significant differences in P sorption whether or not CaCl₂ was used as a background electrolyte. Considering the overall variations within the chronosequence, dithionite extractable Fe and Al are the properties best correlated with P sorption. This support the general finding that crystalline Fe-oxides (e.g. goethite and haematite) appear to be the most important P-sorbing component for soils in the Mediterranean region, rather than amorphous Fe-oxides (e.g. ferrihydrite) as is reported for more mesic areas. Stepwise multiple regression and fractionation data, however, suggest that, provided the soil solution is rich in Ca²⁺, carbonate may also be a significant contributing factor to P sorption, especially in the youngest of these dolomitic soils.     

A mechanistic model for describing the sorption and desorption of phosphate by soil

A model of phosphate reaction is constructed and its output compared with observations for the sorption and desorption of phosphate by soil. The model has three components: first, the reaction between divalent phosphate ions and a variable-charge surface; second, the assumption that there is a range of values of surface properties and that these are normally distributed; third, the assumption that the initial adsorption induces a diffusion gradient towards the interior of the particle which begins a solid-state diffusion process. The model closely describes the effects on sorption of phosphate of: concentration of phosphate, pH, temperature, and time of contact. It also reproduces the effects on desorption of phosphate of: period of prior contact, period and temperature of desorption, and soil: solution ratio. The model is general and should apply to other specifically adsorbed anions and cations. It suggests that phosphate that has reacted with soil for a long period is not ‘fixed’ but has mostly penetrated into the soil particles. The phosphorus can be recovered slowly if a low enough surface activity is induced.     

Boron sorption isotherm: A method to estimate boron fertilizer requirement

Abstract

The boron sorption isotherm method of soil testing may provide an estimate of the fertilizer required to bring the soil to an optimum boron level. Data from the boron isotherm experiment suggests that at low concentrations a plot of added boron vs equilibrium solution boron will be linear. The boron concentration at which this plot becomes linear will depend on the characteristics of the soil tested. The data, from this and other studies, suggest that 0.5 ppm boron in the equilibrium solution should be the approximate upper limit of boron concentration where this relationship is linear. Since boron added is linear with respect to boron in equilibrium solution, boron fertilizer required to adjust the equilibrium solution concentration can be calculated from the least squares regression equation of these two variables. This fertilizer requirement can only be determined when the optimum level of boron in equilibrium solution is known. Thus, further study is needed to establish this optimum level for all plant species.     

Using soil survey information to characterize the soil-water state*

Uses of soil for a wide variety of purposes are largely governed by interactions between soils and climatic conditions. The soil-water state at any given moment depends on the hydraulic properties of the soil horizons, the weather and soil drainage. Emphasis in this presentation is on the manner in which the soil-water state is being characterized in the context of land evaluation. Land evaluation is concerned with the assessment of land performance when used for specified purposes (FAO, 1976). Current and future developments in land evaluation are discussed, emphasizing the particular input of soil survey when using computer simulation models for the soil-water regime. The soil-water regime plays a key role in land evaluation, as it governs the soil-water state at any given time during the year.     

长期施磷对土壤磷素吸附演变的影响

Knowledge of phosphorus （P） behavior in long-term fertilized soils is essential for programming fertilization practices and for sustaining environmental quality. The long-term （1984-1997） effects of various fertilization treatments on P changes and sorption isotherms as well as the relationship of soil properties to P sorption and P forms were evaluated in an Ustic Isohumisol, a calcareous soil, on the Loess Plateau, China. Compared to 1984, after 13 years of crop production, total soil P in the no-P treatments （control and N treatment） decreased by 5%-7%, but in the phosphorus fertilizer alone （P）, nitrogen and phosphorus fertilizers in combination （NP）, manure alone （M）, and nitrogen and phosphorus fertilizers and manure in combination （NPM） treatments, it increased by 22%, 19%, 28%, and 58%, respectively. Residual fertilizer P was found mainly in NH4Ac-soluble P （Cas-P）, followed by NaHCO3-soluble P （NaHCO3-P）, and NH4F-soluble P （Al-P）. Phosphorus sorption in the soils with different fertilization practices fit the Langmuir equations. Phosphorus sorption capacity in the no-P treatments increased, whereas it decreased in the P-included treatments （P, NP, and NPM treatments）. Phosphorus sorption maximum （Qm） was significantly and negatively correlated to inorganic P including NaHCO3-P, Cas-P, NaOH-Na2CO3-soluble P （Fe-P）, and Al-P （P ≤ 0.01）. Moreover, long-term fertilization increased soil organic carbon in the NP, M, and NPM treatments and decreased pH in the NP and NPM treatments. Thus, the ability of the soil to release sorbed P to the environment increased under long-term P fertilization.     

Drainability of some Dutch clay soils: A case study of soil survey interpretation

Riverine and marine non-calcareous Dutch clay soils have moderate limitations for use as grassland under existing conditions due to high ground-water levels in winter and early spring, which have traditionally been attributed to a very low K_sat of the clay. Physical research, which used soil morphology to define sample size and soil maps to locate test sites within defined mapping units, showed that permanent high ground-water levels were primarily due to low hydraulic gradients and not to a low K_sat. Well-maintained tile drainage, to be associated with low water levels in the ditches in winter, resulted in much lower ground-water levels in the soil, thereby effectively reducing use limitations imposed by existing conditions and improving soil suitability. The latter was specifically characterized in this study in terms of the assessment factor: “drainage status”. Tile drainage resulted in a significant increase of K_sat which was thought to be due to increased drying and cracking of the relatively young riverine soil. In the older marine soils, the increase of K_sat upon tile drainage was due to deep earthworm activity. Existing suitability can thus be improved by using appropriate technology, i.e., tile drainage associated with better water management. The detail by which the technology is defined in soil survey interpretation is critical. The detail should not exceed the generality-level dictated by the variability of regional field data.     

面向土壤系统分类的土壤调查制图方法的初步研究

我国的土壤系统分类方案已经基本形成,但还没有相应的土壤调查方法技术研究。按照传统土壤调查的主要剖面、检查剖面、定界剖面的思想与办法,采用空间内插技术,在研究区的4条实验路线上共挖掘了64个剖面点,通过这些剖面点的诊断层和诊断特性确定了研究区的土壤类型并勾绘了土壤类型界线。再用1条检验路线对勾绘的土壤图进行检查,结果表明,在检验路线上设置的20个检查剖面点中,其中19个剖面点与实际情况相符,正确率95%,说明使用内插法进行面向土壤系统分类的土壤调查制图是可行的。再结合土壤景观可以辅助土壤调查工作者更高效地确定土壤类型、勾绘土壤界线。     

Diffusion of strongly sorbed solutes in soil: a dual-porosity model allowing for slow access to sorption sites and time-dependent sorption reactions

We use homogenization techniques to derive a dual (or double) porosity model of solute diffusion and reaction in soil, allowing for slow access to sorption sites within micro-aggregates and time-dependent sorption reactions. We give a means for determining the conditions in which micro-scale concentration gradients affect macro-scale gradients and fluxes. We present equations for a unit volume of soil represented as a series of uniformly-spaced, porous spherical particles, containing and surrounded by solution through which solutes diffuse. The methods we use can, in principle, be applied to more complex geometries. We compare the model's predictions with those of the equivalent single porosity model for commonly used boundary conditions. We show that failure to allow for slow access to reaction sites can lead to seriously erroneous results. Slow access has the effect of decreasing the sorption of solute into soil from a source or desorption from soil to a sink. As a result of slow access, the diffusion coefficients of strongly-sorbed solutes measured at the macro-scale will be time-dependent and will depend on the method of measurement. We also show that slow access is more often likely to limit macro-scale diffusion than rates of slow chemical reactions per se . In principle, the unimportance of slow reactions except at periods longer than several weeks of diffusion simplifies modelling because, if slow access is correctly allowed for, sorption can be described with equilibrium relations with an understanding of speciation and rapid sorption-desorption reactions.     

Soil-geographical regionalization as a basis for digital soil mapping: Karelia case study

Recent development of digital soil mapping (DSM) allowed improving significantly the quality of soil maps. We tried to make a set of empirical models for the territory of Karelia, a republic at the North-East of the European territory of Russian Federation. This territory was selected for the pilot study for DSM for two reasons. First, the soils of the region are mainly monogenetic; thus, the effect of paleogeographic environment on recent soils is reduced. Second, the territory was poorly mapped because of low agricultural development: only 1.8% of the total area of the republic is used for agriculture and has large-scale soil maps. The rest of the territory has only small-scale soil maps, compiled basing on the general geographic concepts rather than on field surveys. Thus, the only solution for soil inventory was the predictive digital mapping. The absence of large-scaled soil maps did not allow data mining from previous soil surveys, and only empirical models could be applied. For regionalization purposes, we accepted the division into Northern and Southern Karelia, proposed in the general scheme of soil regionalization of Russia; boundaries between the regions were somewhat modified. Within each region, we specified from 15 (Northern Karelia) to 32 (Southern Karelia) individual soilscapes and proposed soil-topographic and soil-lithological relationships for every soilscape. Further field verification is needed to adjust the models.     

Soil monitoring: a basic task for soil survey organizations

Abstract. A basic task of national soil survey organizations should be to monitor changes in soil properties. The objectives would be to establish which land-use systems, on which soil types, are causing decline in fertility, and to keep track of the effects of pollution. Unless data are obtained at national level, attempts to monitor global soil changes cannot succeed.     

Evaluation of models to upscale the small scale variability of Cd sorption in a case study

Cadmium sorption, basic soil properties and water retention were jointly analyzed in an acidic sandy podzol under pine forest in the North of Germany. Samples were taken along a 10 m transect at a depth of 0.15 m with a sample-support of 0.15 m. The small-scale Cd sorption variability was upscaled in two steps. Firstly, it was simplified and, secondly, aggregated from the sample to the pedon scale. We evaluated different models to simplify Cd sorption variability at different levels of spatial aggregation. Our evaluation method was the numerical simulation of Cd transport in the topsoil where the variability of Cd sorption is the key input.We described Cd sorption with the Freundlich parameterization and tested three models to simplify its spatial variability. The reference model (model 1) had two and the simplified models only one spatially variable sorption parameter. Model 2 varied the parameter K_f of the Freundlich parameterization and set the exponent constant. Model 3 expressed only the linear variability of sorption. Each sample had a scaling factor that related to a constant sorption reference function. The Freundlich parameter K_f of the third simplification model (model 4), was derived by a local pedotransfer function. Its variability was, therefore, filtered by the available variation of a limited number of basic soil properties.The average sorption was at all aggregation levels not significantly different between the models. However, the corresponding uncertainty was smallest for model 3, intermediate for model 4 and largest for model 2. We evaluated the different sorption variability models with the simulation of Cd transport. The mean Cd concentrations in the topsoil predicted by the different models were statistically not different. However, at all support scales, the uncertainties of the predicted mean Cd concentrations and the RMSE's were smallest when model 3 was used, where the error was about 20% at the sample scale and decreased to below 10% at the pedon scale. Therefore, if measurements of sorption isotherms are available, we recommend to use model 3 to derive the mean sorption behavior with minimal uncertainty.     

非均匀土壤区域SVAT模型中土壤水动力学参数的整合研究

荷兰Cabauw地区一个 10km×10km区域内的四种主要土壤的水动力学参数用一种实验室直接测定法 (Wind氏蒸发法 )和两种间接方法 (“分段土壤推导函数”、“连续土壤推导函数”)确定 ,而该区域水动力学特性参数的整合则采用两组方案 (聚合土壤参数法和有效土壤参数法 )进行。一个SVAT模型的模拟输出结果———感热通量、潜热通量与实测数据的比较分析表明 :(1)对于用“分段土壤推导函数”确定的土壤水动力学参数的区域整合 ,以“逆模拟法”(有效土壤参数法 )较为可行 ,其模拟感热、潜热的精确性接近参比方案 (“模拟 平均法”) ;(2 )对于实验室直接测定的参数 ,则以几何平均vanGenuchten Mualem经验公式参数的方案 (聚合土壤参数法 )为佳 ;(3)对于“连续土壤推导函数”推导的水动力学参数 ,几何平均土壤组分方案 (聚合土壤参数法 )和“逆模拟法”方案 (有效土壤参数法 )二者均可得到优于参比方案 (“模拟 平均法”)的模拟结果 ,其中以前者最佳 ;(4 )所有区域化参数整合方案中 ,以水平几何平均区域内实验室直接测定的参数的方案最优 ;同时 ,“连续土壤推导函数”法的土壤组分几何平均方案的模型输出精确性接近该最优方案