Development and use of a database of hydraulic properties of European soils

Many environmental studies on the protection of European soil and water resources make use of soil water simulation models. A major obstacle to the wider application of these models is the lack of easily accessible and representative soil hydraulic properties. In order to overcome this apparent lack of data, a project was initiated to bring together the available hydraulic data which resided within different institutions in Europe into one central database. This information was then used to derive a set of pedotransfer functions applicable to studies at a European scale. These pedotransfer functions predict the hydraulic properties from parameters collected during soil surveys and can be a good alternative for costly and time-consuming direct measurement of these properties. A total of 20 institutions from 12 European countries collaborated in establishing the database of draulic operties of uropean oils (HYPRES). This database has a flexible relational structure capable of holding a wide diversity of both soil pedological and hydraulic data. As these data were contributed by 20 different institutions it was necessary to standardise both the particle-size and the hydraulic data. A novel similarity interpolation procedure was successfully used to achieve standardization of particle-sizes according to the FAO clay, silt and sand particle-size ranges. Standardization of hydraulic data was achieved by fitting the Mualem-van Genuchten model parameters to the individual θ(h) and K(h) hydraulic properties stored in HYPRES. The HYPRES database contains information on a total of 5521 soil horizons (including replicates). Of these, 4030 horizons had sufficient data to be used in the derivation of pedotransfer functions. Information on both water retention and hydraulic conductivity was available for 1136 horizons whereas 2894 horizons had only information on water retention. Each soil horizon was allocated to one of 11 possible soil textural/pedological classes derived from the six FAO texture classes (five mineral and one organic) and the two pedological classes (topsoil and subsoil) recognised within the 1:1 000 000 scale Soil Geographical Data Base of Europe. Next, both class and continuous pedotransfer functions were developed. By using the class pedotransfer functions in combination with the 1:1 000 000 scale Soil Map of Europe, the spatial distribution of soil water availability within Europe was derived.     

Building and testing conceptual and empirical models for predicting soil bulk density

The development of pedotransfer functions offers a potential means of alleviating cost and labour burdens associated with bulk‐density determinations. As a means of incorporating a priori knowledge into the model‐building process, we propose a conceptual model for predicting soil bulk density from other more regularly measured properties. The model considers soil bulk density to be a function of soil mineral packing structures (ρ_m) and soil structure (Δρ). Bulk‐density maxima were found for soils with approximately 80% sand. Bulk densities were also observed to increase with depth, suggesting the influence of over‐burden pressure. Residuals from the ρ_m model, hereby known as Δρ, correlated with organic carbon. All models were trained using Australian soil data, with limits set at bulk densities between 0.7 and 1.8 g cm^?3 and containing organic carbon levels below 12%. Performance of the conceptual model (r² = 0.49) was found to be comparable with a multiple linear regression model (r² = 0.49) and outperformed models developed using an artificial neural network (r² = 0.47) and a regression tree (r² = 0.43). Further development of the conceptual model should allow the inclusion of soil morphological data to improve bulk‐density predictions.     

Correlations between element concentrations in spruce foliage and forest soils

Abstract

The relationships between foliage element concentrations in red spruce and soil chemical properties were studied to determine if standard soil measurements of individual elements in soils were well correlated with the concentrations of these elements in foliage. Significant positive correlations between O horizon and foliage concentrations existed only for K, Mn and P. Significant negative correlations between the concentrations of the major divalent cations (i.e. Ca, Mg, Mn) and K in the foliage were found suggesting a possible antagonism between the mono‐ and divalent cations for uptake from the soil. Trees with the highest foliage concentrations of Ca also were determined to be growing on soils which were producing the best growth rates. Foliage concentrations of P, and to a lesser extent K and Mg, were below values considered to be adequate for optimum growth in red spruce.     

黑土区水蚀坡耕地土壤穿透阻力时空变异特征及传递函数

[目的] 为探明侵蚀坡耕地黑土硬度的时空特征及关键驱动因素。[方法] 基于典型水蚀坡耕地110个样点土壤穿透阻力动态监测及其相关因素的测定,在阐明土壤穿透阻力时空特征的基础上,利用多元线性回归(MLR)和随机森林(RFR)模型分析土壤穿透阻力的影响因素,并进一步构建其传递函数。[结果] 土壤穿透阻力时空变异性受土层深度、水分条件及农事活动等因素的综合影响,耕作层土壤穿透阻力空间上的异质性显著低于亚表层,变异系数分别为17.4%和26.3%。随土壤由湿变干和距离翻耕的时间增加,空间异质性呈增强趋势。土壤侵蚀影响土壤穿透阻力,强烈侵蚀区土壤穿透阻力高于沉积区,特别是在湿润条件下,差异更为显著(p<0.05)。与自然林地相比,所研究坡耕地73%样点的土壤穿透阻力增加,尤其在强侵蚀区。土壤含水量、容重和有机碳(SOC)是土壤穿透阻力的主要影响因素,Pearson系数分别为-0.69,0.58,-0.54,三者共同解释土壤穿透阻力88%的变异。RFR模型在土壤穿透阻力预测中表现优于MLR模型,在生长季均值的预测中,R²可达0.91,RMSE仅为91.2 kPa。[结论] 研究结果加深对侵蚀背景下黑土硬度空间分异特征的理解,为黑土压实管控提供理论依据。     

Adjustment of soil test interpretation for manganese due to elimination of charcoal during extraction

Abstract

The effect of including charcoal during extraction on the amount of manganese brought into solution was measured on soils from the Coastal Plain, Piedmont, and Mountain physiographic regions. The presence of charcoal increased the level of Mn extracted with dilute acid by a factor of 1.23 for soils with less than 40 ppm extractable Mn. This value was used to adjust the interpretation of the manganese soil test for soybeans based on previous correlation data so that charcoal may be omitted if desired.     

Prediction of soil water retention properties after stratification by combining texture,bulk density and the type of horizon

Among the numerous pedotransfer functions (PTFs) published, class‐PTfs have received little attention because their accuracy is often considered limited. However, recent studies show that performance of class‐PTFs can be similar to the more popular continuous‐PTFs. In this study, we compare the performance of PTFs that were derived from a set of 456 horizons collected in France grouped by combinations of texture, bulk density and type of horizon (topsoil and subsoil). The performance of these class‐PTFs was validated against water retained at ?33 and ?1500 kPa. Our results show that the best performance was obtained with class‐PTFs that used both texture and bulk density (texture‐structural class‐PTFs). They also showed that incorporation of horizon type into the PTF did not improve prediction performance. Comparison of performance at ?33 and ?1500 kPa showed very little difference, thus indicating no bias according to the value of water potential. Finally, the class‐PTFs developed are well suited for predicting water retention properties at the continental and national scales because only very basic soils data are available at these scales. A map of the available water capacity (AWC) was established for France using the 1:1 000 000 Soil Geographical Database of France and an averaged AWC of 104 mm was computed for France.