Models that integrate the influence of soil intrinsic attributes on the estimation of soil compaction are scarce for Hapludox. The present study tested the hypothesis that the compressive behavior of Hapludox with wide variations in intrinsic soil attributes can be estimated based on pedotransfer functions (PTFs). The general goal of this research was to determine the effect of intrinsic soil attributes on the susceptibility to compaction, preconsolidation pressure and compression curve of Hapludox, and to develop PTFs that allow the estimation of these parameters based on easily measurable soil attributes. The study was conducted on a soil toposequence that includes a sandy Typic Hapludox, a loamy Typic Hapludox, and a clayey Rhodic Hapludox. The uniaxial compression test was applied to 50 undisturbed soil samples at matric potential values of −10 and −100 kPa. After load withdrawal, soil bulk density, void ratio, gravimetric soil water content, particle‐size distribution, particle density, and organic matter were determined. The compression curves, the compression index, and the preconsolidation pressure were obtained. The relationship between the compression index, soil bulk density, and clay content was statistically significant with R2 = 0.77. Organic matter and soil water content did not affect the compression index. The preconsolidation pressure was significantly related with soil bulk density, soil water content, and clay content (R2 = 0.70), but was unaffected by organic matter. Soil compressibility was dependent on soil bulk density. A nonlinear model fitted the data with R2 = 0.90 allowing to predict the compressibility of soils for a wide range of stresses and inherent soil properties.

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Phosphorus deficiencies are limiting crop production in agricultural soils worldwide. Locally available sources of raw phosphate rock (PR) are being recognized for their potential role in soil fertility improvement. Phosphorus bioavailability is essential for the efficiency of PRs and can be increased by acid treatments. The utilization of organic acid producing micro‐organisms, notably Aspergillus niger, presents a sustainable alternative to the use of strong inorganic acids, but acid production of A. niger strongly depends on the mineral content of the growth media. This study compared the phosphorus mobilization efficiency of two biological treatments, namely addition of acidic cell‐free supernatants from A. niger cultivations to PRs and the direct cultivation of A. niger with PRs. The results show that addition of PR to cultivations leads to significant differences in the profile of organic acids produced by A. niger. Additions of PR, especially igneous rocks containing high amounts of iron and manganese, lead to reduced citric acid concentrations. In spite of these differences, phosphorus mobilization was similar between treatments, suggesting that the simpler direct cultivation method was not inferior. In addition to citric acid, it is suggested that oxalic acid contributes to PR solubilization in direct cultivations with A. niger, which would benefit farmers in developing countries where conventional fertilizers are not adequately accessible.

The prediction of infiltration of water into field soils requires measurements of the field-saturated hydraulic conductivity (Kfs) and the matric flux potential corresponding to field saturation (qbm). We develop analytical solutions for (1) early-time, onedimensional infiltration into slowly permeable soils such as clay liners under the conditions of an initial constant head followed by a falling head phase and (2) steady state, threedimensional infiltration into permeable soils under the condition of steady state flow at a constant head followed by falling head conditions. Kfs and qbm govern the shape of both solutions. The parameters are simultaneously identifiable, unique, and stable within the early-time solution; however, there is a limited range in which the parameters of the steady state solution are unique. Laboratory and field experiments based on both solutions gave physically realistic best fit parameter values using the solutions in inversion procedures. Field measurements gave an excellent correlation between Kfs from steady state constant head and falling head techniques. The correlation between qbm values was somewhat lower. Introduction Most field procedures for determining field-saturated hydraulic conductivity, Kfs(L T-•) and the mattic flux potential corresponding to field saturation, (•m (L2T-1), (e.g., well permeameters, ring infiltrometers, tension infiltrometers) measure flow under constant ponded head and steady state flow conditions. Constant head conditions have traditionally been used because constant head devices are simple and easy to maintain experimentally and because the analyses are usually relatively easy to invert. A difficulty with this approach, however, is that insufficient information is obtained from the measurement of steady state flow under one constant head to evaluate both Kfs and •)m [Elrick and Reynolds, 1992a, b]. Either one parameter, such as a* (a* = Kf•/rbm), must be measured or estimated independently [e.g., Elrick et al., 1989] or steady state flow measurements need to be taken for two or more ponded heads [e.g., Elrick and Reynolds, 1992b]. If a* is estimated, however, some error can result [e.g., Reynolds et al., 1992], and if steady state measurements are taken at two or more heads, soil heterogeneity can cause a large percentage of invalid (i.e., negative) and unrealistic Kfs and l•m values [Elrick and Reynolds, 1992b; Reynolds et al., 1992]. Infiltration under both early-time falling head conditions and steady state falling head conditions can provide, however, information from which both Kfs and qbm can be uniquely obtained (for the most part) with reasonable accuracy. By "early-time falling head" (EFH) Paper number 95WR01139. 0043-1397/95/95WR-01139505.00conditions we mean that water is rapidly ponded on the infiltration surface and the initial rate of fall of the water level is measured. By "steady state falling head" (SFH) we mean that infiltration is initially allowed to come to steady state under constant ponded head conditions and then the head is a...

S. 2006. Using automated soil water content measurements to estimate soil water budgets. Can. J. Soil Sci. 86: 47-56. The distribution of precipitation into the components of a soil water budget has a profound impact on crop growth, groundwater recharge, soil erosion, and groundwater and surface water contamination levels. The main objectives of this study were to develop a new method of measuring soil water balances and to demonstrate the use of the method in examining differences between partitioning of water in conventional tillage (CT) and no-tillage (NT) management systems. Hourly precipitation, evapotranspiration, and changes in soil water storage data were collected automatically over a 3-yr period at a field site near Elora, Ontario. Runoff and interception were calculated as the difference between measured increases in soil water storage and total rainfall during each significant rain event when the soil was not frozen. Drainage was then calculated, as it was the only component of the soil water balance not measured. The amount of soil water stored in the NT system was greater than the CT system during the latter part of the study as the NT system aged. The amount of drainage calculated for a 3-yr period was greater for CT than the NT treatment, a result that is contrary to many previous studies. The measured amount of runoff plus interception was greater in the NT versus CT treatment. Since NT is generally accepted as a means of reducing runoff, this result could be due to the enhanced amount of interception by the crop residue left on the surface of the NT treatment.Key words: Soil water balance, water content reflectometer, drainage, runoff, tillage, time seriesMcCoy, A. J., Parkin, G., Wagner-Riddle, C., Warland, J., Lauzon, J., von Bertoldi, P., Fallow, D. et Jayasundara, S. 2006. Estimation du bilan hydrique à partir de relevés automatiques de la teneur en eau du sol. Can. J. Soil Sci. 86: 47-56. La répartition des eaux pluviales entre les différentes composantes du bilan hydrique du sol a une profonde incidence sur la croissance des cultures, le renouvellement de la nappe phréatique, l'érosion du sol et le degré de contamination des eaux superficielles et souterraines. La présente étude devait principalement servir à établir une nouvelle méthode pour mesurer le bilan hydrique du sol et à illustrer l'application de cette méthode à l'analyse des variations au niveau de la répartition de l'eau dans les systèmes de travail du sol (TS) et de non-travail du sol (NT). La pluviométrie horaire, l'évapotranspiration et la fluctuation des réserves d'eau du sol ont été mesurées automatiquement pendant trois ans sur un terrain près d'Elora (Ontario). Le ruissellement et l'interception de l'eau correspondaient à l'écart entre la hausse des réserves d'eau du sol et les précipitations totales, établies à chaque événement de précipitation important quand le sol n'était pas gelé. On a également calculé le drainage, seule composante du bilan hydrique qui n'a pas été mesurée. Durant la deuxième moitié de l'étude, l...