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Miscanthus is a productive perennial grass that is suitable as a bioenergy crop in "marginal" lands (e.g., eroded soils) with low water holding capacity. However, little is known about the impact of miscanthus residues on vapor transport and soil water budgets. Laboratory experiments were conducted to measure the vapor conductance through miscanthus residues and its effect on soil water evaporation. The ranges for the length, width, and thickness of residue elements were 0.5–9.0, 0.1–0.5, and 0.1–0.5 cm, respectively. Average residue areal, bulk, and skeletal densities were 0.88 kg m−2, 24 kg m−3, and 1006 kg m−3, respectively, giving a porosity of 0.98 m3 m−3. A power function described the decrease in conductance with increasing residue load. The corresponding conductance for a residue load of 0.88 kg m−2 was 1.6 mm s−1. During the first days of a 60‐day drying experiment, cumulative evaporation showed logarithmic decay with increasing residue load. Conversely, cumulative evaporation during the last days of the study showed little difference between treatments. Measurements indicated that there is a "critical" residue load (∼1.0 kg m−2) beyond which evaporation no longer decreases appreciably when the soil is under the stage 1 evaporation regime. Results suggest that soil water conservation in marginal lands may be accomplished by maintaining moderate amounts of bioenergy grass residue covering the soil. Determining "critical" loads for different residue types is a knowledge gap that merits further research. Core Ideas: Residues had skeletal density of 1006 kg m−3 and porosity of 0.98 m3 m−3.Residue conductance to water vapor decreased with increased areal density.Evaporation decreased with increased residue load during the first 15 days of drying.After 60 days of drying, treatments showed little difference in cumulative evaporation. [ABSTRACT FROM AUTHOR]

The most common method for in situ measurement of saturated hydraulic conductivity (Ksat) of the vadose zone is the constant head well permeameter method. Our general objective is to provide an empirical method for determining volume of water required for measuring Ksat using this procedure. For one-dimensional infiltration, steady state reaches as time (t) → ∞. For three-dimensional water flow from a cylindrical hole under a constant depth of water, however, steady state reaches rather quickly when a saturated bulb forms around the hole. To reach a quasi-steady state for measuring Ksat, we assume an adequate volume of water is needed to form the saturated bulb around the hole and increase the water content outside of the saturated bulb within a bulb-shaped volume of soil, hereafter, referred to as wetted soil volume. We determined the dimensions of the saturated bulb using the Glover model that is used for calculating Ksat. We then used the values to determine the volume of the saturated and wetted bulbs around the hole. The volume of water needed to reach a quasi-steady state depends on the difference between the soil saturated and antecedent water content (Δθ). Based on our analysis, between 2 and 5 L of water is needed to measure Ksat when Δθ varies between 0.1 and 0.4 m3 m−3, respectively. [ABSTRACT FROM AUTHOR]

There has been widespread interest in using compost to improve the hydrologic functions of degraded soils at construction sites for reducing runoff and increasing infiltration. The objective of this study was to determine the effects of compost amendment rate on saturated hydraulic conductivity (Ks) and water retention in order to identify target compost rates for enhancing soil hydrologic functions. Samples were prepared with three soil textures (sandy loam, silt loam, and sandy clay loam), amended with compost at 0%, 10%, 20%, 30%, 40%, and 50%. All soils were tested at a porosity of 0.5 m3/m3, and the sandy loam was further tested at high (0.55 m3/m3) and low (0.4 m3/m3) porosities. The Ks and water retention data were then used to model infiltration with HYDRUS‐1D. With increasing compost amendment rate, Ks and water retention of the mixtures generally increased at the medium porosity level, with more compost needed in heavier soils. As porosity decreased in the sandy loam soil, the amount of compost needed to improve Ks rose from 20% to 50%. Water distribution in pore fractions (gravitational, plant‐available, and unavailable water) depended on texture, with only the highest compost rates increasing plant‐available water in one soil. Results suggest soil texture should be taken into consideration when choosing a compost rate in order to achieve soil improvement goals. Hydrologic benefits may be limited even at a high rate of compost amendment if soil is compacted. [ABSTRACT FROM AUTHOR]

A challenging aspect of educating secondary students is integrating complex scientific concepts related to modern research topics into lesson plans that students can relate to and understand at a basic level. One method of encouraging the achievement of learning outcomes is to use real-world applications and current research to fuel student interest and excitement. This approach can be reinforced by use of demonstrations, which spur in-class discussions and can be integrated into out-of-class assignments. To attempt to develop improved curricular materials, a workshop was organized that combined the teaching expertise of a number of secondary school teachers with the research experience of a number of scientific experts to produce lesson plans centered around trace metal cycling and toxicity. These areas are important current research topics but are often neglected in pre-college education. A significant portion of the material presented at the workshop involved the use of visual and hands-on demonstrations of chemical principles that relate to geochemical processes that impact the environment. Materials provided to the instructors included suggestions for hands-on, interactive activities for use in the classroom, as well as teacher-administered demonstrations that would explore the physical and chemical bases of the principles being discussed. The participants all expressed positive feedback in terms of their confidence to administer student-centered lesson plans on the topic of biogeochemistry and their personal understanding of the subject matter, and a number of lesson plans were developed for use by the teachers to integrate the scientific principles discussed in the body of their courses. (Contains 2 tables and 4 figures.)

Turfgrass managers have suspected that runoff-independent movement of herbicides and fertilizers is partially responsible for uneven turfgrass quality in sloped areas. We hypothesized that subsurface lateral solute transport might explain this phenomenon especially in areas with abrupt textural changes between surface and subsurface horizons. A study was conducted to track solute transport using bromide (Br−), a conservative tracer, as a proxy of turfgrass soil inputs. Field data confirmed the subsurface lateral movement of Br− following the soil slope direction, which advanced along the boundary between soil horizons over time. A model based on field data indicated that subsurface lateral movement is a mechanism that can transport fertilizers and herbicides away from the application area after they have been incorporated within the soil, and those solutes could accumulate and resurface downslope. Our results demonstrate that subsurface lateral transport of solutes, commonly ignored in risk assessment, can be an important process for off-target movement of fertilizers and pesticides within soils and turfgrass systems in sloped urban and recreational landscapes. [ABSTRACT FROM AUTHOR]

Soil particle density (ρs) is often assumed as 2.65 g cm−3 (density of quartz). The objectives of this study were to compare the use of different gases for determining ρs in a gas pycnometer and relate measured ρs to soil particle size distributions. The ρs of 36 natural soil samples representing 12 USDA textural classes, fine glass beads, crushed granite rock, kaolinite, and bentonite were measured by a commercial gas pycnometer using He, N2, and dry air. The ρs of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρs of 36 soil samples determined by He and 30 samples determined by water had narrow ranges with averages of 2.65 and 2.59 g cm−3, respectively. The ρs determined by air and N2 had much wider ranges with averages of 2.93 and 2.97 g cm−3, respectively. There was a near 1:1 relationship between ρs of all samples determined by air and N2 with a highly significant (p <.001) correlation coefficient (r =.99). The average ratio of ρs determined by He and water was 1.03, but the correlation coefficient for their relationship was only.416. Although the relationship between ρs determined by He and either air or N2 was relatively strong (r <.61), the regression coefficient was <.17. There was a strong relationship between soil clay content and ρs determined by N2 or air but a weaker, yet statistically significant (p <.05) relationship when using He. Core Ideas: Average particle density of soils belonging to 12 textural classes determined by helium was 2.65 g cm−3.Average particle density measured by air and nitrogen were 2.93 and 2.97 g cm‐3, respectively.Helium, nitrogen, or air can be used to measure particle density of coarse‐textured soils.Only helium should be used to measure particle density of medium‐ and fine‐textured soils. [ABSTRACT FROM AUTHOR]

Multiple regression analysis is used to establish the link between the physical and chemical properties of three saprolites and their filter efficiency for submicron soil colloids. The study of colloidal interaction with saprolites, which are porous and allow free water movement, is important since they provide insights into the interactions of soil contaminants with groundwater.

Polyacrylamide (PAM) has been demonstrated to reduce erosion under many conditions, but less is known about the effects of its application method on erosion and concentrations in the runoff water. A rainfall simulation study was conducted to evaluate the performance of an excelsior erosion control blanket (cover) and two PAM application methods. The treatments were (i) no cover + no PAM (control), (ii) cover + no PAM, (iii) cover + granular PAM (GPAM), and (iv) cover + dissolved PAM (DPAM) applied to soil packed in wooden runoff boxes. The GPAM or DPAM (500 mg L-1) was surface-applied at a rate of 30 kg ha-1 1 d before rainfall simulation. Rainfall was applied at 83 mm h-1 for 50 min and then repeated for another 20 min after a 30-min rest period. Runoff samples were analyzed for volume, turbidity in nephelometric turbidity units (NTU), total suspended solids (TSS), sediment particle size distribution, and PAM concentration. The cover alone reduced turbidity and TSS in runoff by >60% compared with the control (2315 NTU, 2777 mg TSS L-1). The PAM further reduced turbidity and TSS by >30% regardless of the application method. The median particle diameter of eroded sediments for PAM treatments was seven to nine times that of the control (12.4 µm). Loss of applied PAM in the runoff water (not sediment) was 19% for the GPAM treatment but only 2% for the DPAM treatment. Both GPAM and DPAM were effective at improving groundcover performance, but DPAM resulted in much less PAM loss. [ABSTRACT FROM AUTHOR]

Concerns over runoff water quality from agricultural lands and construction sites have led to the development of improved erosion control practices, including application of polyacrylamide (PAM). We developed a quick and reliable method for quantifying PAM in soil extracts at low carbon content by using a turbidimetric reagent, Hyamine 1622. Three high-molecular weight anionic PAMs differing in charge density (7, 20, and 50 mol%) and five water matrices, deionized (DI) water and extracts from four different soils, were used to construct PAM calibration curves by reacting PAM solutions with hyamine and measuring turbidity development from the PAM-hyamine complex. he PAM calibration curve with DI water showed a strong linear relationship (r² = 0.99), and the sensitivity (slope) of calibration curves increased with increasing PAM charge density with a detection limit of 0.4 to 0.9 mg L-1. Identical tests with soil extracts showed the sensitivity of the hyamine method was dependent on the properties of the soil extract, primarily organic carbon concentration. Although the method was effective in mineral soils, the highest charge density PAM yielded a more reliable linear relationship (r² > 0.97) and lowest detection limit (0.3 to 1.2 mg L-1), compared with those of the lower charge density PAMs (0.7 to 23 mg L-1). Our results suggest that the hyamine test could be an efficient method for quantifying PAM in environmental soil water samples as long as the organic carbon in the sample is low, such as in subsurface soil material often exposed at construction sites. [ABSTRACT FROM AUTHOR]