Edward L. McCoy

Foraging by deep-burrowing earthworms degrades surface soil structure of a Fluventic Hapludoll in Ohio.

The presence of deep-burrowing earthworms can affect soil structure and infiltration, therefore influencing agricultural productivity. We investigated the effects of deep-burrowing earthworm species on soil structure at the surface of chisel-plowed or ridge-tilled cropping systems in Pike County, OH, planted to corn (Zea mays L.). Earthworm populations were experimentally manipulated in field enclosures by adding predominantly deep-burrowing Lumbricus terrestris L., or leaving enclosures unmodified in each tillage system. In 1995, after 2 years of bi-annual additions, we measured surface residue cover, dry sieved aggregates (DSA)- and water-stable aggregates (WSA), and carbon and nitrogen concentration of aggregates by size class, in each treatment combination. Also, in 1998, we used tension infiltrometry to examine crusting effects at the soil surface among earthworm treatments in the chisel-plow treatment. Earthworm additions yielded increased density and biomass of L. terrestris than ambient controls, and to a greater extent in the ridged corn‐soybean (Glycine max L. Mess.)‐ wheat (Triticum aestivum L.) (CSW) than corn‐soybean (CS) rotation. Percentage residue cover in CS cropping decreased with earthworm additions. Earthworm additions decreased the geometric mean weight diameter (GMWD) of DSA and WSA in chisel-plow treatment compared to no additions. Earthworm additions influenced carbon-to-nitrogen (C/N) ratios for smaller DSA and WSA. Water-stable aggregate C/N decreased with size class. The overall effect of earthworm additions was an increase in deep-burrowing earthworms, a decrease in surface residue cover, and more pronounced crusting, which decreased mesopore conductivity. # 2000 Elsevier Science B.V. All rights reserved.

Dissolved nutrients and atrazine removal by column-scale monophasic and biphasic rain garden model systems.

Rain gardens are bioretention systems that have the potential to reduce peak runoff flow and improve water quality in a natural and aesthetically pleasing manner. We compared hydraulic performance and removal efficiencies of nutrients and atrazine in a monophasic rain garden design versus a biphasic design at a column-scale using simulated runoff. The biphasic rain garden was designed to increase retention time and removal efficiency of runoff pollutants by creating a sequence of water saturated to unsaturated conditions. We also evaluated the effect of C substrate availability on pollutant removal efficiency in the biphasic rain garden. Five simulated runoff events with various concentrations of runoff pollutants (i.e. nitrate, phosphate, and atrazine) were applied to the monophasic and biphasic rain gardens once every 5d. Hydraulic performance was consistent over the five simulated runoff events. Peak flow was reduced by approximately 56% for the monophasic design and 80% for the biphasic design. Both rain garden systems showed excellent removal efficiency of phosphate (89-100%) and atrazine (84-100%). However, significantly (p<0.001) higher removal of nitrate was observed in the biphasic (42-63%) compared to the monophasic rain garden (29-39%). Addition of C substrate in the form of glucose increased removal efficiency of nitrate significantly (p<0.001), achieving up to 87% removal at a treatment C/N ratio of 2.0. This study demonstrates the importance of retention time, environmental conditions (i.e. saturated/unsaturated conditions), and availability of C substrate for bioremediation of pollutants, especially nitrates, in rain gardens.

Earthworm additions affect leachate production and nitrogen losses in typical midwestern agroecosystems.

Earthworms affect soil structure and the movement of agrochemicals. Yet, there have been few field-scale studies that quantify the effect of earthworms on dissolved nitrogen fluxes in agroecosystems. We investigated the influence of semi-annual earthworm additions on leachate production and quality in different row crop agroecosystems. Chisel-till corn (Zea mays L.)-soybean [Glycine max (L.) Merr.] rotation (CT) and ridge-till corn-soybean-wheat (Triticum aestivum L.) rotation (RT) plots were arranged in a complete randomized block design (n = 3) with earthworm treatments (addition and ambient) as subplots where zero-tension lysimeters were placed 45 cm below ground. We assessed earthworm populations semi-annually and collected leachate biweekly over a three-year period and determined leachate volume and concentrations of total inorganic nitrogen (TIN) and dissolved organic nitrogen (DON). Abundance of deep-burrowing earthworms was increased in addition treatments over ambient and for both agroecosystems. Leachate loss was similar among agroecosystems, but earthworm additions increased leachate production in the range of 4.5 to 45.2% above ambient in CT cropping. Although leachate TIN and DON concentrations were generally similar between agroecosystems or earthworm treatments, transport of TIN was significantly increased in addition treatments over ambient in CT cropping due to increased leachate volume. Losses of total nitrogen in leachate loadings were up to approximately 10% of agroecosystem N inputs. The coincidence of (i) soluble N production and availability and (ii) preferential leaching pathways formed by deep-burrowing earthworms thereby increased N losses from the CT agroecosystem at the 45-cm depth. Processing of N compounds and transport in soil water from RT cropping were more affected by management phase and largely independent of earthworm activity.

Design and hydraulic characteristics of a field-scale bi-phasic bioretention rain garden system for storm water management.

A field-scale bioretention rain garden system was constructed using a novel bi-phasic (i.e. sequence of anaerobic to aerobic) concept for improving retention and removal of storm water runoff pollutants. Hydraulic tests with bromide tracer and simulated runoff pollutants (nitrate-N, phosphate-P, Cu, Pb, and Zn) were performed in the system under a simulated continuous rainfall. The objectives of the tests were (1) to determine hydraulic characteristics of the system, and (2) to evaluate the movement of runoff pollutants through the system. For the 180 mm/24 h rainfall, the bi-phasic bioretention system effectively reduced both peak flow (approximately 70%) and runoff volume (approximately 42%). The breakthrough curves (BTCs) of bromide tracer suggest that the transport pattern of the system is similar to dispersed plug flow under this large runoff event. The BTCs of bromide showed mean 10% and 90% breakthrough times of 5.7 h and 12.5 h, respectively. Under the continuous rainfall, a significantly different transport pattern was found between each runoff pollutant. Nitrate-N was easily transported through the system with potential leaching risk from the initial soil medium, whereas phosphate-P and metals were significantly retained indicating sorption-mediated transport. These findings support the importance of hydraulics, in combination with the soil medium, when creating bioretention systems for bioremediation that are effective for various rainfall sizes and intervals.

Golf Course Applications of Near-Surface Geophysical Methods: A Case Study

As of the year 2000, there were over 15,000 golf course facilities in the U.S.A. alone. The upkeep of these facilities requires continual maintenance and occasional remodeling. The superintendents and architects responsible for the maintenance and remodeling efforts need non-destructive tools for obtaining information on shallow subsurface features within parts of the golf course, particularly tees and greens. The subsurface features of importance include, but are not limited to, constructed soil layer characteristics and drainage system infrastructure. Near-surface geophysical methods can potentially provide a non-destructive means for golf course superintendents and architects to obtain the shallow subsurface information required to address their maintenance and remodeling concerns. This case study assessment of near-surface geophysical methods in regard to golf course applications focused on electromagnetic induction (EMI) and ground penetrating radar (GPR) techniques. The investigation employed two different EMI ground conductivity meters. Two GPR systems were also tested including the evaluation of antenna center frequencies ranging from 250 to 1,000 MHz. The study incorporated three separate sites. Measurements with both EMI and GPR were collected on a tee and a green at the Muirfield Village Golf Club in Dublin, Ohio, U.S.A. and on a practice green at the Golf Club of Dublin in Dublin, Ohio, U.S.A. GPR was also tested on a golf course green at the Guelph Turfgrass Institute & Environmental Research Centre in Guelph, Ontario, Canada. Results indicate that use of the appropriate EMI equipment can provide information on spatial changes of shallow apparent electrical conductivity (ECa) within golf course green constructed soil layers. This ECa data could potentially be employed to gauge constructed soil layer conditions, including wetness, salinity, etc., within different areas of a green. GPR proved quite capable of obtaining useful information on the golf course tee and greens that were studied, at least in regard to constructed soil layer thicknesses/depths or their areal extent and in locating the subsurface drainage pipe systems present. For the GPR center antenna frequencies evaluated, ranging from 250 to 1,000 MHz, all seemed to work relatively well for mapping tee and green constructed soil layer areal extent and drainage pipe locations. The higher frequency 900 and 1,000 MHz antennas appeared to work best for resolving thicknesses/depths of constructed soil layers within the tee and greens investigated. In addition, computer modeling of synthetic GPR profiles provide valuable insight and help considerably with data interpretation. While more research is certainly warranted, near-surface geophysical methods, especially EMI and GPR, appear to show promise with respect to acquiring the data needed in golf course maintenance and remodeling applications.

Impacts of antecedant moisture and soil surface mulch coverage on water and chemical transport through a no-till soil

Abstract Flow in macropores of no-tillage soils is often implicated as a principal mechanism responsible for accelerated movement of agrochemcials into groundwater. The objective of this study was to assess the impact of a surface mulch coverage and antecedent water content on water and chemical transport characteristics in a Typic Hapludult soil. SrBr2·6H2O and atrazine were surface-applied to four undisturbed 0.3 m × 0.3 m × 0.3 m surface soil blocks. Three simulated 30 mm rains were applied to the block surfaces, and leachate was collected from 64 cells at the bottom of each block. Leachate volume, chemical amounts, and conducting macropore areas were determined for each cell and block. A parameter, m, found by fitting sorted cumulative outflow curves to an exponential function, was used to desctibe the degree of flow preference in a block. The dominant factor producing transport differences betweent the four blocks was pre-rain moisture content, which correlated negatively with degree of flow preference and positively with total leachate volume in each block. In a drier soil only the more rapid flow pathways, marked by high cell leachate volumes, contributed to the flow, while the slower pathways having greater interaction with the bulk soil were mostly truncated. This resulted in a higher degree of flow preference, smaller total leachate volumes and smaller block-averaged concentrations of Br, Sr and atrazine in soil with lower pre-rain moisture content. The peak of chemical transport was observed after the first simulated rain regardless of pre-rain moisture and surface mulch coverage. Following the second and third rains the chemical transport was reduced twofold for the less reactive Br, three-fold for the more reactive atrazine and ten-fold for Sr, apparently due to the by-pass of chemicals by subsequent leaching events. Much had little effect on water movement, but slightly enhanced the Sr and atrazine transport through the block, most likely by prolonging the chemical contact with infiltrating water at the soil surface.

The strain energy function in axial plant growth

A model for axial plant growth is formulated based on conservation of energy. The model derivation assumes that a strain energy function exists to describe the dissipation of potential energy associated with water uptake, mechanical deformation, and biosynthesis during growth. The derivation does not, however, make any further assumption on the mathematical form of this constitutive relation. The model is employed to investigate possible forms of the strain energy function as applied to steady root growth. Solutions of the nonlinear partial differential equations governing growth are given for cases when the third derivative of the strain energy function is >, <, or =0. These three cases encompass a multitude of mathematical forms of the strain energy function. The resulting solutions are compared with the realization of steady axial root growth. The results of this analysis indicate that a quadratic form of the strain energy function best described steady growth. This conclusion is consistent with previous assumptions on the form of constitutive relations for growth, and allows further interpretation on the water relations, mechanical, and biosynthetic energies associated with plant growth.

A bioenergetic model of plant root growth in soil

Abstract Crop simulation models commonly require predictive or experimental information on root growth and the distribution of roots in soil. This model calculates the elongation rate of a single root under the influence of internal biophysical and metabolic processes, and external soil physical constraints. The model is derived from consideration of energy conservation in growing root tissue. The derivation starts with a statement of the change in component thermodynamic potentials that perform the work of root growth. The result is a simplified, algebraic statement for root elongation rate as a function of tissue osmotic potential, turgor, soil water potential, mechanical impedance, biosynthetic heat production, tissue plasticity and meristematic cell production. Simulated results are in qualitative agreement with current knowledge and concepts of plant root growth in soil. The model should thus form the basis of a simplified, mechanistic tool for describing plant root growth suitable for use in crop simulation models.

Performance of Hybrid and Single-frequency Impulse GPR Antennas on USGA Sporting Greens

ABSTRACT The utility of employing ground-penetrating radar (GPR) technologies for environmental surveys can vary, depending upon the physical properties of the site. Environmental conditions can fluctuate, altering soil properties. Operator proficiency and survey methodology will also influence GPR findings. Therefore, GPR equipment performance evaluation involves standardized tests that are frequently conducted indoors within laboratory-controlled environments. This study uses outdoor United States Golf Association (USGA) putting greens as a structure for GPR testing for surveying practitioners. These USGA putting greens provide a tightly controlled environment because many golf courses and sports turf fields adhere to strict USGA construction and irrigation guidelines. Past studies on several USGA greens show that GPR provided precise and accurate profiles of root-mixture depth, gravel-blanket thickness, and drain-tile layout. Results are independent of locale, as all USGA putting greens are virtually i...

Plant uptake and accumulation of soil applied trace organic compounds: Theoretical development

Abstract A model based on the principles of network thermodynamics is presented for the simultaneous, coupled transport of water and trace organic solute throughout the plant. This application of network thermodynamics to short- and long-distance transport processes in plants is unique. The coefficients of the model are the mathematical representation of the physical, chemical, anatomical and physiological processes controlling transport and accumulation in plants. As an example a single leaf and single root representation of a soybean plant is given. Using literature values for model coefficients, the flux of water and the accumulation of a solute in the soybean plant were calculated under conditions of constant transpiration rate. The chemical was assumed to be passively transported throughout the plant. The application demonstrates how local chemical transport mechanisms play a large role in long-distance transport and tissue retention characteristics. Dynamics of the model simulation agree with uptake characteristics of organic chemicals observed experimentally.