James L. Starr

FECAL COLIFORM TRANSPORT AS AFFECTED BY SURFACE CONDITION

Land application of manure is recommended to recycle organic matter and nutrients, thus enhancing the soil quality and crop productivity. However, pathogens in manure may pose a human health risk if they reach potable or recreational water resources. The objective of this study was to observe and quantify the effects of vegetated filter strips (VFS) on surface and vertical transport of fecal coliform (FC) bacteria, surrogates for bacterial pathogens, released from surface-applied bovine manure. A two-sided lysimeter with 20% slope on both sides was constructed with a sandy loam soil on one side and a clay loam soil on the other. Each side of the lysimeter was divided into two subplots (6.0 × 6.4 m), one with grass and the other with bare soil. Plots were instrumented to collect runoff samples along a 6.0 m slope at three equidistant transects. Samples of runoff were also collected in a gutter at the edge of each plot. All plots were equipped with multi-sensor capacitance moisture probes to monitor water content through the soil profile. Bovine manure was applied at the top of each plot in a 30 cm strip. Rainfall was simulated at a 61 mm h-1 intensity using a portable rainfall simulator. Surface runoff rate was measured and water quality sampled periodically throughout the simulation. Soil samples were taken at incremental depths (0-60 cm) after each simulation. Runoff (as % of total rainfall) decreased from 93% to 12% in the bare vs. vegetated clay loam plots and from 61% to 2% in the bare vs. vegetated sandy loam plots. The reduced runoff from vegetated plots decreased the surface transport of FC while increasing its vertical transport. The amount of FC in runoff (as % of applied) decreased from 68% to 1% in the bare vs. vegetated clay loam plots and from 23% to non-detectable levels in the bare vs. vegetated sandy loam plots. These data indicate that VFS can reduce surface transport of FC, even for slopes as high as 20%, especially in soils with high infiltration (e.g., sandy loam).

Real-time soil water dynamics over large areas using multisensor capacitance probes and monitoring system

Better methods are needed to accurately measure and record soil water content in real-time and at specified depths on a field scale. Recent developments of such a system using multisensor capacitance probes offers great potential for rigorous investigation of soil water dynamics over large areas. The purpose of this report is to show some of the kinds of information that can be obtained using this system to study the real-time soil water content dynamics at short time intervals (10 min), typically at four depth positions, under long-term, field-scale conditions, with our probes located as far as 125 m form the data logger. The systems have been used in the field for three years of continuous study (at 10 min increments), to study changes in soil water content, at four soil depths (commonly at 10, 20, 30, and 50 cm) as part of a research project to quantify temporal and spatial variation in soil properties under plow-tillage (PT) and no-tillage (NT) maize (Zea mays, L.). The multisensor capacitance probes and monitoring system have proven to be highly sensitive and robust for field scale soil water research. Viewing the soil water dynamics in real-time provides opportunity for precise control over the timing and amount of water that needs to be applied for optimal crop production yet avoiding excess deep percolation losses of water and agrochemicals to groundwater.

REAL-TIME SOIL PROFILE WATER CONTENT AS INFLUENCED BY WEED-CORN COMPETITION

Weeds compete with crops for belowground resources; however, there is little detailed information on relative dynamics of soil water during competitive interactions. This research was conducted to determine changes in soil-water storage (CSWS) in rain-fed no-tillage corn (Zea mays L.) production in the presence or absence of weed competition over two droughty growing seasons. Weeds at the experimental site were composed primarily of fall panicum (Panicum dichotomiflorum Michx.), which represented >90% of plants present in both years. Corn-row soil-water infiltration and losses as CSWS were studied with multisensory capacitance probes that determined water status at depths of 5-15, 15-25, 25-35, and 35-45 cm on 10-min intervals. Total biomass (corn plus weed) was higher in weedy plots than in weed-free plots. Compared with weed-free plots, corn biomass was reduced by 28% in 1998 and by 21% in 1999 by weeds; a decrease defined by the same linear rate of 0.85 g corn per 1 g of weed in both years. Early-season CSWS was higher in weedy than weed-free corn and was most likely accounted for by water accessed by the approximately 10-fold higher weed than corn population. The differential in early-season CSWS between weedy and weed-free corn was highest at the 15- to 25-cm depth, and corn biomass was most correlated with this early-season CSWS values at 15 to 25 cm. Multisensor probes allowed quantitative assessment of soil-water changes within different soil layers during the growing seasons. These results suggest that the water deficit created by early root proliferation and water uptake by weeds specifically at 15 to 25 cm was most likely the cause of corn biomass reductions in these two experimental years.

Evaluation of vegetable production management practices to reduce the ecological risk of pesticides

The ability of agricultural management practices to reduce the ecological risks of pesticides was evaluated. Risk quotients, a mathematical description of the relationship between exposure and toxicity, and hazard ratings, a rank of the potential risk of pesticides to aquatic environments, were calculated for conventional and alternative cultivation practices for tomatoes: Poly-Bare, raised beds covered with polyethylene mulch with bare-soil furrows; Poly-Rye, raised beds covered with polyethylene mulch with cereal rye (Secale cereale) grown in the furrows; and Vetch, raised beds and furrows planted with hairy vetch seed (Vicia villosa). Evaluations were conducted using measured pesticide concentrations in runoff at the edge-of-field and estimated environmental concentrations in an adjacent creek and a theoretical pond receiving the runoff. Runoff from Poly-Bare presented the greatest risk to ecosystem health and to sensitive organisms, whereas the use of Vetch minimized these risks. Previous studies have shown that harvest yields were maintained and that runoff volume, soil loss, and off-site transport of pesticides measured in runoff were reduced using the alternative management practices (Poly-Rye and Vetch). Together, these results indicate that the alternative management practices (Poly-Rye and Vetch) have a less adverse impact on the environment than the conventional management practice (Poly-Bare) while providing growers with an acceptable economic return. In addition, the present study demonstrates the need to consider the management practice when assessing the potential risks and hazards for certain pesticides.