David M. Crohn

Research Priorities for Coordinating Management of Food Safety and Water Quality

Efforts to exclude disease organisms from farms growing irrigated lettuce and leafy vegetables on Californias central coast are conflicting with traditionally accepted strategies to protect surface water quality. To begin resolving this dilemma, over 100 officials, researchers, and industry representatives gathered in April 2007 to set research priorities that could lead to effective co-management of both food safety and water quality. Following the meeting, research priorities were refined and ordered by way of a Delphi process completed by 35 meeting participants. Although water quality and food safety experts conceptualized the issues differently, there were no deep disagreements with respect to research needs. Top priority was given to investigating the fate of pathogens potentially present on farms. Intermediate priorities included characterizing the influence of specific farm management practices on food safety and improving our understanding of vector processes. A scientific subdiscipline focusing on competing risks is needed to characterize and resolve conflicts between human and environmental health.

Survival of plant pathogens in static piles of ground green waste.

Ground green waste is used as mulch in ornamental landscapes and for tree crops such as avocados. Survival of Armillaria mellea, Phytophthora cinnamomi, Sclerotinia sclerotiorum, and Tylenchulus semipenetrans was assessed for 8 weeks within unturned piles of either recently ground or partially composted green waste. S. sclerotiorum survived at the pile surface and at 10, 30, and 100 cm within the pile for the entire 8 weeks in both fresh green waste (FGW) and aged green waste (AGW). A. mellea and T. semipenetrans did not survive more than 2 days in FGW, while P. cinnamomi persisted for over 21 days in FGW. AGW was less effective in reducing pathogen viability than FGW, most likely because temperatures in AGW peaked at 45 degrees C compared with 70 degrees C in FGW. Survival modeling curves based on pile temperatures indicate the time to inactivate 10 propagules of pathogens was 11, 30, 363, and 50 days for A. mellea, P. cinnamomi, S. sclerotiorum, and T. semipenetrans, respectively. Sclerotia-forming pathogens pose the greatest risk for escape; to ensure eradication of persistent fungi, green waste stockpiles should be turned intermittently to mix pile contents and move pathogen propagules to a location within the pile where they are more likely to be killed by heat, microbial attack, or chemical degradation.

Compost Induced Soil Salinity: A New Prediction Method and Its Effect on Plant Growth

Though composts contain nutrients and can improve soils, there is widespread concern among growers in arid and semiarid regions about their salt content. We have modified an established soil hydrology model to predict the electrical conductivity (ECe) of soil-compost mixtures. The model was validated using three different soils mixed with nine different composts. This method predicted the ECe of the soil-compost mixture with a mean error of 2.7±0.2 percent. To evaluate the impact of compost salinity on plant growth, greenhouse pot experiments were conducted on lettuce, tomato, and blueberry plants amended with nine different composts. Using model predictions, compost application rates were adjusted to create soil mixtures with salinity levels similar to those associated with 10% and 25% rates of yield reduction, as reported in the scientific literature. Results indicate that compost salinity at very high rates without leaching decreases plant growth rates in a manner similar to other sources of soil salinity. However, in all cases, plant growth rates of lettuce, tomato and blueberry were significantly increased relative to the fertilized control suggesting that the benefits of compost use outweigh the possible negative influence of compost salts. At typical agricultural application rates, salinity added with compost amendments is unlikely to negatively impact plant growth.

Composts as Post-Fire Erosion Control Treatments and Their Effect on Runoff Water Quality

Abstract. Erosion from fire-damaged wildlands poses a significant water quality concern. Deprived of vegetation, runoff intensifies, which escalates exports of sediments and other pollutants. Used as mulches, composts shield the soil surface and reduce runoff by absorbing water and promoting infiltration. This field study considered three types of compost used as mulches following the controlled burn of coastal sage scrub vegetation. Nine treatments considered a coarse greenwaste compost (>9.5 mm), a fine greenwaste compost (

Nitrogen Content Curves for Small Grain Forage Crops

The export of N as a pollutant from dairies or other animal facilities can be reduced by land application programs that synchronize plant-available soil N with crop N demand. A simple, but reasonable, representation of N content over time by small grain forages is needed to assist in management of manures in dairy forage systems. Our objective in this study was to discover whether simple parameterized models averaged across a range of conditions and species could adequately predict cumulative N uptake by small grain forages over time. In order to describe N accumulation within the small grain forages commonly used for landspreading in Californias Central Valley, 22 replicated field plots, representing a variety of small grain cultivars, were established and sampled between 1997 and 2002. Crop N development over thermal time was fitted to a highly flexible logistic equation that can be used by planners as a convenient design tool. Historic harvest data can be used to parameterize the resulting function for specific field conditions. Data from the different experiments were combined in four ways so that parameterizations can be selected by users to reflect available information. When all data from all experiments were lumped together, r2 = 0.91. Use of cultivar-specific shape factors and field-specific times of maximum N uptake increased the overall r2 to 0.95. While many uncertainties due to environmental, management, and weather factors limit the precision of prediction for crop N accumulation, the use of the simple logistic relationship may be a reasonable planning alternative.

Characterizing Water Holding Capacity and Runoff during Composting of Greenwaste and Biosolids

ABSTRACT Most composters in the United States use open-windrows. During high intensity precipitation events, uncontained water running off of the surface of the compost piles can potentially contaminate surface waters with nutrients and metals. Water that is absorbed poses no runoff concern but may threaten groundwater quality. To gain insight into these processes, stormwater runoff fractions and water holding capacity of compost piles have been characterized for greenwaste (GW) and biosolids (BS) materials. Laboratory scale experiments were conducted using days 1, 7, and 14 materials representing three different stages of composting. This study also evaluated sloped and flat-top as different pile geometries and surfactant use for promoting infiltration. Results indicate that fresh materials were most hydrophobic and the infiltration rates increased with increased composting times. The water storage capacity of the compost pile increased with the age of the compost pile. Compost water storage capacities could not be reliably estimated as the difference between field capacity and as-received water contents.

A Water Quality Model for Constructed Treatment Wetlands

A mathematical model representing the hydrologic and biogeochemical processes of a wastewater treatment wetland was converted into a user-friendly computer simulation model, using Microsoft ® Visual Basic. Our objectives in developing this model were to (1) increase scientific understanding of the processes governing successful operation of constructed wetlands treating secondary wastewater (2)demonstrate the effectiveness of treatment wetland technology and (3) provide designers and operators with a user-friendly computer tool for anticipating wetland responses to common and unusual environmental circumstances. The model requires a number of input parameters regarding wetland dimensions, volume of inflow, type and quantity of vegetation, and the inflow concentrations of algae, organic N, ammonia-N, nitrate-N, CBOD, and dissolved oxygen. Using empirically-derived rate constants, plant and algae dynamics and the fate and transformation of various nutrients are modeled to ultimately predict the outflow concentrations of treated water exiting the wetland. This paper discusses the simulation program as well as the theoretical background of the model and includes examples of input data and parameter coefficients. The final section presents the results from a one-year simulation using actual data from a constructed wastewater treatment wetland near Hemet, CA and compares predicted outflow concentrations with those measured on-site.