Rick Carr

Rick Carr

Rick Carr

Speaker | Rodale Institute

Kutztown, PA | (610) 683-1415 | rick.carr@rodaleinstitute.org

USCC Member

Rick Carr is the Compost Production Specialist at Rodale Institute in Kutztown, PA. He has spent much of his career studying compost science and utilization, from the laboratory to the field to large-scale production, on topics such as plant disease suppression, nutrient management, and the dynamics of biological decomposition during composting. His work has been presented at regional, national and international conferences, including the USCC Conference.

Presentation One: “Nutrient Dynamics in Windrow Composting”

Session: “CCREF Research Reports”

Time: Tuesday, January 29, 8:15 AM – 9:45 AM

Presentation Summary: Composted substrates provide a diversity of nutrients for plant growth and development. Compost producers can create feedstock recipes that will provide predictable results in compost nutrient content over time, which is attractive to end-users such as landscapers and the agricultural community. However, many composting operations use a variety of feedstocks to generate compost and the nutrient profile may not be as predictable. For instance, certain feedstocks are able to influence the nutrient profile of cured compost, and while part of the goal is organics recycling, some end-users prefer consistent nutrients when amending with compost. Over the last five years, Rodale Institute has been monitoring the nutrient content of finished compost to gain a better understanding of the chemical variability in a large-scale windrow composting operation. Windrows were prepared with a variety of agricultural and municipal compost feedstocks and percent content of each feedstock was measured. Time and temperature was documented in accordance with the USDA National Organic Program. Moisture content, bulk density, volume reduction, weed seed germination and amendment rate bioassays were several other metrics used to further characterize the composting process and finished material. Compost ready for land or greenhouse application was sampled and submitted to Penn State’s Agricultural Analytical Services Lab for compost nutrient analysis. A total of 36 different windrows were sample to date, and the results were analyzed for linear correlations among (1) feedstock content, (2) age of compost at the time of testing, and (3) various chemical properties.Average chemical/biochemical properties were as follows: pH 7.7 (± 0.4), soluble salts 4.6 (± 2.1) mmhos/cm, solids 47.7% (± 8.0), moisture 52.3% (± 8.0), and organic matter 22.8% (± 5.2). Average macronutrient content varied less than most micronutrients that were measured. Linear correlations existed when the percent mixture of leaves:grass was tested. Total nitrogen(N), phosphorus(P), and potassium (K) increased with increasing grass, as well as soluble salt content. When percent grass content in a windrow was held constant and leaves:wood chips was tested there was little to no correlation in total N and P, percent carbon, and organic matter; however, total K and soluble salts tended to increase with increasing wood chip content. These results and several others including micronutrient dynamics in changing compost recipes will be discussed so that compost producers may have a better understanding of the relationship between feedstock recipes and subsequent nutrient content in finished compost.

Presentation Two: “Understanding the Mechanisms of Compost-Mediated Plant Disease Suppression”

Session: “Compost Uses and Markets: Step It Up a Notch”

Time: Wednesday, January 30, 2:00 PM – 3:30 PM

Presentation Summary: Compost and other organic amendments are increasingly being used in agriculture to minimize losses from plant diseases. However, disease suppression with composts has been quite variable, limiting the widespread adoption of compost applications to control plant diseases in diverse cropping systems. Developing a better understanding of how composts suppress pathogens and diseases could increase the predictability of compost-induced disease suppression and, thereby, improve their effectiveness. Despite numerous investigations of compost-induced disease suppression, our understanding of the mechanisms that may lead to disease suppression remain insufficient to predict the pathosystems, soil conditions, and environmental conditions for which disease suppression may occur. Previous approaches to identify factors involved in disease suppression have focused largely on comparative analyses of the bulk properties of suppressive and nonsuppressive composts. A consistent pattern that has emerged from these studies is the central role of microbial activity in compost-induced disease suppression. These studies elucidate the mechanisms commonly associated with disease suppression that is observed when we apply compost and the working hypothesis is that compost suppresses pathogens via(1) nutrient competition, (2) parasitism, (3) antibiosis, and (4) induced systemic resistance (ISR). Nutrient competition occurs when a plant pathogen and the microorganisms found in compost compete for the same resource. For example, competition for plant exudates has been well documented. Several soil-borne plant pathogens are attracted to host plants through seed and root exudates. When compost microbes consume or alter exudates than the host is no longer detectable to the pathogen and suppression occurs. Parasitism is where one organism eats another. Trichoderma harzianum is a biocontrol fungus and a common example of where parasitism occurs in compost-mediated disease suppression. The hyphae of T. harzianum will wind around a pathogen, puncture its cell wall and consume the pathogen. Antibiosis refers to the ability of a biocontrol microorganism to produce antibiotics. Bacterial species such as Bacillus and Psuedomonas naturally produce antibiotics that are toxic to plant pathogens and eventually kill the pathogen. With ISR, a beneficial bacterium stimulates what can be loosely considered the plant’s ‘immune system’ so that it can protect itself from invading pathogens. These mechanisms, and a few others that have been recently identified, will be reviewed during the presentation in the context of cases studies and specific plant-pathogen interactions.