Compost Science Complete scientific data on compost process control and end product quality

PERSPECTIVE

CSU Winter, 2005, Vol. 13, No. 1, p. 3

FROM VERMICOMPOSTING TO MICROBIAL RECOLONIZATION
THE FULL RANGE of research studies into the many areas of composting has been well apparent to readers of Compost Science & Utilization since it began publication in 1993. This Winter 2005 issue provides another example on this continuum.

The first paper reports results comparing nutrient concentrations in composts and vermicomposts from a facility in Patagonia, Spain. “Our results suggest that: 1. Compared to composting, vermicomposting leads to a product richer in available nutrients, associated with a higher hydrolytic activity and lower microbial population size, and 2. Microbial biomass and dehydrogenase activities are stimulated in compost and vermicompost that have undergone a thermophilic phase,” observed Tognetti et al. (see p. 6). They also note the difficulty in making generalizations regarding superior quality.
Examining the nature of compost maturity and the “fast changes in physicochemical and microbiological properties,” Claudio Mondini of the Experimental Institute for Plant Nutrition in Gorizia, Italy and Heribert Insam of the University of Innsbruck in Austria note that standardization of inoculum density appears to be one of the most important factors to interpret data. They conclude in their report which begins on p. 27: “The good separation of compost samples suggests that estimation of the content of whole microbial biomass with substrate induced respiration (SIR) is a suitable technique for standardization of initial inoculum density.”
Looking at management for manure in coldwater aquaculture production systems, Paul Adler and Lawrence Sikora of the USDA Agricultural Research Service search for methods to achieve volume reduction and stabilization. As part of their findings, they observe that mesophilic composting of high liquid content manures does not require excess carbon to reduce water content as is needed with thermophilic composting. ... It is a less resource intense system and is a practical technology that could be readily adopted on fish farms, and other farms with liquid manure systems, using current equipment.”
The topic of disease suppression from compost application continues to be a major research area. In this issue (p. 43) it is illustrated by studies in Idaho on potato crops. “It has been estimated that economic losses to producers in the United States from phasing out fumigation of soils with methyl bromide will be $800 to $900 million. Our study provides some evidence that changing the soil environment to favor biological control or indigenous soil microorganisms to control soil pathogens may give producers an alternative to soil fumigants.”
The avoidance of problems with heavy metal accumulation from long-term application of organic residuals is presented by University of Florida investigators, Monica Ozores-Hampton, Philip Stansly and Tom Obreza (p. 60). Their findings: “Long-term additions of organic amendments such as biosolids and composted organic materials (at the rates tested) did not increase heavy metal loading rates nor increase their concentrations in pepper fruit. Thus, this practice can be considered safe in regard to pollution from heavy metals in Florida's sandy soils.”
The topic of “microbial recolonization” following compost applications is reported by Oregon researchers Steven Scheurell and Walter Mahaffee (p. 65). Their data indicate that disease suppression is biological in nature and due to the introduction of microorganisms from exogenous sources and not from growth of microflora surviving the heating process. “Manipulating compost curing with rapid decreases in compost temperature can create relative microbial voids; filling the void with microbial antagonists could help the nursery industry consistently use a source of naturally disease suppressive material.” - J.G.