From BioCycle Magazine May 1999, Page 62 COMPOST USERS FORUM
Microbial content of compost is helping producers and growers to understand its role as a soil inoculant and plant protector. Vicki Bess
The fact that not all compost is created equal has both producers and growers looking for ways tosuccessfully evaluate compost quality. Traditional compost analysis has focused on NPK and micronutrient concentrations in an effort to mirror fertilizer analysis. Compost, however, is much more complex than fertilizer and its most significant value to the grower may be far more than its mineral contribution to the soil. Compost has an important microbiological component that impacts how it will performas a soil inoculant and plant disease suppressant. This same living portion of the compost can determine what kind of nutrient cycling disposition the compost will add to the soil. Both growers and compost producers have become aware of the importance of this microbiological compost feature and are using it as one of the methods to determine compost quality. At BBC Laboratories, an environmentalmicrobiology laboratory in Tempe, Arizona, the microbiology of compost is evaluated by methods similar for evaluating soil microbiology. A standard analysis for microbiological content in compost is determined by the concentration of six functional groups of microorganisms: aerobic bacteria, anaerobic bacteria, fungi, actinomycetes, pseudomonads and nitrogen-fixing bacteria. Now there are ways toevaluate the concentrations of these organisms in finished compost and these serve as an interpretation guide to determine the quality of the compost as an inoculant of soil microorganisms (see Table 1). Another important indicator of compost quality includes compost maturity which is a term used to express the phytotoxic (plant-toxic) compounds that are frequently associated with unfinished orpoor quality compost. Growers having negative experiences with compost are usually the victims of immature compost, which can inhibit seed germination and cause rapid nitrogen depletion, root tissue damage or even plant death. The maturity testing includes establishing a maturity index for the compost used at two application rates as well as pH and electrical conductivity analysis. Compost, compostteas and other biological products can be tested for the ability to inhibit the growth of plant pathogens. Although this analysis is only a primary screening mechanism, there have been very good correlations between the lab results and field testing, especially if the compost or biological product tested is applied with an understanding of how the pathogen grows, how the pathogen is transmitted,and when the plant is vulnerable. If the screening proves successful, work can be continued on the isolation of specific inhibitory organisms for purposes of enhancing the compost or biological product. How Producers And Growers Improve Their Compost Dan Dinelli of North Shore Country Club in Glenview, Illinois, is concerned about overall turf health and uses compost and compost tea as a part ofhis turf management program. He naturally is interested in the disease suppressive qualities of compost as he looks for sustainable approaches to turf management. Dinelli has both traditional nutrient analysis as well as microbiological analysis performed on the different composts he uses on the golf course. By comparing these analyses with his field evaluations, he is able to draw some conclusionsabout the biological vs. nutrient impact of the compost. This is a tool he uses in choosing the appropriate compost for his turf needs. He looks at compost for general richness of microorganisms along
1 of 2
10/26/2009 8:56 AM
Evaluating Microbiology Of Compost
with specific richness in particular functional groups such as the...