Changes in microbial and nutrient composition associated with rumen content compost incubation Karuna Shrestha a,⇑ , Pramod Shrestha a , Eric M. Adetutu b , Kerry B. Walsh a , Keith M. Harrower a , Andrew S. Ball b , David J. Midmore a a Centre for Plant and Water Science (CPWS), Department of Medical and Applied Science, CQUniversity, Rockhampton, 4702 QLD, Australia b School of Biological Sciences, Faculty of Science and Engineering, Flinders University, Adelaide, 5001 SA, Australia article info Article history: Received 9 August 2010 Received in revised form 11 November 2010 Accepted 19 November 2010 Available online 25 November 2010 Keywords: Compost extract Microbial respiration FDA hydrolysis Biolog™ PCR–DGGE abstract Physico-chemical and microbiological investigations were carried out on rumen content material com- posted for nine months, fresh vermicasts (obtained after passing the same compost through the guts of a mixture of three species of earthworms: Eisenia fetida, Lumbricus rubellus and Perionyx excavates) and microbially enhanced extracts derived from rumen compost, vermicast and vermicast leachate incu- bated for up to 48 h. Compared to composted rumen contents, vermicast was only improved in terms of microbial biomass C, while vermicast leached extract was significantly higher in NH þ 4 -N; PO  4 -P, humic acid, bacterial counts and total microbial activity compared to rumen compost extract. Although no dif- ference between treatments was observed in genetic diversity as indicated by DGGE analysis, community level functional diversity of vermicast leached extract (Biolog™) was higher than that of composted rumen contents, vermicast and rumen compost extract indicating an enhancement of microbial activity rather than diversity due to liquid incubation. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Composting is a process of aerobic decomposition of organic matter under controlled conditions by microbiota, producing a sta- ble organic end product, with carbon-dioxide, water and heat pro- duced as by-products (Rynk et al., 1992). For large scale composting activity, point sources of organic material of uniform quality is required. One such material is the partially digested ru- men contents of cattle, viewed as a waste in abattoir operations. For example, the two abattoirs in Rockhampton slaughter approx- imately 1700 head a day, producing 140 cubic meters of rumen content per day (R. Lang, pers. comm.). Vermicomposting is a process of biotransforming and stabilis- ing organic materials (often waste) into humus (Neuhauser et al., 1988) by the combined activity of earthworms and microorgan- isms (Aira and Dominguez, 2008). Earthworms excrete partially di- gested materials (Parmelee et al., 1990), known as vermicasts or castings, which are more homogeneous in composition than the source material (Albanell et al., 1988), have reduced levels of con- tamination (Ndegwa and Thompson, 2000), and contain elevated levels of plant growth regulators and/or symbiotic microbes (Kale et al., 1992) and organic acids such as humic and fulvic acids (Edwards et al., 2006). There is an emerging commercial trend of aerobically incubat- ing an extract of compost with a carbohydrate and a protein source, producing a microbially enhanced liquid (Ingham, 1999; Pant et al., 2009). Known by the agricultural sector as ‘compost teas’ in the current study this microbially enhanced product is termed ‘‘Compost Extract’’ or ‘‘CE’’ in short. Compost extract con- tains nutrients extracted from compost and thus contributes di- rectly to plant nutrition, and also contains organic matter, improving soil structure and water holding capacity by building soil aggregates. Compost extracts derived from vermicomposts have proven benefits in terms of growth and yield promotion of various agricultural crops (Pant et al., 2009; Tejada et al., 2008). Moreover, compost extract adds microorganisms to the soil and ‘brings the soil back to life’ (Martens, 2001). However, at the typi- cally employed rates of application of 150–200 L/ha, the funda- mental aim of compost extract application is to alter soil microbial populations towards a more plant beneficial community (Hoitink and Boehm, 1999). Many researchers have characterised the composting process (Singh and Sharma, 2002; Vivas et al., 2009), however, there is little documentation on the shift in microbial diversity during the incu- bation and extraction process. Therefore, a comparative study was undertaken on the effect of vermicomposting of rumen content compost and of an extract enhancement process. Physico-chemical, biochemical and microbial characteristics were monitored on the following: rumen compost extract (RCE), vermicast extract 0960-8524/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2010.11.087 ⇑ Corresponding author. Tel.: +61 749232315; fax: +61 749309255. E-mail address: k.shrestha@cqu.edu.au (K. Shrestha). Bioresource Technology 102 (2011) 3848–3854 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech