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Numerous studies have demonstrated that water-based compost preparations, referred to as compost tea and compost-water extract, can suppress phytopathogens and plant diseases. Despite its potential, compost tea has generally been considered as inadequate for use as a biocontrol agent in conventional cropping systems but important to organic producers who have limited disease control options. The major impediments to the use of compost tea have been the lessthan-desirable and inconsistent levels of plant disease suppression as influenced by compost tea production and application factors including compost source and maturity, brewing time and aeration, dilution and application rate and application frequency. Although the mechanisms involved in disease suppression are not fully understood, sterilization of compost tea has generally resulted in a loss in disease suppressiveness. This indicates that the mechanisms of suppression are often, or predominantly, biological, although physico-chemical factors have also been implicated. Increasing the use of molecular approaches, such as metagenomics, metaproteomics, metatranscriptomics and metaproteogenomics should prove useful in better understanding the relationships between microbial abundance, diversity, functions and disease suppressive efficacy of compost tea. Such investigations are crucial in developing protocols for optimizing the compost tea production process so as to maximize disease suppressive effect without exposing the manufacturer or user to the risk of human pathogens. To this end, it is recommended that compost tea be used as part of an integrated disease management system.

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Trinidad and TobagoStudies were undertaken to determine the effects and relationships of compost type, aeration, and brewing time on compost tea properties, phytotoxicity, and efficacy in inhibiting growth of Pythium ultimum in vitro. The effect of compost tea on dry matter of tomato and sweet pepper seedlings cultivated on compost-amended substrate was also investigated. Compost type, aeration, and brewing time significantly affected the microbial and chemical properties of compost teas made from banana leaf (BLC) and lawn clipping (LCC) composts. Both aerated and nonaerated compost teas made from BL and LC composts significantly inhibited mycelial growth of P. ultimum. However, growth inhibition (GI) levels were significantly higher in compost teas produced from LCC. Aerating compost tea (ACT) did not consistently result in higher GI levels across compost types. Neither did increasing brewing time beyond 18 h for ACT and 56 h for nonaerated compost tea (NCT). Across all ACTs, yeast population was positively related to GI whereas bacterial population had a positive relationship with GI across all NCTs. Evidence suggests that multiple groups of microorganisms contributed to GI through antibiosis and competition for resources. All compost teas stimulated seed germination of tomato and root growth in sweet pepper. However, NCTs brewed for 56 h using LCC or BLC, and ACT produced from BLC brewed for 18 h, significantly reduced seed germination of sweet pepper. Application of NCT brewed for 168 h made from BLC significantly increased total dry matter of tomato seedlings by 122% compared with the control.

High-rate composting studies on green waste, i.e. banana leaves (BL) and lawn clippings (LC), were conducted in 0.25-m3 rotary barrel composters to evaluate and model changes in key physico-chemical parameters during composting. Time to compost maturity and antagonistic effects and relationships of composts against Pythium ultimum were also investigated. Higher temperatures were achieved in LC compost (LCC), which did not translate to higher total organic carbon (TOC) loss but resulted in lower carbon to nitrogen ratio (C:N) and a more mature compost. With the exception of electrical conductivity (EC), net decreases were observed in pH, TOC and C:N across compost types. Total Kjeldahl nitrogen (TKN) showed a net increase in LCC and a net decrease in BLC. With the exception of TOC and pH, the results showed that compost type and time had a significant effect on the respective TKN, EC and C:N models. Compost temperature and TOC were best described by the critical exponential and rectangular hyperbola functions, respectively. Whereas TKN, C:N and pH were described using double Fourier functions and EC using Fourier functions. Composts achieved maturity within 19 days and significantly inhibited the growth of P. ultimum. Bacterial population was positively related to growth inhibition (GI) across compost types, whereas total microbial population had a positive relationship with GI in LCC. Evidence suggests that multiple groups of microorganisms contributed to GI through antibiosis and competition for resources. Composts were determined to be suitable for use as components of plant growth substrates based on compost maturity indices.