E. van Rijn: "Disease suppression and phytosanitairy aspects of compost"

Composts are used in horticulture and agriculture as a source of organic matter and nutrients. Increasing the opportunities to use compost as a (potting) soil amendment would contribute to the recycling of waste and reduce the use of non-renewable peat and artificial fertilizers. In this study, significant disease suppressive properties (54%) or no effect (43%) were observed as a result of compost amendment, while stimulation of disease was the exception (3% of the cases). These properties showed to be dependent on compost, plant species and pathogen species involved. Indications were obtained that the microbial change of the peat substrate and rhizosphere as affected by compost amendment correlates positively with disease suppression. The results indicate that there is scope for development of products, designed specifically for certain pathosystems.

For phytosanitary risk assessment associated with the application of compost it is necessary to include all risk factors, like for example the density of infected host material. It seems safe to use VFG-composts although the conditions required for inactivation of some pathogens are still unknown. The determination of the degree of inactivation as function of temperature likely overestimates the temperature needed during composting, since factors like temporary anoxia also contribute to inactivation of pathogens as was demonstrated.