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ISHS Acta Horticulturae 982: International Symposium on Responsible Peatland Management and Growing Media Production

COMPOSTS IN GROWING MEDIA: WHAT'S NEW AND WHAT'S NEXT?

Author:   M. Raviv
Keywords:   compost, growing media, nutrition, peat moss, physical properties, suppressiveness
DOI:   10.17660/ActaHortic.2013.982.3
Abstract:
In the last decades the fraction of fresh produce and cut flowers that are grown in soilless media are constantly growing due to the inherent advantages of substrates over soils. Peat moss is being used for many years as a main component of soilless media, mainly due to its excellent physical properties. Recently peat is frequently replaced by a variety of recycled, aerobically-stabilized materials, also known as composts. This trend is driven by the societal need to recycle organic wastes in an environmentally-sensitive manner, by the rising cost of peat and by peat conduciveness to several soil-borne diseases. Proper composting of many types of organic wastes achieves a number of important objectives. It should eliminate phytotoxicity, pathogens and weed seeds, and stabilize the material with respect to N and oxygen demand of microorganisms. In addition, some composts are suppressive against several soil-borne diseases. Compost maturity is a crucial characteristic in relation to its use in growing media. It ensures minimal medium shrinkage, oxygen consumption, nitrogen immobilization and phytotoxicity. Feedstocks for composts include bark, sawdust, spent mushroom compost, grape marc, composted green wastes, rice hulls, animal manures, biowaste and others. Limitations to the use of composts in growing media are their physical properties (high bulk density, low content of easily available water), salinity, high pH and rate of residual degradation with time. As a result, normally the fraction of the compost in the mixture should not exceed 50%, although some exceptions exist. Advantages of composts as ingredients of growing media include their low cost, nutritional contribution and suppressiveness against soil-borne diseases. A clear advantage of composts used in substrates is that most of them can be further recycled, after the end of the growing cycle, by soil application. Required future research includes the effect of composting techniques and feedstocks on compost characteristics and predicted performance. The effect of compost storage on the shelf life of its desirable properties should also be studied.

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