Use of herbage compost as horticultural substrate and source of plant nutrients

The potential of herbage composts as horticultural substrate and source of nutrients was investigated. The effect of botanical composition of the herb age, as well as the effect of different kinds and amounts of carbon sources , on nitrogen losses during composting and growth properties of the compost were studied. Growth tests with different plant species as well as chemica l analyses of total- and easily-soluble plant nutrients were used to evalua te compost quality. Seven herbage composts were studied and used in growth tests with seven different test plants. The results were evaluated by conve ntional and multivariate statistical methods. Accumulated nitrogen losses tended to vary with carbon source added, and we re 2-25% of the initial N content over a 130-day composting period. Plant g rowth and seed germination were largely explained by the electrical conduct ivity of the compost mixes. Potassium concentrations were very high in the composts. The results showed the possibility of using herbage composts as p art of a substrate for container-grown vegetables and flowers. All of the c omposts which were tested required mixing with nutrient-poor material in or der to become a suitable substrate, mainly to avoid excessive conductivity. In a substrate based on sphagnum peat, 10-100% of the peat might be substi tuted with herbage compost, depending on the amount of carbon source added during composting. A considerable amount of the plant nutrients needed in t he substrate for the initial six weeks of plant growth was found to be supp lied by the herbage compost.