RECYCLING OF CATTLE MANURE - THE COMPOSTING PROCESS AND CHARACTERIZATION OF MATURITY

The utilization of cattle (Bos sp.) manure as a peat substitute in greenhouses has been proposed. This alternative requires certain preparatory procedures, including composting. The objective of this research was to study the composting process, changes occurring in the product during composting and product properties of relevance to its potential use as a container medium, and to evaluate possible criteria indicating compost maturity. Composting of separated cattle manure (CSM) was studied in 1-m3 perforated boxes. Most of the physical and some of the chemical properties exhibited a high rate of change during the first 40 to 60 d of the composting process. Total water-soluble salts, as measured by electrical conductivity (EC), exhibited a constant value for the first 60 d, followed by a sharp increase in EC (from 2.6-5.4 dS m-1). The main ions contributing to this increase were NO3-, Ca2+ and Mg2+. As temperature decreased, nitrate levels increased sharply due to nitrification, from 0.02 cmol L-1 at the beginning to 4.0 cmol L-1 at the end of the composting process. Although most changes took place during the first high temperature phase, slow decomposition persisted after temperature returned to ambient level as measured in the compost water extract. Plant bioassays also indicated that 40- to 60-d old compost inhibited growth and there was limited response to fertilization. Both of these factors were eliminated after 80 to 90 d of composting. Chemical properties of water extracts may therefore serve as indicators of compost maturity and of the material's suitability as an organic component for container media.