Biosolids compost as component of potting media for bedding plants

Abstract

Soilless potting substrates are increasingly used in greenhouse production of bedding plants replacing soil as growth media. These substrates usually consist of a mixture of organic materials like peat or pine bark and inorganic substances such as perlite, vermiculite or sand. Among other possibilities, compost made from municipal and industrial sludges and other solid wastes can effectively replace both peat and soils as they imply little risk to human or to the environment. The objective of this study was to evaluate the effects of different proportions of biosolids compost in substrate mixtures on growth and quality performance for two bedding plants (Petunia hybrida and Vinca sp.). Pots containing different proportions (0 to 100 %) of biosolids compost were used to grow both crops under greenhouse conditions. In plants were determined height, diameter, flower fresh weight, fresh aerial biomass without flowers, leaf area, flower area, number of floral stems, number of flowers, total N, P and K in aerial biomass without flowers. At the end of the experiment particle size distribution, bulk density, degree of compaction, water holding curves, pH, electrical conductivity, total nitrogen and available phosphorus were determined in substrates. Substrates with compost in its composition showed predominance of medium particle distribution. Bulk density and the degree of compaction were higher than the ideal range in treatment 75 to 100 % of compost. The treatments 25 to 75 % compost, were more adequate for normal water supply to roots. Substrates pH varied between 5.4 and 6.0, and the electrical conductivity (1:10) between 0.14 and 0.43 dS m–1. Both plants exhibited adequate vegetative and reproductive parameters in substrates composed of different proportion of compost of biosolids. In Petunia, the differences in plant parameters found among treatments can be mainly attributed to water availability and substrate salt content. Vinca was also related to water availability and substrate pH. Our results indicate that, in horticultural production, peat and soil can be partially replaced by biosolids compost. Considering the different plant parameters, the substrate with 25 % of biosolids compost could be selected among those that produce the best plant quality in both studied species. The substrate made up of only compost of biosolids cannot be considered a commercial alternative