Substitution of peat for municipal solid waste- and sewage sludge-based composts in nursery growing media: Effects on growth and nutrition of the native shrub Pistacia lentiscus L.

Abstract

In this study, the effect of a partial substitution of peat for compost on the growth and nutrition of a native shrub (Pistacia lentiscus L.) was tested. Composts were prepared from pruning and municipal solid wastes or pruning waste and sewage sludge. For preparing growing media each compost was added at a rate of 40%, fresh pine bark at 20% or 40% and peat at 20%, 40% or 60%. Aqueous extracts from the substrates did not impair germination of cress (germination bioassay). In relation to plants growing in peat-based substrate (used as a control), plants of the compost-based substrates reached better growth and nutrition, especially when using the sewage sludge-based compost, and the P uptake was notably enhanced. The concentrations of trace elements were far lower than the ranges considered phytotoxic for vascular plants. Detrimental effect derived from using fresh pine bark was not observed.

Introduction

Most nurseries in the world have based for many years their growing media on peat. However, peat is obtained from wetlands, which are being rapidly depleted, causing environmental concerns that have lead to many individual countries to limit the extent of peat mining, and prices are increasing as a result. Research on peat alternatives is of great interest in the future (Ingelmo et al., 1998, Guerrero et al., 2002, Chong, 2005, Wilson et al., 2006). In this context, different authors have suggested that some organic materials such as well-composted municipal solid waste and biosolid composts could be feasible materials for a partial peat substitution (Bugbee, 2002, Guerrero et al., 2002). The increasing interest in waste recycling is another cause to advocate the recycling and use of organic wastes and composts as soil or potting amendments; it could be one of the most attractive methods of solving the problem of waste disposal.

The combination of peat and compost in growing media is synergistic; peat often enhances aeration and water retention and compost or other additives improves the fertilizing capacity of a substrate. In addition, organic by-products and composts tend to have porosity and aeration properties comparable to those of bark or peat and, as such are ideal substitutes in propagating media (Chong, 2005).

Because the physical and chemical properties of waste and compost-based media may shift with time and source (Hicklenton et al., 2001, Hernandez-Apaolaza et al., 2005), these substrates should always be tested for local conditions. Except perhaps for bark, the use of waste by-products in nursery substrates is not well defined or scientifically documented (Chong, 2005). Organic wastes and waste-derived composts frequently have a high salt content, which may be the most important criterion that limits the potential use of organic wastes and composts in plant propagation (Chong, 2005). Other constraints for use include possible presence of contaminants (trace elements, organic chemicals, glass), potential phytotoxicity (immaturity and/or salt level, pH) and differences in species responses.

Government and commercial peat policies support and encourage the use of sustainable peat alternatives; these alternatives need to satisfy the relevant technical requirements and be readily available in sufficient quantities at reasonable cost. In efforts to use organic waste materials, composts have been utilized to successfully grow a wide range of crops including bedding annuals, perennials, sods, vegetables, woody shrubs and trees, and foliage plants. However, few studies have addressed the use of composts for containerized native shrub production (Wilson et al., 2006). Revegetation and afforestation programs for abandoned and degraded lands, encouraged recently by EU (Murillo et al., 2005), frequently make a pressure on nurseries for a massive young plant availability. Facilities for low-cost substrates other than peat-based media would be thus desirable for this purpose.

The aim of this study was to evaluate the effects of peat substitution by other alternatives, such as municipal solid waste compost, sewage sludge compost and pine bark, on growth and nutrition of the low growing Mediterranean shrub Pistacia lentiscus L.