Use of pruning waste compost as a component in soilless growing media
Introduction
During the last two decades, evolution of plant growth techniques and substrates has increased demands for Sphagnum peat, but the supply has been decreasing (Inbar et al., 1990). Depletion of a non-renewable resource such as peat, and environmental deterioration because of peat mining together with its high price in the market have favoured the utilization of alternative materials as growth substrates (Abad et al., 2001). Developing inexpensive and nutrient-rich organic media alternatives cannot only eliminate environmental impacts, but it also means to reduce fertilization rates, irrigation rates and nursery costs (Wilson et al., 2001).
Traditionally, residues such as urban solid wastes, sewage sludge, spent mushroom substrate and even green wastes were considered as non-desirable or with little value. Nowadays, numerous studies have demonstrated that these organic residues, after proper composting, can be used with very good results as growth media instead of peat (Verdonck, 1984, Verdonck, 1988; Raviv et al., 1986; Chen et al., 1988; Bugbee and Frink, 1989; Piamonti et al., 1997; García-Gómez et al., 2002).
Among organic residues used successfully as plant growing media is the compost from green residues. Hartz et al. (1996) found that tomato production was similar when using either peat or green waste compost mixed with perlite 50% by volume. Spiers and Fietje (2000) got similar conclusions when comparing a mixture of green waste compost (30% v/v), bark (50% v/v) and sand (20% v/v) with pine bark also for tomato production.
Literature shows great variability between pH values, electrical conductivity, or nutrient contents among these types of compost (Hegberg et al., 1991; Hartz et al., 1996; Spiers and Fietje, 2000; Benito et al., 2000), but all conclude that they must be considered as good quality plant growth substrates. The end product variability will depend not only on the predominant vegetation in the area or the composting process but the type of collection as well as the season of the year. For this reason it is essential to know the physical, chemical and biological characteristics of the material and to compare these with those required for its use as a growth medium.
Although there is a wide range of wastes that have been studied as peat substitutes, there is no information concerning the use of pruning waste compost as an alternative to commercial composts used as substrates. The closest materials to pruning waste compost are green wastes or yard wastes but they have a much larger amount of leaves and grass clippings.
The aim of the present work was to evaluate the use of compost made from pruning waste in the preparation of substrates for ornamental plants in pots in order to determine if there is any limitation to its use.
Section snippets
Materials
The Department of Parks and Gardens of the City Hall of Madrid manufactured the compost used in the present study from pruning waste, leaves and grass clippings in the composting facility of “Migas Calientes”. Although there are some seasonal variations in the quantities and characteristics of green waste in the city of Madrid, approximately 60–70% of the waste volume manufactured is woody material, mainly from pine, plane, smoothleaf elm and horse chestnut and the rest of it varies from leaves
Chemical, physical and physico-chemical characteristics of the substrates
Table 2 shows the main physical properties of the different growing media used in this study. The parameters are based on the water retention curve. Easily available water (EAW) is defined as the amount of water released between 10 and 50 cm of suction. Water buffering capacity (WBC) is the amount of water released when the suction is increased from 50 to 100 cm. Air space (AS) is the difference between porosity (or total pore space, TPS) and the water at a suction of 10 cm.
De Boodt and
Conclusions
Although more studies with different ornamental species must be done we can conclude that the PWC could be used as a growing media component. High pH values could limit its use for plants sensitive to alkaline substrate. Among the advantages which PWC can provide, low electrical conductivity, high cation exchange capacity values and a adequate total porosity space should be mentioned.
The mixes made of PWC and peat (PWC + P10 and PWC + P25) decreased pH value, improved the physical properties
Acknowledgments
The authors wish to thank the City Hall of Madrid for providing samples.
This study was supported by Polytechnic University of Madrid. Project I + D-Potential competitive groups (A9911).
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