Orientation towards durable use of growing media for horticulture and mushroom production

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1 Orientation towards durable use of growing media for production Gerrit Wever 1, Kees de Kreij, Simone van Woerden, Gerben Straatsma & Tineke Olijnsma Wageningen UR, Applied Plant Research, Glasshouse Horticulture & Mushrooms Kruisbroekweg 5, 2671 KL Naaldwijk, The Netherlands Peelheideweg 1, 5966 PJ America, The Netherlands Tel: Fax: G.Wever@ppo.dlo.nl Keywords: life cycle analyses, environmental legislation. Summary The social pressure for a wise use of raw materials for growing media production is getting stronger. In the Netherlands therefore the use of less durable media for glasshouse horticulture and mushroom production will have to be reduced. This goal can be achieved by developing other media or by using growing media more efficient. For this purpose a project is set up by the Dutch Ministry of Agriculture, Nature Management and Fisheries. 1 Introduction For the Dutch horticultural sector a lot of different growing media are used. In 2000 this was 6530 ha of total ha (Woerden & Bakker 2000) for Glasshouse horticulture. A grower chooses its growing medium based on technical and economical aspects and less on its durability. Just only for the Netherlands a big amount of 3.4 million m 3 of peat is used (Schie 2001). About 25% is used for pot plants (glasshouse horticulture) and about 10% for casing soil for mushrooms (table 1). Although world-wide enormous amounts of peat are available it is not a never ending story. Also consumers use more and more pressure on using durable or renewable materials. Next to peat many other materials are used as a growing medium. Mineral wool is next most used (table 2). 1.1 Regulations within Europe The main motives to use other materials as peat are the conservation of Peatlands, promoting use of waste materials and organic production. The society s responses by setting up environmental requirements, quality marks for durable media and retailers demanding peat free growing media. The ECO-label of the EU is going for peat free. For non organic production the rules are less strict. The EU waste directive (EC ) says that the compostable waste going to land fill should be reduced in 2006 by 25% (based on the situation in 1995), in 2009 by 50% and in 2016 it should be 65%. The 25% is easily met in the Netherlands by using compost as soil conditioner. There is also a working document of the EU (DG ENV.A ). There is says that public authorities and the public sector should use compost as a substitute for peat and other raw materials extracted from the environment whenever possible, in particular as a component in soil improvers, growing media, mulches, potting soil and in soil dressing for landscaping purposes. Also appropriate measures to encourage the use of compost in public procurement contracts should be established. In the Netherlands there is an ECO hallmark Milieukeur in which for many growing media standards are set concerning durability (Kamminga 2000). For peat it says that peat extracted

2 from nature reserves is only possible if there is a landscape recovery program and there should be more than 20% of bark, compost, etc. in the growing medium. The use of non peat substrates is also promoted e.g. in: Switzerland, Germany and Austria. In Switzerland they have a Suisse ECO Hall mark. The retailers in Europe ask also more and more for products from durable media. In EUREP-GAP there are not yet any standards. In the UK the retailers ask really for peat free media (Holmes et al. 2000). 1.2 Goal The ministry of Agriculture, Nature Management and Fisheries in The Netherlands promotes research to find out if existing media can be used more durable or if other materials should be developed. In this article the orientation part of this project of this 4 year project can be found. The general goal of the project is to examine all growing systems with growing media to find out how the systems can become more durable. 2 Possible scenarios for durable growing systems There are two main solutions thinkable for making growing systems for glasshouse horticulture and mushroom production more durable. The first is to use alternative products like organic fibres and compost types as a growing medium. The other way out is to use and produce materials more efficient. 2.1 Alternative media In the Netherlands different materials are used as a growing medium in glasshouse horticulture. In table 2 the main products can be found but there are many other possibilities (Wever 1999). By far peat is the main growing medium. The situation in other countries like e.g. Germany is more or less the same (Schmilewski 2000). The production of the white button mushroom is the most important mushroom product in The Netherlands. The compost for growing these mushrooms is made from wheat straw, straw bedded horse manure, chicken manure and gypsum (Straatsma et al. 1995). After the composting process an inoculation the compost is covered with limed black peat. After the growing cycle is completed the material is heated to 70 C and removed and sold as a soil improver. Of the media as used now in glasshouse horticulture peat and rockwool are the main products. There are alternatives already available (table 2) but the amounts are small. Some growth is possible for products like coir. There is a potential growth possible to app. 30 million m 3 per annum (Doren 2001). But the industry expects the growth in production will be slow and by 2015 the annual production will be about 4.5 million m 3, in 2000 it was 0.8 million m 3. The annual use of horticultural peat world wide is 35 million m 3. Also from the environmental view this is not the best substitute for peat and mineral wool. LCAs (Life Cycle Analyses) were performed for rockwool, peat, coir, pumice, UF foam and perlite (Schie 2001). It was found that from environmental perspective each substrate has its own specific strength and weakness. UF foam appears to be the least harmful. The weak point of coir and peat are extraction and transport of the raw material. Next to UF foam also good alternatives concerning the environmental aspects could be wood fibre of recycled wood (Herbold 1996). Also fibres of hemp, grass and Miscanthus seem prospective. Another possibility would be to use waste products. Special biocomposts (e.g. composted loppings) seem to be potential substrates. It would be most ideal to use composted vegetable, fruit and garden waste (VFG) as a substitute for peat. The results so far are not to good (Pronk 1995). With fertiliser adjustment, aerobic VFG composts can substitute for 15% or anaerobic

3 VFG for 15-30% of the peat in a potting medium for nurseries. Higher proportions of VFG can cause an appreciable and undesirable rise in ph and EC. But perhaps it is possible to treat the compost such that these problems can be overcome. The material can be flushed to lower the EC content. The nutritional balance and of the absorption complex can be obtained by treating the compost with a special solution as is performed for coir to remove sodium and potassium (Kipp et al. 2000). Heavy metals can be stabilised by using activated clay (Gaast et al. 2001) and the ph can be brought down by treating the product with sulphur (Lopez Aguirre et al. 1999). For all products the standard as set by Kipp et al. (2000) for chemical, physical, biological and environmental characteristics should be met. By blending and processing the products there will be many possibilities to use other materials as a growing medium.. For mushroom production also other products can be used as casing soil. The chemical and physical properties should however be the same as for the black peat now used. The strategy can be the same as for growing media for glasshouse horticulture. Many products can perhaps be used as an alternative durable growing medium. A big problem might however occur concerning the availability in the future. Competition with the energy providing industry can occur because of the Kyoto agreement. For lowering the CO 2 emission they will have to use other energy sources and organic materials are very interesting for them. 2.2 More effective use of present materials More efficient use of media can be gained by using a material longer or by enlarging the product its life cycle. Mineral wool can be recycled to new mineral wool or other materials. For this process however energy is needed. Of course growing media can be reused. Reusing a growing medium without steaming means a considerable danger because of risk of infection. Although mineral wool can be steamed the life time of mineral wool is limited because it breaks down in time (Wever & Kipp 1998). Durable mineral wool means therefore a longer lasting product by higher structure stability. More efficient use of peat in horticulture is possible by improving peat its structure stability. Research has been performed by Prasad et al. (2000) to gain more understanding concerning the breakdown of peat. They developed some techniques to predict the breakdown and found some correlations between ph and lignin content of peat with breakdown of the peat. Peat can also be recycled by reusing the product. This is done already for certain crops (bulbs) if a lower quality is no problem. Also recycled peat is sold on the Dutch market for other purposes. For the mushroom production there can be thought of lowering the addition of gypsum so the residual mixture of compost and casing soil has a higher quality and can have a wider use e.g. in glasshouse horticulture as a base for growing media. Also there can be thought of separating the casing soil form the left over compost. The left over used black peat (casing soil) will have a wider use as the mixture with the compost. 3 Conclusion More durable growing media seem possible by a longer use of a medium and or by using alternative media. The quality of a growing medium should however be guaranteed. The quality and the knowledge concerning the possibilities of product improvement (compost and fibres) are yet insufficient. For the research to be performed within the project some directions can be set based on the presented information. There are two main alternatives: to use other more durable products and or to use and produce materials more efficient. More durable products seem: UF foam, wood fibre, fibres of hemp, grass and Miscanthus. Also waste products like certain composts could be

4 used. Some supplementary fabrication steps should be added concerning the quality. More efficient use of media can be gained by using a material longer or by enlarging the product its life cycle. The structure stability of peat and mineral wool needs some attention. Also the production methods should be tested. Recycling of substrates within the agricultural sectors for high quality use should be considered. In the next phase of the project the research will be focused on one or more of the mentioned possibilities. Choosing the direction will be done with help of LCAs, to determine the most durable solution and knowledge about the possibilities for realisation. References DG ENV.A.2/LM/biowaste/2 nd draft (2001) Working document Biological treatment of biowaste. EU working document 2 nd draft. EC 31 (1999) Council Directive 1999/31/EC of 26 April 1999 on the landfill of waste. Official journal of the European Communities L 182/1. Doren, J.J.M. (2001) Coir pith potentials. Proc. International Peat Symposium, Peat in Horticulture, Peat and its alternatives in growing media. Gaast, van der N., P. Römkens & J. Japenga (2001) In situ immobilisatie zware metalen met geactiveerde klei. Fase 2: Synthese en lab-testen. Interim report 1.0 SKB SV-221. Holmes, S., S. Lightfoot-Brown & N. Bragg (2000) Peat Alternatives, A review of performance, future availability and sustainability for commercial plant production in the UK. Report ADAS Horticulture & DEFRA, Horticulture & Potatoes Division, Kamminga, H. (2000) Milieukeur substraat voor voorlopers. Vakblad voor de Bloemisterij 12 Kipp, J.A., G. Wever and C. de Kreij, International Substrate Guide. Elsevier. Lopeze Aguirre, J.G., J. Farias Larios, S. Guzaman Gonzales, A. Michel Rosales & J.R. de Freitas de Freitas (1999) Effect of sulphur application on chemical properties and microbial populations in tropical alkaline soil. Pedobiologica 43:2, Prasad, M., Verhagen, J.B.G.M. & T.G.L. Aendekerk (2000) Effect of peat type and ph on breakdown of peat using Fourier transform infrared spectroscopy. Com. Soil Sc. And Plant Anal., 31: 17-18, Pronk, A.A. (1995) Composted vegetable, fruit and garden waste as a substitute for peat in container-grown nursery stock. Acta-Horticulturae. 1995, No. 401, Schie. W.L. van (1999) Standardization of substrates. Acta Hort. 481, Schie. W.L. van (2001) Why do we need other materials than peat in growing media? Proc. Int. Peat Symp., Peat in Horticulture, Peat and its alternatives in growing media. Schmilewski, G. (2000) Sustainable horticulture with peat, A German case study. Peatlands International, 1, Straatsma, G., R.A. Samson, T.W. Olijnsma, J.P.G. Gerrits, H.J.M. Op den Camp & L.J.D. Van Griensven (1995) Bioconversion of cereal straw into mushroom compost. Can. J. Bot. 73 (Suppl. 1), Wever, G. and J.A. Kipp, Characterisation of the hydrophysical behaviour of stonewool. Proc. 16th World Congress of Soil Science. Wever, G. (1999) Growing media in The Netherlands. Proc. International Workshop on Greenhouse Production Techniques Suzhou China. Woerden, S.C. van & J.P. Bakker (2000) Kwantitatieve informatie voor de Glastuinbouw Proefstation voor Bloemisterij en Glasgroente, Naaldwijk, The Netherlands.

5 Table 1: The estimated use of peat (total 3.4 miljon m 3 per year) in the Dutch agricultural (based on Schie 1999). Sector % Sector % Raising of young plants 20 Retail market 9 Potplant production 26 Casing soil mushrooms 10 Nursery stock 12 Export 23 Table 2: The estimated amount of substrates used in the Netherlands (Schie 2001). Substrate m 3 /year Substrate m 3 /year White peat Clay Black peat Pumice Mineral wool Expanded clay Coir Rice hulls 5000 Bark Others 5000 Perlite 85000