MICROBIOLOGICALLY IMPROVED PEAT-BASED MEDIA FOR NURSERY PRODUCTION BY ADDITION OF ARBUSCULAR MYCORRHIZAL FUNGI

Autor: S. Kukkonen, M. Vestberg
Rok vydání: 2009
Předmět:
Zdroj: Acta Horticulturae. :403-410
ISSN: 2406-6168
0567-7572
Popis: Growing media based on light peat are commonly used in horticultural production. Although peat possesses a range of positive properties, it may also incur problems. Structural problems are common in long-term use. Light peat has a very low anion exchange capacity resulting in leaching of nitrate and phosphorus. Peat also lacks beneficial symbiotic arbuscular mycorrhizal fungi (AMF) which are important to crops in sustainable systems. The aim of this study was to investigate the possibilities of developing a microbiologically improved peat-based growing medium optimal for the growth of nursery and landscaping plants. It was hypothesized that the chemical, physical and biological properties of peat-based growing media can be optimized for high AMF function. The effects of light and dark Sphagnum peat and dark Carex Bryales peat were studied, as well as their mixtures with minerals like sand, pumice, vermiculite, perlite, clay or zeolite on AMF function were studied in three short-term experiments using daisy as a host plant. Light Sphagnum peat clearly suppressed the function of AMF, resulting in less growth in AMF-inoculated plants and low AMF root colonisation. In mixtures with clay, AMF root colonisation was higher, but the effect of AMF on growth was still negative. However, AMF did not usually affect plant growth negatively when decomposed Sphagnum or Carex Bryales peat was used. Compared with peat alone, the functioning of AMF was improved, especially in peat mixtures with clay or pumice. In mixtures of light and dark peat the effect of AMF inoculation was very similar to that obtained in light peat alone. These results show that the undesirable negative effect of AMF, often observed after inoculation, can at least partly be overcome by using decomposed peats and potting mixes of peat and mineral components, in particular clay. INTRODUCTION In Finland, peat has been the main raw material for industrially produced growing media, in particular in greenhouse production (Sarkka et al., 2004). Due to very large peat reserves, light Sphagnum peat has been the main raw material for horticultural use, while darker decomposed peats have been used mainly for energy production. Light Sphagnum peat possesses a range of positive characteristics, including low bulk density, good waterholding capacity and the presence of antagonistic fungi and bacteria. However, when using growing media mainly containing light peat, problems may arise. Structural problems are common especially in long-term use. Light peat has a very low anion exchange capacity resulting in leaching of nitrate and phosphorus. Peat also lacks symbiotic arbuscular mycorrhizal fungi (AMF) which can be of great benefit to crops in sustainable systems by enhancing growth and decreasing plant mortality. Certain peat qualities can even possess properties that seem to have a negative effect on AMF symbiosis. Incompatibility between AMF and peat (Vestberg et al., 2000; Linderman and Davis, 2003), the reasons of which are still largely unknown, is maybe the greatest obstacle for using AMF in peat-based growing media. Some peat producing countries have experienced a shortage of light peat suitable for horticultural use. This has created a need for developing more stable growing media Proc. IS on Growing Media 2007 Eds.: W.R. Carlile et al. Acta Hort. 819, ISHS 2009 404 for long-term production by utilizing peat of different degrees of decomposition (Bruckner, 1997). There is also a need to decrease the overall use of peat in growing media by using potting mixes including inert materials like sand, clay, vermiculite, perlite, pumice, etc. The main objective of this study was to evaluate the possibilities of increasing the biological activities in peat-based growing media for nursery plant production and landscaping plants. This could increase the general level of sustainability and decrease leaching of nutrients from nurseries and greenhouses. The work focused on developing potting mixes that are optimal for plant growth, whilst at the same time creating optimal conditions for utilization of plant-beneficial AMF. Another aim was to study the possibilities of decreasing the amount of peat in potting mixes. MATERIALS AND METHODS Three pot experiments of a split plot design with AMF inoculation as main plot and growing medium as sub-plot were carried out using an ornamental species of daisy (Leucanthemum vulgare L. ‘Maikonig’) as the test plant. Glomus mosseae BEG29 was used as the AMF treatment. Experiments 1, 2 and 3 were carried out in a greenhouse in natural light conditions between 26 April and 31 May 2006, 17 July and 5 September 2006, 28 May and 4 July 2007, respectively. The daisy seeds were first precultivated. At establishment of the experiments, seedlings were planted into 400 ml pots (VEFI A/S, Larvik, Norway), one seedling in each pot. All experiments comprised 10 replicates with one pot equalling one replicate. The types of peat tested included a commercial Finnish light Sphagnum peat B2 (H1-3 on the von Post scale) (Kekkila Oyj), a Finnish dark Sphagnum peat (H6-8) and an Estonian dark Carex Bryales peat (H7-9). The commercial peat was fertilized and limed. The Finnish and Estonian dark peats were given 8 and 3 g dolomite lime litre peat to yield an approximate pH of 6. They were also fertilized with 1.0 g L peat controlledrelease fertilizer Osmocote Plus (9-month duration, 16N-3P-10K, Sierra Chemical Europe B.V., Heerlen, the Netherlands). Peat quantities and other materials used in the potting mixes in Experiments 1-3 are shown on a volume basis in Table 1. Materials other than peat included vermiculite (3V, Vermipu Oy, Lapinjarvi, Finland), expanded clay (Leca, Maxit Oy Ab, Helsinki, Finland), attapulgite clay (Agsorb, Oil-Dri Coorporation, Chicago, USA), clay granules (2-6 mm, Bara mineraler, Bara, Sweden), clay granules (HortiClay, Lentse Potgrond en Colent, Hortimea Groep, Lent, the Netherlands), zeolite (Zeotech 300, 0.7-1.5 mm, Herbatech s.r.l, Verona, Italy), pumice (Hekla green 0.5-2.5 mm, Bara mineraler, Bara, Sweden), perlite (0.5-1.5 mm, Nordisk Perlite, Hillerod, Denmark) and sand. The results were analysed statistically using the MIXED procedure of SAS EG for Windows. RESULTS AND DISCUSSION Growth of daisy was significantly (F6,117=32.18, p
Databáze: OpenAIRE
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