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ŠUMARSKI LIST 11-12/2020 str. 30     <-- 30 -->        PDF

et al. 2011). To satisfy higher yields and quality, it is important to find a substrate or substrate mixtures with a good performance. Therefore, there is a need for search of new materials and/or mixtures that reduces the high-priced peat content in substrates.
Diatomite (Diatomaceous Earth or DE) is a sedimentary rock primarily composed of the fossilized remains of unicellular freshwater plants known as “diatoms”. Diatomite contains up to 80-90% voids (Khraisheh et al. 2004) and has a large surface area of 50-200 m g-1 (Wu et al. 2005). Diatomite consists of approximately 90% silicon dioxide, which is absorbed into plant tissues and helps to improve plant structure and resistance to pests and diseases. The remainder of its being elemental minerals, which are essential for plant growth (USGS 2008). Recent studies conducted by Aksakal et al. (2012, 2013) have indicated that diatomite might be an alternative soil amendment agent for improving soil physical and mechanical characteristics. Angin et al. (2011) have studied the effects of diatomite on the growth of strawberry and find out that diatomite application not only improved hydro-physical properties of soil but also vegetative parameters of strawberry. All of above-mentioned features and conducted studies have shown that diatomite can be used as an alternative substrate for peat. However, the most limiting factor for its use as a growing media is its organic matter content, which is relatively low.
Sewage sludge is a concentrated suspension of solids, largely composed of organic compounds, plant nutrients, trace elements, inorganic materials, and pathogens (Epstein 2003). The organic nature of sewage sludge, along with plant nutrients and several trace elements, shows that it has great potential for improving soil fertility and crop productivity. The potential outlets commonly considered for sewage sludge use and disposal can be classified as; land-based, product-based, energy recovery, and landfill disposal. The preferred and common management option for sewage sludge is beneficial to use on land, particularly for agricultural production and forestry. Use in this way not only ensures that nutrients and organic matter are recycled to the soil to enhance crop production but also reduces the use of chemical fertilizers. In Turkey, more than 1 million tonnes of sewage sludge is generated each year (Aslantas et al. 2013). Using sewage sludge as a substrate could be a feasible option, especially not only for the protection of the environment but also for decreasing the fertilizer cost. The positive effect of sewage sludge usage as a substitute for peat and soil has been reported by several studies (Raviv et al. 1986; Pinamonti et al. 1997; Ingelmo et al. 1998; Perez-Murcia et al. 2006; Jayasinghe et al. 2010; Méndez et al. 2017). However, its usage along with diatomite as a media component for nursery growth is not investigated yet.
This study was undertaken to evaluate (a) the feasibility of reducing the peat content in substrates by replacing it with different amounts of diatomite and sewage sludge for Scots pine seedling (Pinus sylvestris L.) growth and (b) evaluation of the land performance of Scots pine seedlings grown in different substrates.
In order to evaluate the feasibility of reducing the peat content in substrates by replacing it with different amounts of diatomite and sewage sludge, an experiment was carried out in a temperature-controlled greenhouse under natural light, from 11 April to 22 October 2013, in Erzurum Forestry Research Station, Turkey (39°55´N, 41°61´E). The temperature in the greenhouse was set to 24±2°C and 18±2°C during day and night, respectively. Diatomite (DE) and sewage sludge (SS) passed through 8-mm sieve was applied along with or without peat (P) within the rates (v/v) of 100%SS (1); 25%SS+75%DE (2); 75%SS+25%DE (3); 50%SS+50%DE (4); 25%P+75%DE (5); 25%P+75%SS (6); 25%P+50%DE+25%SS (7); 25%P+25%DE+50%SS (8); 50%P+50%SS (9); 50%P+25%DE+25%SS (10); 50%P+50%DE (11); 75%P+25%DE (12); 75%P+25%SS (13); 100%P (14, Control); and 100%DE (15). General characteristics of the materials used in this study are given in Table 1. pH and electrical conductivity measurements were carried out according to Thomas (1996) and Rhoades (1996). Organic matter was determined using the Smith-Weldon method (Nelson and Sommers 1996). Lime content of the substrates was determined with the ‘Scheibler Calcimeter’ as described in Loeppert and Suarez (1996). A wavelength dispersive X-ray fluorescence spectrometer from Rigaku (ZSX-100e, Rigaku Industrial Corporation, Japan) was used to determine the chemical components of substrates.
Mixtures with defined amounts were conveyed to seedling trays, with an internal cell volume of 190 cc. The used Scots pine (Pinus sylvestris L.) seeds were “Sarıkamış” originated. Two seeds were sown per cell and after 5 days of sowing, they were thinned to one seedling. The experiment was set up in a randomized block design with 15 mixtures and with three replications, as a total of 1170 seeds (15 mixture × 26 Scots pine seeds × 3 replications). No pesticide and fertilizer were applied throughout the experiment. At the end of the experiment (22 October 2013) 10 seedlings from each replication were collected and analyzed for the determination of height, stem diameter, and shoot and root dry weight. Dickson Quality Index (QI) was calculated from the obtained values according to Dickson et al (1960).
To evaluate the land performance of Scots pine seedlings grown in different substrates, a trial was established