Vermicompost as Substrate Amendment for Tomato Transplant Production

Vermicompost may be a promising substitute for peat especially in transplant production. Vermicomposting is a sustainable solution for management of organic wastes. However, due to variability of organic wastes, vermicomposts might have varying nutrient content levels. The study compared vermicomposts from different sources on growth and nutrition of tomato (Solanum lycopersicum L.) transplants. Chemical composition of vermicomposts differed. Common characteristics were high pH and very high electrical conductivity. All vermicomposts stimulated growth of tomato transplants, with up to a 2.2-fold increase occurring in shoot biomass. Differences in growth were attributed mainly to differences in nutrient content of the potting mixtures, but some changes in physical and biological properties of the substrate could also be responsible.


Introduction
Profitability of high-value crops, such as tomato (Solanum lycopersicum L.) necessitates detail cultural management to ensure crop required growing conditions.Production of high quality transplants is a key factor for success.Adequate root and aerial biomass of tomato transplants assure an improved ability to exploit soil resources and higher photosynthetic capacity.Potential consequences are enhanced crop yield and improved fruit quality (Zaller, 2007;Lazcano, Arnold, Tato, Zaller, & Domíngues, 2009).
The choice of growing media is considered a challenge for production of seedlings for transplanting.The medium nutritional quality, structure and stability are of primary importance.Peat is widely used as a component of potting mixes in conventional and organic production but increased concern has risen due to exploitation of these slowly renewable natural resources and degradation of valuable peatland ecosystems (Lappalainen, 1996;Carlile, 2004).Increasing pressure against peat extraction and the demand for low cost substrates leads to an increasing interest on substituting peat with other materials.

Material and Methods
The experiment was conducted during 2010 in a growth chamber (22-25 o C; 14/10 hrs day/night; maximum light intensity 400 μmol•m -2 •s -1 supplied by 36W fluorescent tubes) at the Maritsa Vegetable Crops Research Institute, Plovdiv, Bulgaria.Tomato seed, cv.Miliana, were sown, one seed per cell, in foamed polystyrene plug trays with 198 inverted pyramid cells, filled with peat moss and perlite in the ratio of 1:1 (v/v).Fertilized milled peat (Rekyva AB, Šiauliai, Lithuania), containing 1.0 kg•m -3 of complex PG-Mix™ 14•16•18 fertilizer (Hydro Agri, Yara International ASA, Norway) was used.At the first true leaf stage seedlings were transplanted into plastic pots containing 0.5 L of a mix of peat moss and perlite (1:1 v/v) to which 10% vermicompost was added to all treatments but the control.

Vermicompost Sources
Mature vermicomposts, obtained from five commercial farms located in Bulgaria, were used.All vermicomposts were produced with the "bed" method, which involves applying thin layers of partially matured manure to the surface of beds made up of porous sheets and containing high densities of earthworms (Lumbricus rubellus Hoffmeister, 1843).The commercial products tested were: 1) Biohumus MM (Ecofarm Marinov ECO, Kujlevcha, Bulgaria) produced in northeastern Bulgaria in which fresh manure was settled for 3-4 months under anaerobic conditions, then 80% cow dung and 20% horse dung were added to beds (1-2 m W×0.4-0.5 m H×varying L).Earthworms had been active at least one year and the final product was sieved through 5 mm mesh; 2) Biohumus NN (Ecofarm Nikolova, Panayot Volov, Bulgaria) produced in northeastern Bulgaria in which 4-5 month old cattle dung was placed in beds (2×0.4-0.5×up to 25 m, W×H×L) -earthworms had been active for approximately one year, and the final product sieved through 5 mm mesh; 3) Chirpan vermicompost (Ecofarm Velkov, Chirpan, Bulgaria) was produced in southcentral Bulgaria in which partially decomposed cattle manure (settled for 2-3 months under anaerobic conditions) was applied to beds (1×1×up to 20 m, W×L×H) -the earthworms had been active from April to the end of November and the final product was not sieved; 4) Lumbrical (Ecofarm T. Prazova, Kostievo, Bulgaria) produced in southern Bulgaria was made from cow, pig and horse dung, partially decomposed under anaerobic conditions (settled for 2-3 months to decrease NH 3 content) and mixed so that final product contained 95% cow and 5% pig + horse dung, with the mix placed in beds (1.2-1.5×0.4-0.5×up to 20 m, W×H×L)-earthworms had been active for approximately one year, and he final product sieved through 5-10 mm mesh, and 5) WasteNoMore (Waste No More Farm, Kazanlak, Bulgaria) produced in southcentral Bulgaria made from cattle dung stored for 2-3 years under anaerobic conditions and placed in vermi beds of varying dimensions -earthworms had been active for approximately one year, and the final product sieved through 3 mm mesh.

Experimental Design
The experiment was repeated twice; each lasting 40 days.Treatments were: 1. Control-mixture of peat and perlite 1:1 (v/v), no verimcompost; 2. Biohumus MM; 3. Biohumus NN; 4. Chirpan vermicompost; 5. Lumbrical and 6.Waste no more.Each treatment was replicated three times and each replication was composed of 10 plants.All pots were set in the same growth chamber, arranged in a randomized complete block design.Plants were irrigated with 100 mL non-chlorinated water twice a week.

Compost/Substrate Analysis
Vermicompost samples were analyzed to characterize chemical and physico-chemical properties.Samples from each treatment were analyzed before planting, to determine initial nutrient content.Analysis were performed as follows: plant available P and K-in Ca-lactate extract followed by colorimetric (P) and flame photometric (K) determination; pH, electrical conductivity (EC) and water soluble nutrients were determined in aqueous extracts 1:1.5 (v/v) (Soneveld, van den Ende, & van Dijk, 1974).The following were quantified: NO 3 --ion-selective analysis; Р-colorimetric Mo blue reaction; K-flame photometery; Ca and Mg-complexometrically with EDTA; and organic matter content determined by dry combustion at 550°C.

Plant Analysis
N, P and K were quantified in dried shoots at the end of the experiment by: N-Kjeldahl method; P and Kcolorimetry and flamephotometry, respectively, after dry ashing and subsequent extraction with 2 M HCl.

Microbiological Analysis
Total microbial populations of bacteria and fungi from vermicomposts were enumerated using dilution plates on appropriate medium to support growth of microorganisms; Potato Dextrose Agar for fungi and Nutrient Agar for bacteria.

Plant Growth Analysis
At the end of the experiment shoot fresh weight, shoot length (distance from the substrate level to the top node), leaf number (excluding cotyledons), and leaf area were determined.

Statistical analysis
All results are means of three replicates.Data were subjected to Duncan's Multiple Range Test to separate means.Regression analysis was used to determine relationships between growth parameters and amounts of nutrients supplied by vermicomposts as well as between amounts of nutrients supplied by vermicomposts and nutrient concentrations in plant tissues.

Comparison of Physicochemical, Chemical and Biological Properties of Vermicomposts
The vermicomposts differed in amounts of macronutrients (Table 1).The pH of vermicomposts was not different (avg.pH 7.62) but higher than optimal for growing tomato transplants (Shulgina et al., 1990).The EC was also high, except in WasteNoMore.The most nutrient rich vermicomposts were Biohumus MM and Lumbrical.The latter also contains the highest amount of P. The lowest EC and lowest nutrient content in WasteNoMore could be explained with the used production technology which involves composting and subsequent vermicomposting.High bacterial counts were observed in all vermicomposts (Table 2).Durán and Henríquez (2007) reported bacterial population values of vermicompost produced from cow manure were similar to those reported here.In Lumbrical, WasteNoMore and Biohumus NN fungal loads were higher than those reported by Anastasi, Varese, Voyron, Scannerini, & Marchisio (2004) and Durán and Henríquez (2007).The production technologies used to develop vermicomposts were similar.Differences in their properties could be explained by differences in starting raw material.In all cases the predominant raw material was cow dung from animals that were treated differently, which probably influences vermicompost contents.Based solely on these analyses it is hard to predict how each vermicompost could influence plant growth, since factors, other than nutrient availability influence plant response (Atiyeh, Edwards, Subler, & Metzger, 2000c;Atiyeh, Edwards, Subler, & Metzger, 2001;Hidalgo & Harkess, 2002a;Arancon, Lee, Edwards, & Atiyeh, 2003;Arancon, Edwards, Atiyeh, & Metzger, 2004;Bachman & Metzger, 2008;Yasir, Aslam, Won Kim, Lee, Jeon, & Chung, 2009;Robledo, Grosso, Zoppolo, Lercari, & Etchebehere, 2010).

Chemical and Physicochemical Properties of Potting Mixtures Containing 10% Vermicomposts
Chemical and physicochemical properties of potting mixtures before planting were within acceptable ranges for growing tomato transplants (Shulgina, Simidchiev, Cekleev, & Kanazirska, 1990) (Table 3).Most vermicomposts increased nitrate and soluble P levels in the potting mixtures, compared to the control, the exception was Biohumus NN.The K amount increased only in Biohumus MM treated mixes; while the Ca amount increased only in Chirpan vermicompost treated mixes.Vermicomposts did not affect Mg content in potting mixes.Biohumus MM was the only vermicompost that had a higher EC value than the control, which is attributed to the highest concentration of K. Biohumus MM, Biohumus NN and WasteNoMore, which had comparatively high pH increased pH of mixtures compared to the control.Atiyeh et al. (2000c) observed increased pH in peat-perlite based substrate after application of 10-20% pig manure vermicompost.Chirpan vermicompost and Lumbrical, with comparatively lower pH does not modify mixture pH.These observations suggest that vermicompost could be an important source of nutrients.Hence, it could be also assumed that application of vermicompost will reduce the use of mineral fertilizers or even will replace them.
Table 3. Content of water soluble nutrients (mg•L -1 ), EC (mS•cm -1 ) and pH of the growing media before planting

Effect on Plant Growth
Addition of vermicompost to the potting mixture stimulated plant growth (Table 4).The best shoot fresh weights and lengths were due to amending the medium with Biohumus MM.All vermicomposts caused greater production of leaves than the control.The best leaf area was on plants treated with Biohumus MM and leaf area produced with Lumbrical was similar to the control.The correlation coefficient between shoot fresh weight and electrical conductivity (EC) of the mixtures before planting was r = 0.85 * (asterisk indicate that correlation is significant at 0.05 level).This suggests that differences in EC of the potting mixtures, derived by vermicomposts which consequently affect nutrient availability could explain observed differences in growth response.Promotion of plant growth by vermicompost is attributed mostly to amounts of available nutrients (Atiyeh, Subler, Edwards, & Metzger, 1999;Atiyeh et al., 2001;Paul & Metzger, 2005;McGinnis, Wagger, Warren, & Bilderback, 2010;Theunissen, Ndakidemi, & Laubscher, 2010).However, nutrient content may not be the major factor influencing plant growth.WasteNoMore and Chirpan vermicompost differ in initial nutrient content (Table 1) but both had similar effects on plant growth.WasteNoMore is comparatively poor in nutrients, but it had the highest amount of microorganisms, while Chirpan vermicompost possess the highest organic matter content.Lumbrical is rich in nutrients, similar to Biohumus MM, but the effect on plant growth was not as evident.The observed differences might be due to physical properties of the substrate (Atiyeh et al., 2001;Hidalgo & Harkess, 2002a), and other biological factors including enhanced microbial and enzyme activity and presence of plant growth-promoting substances such as hormones and humates (Atiyeh et al., 2000c;Arancon et al., 2003;Bachman & Metzger, 2008;Yasir et al., 2009;Robledo et al., 2010).

Effect on Nutrients Concentrations in Shoots
Higher than control N, P, K concentrations were found in transplants grown in media supplemented with Lumbrical and WasteNoMore (Table 5).Higher N, K concentrations occurred in transplants treated with Biohumus MM, but P concentration was similar to controls.The N, P, K concentrations in plants treated with Chirpan vermicompost and Biohumus NN, were not different from controls.The P concentration was lower than in the control.Hashemimajd et al. (2004) who also found a moderate correlation (r = 0.42 ** ) between total N content of composts and N in plant tissues.
The study was undertaken to analyze vermicomposts to determine their quality and potential use in transplant production.The chemical composition differed among vermicomposts regardless of similarity in production technologies and raw materials.The general characteristic of the vermicomposts was that they have high pH and electrical conductivity, indicating that they can not be used individually as a substrate for growing tomato transplants, but as a component of the potting mixture.When mixing vermicomposts with peat and perlite nutrient content decreased, due to the dilution, and kept nutrients within acceptable, or optimal, ranges for growing tomato transplants.Differences in growth responses were attributed to differences in nutrient content of potting mixes.Although the present study was focused more on effects of vermicomposts on plant growth rather than on causes leading to these effects, the results indicated that availability of nutrients is an important factor influencing plant growth.But changes in physical and biological properties of the substrate could also be responsible for observed differences.
Vermicomposts can be used in sustainable culture practices in horticulture, but their widespread use depends on economic benefits and farmer awareness about environmental issues.The optimal use rate for transplant production needs to be determined.Nutrient management guidelines for vermicompost application need to be developed, considering that vermicompost composition might vary even between different batches in one farm and is exclusively dependent on the parent material used.

Table 1 .
Chemical and physicochemical properties of vermicomposts Values in rows followed by different letter are significantly different at P<0.05, Duncan's Multiple Range Test. *

Table 2 .
Total amount of bacteria and fungi in vermicompost ± Standard deviation Values in columns followed by different letter are significantly different at P<0.05, Duncan's Multiple Range Test. *

Table 4 .
Comparative effect of vermicomposts on some plant growth indices

Table 5
This indicates that vermicomposts contribute to the plant N supply.This agrees with * Values in columns followed by different letter are significantly different at P<0.05, Duncan's Multiple Range Test A moderate correlation (r = 0.61 * ) occurred between N concentration in plant tissues and nitrate level in potting mixtures before planting.