Growth of bedding plants in commercial potting substrate amended with vermicompost

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1 Bioresource Technology xxx (2007) xxx xxx Growth of bedding plants in commercial potting substrate amended with vermicompost G.R. Bachman a, *, J.D. Metzger b a Department of Agriculture, Illinois State University, Normal, IL , United States b Department of Horticulture and Crop Science, The Ohio State University, Columbus, OH 43210, United States Received 5 July 2006; received in revised form 30 May 2007; accepted 30 May 2007 Abstract Vermicompost has been promoted as a viable alternative container media component for the horticulture industry. The purpose of this research was to investigate the use of vermicompost at different points in the production cycle of tomato, marigold, pepper, and cornflower. The incorporation of vermicompost of pig manure origin into germination media up to 20% v/v enhanced shoot and root weight, leaf area, and shoot:root ratios of both tomato and French marigold seedlings; however amendment with vermicompost had little influence on pepper and cornflower seedling growth. Moreover there was no effect on the germination of seed of any species. When seedlings of tomato, French marigold, and cornflower were transplanted into 6-cell packs there was greater plant growth in media amended with vermicompost compared to the control media, and the greatest growth when vermicompost was amended into both the germination and transplant media. This effect was increased when seedlings in the transplant media were irrigated with water containing fertilizer. Published by Elsevier Ltd. Keywords: Alternative media; Worm castings; Organic by-products 1. Introduction Due to rising costs and uncertain future availability of peat moss, there is a need in the floriculture industry for alternative components in commercial potting substrates. In addition, because peat-based commercial potting substrates have low ion exchange capacities there is concern about the environmental impact of leachates containing high concentrations of chemical fertilizers. The nutrient holding capacity is affected by irrigation volume (Rathier and Frink, 1989). The volume of irrigation leachates from containers has been shown to positively influence the accumulation and movement of nitrate-n in the soil (McAvoy et al., 1992). Extremely high concentrations of nitrate-n have been found under commercial greenhouse ranges in the United States. Concentrations as high as 200 ppm have * Corresponding author. Tel.: ; fax: address: grbachm@ilstu.edu (G.R. Bachman). been reported in the top meter of soil (Walker, 1990). The accumulation of nitrate-n in the soil profile is directly related to the greenhouse practice of irrigating with fertilizer-injected water until leaching occurs. Increased importance is being given to composts and composted material as components in commercial potting substrates because these materials provide required nutrients, increase cation exchange capacity, and improve water-holding capabilities (Tomati et al., 1990). Nutrients are conserved through the composting of organic wastes with many becoming adsorbed onto, or incorporated into, humic particles of the composted material. Composts reportedly stimulate nutrient uptake and assimilation and have hormone-like activity as well (Tomati et al., 1990; Grapelli et al., 1985). One material gaining interest is agricultural manure wastes composted through the action of worms (Edwards, 1998; Handreck, 1986). These materials, called vermicomposts, are being used as organic fertilizers, soil amendments, and potting substrate components. Vermicomposts /$ - see front matter Published by Elsevier Ltd. doi: /j.biortech

2 2 G.R. Bachman, J.D. Metzger / Bioresource Technology xxx (2007) xxx xxx also have characteristics of conventional composts. Vermicomposts are easily handled and supply nutrients during crop growth. Depending on the origin, vermicomposts differ in chemical composition (Handreck, 1986); however, vermicomposts of the same waste origin have reproducible characteristics (Tomati et al., 1990). Vermicomposts have the same reported benefits as conventional composts such as a source of organic matter, increased moisture-holding characteristics, and enhanced nutrient uptake and plant hormone-like activity (Galli et al., 1990; Tomati et al., 1988). The increases in plant growth have mostly been related to improvements in physical and chemical structure of the growth media. However, the use of vermicompost appears to affect plant growth in ways that can not be directly linked to physical or chemical properties (Dash and Petra, 1979). It seems likely that some growth promotion is due to plant hormone-like activity related to microflora associated with vermicomposting and to metabolites produced as a consequence of secondary metabolism (Parle, 1963; Tomati et al., 1987; Atiyeh et al., 2002). Vermicompost incorporated into soil and potting substrates has enhanced plant growth (Atiyeh et al., 2000, 2001). The length, weight, number of seeds, number of shoots in Vinca rosea and tillers in Oryza sativa increased when grown in 50:50 soil to vermicompost mixtures (Reddy, 1986). Root weights of wheat were greater in soil inoculated with earthworms (Edwards and Lofty, 1980). By contrast, soil containing vermicompost did not increase the number of blooms or have an effect on flower size of annual plants when compared to control soil (Bal and Curry, 1977). Growth of nursery stock is affected by the addition of vermicompost. Growth of Acacia mearnsii and Pinus patula was adversely affected by vermicompost in the media mix, however Eucalyptus grandis growth was enhanced in 1:1 pine bark:vermicompost mix provided additional nutrition was added (Donald and Visser, 1989). To date there has not been any research reported on the use of vermicompost in the cropping cycle of bedding plants. The objective of this work was to evaluate how the incorporation of vermicompost into commercial potting substrates affects bedding plant growth and what stage of the bedding plant cycle could plant growth be optimized. 2. Methods Vermicompost (VC) of pig manure origin was added to a commercial potting substrate [Metro Mix 360 (MM360); The Scotts Co., Marysville, OH] to obtain three VC:MM360 ratios of 0% VC, 10% VC, or 20% VC. VC and MM360 media components were mixed for three minutes in a rotary mixer to ensure complete dispersal of the material components of each mix ratio. Seeds of Rutgers tomato (Lycopersicon esculentum Mill. Rutgers ), Queen Sophia French marigold (Tagetes patula L. Queen Sophia ), California Wonder bell pepper (Capsicum annuum L. California Wonder ), and Imperial cornflower (Centaurea cyanus L. Imperial ) were sown into 200 cell (33.3 mm mm) plug trays containing one of the three VC mixes at a rate of one seed per cell. The plug trays were placed in a greenhouse under high humidity and mist until emergence. Seeds were considered emerged when the cotyledons came through the surface of the potting substrate, typically after three days for tomato and marigold and seven days for pepper and cornflower. At that time, the percent seedling emergence was determined. Beginning seven days after emergence, five seedlings of each species were sampled from each media mix treatment for determination of leaf area, and the dry weights of shoots and roots daily for 12 consecutive days. Fourteen days after emergence seedlings of tomato, marigold, pepper, and cornflower were transplanted into large cell six-packs having cell dimensions of 5.7 cm 5.7 cm 8.25 cm in a factorial design (Table 1) containing either 0%, 10%, or 20% VC: MM360 mixes. There were two fertilization treatments. One group received no supplemental fertilization and was irrigated with clear water and the other group received supplemental fertilization from Peter s Peat-Lite Special (20N-4.4P-16.6K) (The Scotts Company, Marysville, OH) at the concentration of 200 mg N L 1 twice weekly with clear water used for the intervening irrigations. The transplanted plugs were grown for 28 days and harvested. There were six replications and treatments were arranged in a complete randomized design within each species of plant. The experiment was repeated once in time. Temperature in the greenhouse was controlled using a computer control system with a set-point of 23 C and a range of C. Data collected for each species included shoot and root fresh weights, shoot and root dry weights, and leaf areas. Analysis of plant growth data included analysis of variance, orthogonal contrasts, mean separation using Fisher s LSD (P = 0.05), and regression analysis. 3. Results Seedling emergence was used as the determining factor regarding seed germination in VC amended media in plug trays. There was no promotion of seed germination in any media treatment (data not presented). The germination percentages were similar to the guaranteed germination of each seed batch within each species. Table 1 Germination and transplant media using different ratios by volume of vermicompost for plugs grown in either plug trays or large cell 6-pack trays Germination media mix Transplant media mix MM360 a MM360, 10% and 20% Vermicompost 10% Vermicompost MM360 and 10% Vermicompost 20% Vermicompost MM360 and 20% Vermicompost a Metro Mix 360 (MM360), The Scotts Co., Marysville, OH.

3 G.R. Bachman, J.D. Metzger / Bioresource Technology xxx (2007) xxx xxx 3 Media amended with 10% VC resulted in increases in leaf area, shoot and root dry weights of marigold when measured at 12 days after germination (DAG) (Table 2). Shoot dry weight was enhanced in the 10% VC with 45% and 64% greater shoot weights compared to the control and 20% VC treatment, respectively. Dry root weight was similar in the 10% and 20% VC and 44% greater when comparing the 10% VC to the control. Leaf area was greater in the 10% VC compared to the control and 20% VC, 37% and 71%, respectively. Shoot:root ratio was greatest in the control and 10% VC and lowest in the 20% VC. Tomato shoot dry weights were greater for the VC amended media at both amendment volumes compared to the control (Table 2). Leaf area for the 20% VC was greater than both the control and 10% VC. There was no difference in media treatments for root dry weights and shoot:root ratio. Shoot and root dry weights and leaf areas were greater for pepper grown in the MM360 control than in the 20% VC amended media (Table 2). There was no difference between 10% VC and 20% VC, nor was there an effect of VC on any of the measured growth parameters for cornflower (Table 2). Comparison of the slopes of the regression lines within each measured parameter revealed that the rate of growth was positively affected by the incorporation of vermicompost into the media (Table 3). There was greater rate of dry matter (shoot and root biomass) accumulation in the tomato when grown in the 20% VC compared to the other media. Leaf area and shoot:root ratio was greatest in the 10% VC compared to the control and 20% VC. Marigold responded with greater rates of shoot and root dry weight accumulation and leaf area in 10% VC than in the other mixes. While less than in 10% VC, there was greater growth in 20% VC than the control (Table 3). There was greater root dry weight in cornflower grown in the 20% VC media treatment with all other parameters being similar (Table 3). Rate of dry matter accumulation and leaf area in pepper was greater in 0% VC than in media containing vermicompost (Table 3). Tomatoes irrigated with clear water had increased growth in media amended with vermicompost. Media containing vermicompost as either germination media or transplant media produced greater fresh shoot weights than 0% VC (Table 4). The greatest fresh shoot weights were in the treatments having vermicompost in both the germination and transplant media. Transplant media amended with 20% vermicompost produced greater dry shoot weight than the control media (Table 4). Leaf area was increased with either 10% VC or 20% VC in both the germination and transplant media or 20% in the transplant media. The remaining VC combinations resulted in greater leaf area than the control media (Table 4). All measured parameters were increased by the incorporation of VC when fertilized twice per week (Table 4). Cornflower had increased growth in VC amended media when irrigated with clear water. Fresh shoot weight increased with 20% VC in the germination and transplant media (Table 4). Vermicompost in the transplant media resulted in greater fresh shoot weights (Table 4). Shoot dry weight was greater with 20% VC in both germination and transplant media than 10% VC germination and 0% VC transplant media with all other treatments being similar (Table 4). Vermicompost in the transplant media produced greater leaf areas than the other treatments (Table 4). Vermicompost in either germination or transplant media resulted in greater fresh shoot weight, dry shoot weight, and leaf area in marigold irrigated with clear water (Table 4). The greatest growth was from 10% VC in both germination and transplant media. In the fertilized treatments, Table 2 The effect of amending commercial potting substrate with vermicompost on shoot and root dry weights, leaf areas, and shoot:root ratios of Rutgers tomato, Queen Sophia French marigold, California Wonder bell pepper, and Imperial cornflower seedling plugs measured 12 days after emergence Media Shoot dry wt (g) Root dry wt (g) Leaf area (cm 2 ) Shoot:root ratio Queen Sophia French marigold 0% VC b A b b 2.37 a 10% VC a a a 2.34 a 20% VC b ab b 1.81 b Rutgers tomato 0% VC b a 8.41 b 4.35 a 10% VC ab a 9.61 ab 4.11 a 20% VC a a a 4.55 a California Wonder pepper 0% VC a a a 4.54 a 10% VC 0.27 ab b ab 4.83 a 20% VC b b 8.20 b 4.72 a Imperial cornflower 0% VC a a 2.44 a 1.57 a 10% VC a a 2.36 a 1.28 a 20% VC a a 2.74 a 1.57 a A Mean separation within columns and species by least significant difference, P = 0.05.

4 4 G.R. Bachman, J.D. Metzger / Bioresource Technology xxx (2007) xxx xxx Table 3 Rate of change of shoot and root dry weight, leaf area, and shoot:root ratio of Queen Sophia French marigold, Rutgers tomato Shoot dry wt Root dry wt Leaf area S:R ratio Tomato MM360 y = x y = x y = 1.454x 8.99 y = x % VC y = x y = x y = x y = x % VC y = x y = 0.002x y = x y = x MM360 10% VC * a * ns ** MM360 20% VC * * ns ns 10% VC 20% VC * ns ns ** Queen Sophia French marigold MM360 y = x y = x y = x y = 0.086x % VC y = x y = x y = x y = x % VC y = x y = x y = x y = x MM360 10% VC ** ** ** ** MM360 20% VC * * ns ns 10% VC 20% VC ** ** * ** Imperial cornflower MM360 y = x y = x y =.1351x y = x % VC y = 3E-05x y = x y =.0629x y = x % VC y = x y = x y = 0.105x y = x MM360 10% VC ns ns ns ns MM360 20% VC ns * ns ns 10% VC 20% VC ns * ns ns California Wonder bell pepper MM360 y = x.0079 y = x y = x y = 0.501x % VC y = x y = x y = x y = 0.219x % VC y = x y = 3E-05x y = 0.849x y = x MM360 10% VC ns ns ns * MM360 20% VC ** ns ** * 10% VC 20% VC * ns * ns California Wonder pepper, and Imperial cornflower seedling plugs grown in commercial potting substrate amended with vermicompost as measured by change in slope of linear regression lines. a ns, *, **, *** Orthogonal contrasts are not significant or significant at P = 0.05, 0.01, and 0.001, respectively. vermicompost in either germination or transplant media resulted in greater shoot fresh weight, shoot dry weight, and leaf area (Table 4). 4. Discussion Vermicompost is reported to have hormone-like activity, and this has been hypothesized to result in greater root initiation, increased root biomass, enhanced plant growth and development, and altered morphology of plants grown in vermicompost amended media (Edwards, 1983, 1985; Grapelli et al., 1985; Satchell et al., 1984; Tomati et al., 1988). Indeed the presence of substances with hormone or hormone-like activity in vermicompost has been reported. Using phytohormone bioassays, compounds with gibberellin, cytokinin and auxin-like activity have been detected in vermicomposted urban and sewage waste (Grapelli et al., 1985). Several researchers have reported that VC enhances seed germination. (Alves and Passoni, 1997; Edwards and Burrows, 1988). However, we did not observe an increased germination percentage or promotion of germination rates by VC. That there were no effects of VC on germination may be due to the fact that the seed used in our experiments were from fresh seed lots from a commercial seed company having high reported germination percentages. Our results do not preclude the possibility that VC may have a positive effect on germination of seeds that have deteriorated or reduced viability. Although germination was not affected, VC promoted subsequent growth in all species after transplantation into the larger cell six-pack trays. In general, marigold displayed the greatest growth promotion of any species studied, with the largest impact occurring in the plug stage. Media containing 10% VC promoted the greatest increases in growth, while there was little difference between 0% VC and 20% VC. The fact that growth in the 20% VC was similar to that of the 0% VC control suggests that increased growth in 10% VC media was not influenced solely by the nutrition status in the media mixes. The possibility of the existence of a non-nutritional growth factor in the vermicompost is further supported by the increased growth of

5 Table 4 The interaction of fertilizer application and vermicompost on shoot and root fresh weights, shoot and root dry weights, and leaf areas of Rutgers tomato, Queen Sophia French marigold, and Imperial cornflower were measured 28 days after transplantation to 6-packs and irrigated twice weekly with clear water or water containing soluble fertilizer (20N 4.4P 16.6K) at 200 mg N L 1 Germination media Transplant media Tomato French marigold Cornflower SFW (g) SDW (g) LA (cm 2 ) SFW (g) SDW (g) LA (cm 2 ) SFW (g) SDW (g) LA (cm 2 ) Clear water MM360 MM MM360 10% VC MM360 20% VC % VC 10% VC % VC MM % VC 20% VC % VC MM Fertilized MM360 MM MM360 10% VC MM360 20% VC % VC 10% VC % VC MM % VC 20% VC % VC MM Germination Media *** a ** *** *** *** *** ** ** ** Transplant media *** *** *** *** *** *** *** ** *** Germination transplant media *** ** ** *** *** *** ns ** ns a ns, *, **, *** Orthogonal contrasts are not significant or significant at P = 0.05, 0.01, and 0.001, respectively. G.R. Bachman, J.D. Metzger / Bioresource Technology xxx (2007) xxx xxx 5 ARTICLE IN PRESS

6 6 G.R. Bachman, J.D. Metzger / Bioresource Technology xxx (2007) xxx xxx seedlings germinated in vermicompost being maintained after the seedlings are transplanted into six-pack trays without added VC. A candidate for such a non-nutritional growth-promoting compound is humate. Earthworms contribute to the biological processes that produce humus or humus-like substances (Hartenstein, 1982; Stoudt, 1983). Humus or humates are believed to stimulate plant nutrient uptake and metabolism, have an influence on protein synthesis, and show hormone-like activity (Barton and Ruocco, 1981; Poapst et al., 1970; Tichy and Phuong, 1975; Vaughan and McDonald, 1971). Vermicompost has been reported to have 40 60% higher levels of humic compounds than conventional composts (Dominguez et al., 1997). Atiyeh et al. (2002) observed that growth of tomato and cucumber was enhanced when treated with up to 500 mg/kg humic acids derived from VC. Fertilization through irrigation increased plant growth for all media mixes. However, media mixes containing vermicompost had greater shoot weights and leaf areas compare to the 0% VC controls. Humic acid has been shown to increase nutrient accumulation in conditions of limited nutrient availability and when additional nutrients were supplied, (David et al., 1994). The researchers concluded that any increase in nutrient accumulation was due to the action of the humic acid and not from any nutrient contained in the humic acid. The fact that VC in the germination media had a long term positive effect on plant growth even after transplanting into media containing no VC is consistent with these observations. 5. Conclusions The addition of vermicompost in media mixes of 10% VC and 20% VC had positive effects on plant growth. The greatest growth enhancement was on seedlings during the plug stage of the bedding plant crop cycle. Growth increases up to 40% were observed in dry shoot tissue and leaf area of marigold, tomato, green pepper, and cornflower. The increased vigor exhibited was also maintained when the seedling plugs were transplanted into larger containers with standard commercial potting substrates without vermicompost. Additionally, there were benefits apparently resulting from the nutritional content of the vermicompost. All of the plugs were produced without the input of additional fertilization. The potential exists for growers to use vermicompost-amended commercial potting substrates during the plug production stage without the use of additional fertilizer. References Alves, W., Passoni, A., Compost and vermicompost of urban solid waste in Licania tomentosa (Benth) seedling production for arboriculture. Pesqui. Agropecu. Bras. 32, Atiyeh, R.M., Subler, S., Edwards, C.A., Bachman, G., Metzger, J.D., Effects of vermicomposts and composts on plant growth in horticultural container media and soil. 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