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for the management of e‚uents from intensively housed livestock. Outlook on Agriculture 18, 3±7. Hopkins, W.G. (Ed.), 1995. Introduction to Plant Physiology.
Bioresource Technology 78 (2001) 11±20

Pig manure vermicompost as a component of a horticultural bedding plant medium: e€ects on physicochemical properties and plant growth R.M. Atiyeh a,*, C.A. Edwards a, S. Subler b, J.D. Metzger c a

Soil Ecology Laboratory, 105 Botany and Zoology Building, The Ohio State University, 1735 Neil Avenue, Columbus, OH 43210, USA b Paci®c Garden Company, HCR1 Box 150, Millheim, PA 16854, USA c Dept. of Horticulture and Crop Sciences, The Ohio State University, Columbus, OH 43210, USA Received 8 June 2000; received in revised form 30 October 2000; accepted 31 October 2000

Abstract This experiment was designed to characterize the physical, chemical and microbial properties of a standard commercial horticultural, greenhouse container, bedding plant medium (Metro-Mix 360), that had been substituted with a range of increasing concentrations (0%, 5%, 10%, 25%, 50% and 100% by volume) of pig manure vermicompost and to relate these properties to plant growth responses. The growth trials used tomatoes (Lycopersicon esculentum Mill.), grown in the substituted media for 31 days under glasshouse conditions, with seedling growth recorded in 20 pots for each treatment. Half of the tomato seedlings (10 pots per treatment) were watered daily with liquid inorganic fertilizer while the other half received water only. The percentage total porosity, percentage air space, pH and ammonium concentrations of the container medium all decreased signi®cantly, after substitution of Metro-Mix 360 with equivalent amounts of pig manure vermicompost; whereas bulk density, container capacity, electrical conductivity, overall microbial activity and nitrate concentrations, all increased with increasing substitutions of vermicompost. The growth of tomato seedlings in the potting mixtures containing 100% pig manure vermicompost was reduced, possibly as a result of high soluble salt concentrations in the vermicompost and poorer porosity and aeration. The growth of tomato seedlings was greatest after substitution of Metro-Mix 360 with between 25% and 50% pig manure vermicompost, with more growth occurring in combinations of pig manure vermicompost treated regularly with a liquid fertilizer solution than in those with no fertilizer applied. Some of the growth enhancement in these mixtures seemed to be related to the combined e€ects of improved porosity, aeration and water retention in the medium and the high nitrate content of the substrate, which produced an increased uptake of nitrogen by the plant tissues, resulting in increased plant growth. When the tomato seedlings were watered daily with liquid inorganic fertilizer, substitution of Metro-Mix 360 with a very small amount (5%) of pig manure vermicompost resulted in a signi®cant increase in the growth of tomato seedlings. Such e€ects could not be attributed solely to the nutritional or physical properties of the pig manure vermicompost. Therefore, it seems likely that the pig manure vermicompost provided other biological inputs, such as plant growth regulators into the container medium, that still need to be identi®ed fully. Ó 2001 Published by Elsevier Science Ltd. Keywords: Manure; Compost; Vermicompost; Tomato; Plant growth

1. Introduction The ability of some species of earthworms to consume and break down a wide range of organic residues such as sewage sludge, animal wastes, crop residues and industrial refuse is well known (Mitchell et al., 1980; Edwards et al., 1985; Chan and Griths, 1988; Hartenstein and Bisesi, 1989). In the process of feeding, earthworms fragment the waste, enhance microbial activity and accelerate rates of decomposition, leading to a *

Corresponding author. Tel.: +1-614-292-3786; fax: +1-614-2922180. E-mail address: [email protected] (R.M. Atiyeh).

humi®cation e€ect through which the unstable organic matter is oxidized and stabilized, as in composting but by a non-thermophilic process (Elvira et al., 1996, 1998). The end product, commonly termed vermicompost, is quite di€erent from the parent waste material. Vermicomposts are usually more stable than their parent materials with increased availability of nutrients and improved physicochemical and microbiological properties (Edwards and Burrows, 1988; Albanell et al., 1988; Shi-wei and Fu-zhen, 1991; Orozco et al., 1996). There is accumulating scienti®c evidence that vermicomposts can in¯uence the growth and productivity of plants signi®cantly (Edwards, 1998). Various greenhouse and ®eld studies have examined the e€ects of a

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ding plant container medium (Metro-Mix 360) that had been substituted with a range of di€erent concentrations (0%, 5%, 10%, 25%, 50% and 100% by volume) of pig manure vermicompost. To relate these changes to plant growth responses, tomato (Lycopersicon esculentum Mill.) plants were grown for 31 days in the substituted media and their seedling growth was measured. Since the pig manure vermicompost can contribute plant nutrients to the container medium, thereby reducing the need for supplemental fertilizer (Chaney et al., 1980), batches of the potting mixtures were used either with no supplemental fertilizer added or received daily liquid fertilizer applications which started immediately after seed germination.

variety of vermicomposts on a wide range of crops including cereals and legumes (Chan and Griths, 1988), vegetables (Edwards and Burrows, 1988; Wilson and Carlile, 1989; Subler et al., 1998; Atiyeh et al., 1999, 2000b), ornamental and ¯owering plants (Edwards and Burrows, 1988; Atiyeh et al., 2000b), and ®eld crops (Mba, 1996; Bucker®eld and Webster, 1998). Most of these investigations have con®rmed that vermicomposts usually have signi®cant bene®cial e€ects on plant growth. Vermicomposts, whether used as soil additives or as components of greenhouse bedding plant container media, have improved seed germination, enhanced seedling growth and development and increased overall plant productivity. The greatest plant growth responses and largest yields have usually occurred when vermicomposts constituted only a relatively small proportion (20±40%) of the total volume of a greenhouse container medium mixture, with greater proportions of vermicomposts substituted into the plant growth medium not always improving plant growth further (Atiyeh et al., 2000a). However, there are very few data available concerning how vermicomposts produce these growth enhancement e€ects although relevant research is underway in our laboratory. The plant growth responses in horticultural container media, substituted with a range of amounts of vermicomposts, were similar to those reported when composts were used in similar ways (Shiralipour et al., 1992; Atiyeh et al., 2000b). The enhancement in plant growth after substitution of soil or greenhouse container media with conventional composts has been attributed to various mechanisms, such as: modi®cations in soil structure, changes in water availability, additional or increased availability of macro and micronutrients, stimulation of microbial activity, augmentation of the activities of critical enzymes, or production of plant growth-promoting materials by microorganisms through interactions with earthworms (Gallardo-Lara and Nogales, 1987; Bugbee and Frink, 1989; Tyler et al., 1993; de Brito Alvarez et al., 1995; Beeson, 1996; SerraWittling et al., 1996; Marinari et al., 2000). It is therefore possible that vermicomposts, in similar ways to composts, can a€ect bedding plant growth by modifying the physicochemical and microbiological characteristics of the plant growth medium bene®cially. The main objective of our experiment was to characterize changes in the physical, chemical, and microbial properties of a standard commercial greenhouse bed-

2. Methods 2.1. Bedding plant potting media The plant growth experiment was in a Horticulture Department greenhouse at The Ohio State University. The plant growth media consisted of a control standard commercial greenhouse container medium, Metro-Mix 360 (Scotts, Marysville, OH), and substitutions of MetroMix 360 with 5%, 10%, 25%, 50% or 100% (by volume) pig manure vermicompost. Metro-Mix 360 is prepared from vermiculite, Canadian sphagnum peat moss, bark ash and sand, and contains a starter nutrient fertilizer in its formulation. The pig manure-based vermicompost was provided by Vermicycle Organics (Charlotte, North Carolina) and consisted of separated pig solids processed by earthworms (Eisenia fetida) in indoor beds. The basic chemical properties of Metro-Mix 360 and the pig manure vermicompost are summarized in Table 1. 2.2. Analyses of the physicochemical and microbial properties of the bedding plant potting media The initial physical properties of the various bedding plant potting mixtures were determined following the procedures described by Bragg and Chambers (1988) and Gabriels et al. (1993). Samples from each of the potting mixtures were wetted thoroughly in bulk batches. Samples of the media were placed into containers of known volumes and weights, with a ®ne mesh cloth was attached to the base. After initial drainage, the mixture level in the container was adjusted so it was

Table 1 Chemical properties of the commercial potting medium (Metro-Mix 360) and the pig manure vermicompost Medium Commercial medium Metro-Mix 360 Vermicompost Pig manure

Organic C (%)

N (%)

P (%)

K (%)

Ca (%)

Mg (%)

Fe (%)

31.78

0.43

0.15

1.59

1.03

3.52

2.58

27.38

2.36

4.50

0.40

8.60

0.50

0.80

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Table 2 Equations used to determine the physical properties of soilless container media (adapted from Inbar et al., 1993) Bulk density (BD) (g/cm3 ) Particle density (PD) (g/cm3 ) Total porosity (% volume) Container capacity (% volume) Air space (% volume) a

ˆ ˆ ˆ ˆ ˆ

dry weight/volume 1/[% organic matter/(100  1:55) + % ash/(100  2:65)]a (1 ) BD/PD)  100 [(wet weight ) dry weight)/volume]  100 (total porosity ) container capacity)  100

1.55 and 2.65 are the average particle densities of soil organic and mineral matter, respectively.

level with the top of the container, saturated with water for 48 h, then allowed to redrain. The containers were weighed twice, before and after drying in an oven for 4 days at 60°C. The ash contents and organic matter contents of the potting mixtures were determined in samples that had been incinerated in a mu‚e furnace at 550°C for 5 h. From these measurements, the bulk density, particle density, porosity, and air and water capacities were calculated using the equations of Inbar et al. (1993) (Table 2). The pHs of the potting mixtures were determined using a double distilled water suspension of each potting mixture in the ratio of 1:10 (w:v) (Inbar et al., 1993) that had been agitated mechanically for 2 h and ®ltered through Whatman no.1 ®lter paper. The same solution was measured for electrical conductivity with a conductance meter that had been standardized with 0.01 and 0.1 M KCl. Dehydrogenase enzymatic activity (DHA), which is used commonly as an indicator of the extent of overall respiratory activity of the microbial community (Frankenberger and Dick, 1983), was measured using a modi®ed method of Casida (1977). One gram of each potting mixture was mixed with 2 ml 0.5% 2,3,5, triphenyltetrazolium chloride in 0.5 M TRIS bu€er (pH 7.6), and incubated at 40°C for 6 h. The accumulation of the end product tryiphenyl formazan (TPF) was determined in a methanol extract (10 ml) using a Bio-Tek EL311sx microplate autoreader (Bio-Tekâ Instruments, Winooski, Vermont) at 490 nm. The mineral N concentrations (NH4 ±N and NO3 ±N) in each of the potting mixtures were determined colorimetrically in 0.5 M K2 SO4 extracts in the ratio of 1:5 (w:v) potting mixture to extractant, using a modi®ed indophenol blue technique (Sims et al., 1995) with a BioTek EL311sx automated microplate reader at 650 nm. All measurements were made on ®ve replicate samples for each potting mixture. 2.3. Plant growth experiment Three tomato (`Rutgers') seeds were sown in plastic pots (10 cm in diameter) containing Metro-Mix 360 substituted with 0% (control), 5%, 10%, 25%, 50% or 100% (by volume) pig manure vermicompost. There were 20 pots per potting mixture. The pots were placed in a mist house until germination. Plants were then thinned to one seedling per pot, and the pots were moved into a glasshouse where half the plants were

watered daily with 20-10-20 (200 ppm N) Peters Professional plant nutrient solution, while the other half received only water, with no fertilizer solution. Peters Professional is a water-soluble fertilizer that is recommended for continuous liquid feed programs of plants, and contains 7.77% NH4 ±N, 12.23% NO3 ±N, 10% P2 O5 , 20% K2 O, 0.15% Mg, 0.02% B, 0.01% Cu, 0.1% Fe, 0.056% Mn, 0.01% Mo and 0.0162% Zn. All pots were watered to saturation (i.e., until water leached from the bottom of the pot). Fourteen and 21 days after germination, 5 pots from each potting mixture were selected randomly. Plant heights (distance from the potting medium level to the top node) and total leaf numbers (including cotyledons) of each of the seedlings were recorded, and the average plant heights and leaf numbers per potting mixture calculated. Plants were removed from the potting mixtures, separated into shoot and root portions, and oven-dried at 60° C for 3 days to determine their dry weights. Leaves were detached from the stems, ground in a ball mill and analyzed for tissue N concentration on a Carlo Erba NA 1500 C/N analyzer. The pH, electrical conductivity, microbial activity, and mineral nitrogen (ammonium±N, nitrate±N) concentrations of each of the potting mixtures on each sampling date were also measured, according to the methods mentioned above. 2.4. Statistical analyses On each sampling date, data were analyzed statistically by a two-way ANOVA using SAS (SAS Institute, 1990), with the treatments: `with and without fertilizer' and `vermicompost concentration' as the main factors. The means of each parameter measured were then separated statistically using Tukey's and Dunnett's multiple range tests, with Metro-Mix 360 without vermicompost set as the control. Signi®cance was de®ned as P 6 0:05, unless otherwise indicated. 3. Results and discussion 3.1. E€ects of vermicompost on the physical properties of the container medium The bulk density of pig manure vermicompost was 2.25 times greater than that of the Metro-Mix 360 control, but its particle density was signi®cantly smaller

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(1.888 g/cm3 ) (Table 3). The percentage container capacity of pig manure vermicompost, de®ned as the percentage by volume of micropores that remain ®lled with water after a saturated substrate has drained (Beeson, 1996), was signi®cantly greater (71%) than that of Metro-Mix 360 (58.3%) (Table 3). The percentage air space (10.04%) of the vermicompost, de®ned as the percentage by volume of air-®lled macropores in a saturated substrate (Beeson, 1996), was signi®cantly less than that of Metro-Mix 360 (33.4%). It also had less percentage total porosity (81.0%), which is the sum of air-®lled macropores and water-®lled micropores in a saturated substrate, than the Metro-Mix 360 (91.7%). Upon substitution of Metro-Mix 360 with pig manure vermicompost, the bulk densities of the potting mixtures increased with the increasing proportions of vermicompost substituted for Metro-Mix 360, and this led to gradual decreases in the total porosity, changed the pore space distribution within the container medium, and resulted in decreased air space and increased water retention (Table 3). The percentages of total porosity of the potting mixtures, after the incorporation of 5% up to 50% vermicompost into Metro-Mix 360, were reduced by 1.1% to 6.4%. The percentages of air spaces were lowered by 33.1% to 52.9%, but percentages of container capacities were increased by 17.3% to 20.2% (Table 3). Tyler et al. (1993) and Beeson (1996) reported similar results from substrates composed of pine bark amended with di€erent concentrations of composts.

High bulk density usually has the disadvantage of increasing the transport cost of the container medium, and reducing porosity and air capacity, which should be avoided in commercial culture media (Corti et al., 1998). On the other hand, very low bulk density can cause excessive aeration of the substrate and concomitantly a decline in available water. Accordingly, de Boodt and Verdonck (1972) proposed an optimum physical properties for an ideal substrate for plant growth: as a minimum of 85% total porosity, container capacity between 55% and 75%, and air space between 20% and 30%. In this experiment, the total porosities and percentage air spaces of 100% pig manure vermicompost were below the acceptable range of variability of substrate characteristics, whereas the percentage air spaces of MetroMix 360 was above the optimum range. By mixing the coarse Metro-Mix 360 with the pig manure vermicompost, Metro-Mix improved the percentage porosity and the air space of the vermicompost, and the vermicompost served as the water-retaining component in the mixture, to result in acceptable levels. 3.2. E€ect of vermicompost on the biochemical properties of the container medium The pHs of both Metro-Mix 360 and pig manure vermicompost were within the optimal range for plant growth (Table 4), i.e., between 5.0 and 6.5 (Goh and Haynes, 1977). Upon incorporation of pig manure ver-

Table 3 Physical properties of a standard commercial potting medium (Metro-Mix 360) substituted with di€erent concentrations of pig manure vermicompost

A B

% (by volume) of vermicompost in Metro-Mix 360

Bulk densityA (g/cm3 )

Particle density (g/cm3 )

Total porosity (%)

Container capacity (%)

Air space (%)

ControlB 5 10 25 50 100

0.160 0.177 0.182 0.202 0.272 0.359

1.931 1.915 1.943 1.927 1.915 1.888

91.7 90.7 90.6 89.5 85.8 81.0

58.3 68.4 67.7 66.5 70.1 71.0

33.40 22.33 22.96 22.98 15.73 10.04

e d d c b a

a ab a ab ab b

a b b c d e

d bc c c ab a

a b b b c d

Means within the same column followed by the same letter are not signi®cantly di€erent at P 6 0:05. Control represents 100% Metro-Mix 360.

Table 4 Chemical properties and microbial activity of a standard commercial potting medium (Metro-Mix 360) substituted with di€erent concentrations of pig manure vermicompost

A B

% (by volume) of vermicompost in Metro-Mix 360

pHA

ControlB 5 10 25 50 100

6.00 5.86 5.89 5.83 5.75 5.68

a ab ab bc bc c

Electrical conductivity (mS/m)

Dehydrogenase activity (lg TPF/g/hr)

NH4 ±N (mg/kg)

NO3 ±N (mg/kg)

116.4 147.6 163.4 194.0 242.0 322.0

6.53 8.16 11.90 14.57 210.35 584.66

315.4 258.2 241.1 206.6 97.4 28.8