There is a stringent need to reduce the environmental impact of peat in the plant nursery production chain. In this experiment, the use of different rates of sewage sludge compost in the preparation of growing media for potted Bougainvillea was evaluated to assess its efficiency for the replacement of peat and to quantify the environmental impact of such alternative substrates by the life cycle assessment (LCA) method. Five substrates containing increasing proportion of composted sewage sludge to peat (0%, 25%, 40%, 55%, and 70% v/v) were used, and their physicochemical properties were measured. Bougainvillea plant growth, biomass production, and macro- and micronutrient absorption were also determined. The main results were that compost addition improved the plant nutrient and increased the substrate pH, electrical conductivity (EC), and dry bulk density values. Globally, the results showed that compost could be used at up to 55% by volume with no negative effects on plant growth. The LCA showed that use of compost reduced the environmental loads of the growth media, except the Global Warming Potential value (GWP100). Environmental implications of the use of compost in the plant nursery chain are discussed.
Ornamental plant nursery production is one of the most specialized examples of intensive agriculture, with the large use of nonrenewable resources to maximize plant growth and reduce production time in an effort to capitalize on-sale profits. Because of this, the “green industry” is often considered a nonpoint (or diffused) polluting industry, due to the low efficiency in the management practices. The most common growing media used in Mediterranean ornamental nursery is peat, alone or mixed with inorganic coarse materials [
Composted organic wastes, properly mixed, can make excellent substrates for vegetable transplants [
Previous studies on compost use in agriculture have focused on specific agronomic aspects such as plant nutrition, water holding capacity, and species specificity. Differently, the choice of a growing media composition is constrained technical considerations (e.g., growing medium characteristics, crop requirements, safety, reliability, availability of constituents, and price). In substituting a peat substrate for a peat-biosolid compost mix, it is essential for the grower to consider crop quality. However few studies have addressed the global quality (agronomical and environmental) of horticultural growing media [
In this research, the use of different rates of sewage sludge compost in the preparation of growing media for potted Bougainvillea was evaluated in order to assess its efficacy as a peat replacement and to quantify the environmental impact of the substrate, by the LCA method, to optimize the ornamental nursery production chain. The simultaneous evaluation of the agronomic quality and environmental impact of the different rates in volume of biosolid compost in the production chain of the growing media consists in the innovative aspect of this research: actually data for the Mediterranean shrubs production does not exist.
In this research, the use of different rates of sewage sludge compost for the preparation of growing media for potted
The compost used as a component of growing media for this experiment (SSC) was obtained by mixing of urban sewage sludge (30% by volume) from Manduria municipality (TA, Southern Italy) and pruning rejects: urban “green” and olive grower (70% by volume), both locally available, in a composting plant. The mixture (about 3 m3) was composted in a pilot plant, using the Rutgers static pile composting system, with forced aeration and controlled temperature. The mixture reached temperature values greater than 60°C and the thermophilic phase lasted 60 days. After 95 days, the biooxidative phase of composting was over and then the pile was allowed to mature for an additional month.
The main physical, physicochemical, and chemical parameters were analyzed in sewage sludge (Table
Physical and physicochemical characteristics of sewage sludge.
Parameter | Value in dry |
Limit value in dry SS (according to |
---|---|---|
Colour | 7.5Y 2/1 | |
Moisture content (%) | 11.8 | — |
Total OM (%)a | 42.3 | — |
Oxidizable OC (%)a | 21.9 | ≥20.0 |
pH (H2O) | 7.64 | — |
EC (dS m−1) | 4.10 | — |
C : N ratio | 6.12 | — |
CaCO3 | 19.8 | |
CHA/CFA | n.d. | — |
Total Kjeldahl Nitrogen TKN (%)a | 3.21 | ≥1.50 |
P2O5 (%)a | 1.91 | ≥0.40 |
K2O (%)a | 0.21 | — |
CEC (cmol(+) kg−1) | n.d. | — |
Pb (%)a | 49.0 | 750 |
Cd (%)a | 5.21 | 20.0 |
Ni (%)a | 24.0 | 300 |
Zn (%)a | 1057 | 2500 |
Cu (%)a | 216 | 1000 |
Hg (%)a | 5.10 | 10.0 |
Cr+6 (%)a | 1.20 | — |
Physical and physicochemical characteristics of sewage sludge compost.
Parameters | Value in sewage sludge compost (SSC) | Limit values in SSC (according to Italian Legislation Lgs D. 75/2010) |
---|---|---|
Colour | 10YR 3/2 | |
Moisture content (%) | 44.4 | ≤50.0 |
Total OM (%)a | 58.6 | — |
Oxidizable OC (%)a | 29.0 | ≥20.0 |
C : N ratio | 10.2 | ≤25.0 |
CHA/CFA | 1.96 | — |
Total Kjeldahl Nitrogen TKN (%)a | 2.83 | — |
P2O5 (%)a | 0.91 | — |
K2O (%)a | 0.71 | — |
CEC (cmol(+) kg−1) | 77.0 | — |
Pb (%)a | 6.40 | 140 |
Cd (%)a | 0.10 | 1.50 |
Ni (%)a | 3.20 | 100 |
Zn (%)a | 394 | 500 |
Cu (%)a | 14.1 | 230 |
Hg (%)a | 0.10 | 1.50 |
Cr+6 (%)a | 0.10 | 0.50 |
Physical and physicochemical characteristics of the raw materials used: compost (SSC), almond shell (A), pumice (Pu), pozzolana (S), and sphagnum peat (P).
Raw materials | pH | EC | Dry bulk density | Easily available water | Shrinkage |
---|---|---|---|---|---|
(dS m−1) | (g cm−3) | (%V) | (%V) | ||
SSC | 7.90 | 5.54 | 0.45 | 9.93 | 13.17 |
A | 5.71 | 0.26 | 0.38 | 1.19 | 00.00 |
Pu | 6.72 | 0.08 | 0.81 | 2.88 | 00.00 |
S | 6.43 | 0.10 | 1.62 | 10.43 | 00.00 |
P | 5.62 | 0.33 | 0.13 | 6.53 | 15.33 |
Data are mean values,
Concerning the dry sewage sludge (Table
The obtained compost showed a good degree of maturity (Table
The compost showed an absence of phytotoxicity, according to the germination index (GI) > 50% (data not shown).
The main physicochemical parameters of the used materials are reported in Table
A greenhouse pot experiment was carried out to evaluate the main physical and chemical properties of five growing media obtained by mixing sewage sludge-based compost and peat in different ratios and to evaluate the potential use of these substrates as growing media for commercial
The five compared substrates were obtained by mixing increasing rates of sewage sludge compost (25%, 40%, 55%, and 70% v/v) with a fixed rate of inert the other materials (30% v/v) to fulfillment to 100% of the substrate volume, including the
Heavy metal content was also determine (Table
The experiment was conducted in a commercial nursery located in Monopoli SE Italy, 40° 57′ 00′′N, 17° 18′ 00′′E 23 m a.s.l.), in a greenhouse at keeping the temperature between
The growing density, on bench, was 8 plants m−2 for a total of 135 plants (27 plants per growing medium). The irrigation system was a microdrip. The plants were irrigated with only water during the first week, and then they were daily fed with a water soluble fertilizer N : P : K (5 : 1 : 7.5) plus microelements in dose of 0.5 g/L water. From the beginning of trial to 90 (days after transplant) DAT the nutrient solution was diluted according to the compost percentage of the substrate (Table
From the beginning of the trial up to 90 DAT the nutrient solution quantity per pot was of 250 mL/d; then, up to the May 6 (trial end), they received 4 interventions per day with a volume of 250 mL/pot per intervention.
The greenhouse experiment ended at 150 DAT when, on average, the plants reached the commercial size. The plant growth was determined after 90, 120, and 150 DAT. On each sampling date nine plants per treatment (three per replicate pot) were randomly harvested and used for the following biometric measurements: number of leaves, leaf area (cm2) (LI-COR 3100 area meter), and fresh and dry weight. The growing media were dried in an air-forced oven at 60°C to constant weight and milled to below 0.25 mm by a Tecator Cyclotec, 1093 PBI. The parts of the plants above ground were separated from the roots and gently washed many times with tap water and then finally with deionized water. A mixed sample of all the replications of each treatment was collected. Next, the samples were dried at 60°C to constant weight and crushed to 0.25 mm. The total Kjeldahl nitrogen (TKN) was measured using 1 g samples of both growing media and plant tissues using the Kjeldahl method after 96% H2SO4 hot digestion. Total phosphorus was determined (P) by the colorimetric molybdovanadate phosphoric acid method. The remaining nutrients and the heavy metal content were determined in digested samples by inductively coupled plasma atomic emission spectrometry (ICP-AES). One gram of dried samples was mineralized using 20 mL of 65% HNO3 solution. After digestion, samples were transferred into 50 mL volumetric flasks and then filtered through a Whatman 42 filter. The analyses were carried out in triplicate.
The main chemical and physicochemical properties of the five growing media were determined according to the following standardized UNI EN methods: 12579 (for sampling), 13037 (for the pH value), 13038 (for electrical conductivity, EC), 13041 (for dry bulk density and shrinkage), 13654-1 (for nitrogen), and 13652 (for quantification of H2O-soluble nutrients and heavy metals) [
The germination index (GI) was calculated using seeds of
The greenhouse experiment was carried out following a randomized block designed with three replications. To compare the differences between specific treatments, the S.N.K. test was used. All statistical tests were conducted using the CoStat software package (2002).
A comparison of the growing media production used in the experimental test was carried out (from June to November 2012) by means of a life cycle assessment (LCA) analysis, to gain more knowledge about the environmental impact and the resource use along the substrate production chain. The LCA is a method to analyse and assess the potential environmental impact caused by the used materials (ISO 14040-44) [
The data were elaborated using GABI 04 software with the CML2010 interpretation method [
Main physicochemical properties of the different raw materials and growing media used are shown in Tables
Physical and physicochemical characteristics of the growing media used (at transplant).
Growing medium | pH | EC | Bulk |
Easily available water | Shrinkage |
---|---|---|---|---|---|
(dS m−1) | (g cm−3) | (%V) | (%V) | ||
Acceptable range (1) | 5.2–6.5 | <0.5 | ≤0.4 | 20–30 | <30 |
| |||||
SSC0 | 5.80c | 0.45e | 0.28c | 13.71a | 15.87a |
SSC25 | 6.36b | 1.52d | 0.35b | 12.01a | 14.97a |
SSC40 | 6.50b | 2.15c | 0.39b | 6.01b | 14.10b |
SSC55 | 6.85a | 2.85b | 0.45ba | 5.86b | 13.40c |
SSC70 | 6.90a | 3.80a | 0.55a | 5.06b | 13.01c |
Significance | * | ** | * | ** | * |
(1): ideal substrate. Data are mean values,
In each column different letters indicate significant differences for
The electrical conductivity (EC) values of the growth media were strongly affected by the addition of CSS; the values exceeded the limit for an optimal growth substrate in the mixtures having more than 25% compost: the SSC0 being the only substrate that fulfilled optimal reference level (Table
The physical parameters at transplanting were influenced by the percentage of compost in the growing media. The increases in bulk density were within acceptable values only in SSC0, SSC25, and SSC40 treatments. Compost addition to the mixtures decreased the values of shrinkage and easily available water, and only the substrate with SSC25 showed similar values to those found in the control treatment as regards the shrinkage. Main macro- and micronutrient contents were also significantly affected by compost rate in the media (Table
Chemical characteristics of the growing media used (at transplant).
Growing medium | mg kg−1 | ||||||
---|---|---|---|---|---|---|---|
Total | |||||||
N | P | K | Ca | Mg | Fe | Mn | |
SSC0 | 330d | 1561d | 1027c | 5927c | 660e | 239c | 69b |
SSC25 | 550c | 2962c | 2058b | 17346b | 1682d | 933b | 114a |
SSC40 | 790b | 3050c | 2765a | 18652b | 2783c | 1056ab | 128a |
SSC55 | 890b | 3858b | 2692a | 20857ab | 3732b | 1188a | 136a |
SSC70 | 1010a | 4413a | 2805a | 22328a | 4040a | 1320a | 151a |
Significance | ** | ** | ** | ** | ** | ** | ** |
Data are mean values
In each column different letters indicate significant differences for
Average values of the heavy metals content of the growing media used (at transplant).
Growing medium | mg kg−1 | |||||
---|---|---|---|---|---|---|
Pb | Cd | Ni | Zn | Cu | Cr+6 | |
Italian Law value | 140 | 1.50 | 100 | 500 | 230 | <0.5 |
| ||||||
SSC0 | 12.04c | 0.06b | 1.58c | 12c | 13b | <0.5 |
SSC25 | 33.23b | 0.19a | 1.78c | 82b | 13b | <0.5 |
SSC40 | 34.00b | 0.22a | 2.56b | 102ab | 15ab | <0.5 |
SSC55 | 35.66b | 0.28a | 3.33ab | 122a | 19a | <0.5 |
SSC70 | 47.49a | 0.31a | 4.13a | 143a | 18a | <0.5 |
Significance | ** | * | ** | ** | ** | n.s. |
Data are mean values,
In each column different letters indicate significant differences for
Dilution ratio of nutrient solution supplied to the growing media from 1 to 90DAT.
Growing medium | Dilution ratio (% V : V) | |
---|---|---|
Nutrient solution | Water | |
SSC0 | 100 | 0 |
SSC25 | 64.29 | 35.71 |
SSC40 | 42.84 | 57.16 |
SSC55 | 21.43 | 78.57 |
SSC70 | 0 | 100 |
Raw materials used for the production of the tested growing media and their transport distance from the production areas to the firm.
Materials | Transport distance (km) |
---|---|
Urban sewage sludge | 130 |
Green wastes | 40 |
Peat | 2500 |
Pumice | 600 |
Almond shell | 150 |
Pozzolana | 100 |
Sewage sludge compost | 0 |
Significant increases were observed in the growth of
Leaves number (a), leaf area (b), fresh (c), and dry (d) weight in Bougainvillea potted plants at 90, 120, and 150 DAT as influenced by growing media. Each point is the mean of three replications. Within the same DAT values with the same letter are nonsignificantly different
On average, at 120 and 150 DAT, leaves number increased in SSC40, SSC55, and SSC70 growing media (Figure
The increase in plant biomass production with the use of compost as a growing media component could be attributed to the high input of nutrients provided by composts, and in our experiment increases in P, Ca, Mg, Fe, Mn, Cu, and Zn (Tables
Concentrations of macronutrients in tissues of Bougainvillea plants as influenced by growing media (150DAT, on dry matter basis).
Growing medium | mg kg−1 | |||||
---|---|---|---|---|---|---|
N | P | K | Ca | Mg | Na | |
SSC0 | 25.1c | 6.53d | 38.3c | 19.7c | 9.63c | 4.01b |
SSC25 | 27.3c | 7.02c | 40.4c | 19.1c | 12.4b | 4.55b |
SSC40 | 30.2b | 7.51b | 45.2b | 20.9b | 14.3b | 5.30a |
SSC55 | 31.5b | 7.74b | 48.3b | 21.1b | 15.7b | 5.70a |
SSC70 | 35.4a | 8.40a | 56.2a | 23.4a | 18.5a | 5.92a |
Significance | * | * | ** | * | * | * |
Data are mean values,
In each column different letters indicate significant differences for
Concentrations of micronutrients in tissues of Bougainvillea plants as influenced by growing media (150DAT, on dry matter basis).
Growing medium |
mg kg−1 | ||||
---|---|---|---|---|---|
Fe | B | Mn | Cu | Zn | |
SSC0 | 138c | 32.1 | 121.0a | 27.9b | 75.4c |
SSC25 | 141c | 30.3 | 90.6b | 30.5b | 124.7b |
SSC40 | 146b | 33.3 | 88.3b | 32.2b | 133.1b |
SSC55 | 156ab | 30.95 | 82.2c | 36.9a | 151.7a |
SSC70 | 169a | 31.4 | 85.4bc | 40.2a | 160.8a |
Significance | * | n.s. | ** | * | ** |
Data are mean values,
In each column different letters indicate significant differences for
A decrease of Mn concentration in plant tissue was observed with increasing compost presence in growing media (Table
Tognetti et al. (2007) reported that the pH increases when mature composts are applied, [
Hidalgo and Harkess [
Concerning the plant growth, positive correlations between the leaf area and the shoot dry weight have been reported by Tremblay and Senecal [
The results of the environmental analysis are reported in Figure
LCA of growing media compared: analysis results.
The environmental burden of SSC25 was considered as a reference value equal to 100% of environmental burden. The growing media environmental loads decreases by reducing the peat content for all the compared indexes apart from GWP100 (Global Warming Potential), even if the compost content increases atmospheric emissions due to the composting process emissions and waste transport (Figure
These results were influenced by the long distance of the peat production areas (North Europe) from the composting and packaging plant. The GWP100 index showed an opposite trend, indicating a potential growing media environmental burden increase as the added compost dose increases. This could be attributed to to the increase of atmosphere emissions associated to the composting process. Our results were in line with previously published data on the environmental impact of growing media [
In addition, a higher use of compost produces C sink phenomena [
Considering the environmental burdens avoided by the accumulation of organic waste in landfills and the reduction of fertilizers, some authors [
The presented results showed that replacement of peat by sewage sludge compost can increase as compared to the typical plant nursery substrates, mainly by increasing macro- and micronutrients supply to plants. In our experiment, replacement of peat up to 55% yielded in Bougainvillea plants of comparable quality as to the typical peat based substrate. The LCA showed that the addition of compost greatly reduced the environmental impact of the plant nursery chain.
This work has been financed by the Italian Ministry of University and Research (MIUR) through “PON 01-01611 So.Pro.Me.” The authors also thank Eden ’94 Composting farm. (Manduria, Italy) and Tony and Gregory Leone for their help in the practical development of this experiment. The experimental tests, the data processing, and the editorial work were shared, within the competencies of the research group, equally between the authors.