Scientia Horticulturae 122 (2009) 244–250 Contents lists available at ScienceDirect Scientia Horticulturae journal homepage: www.elsevier.com/locate/scihorti Evaluation and correction of nutrient availability to Gerbera jamesonii H. Bolus in various compost-based growing media Raymundo Caballero, Purificación Pajuelo, José Ordovás, Eusebio Carmona, Antonio Delgado * Dpto. de Ciencias Agroforestales, Universidad de Sevilla, Ctra. Utrera Km 1, 41013 Sevilla, Spain A R T I C L E I N F O A B S T R A C T Article history: Received 26 May 2008 Received in revised form 8 May 2009 Accepted 11 May 2009 Nutrient deficiencies usually constrain the use of some composted materials as peat-substitute growing media even if some fertilizer is applied to the media. In this work, we assessed the suitability of various composted materials as such or mixed with peat for potted plant production, with special emphasis on their effects on nutrient availability to plants. Further, we examined the effect of vivianite [Fe3(PO4)2
8H2O] as a fertilizer and its mixture with humic substances (HS) on these growing media (particularly their effectiveness in preventing Fe deficiency chlorosis in alkaline substrates). A completely randomized experiment design was developed involving the growth of gerber (Gerbera jamesonii H. Bolus) and two factors, namely (i) the growing medium, specifically composted cork residue (C), compost obtained from a mixture of olive husk and cotton gin trash mixed with rice hulls and peat in a 1:1:1 volume proportion (OH), composted grape marc (GM), Sphagnum peat mixed with spent mushroom compost (M), coconut fibre (CF), and Sphagnum peat; and (ii) the Fe source (control without Fe, Fe-EDDHA, vivianite and vivianite + HS in a weight ratio of 10:1). The highest chlorophyll meter readings were provided by the two media with the lowest pH (peat and CF), and the lowest readings were provided by the medium exhibiting the highest pH (C). Composted grape marc (GM) and M provided the largest amounts of dry matter (DM), whereas peat and M gave the highest flower yields. Flower and DM yield were lower in CF and C than those in other substrates; the low production in the former can be ascribed to Ca deficiency; in fact, the medium was poor in this nutrient; therefore, plants grown on it exhibited low Ca concentration in leaves. On the other hand, the low chlorophyll meter readings and DM yield in C can be largely ascribed to Fe deficiency chlorosis since the application of Fe improved both the parameters, the best results being obtained with the vivianite + HS mixture. Vivianite-based treatments increased P concentrations in leaves, but only in more acidic medium (CF and peat), where the pH of the media facilitated the dissolution of the product. The adverse effects of Fe sources on the Mn and Zn concentrations in leaves were as a result of the antagonistic effect of the Fe supply, which varied with the particular growing medium: Fe-chelate depressed Mn in plants grown on C, whereas vivianite + HS decreased the Mn concentration in plants grown on GM. The results obtained with the different compost-based materials studied and the ability to overcome Fe deficiency in C by using a vivianite + HS mixture are interesting with a view to reduce the use of peat in the potted plant industry. ß 2009 Elsevier B.V. All rights reserved. Keywords: Substrates Fe chlorosis Vivianite Fe-chelates Humic substances 1. Introduction Peat is the most widely used substrate for potted plant production in the nurseries and accounts for a significant portion Abbreviations: C, composted cork residue; CF, coconut fibre; DM, total dry matter in shoots; DTPA, diethylenetriaminepentaacetic acid; EDDHA, ethylenediaminedihydroxyphenylacetic acid; EDTA, ethylenediaminetetraacetic acid; GM, grape marc; HS, humic substances; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; SPAD, soil plant analysis development. * Corresponding author. Tel.: +34 954 486452; fax: +34 954 486436. E-mail address: adelgado@us.es (A. Delgado). 0304-4238/$ – see front matter ß 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.scienta.2009.05.010 of the materials used to grow potted plants (Marfà et al., 2002; Ribeiro et al., 2007). However, sustainable horticultural production cannot rely on expensive, non-renewable natural resources such as peat (Marianthi, 2006). There has been an intensive search for peat-substitute growing media over the last few decades (Robertson, 1993; Abad et al., 2001; Benito et al., 2005). Most of these growing media have been obtained by recycling or transforming (composting) organic residues of different origin (agriculture, forestry, livestock farming, and urban) (Ingelmo et al., 1998; Sánchez-Monedero et al., 2004; Girgatti et al., 2007). Nutrient availability is one of the major factors influencing the suitability of organic substrates for growing plants (Carmona et al., 2002; Caballero et al., 2007), which may depend not only on their R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250 245 evidences (Carmona et al., 2002; Caballero et al., 2007). All composts were obtained by using the method of open windrows, which involves composting in trapezoidal section piles (1.7–2 m high, 2.5–3.5 m wide, 40 m3 volume) that were aerated by mechanical turnover each 2–3 weeks (Carmona et al., 2002, 2004). elemental composition, but also on other factors affecting nutrient forms and dynamics such as adsorption capacity, pH, biological stability of the growing medium, and presence of dissolved organic compounds (Caballero et al., 2007). In general, micronutrient deficiencies, particularly Fe chlorosis, have frequently been described as nutritional imbalance in growing media (Fisher et al., 2003; Smith et al., 2004; Wik et al., 2006). However, Fe chlorosis is not always related to the limited Fe content in these materials; in fact, pH, the specific Fe forms present and their content, and nutrient competition may also influence the Fe availability to plants (Velázquez et al., 2004; de Santiago and Delgado, 2006). Caballero et al. (2007) found iron chlorosis in gerber to be more closely related to a high pH than to low Fe content in various growing media. The effect of an alkaline pH on Fe availability can be ascribed not only to the low solubility of this metal, which is essentially present as ferric oxide (Miller et al., 1984; Mengel, 1994), but also to reduced Fe uptake from the apoplast into the symplast restricting Fe availability to plant cells (Yu et al., 2000; Lucena, 2000). Growing media capable of inducing Fe chlorosis could be extensively used for the potted plant production of plants sensitive to Fe deficiency if a cost-effective method that overcomes nutritional imbalance was available. In soils that induce Fe deficiency, the most effective and widely used method is the application of Fe-chelates (Godsey et al., 2003; Lucena, 2003). However, this type of Fe-containing fertilizers are very expensive; moreover, they have a short-lasting re-greening effect and high risk of leaching in growing media owing to their high solubility (Rombolà et al., 2003; Álvarez-Fernández et al., 2004). Vivianite [Fe3(PO4)2
8H2O] has been proven effective in preventing Fe chlorosis over several growing seasons in various crops (Rosado et al., 2002; Rombolà et al., 2003). Vivianite is long-term effective and can be readily prepared from low-cost products (ferrous sulfate and bi- or mono-ammonium phosphate); moreover, its high P content makes it a useful P fertilizer. The effectiveness of vivianite in preventing Fe chlorosis is enhanced by mixing with humic substances (HS) (de Santiago et al., 2008). The main purpose of this work is as follows: (i) assessing the potential of various composted materials, whether alone or mixed with peat, for potted plant production with special emphasis on their impact on nutrient availability to plants; and (ii) studying the effect of vivianite and its mixture with HS on nutrient supply to plants (particularly its effectiveness in preventing Fe deficiency chlorosis in alkaline substrates). To this end, we used gerber (Gerbera jamesonii H. Bolus) on the grounds of its sensitivity to Fe chlorosis and its importance as an ornamental potted plant (Caballero et al., 2007). Electrical conductivity and pH were determined in an extract with substrate:water ratio of 1:2 after shaking the suspension at 2.5 Hz in an end-over-end shaker for 2 h. NO3-N and NH4-N in this extract were determined according to Mulvaney (1996), and P according to Murphy and Riley (1962). The amounts of Ca, Mg, K, and Na extracted by 1 M ammonium acetate buffered at pH 4.65 (substrate:extractant ratio of 1:5) according to the Australian Standard (1993) for the determination of nutrient levels were used as availability indices for these nutrients. Extraction at a substrate:extractant ratio of 1:2 with 2 mM DTPA buffered at pH 7.3 according to Lindsay and Norwell (1978) was used to determine Fe, Zn, Cu, and Mn availability indices. Both extractions were performed by shaking in an end-over-end shaker at 2.5 Hz for 2 h. After extraction, the suspensions were filtered through Whatman 42 paper and centrifuged at 4150  g for 1 h. K and Na in the supernatants were determined by atomic emission spectrometry; and Ca, Mg, Fe, Zn, Cu, and Mn by atomic absorption spectrometry. All extractions were performed in 1 L polyethylene flasks at 25 8C. Air at water holding capacity and the water holding capacity of the growing media were determined according to the method proposed by Ordovás et al. (1997), and bulk and particle density, and total porosity according to Ordovás et al. (1996). The studied growing media differed widely in terms of chemical properties and nutrient content (Table 1). Thus, pH of the substrates ranged from 5.5 (peat) to 7.62 (composted cork residue, C); and their electrical conductivity in 1:2 substrate extracts ranged from 0.31 (peat) to 3.06 dS m 1 (M). Porosity and water holding capacity of compost-based materials were lower than those in CF and peat (Table 2), which was in agreement with the previous results of Hernández-Apaolaza et al. (2005) and Ribeiro et al. (2007). Overall, the physical properties of studied substrates were within the recommended ranges for ornamental plant production in containers, and there were no significant restrictions to gerber growth from them (Hernández-Apaolaza et al., 2005), particularly with regard to the anoxic conditions due to slow drainage or air content at water holding capacity (Table 2), which could affect nutrient availability to plants. 2. Materials and methods 2.3. Experimental design 2.1. Growing media A complete randomized experiment with six replications and two factors was conducted over a period of 147 days. The factors examined were as follows: Six different plant-growing media were used to study the effect of various Fe-containing fertilizers on nutrient availability to gerber (G. jamesonii H. Bolus) grown in them. The specific substrates studied were as follows: (i) composted cork residue (C); (ii) compost obtained from a mixture of olive husk and cotton gin trash mixed with rice hulls and peat in a volume proportion of 1:1:1 (OH); (iii) composted grape marc (GM); (iv) Sphagnum peat mixed with spent mushroom compost in a volume ratio of 1:1 (M); (v) coconut fibre (CF); and (vi) Sphagnum peat amended with CaCO3 to raise pH (3 g L 1 peat). The composted materials were selected in such a way as to encompass the typical agricultural and agroindustrial residues from South Europe, and included CF and peat as controls. Mixtures of the different materials were also used so as to ensure good growing conditions based on previous 2.2. Substrate characterization (i) Growing medium with six treatments levels as described above. (ii) Fe-containing fertilizer: control without Fe, Fe-chelate (FeEDDHA) applied daily as an irrigating solution with a concentration of 10 mM; vivianite applied at 0.32 g Fe L 1 growing medium (equivalent to 1 g vivianite per L of substrate); and a mixture of vivianite with humic substances (HS) in a weight ratio of 10:1 applied at a rate of 1.1 g mixture per L of growing medium, as recommended by de Santiago et al. (2008). Vivianite and the vivianite + HS mixture were applied as suspensions in deionized water, which was mixed with the growing medium before gerber was planted. 246 R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250 Table 1 Chemical properties of the studied growing media. Growing mediuma EC dS m OH C M CF GM Peat NO3-N + NH4+-N pH 1 0.57 1.20 3.06 0.92 2.42 0.31 mg L 7.30 7.62 7.14 5.87 6.92 5.48 P 1 K gL 23.8 18.3 56.3 23.5 5.5 5.4 4.3 0.9 6.0 0.05 2.9 0.04 Mg Ca Na 1 0.21 0.29 0.72 0.42 0.96 0.01 Fe mg L 0.08 0.21 0.34 0.48 0.38 0.11 1.57 1.95 15.13 0.17 3.42 1.05 0.4 0.09 0.02 0.15 0.04 0.02 17.0 12.3 34.6 2.5 10.5 46.9 Zn Cu Mn 3.0 5.6 8.2 1 4.0 0.9 0.8 0.3 0.9 n.d. 0.4 0.3 6.9 5.0 4.1 2.5 7.2 2.8 1 Electrolytic conductivity (EC), pH, NO3-N + NH4+-N, and P concentration in the 1:2 growing medium:water extract; K, Mg, Ca, and Na expressed in g L 1 growing medium as determined in 1:5 (v/v) growing medium: 1 M ammonium acetate (pH 4.65) extract; Fe, Zn, Cu, and Mn expressed in mg L 1 growing medium as determined in 1:2 (v/v) substrate: 2 mM DTPA (pH 7.3) extract; n.d., not detectable. a C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre. Table 2 Physical properties of the studied growing media. Medium Air at water holding capacity Water holding capacity % (v/v) OH C M CF GM Peat 19.9 13.1 14.3 17.5 21.4 18.6 Bulk density kg L 64.3 68.8 68.6 77.6 56.7 74.5 0.33 0.37 0.35 0.09 0.38 0.11 Particle density 1 Total porosity % 2.07 2.02 2.02 1.56 1.75 1.54 84.2 81.8 82.9 95.1 78.1 93.0 C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre. Vivianite was prepared according to Rosado et al. (2002), by mixing 25 g (NH4)2HPO4 and 75 g FeSO4
7H2O in 1 L of water to produce a suspension containing 5 g of vivianite. The resulting suspension, which was highly saline (32 dS m 1), was washed several times with deionized water until the electrical conductivity was lower than 0.5 dS m 1. The contribution of the suspension to N supply to plants after washing was deemed negligible. Humic substances (HS) were prepared as described by de Santiago and Delgado (2007) from a commercial liquid mixture of humic and fulvic acids (Solfer húmicos1, Valencia, Spain), which was dialyzed into 15-kDa cut-off Visking tubing (Sigma, Barcelona, Spain) against deionized water until the electrical conductivity of the solution was <1 dS m 1. Then, the pH was lowered to 8 with HCl. A detailed description of the main properties of these dialyzed HS can be found elsewhere (de Santiago and Delgado, 2007; de Santiago et al., 2008). 2.4. Growing conditions The experiment was conducted in a greenhouse in the Agriculture School of the University of Seville, Spain (378210 N, 58560 W) from 24 June to 18 November 2004. Plants were grown in 3-L pots (one pot per replication); each of the pots was filled with one growing medium at its bulk density. In order to avoid Cu deficiency owing to the low content of this nutrient in the studied media (Caballero et al., 2007), 40 mg of CuSO4
5H2O per L of growing medium was added prior to transplantation. Plants were transplanted at four true leaves stage (one plant per pot). After planting, the growing media were irrigated to saturation. Before planting, the media were fertilized to ensure a similar initially available nutrient level in all by applying Peters1 M-77 (27% N, 15% P2O5, 12% K2O, 0.125% Fe, 0.25% B, 0.001% Mo, and 0.63% Cu, Mn, and Zn) at 1 g L 1 substrate and Osmocote1 (12–14 month release period; 18% N, 9% P2O5, 10% K2O, 2% MgO, 0.009% B, 0.024% Cu, 0.03% Mn, 0.008% Mo, 0.008% Zn, and 0.20% Fe) at 4 g L 1 substrate. Both fertilizers were supplied by Scotts España, S.A. (Tarragona, Spain) and iron was present as Fe-EDTA. The fertilizer rates were in the usual range for commercial pot production. Overall, no restrictions in nutrient supply to plants were expected based on the available nutrient data (Table 1), additional Cu supply, and fertilizer applied to the growing media before planting (Caballero et al., 2007). Plants were irrigated daily with 125–250 mL deionized water (or 10-mM Fe-EDDHA solution in chelate treatment) in order to facilitate slight drainage. Based on the use of this irrigation regime and the water holding capacity of the media (Table 2), no differences arising from low water availability to plants in the media were to be expected. During the last 7 weeks of growth, plants were irrigated once a week with 250 mL of water (or Fe-EDDHA solution in the chelate treatment) containing 1 g L 1 ammonium nitrate so as to avoid N deficiency (1.75 g of this fertilizer applied per plant during the stated period). pH of the drainage water was determined at 30-day intervals (i.e., five times during the growing period); for this purpose, pots were irrigated with 0.5 L of deionized water to promote drainage and obtain an adequate volume of water sample. 2.5. Plant analysis The chlorophyll content in each plant during cropping was measured on a weekly basis at the same time each day (early in the morning) from 26 June by using a Minolta SPAD 502 chlorophyll meter (Minolta, Osaka, Japan). Twenty SPAD were taken during the growing season. Measurements were made on the five youngest completely expanded leaves. An accurate relation between chlorophyll content and SPAD readings was previously reported for gerber: chlorophyll [mg g 1 fresh weight] = 0.0209 SPAD + 0.0002 SPAD2, R2 = 0.98, P < 0.001 (Caballero et al., 2007). Flower harvesting began on 19 August 2004 (i.e., 56 days after transplantation) and was completed at the end of the experiment. Flower diameter and stem length were measured. Dry matter (DM) in vegetative shoots per pot was measured at the end of the growing season. The five youngest completely expanded leaves in each plant were collected, dried in a forced air oven at 65 8C for 48 h and milled to pass though a 1-mm sieve. An aliquot of the milled plant material (0.5 g) was mineralized by ashing at 550 8C for 8 h and the obtained ash was dissolved in 1 M HCl. The resulting solution was used to determine P and B colorimetrically by using the blue Molybdophosphate method (882 nm) and azomethine-H method (410 nm), respectively; Ca, Mg, Fe, Cu, Mn, and Zn by atomic absorption spectrometry; and K by atomic emission spectrometry. Total nitrogen in the plant samples was determined by using the Kjeldahl method. 247 R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250 Table 3 Analysis of variance of chlorophyll meter readings at 5, 10 and 20 weeks (SPAD 5, SPAD 10, and SPAD 20, respectively), average chlorophyll meter reading for the last 10 weeks (SPAD mean), shoot matter in plants (DM), number of flowers per plant, length of flower stem, flower diameter, and pH of drainage water. Source of variation Growing media (A) Fe treatment (B) AB d.f. P value 5 3 15 SPAD 5 SPAD 10 SPAD 20 SPAD mean DM Flowers per plant Flower stem length Flower diameter pHa 0.0000 0.9044 0.7241 0.0000 0.4728 0.2527 0.0000 0.2868 0.0337 0.0000 0.0854 0.0003 0.0000 0.0159 0.0157 0.0000 0.3596 0.3898 0.1060 0.7726 0.8932 0.8274 0.8611 0.6648 0.0000 0.0435 0.0029 P values lower than 0.05 indicate a significant effect of the source. a Measured 17 weeks after transplanting. 2.6. Statistical analyses Analysis of variance was performed in order to asses the significance of the effect of the substrates and application of Fecontaining fertilizer on plant variables and pH in drainage water. Analysis of variance, regressions, and comparison of means (Tukey’s test) were all done using Statgraphics Plus 5.1 (StatPoint, 2000). 3. Results The growing media under study were found to have a significant effect on shoot dry matter (DM) and flower production and also on the chlorophyll content as determined by using the SPAD meter on gerber plants (Table 3). However, no significant differences were observed in flower quality (diameter and stem length) between the substrates (Table 3). Chlorophyll meter readings in plants grown on peat and CF were higher than those grown in other substrates (Table 4 shows the mean SPAD for the last 10 weeks of growth). Grape marc compost (GM) and M exhibited the highest amount of DM (Table 5), whereas peat and M gave the highest number of flowers per plants (results not shown). Coconut fibre (CF) and C exhibited the lowest amount of DM (Table 5) and lowest flower yield (results not shown). Table 4 Effect of the different growing media and iron sources on the average chlorophyll meter readings for the last 10 weeks of growth. Fe-EDDHA Control without Fe Vivianite + HS Vivianite 55 40 54 60 53 64 54 53 54 57 54 64 55 45 54 60 55 63 The effect of Fe sources on chlorophyll readings and DM production was only significant in C (Tables 4 and 5), which accounts for the significant interaction observed between both factors (Table 3). In this substrate, vivianite + HS was found to be more effective in increasing both plant parameters than Fe-EDDHA and vivianite without HS. The iron sources had a varying effect on pH in drainage water depending on the type of growing medium (Table 3). Thus, vivianite + HS decreased the pH in comparison to the other Fe sources in C and CF, but increased the pH in GM (Table 6). Significant differences were observed in the P, Fe, Mn, and Zn concentrations in plants grown on media with varying Fe sources (Table 7). However, the effect of Fe sources differed across growing media, as revealed by the significant interaction observed between the growing medium and Fe treatment (Table 7). Vivianite and its mixture with humic substances were effective in increasing the P concentration in plants grown on peat and CF (Table 8). However, both vivianite-based treatments increased Fe concentration in comparison to the control containing no Fe only for the former substrate (Table 9). It was also found that the effect of Fe sources on the Mn and Zn concentration in plants varied with the growing medium. Thus, in C, the application of Fe-chelate decreased the Mn concentration in comparison to the control without Fe; in GM, however, the Mn concentration was only reduced by vivianite + HS (Table 10). Overall, Fe supply (especially as Fe-EDDHA) tended to decrease the Zn concentration in C, OH, M, and GM. In peat, however, vivianite + HS increased the concentration of this nutrient in comparison to the control without Fe (Table 11). 4. Discussion Arbitrary units OH C M CF GM Peat 54 46 53 59 53 62 C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances. Table 5 Effect of the different growing media and iron sources on shoot dry matter (DM). Fe-EDDHA g plant OH C M CF GM Peat 29 26 36 22 37 30 Control without Fe Vivianite + HS Vivianite 30 14 33 22 34 28 32 31 34 18 32 25 30 21 32 17 31 25 The increased DM and flower yields obtained with the substrate containing spent mushroom compost (M) in comparison to the other media (Tables 4 and 5) are consistent with previous results of Benito et al. (2005). Compost based on olive husk has been found to induce Fe chlorosis in plants with a similar nutrient supply (Caballero et al., 2007). However, it was found that its mixture with peat lowered the pH of our growing media in comparison to the previous results (Caballero et al., 2007), which may account for the increased chlorophyll content, and DM and flower yields, possibly Table 6 Effect of the different growing media and iron sources on the pH of drainage water 17 weeks after planting. 1 C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances. OH C M CF GM Peat Fe-EDDHA Control without Fe Vivianite + HS Vivianite 6.95 7.48 6.90 5.99 6.74 6.2 6.90 7.58 7.03 6.21 6.73 5.91 6.90 7.17 6.80 5.5 7.02 5.94 6.83 7.70 6.90 5.65 6.80 6.03 C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances. 248 R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250 Table 7 Analysis of variance of nutrient contents in plant leaves after harvesting. Source d.f. Growing medium (A) Fe treatment (B) AB 5 3 15 P value N P K Ca Mg Fe Cu Mn Zn B Fe/Mn 0.0000 0.0538 0.0313 0.0000 0.0000 0.0000 0.0000 0.6903 0.6813 0.0000 0.2454 0.0995 0.0000 0.7579 0.3369 0.0000 0.0086 0.0038 0.0000 0.9515 0.3198 0.0000 0.0236 0.0029 0.0000 0.0000 0.0426 0.0000 0.6506 0.3412 0.0000 0.0000 0.2610 P values lower than 0.05 indicate a significant effect of the source. Table 8 Effect of the different growing media and iron sources on the phosphorus concentration of gerber leaves. Fe-EDDHA g kg OH C M CF GM Peat 1 Control without Fe Vivianite + HS Vivianite 0.18 0.24 0.14 0.19 0.20 0.19 0.16 0.18 0.17 0.38 0.20 0.35 0.17 0.24 0.14 0.40 0.22 0.35 DM 0.15 0.24 0.15 0.20 0.20 0.16 C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter. due to the effect of increased micronutrient availability to plants. The benefits on plant development from the usage of mixtures of composted residues with peat as a result of lowering of pH in the growing media have been previously demonstrated (Benito et al., 2005). Moreover, GM has been reported to induce Fe chlorosis (Caballero et al., 2007). In contrast, our results revealed an interesting potential of GM as a peat-substitute growing medium in combination with commercial Fe-enriched fertilizers. The lowest DM yield was obtained with CF (Table 5) despite the high SPAD readings for plants grown on it (Table 4). This was possibly as a result of restricted Ca supply to plants as revealed by the low Ca concentration in leaves of gerber grown on this substrate, which were approximately five times lower than in the other media (results not shown). The restricted Ca availability to plants can be ascribed to the low concentration of this nutrient in the substrate (Table 1) since no Ca was applied with the fertilizer. Composted cork (C) also exhibited lower DM and flower yields than those for the other media; however, it differed insignificantly from CF in this respect (Table 5, flower results not shown). Chlorophyll meter readings (SPAD) and dry matter (DM) yields were significantly related to pH in drainage water (Fig. 1), with decreasing SPAD readings at increased pH, and decreasing DM yields at extreme pH values. The low DM yield obtained at low pH values can be ascribed to low Ca availability in CF, which exhibited the lowest average pH in drainage water (Table 6 shows the means for each Fe source). The low DM yield obtained at high pH values Table 9 Effect of the different growing media and iron sources on the iron concentration of gerber leaves. Fe-EDDHA mg kg OH C M CF GM Peat 52 43 49 87 74 141 1 Control without Fe Vivianite + HS can be ascribed to deficiencies in other nutrient. Composted cork residue (C) was the substrate exhibiting the highest pH in drainage water; this may explain the low chlorophyll content of plants grown on it by effect of micronutrient deficiencies. The symptoms observed were typical of Fe deficiency, namely, interveinal chlorosis in the youngest leaves. The hypothesis of Fe availability being the main limiting factor for plants grown on C was supported by the efficiency of Fe sources in increasing chlorophyll and DM yield in this substrate (Tables 4 and 5). Dry matter and flower yield in C amended with vivianite + HS were not significantly different from those observed in peat, GM, or OH (Table 5, flower results not shown). Thus, Fe deficiency must be the main nutritional factor limiting plant yield in C. Furthermore, the Mn, Cu or Zn concentration in plants in C were not significantly lower than those in other media, which exhibited a similar DM and flower yields to those registered in peat (Tables 10 and 11 show the Mn and Zn concentrations, respectively); therefore, these micronutrients cannot be considered as the limiting factors. Moreover, Fe supply in the form of applied commercial fertilizers was not sufficient to prevent this nutritional imbalance since the Fe-chelate present in both products (Fe-EDTA) was not as effective as other Fe sources in growing media with high pH values (Wik et al., 2006). The effect of Fe sources on Fe nutrition status in gerber grown on C was not related to the increased Fe concentration in plants (Table 9), and this was consistent with the previous findings of de Santiago et al. (2008). The Fe concentration in plants is not an accurate measure of the Fe nutrition status of plants since Fe Table 10 Effect of the different growing media and iron sources on the manganese concentration of gerber leaves. Fe-EDDHA mg kg OH C M CF GM Peat 21 11 13 44 58 55 Vivianite 58 48 75 101 58 305 C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter. Vivianite + HS Vivianite 20 24 15 66 45 52 17 18 13 41 29 61 16 16 13 49 41 39 Table 11 Effect of the different growing media and iron sources on the zinc concentration of gerber leaves. Fe-EDDHA mg kg 58 62 66 115 60 382 Control without Fe DM C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter. DM 45 50 68 74 51 179 1 OH C M CF GM Peat 3 13 2 29 9 31 1 Control without Fe Vivianite + HS Vivianite 6 20 4 29 13 37 3 12 3 29 13 50 4 19 3 33 11 39 DM C, composted cork residue; OH, olive husk mixed with rice hulls and peat in a 1:1:1 volume proportion; GM, grape marc; M, spent mushroom compost mixed with peat in a 1:1 volume ratio; CF, coconut fibre; HS, humic substances; DM, dry matter. R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250 249 may also have resulted from the fast dissolution of vivianite at a low pH. Application of Fe to the growing media affected the accumulation of Mn and Zn in plants, but the effect was different in each media (Tables 10 and 11). The decreased Mn concentrations observed in gerber plants grown on C treated with Fe-EDDHA (Table 10) were consistent with previous results of Heitholt et al. (2003), who found that Fe supplied as Fe-chelate to decrease the Mn concentration in plant shoots to a greater extent than that for inorganic Fe sources under conditions of restricted Fe availability in the growing media. This can be explained in terms of the antagonistic effect of Fe on Mn accumulation in plants, which is well documented (Ghasemi-Fasaei et al., 2003; Izaguirre-Mayoral and Sinclair, 2005; Chatterjee et al., 2006). The lower efficiency of Fe-chelate in increasing crop yield in C as compared with vivianite + HS can be at least partially ascribed to its enhancing antagonistic effects on Mn. This is supported by previous evidence reported by Ronaghi and Ghasemi-Fasaei (2008), who found that a favourable response to Fe-chelate treatments can be only expected in alkaline growing media if the Fe:Mn ratio in plants is low enough to prevent the antagonistic effect of Fe on Mn. In GM, the antagonistic effect of Fe supply on Mn was observed with vivianite + HS (Table 10), possibly as result of faster dissolution of this Fe source because of the lower pH of this substrate than in C. The adverse effect of Fe-EDDHA on Zn concentration in plants (Table 11) was also consistent with the previous results (Heitholt et al., 2003) and likely to be related to nutrient antagonism (Assimakopoulou, 2006). Furthermore, sorption of Zn on Fe compounds (oxides) formed from applied Fe sources in the growing media can adversely affect the Zn uptake by plants (Montilla et al., 2003). 5. Conclusions Fig. 1. Average chlorophyll meter (SPAD) readings of the five youngest, completely expanded leaves for the last 10 weeks of growth and dry matter production (DM) of gerber (grown on various media amended or not with different Fe sources) as related to the average pH of drainage water during the growing period. chlorosis in sensitive plants has frequently been ascribed to an adverse effect of a high pH on the uptake rate of this nutrient from the apoplast into the symplast (Lucena, 2000; Brand et al., 2000; Yu et al., 2000). The ability of HS to enhance the efficiency of vivianite in increasing SPAD readings and plant development can be partly due to their effects on plant metabolism (Muscolo et al., 1999; Pinton et al., 1999; de Santiago and Delgado, 2007), root development (Cañellas et al., 2002; Chen et al., 2004), and the interaction of HS with Fe forms formed from vivianite applied to the growing media (Fe complexation and inhibition of Fe oxide precipitation, de Santiago et al., 2008), which accounted for more available Fe forms in the growing media, thereby increasing the Fe availability to plants. Vivianite + HS decreased the pH of drainage water in comparison to the control without Fe in C (Table 6), which could also have contributed to increasing Fe availability to plants. The effect of vivianite on the P concentration in peat and CF (Table 8) can be ascribed to the increased dissolution rate of this compound under acidic conditions in comparison to media with a neutral to alkaline pH (Eynard et al., 1992; Rosado et al., 2002). Therefore, vivianite could be an effective P fertilizer in acid media. Moreover, the increased Fe concentration in plants grown on peat amended with vivianite and its combination with humic acids in comparison to the other Fe sources studied in this media (Table 9) Composted grape marc (GM), and mixtures of olive husk and cotton gin trash compost (OH) or spent mushroom compost with peat (M), were found to provide essentially similar flower yields as that for peat typically used for potted gerber production. Dry matter yield was even higher in GM and M than that in peat. Restrictions in coconut fibre can be ascribed to deficiency in Ca availability to plants, and those in composted cork (C) to the incidence of Fe deficiency chlorosis. A mixture of vivianite with humic substances with a weight ratio of 10:1 was applied at a rate of 1.1 g per L of substrate; it was found to be more effective – and inexpensive – in overcoming Fe chlorosis than Fe-chelate (FeEDDHA) in C. Dry matter and flower production in C amended with vivianite + HS was not significantly different from that in peat. The effectiveness of this Fe source in preventing Fe chlorosis in high pH media and the results obtained with the different compost-based growing media studied are interesting with a view of reducing peat consumption in horticulture. Acknowledgements This work was funded by the Spain’s Ministry of Education and Research and also by the Regional Development Funds of the European Union through the National R & D Program (Plan Nacional I + d + i) (Projects AGL2005-06691-CO2-02-02-AGR and AGL2008-05053-CO2-01). The work of Mr. Raymundo Caballero at the University of Seville was funded by a grant from the Mexican Federal Government. References Abad, M., Noguera, P., Burés, S., 2001. National inventory of organic wastes for use as growing media for ornamental potted plant production: case study in Spain. Bioresour. Technol. 77, 197–200. 250 R. Caballero et al. / Scientia Horticulturae 122 (2009) 244–250 Álvarez-Fernández, A., Garcı́a-Laviña, P., Fidalgo, C., Abadı́a, J., Abadı́a, A., 2004. Foliar fertilization to control iron chlorosis in pear (Pyrus communis L.) trees. Plant Soil 263, 5–15. Assimakopoulou, A., 2006. Effect of iron supply and nitrogen form on growth, nutritional status and ferric reducing activity of spinach in nutrient solution culture. Sci. Hortic. 110, 19–21. Australian Standard AS 3743, 1993. Method for determination of nutrient levels. Benito, M., Masaguer, A., De Antonio, R., Moliner, A., 2005. Use of pruning waste compost as a component in soilless growing media. Bioresour. Technol. 96, 597–603. Brand, J.D., Tang, C.T., Graham, R.D., 2000. The effect of soil moisture on the tolerance of Lupinus pilosus genotypes to a calcareous soil. Plant Soil 219, 263–271. Caballero, R., Ordovás, J., Pajuelo, P., Carmona, E., Delgado, A., 2007. Iron chlorosis in gerber as related to properties of various types of compost used as growing media. Commun. Soil Sci. Plant Anal. 38, 2357–2369. Cañellas, L.P., Olivares, F.L., Okorokova-Façanha, A.L., Façanha, A.R., 2002. Humic acids isolated from earthworm compost enhance root elongation, lateral root emergence, and plasma membrane H+-ATPase activity in maize roots. Plant Physiol. 130, 1951–1957. Carmona, E., Avilés, M., Domı́nguez, I., Moreno, M.T., Pajuelo, P., Ordovás, J., 2004. Exploitation of composted agricultural wastes as growing media. In: Bernal, P., Mora, R., Clemente, R., Paredes, C. (Eds.), Proceedings of the 11th International Conference of the FAO ESCORENA Network on Recycling of Agricultural, Municipal and Industrial Residues in Agriculture: Sustainable Organic Waste management for Environment Protection and Food Safety, Murcia, Spain, pp. 141–144. Carmona, E., Ordovás, J., Domı́nguez, I., Sández, J.A., Moreno, M.T., 2002. Sustratos alternativos a la turba para el cultivo en maceta de plantas ornamentales [Alternative growing media to peat for ornamental potted plant production]. Actas de las I Jornadas Ibéricas de Plantas Ornamentales (SECH y APH), Consejerı́a de Agricultura y Pesca de la Junta de Andalucı́a, Sevilla, Spain, pp. 287– 291. Chatterjee, C., Gopal, R., Dube, B.K., 2006. Impact of iron stress on biomass, yield, metabolism and quality of potato (Solanum tuberosum L.). Sci. Hortic. 108, 1–6. Chen, Y., Clapp, C.E., Magen, H., 2004. Mechanisms of plant growth stimulation by humic substances: the role of organo-iron complexes. Soil Sci. Plant Nutr. 50, 1089–1095. de Santiago, A., Delgado, A., 2006. Predicting iron chlorosis of Lupinus albus L. in calcareous Spanish soils from various iron extracts. Soil Sci. Soc. Am. J. 70, 1945– 1950. de Santiago, A., Delgado, A., 2007. Effects of humic substances on iron nutrition of lupin. Biol. Fertil. Soils 43, 829–836. de Santiago, A., Quintero, J.M., Carmona, E., Delgado, A., 2008. Humic substances increase the effectiveness of iron sulfate and vivianite preventing iron chlorosis in white lupin. Biol. Fertil. Soils 44, 875–883. Eynard, A., del Campillo, M.C., Barrón, V., Torrent, J., 1992. Use of vivianite (Fe3(PO4)2
8H2O) to prevent iron chlorosis in calcareous soils. Fertil. Res. 31, 61–67. Fisher, P.R., Wik, R.M., Smith, B.R., Pasian, C.C., Kmetz-González, M., Argo, W.R., 2003. Correcting iron deficiency in calibrachoa grown at high pH. HortTechnology 13, 308–313. Ghasemi-Fasaei, R., Ronaghi, A., Maftoun, M., Karimian, N., Soltanpour, P.N., 2003. Influence of FeEDDHA on iron–manganese interaction in soybean genotypes in a calcareous soil. J. Plant Nutr. 26, 1815–1823. Godsey, C.B., Schmidt, J.P., Schlegel, A.J., Taylor, R.K., Thompson, C.R., Gehl, R.J., 2003. Correcting iron deficiency in corn with seed row-applied iron sulfate. Agron. J. 95, 160–166. Girgatti, M., Giorgioni, M.E., Ciavatta, C., 2007. Compost-based growing media: influence on growth and nutrient use of bedding plants. Bioresour. Technol. 98, 3526–3534. Heitholt, J.J., Sloan, J.J., MacKown, C.T., Cabrera, R.I., 2003. Soybean growth on calcareous soil as affected by three iron sources. J. Plant Nutr. 26, 935– 948. Hernández-Apaolaza, L., Gascó, A.M., Gascó, J.M., Guerrero, F., 2005. Reuse of waste materials as growing media for ornamental plants. Bioresour. Technol. 96, 125– 131. Ingelmo, F., Canet, R., Ibáñez, M.A., Pomares, F., Garcı́a, J., 1998. Use of MSW compost, dried sewage sludge and other wastes as partial substitutes for peat and soil. Bioresour. Technol. 63, 123–129. Izaguirre-Mayoral, M.L., Sinclair, T.R., 2005. Variation in manganese and iron accumulation among soybean genotypes growing on hydroponic solutions of differing manganese and nitrate concentration. J. Plant Nutr. 28, 521–535. Lindsay, W.L., Norwell, W.A., 1978. Development of DTPA soil test for zinc, iron, manganese, and copper. Soil Sci. Soc. Am. J. 42, 421–428. Lucena, J.J., 2000. Effect of bicarbonate, nitrate and other environmental factors on iron deficiency chlorosis. A review. J. Plant Nutr. 23, 1591–1606. Lucena, J.J., 2003. Fe chelates for remediation of Fe chlorosis in Strategy I plants. J. Plant Nutr. 26, 1969–1984. Marianthi, T., 2006. Kenaf (Hibiscus cannabinus L.) core and rice hulls as components of container media for growing Pinus halepensis M. seedlings. Bioresour. Technol. 97, 1631–1639. Marfà, O., Lemarie, F., Cáceres, R., Giuffrida, F., Guérin, V., 2002. Relationships between growing media fertility, percolate composition and fertigation strategy in peat-substitute substrates used for growing ornamental shrubs. Sci. Hortic. 94, 309–321. Mengel, K., 1994. Iron availability in plants tissues—iron chlorosis on calcareous soils. Plant Soil 165, 275–283. Miller, G.W., Pushnik, J.C., Welkie, G.W., 1984. Iron chlorosis, a world wide problem: the relation of chlorophyll biosynthesis to iron. J. Plant Nutr. 7, 1–22. Montilla, I., Parra, M.A., Torrent, J., 2003. Zinc phytotoxicity to oilseed rape grown o zinc-loaded substrates consisting of Fe oxide-coated and calcite sand. Plant Soil 257, 227–236. Mulvaney, R.L., 1996. Nitrogen-inorganic forms. In: Bigham, J. (Ed.), Methods of Soil Analysis. Part 3. Chemical Methods. Soil Science Society of America, Madison, WI, pp. 869–920. Murphy, J., Riley, J.P., 1962. A modified single solution method for the determination of phosphate in natural waters. Anal. Chim. Acta 27, 31–36. Muscolo, A., Bovalo, F., Gionfriddo, F., Nardi, S., 1999. Earthworm humic matter produces auxin-like effects on Daucus carota cell growth and nitrate metabolism. Soil Biol. Biochem. 31, 1303–1311. Ordovás, J., Carmona, E., Moreno, M.T., Ortega, M.C., 1996. Characteristics of internal porosity of container media. HortScience 31, 1177–1179. Ordovás, J., Carmona, E., Ortega, M.C., Aguado, M.T., 1997. Caracterı́sticas fı́sicas de sustratos de corcho y turba en macetas tras 2,5 meses de cultivo.(Physical properties of cork and peat substrates after 2.5 months of growing in pots). Acta Horticult. 18, 464–467. Pinton, R., Cesco, S., Santi, S., Agnolon, F., Varanini, Z., 1999. Water-extractable humic substances enhance iron deficiency responses by Fe-deficient cucumber plants. Plant Soil 210, 145–157. Ribeiro, H.M., Romero, A.M., Pereira, H., Borges, P., Cabral, F., Vaconcelos, E., 2007. Evaluation of a compost obtained from forestry wastes and solid phase of pig slurry as a substrate for seedlings production. Bioresour. Technol. 98, 3294–3297. Robertson, R.A., 1993. Peat, horticulture and the environment. Biodivers. Conserv. 2, 541–547. Rombolà, A.D., Toselli, M., Carpintero, J., Ammari, T., Quartieri, M., Torrent, J., Marangoni, B., 2003. Prevention of iron-deficiency induced chlorosis in kiwifruit (Actinida deliciosa) through soil application of synthetic vivianite in a calcareous soil. J. Plant Nutr. 26, 2031–2041. Ronaghi, A., Ghasemi-Fasaei, R., 2008. Field evaluations of yield, iron–manganese relationships, and chlorophyll meter readings in soybean genotypes as affected by iron-ethylenediamine di-o-hydroxyphenylacetic acid in a calcareous soil. J. Plant Nutr. 31, 81–89. Rosado, R., del Campillo, M.C., Martı́nez, M.A., Barrón, V., Torrent, J., 2002. Long-term effectiveness of vivianite in reducing iron chlorosis in olive trees. Plant Soil 241, 139–144. Sánchez-Monedero, M.A., Roig, A., Cegarra, J., Bernal, M.P., Noguera, P., Abad, M., Antón, A., 2004. Composts as media constituents for vegetable trasplant production. Compost Sci. Util. 12, 161–168. Smith, B.R., Fisher, P.R., Argo, W.R., 2004. Water-soluble fertilizer concentration and pH of a peat-based substrate affects growth, nutrient uptake, and chlorosis of container-grown seed geraniums. J. Plant Nutr. 27, 497–524. StatPoint, 2000. Statgraphics Plus 5.1. StatPoint, Herndon, VA. Velázquez, M., del Campillo, M.C., Torrent, J., 2004. Temporary flooding increases iron phytoavailability in calcareous vertisols and inceptisols. Plant Soil 266, 195–203. Wik, R.M., Fisher, P.R., Kopsell, D.A., Argo, W.R., 2006. Iron form and concentration affect nutrition of container-grown Pelargonium and Calibrachoa. HortScience 44, 244–251. Yu, Q., Tang, C., Kuo, J., 2000. A critical review on methods to measure apoplastic pH in plants. Plant Soil 219, 29–40.