NEW MULCHING MATERIALS FOR POTTED ORNAMENTALS

Agr. Med. Vol. 137, 000-000 (2007)

NEW MULCHING MATERIALS FOR POTTED ORNAMENTALS L. Martinetti1, G. Amoroso2, P. Frangi2 Department Produzione Vegetale – Section Agronomia, University of Milan, Italy –MiRT Center, Vertemate con Minoprio (Como), Italy (1)

Fondazione Minoprio

(2)

SUMMARY – In this study two new mulching materials were tested for weed control in container cultivation of Acer platanoides, Prunus laurocerasus and Thuja plicata nursery stocks: a biodegradable film composed by viscose fibre (90%) and polyvinyl alcohol (10%), and a mineral mixture that solidifies and forms a compact layer permeable to air and water. For each species, a randomised block experimental design was used with four blocks and five replicates per plot. Both mulching materials were very effective in weed control. The persistence of the mineral mixture was very long, whereas the viscose film began to decompose after two months. In all species, the growth was slightly affected by different mulching materials. However, the mineral mixture caused serious injury to the root collar; although no reduction of plant growth was observed in the short period of the experiments, this injury might compromise the stability and make the plants unmarketable. Key words: Acer platanoides, Prunus laurocerasus, Thuja plicata, weed control, nursery stock production.

INTRODUCTION

market requires weed-free potted plants, growers often control weeds by herbicides (Simpson et al., 2002). Unfortunately, in Italy there are few herbicides registered to be use in ornamental. Weed infestations in pots are not limited to higher plant forms, since some mosses are highly invasive and very difficult to control (Fausey, 2003). Direct application of herbicides to the pots leads to an amount of runoff that depends on several factors, such as pot spacing, plant canopy, substrate water retention, irrigation regime, rainfall distribution in addition to the water solubility of the chemical under consideration (Keese et al., 1994; Manhnken et al., 1994). For instance, Riley (2003) reported that more than 7% of isoxaben applied was found in runoff water in the following eight days after treatment. A different approach to control weeds in potted plant production is the use of mulching to keep the media covered, thus preventing seed germination (Wilen et al., 1999). Some organic mulching materials were tested for weed suppression: bark of various

In the last years, outdoors container cultivation of nursery stocks has rapidly increased in Italy and in many other countries in consideration of the better standardization of the production and the possibility to transplant the marketed plants all year round. In container cultivation, weed control is a serious problem, as the limited volume of the container causes a strong competition for air, water and nutrients between the cultivated plant and weeds (Gilliam et al., 1990; Case et al., 2005). Several studies pointed out the influence of weeds on plant growth (Walker and Williams, 1989; Berchielli-Robertson et al., 1990; Norcini and Stamps, 1994). For instance, Fretz (1972) found that the presence of just one well-developed plant of Amaranthus retroflexus or Digitaria sanguinalis can reduce the growth of Ilex crenata by 47% and 60% respectively. Obviously, the manual removal of weeds is very expensive, up to 1.3 $ per pot, according to Darden and Neal (1999). As the

*Corresponding Author: via Celoria 2, 20133 Milano – E-mail: [email protected]; tel. +39 02 50316589



AGRICOLTURA MEDITERRANEA

tree species, rice hulls, pelletized waste wool or waste paper (Billeaud and Zajicek, 1989; Smith et al., 1998; Bilderback and Neal, 2004). Weed disks, equipped with a slit in the centre to fit around the plant stem, were proposed in the United States and in Canada since early 1980s (Chong, 2003). In the last years¸ different materials ave been proposed and testedto be used as a weed disks: non-woven fabric, polypropylene, coconut, flax and jute fibres. The desirable traits of these disks are water permeability and a minimum duration of 4-6 months; furthermore, they must be enough rigid in order to prevent lateral rising and wind-blown and of course their cost must be reasonable. Another way to keep containers free of weeds is to cover the surface of the substrate with a mixture of minerals that solidifies after wetting without any important changes in water permeability. In this study two new mulching materials were tested for weed control in container cultivation of Acer platanoides, Prunus laurocerasus and Thuja plicata nursery stocks: a biodegradable film composed by viscose fibre (90%) and polyvinyl alcohol (10%), and a mineral mixture that solidifies and forms a compact layer permeable to air and water.

8-12; Ficote; 4 kg/m3) were incorporated in the medium. A. platanoides plants were spaced 40 x 40 cm (about 6 plants/m2), Prunus laurocerasus and Thuja plicata 30 x 30 cm (11 plants/m2). The mulching materials under investigation were the following: i) a biodegradable film (Giotto, Giotto Industrial Networking, Riva San Vitale, Switzerland) composed by viscose fibre (90%) and polyvinyl alcohol (10%), with a density of 43 g/m2; ii) a mineral mixture (Gerval, Gerval s.r.l., Reggio Emilia, Italy) that solidifies and forms a compact layer permeable to air and water. The vicose film were put on the surface of substrate around the stems of the plants and fixed to the pots with adhesive tape. The mineral mixture was pugged with water (4:1, wt/v) and applied to the top of pots around the plant trunk; the mulching thickness was about 2 cm. Control plants were not mulched and the weeds were removed manually. A randomised block experimental design was used for each species, with four blocks and five replicates per plot. The number of weeds per pot was monitored fortnightly. At the end of the growing season, the following parameters were measured: plant height; stem diameter at 10 cm above the substrate in Norway maple; the number of branches in cherry laurel; the leaf greenness (by Minolta SPAD-5029 in Norway maple and cherry laurel; leaf fresh and dry weight of the leaves of Norway maple; root fresh and dry weight in cherry laurel and western red cedar. Moreover, During the trial, the water tension of the substrate was continously monitored with a tensiometer in A. platanoides and P. laurocerasus.

MATERIALS AND METHODS In the period from June to October of 2004, plants of Norway maple (Acer platanoides L.), cherry laurel (Prunus laurocerasus L. var. rotundifolia) and western red cedar (Thuja plicata L. var. atrovirens) were grown into pots under a shaded tunnel at the Fondazione Minoprio (Vertemate con Minoprio, Como, Italy). Three years old seedlings of Norway maple, 150 cm high, were potted into 24 cmdiameter pots (7.5 L); the plants of cherry laurel and western red cedar (propagated by cutting, one and two years old, respectively), on the average 45 cm high, were potted into 18 cm diameter pots (3 L). The growing medium was a peat:pumice mixture (4:1, v/v). CaCO3 (4 kg/m3) and a controlled release (8-9 months) fertiliser (15-

RESULTS AND DISCUSSION No differences in leaf and root growth were found among treatments for A. platanoides and P. laurocerasus (Tab.1-2). Conversely, the plants of Thuja plicata were taller when mulched with viscose film as compared to



l. martinetti, g. amoroso, p. frangi

Tab. 1. The influence of pot mulching with different materials on the growth, leaf chlorophyll content (Spad value) and the number of weeds determined per pot in container-grown plants of Acer platanoides. Control pots were not mulched. Mean separation by Duncan’s test (P=0.05). Control Viscose film Mineral mixture

Plant height Plant diameter (cm) (mm) 208.6 a 204.0 a 192.8 a

Leaf fresh Dry matter Spad values Weeds matter (g) partitioning (%) per pot (n.)

18.9 a 18.5 a 17.7 a

90.0 a 92.3 a 87.6 a

71.7 a 69.7 a 72.5 a

44.8 a 45.5 a 42.9 a

19.5 a 3.6 b 0.4 b

Tab. 2. The influence of pot mulching with different materials on the growth, leaf chlorophyll content (Spad value) and the number of weeds determined per pot in container-grown plants of Prunus laurocerasus. Control pots were not mulched. Mean separation by Duncan’s test (P=0.05).     Control Viscose film Mineral mixture

Plant height (cm)

Leaf fresh matter (g)

75.6 a 77.7 a 76.8 a

226.6 a 252.5 a 245.3 a

Dry matter Root fresh partitioning (%) matter (g) 46.2 a 42.8 a 43.5 a

the other mulching material. The dry matter allocation to the leaves was slightly higher in the mineral mixture treatment, as compared to the other treatments (Tab.3). The SPAD values, correlated with the leaf chlorophyll content, were not statistically different in all the treatments. Plant growth was satisfactory in the controls as well, thus suggesting that manual removal of weeds was effective, although it was quite expensive owing to the large weed infestation. The mineral mixture mulching damaged the root flare of plants, because its reduced elasticity prevented the stem radial growth in the area of contact with the mixture. In the relatively short period of the experiments, this drawback did not affect significantly plant growth, but especially in T. plicata it compromised plant stability and made them

178.9 a 196.8 a 165.9 a

Root dry Weeds matter (%) per pot (n.) 45.0 a 44.5 a 46.1 a

23.7 a 3.0 b 0.0 b

unmarketable. The reduced elasticity of the mineral mixture caused also some cracks on the mulching surface, which were observed at the end of the trial. The total number of weeds observed during the trial was significantly higher in the control treatment as compared to mulched pots; only in Thuja plicata the mineral mulching gave better results than viscose film (Tables 1-3). Most of the weeds found in the containers were dicotyledonous; in order of frequency they were: Oxalis corniculata, Sagina subulata, Polygonum persicaria, Euphorbia maculata, Euphorbia peplus, Stellaria media, Cardamine hirsuta, Capsella bursa-pastoris, Sonchus oleraceus, Portulaca oleracea, Lamium amplexicaule, Potentilla reptans, Erigeron annuus, Cerastium holosteoides, Veronica persica, Galinsoga ciliata.

Tab. 3. The influence of pot mulching with different materials on the growth, leaf chlorophyll content (Spad value) and the number of weeds determined per pot in container-grown plants of Thuja plicata. Control pots were not mulched. Mean separation by Duncan’s test (P=0.05).     Control Viscose film Mineral mixture

Plant height (cm) 65.3 b 68.8 a 59.9 c

Leaf fresh Dry matter Root fresh matter (g) partitioning (%) matter (g) 91.1 a 92.6 a 80.0 a

54.8 B 54.5 B 59.6 A



67.3 a 62.1 a 57.8 a

Root dry matter (%)

Weeds per pot (n.)

53.8 a 57.0 a 57.7 a

45.5 a 17.9 b 1.5 c

AGRICOLTURA MEDITERRANEA

covered the substrate much less effectively than other species. In the pots mulched with viscose film, the weeds grew on the bare substrate or near the slit in the film disk. At the end of the growing season, also in A. platanoides the mineral mixture performed better than the viscose film. Both mulching materials reduced the water tension of the substrate in the afternoon in P. laurocerasus (Fig.2): this result suggest that this material may provide a mean to reduce irrigation volume and/or frequency. In A. platanoides pot mulching hardly affected substrate water tension, which showed little variation during the day, probably in consequence of the large container (7.5 L) used

Fig. 1. The influence of pot mulching with different materials on the number of weed determined in different occasions during the growing season in container-grown plants of Acer platanoides, Prunus laurocerasus and Thuja plicata. Control pots (test) were not mulched. Mean separation by Duncan’s test (P=0.05).

Among monocotyledons, Cynodon dactylon and Digitaria sanguinalis were observed. Weed number generally increased in the controls during the growing season, whereas it was rather low and constant with the mulches (Fig. 1). The mineral mixture completely prevented the establishment of weeds, although some of them just appeared at the end of the growing season at the pot border or in the fractures. The viscose film provided an excellent weed control, however it began to decompose about two months after potting; this film degradation was clearly evident in Thuja plicata, which

Fig. 2. The influence of pot mulching with different materials on the substrate water tension in a typical day during growing season in container-grown plants of P. laurocerasus and A. platanoides. Control pots were not mulched. Mean separation by Duncan’s test (P=0.05).



l. martinetti, g. amoroso, p. frangi

for this species compared to the 3.0-L pots adopted for the other two species. In conclusion, our experiment showed that both the mulching materials were very effective for weed control. The life-span of the mineral mixture was very long, whereas the viscose film began to deteriorate after two months, when summer temperatures were very high. This deterioration was faster in Thuja plicata, since its canopy covered the pot surface substrate less effectively than other species. The elasticity of the mineral mixture must be improved, in order to avoid collar injuries; furthermore, it must be considered that this material increases considerably the weight of the pots and this may be a serious inconvenient from the point of view of nursery operation.

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Received: 00/00/200?

Accepted: 00/00/200?

ACKNOWLEDGEMENTS The work was supported by Regione Lombardia, Project “FLOROBIO (Produzioni florovivaistiche a basso impatto ambientale)”. REFERENCES