THE EFFECT OF COMPOST FROM POST-CONSUMER WOOD ON VEGETATIVE GROWTH OF CANNA X GENERALIS L.H. BAILEY

Hanna Wróblewska¹, Anita Schroeter-Zakrzewska^2
1 Environmental Protection and Wood Chemistry Department, Wood Technology Institute, Poznań, Poland
² Department of Ornamental Plants, University of Life Sciences in Poznań, Poland

ABSTRACT

The aim of the study was to identify the effect of composts obtained from post-consumer wood on the dynamics of vegetative growth and greening of leaves of canna lily (Canna x generalis L.H. Bailey) ‘Tropical Yellow’.

Key words: waste, wood, composting, peat, SPAD, Canna x generalis.

INTRODUCTION

In times of growing concern for environmental protection, increasingly often replacements for peat substrates, which are commonly used in horticulture and imported mostly from Eastern European countries, are sought. The intense exploitation of peat deposits in Poland, as well as in Europe, has led to considerable depletion of peat resources and caused significant disturbances in functioning of peat bog ecosystems. Not only are peat bogs a source of valuable organic material, but primarily they are important ecosystems playing a significant role in water storage, climate control and creation of living conditions for many species of animals and plants [7]. Inappropriate management may contribute to destruction of these hardly renewable resources. Therefore, it is necessary to introduce other components of horticultural substrate, which will completely, or at least partially, substitute for this natural resource. Compost is often used as a supplement of peat in plant cultivation [6]. It is a product of microbiological aerobic transformation of organic waste mixture [8]. Production and natural use of composts brings a double benefit to the environment, i.e. conservation of the natural resource that is peat and management of burdensome organic waste, such as wood waste (including post-consumer wood). Post-consumer wood is a recyclable material obtained from old, worn out furniture, carpentry and joinery products (doors, windows, floors, walls) and building structures (joists, roof trusses). This heterogeneous material consists of solid wood and composite wood materials (fibreboards, chipboards, plywood). Due to functional aspects (appearance, extended durability) the surface of wood products is finished with various chemical agents. Hence, post-consumer wood, in addition to the wood itself, contains fixed synthetic or natural additives such as paints, lacquers, wood stains, enamel paints, waxes, glues, resins, laminates, and foils. The proportion of these additives may be as high as 10% of the weight. The remaining 90% is biodegradable organic matter, mainly lignocellulose.

Every year the environmental protection regulations limit the possibilities of depositing organic waste at storage yards. This waste should be used for energy or raw material purposes. The waste hierarchy of utilisation of all types of waste places material use before use for energy purposes. One way of material use of post-consumer wood is its aerobic biological utilisation in the process of composting, which is preferred in the case of wood waste due to the high content of lignin in wood (~25%) [8].

According to the literature, composts of various origins, for instance from industrial, municipal, wood and other waste, may be successfully used for cultivation of ornamental plants [4, 17, 22]. These composts are a valuable source of organic fertilizers and minerals that are missing in barren soils [11, 12]. Composts from post-consumer and industrial wood waste are usually characterised by overabundance of nitrogen and deficiency of other nutritional elements compared to commercial horticultural substrate [19, 20, 21]. Due to the diverse requirements of different plants in terms of soil and fertilizers, it is recommended that the usefulness of composts for cultivation of particular species be checked by means of individual tests [5, 10, 19, 20, 21].

The aim of the present study was to determine the effect of composts obtained from post-consumer wood on the dynamics of vegetative growth and greening of leaves of canna lily (Canna x generalis L.H. Bailey) ‘Tropical Yellow’.

MATERIALS AND METHODS

The experiment, aimed at determination of the usefulness of composts prepared from wood waste in the Wood Technology Institute, was carried out in a greenhouse of the Department of Ornamental Plants of Poznan University of Life Sciences. The test object was canna lily (Canna x generalis L.H. Bailey) ‘Tropical Yellow’, reproduced generatively and characterised by green leaves and yellow flowers.

Seedlings with two or three leaves were planted on the third day of April 2012 into pots of a diameter of 17 cm and a capacity of 2100 cm³. Two types of composts, marked OPA and OPB, were used in the experiment. These composts differed in the additives of urea and macroelements at the stage of composting in the form of heaps. Both composts contained post-consumer wood waste (OP) (70% dry matter) mixed with dust waste from processing of MDF boards (6% dry matter), mature compost from fibreboard waste (19% dry matter), high-moor peat (4% dry matter), water (60%), and the biological inoculum Activit Las. Additionally, the OPA variant contained 30 kg of urea per heap of a volume of ~5m³, and the OPB variant contained 1.5 kg of ammonium nitrate, 0.4 kg of magnesium sulphate, 0.8 kg of potassium phosphate, and 0.9 kg of calcium phosphate per heap of the same volume.

The plants were cultivated on substrates composed of peat with a supplement of composts in different volumetric proportions. The control was a group of plants growing on high-moor peat limed to pH in H₂O = 6.3. No mineral fertilizer was used in the cultivation of canna lily. The individual combinations are presented below:

I – 100% compost,
II –  75% compost + 25% peat,
III – 50% compost + 50% peat,
IV – 25% compost + 75% peat.

The experiment consisted of 9 combinations, with 11 replications, one plant constituting a replication.

Every two weeks during the cultivation period the plant height was measured, the number of leaves counted, and the index of leaf greening (SPAD) was determined using the N-Tester apparatus by Yara. This measurement enables determination of the intensity of the green colour of leaves and consists in calculation of the quotient of light absorption connected with the presence of chlorophyll at a wavelength of 650 nm and absorption by the leaf tissue at a wavelength of 940 nm [13].

The obtained results were statistically processed using one–way analysis of variance, and the means were grouped using the Duncan test at a significance level of α = 0.05.

Prior to the start of cultivation the content of macronutrients (N-NO₃, P, K, Ca, Mg, Cl), salinity and pH in H₂O, as well as volumetric weight, were determined for the substrate (Tab. 1).

Macronutrients were analysed in a universal extract (CH₃COOH of a concentration of 0.03 mol∙dm^-3) by Nowosielski’s method [1]. Nitrate nitrogen was determined potentiometrically, phosphorus spectrophotometrically, potassium and calcium by flame photometry, magnesium by atomic absorption spectroscopy (AAS) with flame atomization, chlorides potentiometrically, salinity conductometrically, pH potentiometrically, and volumetric weight by the weight method.

RESULTS AND DISCUSSION

Composting is a method that enables utilisation of many different, seemingly useless, types of waste [3, 4, 8, 14]. Depending on the origin, composts may contain very different, often high quantities of mineral salts. Therefore, in order to minimise the negative effect of the compost itself, it is most often used in mixtures with high-moor peat or mineral soil [6, 19, 20, 21]. Too high doses of composts may lead to an increase in salinity and to inhibition of plant growth due to unfavourable properties of substrate. This is confirmed by chemical analyses, carried out as part of the authors’ own research, which showed that the tested composts contained more nitrogen and potassium, but less calcium, phosphorus, magnesium and chlorides. Moreover, the composts OPA and OPB were characterised by higher salinity (297 and 430 g NaCl∙dm^-3) and a low pH in H₂O (pH = 3.6 and pH = 3.7 respectively). The content of macronutrients, as well as pH and salinity, characterising a particular substrate was a derivative of the proportion of compost and peat (Tab. 1). The composition of the substrate was reflected by the dynamics of plant growth, the number of leaves and their greening level.

Monitoring of the growth dynamics, irrespective of the compost type, indicated that the higher was the proportion of compost in the substrate, the shorter were the plants (Fig. 3 and 4), whereas the analysis of the last measurement indicated that, compared to control plants, the plants growing on the OPA and OPB composts alone, and on the substrates containing 75% additives of composts, were shorter by, respectively, 61, 43, and 35%. A similar trend was observed during the cultivation period (Tab. 2 and 3, Fig. 1 and 2). According to Wraga [18], an increasing proportion of compost, which is made from vegetable waste, in the substrates has an adverse influence on the height of the star cluster (Pentas lanceolata). The negative influence of a high dose of compost results primarily from the excessive content of mineral salts and deteriorating physical properties of the substrates [16]. This is confirmed by the results of the analysis of substrate carried out as part of the authors’ own experiment. In the case of compost OPA the content of nitrogen was 546 mg∙dm^-3, and in the case of compost OPB it was 733 mg∙dm^-3. The high content of nitrate ions caused in salinity of peat-free composts (Tab. 1). Salinity above the tolerance level has a negative effect on plant growth because it reduces the osmotic potential. This applies especially to young plants and those that are very sensitive to this parameter of the substrate. The tolerance of plants to salinity depends on the species and variety. Very sensitive ornamental plants such as geranium and chrysanthemum show damage at EC 0.8–1.0 mS∙cm^-1, and slightly sensitive such as amaryllis and sansevieria tolerate salinity up to 1.4 mS∙cm^-1 [2, 15]. The plants grown on the substrate with 25% compost, irrespective of the compost  type (OPA or OPB), did not differ significantly from the plants grown on peat (Tab. 2 and 3, Fig. 5). According to Wróblewska et al. [20], a 25% admixture of composts OPA and OPB to mineral soil stimulated the growth of willow shoots (Salix alba). A positive influence of a small amount of additives of compost on the plant height was also observed by Klock-Moore [9].

One of the factors that decide the quality of plants is the colour of leaves, which may be determined based on the greening index (SPAD). In the authors’ own experiment, in the case of plants grown on substrates consisting of pure compost and substrates containing 75% compost, the obtained leaves were characterised by significantly lower values of SPAD compared to control plants. Moreover, chlorosis was visible on the leaves (Fig. 3 and 4). In the case of plant cultivation on substrates containing 50 and 25% compost, the values of SPAD were not significantly different or were higher when compared with plants grown on peat (Tab. 2 and 3). The probable cause of the weak intensity of the leaf green colour and the low levels of other biometric parameters could be the strongly acidic (pH < 5) substrates containing higher doses of composts (100%, 75%) (Tab. 1). Reaction of the soil affects plant growth and development as it regulates the absorption of nutrients. For most plants grown in pots (containers) optimum pH of the soil is 6.0–6.5 (slightly acid) [2, 15].

The statistical analysis showed that the plants cultivated on compost alone produced fewer leaves compared to the rest of the plants (Tab. 2 and 3).

The conducted tests proved that composts obtained from post-consumer wood may be used in a mixture with peat, in an amount of compost not exceeding 50%, for the cultivation of canna lily. The authors think that in the cultivation of Canna x generalis could be used higher doses of composts from post-consumer wood waste provided that they are limed to slightly acid pH.

CONCLUSIONS

1. The type of substrates had a significant effect on the vegetative growth and greening of leaves of canna lily (Canna x generalis L.H. Bailey) ‘Tropical Yellow’.
2. Our results show that the higher doses of compost (100 and 75%) in the substrates inhibited the growth of plants.
3. Lower doses of compost (50 and 25%) gave results which were comparable to control plants.

The scientific work was financed by funds for science in the years 2010–2013 as a part of research project no. NN309281637.

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