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ISSN : 1598-5504(Print)
ISSN : 2383-8272(Online)
Journal of Agriculture & Life Science Vol.50 No.6 pp.69-80
DOI : https://doi.org/10.14397/jals.2016.50.6.69

Optimum Mixing Ratio of Growing Media and Soil for Water Maintenance in Pot Culture

Ju-Hyun Choi1 , Si Young Ha2,3, Ji Young Jung2,3, Jeong Bin Nam2,3, Ji-Su Kim2, Jae-Kyung Yang2,3*
1Department of Textile Design, Gyeongnam National University of Science and Technology, Jinju, 52725, Korea
2Division of Environmental Forest Science, Gyeongsang National University, Jinju, 52828, Korea
3Institute of Agriculture & Life Science, Gyeongsang National University, Jinju, 52828, Korea
Corresponding author : Jae-Kyung Yang +82-55-772-1862+82-55-772-1869jkyang@gnu.ac.kr
September 9, 2016 November 2, 2016 November 23, 2016

Abstract

The efficacy of the natural amendments in improving physical condition as well as water retention characteristics of the growing media in pot culture was studied on seven different mix ratio of growing media applied to soil. Growing media was prepared from peat, perlite, pruning waste, pulp(3:1:3:3(w/w/w/w)). Growth substrates were prepared by mixing growing media at the rates of 0%, 10%, 20%, 30%, 40%, 50% and 100% with soil at 100%, 90%, 80%, 70%, 60%, 50% and 0%, respectively. The bulk density tended to decreased with increasing growing media proportions. The particle density was lowest(0.6 g/cm3) in sole growing media treatment and the porosity of all the soil mixed growing media(63.2~83.3%) was significantly higher than that of the soil as sole medium(60.7%). The water content was lowest in sole soil treatment(5.1%) and growing media as sole medium(57.8%) was the closely ideal range for pot culture(>60%). Although substrates were varying water to the atmosphere at similar rates which retained water for longer, growing media as sole still remain constant on high water content. It was confirmed that strongly correlated between bulk density and water retentivity(correlation-0.85).


초록


    Introduction

    The culture of shrubs in containers has shown a marked increase in recent years(Fascella & Rouphael, 2015), and during the last two decades, the potted plant industry for shrubs has undergone a dramatic expansion, with potted plants now being readily available in retail stores, as well as nurseries(Clark & Zheng, 2015). The marketability of potted plants is greatly influenced by the quality of plants produced, which has increased the need for a regular supply of a uniform growing media that has the ability to support vigorous plant growth(Ouldboukhitine et al., 2014).

    The concept of growing plants in containers is markedly different than growing them in open soil. For example, when pots are used, the volume of medium from which the plant can absorb water is limited and is usually smaller than that available to plants growing in field(Sala et al., 2012). Thus, in order to take full advantage of these pots conditions, an adequate amount of easily available water must exist within the root zone. However, whenever such a water regime is being maintained, the problem of aeration arises. Fortunately, since artificial growth media are usually porous and because the root zone is homogenous, strict control of water and air contents is attainable.

    The beneficial physical environment means the physical make-up of the growing media, bulk density, particle density, porosity and water content at a particular matric potential and the mechanical support to the water maintenance and plant growth(Li et al., 2002). Madankumar(1985) showed that soil water characteristics can be established directly from the physical properties of soil such as mechanical analysis and bulk density. High water content is related to water retention function(Campbell, 1974) and support increasing of plant shoot dry weight(Young et al., 2014). On the other hand, low water content may lead to poor nutrient accessibility, subsequently resulting in poor microbial growth (Pandey, 2003). The porosity of a growing media mix is the volume of air remaining after the media has been watered heavily and then allowed to drain. If the growing media mix is very dense and porosity is too low(<10%), then the roots will not be properly aerated and the plant will suffer, especially in containers with limited drainage capacity. Although plants can extract more than the available water, doing so requires the exertion of extra energy, which restricts plant growth.

    Materials, such as natural soils, are commonly used for the production of substrates for ornamental plants; however, for over 25 years, the container production of ornamental trees and shrubs has depended almost entirely on quality soilless growing media derived from both organic constituents, since many soils possess relatively low porosity and heterogeneous profiles(Landis & Morgan, 2009). Therefore, soil with simultaneous control over both water and air regimes is difficult to achieve. Owing to difficulties in producing soil with a consistent quality and the possibility of adverse physical problems when soils are potted, most growers use soilless potting substrates. Soils alone are generally not recommended for container cultures, as they do not provide the required aeration, drainage, or water holding capacity, which suppresses root growth and increases the susceptibility of plants to soil-borne diseases(Beattie & White, 1992). Thus, several growing media have recently been used.

    The commercial use of different organic materials as soil is common in container culture, owing to their beneficial effects on the soil physical environment(Raviv et al., 1986). The suitable use of growing media is of importance for production of quality pot plants(Benito et al., 2005). It directly influences the plant roots grow, fundamental to good nursery management and foundation of a healthy root system(Diane et al., 2016). It is important to maintain optimal aeration and water status of growing media, in order to avoid drought or excess water stress, which can result from the shallow depth and limited volume of the soil in containers(Felix et al., 2003). The ability of growing media to ensure a balanced water content is critical for maintaining the quality of ornamental plants. Thus, organic materials are usually mixed with soil, in order to provide an optimal physical environment for the growing plants(Abad et al., 2002).

    Peat, perlite, pruning waste, and pulp are the most commonly used growing media in growing containerized plants. Recently the use of pruning waste(Benito et al., 2005; Ostos et al., 2008; Nieto et al., 2016) and pulp(Humara et al., 2002; Khan et al., 2015) has been well accepted in plant nurseries owing to its promising physical properties and ability to balance the supply of air and water to roots. These non-soil materials can be manipulated or processed in different ratios and then applied to soil, in order to provide a superior physical and chemical environment for optimum plant growth.Thus the success of plants grown in pot culture can be summed up by the physical attributes of the growing media that influences its ability to provide sufficient water to the root systems without any oxygen shortage(Michel, 2010) which is the most determining factor in containerised cultivation.

    The balance between water availability and air space depends on the size and shape of the particles in the growing media or, more precisely, the pore space between the solid particles(Handreck, 1983). And solely growing media have problems because of it is more expensive than the soil and does not have a characteristic unique(e.g., minerals, microbes) of soil(Tilak et al., 2005). Therefore, the ideal mix should possess a balance between growing media and soils.

    Accordingly, the present study was conducted to identify the best mix ratio for water maintenance and for evaluating the growth of plants cultivated under different media mix ratios. In addition, we also evaluated the relationships between physical properties and water retention find to major factor that physically effects the water maintenance.

    Materials and Methods

    1.Preparation of raw materials

    The raw materials used in this study were commercial peat classified as brown peat(pH 3.5-4.5, LA FLORA, Europe), commercial perlite(particle size 2 mm, Landscape architecture company, Korea), pruning wastes and pulp collected by the public company. In our case, the pruning residue was prepared as steam explosion at 225°C, 5 min(Jung et al., 2015). Pulp was disintegration for 3000 rpm, 10 min at a corrugated cardboard/water ratio of 1/20. All materials were sieved below 2 mm(perlite excepted for drainage).

    2.Growing media and substrates preparation

    Mixtures of the raw materials(peat, perlite, pruning waste and pulp) were prepared mixing at a 3:1:3:3(w/w/w/w) ratios for growing media. Soil as sole medium was used as control. Table 1 summarizes the weight/weight ratio the different growing media tested in the substrates. The treatments comprised by mixing growing media at the rates of 0%, 10%, 20%, 30%, 40%, 50% and 100% with soil at 100%, 90%, 80%, 70%, 60%, 50% and 0%, respectively.

    3.Physical properties of substrates

    The bulk density of the substrate was determined according to the methods of Liu et al.(2011). Briefly, the cutting rings(W0, 105℃, 24 h oven dried) with one side covered with cap, filled with air dried substrate and then press used 500 g weight for 3 min. The samples were cutting on the rings and the cutting rings with substrate were kept at 105°C until constant weight(W1). The following formula was employed to calculate the needed parameters:

    Bulk density (g/cm 3 )=(W 1 /W 0 )/98(cuttingringvolume)

    The particle density and porosity were determined according to the method of GLOBE(2005), samples of air dry substrate were weighed, sieved substrate from a horizon, mix it with distilled water and then boil the mixture to remove any air. The mixture cools for a day and then add water until the volume of the mixture is 100 mL. Temperature and mass of the final mixture was measured and use the expression to calculate the substrate particle density. The particle density of the substrate is calculated according to the following equation:

    Particle density(g/cm 3 )=Mass of dry substrate (g) / Volume of soil particles only(air removed) (g)

    The porosity of the substrate is calculated according to the following equation:

    Porosity(%) = 1 - (Bulk density / Particle density) ×100

    4.Water retentivity in pot condition

    The water content was established using Medina et al.(2009) method and oven drying to constant weight at 150 ± 5℃ for 12 h. The water content measurements were used as indicators of the water retentivity of the substrate. We confirmed the maintenance of water by testing the substrate for three months. The experiment was run outdoors using a randomised block design of three replicates per substrate treatment. Highest temperature and lowest temperature were 29.7℃ and 15.1℃ during the period, respectively. This temperature was collected from the Korea Meteorological Administration.

    5.Correlation analysis

    Correlation coefficients were determined in order to identify correlationships between the measured physical properties, growing media mix ratio and water content. Where a number of properties are correlated, water retentivity may appear to respond to changes in all of these properties even when differences are attributable to only one factor. Correlated variables were identified in order to aid in finding the real causes of water retentivity variation. Pearson analysis(R program, i386 3.2.2 version) was performed for each substrate and variations were assessed based on variations in the physical property and experiment time.

    6.Plant growth experiment

    The pot experiment was carried out to evaluate the potential use of substrates in plant(Lespedeza cyrtobotrya Miq.) growth. The suitability of the potential growing media was studied in a pot experiment using L. cyrtobotrya Miq. as indicator and the different substrates(Table 1) as treatment. L. cyrtobotrya Miq. was selected because of its rapid growth and ability to keep growing after being cut several times. L. cyrtobotrya Miq. 50 seed was sown into each pot(175 mL capacity). A randomised block design was used, with three replication for each treatment. The germination rate was obtained by counting the number of germinated seeds three months from seeding. Percentage of germination was calculated using the following equation :

    Total number of seeds germinated(n) / Number of seeds brewed into pot at the beginning(n) ×100

    The stem length of the L. cyrtobotrya Miq. seeding was measured immediately after harvest at three months after seeding. The length from seed to the top of the leaf measured by a Vernier Caliper.

    7.Statistical analysis

    Data were analyzed using SAS statistical software (version 9.4) comparing data means to Duncan’s test. Duncan’s multiple comparison range test was used to determine significant differences between the means.Fig. 1Fig. 2

    Results and discussion

    1.Physical characteristics of substrates

    The bulk density of the substrates tended to decrease with increasing proportions of growing media(Fig. 1). The bulk densities of 70S30G, 60S40G, 50S50G and 100G ranged between 0.1 and 0.3 g/cm3 and were within the ideal bulk density (0.4 g/cm3) for substrates used for containerized culture(Abad et al., 2002). Bengough & Young(1993) demonstrated that the daily elongation rate of pea roots which were growing through a high bulk density medium(1.4 g/cm3) was only about 65% of that of roots which were growing through the weaker low bulk density medium(0.85 g/cm3) in pots. In the present study, the bulk density of 90S10G was closely 0.85 g/cm3 which was low bulk density. Therefore, it is supposed that there is a no problem to the root growth in the 90S10G. Li et al.(2002) confirmed that microbial numbers in pots were negatively and linearly related to soil bulk density. In detail, with increase in soil bulk density from 1.00 to 1.60 g/cm3, total numbers of bacteria, fungi and actinomycetes declined by 26-39%. We may assume that 100S will be affected by microbial numbers due to bulk density of more than 1.00. Furthermore, high bulk density values have the disadvantage of increasing the transportation costs(Corti et al., 1998) and the uptake of water and nutrients may become limiting because roots have difficulty penetrating the substrate(Stirzaker et al., 1996). Therefore, we expect, water retentivity and plant growth is not adversely affected by the mixed growing media.

    The particle density was within the ideal range– 2.0)(Jayasinghe, 2012) for pots when addition 20%, 30%, 40% and 50% growing media to the substrates. 100S, 90S10G and 100G were not within the ideal limit and 100G was exceeded the ideal limit. This may be mainly due to the addition a lot of perlite (particle size 2 mm). Potting substrates containing different ratios of soil-growing media gave increased particle density compared to soil as sole. This may be due to addition of growing media having higher particle density. Similarly, incorporation of fly ash from 25% to 100% in garden soil increases the particle density from 3.98% to 26.14% than 100% garden soil(Pandey et al., 2009). Guerrero et al.(2002) reported that particle densities of pot culture increase with the addition of sludge. Consequently, substrates mixed growing media has expected that potential for water retentivity in pot culture. Interestingly, this result shown that the particle density in contradiction to the bulk density.

    The porosity(Fig. 3) of all the substrates was significantly higher than that of 100S(60.7%) and 100G was closely the ideal range(> 85%)(De boodt & Verdonck, 1972; Abad et al., 2002), suggesting possible adverse effect on water retention because of limited oxygen availability and gas exchange in the substrates with the high growing media proportions (Benito et al., 2005). Lemaire(1995) reported that the high porosity allows to keep air and water in the substrate. Therefore, some of the water retention enhancement in these mixtures seemed to be related to the combined effects of improved porosity in the growing media. The other point being that the amount of water retained at high soil water potentials depends primarily on the pore size distribution, and thus strongly affected by high porosity(Rawls et al., 1991). Porosity increased with the addition of growing media in this study. Benedetto & Klasman(2007) reported similar results from substrates of river wastes with different concentrations of growing media. Porosity was closely related bulk density and particle density. Low bulk density values and high particle density values have the advantage of increasing porosity (Corti et al., 1998). Consequently, 100S was assumed to represent a low porosity caused highest bulk density value and lowest particle density.

    2.Water retentivity in pot condition

    More detailed conclusions of the impact of the pots on the water comfort conditions have resulted from a thorough analysis of the measured data, recorded by measure the content of water. The results, presented in Fig. 4, show that for the three month periods, the water content in the pots with the growing media of high mix ratio are higher during the period. Moreover, it is obvious that the water content are higher and more constant due to the growing media. The water content of the 100G was from 3 times to 11 times higher than soil as sole within three months.

    In our experiment, growing media was used to maintain the water content of the substrate in an efficient manner. With regard to pot condition, we need to know the optimum water content in substrate. Kirkham & Powers(1972) reported that optimum water content for pot culture is over 25% of the growing media volume. We result included, ‘70S30G’, ‘60S40G’, ‘50S50G’ and ‘100G’. Similarly, Son et al.(2006) reported the water content range of 30% to 60% in growing media on pot culture. Thus, we can estimate that soil was required in pot to increase the growing media mix ratio to more than 30%.

    3.Correlation exploration

    It is well known that growing media bulk density and porosity are important factors affecting water content. This paper, also, provide bulk density and porosity has relationship the water content. Fig. 5 shows pair plots between the four transformed substrate indicator variables, where transformation was applied to increase the water content. The lower diagonal plots show one indicator against a second, overlaid with a smooth curve to show the trend. The upper diagonal of Fig. 5 indicates the correlation estimate between pairs of indicator variables. The result, bulk density and porosity are strongly correlated(correlation –0.75), while porosity and water content are poorly correlated(correlation 0.18). Several workers have shown an empirical relationship between bulk density and porosity(Beardsell et al., 1979). Prasad(1979) reported similar results which was closely related between bulk density and porosity(correlation -0.65) from substrates of wood wastes with different concentrations of growing media. Also, the result confirmed growing media mix ratio and water content are highest correlated (correlation 0.88).

    4.Seed germination and stem length

    The germination rates of L. cyrtobotrya Miq. seeds from the studied substrates include out 100G gave comparable values(5.4-8.0%) which were evidently higher than that with 100% growing media(100G, 3.1%)(Table 2). The stem length of 3 month old seedlings were tallest when grown on 60S40G, taller than those of seedlings grown on 100S, and significantly higher than those of seedlings grown on 100G. This could be due to the notably lower pH(3.8, not shown) and higher EC levels(283.7 μ S/cm, not shown) in substrate 100G than in 60S40G that caused undesirable conditions for germination and stem development in substrates. Reduced plant emergence from growing media with high EC levels resulting from a relatively high proportion of waste was also reported by Sάnchez-Monedero et al.(2004) and Bustamante et al.(2008) in studies using mixtures of peat and substrates for ornamental plants.

    The present study demonstrated that the addition of growing media has a positive effect on the water retention properties of substrates. The impact of growing media, which is environmentally safe and cheap, was much more pronounced among the soil amendments. Therefore, the application of growing media is a viable option for improving substrate water retentivity to the plants as well as bulk density, particle density and porosity of the substrates which has long been a challenge for pot culture in greenhouses and nurseries. In addition, we also met our ultimate goal of determining which physical properties significantly affect water retention. Although plant growth trend is not matches the physical properties and water content due to influence of other factors for plant growth, we propose that estimating water retentivity from bulk density and particle density.

    Acknowledgement

    This work was supported by Gyeongnam National University of Science and Technology Grant 2015, Korea.

    Figure

    JALS-50-69_F1.gif

    Bulk density of soil as affected by different non-soil amendments. Bar marked by the same letter are not significantly different for bulk density according to Duncan’s test(p<0.05). 100S: Soil as sole medium; 90S10G: Soil 90% + growing media 10%; 80S20G: Soil 80% + growing media 20%; 70S30G: Soil 70% + growing media 30%; 60S40G: Soil 60% + growing media 40%; 50S50G: Soil 50% + growing media 50%; 100G: Growing media as sole medium.

    JALS-50-69_F2.gif

    Particle density of soil as affected by different non-soil amendments. Bar marked by the same letter are not significantly different for particle density according to Duncan’s test(p<0.05). 100S: Soil as sole medium; 90S10G: Soil 90% + growing media 10%; 80S20G: Soil 80% + growing media 20%; 70S30G: Soil 70% + growing media 30%; 60S40G: Soil 60% + growing media 40%; 50S50G: Soil 50% + growing media 50%; 100G: Growing media as sole medium.

    JALS-50-69_F3.gif

    Porosity of soil as affected by different nonsoil amendments. Bar marked by the same letter are not significantly different for porosity according to Duncan’s test(p<0.05). 100S: Soil as sole medium; 90S10G: Soil 90% + growing media 10%; 80S20G: Soil 80% + growing media 20%; 70S30G: Soil 70% + growing media 30%; 60S40G: Soil 60% + growing media 40%; 50S50G: Soil 50% + growing media 50%; 100G: Growing media as sole medium.

    JALS-50-69_F4.gif

    Variation of water content in seven substrates application for three month periods. 100S: Soil as sole medium; 90S10G: Soil 90% + growing media 10%; 80S20G: Soil 80% + growing media 20%; 70S30G: Soil 70% + growing media 30%; 60S40G: Soil 60% + growing media 40%; 50S50G: Soil 50% + growing media 50%; 100G: Growing media as sole medium.

    JALS-50-69_F5.gif

    Plots of the relationship between substrate properties and water content. The lower left diagonal shows on indicator against a second. The upper right diagonal shows the correlation value between the indicators. BD: Bulk density; PD: Particle density; PO: Porosity; GR: Growing media mix ratio; WC: Water content.

    Table

    Composition of substrates used in the study (w/w)

    1Peat:perlite:pruning waste:pulp(3:1:3:3, w/w/w/w)

    Plant growth in seven different substrates

    1100S: Soil as sole medium; 90S10G: Soil 90% + growing media 10%; 80S20G: Soil 80% + growing media 20%; 70S30G: Soil 70% + growing media 30%; 60S40G: Soil 60% + growing media 40%; 50S50G: Soil 50% + growing media 50%; 100G: Growing media as sole medium.
    2± Standard deviation, n=3.
    3Means with different letters indicate significant differences among columns for each sample(p<0.05).

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