Peat Pots
INTRODUCTION
1.0 Recently biodegradable plant pots have been popularised with professionals and amateurs alike due to the growing trend of sustainability and environmental awareness. Horticulturists have been investing into sourcing a suitable alterative to the traditional plastic pots which have a greater carbon footprint compared to its counterparts (Anderton, 2011). The main focus of this new avenue of research has been on peat pots as an emerging alterative for mass production of plants especially annuals.
1.1 Within plastic containers there are 2 key types of plastics hard and soft. The majority of plant pots contain hard plastic which cannot be recycled as it contains polypropylene (C3H6)n; being similar to the plastic polymers found in bottle tops (Aggarwai and Nirmala, 2012). Furthermore polypropylene is not seen as a priority for many local authorities to recycle, so the majority of them end up in landfill (Albers-Nelson et al., 2000). Soft plastic which is the main ingredient in celled containers can be easier to recycle due to their mixture of phthalate plasticisers which make the bonds between the polymers more flexible. However, these soft plastics only make up 35% of the total plastic containers used in the UK (Dennis et al., 2010). Although peat pots require peat which is a sustainable product, there has been much research on alterative materials including compressed green waste to make them more sustainable. Since the UK government is set to phase out peat from mass production by 2030; producers are investing into novel methods of using peat pots in production to reduce their carbon emissions (Doyle et al., 2009).
1.2 Grazulevciene et al.’s (2007) research had established that peat pots weather made out of compressed green waste or peat could enhance Pelargonium graveolens root growth by 39% when compared with traditional containers. However, there has been little research carried out which directly compares peat pot performance with plastic containers post-planting as stipulated by Amoroso et al. (2010). The effects of transplanting on the root systems of annual plants have been greatly studied. One major study by Hall et al. (2010) uncovered that it could delay plant development by as much as 21% as the fibrous roots; essential to water uptake can easily get damaged or broken off. Lopez and Camberato (2010) revealed that peat pots are more cost effective, allows better gas exchange with the roots, reduces plant stress when potting up or planting outdoors and are versatile in regards to what ingredients can be included.
1.3 Much research has been conducted on the performance of crop yield and gas exchange of plant roots which has been funded by manufactures of ‘air pots’. Since roots grow and develop in soil, they cannot photosynthesise. To generate energy they use sugars that have been produced by the photosynthetic apparatus in cellular respiration, requiring the presence of 02 and the expulsion of C02 (Larcher et al., 2011; Blankenship, 2001). Therefore the soil must have enough openings between the soil particles (commonly referred to as texture) to allow 02 to diffuse into the substrate for the roots to absorb. If a plant’s substrate becomes water-logged for an extended period the fibrous roots being to decay, as this gas exchange cannot occur leading to the evidential death of the plant (Yue et al., 2010).
1.4 As an industry that operates within the outdoor environment, horticulture should become a frontrunner of sustainability and low carbon generation to increase its environmental credibility. By studying and comparing the effects of Tropaeolum majus yield when using peat pots, could provide a solution of making mass production horticulture cheaper and more sustainable.
HYPOTHESES
1.5 The aim of this study is to examine the effectiveness of using peat pots for the commercial production of annual plants by using Tropaeolum majus as a case study. This will be achieved by growing T. majus in peat pots and comparing them with the results of the more traditional method of plastic pots. The following are to be investigated throughout this study:
Alternative Hypothesis
The plant height, leaf span, root density and dry weight will be altered within the specimens cultured in the peat pots.
Null Hypothesis
The plant height, leaf span, root density and dry weight will not be altered within the specimens cultured in the peat pots.
LITERATURE REVIEW
Gravitropic responses
2.0 It has been known for many centuries that a plant's root network grows in response to a gravitational stimulus in the form of gravitropism. This tropic response is a 3 stage process: perception, signal transduction and differential growth (Cox et al., 2003; Hangarter, 1997). Root growth occurs when the division of stem cells within the root meristem, causes the expansion of cells in the region proximal to the tip. This results in the pushing of the elongation zone through the soil (Barlow, 2003; Arnaud et al., 2010). In accordance with the Cholodny-Went model, gravitropism is perceived by the columella cells of the root cap. Whereas the differential growth response associated with gravistimulation occurs in the elongation zone. This zone is a stretch of parenchyma cells which can rapidly expand (Bengough et al., 2006; Blancaflor et al., 2008; Clark et al., 2003).
2.1 The main driver behind gravitropism is the plant hormone, auxin indolyl-3-acetic acid or Auxin IAA. Auxin IAA drives the development of most organs in plants such as the photosynthetic apparatus, hypogeal and roots (Friml et al., 2002; Hansen and Grossmann, 2000). As stipulated by the Starch-Statolith hypothesis, the force of gravity can deform or displace objects of specific mass. Hence, a biological gravity-sensing device would contain a molecular receptor that perceives the physical information generated by the deformation or displacement of specific objects, known as receptors (Brock et al., 2004; Leyser, 2002; Chaabouni et al., 2009). In multicellular plants the gravity receptors or statoliths are known to be dense amyloplasts that sediment in specialised cells or statocytes (Chae et al., 2003).
2.2 The statocytes are highly polarised cells that contain a peripheral endoplasmic reticulum, a nucleus positioned in the middle or at the top and dense amyloplasts sediment at the bottom. When a plant organ is tilted within the field of gravity, amyloplasts sediment is sent to the new physical bottom of the statocytes (Ottenschläger et al., 2003; Price et al., 2000). Amyloplasts sedimentation is theorised to activate receptors that trigger a signal transduction pathway leading to the formation of a physiological signal which is responsible for organ tip curvature (Morita, 2010).
2.3 The gravitational pressure model proposes that plant cells perceive gravity by sensing their buoyancy within the surrounding medium (Massa and Gilroy, 2003; Marchant et al., 1999). Therefore, gravity may tend to displace the protoplast within the cell wall, exerting a tension between the plasma membrane and the extracellular matrix on the topside and compression at the bottom (Hodge et al., 2009; Iijima et al., 2008; Dubrovsky et al., 2008). The tension and compression may result in the activation of specific stretch-activated channels that trigger signal transduction pathways, leading to the final cellular responses. The dense amyloplasts contribute to gravity sensing by increasing the total weight of the cell, thus increasing the differential tension and compression exerted by the cell on its extracellular matrix (Iijima et al., 2003; Vanneste and Friml, 2009).
Root cap dynamics
2.4 Auxin IAA is produced in the apical meristem and travels down the phloem in the stem and suppresses lateral growth. It also is responsible for cell elongation in the cells just below the apical meristem (Benková and Hejátko, 2009; Buer et al., 2006). According to the reverse-fountain model, shoot-derived auxin IAA is acropetally transported to the root cap through the root vascular tissue and after radial distribution in the root cap. In the epidermal tissues it is basipetally transported back to the elongation zone of the roots where it regulates growth (Luschnig et al., 1998; Müller et al., 2008; Swarup et al., 2002). The biosynthesis of ethylene is required to achieve a maximum gravicurvature; to both inhibitory and stimulatory effects of ethylene on the elongation zone. Furthermore, ethylene regulates the transport of auxin IAA from its production in leaves to the roots (Breyne et al., 2002).
2.5 Despite the important roles of auxin IAA and ethylene in regulating root development, little is known about the relative functions of these hormones in regulating the penetration of roots into the soil (Arnaud et al., 2006; Clark et al., 2003). Examination of roots exposed to mechanical impedance to penetrate the medium has shown that increases in ethylene synthesis and signaling mediate the reduction of root growth. This is accompanied by an increase in root diameter and a decrease in root cell elongation (Arnaud et al., 2010; Wolverton et al., 2011). These morphological changes alter the ability of roots to overcome the physical resistance during soil penetration (Jones et al., 2009).
2.6 The root cap or calyptra contains statocytes which are involved in gravity perception (Wei et al., 2009; Baluška et al., 2010). If the cap is carefully removed the root will grow randomly. Calyptra secretes mucilage which acts as a lubricant to ease the movement of the root through soil. It may also be involved in communication with the soil microbiota such as mycorrhizal fungi which is essential in nitrogen fixation (Hawes et al., 2012; Coudert et al., 2010; Li et al., 2011). The cells of the calyptra are continuously destroyed and ‘sloughed’ off; new parenchyma cells replace the destroyed ones by a special internal layer of meristematic cells called the calyptrogen (Meng et al., 2010). The mucilage excretion has been extensively studied and it has be verified that it is a mixture of polysaccharide made up of >100 species of proteins (Li et al., 2011; Endo et al., 2009). It is this anatomy that follows the root tips to perceive gravitational pull and to penetrate through the soil and membranous barriers.
Review
2.70 A study carried out by Evans et al. (2011) compared the strength, decomposition rate and root penetration of 5 different types of biodegrable containers; with the additional of polythene plastic containers as a control. Their experiment consisted of a laboratory test and a field experiment. During the laboratory test the containers were subject mechanical tests to examine their dry strength, wet strength and decomposition rate in water. The field experiment consisted of 3 trials with 10 of each different biodegrable container being used to plant up Pelargonium x hortorium. After being potted up the Pelargonium were planted into a field and left for 8 weeks.
2.71 Weekly measurements followed to monitor the natural decomposition rate and a count of how many roots penetrated the pots. The following biodegrable pots were used for the trials: coconut fibre, peat pots, composted dairy manure, rice hull and coir. After each trial, the plants were dug up and the total number of roots counted that penetrated the containers. Furthermore, biomass of both the plant and container were carried out to determine how much of the pot had decayed and to determine the health of the plants. Evans et al. (2011) carried out daily temperature, rainfall, humidity and wind speed readings.
2.72 Evans et al. (2011) uncovered that the most efficient decomposition rate was the composted dairy manure which decomposed by 62% cover an 8 week period. However rice hull and coconut fibre decomposed the least by 9-10%. Though peat pots did not have the most efficient rate of decomposition (53%). The researchers found that they acquired and development an algal and fungal soil association. This was an interesting finding as none of the other containers were found to have developed this relationship.
2.73 In regards to the most effective container to have allowed the roots to penetration was the composted dairy manure. It allowed 72% of roots to pass through. Peat pots however were found to have allowed the least amount of roots to penetrate at 47%. In some cases this prevents much of the above development of the Pelargonium; these results were support by McKenziel et al. (2011), Peltonen-Sainio et al. (2011) and Lipiec et al. (2012). Within the laboratory test, unsurprisingly the control was found to be the strongest when dry or wet. Peat pots were found to be the least supportive when subject to water. Nevertheless, peat pots were found to have the shortest decay period when submerged under water. Coir and rice hull were found to be the least effective at breaking down when submerged and under dry and wet strength examinations. The least effective at dry strength was the composted dairy manure. Evans et al. (2011) recommended that a further study was required to develop their understanding of the effects on the root network of plants when in biodegrable containers.
2.80 Kuehny et al. (2010) performed an investigation into biocontainers effectiveness in a commercial grower’s bedding crop. The researchers arranged field trials in 3 different locations across Louisiana. 3 different bedding plants were used: Pelargonium x hortorium, Catharanthus roseus and Impatien walleriana. There was only 1 trial for each of the different locations which lasted 4 months. 4 different types of biocontainers were utilised: straw, peat pots, coconut and recycled paper. Plastic containers were used to cultivate the control plants which were then transplanted directly into the ground. Root to shoot ratio, plant height, root penetration and percentage of decay were utilised as independent variables.
2.81 Kuehny et al.’s (2010) investigation uncovered that the greatest shoot growth in the Impatien and Catharanthus occurred within the control containers. Furthermore, Catharanthus had the largest root to shoot ratio within the control. However paper containers were found to harbour the most root growth for all of the groups by 89%, for the Impatien. Peat pots were found to cap the growth of the Impatiens and Pelargonium which when compared to the control, was on average 45% smaller which is supported by Evans et al. (2011). Both straw and coconut biocontainers were found to have stunted the growth of all the species. When Pelargonium were subject to paper pots their root to shoot value increased by 67%. In relation to decomposition, the coconut and straw were found to have decayed by 54%, peat by 67% and paper by 88%. An interesting point which was highlighted by Kuehny et al. (2010) was that the peat pots decayed faster when submerged below ground. Above ground they were found to have hardened and prevented any growth to penetrate through without damage, this was also found by Santisree et al. (2011).
2.90 Research conducted by Nechita et al. (2010) evaluated the effects on the soil and association between soil microbiota and roots by using lignocellulosic containers. These containers are a form of biodegradable mixture of 70% recycled paper and 25% cardboard. This study grew 3 species of annual vegetable crop over a period of 5 months; Beta vulgaris, Lactuca ‘Iceberg’ and Cucumis sativus were used in 2 groups. The lignocellulosic containers formed the first group and the seconded were cultivated in plastic containers which were then directly planted into the ground. Nechita et al. (2010) measured the height of the plants weekly.
2.91 After the investigation, the plants with the location of the containers were dug up. The specimens were then put through biomass readings followed by the containers. Moreover, a root to shoot ratio was measured followed by root containment percentage. This percentage measured how many roots managed to penetrate the container. The higher the percentage the fewer roots managed to penetrate. This investigation revealed that on average the lignocellulosic containers decomposed by 82% after 5 months.
2.92 Once the containers started to decay the researchers found that this encouraged an associated with heterotrophic bacteria and mycorrhizae. This in turn aided the development of the root to shoot ratio; on average plants grown in the lignocellulosic containers grew 65% more. The main explanation behind this increase in growth was due to the increased associated with the soil microbiota. This association caused an increase in root area which in turn resulted in more nutrients and water being received by the plants. This finding has been supported by Mohsenzadeh et al.’s (2010) and Hohmann et al.’s (2012) studies.
2.10 Albers-Nelson et al. (2000) carried out an investigation into improving the establishment technique for Xanthium strumarium. The researchers examined a curial step in the culture of Xanthium which is the transfer from a glasshouse to the outdoors. This experiment each took 30 Xanthium strumarium that were established from seed and planted them into plastic containers (control), peat pots and peat tablets.
2.101 Each trial took 8 weeks and was repeated 3 times. Each of the plants had their height and leaf span measured weekly. After the trials all the plants had their dry weight measured alongside the containers. Furthermore, a root proximity percentage was used to determine what percentage of root managed to penetrate the biocontainers.
2.102 Albers-Nelson et al. (2000) revealed when Xanthium was grown in peat pots, they were 43% heavier compared to the control. According to the height and leaf span measurements the plants grew 37.5% taller and 22.4% wider. However when plants were subject to peat tablets plants they were 64.3% shorter and 13% less wide. When unearthed, the researchers found that the peat tablets decomposed by 32.7% but the peat pots decomposed by up to 85.2%. As stipulated by Albers-Nelson et al. (2000) the decomposed matter propagated a higher mycorrhizal association when compared to Xanthium grown directly into the soil. The peat tablets were found not to have such an association with mycorrhizae as they were 67.5% thicker than the peat pots; this was reflected by the percentage of penetrated roots. Plants grown in peat pots had on average had a root proximity of 48.6%. This was 62.2% higher when plants were grown in peat tablets.
2.110 An examination carried out by Grazuleviciene et al. (2007) used 3 different types of container to study the effects of transplanting verses non-transplanting of Tropaeolum majus. The researchers grew 20 each of T. majus specimens in biodegrable starch, PVA and peat composites. Each trial lasted for 2 months and this was repeated 3 times. After propagation the plants were planted up into a field with the plants in the PVA pots being the transplanted group. Grazuleviciene et al. (2007) used the following as their independent variables to determine plant health: root to shoot ratio, plant height, root density measurements and root percent values. They also measured the decay percent at the end of reach trial. Prior to the trials, dry and wet strength of the containers were tested.
2.111 Grazuleviciene et al.’s (2007) study uncovered when T. majus were subject to the biocontainers they grew 44.7% taller when compared with PVA. However, the PVA group’s root to shoot and root percentage values was 50% higher when compared to the biodegrable containers. As predicted by their strength measurements, the PVA came on top followed by the biodegrable starch which was 23% less robust. Peat pots were found to be the weakest when subject to both conditions. Peat containers were 67.6% weaker when compared to the PVA and 45.3% when compared to biodegrable starch. This study also revealed that the peat pots were the only containers to have developed a strong association with soil dwelling heterotrophic bacteria and fungi. This came to a surprise to the investigators, as the peat pots did not perform well as suggested by the root percentages and root to shoot values.
2.120 A study performed by Yue et al. (2010) looked into the effectiveness of using peat pots in the commercial production of Lavendula angustifolia. As well as a field experiment the investigators carried out a survey of 1,000 consumers of Lavendula to determine if switching to peat pots would be commercially viable from a customer’s perspective. The field trials involved the cultivation of 40 Lavendula angustifolia in peat pots compared to the more traditional means of polythene containers. All the specimens were planted into a field with the control being transplanted and the peat pots being planted in with the plants. This was repeated another 2 times. After each trial the researchers determined what percentage of the containers decayed, what associations developed by what species and the frequency of root penetration. During the trials plant height and number of leaves counted.
2.121 After the completion of Yue et al.’s (2010) field trials, they carried out a survey to over 30 nurseries in Texas to determine what percentage of consumers would prefer peat pots to plastic and how much they would be willing to pay for this alteration. Their surveys revealed that 73% of the participants would prefer to see plants in biodegrable containers. The main rational behind this is that many customers do not use the plastic containers and do not dispose of them correctly. Many of the consumer’s stipulated that if you could not recycle plastic pots and they preferred to have compostable ones for ease of disposal. 66% of the participants stated that they would prefer to use biodegrable containers as they require less time to plant out. Additionally, most customers questioned revealed that it would be more beneficial to the plants if they were not transplanted by merely placed into the ground. This finding was comparable to Vanneste and Friml’s (2009) study.
2.122 Yue et al.’s (2010) field trial revealed that plants grown in peat pots grew 45% taller and had 25.4% more leaves. Moreover they stipulated that 67% of roots including fibrous were able to penetrate the biocontainers without damage. On average the root percentages were 23% less than the control. The decay rate of the peat pots on average was 73.5% which may contradict Evans et al. (2011) and Nechita et al.’s (2010) findings.
METHODOLGY
3.0 The effects of transplanting and gas exchange on roots has been understood for many years, but there is little research carried out which directly compares the residual effects of using peat pots with traditional plastic pots post-planting. Thus are the roots of the plants cultured in peat pots able to break through?
Samples
3.1 Tropaeolum majus was chosen because of the recommendation from Schreinera et al.’s (2009) study. T. majus had been verified to have a fast root growth which will be ideal for testing the performance of the peat pots over a short amount of time. Specimens were grown from seed 3 weeks period to this study in their test containers; 6 T. majus in individual plastic pots and 6 in individual peat pots. The specimens were cultured within the experiencer’s glasshouse with a day and night cycle of 12 hours to promote leafy growth. An heating system was in place to ensure that the temperature did not go below 5°C, see Procedure 3.2. To ensure validity, 2 seeds were planted in each container to reduce changes of confounding variable from undeveloped seeds. In the case of both seeds developing one was removed. This experiment occurred within the researcher’s own garden, Newcastle upon Tyne within a south-westerly facing border, due to the limitations of funding and resources. Once the majority of seedings reached 2cm they were used for the trials.
Procedure
3.2 1 week prior to this experiment the border was weeded, tilled and was reconditioned by adding John Innes multiuse-purpose compost and slow release fertiliser. Furthermore, environmental conditions were monitored to examine the environmental variances, 2 weeks prior. There was an approximate 12:12 day and night cycle followed to prevent wasted energy in flowering. The specimens were each given ~200ml of water per day if it did not rain. The control comprised of 6 T. majus specimens that ran alongside the trials. The average day temperature of 15˚C and 10̊C during the night were followed. The control examined the effects on the roots when the specimens were transplanting into the ground. Day and night temperature, light level, humidity and wind speed were recorded daily. The peat pots were purchased online from Wyevale Garden Centre Group in 2, 20 multi-packs. Peat pots are commonly derived from a ratio of 30:70 of organic soil with peat as stipulated by Krasinskaya (2011).
3.3 Prior to the trials all the peat pots were weighed and the ones with the average weight of 30g were included in the experiment. Furthermore, the specimens were grown 3 weeks prior to the trials from seed which was purchased from Wilkinson. On the first day of the trials the specimens were planted into the border. This was repeated a further 12 times to complete each trial. This procedure was repeatedly carried out at 9am prior to full sun conditions with sterilised gloves to prevent cross-contamination. To further reduce chances of contamination 70% ethanol solution was used to sterilise the equipment that was in contact with the plants. An outdoor experiment was chosen as a more variable environment to test the peat pot integrities, though many annual plants would be produced in more controlled conditions such as a glasshouse (Friend, 2009).
Apparatus
3.4 7cm containers were filled with 100ml of multi-purpose compost as recommended by Hadar (2011). 12 T. majus were used per trial and there were was 3 trials, totalling 36 plants. The control comprised of 6 plants per trial. The media used for the trials was pH tested and was brought 7.0 before seed planting as suggested by Poorter et al. (2012). To ensure a consistence supply of N7:P7:K7 macronutrients a general liquid fertiliser specialised for annuals was used and purchased from Wyevale Garden Centre Group. Fertiliser was applied weekly during the trials and to reduce damage caused by evapotranspiration the specimens were watered twice daily with rainwater.
3.5 During the testing period, the temperature was recorded by using a Silverline 469539 Digital Thermometer. The average light intensity levels were measured between the specimens at 4 random locations using a Sekonic L-358 Luxmeter. A GX-Optical compound microscope was used to photograph the cells by up to x250. Although this is not enough to take detailed photographs of individual cells, it can show the behaviour of T. majus. See Appendix 2 for Environmental Specifications. As a summary there were 3 trials each consisting of 6 peat potted specimens and 6 potted containers in the control groups, as shown in Table 1 below.
3.6 To determine the effects of using peat pots, weekly plant height, leaf span, root density (%) and dry weight were used as a measure of growth. With addition, wet weight will be used to provide a direct comparison to the dry weight to see what ratio had been achieved. All 5 measurements were recorded weekly alongside observations by using a Nikon camera. The experimenter was the only one who carried out each of the measurements. This was to reduce chances of human error. Plant height was determined by measuring from the base to the tip of the plant in cm using a steal ruler. Leaf span was carried out by measuring a cross-section of a random leaf per plant in cm by using the above ruler. Root density (%) was determined by following the Root Phenotyping Method Protocol, in where the specimens were dug up and the substrate removed under a steady flow of water. Once the substrate was removed all the lateral roots were measured in length (mm) and totalled, see below for calculation:
Where:
LT = Lateral root total (mm)
*Total substrate (cm3)
3.7 To gain dry weight, specimens were removed from the medium and briefly washed. Plants were then blotted to remove any free surface moisture. Specimens were placed into a drying oven at 100°C for 48 hours. Plants were left to cool for 3 hours and weighed on a scale which measures in milligrams (Reed et al, 2007). Wet weight was determined by measuring the specimen with roots intact by using an mg scales prior to the dry weight testing.
Statistical Analysis
3.8 The data from the container studies at weeks 1 and 4 were analysed by using an Anderson-Darling test which examined the normal distribution within the data. Subsequently a Levene’s test was carried out to identify any significant variances in the data. A One-way Independent ANOVA test occurred to identify the P-value of the trials when compared with the control. Finally a Tukey Post-hoc test was required to identify significant differences between the groups (Clewer and Scarisbrick, 2001; Adams, 2003). The statistical program Minitab 16 was used to execute these tests.
RESULTS
Plant Height
4.0 From the descriptive statistics that occurred it was found when Tropaeolum majus was cultivated within the peat pots, there was a 0.47% difference in plant height when compared with the control. When comparing the height differential from weeks 1 and 4, the control increased by 20.45%. When weeks 1 and 4 there compared within the trial there was a 24.69% increase in height, as demonstrated in Figure 1.
4.1 Two inferential analyses occurred to determine normality and equal variance. The Anderson-Darling test show there was normality within the trial data: peat pot P= 0.314. Furthermore it revealed there was normality within the control as demonstrated by P=0.143. The Levene’s test returned a P-value of 0.678 which showed there was equal variance within the control and within the trial (P=0.700). A Paired-t test occurred due to both data sets being parametric. The test was to determine if there was a significant difference between the trial and control:
Paired-t test T= 0.17, P 0.869, n= 6,6
This established that there was no significant difference between the heights of T. majus grown in the peat pots or directly planted in the substrate.
Leaf Span
4.2 From the descriptive statistics it was found when Tropaeolum majus was cultivated within the peat pots, there was a 0.23% difference in leaf span when compared with the control. When comparing the leaf span differential from weeks 1 and 4, the control increased by 10.31%. When weeks 1 and 4 there compared within the trial there was an 8.16% increase in leaf span, as demonstrated in Table 2.
4.3 Two inferential analyses occurred to determine normality and equal variance. The Anderson-Darling test show there was normality within the trial data: peat pot P= 0.446. Furthermore it revealed there was normality within the control as demonstrated by P=0.727. The Levene’s test returned a P-value of 0.224 which showed there was equal variance within the control and within the trial (P=0.332). A Paired-t test occurred due to both data sets being parametric. The test was to determine if there was a significant difference between the trial and control:
Paired-t test T= 1.01, P 0.326, n= 6,6
This established that there was no significant difference between the leaf spans of T. majus grown in the peat pots or directly planted in the substrate.
Root Density
4.4 From the descriptive statistics it was found when Tropaeolum majus was cultivated within the peat pots, there was a 6.73% difference in root density when compared with the control. When comparing the root density differential from weeks 1 and 4, the control decreased by 2.32%. When weeks 1 and 4 were compared within the trial there was a 12.02% increase in root density, as demonstrated in Figure 2.
4.3 Two inferential analyses occurred to determine normality and equal variance. The Anderson-Darling test show there was normality within the trial data: peat pot P= 0.070. Furthermore it revealed there was normality within the control as demonstrated by P=0.550. The Levene’s test returned a P-value of 0.209 which showed there was equal variance within the control and within the trial (P=0.344). A Paired-t test occurred due to both data sets being parametric. The test was to determine if there was a significant difference between the trial and control:
Paired-t test T= 10.20, P>0.001, n= 6,6
This established that there was a significant difference between the root densities of T. majus grown in the peat pots or directly planted in the substrate.
Dry Weight
4.5 From the descriptive statistics it was found when Tropaeolum majus was cultivated within the peat pots, there was a 3.85% difference in dry weight when compared with the control. When comparing the dry weight differential from weeks 1 and 4, the control decreased by 50%. When weeks 1 and 4 there compared within the trial there was a 49.09% increase in dry weight, as demonstrated in Table 3.
4.6 Two inferential analyses occurred to determine normality and equal variance. The Anderson-Darling test show there was normality within the trial data: peat pot P=0.05. Furthermore it revealed there was no normality within the control as demonstrated by P=0.026. The Levene’s test returned a P-value of >0.001 which showed there was equal variance within the control and within the trial (P=0.05). A Mann-Whitney U test occurred due to both data sets being nonparametric. The test was to determine if there was a significant difference between the trial and control:
Mann-Whitney U test W= 271.5, P 0.051, n= 6,6
This established that there was a significant difference between the dry weight of T. majus grown in the peat pots or directly planted in the substrate.
4.7 Figure 3 compares the plant height and leaf span of the control and trials. As illustrated, plant height peak at 9.76cm when L. major was cultivated in the peat pots. Additionally the leaf span peak at 4.56cm, within the control group. The largest weekly increases in plant height of 95.16%, 84.17% and 94.03% were seen in the trial group. The largest weekly increases in leaf span of 96.77%, 98.94% and 95.92% were also from the peat pot group.
4.8 Figure 4 compares the root density and dry weight of the control and trials. As illustrated, root density peak at 46.33% when L. major was cultivated in the peat pots. Additionally, the dry weight peak at 0.95g, within the control group.
Figure 4 Root density (%) and dry weight (g) correlation of the trial and control (n= 6,6) at week 4.
4.9 Below are Figures 5 and 6 which demonstrate the progressive growth of the plant height and root density throughout the trials.
DISCUSSION
5.0 There was no significant difference found in plant height of the Tropeaolum majus grown in the peat pots and the ones grown without. When further analysed, there was only a 0.47% difference when weeks 4 were compared with weeks 1, refer to Chapter 4, page 4.0 for further information. From the probability value of 0.17 the null hypothesis can be accepted.
5.01 Evans et al.’s (2011) study established that peat pots had a degraded by 53% after 8 weeks of being submerged underground. Furthermore Evans et al. (2011) demonstrated that peat pots were the only biodegradable container to have developed an algae or mycorrhizal fungi association. This finding seems to contradict the overall findings of the research; when the pots were exposed to the atmosphere they seemed to have hardened. Moreover, below ground the peat pot’s circumference did not decay as much as was expected. The bottom of the peat pots were the only areas subject to high rates of decay. Though there was not much decay overall in the peat pots, some of the roots of T. majus managed to penetrate effectively. From this investigation, this degraded effect was verified not to adversely affect the height of the specimens. Under further study, the researchers stipulated that peat pots were ranked second when they were tested for integrity. When the above study measured heights of Pelargonium xhortorium, they found that there was little variation in the groups grown in the control and peat pots, as observed in this study.
5.02 Evans et al. (2011) found that annual plants can cope with denser root clusters when compared with perennial plants. Annual plants require less root area as they have a short lifecycle. According to their observations when there was over a day of no rain they irrigated their specimens. It is known that providing such watering can encourage plants to have density root systems. In some cases this can encourage roots to break through the soil, depending on the amount and frequency of irrigation. Another study conducted by Kuehny et al. (2010) measured the heights of both perennial and annual plants grown in 5 different types of biocontainer including peat pots. Kuehny et al. (2010) found when Catharanthus roseus (perennial habit) were subject to peat pots their heights were 17% less when compared with their control. However when Impatient walleriana was grown in peat pots it was uncovered that they grew 12% taller. When both plants were cultured in paper pots, they were found to have grown the same as if they were transplanted directly into the ground. When the researchers examined the papers pots they found that they rapidly broke down when subject to wet or dry conditions unlike peat pots. This rapid break down allowed for more effective root penetration, resulting in comparable heights with the control. They also suggested the theory that perennials were adversely affected when they were grown with the peat pots; also established in Gross and Karla’s (2002) and Grigat et al. (1998) studies.
5.1 There was no significant difference found in the leaf span of T. majus grown in and out of peat pots. When further analysed, there was a 2.15% difference when weeks 4 were compared with weeks 1, refer to Chapter 4, page 4.1 for more. From the P-value (0.326) the null hypothesis can be accepted.
5.11 In accordance with Evans et al.’s (2011) earlier research, there was no significant difference in leaf span when comparing peat pots with their control. Interestingly they found when Tropeaolum majus was subject to coir and rice hull biocontainers their leaf spans were 11% smaller when compared with the control. Kuehny et al. (2010) went on to further explain why leaf span may be effected by the biocontainer their specimens were grown in. They found that growing Catharanthus roseus within these pots their leaf spans were restricted as their roots could not penetrate the peat pots effectively, only 32% could penetrate through. With this restriction in mind, the researchers realised that if the root surface was concentrated within a small area they could not take in as much water. Thus restricting the expansion of the leaves. This investigation however uncovered that the leaf span of T. majus was unaffected by the peat membrane though the specimens were annual. Kuehny et al. (2010) suggested that as well as the limitation of water availability within these pots, the pots limited the association between mycorrhizal fungi and the root system.
5.12 To contrast the above researchers, Albers-Nelson et al. (20000) investigation revealed that when Xanthium strumarium (perennial habit) was subject to peat pots they grew 37.5% taller and 22.4% wider when compared with the control. When X. strumarium was subject to peat tablets they grew 64.5% smaller and were 23% wider compared with the above. Albers-Nelson et al. (20000) carried out a second study to uncover the underlying cause of this result. They found there was a direct correlation between the thickness of the peat pot and plant leaf span and height. Since peat table are on average 78% thicker than peat pots they are harder to decay because of their higher integrity. When the Researchers reduced the thickness of the peat pots by 50% they found that the leaves were 12.3% wider compared with before. However as a result the peat pots became weaker and began to break down before the desired time of planting. The team concluded that there was a point at which the peat pots can be thin enough to keep its integrity until the desired time; to allow the root penetration. According to Kolybaba et al. (2003) this desired thickness was between 3 and 5 mm. Within this study, peat pot thickness was between 6 and 8 mm. However they can still hardened if not regularly subject to irrigation. This can have a long-term impact upon the leaf span of Antirrhinum majus.
5.2 There was a significant difference found in the root density of T. majus grown in and out of the peat pots. When further analysed, there was a 6.73% increase in root density within the control and a 12.02% increase within the trial, refer to Chapter 4, page 4.2 for more. From the P-value (>0.001) the null hypothesis can be rejected.
5.21 Albers-Nelson et al. (2000) verified when Xanthium was subjected to peat pots for an 8 week period, they found that the root proximity was 48.6%. Within their peat tablets, root proximity was 62.2% and within their control root proximity of 32.4%. This observation is a direct result of the thickness of the peat pot walls. Albers-Nelson et al. (2000) and Nechita et al. (2010) both revealed that the mechanical strength of the peats directly affected the root penetration rate. In accordance with the expulsion of Auxin IAA which controls the directional growth of the root caps, peat pot biocontainers do not fully allow the diffusion this hormone.
5.22 Since most Auxin IAA cannot diffuse across the peat membrane, the roots begin to prevent penetration as seen within this study. Both studies in the above suggested that this may influence the root proximity of the specimens. Plants in their natural state will have a root density percentage of between 25 and 30. However when the specimens were subject to the peat pots, root density of Beta vulgaris and Lactuca ‘Ice Berg’ was 62% higher. Nelson et al. (2000) and Nechita et al. (2010) tested the mechanical strength of peat post in their dry and wet state. From these tests, the researchers found that there may be a correlation with the type of biomaterial used.
5.23 As stipulated by Grazuleviciene et al.’s (2007) study root density is influenced by the method employed of transplanting. When T. majus was cultured in plastic pots and then transplanted into the ground, the researchers found that the root density increased when the outer most roots were damaged. Under further scrutiny, they found when damaging the outer roots, they grew lateral roots; as observed within this investigation at weeks 3 to 4. Just like pruning stems, the specimens release ethylene. The ethylene increased the root density just like the dense growth of a pruned shrub. Moreover, then the researchers transplanted their seedlings into peat pots they found that ethylene just like Auxin IAA was mostly confined within the pot. This effect was found to further encourage lateral growth within the roots, thus increasing the root density. Naturally there will be some density (See Appendix 4 Photographic Plates, Figures 1.0 to 1.15) but the peat membranes only allow 38.5% of the ethylene to diffuse. This effect was also described by Yue et al. (2010), Yano et al. (2000) and Hoitink et al. (1998). One of the long-term effects of a higher root density is reduced plant height and leaf span as observed in Kuehny et al.’s (2010) research.
5.3 There was a significant difference found in dry weight of T. majus grown in and out of the peat pots. When further analysed, there was a 3.85% difference in the dry weight of the control and the trial, refer to Chapter 4, page 4.3 for more information. From the probability value of 0.051 the null hypothesis can be rejected.
5.31 Yue et al.’s (2010) study established when Lavendula augustifolia was cultured in peat pots for 10 weeks, their biomass increased by 73.5% from week 1. When the biomass of their control was analysed they found that the peat pot trial was 33.2% heavier. To contrast Grazuleviciene et al. (2007), Kuehny et al. (2010) and Yue et al.’s (2010) found that 67% of the fibrous roots of L. augustifolia were able to penetrate through the pots. Though the above study seems to contradict other studies reviewed, the researchers had come to a similar conclusion about their root densities. They stipulated that as the root density increased so did the biomass. In this investigation this effect was verified. Vanneste and Friml’s (2009) investigation when further to distinguish that on average dry weight of their Solanum lycopersicon increased by 34% when compared to their control. These verdicts support Yue et al.’s (2010) findings.
5.32 Nechita et al. (2010) demonstrated the dry weight of Beta vulgaris, Lactua ‘Iceberg’ and Cucumis sativus were on average 33% heavier, when grown in peat pots for 4 weeks. This result was unexpected as the height and leaf span of their specimens were significantly smaller when compared with their control. When further investigated, the researchers uncovered that the roots of their annual crops had elevated growth patterns. After much testing, Nechita et al. (2010) found the peat pots were not as impermeable to water as they had initially predicted. The peat pots were found to have hardened even semi-submerged owed to a lack of water; as seen within this investigation. The hardening of the peat pots made it more difficult to absorb water in a short period (see Appendix 4 Observations weeks 2 and 3) for example, during short showers or irrigation times. This hardening made it more difficult for the fibrous outer roots to penetrate which increased the ethylene levels; also suggested by this investigation and Grazuleviciene et al.’s (2007) research. This increase in ethylene resulted in more fibrous roots, thus increasing the overall dry weight of the plants. By increasing the root density and making it harder for the roots to penetrate the height and span of the plants were negatively affected. This was also verified by Ward et al. (2011) and Zinati et al. (2011).
5.4 One improvement which could have been made to this investigation would have been to extend the period of the field trial. By extending this period from 4 weeks to the entire growing season of Tropeaolum majus (~3 months), the accuracy and repeatability could have been enhanced. By growing 3 groups of peat pots and 3 groups of the control, each trial could have been run at the same time. This has the advantage of ensuring consistent environmental conditions. Furthermore increasing the number of T. majus from 6 to 50 per trial would have improved the investigation’s validity. As in Evans et al.’s (2011) investigation each trial was run at the same time and over the entire growing season. Nevertheless by increasing the length of testing and by expanding the numbers of plants, this would have enviably increased the labour and investment required for this study.
5.5 Another improvement which could have been made was to expand the diversity of plants used. This researcher’s main aim was to investigate the effectiveness of using these biocontainers on annual plants; as recommended by previous studies. The most common annual crops grown in UK nurseries includes: Petunia tumbelina, Petunia varieties, Pelargonium grandiflorum and Impatiens walleriana. By expanding the different genera used within this experiment, would have ensured that the effects noted on T. majus were not confined to T. majus. Grazuleviciene et al. (2007) and Kuehny et al. (2010) for instance used 10 different annual genera to verify that the effects noted on one genus affected the others. Since there is a great diversity of annual genera and species sold on the UK market, one needs to be certain that biodegradable containers have a universal effect on them. This is to make them more effective for application (Zhou, 2012). Nonetheless a pilot survey would have to occur to uncover the most grown annual bedding crop in the UK. Yet again this would increase the investment required for this investigation.
5.6 Future research is required to further understand the long-term effects, of annual plant health when using peat pots. By propagating plants like T. majus in these peat pots until they die may demonstrate if these peat pots could degrade and allow effective root penetration over a lifecycle. The chief aim of peat pot producers is to create a desirable biodegrable container that results in the reduction of stress that a plant undergoes whilst being transplanted. This means plants must be kept in these peat pots until they decay. In the research reviewed and in this investigation it has been established that peat pots do not degrade as efficiently as other biocontainers, especially during periods of low rainfall or irrigation. Another facet that needs to be investigated further is the hardening effect when these peat pots dry out. A solution needs to be found to prevent this hardening. Perhaps the insertion of microzeal fungi or algae in the peat walls to aid the process of decay and to prevent hardening (Zinati et al., 2011; Yano et al., 2003).
5.7 Though peat pots could be improved they are quite unsustainable due to their requirement of peat. More research is needed to find alternative environmentally friendly and sustainable materials. Materials like compressed green waste, organic ligneous containers, green waste (including leaves) pots and recycled topsoil containers. Little research has been undertaken to understand the above material’s effects on the surrounding substrate, how fast they degrade and their ability to encourage and proliferate a microbiota association. Since the increase in popularity of sustainable products, there is a need to develop these products to enable producers to send them to market. Furthermore this avenue of research could be expanded for perennial, shrub or tree storage, if the right balance between integrity and permeability is reached as discussed by Grazuleviciene et al. (2007) and Kuehny et al. (2010).
5.8 To summarise, plant height, leaf span, root density and dry weight were used to determine the effectiveness of using peat pots as a sustainable and environmentally friendly method of culturing Tropeaolum majus. The root density and dry weight were the variables that had significantly differences between the trial and control which demonstrated that peat pots could in fact increase root compaction and thus encouraging an increase in dry weights. Though the other variables had no significant differences between them it has verified that peat pots do not influence the height of T. majus and the leaf span. Though this may seem like a negative finding it verifies that peat pots do not have a negative effect upon T. majus height and leaf span. If a plant’s root system was too compacted by the peat pots then enviably the height and leaf span would have decreased, as demonstrated in Albers-Nelson et al.’s (2000) and Nechita et al.’s (2010) studies. By increasing the amount of time and the number of specimens used per trial could have increased this study’s validity. More research is required to uncover more environmentally and sustainable materials to improve the product’s creditability. By increasing this understanding, growers would be able to reduce their carbon footprint and to become more sustainable in their procedures of production.
CONCULSION
6.0 Biodegradable plant pots have been popularised with professionals and amateurs alike due to the growing trend of sustainability and environmental awareness. Much research has been conducted on the performance of crop yield and gas exchange of plant roots which has been funded by manufactures of ‘air pots’. Since roots grow and develop in soil, they cannot photosynthesise. To generate energy they use sugars that have been produced by the photosynthetic apparatus in cellular respiration, requiring the presence of 02 and the expulsion of C02 (Larcher et al., 2011). Therefore the soil must have enough openings between the soil particles to allow 02 to diffuse into the substrate for the roots to absorb. If a plant’s substrate becomes water-logged for an extended period the fibrous roots being to decay, as this gas exchange cannot occur leading to the evidential death of the plant (Yue et al., 2010).
6.1 From this research, it was found that the height and leaf span of Tropeaolum majus was unaffected by the peat pots. However the peat pots significantly increased the root compaction and dry weight. Using T. majus as a frequently studied specimen for biocontainer research led to the following outcomes: when subject to peat pots root density was 14.34% increase when compared with the control, there was a 0.91% difference in dry weight, a 4.23% difference in height and 2.15% difference in leaf span between peat pots and the control. Though there was no significant difference in plant height and leaf span, it demonstrates that there were no adverse effects upon the above ground growth. However, there were significant differences in dry weight and root density. As the development of T. majus progressed the peat pots prevented most of the roots from penetrating. This lack of penetration caused the dry weight to increase. Eventually this increase would have constricted the height and leaf span of the plants as illustrated in Yue et al.’s (2010) study. From the findings of this research, it is clear that peat pots have a potential for increasing yield and sustainability of crop production. The hardening effect noted in this study and many others was owed to a lack of regular watering. According to Clark et al. (2003) it takes 5.3 extra litres (over a 3 month period) to crops that are subject to peat pots with a diameter of 7cm to ensure that they do degrade, within the time allowance of their manufacturers.
6.2 One improvement which could have been made was to expand the diversity of plants used. This researcher’s main aim was to investigate the effectiveness of using these biocontainers on annual plants; as recommended by previous studies. The most common annual crops grown in UK nurseries includes: Petunia tumbelina, Petunia varieties, Pelargonium grandiflorum and Impatiens walleriana. By expanding the different genera used within this experiment, would have ensured that the effects noted on T. majus were not confined to T. majus. Since there is a great diversity of annual genera and species sold on the UK market, one needs to be certain that biodegradable containers have a universal effect on them.
6.3 More research is needed to find alternative environmentally friendly and sustainable materials. Materials like compressed green waste, organic ligneous containers and recycled topsoil containers. Little research has been undertaken to understand the above material’s effects on the surrounding substrate, how fast they degrade and their ability to encourage and proliferate a microbiota association. Since the increase in popularity of sustainable products, there is a need to develop these products to enable producers to send them to market; to reach the right balance between integrity and permeability as discussed in Grazuleviciene et al.’s (2007) and Kuehny et al.’s (2010) research.
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