Vermicomposting primary and secondary solids from the pulp and paper industry

Transcription

1 Vermicomposting primary and secondary solids from the pulp and paper industry Michael Quintern, Hailong Wang, Guna Magesan and Alison Slade June

2 The information and opinions provided in the Report have been prepared for the Client and its specified purposes. Accordingly, any person other than the Client, uses the information and opinions in this report entirely at its own risk. The Report has been provided in good faith and on the basis that reasonable endeavours have been made to be accurate and not misleading and to exercise reasonable care, skill and judgment in providing such information and opinions. Neither Scion, nor any of its employees, officers, contractors, agents or other persons acting on its behalf or under its control accepts any responsibility or liability in respect of any information or opinions provided in this Report.

3 EXECUTIVE SUMMARY The pulp and paper industry generates large volumes of organic solid waste from its pulping and papermaking processes, and its subsequent wastewater treatment operation. Currently these wastes are predominantly landfilled. Vermicomposting had been identified as a potential short-medium term option for the beneficial re-use of these solids, and a feasibility study was undertaken. OBJECTIVES The objectives of this feasibility study were therefore to: Determine the feasibility of vermicomposting of primary solids, secondary solids, and a combination of both. Characterise the resultant vermicompost product. Evaluate potential toxicity of the vermicast to plants. Test the vermicast as a substitute in potting mix. RESULTS Compost worms were able to process primary and secondary solids (bio wastes) from the Tasman Mill in a batch trial under laboratory conditions. The preferred order in which compost worms processed the feedstock and were able to breed in the medium: secondary solids > blend of primary and secondary solids > primary solids. The results suggests that vermicomposting of primary solids exclusively is very unlikely to be successful as compost worms will probably not colonise the feedstock. Vermicast from pulp and paper bio wastes have a high C/N ratio as no nitrogen rich products were added during the vermicomposting process. The C/N ratios of the vermicast from primary solids, mix of primary solids with secondary solids, and secondary solids were 162, 61, and 47, respectively. The total nitrogen (% dry matter) was 0.21, 0.54, and 0.70 respectively. A total nitrogen content of 0.6% of the dry matter is required for vermicast to pass the New Zealand standard for composts, mulches and soil conditioners. The results suggest only vermicast from secondary solids will pass the NZ standard. Vermicast did not cause any toxicity to plant germination or root growth and is therefore suitable as a substrate for potting mixes. Adding vermicompost from pulp and paper bio wastes to potting mix did not enhance plant growth. Vermicast from primary solids may have immobilised plant available nitrogen in the potting mix. Adding nitrogen-rich bio wastes to the vermicomposting process may result in a vermicast with a higher plant nutrition value. The impact of vermicast on macro- and micro-nutrient availability requires further investigation. FURTHER WORK Field trials would be required to generate sufficient vermicompost to undertake more comprehensive germination/growth tests and determine the value of pulp and paper bio waste derived vermicompost. (ii)

4 TABLE OF CONTENTS EXECUTIVE SUMMARY... ii OBJECTIVE... ii FURTHER WORK... ii 1 GLOSSARY OF TERMS INTRODUCTION MATERIALS AND METHODS Vermicomposting feasibility trial Vermireactor and trial design Feedstock preparation and application Harvesting of casting Analysis Toxicity test to plants Potting trial Statistics RESULTS AND DISCUSSION Vermicomposting feasibility trial Feedstock and vermicast quality Toxicity test Potting trial Tomato Rye grass CONCLUSIONS AND RECOMMENDATIONS REFERENCES...22 (iii)

5 1 GLOSSARY OF TERMS Green waste Green waste includes the yard trimmings, leaves, shrubs, plants, grass, street trees, or tree trunks, park trees or tree trunks etc. that arise from households, Council parks and garden maintenance, and commercial premises. Bio waste Bio waste is the term used to describe those wastes that are readily biodegradable, or easily breakdown with the assistance of micro-organisms. Bio wastes consist of materials that contain molecules based on carbon. This includes food waste, green waste, putrescible waste and also wastes arising from grease traps. Bio waste however, does not include for example, plastic or mineral oil products. Vermicast A single worm casting or a quantity of worm castings. Worms work material by ingesting, excreting and re-ingesting it. Vermicast is extensively wormworked and re-worked. It may be overworked and has probably lost plant nutrients as compared to vermicompost. Vermicast has a fine, smooth texture which may dry with a crust on the surface. Vermicompost Mixture of partially decomposed organic waste, bedding and worm castings. Contains recognizable fragments of plant, food or bedding material as well as cocoons, worms and associated organisms. Vermicomposting The process of using worms and associated organisms to break down organic waste into material containing nutrients for plant growth

6 2 INTRODUCTION The pulp and paper industry generates large volumes of organic solid waste from its pulping and papermaking processes, and its subsequent wastewater treatment operation. Currently these wastes are predominantly landfilled. A sustainable and acceptable option for the disposal of pulp and paper wastewater solids into the future must be one that (1) overcomes current negative perceptions towards beneficial re-use of industrial wastes, (2) minimises or eliminates waste residues, (3) eliminates any potential toxicity issues, (4) generates value, and (5) preferably can be implemented on-site to minimise transportation costs. A review of existing disposal/reuse technologies identified vermicomposting as a potential, short- medium term option for the benefical reuse of these solid waste streams (Slade et al. 2006). Subsequently an initial feasibility trial and testing of the resultant vermicast was undertaken. Vermicomposting is the breakdown of organic material that, in contrast to composting, involves the joint action of earthworms and micro-organisms and does not involve the generation of high heat as is with composting. The worms consume organic wastes such as food waste, animal waste and sewage sludge; and turn and fragment the waste, which produces a soil conditioner (EMRC, 2008). Vermicomposting is a widely used processing technology (Edwards & Arancon, 2004; Edwards & Neuhauser, 1998; Kale, 2004) with minimal environmental effects such as odour and leachate. Compost worms are surface feeders and are only found in organic horizons in ecosystems. They do not live in mineral soil horizons. The ecosystem of these organic horizons is characterised by a wide community of decomposition specialists mostly dominated by fungi and bacteria. Other species such as collembolans and compost worms feed on decomposed organic material and on bacteria and fungi. The digestion system of compost worms is highly effective in grinding coarse feedstock. The decomposed organic matter is mixed with mineral particles and is released as vermicast. Traditional composting of bio waste results in a volume reduction of one third. Vermicomposting reduces the volume by two thirds. The vermicast is a much more stable product compared to compost and is characterised by higher contents of humic and fulvic acids. Vermicast is an organic fertiliser which releases nutrients slowly and is therefore a preferred fertiliser for organic farming and horticulture. The final products such as vermicompost and vermicast are both standardised in the New Zealand Standard for Composts, Soil Conditioners and Mulches (Anonymous, 2008). Various species of compost worms are found in vermicomposting systems world wide. In New Zealand, Tiger worms (Eisenia fetida) and Red worms (Lumbricus rubellus) are the most common compost worms in commercial worm farms. Some regions in the North Island successfully use Indian blue worms (Perionyx excavatus). Worm farms in the Bay of Plenty region operate with compost worm populations of 95% Tiger worms and 5% Red worms

7 The most common vermicomposting technologies in New Zealand are windrow technology (e.g. Perry Industries in New Plymouth, Wormtech in Edgecumbe, Worm-R-Us in Auckland), followed by box systems (e.g. Ashburton Meat Processors), and Tat-G (e.g. Auckland Zoo, Northland Regional Council, supermarkets in Auckland region) which is a continuous flow system. New Zealand Industrial vermicomposting operations mainly process their organic wastes in windrow systems (Quintern et al., 2008). The most common bio wastes processed in New Zealand s worm farms are pig manure, solids from dairy effluent, fruit wastes, and green wastes. No pulp and paper biosolids have been vermicomposted at a large scale in New Zealand to date. Internationally, vermicomposting industries also process municipal sewage sludges, pulp and paper biosolids and other bio wastes (Butt, 1993; Elvira et al., 1996). Pulp and paper biosolids are most commonly vermicomposted in combination with nitrogen rich bio wastes (Elvira et al., 1997). Combinations of manure and pulp with pulp and paper biosolids (Arancon et al., 2003; Arancon et al., 2005; Arancon et al., 2008; Elvira et al., 1998) and municipal sewage sludge with pulp and paper biosolids have been tested in the USA and Europe. However, even though there have been various studies conducted on vermicomposting pulp and paper biosolids, the biosolids produced at different mills, with different pulping and papermaking processes, must be dealt with on a case-by-case basis (Bostan et al., 2005). Advantages of vermicomposting include creation of new marketing options for vermicast, a higher volume reduction, and benefits to soil plant systems when land applied. The disadvantages may include finding a nitrogen rich source if required, processing costs, higher capital gain for purchasing large quantities of composting worms, and overcoming the cash flow in the first years when vermicast cannot be traded. If considering a large scale operation the end user market also needs to be evaluated. Vermicomposting has a potential to increase the rate of decomposition of bio wastes and to stabilise organic residuals (Edwards & Arancon, 2004; Edwards & Neuhauser, 1998). As vermicomposting leads to more aerobic decomposition, less methane is generated (Mitchell et al., 1980) and could be part of a strategy for greenhouse gas mitigation for the agricultural sector such as intensive dairy farming (Dynes, 2008). The Tasman Mill was the focus for this work as 40% of its primary solids are already composted for potting mix by a private operation. The pulp and paper industry produces two types of bio wastes, primary solids and secondary solids. Tasman s primary solids are characterised by a high C/N ratio of 198 and secondary solids with a C/N ratio of 58 (Garrett & Wang, 2006). Based on these C/N ratios, the secondary solids have the potential to be used as a feedstock to compost worms, however it is very unlikely that primary solids could be used as feedstock on their own as essential nutrients such as nitrogen and phosphorus are insufficient. Various studies have demonstrated that a C/N ratio of 25 is most effective for vermicomposting (Butt, 1993; Ndegwa & Thompson, 2000). Slightly higher C/N ratios can increase breeding success (Aira et al., 2006), whereas C/N ratios higher than 40 tend just to increase worm body weight (Sharma et al., 2005). Blending of both sources of bio wastes could offer the best option for processing primary solids by vermicomposting

8 The specific aims of this study were therefore to: Determine the feasibility of vermicomposting of primary solids, secondary solids, and a combination of both. Characterise the resultant vermicompost product. Evaluate potential toxicity of the vermicast to plants. Test the vermicast as a substitute in potting mix. 3 MATERIALS AND METHODS 3.1 Vermicomposting feasibility trial Vermireactor and trial design A common commercial small scale vermicomposting system Can-O-Worms was chosen for vermicomposting of pulp and paper primary and secondary biosolids (bio wastes). The Can-O-Worms is a closed vermireactor that forces compost worms to compost even unpalatable feedstock. Figure 1: Diagram of a small scale vermireactor Can-O-Worms (Nattrass, 1995). The vermireactor (vermicomposting unit), as shown in Figure 1, consists of a collector tray to collect and harvest leachate (bottom), three working trays, and a lid. The bottom working tray, also termed bedding tray, holds the worm bedding (soaked coconut fibre) and compost worms. The tray stacked on top of the bedding tray is the feeding tray where the feedstock is applied. Each - 7 -

9 working tray is perforated with 2 mm holes allowing the worms to migrate from bedding to feedstock. Air can percolate throughout the whole system. At the beginning of the trial, 6 kg of live Eisenia fetida were equally distributed over three treatments with three replications: (i) primary solids; (ii) mix of primary and secondary solids; and (iii) secondary solids. Thus 666 g of compost worms were added to each vermireactor. The quantity of 2 kg worms per replication was chosen to process sufficient casting for further testing to determine if the feedstock were suitable for vermicomposting. Table 1 shows the mixtures of pulp and paper waste solids used as feedstock (treatments) in the vermicomposting feasibility trial. Table 1: Feedstock (treatments) from primary and secondary pulpmill solids used in the vermicomposting feasibility trial Treatment Abbreviation Feedstock components Primary solids [vol.-%] Secondary solids [vol.-%] Primary solids PS Mix of primary and secondary solids PS/SS Secondary solids SS The nine vermireactors (3 treatments x 3 replicates) were arranged in a Latin square in a constant temperature laboratory at 20 C. Light was kept switched on for 24 hours a day to ensure no worms escaped Feedstock preparation and application Primary solids were taken directly from the separation/dewatering operation at the Tasman Mill. Primary solids were stored in an open bag in cool conditions and protected from sunlight and rain. Secondary solids were dug up by hand at approximately 2 m from the edge of the last dewatering pond. This pond was chosen as it was not visibly covered with plants or dirt, and allowed safe sampling. The top 5 cm was not harvested as it may have contained high seed content from weeds growing around the ponds. The secondary solids were stored in cool dark conditions in unsealed 20 litre buckets to minimise anaerobic decomposition. New solids were harvested every two to three months. A 3 cm layer of feedstock was applied into the feeding trays. PS/SS were applied in equal volumes layered into feeding trays and carefully mixed by hand. As the water content of the primary solids was slightly below the optimum water content for vermicomposting (57.4%), 10 vol.-% of tap water at 20 C was sprinkled over the feedstock after application

10 Worms were checked three times a week and new feedstock was applied when old feedstock had been processed by more than 80 % by volume as determined by visual appraisal Harvesting of casting Castings of PS/SS and SS were harvested after 7 months. Insufficient casting was available from the PS vermireactor at this time. A final harvest of casting of PS was conducted two months later which provided sufficient casting for the potting trial. By exposing composting worms to highly intensive light, the worms were forced to burrow deeply into the casting. The top worm-free layer was harvested from each treatment. The casting harvested from each replication was homogenised and a sub sample was taken for analysis Analysis Samples of the final casting were analysed for total carbon (C) and total nitrogen (N) with a LECO CNS 2000 analyser (modified Dumas method). Electrical conductivity (EC), ph, and moisture content were also measured according to AS 4454 (SAC, 1999). 3.2 Toxicity test to plants The toxicity test is a standard method for determining whether a product, in this case vermicast from pulp and paper bio wastes, is sufficiently toxic to inhibit the germination of seed or growth of roots. Seeds were germinated on vermicast and a reference sample that was known to be non-toxic. The fresh vermicasts from Primary Solids (PS), Secondary Solids (SS), and a blending of Primary Solids with Secondary Solids (PS/SS) were tested for toxicity against a standard all purpose potting mix from Yates (control). The effect on germination of seed (radish Long Scarlet ) and growth of roots according to AS 4454 Appendix E (SAC, 1999) was analysed. The early growth of roots of germinated seeds from the vermicast sample was compared against the control. 3.3 Potting trial The various vermicast samples were tested in a potting trial to examine the effect on plant growth of tomato and rye grass. Tomato varieties have been used in several studies to test the effect of vermicompost in seedling potting media (Zaller, 2007a and Zaller, 2007b). Such data would be useful to potential end users such as market gardeners. Rye grass was also tested to provide information for agricultural end users, such as dairy farmers, who could use vermicast on pasture. Vermicast from all treatments produced in this trial were blended with standard, all-purpose potting mix from Yates. Vermicast replaced potting mix in amounts of 0, 10, 25, and 50 % by volume (Table 2). Potting mix and - 9 -

11 vermicast were mixed thoroughly and, after calculating individual density, measured by weight and poured into pots of two litre capacity. Two varieties of plants were used for testing the treatments: tomato plants ( Money Maker ) 5 cm high; and 20 g of rye grass seed per pot. Rye grass seed was applied through a moulding tool for exact replication. Table 2: Mixtures of vermicast and potting mixes used in potting trial Treatment All purpose potting mix Substrate components [vol-%] primary solids Vermicast from primary solids and secondary solids secondary solids Control PS PS PS PS/SS PS/SS PS/SS SS SS SS Pots were arranged in four blocks. Within each block all treatments were randomised. After watering, pots were rearranged to minimise fringe effects. All plants were planted and sown on the 01/10/2007. Tomato plants were harvested on the 22/12/2007. Rye grass was first cut on 22/12/2007 and again on the 29/02/ Statistics Data were analysed with a one-way ANOVA; feedstock or different mixtures for potting mixes were used as factors in the software package Minitab (Version 15). Tukey s least squares means test (p = 0.05%) was used for mean comparisons

12 4 RESULTS AND DISCUSSION 4.1 Vermicomposting feasibility trial The feasibility trial of vermicomposting pulp and paper bio wastes was conducted in a temperature controlled (20 C) laboratory using Can-O-Worms vermireactors. Images taken during the trial are given in Table 3. The images show the applied feedstock from Primary Solids (PS), mix of Primary and Secondary Solids (PS/SS), and Secondary Solids (SS). Worm activities in the different feedstock decreased from PS, PS/SS to SS. In the bottom right image (SS) the surface is covered with fine dark vermicast, whereas the top right image (PS) shows only a small amount of greyish vermicast at the surface. The image in the centre right shows a medium worm activity resulting in some greyish and some darker casting at the surface. As the worms were locked in the vermicomposting unit they were forced to process the applied feedstock. They were not able to migrate to potentially more preferable food resources as they would in open space systems that occur in windrow vermicomposting technology. Therefore transferring the results from the vermireactors to field scale would require a large-scale trial under real conditions. It is most likely that the success of a windrow trial would improve with increasing content of secondary solids. It is very unlikely that worms would process primary solids alone

13 Table 3: Images from feasibility trial of vermicomposting pulpmill solids in Can-O-Worms vermireactors. Treatment View from top View from side Primary solids (PS) Primary solids / secondary solids 50vol.-% each (PS/SS) Secondary solids (SS)

14 4.2 Feedstock and vermicast quality Vermicast quality was tested on 21/11/2006 (1 st period) and 15/01/2007 (2 nd period) for each individual vermireactor. Characteristics of the primary and secondary solids are given in Table 4 (Garrett and Wang, 2006). Table 4: Concentration of constituents in primary and secondary solids. Data from (Garrett and Wang, 2006) Constituent Primary solids Secondary solids C (%) N (%) C/N S (%) Ca (%) K (mg kg -1 ) Mg (mg kg -1 ) Na (mg kg -1 ) P (mg kg -1 ) B (mg kg -1 ) Mo (mg kg -1 ) <0.1 <0.1 As (mg kg -1 ) < Cd (mg kg -1 ) Cr (mg kg -1 ) Cu (mg kg -1 ) Pb (mg kg -1 ) Ni (mg kg -1 ) Zn (mg kg -1 ) Table 5 presents the basic analysis of vermicast taken from the vermicomposting feasibility trial. The C/N ratio was chosen to determine the extent of decomposition. Over time the C/N ratio of secondary solids decreased from 58 to 47 at the first sampling and to 42 by the end of the trial. The primary solids decreased marginally from 198 to 162 during the first period of vermicomposting. During the second period, the C/N ratio decreased clearly from 162 to 98. The mixed feedstock of primary and secondary solid had a calculated C/N ratio of 128 which decreased to 61 during vermicomposting and did not decrease any further over the study time. These findings were in line with results from other studies on vermicomposting (Suthar & Singh, 2008)

15 The stabilisation of pulp and paper biowastes by vermicomposting created a vermicompost with a reduced C/N ratio which would be suitable for land application or for potting mix use in general. The vermicomposting process increased the nitrogen content of the product. According to the New Zealand compost standards the vermicasts must have a total nitrogen content of 0.6 or more to contribute to plant growth (Anonymous, 2008). The results of this study showed that only vermicast derived from secondary solids fulfilled this requirement and hence could be suitable for vermicomposting. The ph of all vermicast was within the required range of the standard for vermicast. Table 5: Analysis of vermicast from vermicompost of pulp and paper primary and secondary solids (21/11/2006 and 15/01/2007). Feedstock (waste) Total C (%) Total N (%) C/N ph EC (µs/cm) Moisture content (% wet weight) Sampling 21/11/2006 PS PS/SS SS Sampling 15/01/2007 PS nd nd nd PS/SS nd nd nd SS nd nd nd PS = primary solids, SS = secondary solids; nd = not determined 4.3 Toxicity test Vermicast from vermicomposting was tested for negative effects on germination or root growth. The method was chosen after a discussion with the manager of Plateau Bark & Composts, who composts 30,000 tonnes of primary solids at Tasman Mill for Yates potting mixes. The method is fundamental for products used as potting mixes for domestic and commercial purposes. The testing treatments were Primary Solids (PS), Secondary Solids (SS), a blend of Primary Solids with Secondary Solids (PS/SS), and an all purpose potting mix from Yates as a control (Figure 2). The results of germinated seeds are shown in Table 6. Germination of radish seed was similar in all vermicast mixes as well as in the potting mix. These results demonstrate that vermicast from pulp and paper bio wastes from the Tasman Mill did not harm germination and can be recommended as a potting mix additive for nurseries and horticulture industries and as peat substitute (Zaller, 2007a; Zaller, 2007b)

16 Figure 2: Radish seedlings during a toxicity test, after 72 hours. Root growth of young seedlings was measured after 3 days of growth in a climate chamber (Table 6). Average root growth achieved in vermicast derived from primary solids was 43.3 mm per plant; from a mix of primary and secondary solids was 41.6 mm; and from secondary solids was 42.3 mm. Yates all purpose potting mix had an average root length of 33.5 mm. However, there was no significant difference between treatments according to a one-way ANOVA test. Table 6: Effects of vermicompost from pulpmill solids and potting mix (control) on germination of seeds and growth of roots after 72 hours (toxicity test). Results show means from 20 seeds. Treatment Seeds germinated (n) Root length (mm/plant) Vermicast - PS ns Vermicast - PS/SS ns Vermicast - SS ns Potting Mix PS = primary solids, SS = secondary solids, ns = not significantly different from potting mix (P < 0.05, Tukey s) Better root growth of up to 33% (although not significant in this test) could be the result of beneficial plant-growth promoting (PDP) and growth-influencing substances and plant growth regulators (PGRs) (Brown et al. 2004)

17 4.4 Potting trial The general effect of vermicast from pulp and paper bio wastes on plant growth was studied in a potting trial. Vermicast is recommended in several studies to add quality to potting mix (Zaller, 2007a; Zaller, 2007b). The three different vermicasts from pulp and paper bio wastes: primary solids (PS), mix of primary with secondary solids (PS/SS), and secondary solids (SS), were added to standard, all purpose potting mix from Yates. All vermicasts were tested in three quantities at 10, 25, and 50 % by volume. Two types of plants were chosen for the potting trial (Figure 3). Tomato plants at first true leaf stage are widely used for trials to demonstrate short term results. These results are essential in order to market a vermicast product to end users such as potting mix industries and horticulturalists. Rye grasses can be harvested at various times and were used to assess medium and long term results. Figure 3: Potting trial for testing various vermicast from pulp and paper bio wastes on plant growth. The rye grass trial is at the front and the tomato plant trial is at the rear Tomato Tomato plants grew well after planting into various blends of vermicast and compost. Plant heights were similar throughout all pots and as the trial was completely randomised it was not possible to determine individual treatments by observation from a distance. All lateral shoots were removed weekly. Tomato plants grew for 11 weeks and were harvested on the 22/12/2007. Prior to cutting, plant height was measured, and the set of flowers and total numbers of fruits larger than 5 mm were counted. Fresh matter of fruits and

18 total plant (without roots) and dry matter of total plant (without roots) were determined. All results are shown in Table 7. The average heights of the tomato plants in the control (potting mix) were cm. The average heights of the tomato plants in the vermicast treatments were similar. All vermicast treatments, except SS 25, showed a slight decrease in the number of sets of flowers. All treatments showed a decrease in the number of fruit larger than 5 mm, although the fruit were larger as there was little difference in the fresh fruit matter. As more vermicast from primary solids was added to the potting mix, less fresh and dry matter was produced for the same height of plant. A decrease in yield was found in treatment PS 50 with 83.0 g fresh matter and 11.7 g dry matter compared to the control with g fresh matter and 29.0 g dry matter. Table 7: Effect of vermicomposting from pulp and paper bio wastes added to standard potting mix (containing long term fertiliser) on tomato growth in pots 22/12/2007. Results are shown as averages of 4 replications. Treatment Height (n) Set of flowers (n) Fruits (n) Fruits fresh matter (g) Total plant fresh matter (g) Total plant dry matter (g) PS * * 25.8 * PS * * 18.4 * PS * 2.50 * * 83.0 * 11.7 * PS/SS * PS/SS * 4.00 * PS/SS * * * 24.5 * SS * SS * * 26.1 SS * Potting mix PS = primary solids, SS = secondary solids * Significantly different from control (P < 0.05, Tukey s) The general reduction in fruits, and the reduction of plant fresh and dry matter when planted in high volumes of vermicast from primary solids, requires further investigation. It is possible that the high levels of vermicasts from the primary solids reduced the availability of some nutrients and not others. For example, nitrogen, potassium and phosphorus, all key plant macro-nutrients, may behave differently in the presence of vermicast. The poor fruit set from similar numbers of flowers in the vermicast treatments is also worthy of further investigation. It is possible that the presence of vermicast impacted on micronutrient availability

19 It is recommended that a potting trial be carried out in conjunction with potting mix industries as their requirements must be considered in the mixtures and fertiliser compounds. Alternatively the plant growth index can be determined according to NZ composts standards (Anonymous. 2008) where composts are tested against non fertilised sand as a control Rye grass Rye grass was used to test the effect of vermicompost from pulp and paper bio wastes on pasture. Dairy farming has a growing demand for replacement of soil organic carbon, as pasture in New Zealand is losing approximately one ton of carbon ha -1 annually (Schipper et al., 2007). Dairy farming on the low fertile ash soils around the Tasman Mill in Kawerau could benefit from using vermicast derived from pulp and paper bio wastes. Vermicompost has been recognised by farmers as beneficial to soil fertility in agricultural soils, improving soil ph, root growth, and yields (Gutierrez-Miceli et al., 2007). The rye grass yields of the first cut at 22/12/2007 are given in Table 8. Fresh matter production from rye grass in the potting trial was higher in all vermicast treatments from secondary solids, SS 10, SS 25, and SS 50, as well as from PS/SS 10 compared to the control. Those treatments with primary solids, PS 10, PS 25, and PS 50 and higher content of primary solids in the mix such as PS/SS 25 and PS/SS 50 showed a reduction in fresh matter production. This observation suggests that SS 10, SS 25, SS 50, and PS/SS 10 did not suffer from nitrogen deficiency, whereas higher volumes of PS-derived vermicast in the potting mix may have caused immobilisation of plant available nitrogen. Again this hypothesis must be investigated in further trials. In practice vermicast from solely primary solids is very unlikely to be produced and used as discussed previously. However, vermicast from secondary solids would be more realistic and would provide a product with some potential for improving pasture on poorly fertile soils resulting from low soil organic matter content. The rye grass production of the second cut on 29/02/2008 is shown in Table 9. At this stage all treatments containing vermicast from pulp and paper bio wastes showed a reduction in rye grass yields compared to the fertilised potting mix as a control. The yield of the control dropped from g per pot to g per pot, suggesting that the applied nutrients in the potting mix could have been depleted. When watering on a daily basis the treatments with high contents of primary solids PS 10, PS 25, and PS 50 showed less water stress than other treatments. PS derived vermicast might have a positive impact on water holding capacity of the potting mix. This could have led to slightly higher yield of these treatments at the second cut compared to the other vermicast treatments

20 Table 8: Effect of vermicomposting from pulp and paper bio wastes added to standard potting mix (containing long term fertiliser) on rye grass growth in pots - first cut 22/12/2007. Results are shown as mean of 4 replications. Treatment Fresh matter Dry matter (g) (%) (g) (%) PS * * 81.8 PS * * 76.1 PS * * 47.7 PS/SS * 91.3 PS/SS * 91.5 PS/SS * * 85.2 SS SS * * 99.4 SS * 95.5 Potting mix (control) * Significantly different from control (P < 0.05, Tukey s)

21 Table 9: Effect of vermicomposting from pulp and paper bio wastes added to standard potting mix (containing long term fertiliser) on rye grass growth in pots second cut 29/02/2008. Results are shown as average of 4 replications. Treatment Fresh matter Dry matter (g) (%) (g) (%) PS * * 75.9 PS * 77.8 PS * 83.9 PS/SS * * 67.2 PS/SS * * 69.4 PS/SS * * 66.7 SS * 81.1 SS * * 57.0 SS * * 62.6 Potting mix (control) * Significantly different from control (P < 0.05, Tukey s) To evaluate the effect on pasture on poor soils such as those found in the Kawerau region, vermicast from pulp and paper bio wastes should be tested in field trials to measure the impact on nitrogen availability, yield and water holding capacity. 5 CONCLUSIONS AND RECOMMENDATIONS A trial was undertaken to assess the feasibility of vermicomposting pulp and paper primary and secondary solids (bio wastes) using small scale Can-O- Worms vermireactors. A review of existing technologies had identified vermicomposting as a potential short-medium term solution for the beneficial reuse of these wastes. Solids from the Tasman Mill were selected for the trial, as a commercial operation is already converting 40% of the primary solids into potting mix. Vermicast from pulp and paper bio wastes have a high C/N ratio as no nitrogen rich products were added during the vermicomposting process. The C/N ratios of the vermicast from primary solids, mix of primary solids with secondary solids, and secondary solids were 162, 61, and 47, respectively. The total nitrogen (% dry matter) was 0.21, 0.54, and 0.70 respectively. A total nitrogen content of 0.6% of the dry matter is required for vermicast to pass

22 the New Zealand standard for composts, mulches and soil conditioners. The results suggest only vermicast from secondary solids will pass the NZ standard. The following general conclusions were drawn: Secondary solids, and a mix of primary and secondary solids were found to be suitable for vermicomposting. Primary solids were not found to be suitable for vermicomposting on their own. Alternative nutrient rich bio wastes could be added to the vermicomposting process to achieve vermicast with higher nutrient contents. Toxicity tests indicated no negative effects on germination for the primary, secondary and the mix of primary/secondary solids. Tomatoes were used in potting trials to test a horticultural application. There were no positive plant growth effects, indeed there was a general reduction in the number of fruit larger than 5mm, and addition of vermicasts from primary solids reduced yields. Rye grass was used in potting trials to test an agricultural application. Initial results indicated a positive impact of the vermicast from secondary solids, however this result was reversed over the longer term, with decreased yields from all vermicast applications. Vermicast from primary solids may have immobilised plant available nitrogen in the potting mix. Adding nitrogen-rich bio wastes to the vermicomposting process may result in a vermicast with a higher plant nutrition value. Field trials would be required to provide sufficient vermicompost to undertake more comprehensive germination/growth tests and determine the impact of vermicast on macro- and micro-nutrient availability

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