Transfer of Weeds to Queensland Native Forests by Horse Faeces — The viability and germination of plant seeds found in horse faeces —
RIRDC Publication No. 11/109
RIRDCInnovation for rural Australia
Transfer of Weeds to Queensland Native Forests by Horse Faeces The viability and germination of plant seeds found in horse faeces
by Christopher C Pollitt and Longbin Huang
October 2011
RIRDC Publication No. 11/109 RIRDC Project No. PRJ-000525
© 2011 Rural Industries Research and Development Corporation. All rights reserved.
ISBN 978-1-74254-289-8 ISSN 1440-6845
Transfer of Weeds to Queensland Native Forests by Horse Faeces Publication No. 11/109 Project No. PRJ-000525
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Researcher Contact Details
Christopher C Pollitt Longbin Huang (Senior Research Fellow) School of Veterinary Science Centre for Mined Land Rehabilitation The University of Queensland Sustainable Minerals Institute Gatton QLD 4343 The University of Queensland Brisbane QLD 4072 Phone: 0419 721 682 Email: [email protected] Phone: 07 3346 3130 Email: [email protected]
In submitting this report, the researchers have agreed to RIRDC publishing this material in its edited form.
RIRDC Contact Details
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PO Box 4776 KINGSTON ACT 2604
Phone: 02 6271 4100 Fax: 02 6271 4199 Email: [email protected]. Web: http://www.rirdc.gov.au
Electronically published by RIRDC in October 2011 Print-on-demand by Union Offset Printing, Canberra at www.rirdc.gov.au or phone 1300 634 313
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Foreword
There are environmental concerns associated with horse riding in conservation areas and national parks in Australia. One of the concerns is the potential risk of weed invasion into natural plant communities, through viable seeds contained in horse faeces, when environmental conditions are suitable (e.g. adequate nutrients and water). Both controlled and field studies are required to obtain further evidence for assessing the risk of weed invasion caused by horse faeces during horse riding in natural reserves and national parks in Queensland.
Horse riding in safe, natural environments is a part of daily activities for many Australians and is likely to continue for either recreation or economic purposes. Management strategies based on empirical scientific knowledge are required to promote recreational riding with the minimum impact on natural ecosystems.
This project investigated the following question: does horse faeces contain viable seeds which may be germinated under suitable conditions or persist in surface soil? The results showed that many plants germinate from horse faeces especially if the horses are grazing weed infested pastures. On the other hand, the faeces of stabled horses, fed manufactured feeds, contain relatively few viable seeds. To determine the role of horse faeces as a source of weeds in natural forests, plants growing on 100 m transects of the sampled pasture and transects of the trails in nearby native forests need to be compared. When complete these studies will supply objective data to assess the level of threat of weed invasion posed by horse riding in areas of native vegetation and will help formulate rational management strategies for recreational horse riding.
The project was funded from industry revenue which is matched by funds provided by the Australian Government.
This report is an addition to RIRDC’s diverse range of over 2000 research publications and it forms part of our Horse R&D Program, which aims to assist in developing the Australian horse industry and enhancing its potential.
Most of RIRDC’s publications are available for viewing, free downloading or purchasing online at www.rirdc.gov.au. Purchases can also be made by phoning 1300 634 313.
Craig Burns Managing Director Rural Industries Research and Development Corporation
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Acknowledgments
David Bowen of the School of Land & Food Science, Faculty of Natural Resources, Agriculture and Veterinary Science, The University of Queensland, assisted greatly in the experiments in this report and is sincerely thanked.
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Contents
Foreword ...... iii Acknowledgments ...... iv Executive Summary...... vii Introduction ...... 1 Objectives ...... 1 Methodology ...... 2 Sieving and seed viability testing ...... 2 Germination under controlled glasshouse conditions ...... 2 Data collection and Analysis...... 3 Results ...... 4 Viability testing ...... 4 Glasshouse trial: HU manure treatments ...... 4 Glasshouse trial: EF manure treatments ...... 14 Comparison of seed viability with glasshouse emergence ...... 15 Discussion ...... 17 Recommendations...... 19 Appendix 1. Numbers of seedlings in manure treatments (per 200g manure) at 36 days ...... 20 Appendix 2. Percent water in manure types ...... 21 References ...... 22
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Tables
Table 1 Sources of horse manure...... 2 Table 2 Percent viability of seed extracted from 3 horse manure types ...... 4 Table 3 Mean numbers of seedlings in manure treatments (/200g manure) at 36 days ...... 11 Table 4 Concordance between species extracted by wet sieving from manure and from glasshouse emergence...... 16 Table 5 Weed species germinating in horse manure ...... 17
Figures
Figure 1 Mean number of monocotyledon and dicotyledonous seedlings in treated HU manure at 14 days ...... 5 Figure 2 Mean number of monocotyledonous seedlings in treated HU manure at 21 days ...... 6 Figure 3 Mean number of seedlings of 4 dicotyledons and 1 monocotyledon (Cyperus polystachyos) in treated HU manure after 21 days ...... 6 Figure 4 Mean number of seedlings of Queensland Blue couch (Digitaria didactyla) in 200g of HU manure (fresh and dried treatments) in 4 replicate trays (36 days) ...... 12 Figure 5 Mean number of seedlings of Queensland Blue couch (Digitaria didactyla) in 1kg HU manure at 36 days ...... 13 Figure 6 Mean number of seedlings per kg of the most frequently found forb, grass and sedge species in HU manure ...... 13 Figure 7 Mean number of seedlings of Amaranthus powellii per kg of EF manure ...... 14
Plates
Plate 1 Glasshouse trial inception ...... 3 Plate 2 Seedlings of Queensland blue couch (Digitaria didactyla) at 14 days...... 5 Plate 3 Seedlings of monocots outnumber dicots seedlings at 21 days ...... 7 Plate 4 Seedlings of pigweed (centre), emu foot (left fore/centre/ground) and Queensland blue couch ...... 8 Plate 5 Control trays at 36 days ...... 8 Plate 6 Seedlings in dry HU manure ...... 9 Plate 7 Seedlings in fresh HU manure ...... 9 Plate 8 Seedling of Eleusina indica at 36 days ...... 12 Plate 9 Seedling of Psoralea tenax at 36 days ...... 14 Plate 10 Mature plants of Amaranthus powellii at 36 days ...... 15
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Executive Summary
What the report is about This study determined the viability of weed seeds in horse manure and the composition and magnitude of weed establishment from horse manure, in a glasshouse germination trial.
Background In Queensland 32% of Regional Ecosystems are currently threatened and weeds accidentally introduced since European settlement contribute significantly to the degradation of native plant communities. Weeds may be introduced into native ecosystems on vehicles, by human and animal vectors and there is anecdotal evidence that horse manure contains weed seed. Rigorous scientific studies are necessary to derive the required data on the extent of weed seeds borne in horse manure and the consequences of allowing horses onto areas of conservation significance, such as National Parks and State Forests.
Aims/objectives This study had the objective of determining if horse faeces contain viable seeds that may persist in surface soil and germinate under suitable conditions.
Methods used Samples of manure were collected from 3 locations in the Brisbane Metropolitan area where horses are kept. One was a racehorse stable where horses were fed prepared feed with no free paddock grazing and the other two were large paddocks with little or no weed control and with lantana and groundsel present. The number of viable seeds was determined for each manure type and expressed as a percentage of the number of seeds observed. The fresh and dried manure was mixed into sterile potting mix and monitored daily for weed germination over a period of 45 days. Species germinating in trays were identified wherever possible.
Results/key findings At 14 days after sowing, a large number of monocotyledons (125) had emerged in the dry manure but only a fifth as many had emerged in the fresh manure. A large proportion (>95%) of these seedlings were Queensland blue couch (Digitaria didactyla), a grass species native to Madagascar, despite the erroneous “Queensland” epithet. By comparison, numbers of dicotyledons were low after 14 days, irrespective of treatment. Control trays remained free of plant colonization throughout the trial. Data at 36 days were subjected to statistical analysis and manure type was found to significantly different in germination of D. didactyla seedlings. The number of seedling in dry manure (mean of 99 seedlings/tray) was significantly higher (P<0.001) than in fresh manure (mean of 43 seedlings/tray). The difference was possibly due to the wet anoxic conditions in the fresh manure
When extrapolated to a kilogram basis the seed load of Queensland blue couch in dry paddock manure was above 500 viable seed/ kg while that in fresh manure was less than half that amount. The nitrogen fixing forb, emu foot (Psoralea tenax), was the most numerous of the dicotyledons with approximately 30 seedlings/ kg of paddock manure, irrespective of the moisture content of the manure. Numbers of other minor species did not exceed 15/ kg of manure. In contrast to the results for the paddock manure, only did one species, Powell’s amaranth (Amaranthus powellii), emerge in the stable manure. This species was absent in paddock manure and may have originated from the manufactured feed fed to the stabled horses. A total of 12 species were extracted from sieved manure while 10 species emerged in the glasshouse trial. Of the 6 species found as seed from manure that were not found in the glasshouse trial four had nil viability, albeit from the very low number of seed extracted. The remaining 2 species had viability ranging from 50% to 60%.
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The results of the seed viability testing and the glasshouse germination data demonstrated that the horse manures tested contained viable seeds of species known to be weeds. The results also suggest that horses, particularly those allowed to browse in paddocks without stringent weed control, are potentially significant dispersal agents for a range of weed species. The species germinating in paddock manure comprised 6 grasses and 4 herbaceous forbs. Of those species only one native species, emu foot (Psoralea tenax) was found. All species that germinated in manure have current weed status
Implications for relevant stakeholders This study has broadened the data on the number of herbaceous weed species that can survive passage through the equine alimentary tract and also suggests that, in general, seeds of grass species retain viability better than seed of herbaceous dicotyledons after ingestion.
The potential for spread of weed species via horse ingestion is very high. Even when the frequency of the species germinating in manure was low, the magnitude of their immediate threat as weeds is well documented due to their potentially rapid proliferation from self-recruitment in the field. This is especially true for couch grass (Cynodon dactylon), pigface (Portulaca oleracea) and crows foot grass (Eleusine indica), one of the world’s worst weeds (50,000 seeds/plant). There was no evidence that seeds of groundsel and lantana, weeds of major importance in areas of natural vegetation in Queensland, were present in the horse manure of this study even though the latter was well established in the paddocks grazed.
Recommendations The key finding of this project is that some weed species have the potential to be transferred to areas of native vegetation via horse faeces. However most horse riding in State Forests is along established tracks and firebreaks and it is not known if seeds germinate in these locations. It is thus recommended that the species composition of weeds found along tracks used as horse riding trails be documented and compared to the paddock data obtained in this trial. Management strategies, based on empirical data can then be developed by users and caretakers of native vegetation, to minimise weed transfer by horse faeces in areas used for recreational horse riding.
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Introduction
In Queensland 32% of Regional Ecosystems are currently threatened (Sattler and Williams, 1999). Weeds accidentally introduced since European settlement constitute a significant component of the threatening processes to biodiversity and ecological sustainability of native plant communities. Weeds may be introduced into native ecosystems on vehicles, and by human and animal vectors (Sindel, 2000). Beavis (2005) suggested that invasion of lantana and groundsel along established tracks used by horse riders was unlikely due to horses because the plants are unpalatable and never eaten by horses.
There is anecdotal evidence that horse manure contains weed seed. Since horse riding in areas of National Parks, particularly those with threatened flora and fauna, is currently a politically charged issue, care must be exercised when relying on anecdotal evidence to drive management decisions. In order to assess the likely impacts on biodiversity from horse riding, rigorous scientific studies are necessary to derive the required data on the extent of weed seeds borne in horse manure and the consequences of allowing horses onto areas of conservation significance, such as National Parks (Beavis, 2005).
To date the few reports in the scientific literature have focussed on trail or track degradation by horses. Less emphasis has been placed on investigating the potential of horses to cause weed outbreaks due to weed seeds contained in their manure. In addition, the reports have focussed on a small number of ecosystem types such as Alpine National Parks in Victoria (Weaver and Adams, 1994), Tasmania (Whinam et al, 1996) and in woodland/forest communities of the Hawkesbury Sandstone near Sydney (Uptis, 1980). Nevertheless Weaver and Adams (1994) found 29 species of weed dispersed in horse manure, while Whinam et al (1996) reported that 10 weed species germinated from manure in situ or from manure in a glasshouse study.
Currently weeds known to survive the equine digestive tract include species of Avena, Medicago, Melilotus, Plantago, Rumex and Trifolium (Weaver and Adams, 1994). These authors found that some weeds (Oxalis sp) were only recorded in a small number of manure samples suggesting that either these species do not retain high viability in the digestive tract of horses or that only small numbers were ingested in the first place. In addition some species recorded from less than 1% of samples had become successfully established along track verges. Clearly, more work needs to be carried out to determine which species do survive passage through horses and the other factors governing weed establishment in native vegetation.
This study determined the viability of weed seeds found in horse manure and the composition and magnitude of weed establishment in horse manure, as fresh and dry treatments, in a glasshouse germination trial.
Objectives
To determine if horse faeces contain viable seeds which may be germinated under suitable conditions or persist in surface soil.
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Methodology
Samples of manure were collected from 3 locations in the Brisbane Metropolitan area where horses are kept. These were designated as EF, HU and LM manure types (Table 1). Fresh manure was weighed and samples divided into 11 equal aliquots to accommodate for 2 manure treatments (fresh and dry) and 4 replicates for a glasshouse trial, and 3 replicates for seed viability testing. Two hundred grams of fresh manure was used for each replicate. However there was only enough of the LM manure to do seed viability testing (not the germination test). Air-dried weight estimations were also made for each manure type (Appendices 1 and 2).
Table 1 Sources of horse manure Symbol Location HU University of Qld farm, Pinjarra Hills, 4069 EF Eagle farm racehorse stable, 4009 LM Paddocks adjacent to Lake Manchester, 4306
Sieving and seed viability testing Three replicates of fresh manure (200g each)) were wet-sieved repeatedly through a series of nested sieves (diameters of 10mm, 5mm, 2mm, 1mm and 0.5mm) with running water until all nitrogenous waste was purged. Seeds retained in sieves were washed and separated from adhering debris and cellulose fibres and transferred to clean petri dishes, into which moistened filter paper was placed. A further transfer to a new petri dish was made prior to testing for seed viability.
Seed viability was assessed by the tetrazolium reaction test (Wallander et al, 1998). The tetrazolium test is a method of evaluating a seed lot for potential germination. A colourless solution of 2,3,5- triphenyl tetrazolium chloride is used as an indicator of the reduction processes which occur within living cells. Seeds of adequate size for dissection was excised with a sterile scalpel in a longitudinal plane and immersed in 0.5% tetrazolium chloride. Seeds of small size for dissection were pricked with a sterile needle to allow absorption of the tetrazolium salt. Excised seeds were then immediately immersed in 0.5% tetrazolium chloride in deionised water and allowed to imbibe for 24 hours at 200 C. After this period seed sections exhibiting a developed pink-red colour were considered viable.
The number of viable seeds was determined for each manure type and expressed as a percentage of the number of seeds observed. Seed taxonomy was identified cording to Friends (1983) and Lazarides (1997). Julie Trindall (Australian Seed Testing Laboratories) also assisted with seed identification.
Germination under controlled glasshouse conditions For the glasshouse component of the study there were 2 sources of manure: HU and EF. Each source had two types: fresh , dry, for assessing possible effects of the drying process on seed germinability. The dry manure treatment entailed the drying of 200g aliquots for 1 week at ~ 250 C in a glasshouse. After being dried, the 200g fresh manure weighed 54g and 74g for HU and EF, respectively (Appendix 1 and 2). There were 4 replicates of each manure type. Four control trays were set up with no manure addition.
The manure (fresh and dried) aliquots were mixed into sterile potting mix (UC mix) such that the surface 3cm of a 5cm deep tray was comprised of potting mix and manure in the ratio of 9 to 1 part, respectively. The underlying stratum of the germination tray was comprised entirely of UC potting mix. Trays were placed in a completely randomised manner on the glasshouse bench at 250 C (Plate 1) and watered to 75% of field capacity throughout the course of the trial. Trays were monitored daily for weed germination over a period of 45 days.
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Data collection and Analysis Species germinating in trays were identified wherever possible initially, or later when further diagnostic characters were available. Data collection throughout the period of the glasshouse trial comprised the enumeration of the number of individuals of each broad botanical group (monocotyledons and dicotyledons) at 14 and 21 days. By 36 days identification to specific level was possible. After this time the number of individuals of each plant species in each tray was converted to a per kg of manure. In addition a photographic record was made of the progress of the glasshouse trial and each specific plant group/species occurring in trays throughout.
One-way analysis of variance (ANOVA) was performed by using GenStat 7 (GenStat, 2003), on the number of seedlings for each of the manure treatments. Comparisons were made between means using Fisher’s protected least difference (LSD) test.
Plate 1 Glasshouse trial inception
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Results
Viability testing When manure was washed through the nested sieves 12 species were extracted. Of those, 9 species were found in HU manure, 3 in EF manure and 1 in the LM type (Table 2) with seed of 1 species (Queensland blue couch, Digitaria didactyla) found in both HU and LM manure. Seed of species consistently found in all replicates within a manure type comprised Cyperus polystachyos (HU manure), Digitaria didactyla (HU manure), Avena sativa (EF manure), and Hordeum vulgare (EF manure) (Table 2).
The separation of seed from the matrix of cellulose fibres was difficult resulting in seed not always being deposited according to size in the correct sieve. The technique thus had deficiencies in that seed of various sizes was often found in the 2mm and 5 mm sieves. Seeds of a total of 9 species were extracted in low numbers (<10) (Table 2).
Table 2 Percent viability of seed extracted from 3 horse manure types Species Viability (%) Manure type A chenopod 0 (5) HU Chaemaecrista rotundifolia 0 (5) HU Crotalaria sp 0 (8) HU Cynodon dactylon 10 (32) HU Cyperus sp. 17 (60) HU Digitaria didactyla 19 (480) HU Eragrostis tenuifolia 100 (7) HU Oxalis corniculata 0 (8) HU Paspalum sp 100 (5) HU
Amaranthus powellii 100 (30) EF Avena sativa 50 (5) EF Hordeum vulgare 60 (5) EF
Digitaria didactyla 33 (6) LM Numbers in brackets represent the mean number of seed extracted from 3 replicates of 200g fresh manure.
Glasshouse trial: HU manure treatments At 14 days a large number of monocotyledons (125) had emerged in the dry HU manure treatment. By comparison only a fifth as many had emerged in the fresh manure treatment (Figure 1).
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160 dicots 140 monocots
120
100
80
60
40
manure HU seedlings/200g # Mean 20
0 fresh manure dry manure
Figure 1 Mean number of monocotyledon and dicotyledonous seedlings in treated HU manure at 14 days
A large proportion (>95%) of these seedlings had vegetative morphology which conformed to that for the description for seedling Queensland blue couch (Plate 2), a grass species native to Madagascar and the Mascerene Islands, despite the erroneous “Queensland” epithet. By comparison, numbers of dicotyledons were low after 14 days, irrespective of treatment (Figure 1).
Plate 2 Seedlings of Queensland blue couch (Digitaria didactyla) at 14 days
5
800
700
600
500
400
300
200 Mean # seedlings/200g HU manure HU seedlings/200g # Mean 100
0 fresh manure dry manure
Figure 2 Mean number of monocotyledonous seedlings in treated HU manure at 21 days
6 fresh manure dry manure 5
4
3
2
1
Mean seedlings/200g of number HU manure
0 Portulaca Psoralea tenax Trifolium Cyperus Portulaca pilosa oleracea repens polystachyos
Figure 3 Mean number of seedlings of 4 dicotyledons and 1 monocotyledon (Cyperus polystachyos) in treated HU manure after 21 days
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By day 21 numbers of the dominant monocot, Queensland blue couch, had risen marginally from that at 14 days, and were still more numerous than that for all dicotyledons combined (Figures 2 and 3) (Plate 3). Numbers of Queensland blue couch did not increase from 14 days in either manure treatment (Figure 2).
Plate 3 Seedlings of monocots outnumber dicots seedlings at 21 days
Dicotyledons numbers had increased marginally from 14 days. Seedlings had developed to an extent where identification was possible (Figure 3). Thus 4 species of dicotyledonous forbs, and one monocotyledon (Cyperus polystachyos), were identified (Figure 3) Both forbs, emu foot (Psoralea tenax) and white clover (Trifolium repens), are perennial nitrogen fixing species, the former a native forb while the latter is a pasture weed. Numbers of dicotyledons were low with a treatment effect apparent only with pigweed (Portulaca oleracea) and emu foot (Figure 3). Seedling numbers were higher in the fresh manure treatment for both species (Plate 4).
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Plate 4 Seedlings of pigweed (centre), emu foot (left fore/centre/ground) and Queensland blue couch
The glasshouse trial was quantitatively assessed at 36 days. Control trays remained free of plant colonization throughout the trial (Plate 5), while HU treatments were overrun with seedlings, most of which were Queensland blue couch (Plate 6). At 36 days there was variation in colonization among replicates in the numbers of Queensland blue couch seedlings (Figure 4). Fresh manure trays generally supported a lower seedling frequency than that for dry treatments (Figure 4).
Plate 5 Control trays at 36 days
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When that data for 36 days was subjected to statistical analysis, manure type was found to significantly affect germination of D.didactyla seedlings (P<0.001, LSD (5%) = 21.5). Seedling number in dry HU manure (mean of 99 seedlings/tray) was significantly higher than in fresh manure (mean of 43 seedlings/tray) (Table 4) (Plates 6 and 7).
Plate 6 Seedlings in dry HU manure
Plate 7 Seedlings in fresh HU manure
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Similarly, statistically significant differences were evident in 2 species of Portulaca, where P.oleracea seedlings were more numerous in fresh HU manure (P<0.015, LSD (5%) = 0.757, and P.pilosa seedlings were more numerous in dry HU manure (P<0.001, LSD (5%) = 0.744).
Mean number of seedlings of each species that germinated in manure are shown in Table 4 (Appendix 1). With the exception of Eleusine indica (fresh HU manure) (Plate 8) and Paspalum sp (dried HU manure), the remaining 8 species were found in both HU manure treatments (Table 4).
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Table 3 Mean numbers of seedlings in manure treatments (/200g manure) at 36 days Treatment Species Amaranthus Cynodon Cyperus Digitaria Eleusine Eragrostis Paspalum Portulaca Portulaca Psoralea Trifolium #s/200g powellii dactlyon polystachyos didactyla indica tenuifolia sp oleracea pilosa tenax repens HU fresh 0 2.75 2.5 42.5 0.75 1 0 2.25 0.25 5.75 0.5 HU dry 0 1.25 1.5 99 0 1.75 0.25 0.5 1.25 6.25 0.75 EF fresh 0.75 0 0 0 0 0 0 0 0 0 0 EF dry 0.5 0 0 0 0 0 0.25 0 0 0 0
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Plate 8 Seedling of Eleusina indica at 36 days
140
120
100
80
60
40
manure Mean seed/200g number 20
0 fresh 1 fresh 2 fresh 3 fresh 4 dry 1 dry 2 dry 3 dry 4
Figure 4 Mean number of seedlings of Queensland Blue couch (Digitaria didactyla) in 200g of HU manure (fresh and dried treatments) in 4 replicate trays (36 days)
12
600
500
400
300
200
Mean # seedlings/kg HU manure HU Mean # seedlings/kg 100
0 fresh manure dry manure
Figure 5 Mean number of seedlings of Queensland Blue couch (Digitaria didactyla) in 1kg HU manure at 36 days
When extrapolated to a kg basis the seed load of Queensland blue couch in dry HU manure would be above 500 viable seed per kg while that in fresh manure would be less than half that amount (Figure 5). The dry manure seed load is also a more realistic estimate than that for fresh manure.
40 elastic grass(E.tenuifolia) 35 a sedge(C.polystachyos) pig weed (P.oleracea) 30 portulaca(P.pilosa) emu foot(P.tenax) 25
20
15 Mean # seed/kg manure Mean # seed/kg 10
5
0 fresh manure dry manure
Figure 6 Mean number of seedlings per kg of the most frequently found forb, grass and sedge species in HU manure
By comparison with the high frequency of Queensland blue couch, dicotyledons numbers were substantially lower overall. However, in similarity with D. didactyla, treatment effects occurred in the 2 species of Portulaca, as previously noted (Figure 6). The nitrogen fixing forb, emu foot (Psoralea
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tenax) (Plate 9), was the most numerous of the dicotyledons with approximately 30 seedlings per kg of HU manure, irrespective of the moisture content of the manure treatment. Numbers of other minor species did not exceed 15 per kg of manure (Figure 6).
Plate 9 Seedling of Psoralea tenax at 36 days
Glasshouse trial: EF manure treatments By contrast with the results for the HU manure, the species richness and seedling number for EF manure was singularly low (Table 4, Appendix 1). Since there was no change in seedling numbers at 14, 21 and 36 days, data presented for this manure type is given at 36 days. In all only one species, Powell’s amaranth (Amaranthus powellii) emerged in the EF manure with no evidence of a treatment effect. This species did not emerge in HU manure. Mean numbers of seedlings of Powell’s amaranth, when converted to a per kg basis, were very low in EF manure treatments (Figure 7) (Plate 10).
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5
4
3
2 Mean # seed / kg EF manure EF kg / Mean # seed
1
0 fresh manure dry manure
Figure 7 Mean number of seedlings of Amaranthus powellii per kg of EF manure
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Plate 10 Mature plants of Amaranthus powellii at 36 days
Comparison of seed viability with glasshouse emergence When the data for the seed viability was compared with those from the glasshouse trial (Table 5) there were 16 species found in total. Six of those species were common to both data sets (Table 4). Thus a total of 12 species were extracted from sieved manure while 10 species emerged in the glasshouse trial. Of the 6 species found as seed from manure that were not found in the glasshouse trial 4 (Chaemaecrista rotundifolia, Crotalaria sp, Oxalis corniculata and a chenopod) had nil viability, albeit from the very low number of seed extracted. The remaining 2 species (Avena sativa and Hordeum vulgare) had viability ranging from 50% to 60% but numbers of seeds extracted were also very low (<10 per 200g manure).
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Table 4 Concordance between species extracted by wet sieving from manure and from glasshouse emergence Species Extracted from Germinated in manure by sieving glasshouse trial Dicotyledons A chenopod + Amaranthus powellii + + Avena sativa + Chaemaecrista rodundifolia + Crotalaria sp + Hordeum vulgare + Oxalis corniculata + Portulaca oleracea + Portulaca pilosa + Psoralea tenax + Monocotyledons Cynodon dactylon + + Cyperus polystachyos + + Digitaria didactyla + + Eleusine indica + Eragrostis tenuifolia + + Paspalum sp. + + Total # species 12 10
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Discussion
The objective of this study was to determine if horse faeces contains viable seeds which may persist in surface soil and be germinated under suitable conditions..
The results of the seed viability testing and the glasshouse germination data demonstrated that the horse manures tested contained viable seed of species known to be weeds (Table 5). Results also suggest that horses, particularly those allowed to browse in paddocks, are potentially significant dispersal agents for a range of weed species. Thus the objective of the project was achieved.
Ten species germinated from 2 manures, although there was a definite bias towards plant colonization in HU manure. Species germinating in HU manure comprised 6 grasses and 4 herbaceous forbs. Of those species only one native species, emu foot (Psoralea tenax) was found. All species that germinated in manure have current weed status (Table 5).
Table 5 Weed species germinating in horse manure Species Comments Amaranthus powellii Annual weed in tropical zones Cynodon dactylon Perennial weed worldwide Cyperus polystachyos Annual/perennial weed worldwide Digitaria didactyla Stoloniferous perennial weed of tropics Eragrostis tenuifolia Annual/biennial/perennial weed of tropics Eleusine indica Annual/perennial weed of tropics and subtropics Paspalum sp. A genus of perennial weeds sens lat Portulaca oleracea Serious annual weed of crops and gardens Portulaca pilosa Perennial weed of crops and gardens Psoralea tenax Nitrogen fixing perennial native forb and weed Trifolium repens Nitrogen fixing perennial weed worldwide
Results indicated a significant treatment effects for 3 species with HU manure treatments. Among those the predominant species in terms of the most number of individuals was Queensland blue couch, which was in very high numbers in dried manure. Since fresh manure by definition dries out after deposition, the numbers of seedlings of this grass in the dried HU manure represent a more realistic measure of the seed load than that of fresh manure. With the exception of Portulaca pilosa seedlings, this difference was not however a factor determining germination frequency in all other species that germinated, irrespective of manure type.
The significantly lower number of Queensland blue couch seedlings in fresh manure was possibly due to the wet anoxic conditions in the fresh manure. Anoxia in fresh manure may have induced dormancy in otherwise viable seed of Avena sativa and Hordeum vulgare thus perhaps explaining the failure of these species to germinate in manure.
This study has broadened the data on the number of herbaceous weed species that can survive passage through the equine alimentary tract. Weaver and Adams (1994) reported that the genera Avena, Medicago, Melilotus, Plantago, Rumex and Trifolium survive in horse manure. This study has confirmed the data of other workers firstly that the soft seed coated Trifolium repens remains viable after ingestion through a horse (Weaver and Adams, 1994; Whinam et al, 1996). Secondly the list of plant genera that can survive ingestion by horses includes species of the herbaceous weeds Portulaca, Psoralea and Amaranthus. Conversely results of seed viability testing revealed the dicotyledons that
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will not survive ingestion (Table 2). The data also suggests that in general seed of grass species may retain viability better than seed of herbaceous dicotyledons after ingestion.
In this his study, the horses from the HU area were more likely to be able to browse thereby encountering many plant species. The diversity of the diet was reflected in the relative abundance of species associated with the HU manure as compared to the paucity in that of grain fed EF horses in which only 1 species germinated. Dried stock feeds are reported to contain large numbers of weed seeds (Landsberg et al, 2001). Thus in this study grain fed EF horses had 3 species, 2 of which proved to be non viable, and the one contaminant species emerging (A.powellii) in the manure. The high viability for seed of A. powellii means that only a few seeds need to be ingested to ensure spread. Weaver and Adams (1994) suggested low numbers of ingested seed could be the reason why some species were found in low frequencies, such as that found in this study with A.powellii in EF manure. By contrast large numbers of seed of low viability, of stoloniferous species such as Queensland blue couch, need to be ingested to maintain spread of this grass species. In all the potential for spread of these 2 weed species via horse ingestion is very high.
While the frequency of the other species germinating in manure was low the magnitude of their threat as weeds is well documented, such as for couch grass (Cynodon dactylon), pigface (Portulaca oleracea) and crows foot grass (Eleusine indica), one of the world’s worst weeds (50 000 seeds/plant) (Friend, 1983). There was no evidence that seeds of groundsel and lantana, weeds of major importance in areas of natural vegetation in Queensland, were present in the horse manure of this study even though the latter was well established in the paddocks grazed. This confirms the premise of Beavis (2005) that the unpalatability of these plants to horses precludes their being spread in their faeces.
Results for the LM manure were limited, both in the single species extracted from manure and in the lack of glasshouse data with which to interpret the potential for this manure type to contain weed seed. In addition the presence of higher viability seed of Queensland blue couch in LM manure compared to that in HU manure is difficult to interpret and suggests that factors unrelated to plant genetics may affect seed viability.
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Recommendations
This project establishes that weed species have the potential to be transferred to areas of native vegetation via horse faeces. Whether they do or not has not been established in this study. Most horse riding in State Forests is along established tracks and firebreaks and seeds may never germinate in these locations. The species composition of weeds found along tracks used as horse riding trails needs to be investigated to fully understand the dynamics of horse vectors as weed dispersal agents. Thus a field survey is required to determine species composition and frequency along sampling transects in native vegetation e.g. along horse riding tracks near Lake Manchester in Brisbane Forest Park, North West of Brisbane. Only when empirically gathered data is available can management strategies be developed to minimise weed transfer by horse faeces in areas of native vegetation used for recreational horse riding.
It is recognised that the present investigation only tested a limited number of horses in terms of their feeding behaviour and geographical distribution. To develop state-wide information on the risk of horse-transferred weeds, more horse feeding scenarios should be investigated in the near future. This will provide more comprehensive information about the potential of seed survival in the digestive tract of horses, for a diversity of weed species.
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Appendix 1. Numbers of seedlings in manure treatments (per 200g manure) at 36 days
Treatment Species
Amaranthus Cynodon Cyperus Digitaria Eleusine Eragrostis Paspalum Portulaca Portulaca Psoralea Trifolium #s/200g powellii dactlyon polystachyos didactyla indica tenuifolia sp oleracea pilosa tenax repens HU fresh 1 0 1 2 70 1 3 0 3 0 6 0 2 0 6 4 44 0 0 0 3 0 3 1 3 0 2 2 28 0 1 0 2 1 8 1 4 0 2 2 28 2 0 0 1 0 6 0 HU dry 1 0 2 0 77 0 2 0 0 0 6 0 2 0 1 1 106 0 0 0 1 2 6 1
20 3 0 2 0 125 0 3 0 1 1 8 2
4 0 0 5 88 0 2 1 0 2 5 0 EF fresh 1 0 0 0 0 0 0 0 0 0 0 0 2 3 0 0 0 0 0 0 0 0 0 0 3 0 0 0 0 0 0 0 0 0 0 0 4 0 0 0 0 0 0 0 0 0 0 0 EF dry 1 0 0 0 0 0 0 0 0 0 0 0 2 0 0 0 0 0 0 0 0 0 0 0 3 1 0 0 0 0 0 0 0 0 0 0 4 1 0 0 0 0 0 1 0 0 0 0
Appendix 2. Percent water in manure types
100
75 % water 50
25
0 HU manure EF manure LM manure
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References
Beavis S. (2005) Biophysical impacts of recreational horse riding in multi-use national parks and reserves. Australasian J. Env. Management. 12:109-116.
Friend, E. (1983). Queensland Weed Seeds. Queensland Department of Primary Industries. Miscellaneous Publication 81013.
GenStat 2003 GenStat for Windows. Release 7.2. Seventh Edition. VSN International Ltd., Oxford.
Lansdberg, J., Logan, B and Shorthouse, D. (2001). Horse riding in urban conservation areas: Reviewing Scientific Evidence to Guide management. Ecological Management and Restoration, vol2, No. 1.
Lazarides, M. (1997). CSIRO Handbook of Australian Weeds. Australian National Herbarium, CSIRO Plant Industry Canberra ACT.
Newsome, D., Milewski, A., Phillips N and Annear R. (2002). Effects of horse riding on national parks and other natural ecosystems in Australia: Implications for Management. Journal of Ecotourism 1, pp 52-72.
Sindel, B.N. (2000). Weeds and their impact. In Australian Weed Management Systems. CRC for Weed Management Systems.
Sattler, .S. and Williams, R.D. (eds) (1999). The Conservation Status of Queensland’s Bioregional Ecosystems. Published by Environmental Protection Agency, Brisbane.
Uptis, A.I. (1980). An integrated study of tracks in Ku-ring-gai Chase National Park with implications for management. BSc Hons Thesis, Macquarie University, Sydney.
Wallander, R.T., Olson, B.E. and Lacey, J.R. (1995) Spotted knapweed seed viability after passing through sheep and mule deer. J. Range Manage. 48, 145-149.
Weaver, V. and Adams, R. (1996). Proceedings of the Eleventh Australian weeds Conference. Pp. 383-397.
Whinam, J., Cannell E.J., Kirkpatrick, J. B. and Comfort, M. (1994). Studies on the potential impact of recreational horse riding on some alpine environments of the Central Plateau, Tasmania. Journal of Environmental Management 40, 103-117.
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Transfer of Weeds to Queensland Native Forests by Horse Faeces
— The viability and germination of plant seeds found in horse faeces —
by Christopher C Pollitt and Longbin Huang
Publication No. 11/109
In Queensland 32% of Regional Ecosystems are currently RIRDC is a partnership between government and industry threatened and weeds accidentally introduced since European to invest in R&D for more productive and sustainable rural settlement contribute significantly to the degradation of native industries. We invest in new and emerging rural industries, a plant communities. Rigorous scientific studies are necessary to suite of established rural industries and national rural issues. derive the required data on the extent of weed seeds borne in horse manure and the consequences of allowing horses onto Most of the information we produce can be downloaded for free areas of conservation significance, such as National Parks and or purchased from our website
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