Initiating temperate grassland restoration by controlling the dominant weed species; a case study with Nassella trichotoma
- Authors: Humphries, Talia
- Date: 2022
- Type: Text , Thesis , PhD
- Full Text:
- Description: Temperate grasslands are globally important biomes, in that they (i) provide habitat for a wide diversity of species, (ii) sequester large stocks of carbon, and (iii) provide forage for important pollinators (Chapter 1). These ecosystems often fall within highly fertile areas, and consequently humans have come to depend on them to provide high quality forage for grazing livestock and land for agricultural development. Temperate grasslands are considered to be critically endangered on a global scale. The grazing industry relies upon healthy and productive grasslands for the production of a substantial proportion of human food products, however, when these systems incorporate unsustainable land-management practises, such as over-grazing and continual fertilisation with inorganic matter, has resulted in a significant decline in important native grass species. This has resulted in encroachment of unpalatable, noxious plants, which decrease the quality of available forage. One such noxious weed species, Nassella trichotoma, known commonly as serrated tussock, is having a significance impact on the constitution of temperate grasslands and grazing systems, globally, due to its unpalatability and competitive growth form. In order to return temperate grasslands to a fully-functional and a high-quality forage state, human intervention in terms of ecosystem restoration is required. The control of noxious species, together with the reintroduction and establishment of native species, is a critical step for restoration efforts with the return of native plant diversity, and the re-establishment of ecosystem services, such as habitat for higher trophic levels. This thesis reviews and overlaps the scientific disciplines of ecosystem restoration (Chapter 2), weed science relating to N. trichotoma (Chapter 3), and environmental management in order to provide solutions for controlling N. trichotoma in non-native grassland communities (Chapter 4). The effect of direct herbicide application, soil tillage, grazing exclusion, fire, and broadcasting native seeds for the control of this dominant weeds in a total of 13 different combinations is investigated. The experimental plots were surveyed over a four-year period and soil cores were collected over a three-year period to survey the seedbank density. It was found that the inclusion of fire significantly increased the establishment of the native broadcast species. Also, without the integration of fire or tillage, N. trichotoma recovered, and consequently was observed to be the dominant species in the final sampling period. To support the findings of Chapter 4, research into the seed longevity and seedbank persistence of N. trichotoma was undertaken in Chapter 5. It was found that less than 10% of the seeds were observed to be viable after 12 months of burial in field. In addition to this, the longevity of the seeds was determined by rapidly ageing the seeds through exposure to high relative humidity and temperature. This process determined that N. trichotoma produces transient seedbanks, referring to those that persist for 12 months or less, and therefore the seedbank would be reliant on new seed input annually to remain a competitive threat. This implies that management control of new seed fall is essential to prevent the reestablishment of the seed bank. The seedbank persistence for N. trichotoma is complicated by disturbance events such as fire. To investigate this impact, four different collection years; 2016, 2017, 2018, and 2019 were subjected to increasing heat (80, 100, 120, or 140OC) and time of exposure (1, 3, 6 or 9 minutes) by placing them into a temperature-controlled oven for the given treatment. It was found that only the 140OC treatment was significant for killing N. trichotoma, as detailed in Chapter 6. High moisture content (95%) increased the seeds sensitivity to radiant heat, with all tested temperature effective for killing this species. The seedlings were not killed by the tested treatments. Management implications and recommendations for the control of N. trichotoma in temperate grasslands (Chapter 7) include; (i) the use of herbicide in Autumn to prevent seed set in the following summer, and (ii) in addition to initial herbicide, use, subsequent fire treatment and broadcasting native seeds appear to provide ongoing competition against N. trichotoma reestablishment in treated areas. Further, high fire intensities, where the soil is heated to 140OC or more, can kill N. trichotoma’s seedbank and prevent its recruitment. In all cases of treatment, monitoring recruitment from the seedbank is recommended for up to one year after treating a site. This thesis suggests that localised eradication of N. trichotoma is achievable in as little as three years if (i) above-ground plants are treated, (ii) seedling recruitment from the seedbank is managed intensely within the first year, (iii) high densities of native grass is established to provide competition, and (iv) the addition of new seed is prevented.
- Description: Doctor of Philosophy
- Authors: Humphries, Talia
- Date: 2022
- Type: Text , Thesis , PhD
- Full Text:
- Description: Temperate grasslands are globally important biomes, in that they (i) provide habitat for a wide diversity of species, (ii) sequester large stocks of carbon, and (iii) provide forage for important pollinators (Chapter 1). These ecosystems often fall within highly fertile areas, and consequently humans have come to depend on them to provide high quality forage for grazing livestock and land for agricultural development. Temperate grasslands are considered to be critically endangered on a global scale. The grazing industry relies upon healthy and productive grasslands for the production of a substantial proportion of human food products, however, when these systems incorporate unsustainable land-management practises, such as over-grazing and continual fertilisation with inorganic matter, has resulted in a significant decline in important native grass species. This has resulted in encroachment of unpalatable, noxious plants, which decrease the quality of available forage. One such noxious weed species, Nassella trichotoma, known commonly as serrated tussock, is having a significance impact on the constitution of temperate grasslands and grazing systems, globally, due to its unpalatability and competitive growth form. In order to return temperate grasslands to a fully-functional and a high-quality forage state, human intervention in terms of ecosystem restoration is required. The control of noxious species, together with the reintroduction and establishment of native species, is a critical step for restoration efforts with the return of native plant diversity, and the re-establishment of ecosystem services, such as habitat for higher trophic levels. This thesis reviews and overlaps the scientific disciplines of ecosystem restoration (Chapter 2), weed science relating to N. trichotoma (Chapter 3), and environmental management in order to provide solutions for controlling N. trichotoma in non-native grassland communities (Chapter 4). The effect of direct herbicide application, soil tillage, grazing exclusion, fire, and broadcasting native seeds for the control of this dominant weeds in a total of 13 different combinations is investigated. The experimental plots were surveyed over a four-year period and soil cores were collected over a three-year period to survey the seedbank density. It was found that the inclusion of fire significantly increased the establishment of the native broadcast species. Also, without the integration of fire or tillage, N. trichotoma recovered, and consequently was observed to be the dominant species in the final sampling period. To support the findings of Chapter 4, research into the seed longevity and seedbank persistence of N. trichotoma was undertaken in Chapter 5. It was found that less than 10% of the seeds were observed to be viable after 12 months of burial in field. In addition to this, the longevity of the seeds was determined by rapidly ageing the seeds through exposure to high relative humidity and temperature. This process determined that N. trichotoma produces transient seedbanks, referring to those that persist for 12 months or less, and therefore the seedbank would be reliant on new seed input annually to remain a competitive threat. This implies that management control of new seed fall is essential to prevent the reestablishment of the seed bank. The seedbank persistence for N. trichotoma is complicated by disturbance events such as fire. To investigate this impact, four different collection years; 2016, 2017, 2018, and 2019 were subjected to increasing heat (80, 100, 120, or 140OC) and time of exposure (1, 3, 6 or 9 minutes) by placing them into a temperature-controlled oven for the given treatment. It was found that only the 140OC treatment was significant for killing N. trichotoma, as detailed in Chapter 6. High moisture content (95%) increased the seeds sensitivity to radiant heat, with all tested temperature effective for killing this species. The seedlings were not killed by the tested treatments. Management implications and recommendations for the control of N. trichotoma in temperate grasslands (Chapter 7) include; (i) the use of herbicide in Autumn to prevent seed set in the following summer, and (ii) in addition to initial herbicide, use, subsequent fire treatment and broadcasting native seeds appear to provide ongoing competition against N. trichotoma reestablishment in treated areas. Further, high fire intensities, where the soil is heated to 140OC or more, can kill N. trichotoma’s seedbank and prevent its recruitment. In all cases of treatment, monitoring recruitment from the seedbank is recommended for up to one year after treating a site. This thesis suggests that localised eradication of N. trichotoma is achievable in as little as three years if (i) above-ground plants are treated, (ii) seedling recruitment from the seedbank is managed intensely within the first year, (iii) high densities of native grass is established to provide competition, and (iv) the addition of new seed is prevented.
- Description: Doctor of Philosophy
Herbicide application strategies for wild radish management in Imidazolinone tolerant faba bean
- Authors: Welgama, Amali
- Date: 2020
- Type: Text , Thesis , PhD
- Full Text:
- Description: The extensive and continual use of herbicides in cropping situations has inevitably led to the phenomenon of "herbicide-resistance" in weeds and this has become one of the most challenging issues in modern agriculture. Herbicide-tolerant crops (HTC) were introduced to diversify weed management practices, but the lack of integrated weed management strategies, along with the continuous use of the same herbicide mode of action (MOA) demanded by the HTC has continued to impose selection pressure on weeds to evolve with herbicide resistance. Consequently, this thesis has been focused on the introduction of herbicide MOA combinations into HTC systems in an attempt to reduce the rate of herbicide resistance evolution in weeds. Raphanus raphanistrum is the number one broadleaf weed in Australia, and for this case study, the newly released ALS-inhibiting imidazolinone tolerant faba bean cultivar PBA Bendoc with its conventional cultivar, PBA Samira, were selected as the study species. ALS-inhibiting (imazamox + imazapyr and imazethapyr) and PSII-inhibiting (metribuzin) herbicides were used as the two herbicide MOAs. The herbicide sensitivity of R. raphanistrum was initially evaluated at different growth stages, in glasshouse studies using herbicide-resistant and susceptible biotypes to ALS-inhibiting herbicides. The highest susceptibility was observed at the earliest growth stage regardless of the biotype and Imazamox + imazapyr proved to be more effective in controlling both biotypes compared to imazethapyr. The same two herbicides were tested on faba bean cultivars at different growth stages to assess crop tolerance and identify the herbicide application window. The field trials conducted in 2018 and 2019 showed increased ALS-inhibiting herbicide tolerance in PBA Bendoc compared to PBA Samira even at the most advanced growth stage. Both faba bean cultivars were then evaluated for their tolerance to metribuzin in-crop application at different herbicide rates. Both cultivars responded similarly, showing progressive herbicide damage with increasing application rates. However, the reduced pod number, even at the lowest rate used, flagged the possible yield penalties that may result in using in-crop metribuzin applications. It is thus suggested that metribuzin must be used post sowing pre-emergent (PSPE) respecting the label recommendations. The potential herbicide combinations were then tested on herbicide-resistant R. raphanistrum and PBA Bendoc to evaluate their efficacies. Metribuzin was initially used as PSPE in all combinations, and was to be followed by imazamox + imazapyr applications at the same growth stages of the weed and the crop as in previous experiments. However, 100% control of R. raphanistrum was achieved using metribuzin alone, and thus no second herbicide was required. All the assessed herbicide combinations were tolerated by PBA Bendoc, proving the suitability of these herbicide combinations for incorporation into the PBA Bendoc cropping system. These results led to two potential herbicide combination strategies: (i) herbicide rotations, with metribuzin as PSPE in one year along with another potential herbicide MOA in the following year, (ii) herbicide sequential application, with metribuzin applied at PSPE and imazamox + imazapyr applied at the 2-4 leaf stage if R. raphanistrum plants survived the metribuzin treatment. A seed germination study was conducted under different temperature/photoperiods, pH levels, osmotic potentials, salinity and burial depths to identify the optimal germination conditions for R. raphanistrum. The optimum germination conditions for both herbicide-resistant and susceptible biotypes of R. raphanistrum were found to be 25ºC/15ºC temperature range under 24 hours complete dark. However, the significant interaction between photoperiod and temperature indicated that the seed germination under higher temperatures is less favoured by 24 hours dark conditions regardless of the biotype. An increased moisture stress tolerance in herbicide-resistant seeds was observed, whilst both biotypes reacted similarly to different pH levels and burial depths. In summary, this thesis has elucidated the effectiveness of two herbicide MOAs in controlling R. raphanistrum while addressing the crop tolerance to these herbicide MOA combinations. These findings will help in setting up stewardship guidelines to be used with the PBA Bendoc faba bean cultivar to mitigate the misuse of herbicides, thus ensuring their sustainable application. In addition, the demonstration of differential seed germination requirements of resistant and susceptible R. raphanistrum seeds has provided further information to help with its systematic management. Overall, this study can be used as a case study to investigate herbicide options that can be used in different HT crop cultivars to control a range of weed species.
- Description: Doctor of Philosophy
- Authors: Welgama, Amali
- Date: 2020
- Type: Text , Thesis , PhD
- Full Text:
- Description: The extensive and continual use of herbicides in cropping situations has inevitably led to the phenomenon of "herbicide-resistance" in weeds and this has become one of the most challenging issues in modern agriculture. Herbicide-tolerant crops (HTC) were introduced to diversify weed management practices, but the lack of integrated weed management strategies, along with the continuous use of the same herbicide mode of action (MOA) demanded by the HTC has continued to impose selection pressure on weeds to evolve with herbicide resistance. Consequently, this thesis has been focused on the introduction of herbicide MOA combinations into HTC systems in an attempt to reduce the rate of herbicide resistance evolution in weeds. Raphanus raphanistrum is the number one broadleaf weed in Australia, and for this case study, the newly released ALS-inhibiting imidazolinone tolerant faba bean cultivar PBA Bendoc with its conventional cultivar, PBA Samira, were selected as the study species. ALS-inhibiting (imazamox + imazapyr and imazethapyr) and PSII-inhibiting (metribuzin) herbicides were used as the two herbicide MOAs. The herbicide sensitivity of R. raphanistrum was initially evaluated at different growth stages, in glasshouse studies using herbicide-resistant and susceptible biotypes to ALS-inhibiting herbicides. The highest susceptibility was observed at the earliest growth stage regardless of the biotype and Imazamox + imazapyr proved to be more effective in controlling both biotypes compared to imazethapyr. The same two herbicides were tested on faba bean cultivars at different growth stages to assess crop tolerance and identify the herbicide application window. The field trials conducted in 2018 and 2019 showed increased ALS-inhibiting herbicide tolerance in PBA Bendoc compared to PBA Samira even at the most advanced growth stage. Both faba bean cultivars were then evaluated for their tolerance to metribuzin in-crop application at different herbicide rates. Both cultivars responded similarly, showing progressive herbicide damage with increasing application rates. However, the reduced pod number, even at the lowest rate used, flagged the possible yield penalties that may result in using in-crop metribuzin applications. It is thus suggested that metribuzin must be used post sowing pre-emergent (PSPE) respecting the label recommendations. The potential herbicide combinations were then tested on herbicide-resistant R. raphanistrum and PBA Bendoc to evaluate their efficacies. Metribuzin was initially used as PSPE in all combinations, and was to be followed by imazamox + imazapyr applications at the same growth stages of the weed and the crop as in previous experiments. However, 100% control of R. raphanistrum was achieved using metribuzin alone, and thus no second herbicide was required. All the assessed herbicide combinations were tolerated by PBA Bendoc, proving the suitability of these herbicide combinations for incorporation into the PBA Bendoc cropping system. These results led to two potential herbicide combination strategies: (i) herbicide rotations, with metribuzin as PSPE in one year along with another potential herbicide MOA in the following year, (ii) herbicide sequential application, with metribuzin applied at PSPE and imazamox + imazapyr applied at the 2-4 leaf stage if R. raphanistrum plants survived the metribuzin treatment. A seed germination study was conducted under different temperature/photoperiods, pH levels, osmotic potentials, salinity and burial depths to identify the optimal germination conditions for R. raphanistrum. The optimum germination conditions for both herbicide-resistant and susceptible biotypes of R. raphanistrum were found to be 25ºC/15ºC temperature range under 24 hours complete dark. However, the significant interaction between photoperiod and temperature indicated that the seed germination under higher temperatures is less favoured by 24 hours dark conditions regardless of the biotype. An increased moisture stress tolerance in herbicide-resistant seeds was observed, whilst both biotypes reacted similarly to different pH levels and burial depths. In summary, this thesis has elucidated the effectiveness of two herbicide MOAs in controlling R. raphanistrum while addressing the crop tolerance to these herbicide MOA combinations. These findings will help in setting up stewardship guidelines to be used with the PBA Bendoc faba bean cultivar to mitigate the misuse of herbicides, thus ensuring their sustainable application. In addition, the demonstration of differential seed germination requirements of resistant and susceptible R. raphanistrum seeds has provided further information to help with its systematic management. Overall, this study can be used as a case study to investigate herbicide options that can be used in different HT crop cultivars to control a range of weed species.
- Description: Doctor of Philosophy
Investigating factors affecting restoration of native grassland in ex-cropland
- Authors: Shakir, Shakir Bahaddin
- Date: 2019
- Type: Text , Thesis , PhD
- Full Text:
- Description: Native grasslands are one of the most endangered ecosystems in Australia. Approximately 99% of native grasslands have been disturbed for agriculture and pastoralism. Today, however, many agricultural and grazing lands have been abandoned. Restoring abandoned areas to native grassland is a challenge that must be met if these systems are to persist. This thesis sought to gain a better understanding of the biotic and abiotic barriers to restoring native grasslands in ex-cropping land, and to investigate novel techniques to overcome them in degraded native grassland in the Victorian Volcanic Plains. Firstly, I compared ex-cropland to high-quality remnant grassland, and showed that excropland supports a high number of exotic weeds, a lack of native species propagules, high nutrient levels (especially phosphorus and nitrogen), and an absence of organic carbon—all barriers which must be overcome if native grassland restoration is to succeed. I conducted a replicated field experiment in ex-cropland, to investigate four restoration approaches to overcoming barriers to restoration: (i) adding urban green waste to heat and kill the exotic seed bank (ii) adding sugar and/or mulch to promote microorganism and draw down soil nitrogen, (iii) using a modified clay product called Phoslock to reduce soil phosphorus levels, and (iv) scalping of topsoil 10 cm on ex-cropland site to remove the exotic seed bank and high nutrient soil. After each treatment, native grass seed was added, and the vegetation, seed bank, soil nutrients and microbial activity were monitored over 2.5 years. The hot mulch, scalping and sugar treatments all achieved significantly greater cover of native grasses than the control treatments. The hot waste treatment also effectively eliminated the exotic weed seed bank, but the soil N levels increased dramatically, which is counterproductive to the long-term goals of grassland restoration. Scalping out-performed all other treatments with regard to reducing soil N and P. All treatments suffered from reinvasion by exotic species, suggesting that any grassland restoration technique needs to be coupled with ongoing exotic weed management. Abstract ii High soil phosphorus is a difficult barrier to restoration of native grassland. A possible way to address this is to use plants with high P uptake to help draw down soil P. Native grassland taxa from the genus Ptilotus have been shown to have high P-uptake. I conducted two studies of Ptilotus macrocephalus and Ptilotus polystachyus to investigate their potential in this role. The first of these was an examination of techniques to break their seed dormancy, and to find their optimum germination conditions. I tested their response to smoke water, heating shock, cold stratification and gibberellic acid. The highest germination rates (62% and 38% for P. microcephalus and P. polystachyus, respectively) were achieved when the seeds were pre-treated with GA500 and exposed to a temperature range of (20/18OC) and a 12h dark/12h light regime. Smoke water, heat shock and the removal of floral bracts also improved germination rates, but not at the same magnitude as GA. The second study of Ptilotus was a glasshouse trial that examined the effectiveness of the two taxa at reducing available soil phosphorus. This trial included a third high P-uptake species (Lupinus albus) for comparison, and also investigated if the addition of Phoslock® could bind soil P into insoluble forms. P. macrocephalus and P. polystachyus accumulated high amounts of soil P. Thus, several years of seeding and harvesting of these plants is anticipated to provide a useful option for soil P reduction. Phoslock® reduced soil available P, but only at high concentration of Phoslock 1500 g/m2 and at very high soil P concentrations; it was less effective at levels that typically expect in ex-cropping paddocks. The findings of this thesis have advanced our current knowledge of the restoration of excropland. The research has tested methods to overcome biotic and abiotic barriers to restoration of the Victorian Volcanic Plains grasslands, and has demonstrated some practical approaches to begin the treatment. It was suggested that many of the methods and techniques used in this study could be useful technique in broad areas of grassland restoration within Australia as well as in similar situations in temperate climate conditions across the globe.
- Description: Doctor of Philosophy
- Authors: Shakir, Shakir Bahaddin
- Date: 2019
- Type: Text , Thesis , PhD
- Full Text:
- Description: Native grasslands are one of the most endangered ecosystems in Australia. Approximately 99% of native grasslands have been disturbed for agriculture and pastoralism. Today, however, many agricultural and grazing lands have been abandoned. Restoring abandoned areas to native grassland is a challenge that must be met if these systems are to persist. This thesis sought to gain a better understanding of the biotic and abiotic barriers to restoring native grasslands in ex-cropping land, and to investigate novel techniques to overcome them in degraded native grassland in the Victorian Volcanic Plains. Firstly, I compared ex-cropland to high-quality remnant grassland, and showed that excropland supports a high number of exotic weeds, a lack of native species propagules, high nutrient levels (especially phosphorus and nitrogen), and an absence of organic carbon—all barriers which must be overcome if native grassland restoration is to succeed. I conducted a replicated field experiment in ex-cropland, to investigate four restoration approaches to overcoming barriers to restoration: (i) adding urban green waste to heat and kill the exotic seed bank (ii) adding sugar and/or mulch to promote microorganism and draw down soil nitrogen, (iii) using a modified clay product called Phoslock to reduce soil phosphorus levels, and (iv) scalping of topsoil 10 cm on ex-cropland site to remove the exotic seed bank and high nutrient soil. After each treatment, native grass seed was added, and the vegetation, seed bank, soil nutrients and microbial activity were monitored over 2.5 years. The hot mulch, scalping and sugar treatments all achieved significantly greater cover of native grasses than the control treatments. The hot waste treatment also effectively eliminated the exotic weed seed bank, but the soil N levels increased dramatically, which is counterproductive to the long-term goals of grassland restoration. Scalping out-performed all other treatments with regard to reducing soil N and P. All treatments suffered from reinvasion by exotic species, suggesting that any grassland restoration technique needs to be coupled with ongoing exotic weed management. Abstract ii High soil phosphorus is a difficult barrier to restoration of native grassland. A possible way to address this is to use plants with high P uptake to help draw down soil P. Native grassland taxa from the genus Ptilotus have been shown to have high P-uptake. I conducted two studies of Ptilotus macrocephalus and Ptilotus polystachyus to investigate their potential in this role. The first of these was an examination of techniques to break their seed dormancy, and to find their optimum germination conditions. I tested their response to smoke water, heating shock, cold stratification and gibberellic acid. The highest germination rates (62% and 38% for P. microcephalus and P. polystachyus, respectively) were achieved when the seeds were pre-treated with GA500 and exposed to a temperature range of (20/18OC) and a 12h dark/12h light regime. Smoke water, heat shock and the removal of floral bracts also improved germination rates, but not at the same magnitude as GA. The second study of Ptilotus was a glasshouse trial that examined the effectiveness of the two taxa at reducing available soil phosphorus. This trial included a third high P-uptake species (Lupinus albus) for comparison, and also investigated if the addition of Phoslock® could bind soil P into insoluble forms. P. macrocephalus and P. polystachyus accumulated high amounts of soil P. Thus, several years of seeding and harvesting of these plants is anticipated to provide a useful option for soil P reduction. Phoslock® reduced soil available P, but only at high concentration of Phoslock 1500 g/m2 and at very high soil P concentrations; it was less effective at levels that typically expect in ex-cropping paddocks. The findings of this thesis have advanced our current knowledge of the restoration of excropland. The research has tested methods to overcome biotic and abiotic barriers to restoration of the Victorian Volcanic Plains grasslands, and has demonstrated some practical approaches to begin the treatment. It was suggested that many of the methods and techniques used in this study could be useful technique in broad areas of grassland restoration within Australia as well as in similar situations in temperate climate conditions across the globe.
- Description: Doctor of Philosophy
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