Seaton Park Research Articles

Mapping the intersection of helicopter routes and public lands in Northeast Scotland

During the various COVID lockdowns, public narratives about the changing soundscape emphasized the reduction in commercial air traffic. However, other forms of air traffic were not reduced. Due to the need to service North Sea oil and gas operations, helicopter overflights from Aberdeen Airport (ABZ) remained a prominent feature of the local soundscape in Northeast Scotland. The primary route used by these helicopters (HMR WHISKEY) crosses public lands at several points, making the sound of overflights a prominent source of noise at these locations. These public lands include locations controlled by the city, like Seaton Park and Donmouth Local Nature Reserve, and others controlled by national entities, like the Forvie National Nature Reserve. This presentation will map several public lands in Northeast Scotland where noise from frequent helicopter overflights impacts the soundscape. The author will present field recordings and other documentation of helicopter overflights from February to June 2021, both during and immediately after the United Kingdom's third COVID lockdown, and invite discussion about potential for further study of noise pollution in this coastal region.

Understanding Why Effective Fungicides Against Individual Soilborne Pathogens Are Ineffective with Soilborne Pathogen Complexes.

Annual forage legumes across southern Australia continue to be devastated by soilborne diseases. Nine fungicide seed treatments (thiram, metalaxyl, iprodione, phosphonic acid, propamocarb, fluquinconazole, difenoconazole + metalaxyl, ipconazole + metalaxyl, sedaxane + difenoconazole + metalaxyl) and four foliar fungicide treatments (phosphonic acid, metalaxyl, propamocarb, iprodione) were tested on four subterranean clover cultivars against individual oomycete soilborne pathogens Pythium irregulare, Aphanomyces trifolii, and Phytophthora clandestina and the fungal pathogen Rhizoctonia solani. Best treatments were then further tested across southern Australia in 2 years of field experiments. Under controlled conditions, seed treatment with thiram was best against damping-off caused by P. irregulare across the four cultivars (Woogenellup, Riverina, Seaton Park, Meteora), while metalaxyl was the most effective for maximizing root and shoot weights. Against A. trifolii, metalaxyl, iprodione, difenoconazole + metalaxyl, ipconazole + metalaxyl, and sedaxane + difenoconazole + metalaxyl, all reduced damping-off; sedaxane + difenoconazole + metalaxyl, fluquinconazole, and ipconazole + metalaxyl all reduced lateral root disease across two or more cultivars; while iprodione, thiram, and sedaxane + difenoconazole + metalaxyl increased shoot dry weight. Against P. clandestina, metalaxyl was the most effective in reducing tap and lateral root rot followed by ipconazole + metalaxyl or phosphonic acid for tap and lateral rot, respectively. Against R. solani, there were no effects of fungicides. For P. irregulare and P. clandestina, there were strong seed fungicide × cultivar interactions (P < 0.001). Under controlled conditions for foliar fungicide spray treatments, phosphonic acid was best at preventing productivity losses from A. trifolii, but was ineffective against P. clandestina, P. irregulare, or R. solani. Overall, controlled environment studies highlighted strong potential for utilizing seed treatments against individual pathogens to ensure seedling emergence and early survival, with seed and foliar sprays enhancing productivity by reducing seedling damping-off and root disease from individual pathogens. However, in field experiments over 2 years across southern Australia against naturally occurring soilborne pathogen complexes involving these same pathogens, only rarely did fungicide seed treatments or foliar sprays tested show any benefit. It is evident that currently available fungicide seed and/or foliar spray treatment options do not offer effective field mitigation of damping-off and root disease on annual forage legumes that underpin livestock production across southern Australia. The main reason for this failure relates to the unpredictable and ever-changing soilborne pathogen complexes involved, highlighting a need to now refocus away from fungicide options, particularly toward developing and deploying new host tolerances, but also in deploying appropriate cultural control options.

Environmental factors determine severity of Rhizoctonia damping-off and root rot in subterranean clover

This study defines the importance of environmental conditions occurring across southern Australian subterranean clover (Trifolium subterraneum) forages on the severity of Rhizoctonia (Rhizoctonia solani) damping-off and root rot and on consequent plant productivity. Environmental factors tested included temperature regimes 14/9; 18/13 and 22/17 °C day/night, high vs. low soil moisture; sand vs. loam soil; high vs. low nutrition, and clover cultivars Riverina, Seaton Park and Woogenellup. Environmental factors significantly affected the severity of damping-off, root disease and root and shoot productivity. Damping-off was at or close to 100% at the two cooler of the three temperature regimes. At the warmest of the three temperature regimes (22/17 °C), significant numbers of subterranean clover plants germinated and survived, and germination, dry root and shoot weights all increased conversely with decreased tap and lateral root disease under higher moisture, better nutrition and under ‘heavier’ soil conditions. Findings demonstrate how variations in environmental factors like temperature in particular, but also soil type, nutrition, moisture, individually and interacting, have profound effects on the expression and severity of Rhizoctonia damping-off and root disease and the consequent productivity of subterranean clover forages. Findings explain the severe devastation to subterranean clover pastures observed in the presence of this pathogen when cool seasonal conditions occur across the critical autumn feed-gap period; especially under relatively drier soil conditions and in nutritionally impoverished sandy soils where there is little competition from other soil microbes.

Cultivation offers effective management of subterranean clover damping‐off and root disease

AbstractSoil cultivation studies involving subterranean clover pastures were undertaken utilizing field cores from five farms and two in‐field trials. Tap and lateral root disease in cores was less (p &lt; .001) severe and root and shoot weights greater (p &lt; .001) following simulated cultivation. Germination and severity of root disease were both affected (p &lt; .005) by three‐way interactions with cultivation, cultivar and field site. Cultivation in cores suppressed tap root disease for cultivars Meteora and Riverina across the five sites and Seaton Park for two sites. In‐field trials confirmed cultivation reduces root disease severity and increases germination and plant productivity. The best in‐field treatment was cultivation + fumigation that reduced (p &lt; .05) tap and lateral root disease and increased nodulation and root and shoot weights for Riverina, Seaton Park and Woogenellup. Cultivation + fumigation also increased (p &lt; .05) germination for Woogenellup and Seaton Park. There were negative correlations (all p &lt; .001) between tap and lateral root disease with nodulation (R2 = .85, R2 = .58, respectively); tap root disease with root and shoot weight (R2 = .58, R2 = .854, respectively); and lateral root disease with root and shoot weight (R2 = .83, R2 = .64 respectively). This study highlights the close relationship between severe root disease and reduced nodulation, likely explaining much of the widespread poor nodulation in subterranean clover pastures. This study confirms that damping‐off and root disease can be mitigated by cultivation, offering producers flexibility in disease management, especially where autumn–winter feed shortages occur on a regular basis.

Severity of phytophthora root rot and pre‐emergence damping‐off in subterranean clover influenced by moisture, temperature, nutrition, soil type, cultivar and their interactions

Studies were carried out in controlled environment rooms reflecting field situations. In the presence of the devastating soilborne pathogen Phytophthora clandestina, subterranean clover (Trifolium subterraneum) seedling emergence was significantly affected by moisture, soil type, temperature and cultivar. The level of rotting of tap and lateral roots was significantly affected by nutrition, soil type, temperature and cultivar. There were significant interactions involving temperature, moisture, soil type and cultivar; cultivar resistance, high moisture, high or medium temperature, high nutrition and sand soil all contributed towards less pre‐emergence damping‐off and tap and lateral root disease and to greater clover productivity. Host resistance of subterranean clover cultivars was critical for reducing disease severity and increasing productivity, even when favourable environmental conditions for severe disease occurred. In the presence of P. clandestina, the most resistant cultivar, Seaton Park, performed best under a high temperature, high nutrition and high moisture combination, but showed lower productivity under conditions of low nutrition or lower temperature, even when moisture level was high. In contrast, less resistant cultivars Riverina and Meteora had less disease and greater productivity under low moisture conditions. Findings reflect field observations that pre‐emergence damping‐off and root disease from P. clandestina in subterranean clover is particularly severe under colder conditions and in nutritionally impoverished sandy soils, and demonstrate how variations in soil type, nutrition, moisture, temperature and cultivar have profound effects on the expression and severity of phytophthora pre‐emergence damping‐off and root disease and the productivity of subterranean clover forages.

Thread: Somatic Lives of a Thing

Thread: Somatic Lives of a Thing

Interrupted everyday motions – journeying with threads and lives

This piece of poetry was written as a response to the event which gave birth to the Walking Threads project, which happened in Seaton Park on March 21 2014.

"Walking Threads, Threading Walk": Embroidering Reflection

This both visual and textual contribution consists of a series of four separate embroideries on textile (Fig. 1, 2, 3, 4), which can be assembled into a unique piece (Fig. 5), and of a text, that engages with a reflection on the overall process of creation with and transformation of a particular daily object: a yarn of golden thread. The contribution has been inspired by the first ‘Walking Threads’ walk and event in Seaton Park, Old Aberdeen, March 2014, from which the ongoing ‘Walking Threads’ project has been initiated. The work is intended as a specific way of ‘thinking through making’ (Ingold 2013) and of further developing the research insights that appeared during and after that walk. In what ways materials, artefacts, skill apprenticeship, gesture, , lines, breathing and the ‘weather-world’ (Ingold 2007a, b, 2015) can relate to each other? It is also a personal attempt to respond to the Ingoldian call towards a ‘Graphic’ Anthropology’, within which ‘to follow the materials, to learn the movements and to draw the lines’ (Ingold 2013) are the main points at the very core of its agenda.

Effect of timing of forage conservation on forage yield and quality, seed yield and seedling regeneration of four subterranean clover (Trifolium subterraneum) cultivars

Swards of four cultivars of subterranean clover (Trifolium subterraneum L.) were cut at three different times to determine the effect on forage yield and quality, seed set and seedling regeneration in two successive seasons in southern New South Wales. The four cultivars of subterranean clover (Seaton Park LF, Junee, Goulburn and Clare) were cut on 23–25 September (early cut), 8–10 October (mid cut) or 22–23 October (late cut), to simulate an early silage, late silage or hay cut. Additional treatments imposed included either grazing or leaving the regrowth after cutting and raising the cutting height from 3 to 6 cm. Forage yields ranged from 3.5 to 9.3 t dry matter (DM)/ha in the first year and from 2.0 to 5.9 t DM/ha in the second year. Herbage yield was influenced by both cultivar and harvest time with the highest yields achieved with the mid cut. Lower forage yields at the later cut were attributed to losses due to respiration and decay under dense leaf canopies. Changes in forage quality were consistent across both years, with in vivo DM digestibility declining from 76–79% to 69–70% as cutting time was delayed. Crude protein fell from 22–24% to 14–17% over the same period, depending on cultivar. Seed yields in both years were influenced by both cutting time and cultivar with a positive relationship (R2 = 0.45–0.61) between herbage present in late spring after a period of regrowth and subsequent seed yield. The early flowering cultivar Seaton Park LF had the highest seed yield in both years and the more erect cultivar Clare had the lowest. Seed yields declined with later cutting time but increased by an average of 39% when the cutting height was raised from 3 to 6 cm. Seedling regeneration reflected seed yield responses with the largest seedling regeneration occurring in treatments cut early. The study found that forage conservation in early October is likely to yield more and be of higher quality than swards cut later in the season. Seed set is greatly reduced by all cutting strategies to levels unprofitable for seed harvesting but may be adequate for pasture regeneration.

Stable carbon isotope ratios from archaeological charcoal as palaeoenvironmental indicators

The potential to provide environmental proxies using stable carbon isotopes from modern and archaeological charcoal is explored. Experiments on modern Podocarpus (Yellowwoods) show that δ 13C values of stems, branches and charcoal preserve proxy environmental conditions, including rainfall, humidity and temperature. An additional experiment showed that combustion temperature affects the carbon isotope signature of charcoal. Burning at 450 °C to 500 °C depletes δ 13C values with respect to the original wood, but the charcoal retains the seasonal and inter-annual isotopic trends recorded during the growth of the tree. The δ 13C of Podocarpus charcoal from three levels from the Middle Stone Age site of Sibudu Cave, KwaZulu-Natal, South Africa, was compared with modern analogues from two different environments, Seaton Park (KwaZulu-Natal) and the Baviaans Kloof (Eastern Cape). Other environmental proxies from levels dated from > 70 ka and ~ 48 ka, show that environmental conditions changed from warmer and wetter to colder and drier and finally becoming warmer and drier. The isotope data is consistent with this reconstruction. The results from this series of experiments indicate that it is possible to obtain meaningful palaeoenvironmental information from δ 13C values of archaeological charcoal.

Evaluation of annual pasture legumes in northern New South Wales. 1. Trifolium subterraneum cultivars and lines

Two subterranean clover (Trifolium subterraneum var. subterraneum and T. subterraneum var. brachycalycinum) evaluation studies were sown in replicated plots. The first study (experiment 1) comprised 30 entries sown in 1993 and 1994 and the second (experiment 2) had 85 entries sown in 1998. Green herbage mass (kg DM/ha) was assessed until spring 2000 (experiment 1) or 2001 (experiment 2). Limited data were also collected in experiment 1 to estimate hardseededness, seed yield and seedling regeneration. For each experiment, green herbage mass was examined using cubic smoothing splines. Plots of initial and final values assisted with data interpretation, and predicted values at the end of each experiment were used to assess significant (P = 0.05) cultivar/line differences. CPI 89846B (York), Junee and Clare performed better (P &lt; 0.05) than Woogenellup, Seaton Park, Rosedale, Nuba and Goulburn (experiment 1, previously cultivated site). For the native pasture site, CPI 89846B, Junee, Clare and Woogenellup were better (P &lt; 0.05) than Goulburn, Nuba and Rosedale. In experiment 2, the three cultivars, Clare, Antas and Rosedale, had similar predicted green herbage mass in spring 2001. In experiment 1, CPI 28012 had the lowest predicted green herbage mass in spring 2000. This line also had low seedling establishment and seed yield in 1993 and low seedling regeneration in 1994, 1995 and 1997. Early maturing cultivars/lines generally performed poorly in experiment 1 and, of the other lines, CPI 70100 performed best. However, in experiment 2, crosses with this line as a parent had variable green herbage mass in spring 2001.

Comparing the potassium requirements of five pasture species

Potassium (K) deficiency is now common in sandy soils of south-western Australia and the K requirements of most pasture species grown in rotation with crops in the region are not known. In a glasshouse experiment using a K deficient yellow sand, we compared the K requirements of 5 pasture species now commonly grown in the region: French serradella (Ornithopus sativus Brot.) cv. Cadiz, yellow serradella (Ornithopus compressus Brot.) cv. Santorini, balansa clover [Trifolium balansae, classified as T. michelianum Savi var. balansae (Boiss)] cv. Paradana, 2 subterranean clover (Trifolium subterraneum L.) cultivars, cv. Seaton Park (subspecies subterraneum) and cv. Trikkala (subspecies yanninicum), and annual ryegrass (Lolium rigidum Gaud) cv. Wimmera. After 56 days of growth, above-ground growth was harvested and analysed for total K. Mitscherlich curves were fitted to yield of dried shoots, K concentration and K content (K concentration multiplied by yield) of the shoots. These fitted curves were used to determine the amount of K required to produce 75% of the maximum yield of dried shoots, K required to attain a K concentration in dried shoots of 25 g/kg, and K required to achieve a K content in dried shoots of 250 mg K/pot. Annual ryegrass and yellow serradella more effectively used indigenous soil K and applied K to produce dried shoots than the other species and cultivars, with the other species and cultivars requiring about 55% more applied K to produce 75% of the maximum shoot yield. The K content in dried shoots estimated the total K taken up from the soil, and annual ryegrass took up least K from soil, but it required least applied K to produce 75% of the maximum shoot yield, indicating it used the K it took up very effectively to produce shoots. Yellow serradella took up most K and, after annual ryegrass, it needed least applied K to produce the target yield of dried shoots. After yellow serradella, subterranean clover cv. Trikkala took up most K from soil, but it required nearly the most applied K to produce the target shoot yield so it was inefficient at using K taken up to produce the shoots. For all the other species and cultivars, K requirement was similar as assessed by yield or K content data. The critical concentration of K required for 90% maximum yield of dried shoots was about (g K/kg) 24 for balansa clover, 23 for both subterranean clover cultivars, 21 for yellow and French serradella, and 15 for annual ryegrass.

New sources of resistance in Trifolium subterraneum to rust (Uromyces trifolii-repentis)

Fifty-seven genotypes, including 10 cultivars, of Trifolium subterraneum var. subterraneum and var. yanninicum were screened in the field for resistance to rust (Uromyces trifolii-repentis) using artificial inoculation. There was outstanding resistance among the var. yanninicum, types with all but 1 genotype showing no rust symptoms. Several var. subterraneum genotypes also showed only a low rust incidence (≤3.5 on a 0–10 scale) with little or no leaf collapse from rust infection, including 83S19–07, CPI 103906F, EP132Sub-E, 84S20–02, and 84S20–01. Several other lines had a significant incidence of rust, while little leaf collapse from the disease was evident. Several highly susceptible lines were identified, including cultivars Green Range, Seaton Park and York, all with 100% of leaves affected by rust and extensive leaf collapse. There was excellent positive correlation between rust incidence and leaf collapse across the genotypes tested (R2 = 0.91). The excellent rust resistance observed in the majority of var. yanninicum lines and the good resistance in some var. subterraneum lines, indicates that these are useful sources of resistance that can be exploited, either directly as new cultivars to minimise leaf collapse from this disease or as parents in breeding programmes to develop more rust-resistant cultivars.

Effects of continuous and seasonal grazing strategies on the herbage mass, persistence, animal productivity and soil water content of a Sirosa phalaris - subterranean clover pasture, North-West Slopes, New South Wales

An experimental site was established in 1997 on the North-West Slopes of New South Wales to further investigate the use of strategic grazing management to improve the persistence of phalaris (Phalaris aquatica cv.�Sirosa) and subsequent effects on animal production and soil water content. The pasture was sown in 1992 to Sirosa phalaris, subterranean clover (Trifolium subterraneum var. subterraneum cv. Seaton Park) and lucerne (Medicago sativa cv. Aurora). Four grazing treatments were applied in a randomised 3-replicate design. Treatments consisted of continuous grazing at 12.3 sheep/ha (C12 or control); continuous grazing at 6 sheep/ha (C6), and 2� spring and autumn strategies of either resting from grazing for 6 weeks in each season (SAR0), or reducing stocking rate from 12.3 to 4.0 sheep/ha (SAR4). Despite annual applications of fertiliser and high clover content, Sirosa phalaris herbage mass in plots continuously grazed at 12.3 sheep/ha declined from a mean of 3300 kg DM/ha in spring 1997 to &lt; 700 kg DM/ha by May 1998. At the end of the study (February 2001), Sirosa mean herbage mass in these plots was 670 kg DM/ha and lower (P &lt; 0.05) than for the other treatments (mean value 5400 kg DM/ha). These marked changes in herbage mass, and the degradation of the Sirosa-based pasture to an annual pasture by continuous grazing at 12.3 sheep/ha, were not generally reflected in either short-term animal production or substantial differences in soil water content. Wool production (kg/head) was not significantly different among treatments each year. Compared with continuous grazing at 12.3 sheep/ha, sheep liveweights were higher (P &lt; 0.05) in plots continuously grazed at 6.1 sheep/ha from November 1997 to February 1999. However, from February 1999 to 2001, sheep liveweights in the 2 treatments with the highest Sirosa phalaris content were lower (P &lt; 0.05) than those continuously grazed at 12.3 sheep/ha. Only the soil water content for the C6 and SAR4 treatments at 0–30�cm was significantly different to the control treatment, but the differences were predicted to be &lt; 2.5 mm/year. In the root zone (0–90 cm), mean soil water content ranged from 159 to 309 mm (mean 220 mm), while plant available water (soil water content – soil water content at –1500 kPa) was a mean of 79 mm, ranging from 11 to 168 mm.

Abscisic acid added to the nutrient solution induces a water deficit‐like response in Trifolium subterraneum

SummaryThe response of subterranean clover (Trifolium subterraneum) to the addition of increasing concentrations of abscisic acid (ABA) in the nutrient solution (10−3, 10−2 and 10−1 mol m−3) was studied under growth room conditions. Six cultivars of contrasting yield capacity were compared.Plants were grown in Hoagland's solution until they had produced at least four fully developed leaves. ABA was then added and its effect on the fresh weight, leaf number and longest root length was determined, 1 day, 4 days, 7 days and 11 days after addition. The addition of ABA caused significant reductions in all the measured growth parameters, as well as a significant decrease in leaf water potential, which was dependent on the ABA concentration. The average growth reduction after 11 days under 10−1 mol m−3 ABA were within previously reported ranges for this crop under drought, in field conditions. The average leaf number, area of a fully developed leaf and the dry weight per plant of the six cultivars decreased by approximately 50%, whereas the root/shoot ratio increased by 80%.The variation and ranking for this treatment resembled closely those obtained for the same cultivars in field experiments. The cvs Clare, Nuba and Seaton Park, showed the best results under both control and ABA treated conditions. The correlation between the response to ABA in nutrient solution and previous water deficit studies raises the possibility of using this approach as an alternative way to quantify the drought sensitivity of subterranean clover cultivars.

Effects of continuous grazing and seasonal closures on the performance and persistence of some sown temperate perennial grasses, North-West Slopes New South Wales

A split-plot experiment was sown at Tamworth in 1992 to examine the effects of continuous sheep grazing and seasonal closures (autumn, spring, spring + autumn, and summer + winter) on the herbage mass, plant frequency and basal cover of 5 perennial grasses, when sown as monocultures or with a perennial (Trifolium repens cv. Haifa) or annual legume (Trifolium subterraneum var. subterraneum cv. Seaton Park). Plant basal area and crown density data were also collected. The perennial grasses were Phalaris aquatica cv. Sirosa, Festuca arundinacea, cv.� Demeter, Lolium perenne cv. Kangaroo Valley, Austrodanthonia richardsonii (syn. Danthonia richardsonii) cv.�Taranna, and A. bipartita (syn. D. linkii) cv. Bunderra. There was no significant effect of legume presence on the herbage mass or persistence of the perennial grasses. The only treatment that had a significant effect (P&lt; 0.05) on either herbage mass, plant frequency or basal cover data was the grazing treatment × perennial grass interaction in each of the years 1993-98, except for herbage mass in December 1993 and basal cover in October 1998. In all of the grazing treatments examined, Kangaroo Valley ryegrass failed to persist after spring 1994; Demeter fescue had failed by spring 1997 and Sirosa phalaris by spring 1998. Six years after sowing the only temperate grass cultivars that were persisting in all grazing treatments were the native perennials, Taranna and Bunderra. Hence, the data represent the entire stand life from sowing to eventual failure for the 3 introduced cultivars. While grazing treatment effects within years for individual species were significant, overall grazing had little effect on the rate of decline in herbage mass and persistence of Kangaroo Valley, Demeter and Sirosa. By 1998, grazing treatment had no significant effect on the herbage mass and basal cover of Taranna and Bunderra, but their plant frequencies were lowest in the spring rest and summer + winter rest treatments.

Occurrence of Phytophthora clandestina in Trifolium subterraneum paddocks in Australia

In 1995–96, a survey of soil samples from subterranean clover (Trifolium subterraneum L.) paddocks was conducted across Victoria, South Australia, New South Wales and Western Australia, to determine the distribution and the prevalence of races of Phytophthora clandestina (as determined by the development of root rot on differential cultivars), and the association of its occurrence with paddock variables. In all states, there was a weak but significant association between P. clandestina detected in soil samples and subsequent root rot susceptibility of differential cultivars grown in these soil samples. Phytophthora clandestina was found in 38% of the sampled sites, with a significantly lower prevalence in South Australia (27%). There were significant positive associations between P. clandestina detection and increased soil salinity (Western Australia), early growth stages of subterranean clover (Victoria), mature subterranean clover (South Australia), recently sown subterranean clover (South Australia), paddocks with higher subterranean clover content (Victoria), where herbicides were not applied (South Australia), irrigation (New South Wales and Victoria), cattle grazing (South Australia and Victoria), early sampling dates (Victoria and New South Wales), sampling shortly after the autumn break or first irrigation (Victoria), shorter soil storage time (Victoria) and farmer’s perception of root rot being present (Victoria and New South Wales). Only 29% of P. clandestina isolates could be classified under the 5 known races. Some of the unknown races were virulent on cv. Seaton Park LF (most resistant) and others were avirulent on cv. Woogenellup (most susceptible). Race 1 was significantly less prevalent in South Australia than Victoria and race 0 was significantly less prevalent in New South Wales than in South Australia and Western Australia. This study revealed extremely wide variation in the virulence of P. clandestina. The potential importance of the results on programs to breed for resistance to root rot are discussed. in South Australia.

Effect of phalaris (Phalaris aquatica L.) and lucerne (Medicago sativa L.) density on seed yield and regeneration of subterranean clover (Trifolium subterraneum L.)

A mixture of 3 subterranean clover (Trifolium subterraneum L.) cultivars (cvv. Goulburn, Seaton Park, and Dalkeith) was grown with 5–40 plants/m2 of phalaris (Phalaris aquatica L.) or lucerne (Medicago sativa L.) for 3 years at Wagga Wagga, NSW (147°21´E, 35°03´S). Clover seed yield was assessed each year, the number of regenerating clover seedlings was counted, herbage yield of clover and the perennials was measured, and the change in perennial density recorded. The influence of perennials on water availability in spring and light during clover seed set was also examined. The impact of perennial density on clover was assessed using regression analyses. In each of the 3 years, subterranean clover seed yield was negatively related to perennial density, but phalaris suppressed clover seed yield more than equivalent densities of lucerne in 2 of the years. Clover seed yield was positively related (R2 = 0.30–0.85) to clover biomass in spring in all 3 years (except for subterranean clover in phalaris in 1994) and to the proportion of total photosynthetically active radiation reaching the clover canopy beneath the perennial (R2 = 0.33–0.83) in 2 of the 3 years. There was a positive relationship between clover seedling regeneration in autumn and size of the summer seed bank in both years in lucerne (R2 = 0.40–0.76) and in 1 year in phalaris (R2 = 0.76) and a negative association between perennial density and clover seedling regeneration. The rate at which the surface profile (0–37 cm) dried in spring was independent of phalaris and lucerne density over the 3 years and did not differ from that of pure clover. The late season clover cultivar, Goulburn, constituted between 57% and 79% of the seed bank following seed set, substantially more than the earlier flowering cultivars, Seaton Park and Dalkeith. Neither perennial density nor species changed the relative competitiveness of the 3 cultivars. The high seed yield of Goulburn and the lack of a perennial-induced change in surface soil water in spring suggest that growing perennials in association with subterranean clover does not increase the level of moisture stress during clover seed set. The good performance of Goulburn is attributed to superior competitive ability for light in late spring. The basal area occupied by lucerne and phalaris increased with perennial density in each of the first 2 years. However, in the third year, phalaris basal area was similar at all densities. The findings suggest that sowing low densities of lucerne should assist in promoting seed yield and regeneration of subterranean clover. Management of phalaris, which has the capacity to substantially increase plant size at low densities, may require additional strategies such as more frequent grazing in spring.

Colonization of roots of subterranean clover cultivars by virulent and avirulent races of Phytophthora clandestina

The colonization of the roots of four cultivars of subterranean clover by isolates representing four races of Phytophthora clandestina was studied. There was a highly significant race × cultivar interaction in the growth of inoculated tap roots and the degree of colonization of roots by the pathogen. While all races were able to infect the roots of all cultivars tested, roots of the susceptible cultivars were colonized more rapidly and extensively than those of the resistant cultivars. In compatible combinations, fungal colonization extended for a few centimetres in the tap root and lateral roots in the moderately susceptible cultivars Trikkala and Meteora, or throughout the whole root system leading to the death of the host in the very susceptible cultivar Woogenellup. In contrast, limited fungal colonization of the tap root and lack of extension of the fungus into lateral roots was typical of incompatible combinations. In all cultivars, lateral roots were as susceptible to infection as tap roots. The number of lateral roots of Woogenellup was significantly reduced by infection. However, neither the rate of lateral root formation nor the total number of lateral roots of Seaton Park, Meteora and Trikkala was reduced by infection with virulent or avirulent races of the pathogen.

Genotypic variation of plant species to the allelopathic effects of vulpia residues

Summary. The germination and seedling growth of 12 plant species and 12 cultivars from 2 plant species were tested in the presence of aqueous extracts of vulpia dry matter residues. Concepts of whole-range assessment and inhibition index were developed, and used, with principal component analysis, for assessing results. Species were grouped according to the inhibition index. Average threshold concentration, average I50 (the extract concentration required to cause 50% inhibition in plant response) and average root and coleoptile lengths were used as auxillary indices for each group. Marked differences in tolerance toward the phytotoxicity of vulpia residue extracts were observed among species and cultivars. Such differences were widespread among plant species, with generally cocksfoot, Vulpia spp., subterranean clover (cv. Trikkala), phalaris, canola, medics, and oats being relatively tolerant, while lupins, barley, and wheat (cvv. Janz, Vulcan) were the most susceptible, and subterranean clover (cvv. Seaton Park, Karridale, Clare, Woogenellup, Junee), field peas, and wheat (cvv. Ford, Darter, Dollarbird, Rosella) were relatively susceptible. The findings of this study suggest that choice of species and cultivar may be a valuable management option for minimising the negative effects of vulpia residues. The whole-range assessment developed in this study proved to be a statistically efficient summary of the plant response profiles. Together with the bioassay techniques adopted, it provides a simple and rapid screening methodology for assessing the relative tolerance of plant species to the allelopathic effects of weed residues.