Yellow Serradella Research Articles

Yield and grain protein of wheat following phased perennial grass, lucerne, and annual pastures

The effect of using 4 perennial grasses or lucerne (Medicago sativa L.) in the pasture phase on subsequent wheat grain yield, protein, and grain hardness was investigated at 2 sites (Kamarah and Junee) in the south-eastern Australian cereal belt. The 6 perennial treatments were 5 mixtures of subterranean clover (Trifolium subterraneum L.), with one of lucerne, phalaris (Phalaris aquatica L.), cocksfoot (Dactylis glomerata L), wallaby grass (Austrodanthonia richardsonii (Cashm.) H.P. Linder), or lovegrass (Eragrostis curvula (Schrader) Nees cv. Consol), or one mixture of cocksfoot, phalaris, and lucerne. The results were compared with wheat after one of 3 annual pastures consisting of either pure subterranean clover, subterranean clover with annual volunteer broadleaf and grass weeds, or yellow serradella (Ornithopus compressus L.). The duration of the pasture phase was 3 years at the drier Kamarah site (av. annual rainfall 430 mm) and 4 years at Junee (550 mm). The effect of time of removal of the pastures in the year prior to cropping (28 August–3 September or 6–7 November) and the effect of nitrogen (N) fertiliser application were also examined. In the absence of applied N, wheat grain yields at Kamarah were highest (4.7–4.9 t/ha) and grain protein lowest (10.3–11.1%) following phalaris, wallaby grass, and cocksfoot. Grain protein levels were highest (12.9–13.9%) in wheat following the 3 annual legume swards at both sites. Previous pasture type had no effect on wheat yields at the Junee site. Wheat grain protein and total N taken up by the crop were positively related to available soil N to 100 cm measured at sowing at both sites. Grain protein was inversely related to grain yield at both sites where additional N fertiliser was added, but not in the absence of fertiliser N. There was a positive response in grain protein to delayed time of pasture removal in second year wheat at Junee. The application of additional N fertiliser increased grain protein of wheat following all 9 pasture types at the drier Kamarah site, but at the Junee site there was only a positive grain protein response following phalaris, cocksfoot, and wallaby grass. Early removal of the pasture prior to cropping increased soil water (10–130 cm) at sowing by 18 mm, delayed wheat senescence, and increased crop yield by 11% (0.44 t/ha) at the drier Kamarah site. Early removal of the pasture at Junee increased soil water by 29 mm, crop yields by 2% (0.14 t/ha), and increased grain protein in wheat following cocksfoot, wallaby grass, and phalaris, but not following the 3 annual legume treatments. The study demonstrated that perennial grasses can be successfully incorporated into phased rotations with wheat without affecting grain yield, but protein levels may be lower and timing of pasture removal will be important to limit the effect of water deficits on grain yield.

Effect of temperature and state of hydration on rate of imbibition in soft seeds of yellow serradella

Seeds were removed by hand from pods of yellow serradella (Ornithopus compressus L.) cvv. Santorini and Charano and accession GRC5045-2-2 that were taken from the field on 26 March after burial treatment to initiate seed softening. Times taken for soft seeds to imbibe were determined at constant temperatures of 8�, 20�, and 30�C. Rates of moisture uptake and loss were measured in seeds held in a moist (76% RH) or dry (over sulfuric acid) atmosphere and the effects of hydration and dehydration on subsequent imbibition times determined at 20�C.Temperature had negligible effect on imbibition times in GRC5045-2-2, in which nearly all soft seeds imbibed within 24 h of wetting. Imbibition times in individual seeds of both Charano and Santorini varied from a few days to more than 200 days and were markedly reduced by increasing temperatures. Times taken to approach constant weight in the moist atmosphere were approximately 75, 165, and 430 days in GRC5045-2-2, Charano, and Santorini, respectively. By contrast the rate of moisture loss in the dry atmosphere was similar in all lines. Imbibition times in GRC5045-2-2 were little affected by state of hydration, but in both Santorini and Charano, imbibition was delayed by dehydration and accelerated by hydration.It is proposed that slow imbibition is attributable to the presence of a minute opening in the seed at an as yet unidentified site (possibly the micropyle or hilum) that restricts moisture uptake until a threshold is reached when seeds in contact with water imbibe rapidly. It is hypothesised that the moisture threshold coincides with the build up of sufficient moisture in tissues associated with the underside of the lens, to cause its rupture, thereby allowing rapid uptake of free water.

Effect of surface-sown pod:seed mixtures on serradella establishment and persistence on rangelands in central New South Wales

Aerial sowing is the only option for introducing improved pasture species into much of the non-arable, acid soil rangelands in central New South Wales. However, low germination of seeds in serradella pods is a major problem causing poor establishment. Sowing different combinations of pod and seed was investigated as a means of improving germination and subsequent persistence in an experiment between 1993 and 1997. Results indicated that a pod:seed mixture of 75:25 was the most suitable ratio for establishing yellow serradella (Ornithopus compressus) when broadcast into native grassland on hardsetting, non-arable, acidic hill country. Nodulation failure observed at this cold tablelands site confirmed the need for a more winter-active inoculant for yellow serradella.

Seed softening, imbibition time, and seedling establishmentin yellow serradella

The first (preconditioning) and final stages of seed softening were studied over a 4-year period in 4 lines of yellow serradella (Ornithopus compressus L.): cvv. Santorini and Charano, and accessions GEH72-1A and GRC5045-2-2. Pods grown in 1997 were collected in December (start of summer) and placed on the soil surface or buried at a depth of 1 cm. Measurements of seed softening between years were made from pod samples removed in June each year. The progress of preconditioning and seed softening within the first 3 years was determined from samples taken at the end of February. Numbers of soft and viable seeds were determined from each sampling. Preconditioned seeds were identified by subjecting seeds to 7 gradual diurnal temperature cycles of 48/15°C in darkness before testing for permeability. Seed softening was markedly accelerated by pod burial in all 4 lines, with most buried seeds of GEH72-1A and Santorini softening during the first year. Seed softening was slower in GRC5045-2-2 and Charano, approaching a constant annual rate over the 4 years of the experiment. Despite this marked effect of burial the differences between lines in rates of softening of buried seeds were sufficient to have important implications for persistence under some management systems. Most seeds of all lines softened between February and June, indicating that shallow pod burial could be delayed in these lines until at least the end of February to promote the final stage of seed softening. Although large numbers of seeds of GEH72-1A and GRC5045-2-2 had preconditioned at the soil surface by the end of February, few went on to complete the softening process by June, when most had lost their preconditioned state. Treatment at 48/15°C was less successful in identifying preconditioned seeds of Santorini and Charano. Rates of imbibition differed markedly between lines. Most soft seeds of GEH72-1A and GRC5045-2-2 imbibed within days, whereas they took weeks in Santorini and an intermediate time in Charano. Seedling age distributions in the 4 lines in June closely reflected the times their soft seeds took to imbibe in the laboratory. Imbibition time can be an important germination regulating mechanism having implications that may be either favourable or unfavourable depending on rainfall distribution around the break of season and the system of management.

Hardseededness and the pattern of softening in Biserrula pelecinus L., Ornithopus compressus L., and Trifolium subterraneum L. seeds

Experiments measuring seed bank size, hardseededness, and seed softening of biserrula (Biserrula pelecinus L.) were conducted at Merredin and Perth in Western Australia. At Merredin, a mixture of 2 biserrula accessions was grazed, shallow cultivated, or left uncultivated and ungrazed. Seed bank size, seedling regeneration, and seed softening were measured over 2 years. At Perth, softening of biserrula, yellow serradella, and subterranean clover seeds grown at 2 sites (Binnu and Northam) was compared on the soil surface and after burial at 2 and 10 cm over a period of 2 years. Seed bank size of biserrula at Merredin ranged from 14000 to 17500 seeds/m2. Regeneration was greater in the second year (800–1700 seedlings/m2) than in the first year (40–600 seedlings/m2). In both years the shallow cultivated treatment recorded the highest number of seedlings. About 90% of biserrula and serradella seed remained hard after 2 years on the soil surface, compared with only about 10% of subterranean clover. Serradella softened more rapidly when buried 2 cm below the soil surface (8–12% hard) than it did on the soil surface (84–92% hard) (P<0.05). In contrast, the softening of subterranean clover decreased with increasing depth. Biserrula was intermediate, although it too softened most rapidly at 2 cm (78–95% hard compared with 82–97% on the surface) (P<0.05). Rate of seed softening in all species decreased with increasing depth of burial below 2 cm. Of the 4 accessions of biserrula, an accession from Greece (83% hard after 2 years exposure) was significantly softer than the other accessions. The results indicate that biserrula is very hardseeded, although there is sufficient variation in hardseededness for the selection of somewhat softer lines. Its pattern of softening suggests that biserrula may be successful in the ley farming system (crop/pasture rotations) of southern Australia.

Genetic variation in populations of two Mediterranean annual pasture legumes (Biserrula pelecinus L. and Ornithopus compressus L.) and associated rhizobia

Genetic variation between and within populations of Biserrula pelecinus L. (biserrula) and Ornithopus compressus L. (yellow serradella) and associated rhizobia was studied using germplasm collected from sites in central-eastern and south-eastern Sardinia (Italy). Pods and root-nodule bacteria were collected on diagonal transects at each site. Plants were characterised in nursery rows and the rhizobia were isolated and tested for their effectiveness. Thirteen morphological traits were recorded and the results were analysed using cluster analysis. Genetic and phenotypic variation of rhizobia were assessed using DNA analysis (PCR, RAPDs) and effectiveness indices, respectively. Genetic variation based on morphological traits was found between and within sites for both species. Pod characteristics and flowering time were the most important traits assisting in discriminating between accessions. Flowering time varied more in serradella than in biserrula, particularly at Cantoniera Cannas. Although all rhizobial strains nodulated all accessions of biserrula, great variability in capacity to fix nitrogen was evident between and within sites. Distinct PCR amplification profiles were generated for individual rhizobial strains, which confirmed the phenotypic variability (effectiveness indices) of the strains. No relationship was found between host and rhizobia variation. The results are discussed in terms of (a) genetic differences for each species within and between sites; (b) differences in behaviour in respect to genetic variation between biserrula, serradella, and other Mediterranean annual legumes; and (c) spatial variability and symbiotic effectiveness of rhizobia.

Effect of length of growing season on development of hard seeds in yellow serradella and their subsequent softening at various depths of burial

Effect of length of growing season on development of hard seeds in yellow serradella and their subsequent softening at various depths of burial

Effect of length of growing season on development of hard seeds in yellow serradella and their subsequent softening at various depths of burial

Effects of withholding water at 4 (W4) and 8 (W8) weeks after commencement of flowering on seed development in 2 accessions of yellow serradella (Ornithopus compressus L.), cv. Avila and accession GEH72-1A, were investigated in swards at a site near Perth, Western Australia. Softening of resulting hard seeds during the following summer and autumn was then studied in newly ripened pods placed at the soil surface, and at depths of 0.5 and 2 cm in the soil at Merredin in the first week of January. Proportions of soft seeds were determined in the original seed populations and in pods taken from the field in March and June. In 2 further treatments, proportions of soft seeds were determined in June in (i) pods that had been at the soil surface until they were buried at 2 cm in March, and (ii) in pods that had been buried at 2 cm until March, when they were returned to the soil surface. Seed yields from W4 were about 35% of those from W8 owing to reductions in pod numbers (partly as a result of more flower shedding in W4), number of seeds per pod, and seed size. Developing seeds became germinable between 21 and 29 days after anthesis when seed dry weights were between 0.9 and 1.4 mg, which was about the same time that they developed the capacity for seed coat impermeability. Viability of hard seeds was almost 100% from W8 but only 65% from the W4 treatments. Less than 5% of the newly ripened viable seeds were soft in any of the treatments. Length of growing season had no effect on seed softening at the soil surface and only a relatively small and variable effect on softening in buried pods. At the June sampling, up to 16% of Avila and 5% of GEH72-1A seeds had softened at the soil surface. Burial of pods increased proportions of soft seeds up to 85% in Avila and 53% in GEH72-1A. Whereas most of the seed softening in Avila occurred before March, similar amounts of softening occurred before and after the March sampling in GEH72-1A. Burial of pods in March increased seed softening by June in GEH72-1A but reduced softening in Avila, whereas transfer of buried pods to the soil surface in March had the reverse effect. This seed softening behaviour is explained in terms of the 2-stage seed softening mechanism. Burial of newly ripened seeds by tillage or stock trampling during the first summerŒautumn appears a feasible management option for improving first year regeneration in at least the softer seeded accessions of yellow serradella.

Effect of pod burial, light, and temperature on seed softening in yellow serradella

Studies were made on the preconditioning stage (which produces latent soft seeds) and the final stage of seed softening in newly ripened seeds of the GEH72-1A accession of yellow serradella (Ornithopus compressus L.). Pods grown at Yelbeni, Western Australia, in 1996 were collected in December and placed on the soil surface or buried at a depth of 0.5 cm at a site near Perth. Other pods were subjected to a gradual diurnal temperature fluctuation of 60/15°C in darkness in a laboratory chamber. Pod samples were taken from the field at intervals from January to June in 1997, and over 336 days from the 60/15°C treatment. Pods were broken into segments and the number of soft seeds determined. Numbers of latent soft seeds were then determined by subjecting residual hard seeds to 7 gradual diurnal temperature cycles of 48/15°C in darkness and retesting for permeability. In a second experiment, seeds preconditioned at the soil surface until 3 March were subjected to a range of light levels in the field in March before testing for permeability. The time taken for seeds to precondition under a range of constant temperatures between 30° and 70°C was determined in a third experiment. Preconditioning commenced early in summer in both surface and buried seeds. All buried seeds that preconditioned completed the softening process to produce about 80% soft seeds, with most seeds softening in March when diurnal temperatures fluctuated between maxima of 45–50°C and minima of 10–20°C. Only 15% of the seeds at the soil surface softened so that relatively few preconditioned seeds completed the softening process. Preconditioning occurred more rapidly than did the completion of softening in the 60/15°C treatment, indicating that this temperature regime was above optimum for the final stage of softening. Reversal of the preconditioning process took place in the field as temperatures declined during May. Effects of reduced temperatures in causing this reversion were confirmed in the laboratory on seeds preconditioned at 60/15°C. The final stage of softening was inhibited in some seeds by light levels as low as 0.3% of daylight, and in all seeds at a light level between 5 and 25%. A close negative linear relation was obtained between the log of the time taken for 50% of seeds to precondition and the constant temperature treatment between 30°C and 70°C, with the rate of preconditioning doubling with every 5.2°C rise in temperature within this range. Although many seeds preconditioned at the soil surface, the main constraint to completion of the seed softening process during autumn was the inhibitory effect of light.

Long-term softening of surface and buried hard seeds of yellow serradella grown in a range of environments

A 3-year field experiment was conducted to investigate seed softening in yellow serradella (Ornithopus compressus L.) in a low rainfall Mediterranean environment at Merredin, Western Australia. The study examined seeds of 4 accessions of serradella from separate growing sites (Pindar, Merredin, and Badgingarra), and included the effect of pod burial (only for accessions grown at Merredin). Pods were placed on the soil surface in December 1992 and sampled in March, June, and October for the next 3 years. Burial treatments (2 and 6 cm beneath the surface) commenced in June 1993 after pods had been on the soil surface for one summer. Samples were collected in June for the next 2 years. Softening of seeds over the first summer in the field was compared with that obtained in the laboratory with 16 weeks at a diurnally alternating temperature of 60/15ºC. Few seeds of any accession softened (generally <6%) at the soil surface during the first summer but the rate of softening increased over the next 2 years. The highest annual rate of softening was about 55% in the third year in accessions GEH72-1A and GEH72-2A. Accession of serradella hadmore influence on pattern of seed softening than site at which seeds were produced. Burial of pods at 2 cm markedly accelerated seed softening in all strains, particularly GEH72-1A and cv. Madeira, in which over 95% of hard seeds softened during the first year of burial. Softening at 6 cm was similar to that at the soil surface. Shallow burial of pods, as would occur during cereal cropping in one year,could improve regeneration of serradella, but reduce the longevity of its seed bank. Laboratory treatment at 60/15ºC generally over-estimated field softening during the first summer.The spread of germination in time in laboratory tests differed between accessions and was much wider in GEH72-2A than in others, extending up to 35 days. Such behaviour could provide insurance against total seedling loss following false breaks of season.

Field persistence of Bradyrhizobium sp. (Lupinus) inoculant for serradella (Ornithopus compressus L.)

Experiments were conducted, in situ in north-western New South Wales and in the laboratory, to evaluate the longevity of Bradyrhizobium sp. (Lupinus) inoculated as a peat culture onto seed of yellow serradella (Ornithopus compressus L.). Observations were made on the field persistence of the inoculant strain over 2 years. Two categories of seed were examined: seed encased in a segment of pod coat (hulled), and seed from which the pod coat had been removed (dehulled). The use of adhesive (methyl cellulose or gum arabic) ensured that the inoculant adhered to the seed. At a constant temperature of l8�C, inoculant applied to hulled seed survived for >8 months without loss of viability. Type of adhesive did not affect survival. At the 2 field sites, inoculated seed was sown into dry soil. Inoculant was sufficiently viable for 77-159 days to colonise the rhizospheres of young serradella and to form nodules on a significant (P<0.05) proportion of the plants. Rhizosphere colonisation and nodulation were better with hulled seed than with dehulled seed but were not affected by type of adhesive. Evidence is presented that the inoculant was able to establish in these soils as a permanent component of the soil microflora and to persist as a reservoir of inoculum for annually regenerating serradella.

Genetic Structure and Symbiotic Characteristics of a Bradyrhizobium Population Recovered from a Pasture Soil

We examined the genetic structure and symbiotic characteristics of Bradyrhizobium isolates recovered from four legume species (Lupinus albus [white lupine], Lupinus angustifolius [blue lupine], Ornithopus compressus [yellow serradella], and Macroptilium atropurpureum [sirato]) grown in an Oregon soil. We established that multilocus enzyme electrophoresis (MLEE) can provide insights into the genetic relatedness among Bradyrhizobium strains by showing a positive correlation (r = >/=0.90) between the relatedness of Bradyrhizobium japonicum strains determined by MLEE at 13 enzyme loci and that determined by other workers using either DNA-DNA hybridization or DNA sequence divergence estimates. MLEE identified 17 electrophoretic types (ETs) among 95 Bradyrhizobium isolates recovered from the four hosts. Although the overall genetic diversity among the ETs (H = 0.69) is one of the largest measured to date in a local population of any soilborne bacterial species, there was no evidence of multilocus structure (linkage disequilibrium) within the population. The majority of the isolates (73%) were represented by two closely related ETs (2 and 3) which dominated the root nodules of white lupine, serradella, and siratro. In contrast, ET1 dominated nodules of blue lupine. Although representative isolates from all of the 17 ETs nodulated siratro, white lupine, blue lupine, and big trefoil (Lotus pedunculatus), they were either completely ineffective or poorly effective at fixing nitrogen on these hosts. Despite the widespread use of serradella as a surrogate host for lupine-nodulating bradyrhizobia, 7 of the 17 ETs did not nodulate this host, and the remaining 10 ETs were ineffective at fixing nitrogen.

Critical phosphorus concentrations for burr medic, yellow serradella, subterranean clover, and wheat

Abstract The relationship between plant yield and the phosphorus (P) concentration in dried tops and seed of burr medic (Medicago polymorpha), yellow Serradella (Ornithopus compressus), subterranean clover (Trifolium subterraneum), and wheat (Triticum aestivum) was determined, and critical P, which is the P concentration in tissue that is related to 90% of the maximum yield of each species at each harvest, was interpolated. Critical P data are limited for subterranean clover and wheat, which are widely grown in south‐western Australia. There are no critical P data for burr medic and yellow senadella, two new pasture legumes. For each species, critical P varied, often markedly, for different experiments. For all species, (i) critical P in dried tops generally decreased with increasing maturity, (ii) critical P was larger for seed than dried tops near maturity.

Effect of grazing intensity and number of grazings on herbage production and seed yields of Trifolium subterraneum, Medicago murex, and Ornithopus compressus

The impact of grazing intensity and number of grazings was assessed on the growth and seed production of 5 annual pasture legumes [Trifoliunz subterraneum var. subterraneum cv. Karridale, var. brachycalycinum cv. Clare, var. yanninicum cv. Trikkala; Medicago murex (murex medic) cv. Zodiac; Ornithopus compressus L. (yellow serradella) cv. Avila]. There were 7 grazing treatments: an ungrazed control; and 2 grazing intensities (light and heavy), each for 3 periods of grazing (winter, winter-early spring, winter-late spring). Tethered sheep in small experimental plots were used to provide controlled herbage removal across all cultivars through winter and winter-spring grazing. This grazing system resulted in significantly different levels of herbage being present in the light and heavy grazing treatments following each grazing period. Grazing had variable effects on seed production: <35% increase for Trikkala, and no significant effect for Karridale. Both cultivars continued growth and seed production late in the season after grazing pressure was removed on 8 November. Seed yield of Clare was reduced by 46-49% by heavy grazing treatments. Seed yield of murex medic was not significantly affected by grazing, while that of serradella was reduced by 30-55% by grazing late in the season. The seed yield responses show that cultivar and species responses to grazing may be highly variable. Under favourable spring conditions, Trikkala, Karridale, and murex medic can be grazed heavily until late in the season without adversely affecting seed yield, whilst Clare and Avila cannot.

Effect of external phosphorus and seed phosphorus supply on the shoot and root growth of yellow serradella, burr medic, and subterranean clover

Abstract Glasshouse studies were undertaken to compare the responses of yellow sertadella, subterranean clover, and burr medic to changes in phosphorus (P) supply. Shoot growth at 35–50 days after sowing was related to differences in their physical root characteristics and their ability to take up P under conditions of limiting and adequate P supply. Subterranean clover and burr medic were also compared in their shoot response to applied P when seed with differing concentrations of P was sown. Where P supply limited the growth of subterranean clover shoots by at least 40%, yellow sertadella produced more shoot weight, had a lower root and shoot ratio, and longer, thinner roots than both subterranean clover and burr medic. Burr medic produced less shoot weight, had a higher root and shoot ratio and shorter, thicker roots than the other two species. Yellow serradella was also able to take up more P (greater shoot P content per gram root and per meter length root) than subterranean clover, whereas burr medic...

Comparison of the phosphate requirements of burr medic and yellow serradella with that of wheat in the low rainfall wheatbelt of Western Australia

The responses of burr medic (Medicago polymorpha) and yellow serradella (Ornithopus compressus) to topdressed phosphate were compared with the response of wheat (Triticum aestivum) to drilled phosphate on a range of soils in the low rainfall wheatbelt of Western Australia. Species were compared firstly on the amount of applied phosphorus (P) required for 90% maximum yield at 3 harvests, and secondly on the ratio of their curvature coefficients from the Mitscherlich relationship between absolute yield and P applied. On 7 marginally acidic, medium-textured soils, the comparative requirements of burr medic (cvv. Serena or Santiago) and wheat (cv. Gutha) for applied P changed with harvest. At harvest 1 152-55 days after sowing (DAS)], burr medic generally had a larger curvature coefficient and required less applied P for 90% maximum yield than wheat. At harvest 2 (107-111 DAS) and for harvest 3 (seed yields), the curvature coefficients for burr medic were smaller than those for wheat, and burr medic generally required more applied P at 90% maximum yield. The average P requirement at 90% maximum yield of burr medic was 14 kg P/ha at harvest 1, 22 kg P/ha at harvest 2, and 19 kg P/ha for seed production. The average P requirement of wheat was 28 kg P/ha at harvest 1,11 kg P/ha at harvest 2, and 15 kg P/ha for seed production. On 3 acidic, light-textured soils, yellow serradella (cv. Madeira) generally had a lower requirement for applied P at 90% maximum yield, and a larger curvature coefficient, than wheat (cv. Gutha) at all harvests in each experiment. The requirements of yellow serradella and wheat also varied between harvests. The average P requirement at 90% maximum yield of yellow serradella was 16 kg P/ha at harvest 1 (52-55 DAS), 21 kg P/ha at harvest 2 (105-110 DAS), and close to 26 kg P/ha for seed production. The average P requirement of wheat was 29 kg P/ha at harvest 1,25 kg P/ha at harvest 2, and >33 kg P/ha for seed production. In most experiments burr medic had a larger absolute response to applied P at harvests 1 and 2 and a lower absolute response for seed production than wheat. Yellow serradella had a smaller absolute yield response to applied P than wheat over all 3 harvests. When converted to a percentage of maximum yield, burr medic and yellow serradella had a lower percentage response to applied P at harvest 1, and a higher percentage response at harvest 2 and for seed production than wheat.

Comparison of the phosphate requirements of burr medic and yellow serradella with subterranean clover in the low rainfall wheatbelt of Western Australia

Burr medic (Medicago polymorpha) and yellow serradella (Ornithopus compressus) were compared with subterranean clover (Trifolium subterraneum) in their response to freshly topdressed phosphate in the low rainfall wheatbelt of Western Australia. Species were compared on the amount of applied phosphorus (P) required for 90% maximum yield and the ratio of their curvature coefficients from the Mitscherlich relationship between P applied and absolute yield. On marginally acidic, medium-textured soils, burr medic had a higher external shoot requirement for applied P than subterranean clover. Relative differences between the species were affected by season, initial concentration of bicarbonate-extractable P in the soil (0-10 cm), and timing of plant harvest during the growing season. Burr medic generally achieved a higher absolute maximum yield at each harvest, a larger absolute yield response, and a larger percentage response to applied P than subterranean clover. There was no difference between burr medic and subterranean clover with respect to the internal efficiency of P use for shoot production. For seed production, the external requirements of burr medic and subterranean clover for applied P were similar according to the criterion of P required at 90% maximum yield, but burr medic had a higher requirement if curvature coefficient was the criterion for comparison. Burr medic also had a higher internal efficiency of P use for seed production than subterranean clover. On an acidic, light-textured soil, yellow serradella had a lower requirement for applied P than subterranean clover, according to both criteria for all harvests in 2 separate years.

Response of defoliated swards of subterranean clover and yellow serradella to superphosphate applications

The effect of superphosphate applications (0, 25, 50, 75, 100 and 125 kg P/ha to the soil surface) on the dry matter (DM) herbage production of dense swards of subterranean clover (Trifolium subterraneum cv. Junee) and yellow serradella (Ornithopus compressus cv. Tauro) was measured in a field experiment on deep, sandy soil in south-western Australia. The swards were defoliated with a reel mower at weekly intervals from 88 to 158 days after sowing, to a height of 2 cm for the first 9 cuts, 4 cm for the tenth cut and 5 cm for the eleventh cut. Yellow serradella was more productive than subterranean clover. Consequently, for the relationship between yield and the level of phosphorus (P) applied, yellow serradella supported larger maximum yields and required less P than subterranean clover, to produce the same DM herbage yield. Maximum yields of yellow serradella were 12-40% larger. To produce 70% of the maximum yield for yellow serradella at each harvest, yellow serradella required about 50% less P than subterranean clover. However, when yields were expressed as a percentage of the maximum yield measured for each species at each harvest, the relationship between yield and the level of P applied was similar for both species, and they had similar P requirements.

Comparative phosphate requirements of yellow serradella (Ornithopus compressus) burr medic (Medicago polymorpha var. brevispina) and subterranean clover (Trifolium subterraneum)

The phosphate (P) requirements of burr medic (Medicago polymorpha) on marginally acidic, medium-textured soils and yellow serradella (Ornithopus compressus) on acidic, light-textured soils in the low rainfall (<400 mm) wheatbelt of Western Australia are not known. The hypothesis that yellow serradella, subterranean clover (Trifolium suhrerraneum) and burr medic have the same external requirement for applied P was tested in a glasshouse trial on 2 P-deficient soils. Species were compared on an equal total seed weight and similar maturity length basis. It was found that yellow serradella required less soil applied P to achieve 90% maximum shoot production or total plant (shoots + roots) growth and had a greater curvature co-efficient from fitted Mitscherlich functions than either subterranean clover or burr medic. Burr medic was the most responsive to applied P and had the largest external requirement for applied P. These differences in external P requirements were related to differences in ability of the 3 legumes to absorb P and to transport it to their shoots and were not due to differences in internal efficiency of the shoots. Yellow serradella was able to take up more P (total plant P content) per g roots than subterranean clover, and subterranean clover more than burr medic. The same relationship applied to the translocation of absorbed P from roots to shoots.

Effect of seed source and seed phosphorus concentration on the yield response of yellow serradella to superphosphate applications

A field experiment at Medina, Western Australia, was designed to test whether seed produced at different locations and containing different phosphorus (P) concentration in the seed would change the relationship between yield and the level of superphosphate drilled with the seed. To produce the seed for the experiment, subsamples of the same source of seed of yellow serradella (Ornithopus compressus cv. Madeira) were grown at Medina and Esperance, Western Australia. Seed of the same size produced at each location, and containing 3 different P concentrations, was sown in the experiment at Medina. Three levels of superphosphate were drilled with the seed. Yields (of dried herbage and seed) were increased 2- to 4-fold as the amount of P drilled with the seed was increased from 5 to 40 kg P/ha. Although the Medina seed contained >0.40% P and the Esperance seed contained <0.40% P, plants grown from Esperance seed produced larger yields than plants grown from Medina seed for each of the 3 levels of P drilled with the seed; yield difference increased from about 14 to 70% as the level of P drilled with the seed increased from 5 to 40 kg P/ha. Higher P concentration in the sown seed increased herbage and seed yields by 35-70% when 5 kg P/ha superphosphate was drilled with the seed, and by about 616% when 40 kg P/ha was P drilled with the seed. Seed grown at Esperance produced larger yields for each seed P concentration than Medina seed; yield differences were about 30-90%. The P concentration measured in dried herbage and seed depended only on the amount of P drilled with the seed. It was unaffected by the P concentration in the seed sown, and for dried herbage, it was unaffected by where the seed sown was produced. However, for seed production, the relationship between yield and P concentration in the seed differed depending on where the seed was grown.