Subterranean Clover Cultivars Research Articles

Hard seed breakdown patterns of serradella (Ornithopus spp.) in two contrasting environments of south-eastern Australia

Context There is interest in using serradella (Ornithopus spp.) in permanent pastures of the high rainfall zone of south-eastern Australia. However, there is little information concerning levels of hardseededness or patterns of seed softening in these environments. Aim This study quantified seed softening of serradella species in comparison with subterranean clover (Trifolium subterraneum L.) in the Southern Tablelands and Central Slopes districts of eastern Australia. Methods Mature seeds were placed in mesh pouches on the soil surface and were retrieved periodically to assess residual hard seed proportions throughout the growing season(s) in four experiments conducted over 2018 and 2019. Key results Patterns of seed softening among adapted cultivars of subterranean clover were consistent: initially high proportions of hard seed, followed by rapid softening from mid-summer to the end of autumn with the remnant portion of seeds remaining hard. In contrast, diverse patterns of seed softening were observed among serradella cultivars, ranging from highly soft-seeded through to high initial hard seed portions that either softened rapidly or softened over a lengthy period. Rates of seed softening were faster in the warmer/drier environment of Cowra compared to the wetter/cooler environment of Canberra. Conclusions The study revealed seed softening patterns among serradellas to be diverse and different to subterranean clover. This will affect management and suitability of serradella cultivars for permanent pastures. Implications In permanent pastures, serradellas that soften slowly over several years are likely to have limited regeneration in the year after pasture establishment with a high potential for weed invasion.

Phenological development of subterranean clover cultivars under contrasting environments

AbstractSix subterranean clover cultivars (representing early and late flowering genotypes from three subspecies) were used to describe and quantify their phenological development. The vegetative (V) and reproductive (R) development phases, in response to different environments created by eight sowing dates were quantified. The period from sowing to emergence was constant in thermal time at 110°Cd and the first trifoliate appeared at ~300°Cd. Crops sown in autumn had the longest period from runner initiation until floral bud initiation (R1), which would allow an extended period of grazing, particularly for later flowering cultivars like ‘Denmark’. To maximise seed set (particularly in year 1) a maximum period between R3 and R11 is required (seed set window). This ranged from 319 ± 42.3°Cd for ‘Leura’ to 661 ± 73.1°Cd for ‘Narrikup’. The complete crop life cycle from sowing (V0) to maturity (R11) ranged from 1269 ± 31°Cd (equivalent of 123 ± 6.3 days) for ‘Antas’ sown in July to 2799 ± 47°Cd (300 ± 3.9 days) for ‘Woogenellup’. When sowing occurred in an increasing photoperiod (June–November) the life cycle of all cultivars was 59% shorter than when sown in a decreasing photoperiod. The numeric scale was able to describe all the variation in the phenological phases and could be used to quantify thermal time requirements for specific phenophases. This would allow subterranean clover management to be optimised (husbandry, grazing and seed harvest) at a local level, and provides the basic parameters for inclusion in annual pasture simulation models.

Causes of leaf reddening in subterranean clover cultivars

ABSTRACT Subterranean clover (Trifolium subterraneum L.) is an important legume in dryland hill pastures in New Zealand. In this environment plants adapt to low temperatures (<10°C) through a series of physiological mechanisms, such as the foliar biosynthesis of pigments, to protect vulnerable tissues. The biosynthesis of anthocyanins is one of the most important physiological responses for cold acclimation in plants. In this study we investigated anthocyanin concentration by accessing leaf reddening in 14 cultivars from three subspecies (yanninicum, brachycalycinum or subterraneum) during winter growth. The effect of anthocyanin production on spring herbage productivity was further quantified in the field and in the glasshouse. Leaf concentration of anthocyanins increased 10-fold as a consequence of cold exposure (mean daily air temperature was below ∼7°C) in red leaves compared with green leaves. There were large cultivar differences with yanninicum ssp. cultivars having the highest leaf reddening at >60%. Lowest values were observed in ‘Antas’ (brachycalycinum ssp.) and ‘Denmark’ (subterraneum spp.) at <20% of leaf reddening. Australian subterraneum ssp. cultivars had 13% higher leaf reddening values than Italian cultivars. Leaf reddening was a temporary, cold induced, anthocyanin response that did not affect subsequent subterranean clover plant growth.

Morphological diversity within a core collection of subterranean clover (Trifolium subterraneum L.): Lessons in pasture adaptation from the wild.

Subterranean clover (Trifolium subterraneum L.) is a diploid self-pollinated annual pasture legume native to the Mediterranean region and widely sown in southern Australia and other countries with Mediterranean-type climates. This study utilised a core collection of 97 lines, representing around 80% of the genetic diversity of the species, to examine morphological diversity within subterranean clover. A total of 23 quantitative agro-morphological and 13 semi-quantitative morphological marker traits were assayed on the core collection and 28 diverse Australian cultivars as spaced plants in a replicated common garden experiment. Relationships between these traits and 24 climatic and edaphic parameters at their sites of origin were also examined within the core collection. Significant diversity was present for all traits. The Australian cultivars had similar levels of diversity to the core collection for several traits. Among the agro-morphological traits, time to flowering, leaf size and petiole diameter in mid-winter, plant area in late winter, maximum stem length, content of the oestogenic isoflavone biochanin A and total isoflavone content, were correlated with seven or more environmental variables. These can be considered highly adaptive, being the result of strong environmental selection pressure over time. For the first time in a clover species, morphological markers, including leaf mark, anthocyanin pigmentation and pubescence traits, have been associated with rainfall and soil parameters. This suggests they either have an adaptive role or the genes controlling them may be linked to other genes controlling adaptive traits. This study demonstrated the value of core collections to examine diversity within much larger global collections. It also identified adaptive traits from wild plants that can be utilised to develop more productive and persistent subterranean clover cultivars. The high heritability of these traits indicates that selection gains can be readily made.

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.

Thermal time requirements for germination of four subterranean clover cultivars

ABSTRACT In vitro germination tests were performed at 11 constant temperatures (range 2.5–35°C) to quantify the maximum germination percentage and germination rate of four subterranean clover cultivars (‘Antas’, ‘Denmark’, ‘Monti’ and ‘Narrikup’). These were used to estimate their cardinal temperatures, base (Tb ), optimum (T opt) and maximum (Tmax) and the thermal time requirements for seed germination. Germination percentages were ≥ 88% in the 5–25°C temperature range for all cultivars. The time to reach 50% of final germination (T 50) decreased from 12 to 2 days as the temperature increased from 2.5 to 17.5°C. The determined T opt were 16°C for ‘Monti’ and ‘Narrikup’ and 22°C for ‘Antas’ and ‘Denmark’. At a common Tb of 0°C the thermal time requirements for T 50 were 32 ± 1°Cd for ‘Antas’ and ‘Denmark’ and 39 ± 1°Cd for ‘Narrikup’ and ‘Monti’. ‘Antas’ and ‘Denmark’ (both from Italy) germinated at the widest range of temperatures.

Prospects for improving perennial legume persistence in mixed grazed pastures of south-eastern Australia, with particular reference to white clover

This review examines the prospect of improving perennial legume adaptation to grazed mixed pasture swards across the higher-altitude regions of south-eastern Australia through improved management, particularly as it relates to soil fertility. The range of adapted perennial species available to farmers often remains limited to only one perennial forage legume species, white clover (Trifolium repens L.). Despite recent advances in cultivars for increased persistence in dryland environments, white clover remains sensitive to drought with its inherently shallow root system and limited capacity to restrict water loss from herbage. With few alternative species likely to become widely available in the foreseeable future, prospects for extending the boundaries of perennial legume adaptation likely rely on a dual approach of improving soil fertility and further genetic improvement in white clover. Improved soil fertility would focus on overcoming soil acidity and addressing nutrient deficiencies, particularly of phosphorus, potassium, boron and molybdenum, which tend to be more widespread in the target region. Addressing these soil constraints would alleviate periodic moisture stress by: (1) increased water availability through improved infiltration and soil hydraulic properties; (2) increased root growth to maximise exploration of the soil volume; and (3) better maintenance of plant cell structures to foster improved osmotic regulation. However, the extent to which white clover adaption may be extended remains an issue of further research. This review highlights an opportunity for further genetic improvement of white clover by focusing on improving the capacity to recover from periodic droughts through seedling regeneration. Further breeding efforts in white clover should examine the feasibility of selecting for hard seed characteristics more similar to the best-adapted subterranean clover (Trifolium subterraneum L.) cultivars across this region to promote ongoing seedling regeneration.

Establishment, production and regeneration of subterranean clovers in the Mackenzie Basin, New Zealand

The ‘Red Flats’ on Omarama Station in the Mackenzie Basin, has a winter cold, summer dry environment and soils with low plant available water (&lt;60 mm in the top 1 m), and low pH(H2O) (5.2) and high aluminium (8 mg/kg) below 75 mm. The site received 3 t of lime, 300 kg sulphur-super, boron (B), molybdenum (Mo) and herbicides to eliminate hieracium (Hieracium pilosella). Twelve cultivars of subterranean clover (Trifolium subterraneaum), ‘Bolta’ balansa clover (T. michelianum), and perennial ‘Rossi’ red clover (T. pratense), were direct-drilled in February 2016. Over the next 3 years their frost tolerance, productivity and persistence were compared with the resident haresfoot clover (T. arvense). Balansa and the subterranean clovers all survived the 2016 and 2017 winters. The subterranean clovers maximum yield was 4.3 t DM/ ha after successful germination in February 2016 when sufficient rain extended the spring growing season into November. Subterranean clover cultivars from subspecies subterraneum yielded well in 2016, averaging 3.3 t DM/ha, as did the brachycalycinum ‘Antas’ with 3 t DM/ha. During the short season of 2017, the subterraneum ssp. cultivars ‘Denmark’ and ‘Karridale’ established the highest ground covers and ‘Antas’ the lowest. In 2018, ‘Antas’ had the lowest emergence rate and autumn yield. ‘Karridale’ had the highest re-establishment rate and the yanninicum ‘Trikkala’ the highest autumn yield (1.3 t DM/ha). Cultivars with low hardseededness ratings were the most successful at re-establishment in autumn 2017. Balansa clover was also persistent. In the favourable 2016 growing season the late-flowering resident haresfoot clover grew into early summer and yielded 3.7 t DM/ha. Red clover yielded 1 t DM/ha in 2016, but did not persist. Results suggest that medium-late flowering softer seeded subterranean clover cultivars and ‘Bolta’ balansa clover, are suitable for this environment.

Seed yield and subsequent emergence pattern of subterranean clover cultivars in response to summer rain

At Lincoln University, Canterbury, seven subterranean cultivars rated in Australia as having different levels of ‘hardseedeness’ were established. Monocultures were sown in autumn and allowed to grow and set seed. Seed yields ranged from 340 to 1050 kg/ha. Heavy rain in early January 2016 resulted in a “false strike” of ≤ 4.0% of seeds during the subsequent dry February. A second emergence event in March also resulted in a “false strike” with a further 7 to 15% of total seeds lost. However, cultivars established &gt;1000 seedlings/m2 after early winter rain, which is considered adequate for future persistence. Emergence was consistent with Australian hardseededness rankings. Cultivars with hardseed ranks &lt;4 may be more suitable for dryland systems in New Zealand due to their early emergence and the ability to exploit the late summer and autumn rains.

Adaptation of ecotypes and cultivars of subterranean clover (Trifolium subterraneum L.) to German environmental conditions and its suitability as living mulch

Abstract A total of 320 accessions of subterranean clover (Trifolium subterranenum L.) were screened for adaptation to the environmental conditions in southern Germany, as well as their suitability as cover crops or living mulches. The accessions, derived from collections of the Department of Agriculture and Food Western Australia and the International Research Center for Agriculture in Dry Areas, were propagated in the greenhouse and grown in rows. Selected accessions were then tested in plots and as an intercrop in wheat, in order to test their suitability as living mulch. Moreover, a frost resistance screening was carried out in a climate chamber. Adaptation to southern German conditions and frost tolerance was generally better than expected, as most accessions survived winters with snow cover and transitory temperatures as low as \(-\,10\,^\circ \)C. Accessions with particularly high frost tolerance were identified and several accessions persisted over four generations of self-reseeding. Although there was a large range of morphological characteristics, no differences concerning their suitability as living mulch could be observed. The results suggest that subterranean clover is sufficiently winter hardy to be grown as an overwintering cover crop or living mulch in southern Germany. Commercially available cultivars appear suitable in the first instance, even though these have not been selected for cold winters. However, adaptation might be further improved by targeted selection among accessions.

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.

Investigating and modeling the combined effects of pH and osmotic pressure on seed germination for use in phytoactivity and allelopathic research

Phytoactivity and allelopathic studies are heavily dependent on germination bioassays of water solutions of allelochemical(s), which necessarily imply that pH and osmotic pressure vary among treatments and between treatments and controls and are therefore a confounding factor in the assessment of seed germination responses to allelochemical(s). When the contribution of pH and osmotic pressure to seed germination responses is considered in experimental designs their effects are almost without exceptions examined separately being assumed, without any evidences, that pH and osmotic pressure act independently on seed germination responses. The objectives of this work were to examine experimentally such assumption using wheat, lettuce, and subterranean clover cultivars to evaluate and model the combined effects on germination of pH and osmotic pressure in the range between 3.0–6.0 and 0–100 mOsmol kg−1, respectively. Empirical equations are fitted, discussed, and the need to consider the simultaneous effects of pH and osmotic pressure firmly established. Finally, the use of the equations fitted and its impact on conclusions is exemplified in a dose-response bioassay of water extracts of Cistus ladanifer on seed germination using subterranean clover as target species where hormesis was found before allelochemical effects were corrected for pH and osmotic pressure values of control and extracts.

Diversity within subterranean clover and biserrula for persistence traits with potential use in New Zealand hill country

As part of an investigation into the potential of alternative forage species and/or germplasm in New Zealand's hill country and the traits required for their success, two F2 populations, their original parents, and 34 cultivars of subterranean clover (Trifolium subterranean) were evaluated for hardseededness in Australia. The 34 cultivars were also screened for burr burial strength and flowering time. Microsatellite markers were also used to investigate their association with these traits. The polygenic nature of hardseededness was confirmed and markers associated with this trait were detected and traits for New Zealand's hill country were identified. Additionally, a core collection of 30 (two cultivars and 28 wild) biserrula (Biserrula pelecinus) accessions was screened for flowering time, growth habit and leaflet size. Also, a subset of five accessions of biserrula exhibited traits that are desirable for hill country, namely, mid-late flowering and adaptation to lowmedium rainfall. Keywords: biserrula, flowering time, hardseededness, hill country, subterranean clover

Selection of sub clover cultivars for New Zealand dryland pastures

New Australian-bred cultivars of subterranean (sub) clover with high levels of hardseededness are being promoted in New Zealand based on their superior performance in Australia. These new cultivars may not be suited to cooler New Zealand conditions. The "soft" seeded sub clover 'Denmark' dominated the hardseeded cultivar 'Rosabrook' in the second year of a dryland grazing experiment near Lincoln (630 mm mean annual rainfall), but in autumn of the third year the 'Rosabrook' population recovered to contribute 30% of total sub clover plants. A second field experiment, sown in March 2014 at Lincoln University, compared 10 sub clover cultivars sown with cocksfoot. 'Antas', 'Narrikup' and 'Woogenellup' were most productive at the September 2014 harvest. 'Antas', 'Woogenellup' and 'Leura' had the highest dry matter yields at the November 2014 harvest. In autumn 2015 'Narrikup' re-established most seedlings and 'Antas' the least. Until we have better knowledge of the production and persistence of "new" sub clover cultivars under New Zealand conditions, farmers are urged to sow binary mixtures (50:50) of a "new" plus an "older" cultivar. Keywords: cocksfoot, Dactylis glomerata, grazing experiment, hardseededness, re-establishment, Trifolium subterraneum

Genetic improvement of subterranean clover (Trifolium subterraneum L.). 2. Breeding for disease and pest resistance

Subterranean clover (Trifolium subterraneum L.) is the most widely sown pasture legume in southern Australia and resistance to important diseases and pests has been a major plant-breeding objective. Kabatiella caulivora, the cause of clover scorch, is the most important foliar fungal pathogen, and several cultivars have been developed with resistance to both known races. Screening of advanced breeding lines has been conducted to prevent release of cultivars with high susceptibility to other important fungal foliar disease pathogens, including rust (Uromyces trifolii-repentis), powdery mildew (Oidium sp.), cercospora (Cercospora zebrina) and common leaf spot (Pseudopeziza trifolii). Several oomycete and fungal species cause root rots of subterranean clover, including Phytophthora clandestina, Pythium irregulare, Aphanomyces trifolii, Fusarium avenaceum and Rhizoctonia solani. Most breeding efforts have been devoted to resistance to P. clandestina, but the existence of different races has confounded selection. The most economically important virus diseases in subterranean clover pastures are Subterranean clover mottle virus and Bean yellow mosaic virus, while Subterranean clover stunt virus, Subterranean clover red leaf virus (local synonym for Soybean dwarf virus), Cucumber mosaic virus, Alfalfa mosaic virus, Clover yellow vein virus, Beet western yellows virus and Bean leaf roll virus also cause losses. Genotypic differences for resistance have been found to several of these fungal, oomycete and viral pathogens, highlighting the potential to develop cultivars with improved resistance. The most important pests of subterranean clover are redlegged earth mite (RLEM) (Halotydeus destructor), blue oat mite (Penthaleus major), blue-green aphid (Acyrthosiphon kondoi) and lucerne flea (Sminthurus viridis). New cultivars have been bred with increased RLEM cotyledon resistance, but limited selection has been conducted for resistance to other pests. Screening for disease and pest resistance has largely ceased, but recent molecular biology advances in subterranean clover provide a new platform for development of future cultivars with multiple resistances to important diseases and pests. However, this can only be realised if skills in pasture plant pathology, entomology, pre-breeding and plant breeding are maintained and adequately resourced. In particular, supporting phenotypic disease and pest resistance studies and understanding their significance is critical to enable molecular technology investments achieve practical outcomes and deliver subterranean clover cultivars with sufficient pathogen and pest resistance to ensure productive pastures across southern Australia.

Sheep grazing bladder clover (Trifolium spumosum L.) had similar productivity and meat quality to sheep grazing subterranean clover (Trifolium subterraneum L.)

An accession of bladder clover, a new species to agriculture, was selected for commercial release in Australia with the cultivar name of AGWEST Bartolo. As part of a duty-of-care assessment, we tested the hypothesis that sheep grazing the bladder clover cultivar will have similar liveweight, condition scores and wool production to sheep grazing a widely adopted subterranean clover cultivar (cv. Dalkeith). Further, we hypothesised that sheep grazing bladder clover and subterranean clover will have similar meat quality (after 48 days of grazing) and health as indicated by muscle, liver and kidney panel analysis. The data supported the hypotheses. While there were significant initial differences in liveweight between the two groups of sheep, there were no significant differences in liveweight at later time points during the grazing period and no significant differences in mean daily growth rate between weighing times. There were no differences in wool growth between sheep grazing the bladder or subterranean clover cultivars. Sheep in the subterranean clover plots had significantly higher condition scores after the first 24 days of grazing; however, these differences were not apparent after another 24 days of grazing. There were some differences in indications of animal health; however, there were no significant detrimental effects associated with bladder clover and sheep grazing both species had mean plasma indicators that were deemed ‘healthy’. There were no differences in meat eating quality as estimated by a consumer panel for tenderness, juiciness or flavour. Dry seasonal conditions limited biomass growth and the sheep were removed from the subterranean clover plots on Day 48 of grazing. The sheep grazing the bladder clover plots remained on the plots for a further 26 days. The data indicate that, for the conditions of this experiment, the clovers had the same relative feeding value. Laboratory analysis of herbage from across the clover plots (bulked before analysis) suggest that the bladder clover had higher in vitro digestibility, crude protein and lower fibre than the herbage sample from the subterranean clover plots. The biomass data indicate that the bladder clover cultivar can support more grazing days per ha in a relatively dry season than the subterranean clover cultivar.

The career and contribution to Australian and international agricultural science of Clive McDonald Francis: an introduction

Dr Clive Francis is amongst a small group of scientists whose efforts have changed the face of Australian agriculture. This special issue of Crop &amp; Pasture Science highlights his broadranging impact delivered through the pasture cultivars he bred, the knowledge that he generated and the influence that he had on peers and policy makers. His cultivars of subterranean clover are still grown on many millions of hectares across southern Australia and his efforts were pivotal in generating momentum for creative research on a wide array of crop and pasture legumes, particularly the collection, evaluation and preservation of genetic resources for use in current and future breeding initiatives.

Infertility in the Southern White Rhino: Is Diet the Source of the Problem?

Infertility in the Southern White Rhino: Is Diet the Source of the Problem?

Estimating the contribution of nitrogen from legume cover crops to the nitrogen nutrition of grapevines using a 15N dilution technique

Cover cropping is increasingly being used as a form of sustainable soil management in grapevine (Vitis vinifera L.) production. The objective of the current study was to determine the effect of a legume cover crop on a set of growth and production variables of a vineyard, and to quantify the relative importance of legume nitrogen (N) as a source of N for the vine plants and to compare this to the current recommended practice of annually applying 40 kg fertilizer-N ha-1. The study was carried out in a 5-yr-old vineyard cv. Cabernet Sauvignon at the Cauquenes-INIA Experimental Center in one of the wine production areas of Chile. The treatments were: control without cover crop (C); a legume mixture of early maturing cultivars of subterranean clover (Trifolium subterraneum L.) and burr medic (Medicago polymorpha L.) (EMC); or a legume mixture of late maturing cultivar of subterranean clover and balansa clover (T. michelianum Savi) (LMC). Average inputs of legume N generated by the EMC and LMC treatments represented 112 and 161 kg above-ground legume N ha-1yr-1, respectively. Grape dry matter production was increased significantly (P ≤ 0.05) by 48–61% and the amount of N accumulated in grape bunches was enhanced by 74–105% after 2 years of legume cover crop. However, no significant (P > 0.05) effects of cover cropping were observed on vine leaf, canes, roots or trunk biomass. To estimate the relative contribution of legume and fertilizer N to the N nutrition of grapevines 15N-enriched fertilizer (10 atom% 15N excess) was applied to the soil in micro-plots within all treatments as two split applications of 20 kg N ha-1. The 15N composition of vines grown with or without cover crops were subsequently compared. Any measured reduction in the 15N enrichment of the tissues of cover cropped vines relative to the nil cover crop control was assumed to have resulted from the uptake of legume N. Recovery of 15N in vine plant parts was used to calculate the efficiency of use of fertilizer N. Surprisingly the 15N data indicated that the fruit had the lowest reliance upon legume N for growth (only 7–13% cf 14–56% of the N in other organs), even though grape bunches were the only plant part to positively respond to the cover cropping treatments. This suggested that either the temporal patterns of N mineralization in soil and N uptake by vines over the growing season was such that much of the mineral N utilized during fruit development was not directly derived from legume residues, or that N remobilized from other plant parts within the vines was the major source of N for grape production rather than N newly assimilated from soil. The amount of legume N estimated to be recovered by cover cropped vine plants (12–15 kg N ha-1), was similar to the calculated contribution from 40 kg of fertilizer-N applied to vines (11-12 kg ha-1). This amount of N represented <10% of the amounts of N annually returned to the soil in above-ground legume material in the case of the cover cropping treatments, and was equivalent to a recovery of 27–30% of the N applied in fertilizer.

Effect of gypsum on establishment, persistence and productivity of lucerne and annual pasture legumes on two grey Vertosols in southern New South Wales

Changes in pasture yield and botanical composition due to gypsum application were examined on Vertosols at two locations of differing soil sodicity, Grogan and Morangarell, in southern New South Wales. Two pasture treatments were examined. One was an annual pasture comprised of 3 annual legumes (2 subterranean clover Trifolium subterraneum L. cultivars, Clare and Riverina, and balansa clover T. michelianum Savi cv. Paradana), while the second treatment consisted of lucerne (Medicago sativa L.) cv. Aquarius sown in a mixture with the same annual legumes. Gypsum had no effect on the establishment or persistence of lucerne at either site. Gypsum increased the number of subterranean clover seedlings present in autumn in annual swards at the more sodic Grogan site in each of the 4 years, but provided no difference when the clover was in a mixture with lucerne. Annual legume seed yields in annual-only swards increased with gypsum by up to 58% at Grogan and 38% at Morangarell. Seed yields of both cultivars of subterranean clover declined as a proportion of the total annual legume seed bank when lucerne was included in the mixture, in contrast to balansa clover (at Grogan) and the naturalised annual legumes, burr medic (M. polymorpha L.) and woolly clover (T. tomentosum L.), which all increased in relative seed yield in the presence of lucerne. Total pasture production at the Grogan site increased with gypsum by up to 15% per annum in annual swards and 36% in lucerne swards depending on the season. Yield responses to gypsum by the lucerne component were observed in 10 of the 13 seasonal yield measurements taken at Grogan. However, total pasture yield and seasonal yields were unaffected by both gypsum and pasture type at the less sodic Morangarell site. It was concluded that sowing a diverse mixture of annual legumes or polycultures was conducive to maintaining productive pastures on these spatially variable soils. Lucerne dried the soil profile (0.15–1.15 m) more than annual pastures at both sites. The combination of gypsum and lucerne enhanced water extraction at depth (0.6–1.15 m) at the Grogan site increasing the size of the dry soil buffer whereas gypsum increased soil water at depth (&gt;0.6 m) under annual swards.