Ronald J Yates

Deep sand soils are inherently fragile with surface layers that are very low in organic matter and clay. Previous studies demonstrate that strategic deep tillage such as soil inversion and deep soil mixing can increase crop production on these soils in Southern Australia. However, the majority of the organic matter and nutrients are concentrated in the top organically stained layer and deep tillage incorporates 50-60 % of the organic layer into the subsoil below 200 mm. The physical composition of the soil (percentage of sand, silt, clay and organic matter) and the chemical properties of the soil (pH, nutrient levels, cation exchange capacity) can strongly influence the soil adsorption of trifluralin. Modest levels of organic matter and clay particles in the topsoil particularly following deep tillage equate to the scant attenuation of herbicides on sandy textured soils. Soil samples (0-100 mm) were collected from three experimental sites; two Arenic Solonetz soils near Esperance and one Arenic Arenosol soil near Geraldton in Western Australia. At all three sites, three experimental treatments were sampled; control (no tillage), deep mixed with a spader to 350 mm and soil inversion with a mouldboard plough to 350 mm. Soil samples were taken on two growing seasons post tillage at Geraldton, three post tillage at Esperance TJM and twelve post tillage at Esperance E1. Tillage reduced the measured soil-liquid partition coefficient (Kd) of trifluralin (p <= 0.05) at all three experimental sites. A greenhouse bioassay was developed to determine if soil changes from strategic tillage at one of the Esperance sites and the Geraldton site could be directly related to herbicide bioavailability at two of the experimental sites. Intact cores were used to maintain integrity of the field soils. Cores from both field sites demonstrated that soil inversion reduced the effective dose of trifluralin (p <0.01) for the bioassay species Lens culinaris. Together these experiments illustrate that strategic deep tillage can increase the bioavailability of trifluralin. These findings offer a valuable insight into the soil behaviour of trifluralin and can help farmers estimate the risk of phytotoxicity based on measurable soil characteristics.

Physical dormancy in seeds is caused by a water-impermeable seed coat. It plays a crucial role in the sustainability of ley farming systems in Mediterranean climates by enabling pasture legumes to regenerate from a soil seed bank. Sophisticated management of the pattern of physical dormancy break can synchronize germination of plants with the optimal growing season, essential to the sustainability of the system. The ability of the maternal plant to reproduce and provide its progeny (seed) with sufficient resources is influenced by both genetic and environmental factors. However, when abiotic (e.g., drought, temperature) or biotic (e.g., pests, diseases) stressors affect the maternal plant during its reproductive phase, the allocation of resources to seeds can vary, leading to variability in physical dormancy outcomes. This genetic × environment interaction is well documented; however, a third factor, management, is less understood. Herein lies a significant knowledge gap, and this is the first review that examines physical dormancy from an agricultural management perspective. In the manuscript, we explore the evolution of physical dormancy in pasture legumes in ley farming systems and how the intensification of agricultural management practices inadvertently affects physical dormancy development and the pattern of release. This intensification threatens the sustainability of ley farming by changing the timing of physical dormancy release, which concomitantly occurs under changed climatic conditions. Therefore, climate change combined with the intensification of agricultural management practices, including pesticide use, altered grazing regimes, and frequency of crop rotation, poses significant challenges to physical dormancy regulation and soil seed bank dynamics in ley farming. We suggest that to combat the impacts of agricultural intensification, detailed studies and breeding programs should focus on selecting legumes with both agricultural and climatic resilience for successful adaptation to evolving agricultural landscapes and ensure continued sustainable productivity.

Forage legumes play a fundamental role in the sustainability of cropping systems, as rotating species with grain crops, intercrops, or winter cover crops. However, their compatibility with rhizobial inoculants needs context-specific studies. The objectives were to evaluate the effectiveness of three species-specific inoculants [Australian granular (AUG), Australian peat (AUP), and American peat (USP)], compared with a non-inoculated control (CNT). These were applied at the recommended and double dose on five Mediterranean forage legumes ( Vicia sativa , Medicago polymorpha , Trifolium michelianum , T. subterraneum , and T. pratense ). Plant growth, nodulation, and relative N 2 fixation were measured. Species-specific variations were observed for each inoculant. Across the average of legume species, AUG demonstrated the highest growth- and nodulation-promoting effects at both standard and double inoculum doses. The USP was the worst inoculant at the standard dose but induced positive effects at double dose. The relative N 2 fixation was only improved at double dose, especially by USP and AUG, whereas only AUP provided significant N 2 fixation enhancements at standard dose. Overall, the double dose was the best strategy for all tested forage legumes. These findings suggest that inoculating Mediterranean forage legumes with selected inoculants, especially at double dose, may be an effective solution to increase their N 2 fixation ability, reduce the use of mineral N fertilizers, and identify the optimal forage legume × inoculant combinations for intercropping systems with cereals.

Context or problem
Selective herbicides control weeds in cereal crops and break down over time, allowing safe planting of legumes in the following years. However due to climatic inconsistencies and changing farming practices, this is not always the case, and residues can inhibit formation of legume/rhizobia symbioses.

Objective or research question
The objectives were to determine whether: i) exposure to triasulfuron, even at extremely low levels, reduces shoot and root growth and nodulation of five diverse and widely sown legume pasture cultivars in Australian farming systems; and ii) sowing legumes prior to recommended plant-back criteria being met for chlorsulfuron, triasulfuron herbicide, clopyralid, and pyroxasulfone herbicides results in unacceptable damage to subsequently sown pasture and crop legumes, causing reduced root and shoot growth, nodulation and N fixation.

Methods
A series of glasshouse and field experiments explored herbicide residue impact on commonly used legumes in dryland farming systems.

Results
A glasshouse study determined triasulfuron at concentration 0.000225 g a.i/ha, a (1/100,000) dilution of the label rate caused significant (p < 0.001) decrease in nodule count, root length, root, shoot weight for Trifolium spumosum cv. Bartolo and T. subterraneum cv. Dalkeith, and at 0.225 g a.i/ha and 2.25 g a.i/ha for all five cultivars tested. A bioassay assessed T. subterraneum cv. Dalkeith health when grown in field soil-cores taken 4, 7 and 10 months after herbicide application (chlorsulfuron, triasulfuron, clopyralid and pyroxasulfone) to a wheat crop. For all three, herbicide residues significantly decreased (p < 0.001) nodule number, shoot weight, root length and whole plant weight of T. subterraneum cv. Dalkeith compared to control. A field experiment assessed nodulation of five pasture and two crop legumes sown dry (dormant summer sowing), or following rainfall 10.5 months after initial herbicide application. Nodulation of all legume cultivars decreased in plots treated with clopyralid. Chlorsulfuron decreased nodulation for all cultivars except T. glanduliferum and T. subterraneum. Triasulfuron reduced nodulation for all cultivars except Ornithopus sativus and T. spumosum. Pyroxasulfone decreased nodulation of Biserrula pelecinus cv. Casbah and Lupinus angustifolius cv. Mandalup.

Conclusions
Herbicide residues from preceding cereal crops reduced fitness and symbiotically fixed N in subsequently sown pasture or crop legumes.

Implications or significance
Our study highlighted label plant-back recommendations should be strictly adhered to, despite conflict with modern farming approaches of dry or early sowing) to combat climate change. This outcome may consequently lower profitability and increase the carbon footprint of farming systems.

Wheat proteins provide around 20% of all human dietary protein, but their end-use qualities are determined by the form and quantity of nitrogen in the endosperm. In the developed world, there is a heavy reliance in grain production on nitrogen supplied from synthetic fertilisers, and this fertiliser can contribute up to 50% of the on-farm emissions of greenhouse gasses in agriculture. However, despite increasing rates of application of synthetic nitrogen to cereals, wheat grain protein levels, in developed nations, have been frequently failing to reach the premium grade required by the bread-making market. Here, for the first time, we report that biological nitrogen fixation from a new generation of hardseeded annual forage legumes, when grown in rotation with cereal crops, can replace fertiliser N without compromising grain protein. The forage legumes were grown in rotation with Triticum aestivum, and compared with rotations that included a fallow, or a cereal crop at three rainfed sites in Western Australia with differing soil types for 2–4 years. The wheat received low, medium and high rates of urea to indicate if forage legumes can provide sufficient nitrogen for sustainable wheat production. At all sites and years studied, we discovered that cereal grains produced following a year of forage legumes had significantly higher protein levels than when grown as part of a continuous cereal rotation. These results were achieved in combination with a reduction in on-farm emissions (by over 200 kg/ha of CO2) without compromising yield as indicated by emissions accounting. Including appropriate forage legumes in farming systems allows production of low emission intensity grain proteins in dryland farming.

The sandplain soils of WA are inherently fragile with surface layers that are very low in organic matter and clay content. The advent of minimum- and no-till farming has seen the increase in frequency and intensity of cropping on these soils. However, a combination of soil physio-chemical constraints and agronomic issues remain a challenge to the sustainability of cropping systems on them. These constraints include sub-soil compaction, soil water repellence, sub soil acidity and herbicide resistant weeds. Strategic deep tillage such, as soil inversion and deep soil mixing, have been shown to ameliorate these multiple constraints and dramatically increase crop production. For WA soils, an increase in herbicide usage is correlated with a decrease in regular tillage, and how the two interact is imperfectly understood. As a result, current herbicide strategies and rates are designed to perform optimally in a minimum tillage environment. Two field experiments were established to compare crop damage from a range of commonly used pre-emergent herbicides when grown in soil that remained under minimum tillage, was deep mixed or inverted. These trials demonstrated that both strategic tillage methods significantly changed the soil surface composition that would be expected to directly affect the bioavailability of some herbicides. Two commonly used herbicides, Metribuzin and Diuron, detrimentally impacted crop performance following tillage in both trials. These same treatments reduced yield by a greater extent on both the soil inversion and deep mixing treatments (p < 0.001). No other herbicides, when applied at either label or triple label rates, significantly impacted yield on any of the soil treatments. There was a substantial crop production benefit from strategic deep tillage at Esperance but not at Geraldton. These results reflect that the influence of deep tillage on the toxicity of herbicides is highly dependent upon soil properties and rainfall.
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Nitrogen fixation from pasture legumes is a fundamental process that contributes to the profitability and sustainability of dryland agricultural systems. The aim of this research was to determine whether well-managed pastures, based on aerial-seeding pasture legumes, could partially or wholly meet the nitrogen (N) requirements of subsequent grain crops in an annual rotation. Fifteen experiments were conducted in Western Australia with wheat, barley or canola crops grown in a rotation that included the pasture legume species French serradella (Ornithopus sativus), biserrula (Biserrula pelecinus), bladder clover (Trifolium spumosum), annual medics (Medicago spp.) and the non-aerial seeded subterranean clover (Trifolium subterraneum). After the pasture phase, five rates of inorganic N fertilizer (Urea, applied at 0, 23, 46, 69 and 92 kg/ha) were applied to subsequent cereal and oil seed crops. The yields of wheat grown after serradella, biserrula and bladder clover, without the use of applied N fertilizer, were consistent with the target yields for growing conditions of the trials (2.3 to 5.4 t/ha). Crop yields after phases of these pasture legume species were similar or higher than those following subterranean clover or annual medics. The results of this study suggest a single season of a legume-dominant pasture may provide sufficient organic N in the soil to grow at least one crop, without the need for inorganic N fertilizer application. This has implications for reducing inorganic N requirements and the carbon footprint of cropping in dryland agricultural systems.

The transition from mining to agriculture is hampered by a range of abiotic challenges to crop growth, including nutritional issues and heavy metal stress. Building on our previous work showing that potassium (K) limits legume growth in post-phosphate mining substrates on tropical Christmas Island, Australia, we undertook two field trials. The first compared the efficacy of controlled release K fertilisers (CRFs: KCl 2-month release, K2SO4 3-month and K2SO4 9-month) with immediately available potassium sulfate (K2SO4) fertiliser, on the legume Lablab purpureus. The second trial tested responses of L. purpureus to different rates of K2SO4 9-month CRF, and a combination treatment (CRF and K2SO4). Both trials were undertaken to determine how CRFs compare with immediately available K2SO4 in terms of increasing biomass, reducing cadmium (Cd) concentrations, maximising plant K concentrations and maintaining K soil retention. The first trial revealed that K2SO4 3-month and 9-month CRFs were similar to the 160 kg/ha K2SO4 treatment in significantly increasing L. purpureus biomass. Plant Cd and other heavy metal concentrations were significantly lower as plant biomass increased with increasing K, including with CRFs. The second trial showed no difference between various rates of K2SO4 9-month CRF and immediately available 160 kg/ha K2SO4 to increase biomass, reduce Cd or increase K concentrations. We have shown that although post-phosphate mining substrates can limit legume growth, high biomass can be attained with some CRFs, or K2SO4 at 160 kg/ha. Optimising nutrient input in post-mining agriculture is critical for developing safe, sustainable crops.

Knowledge of the hard seed content of annual legumes, and its pattern of breakdown, is critical to the understanding of their ecology and management within farming and natural ecosystems. For logistical reasons, seed that has been stored for varying lengths of time is often used for pasture establishment and agronomy experiments. However, the implications of storage on hard seed physiology are unknown. The aim of this study was to explore the impact of seed storage on its subsequent pattern of hard seed breakdown when exposed to field conditions. Experiments examined seed from six different annual legume genotypes that had been either produced the prior year or stored under ambient conditions for 11–22 years. Comparisons were then made between the two seed sources on hard seed breakdown patterns in situ. Although initial hard seed levels were mostly unaffected by storage (seed of five genotypes remained over 93% hard after more than 11 years of storage), the patterns of release from dormancy during exposure to hard seed breakdown conditions of stored seed differed greatly (p < .05) from freshly produced seed. Hard seed in the stored seed of most genotypes was reduced from >90% to <10% within 68 days over autumn, with shallow burial, whereas fresh seed remained >90% hard during the same period. Given this large and consistent impact, it is recommended that studies of the patterns of hard seed breakdown in legumes compare seed stored under consistent and well‐defined conditions.

This paper reports on the evaluation of “summer sowing,” an innovative approach to increase the adoption of recently domesticated species of hard seeded annual legumes in Mediterranean and temperate Agriculture. The research revealed that several species of annual legumes whose seed can be readily harvested on‐farm and which possess natural hard seed dormancy, may be sown into dry soil in late summer without additional processing. These studies proved that the hard seed dormancy was broken down sufficiently in the soil over 4–6 weeks to produce robust legume pastures with more than 150 seedlings per m2 following the first winter rains, in replicated field sites established across wide agro‐ecological zones in Western Australia (WA) and New South Wales (NSW). Ornithopus sativus Brot., O. compressus L. and Trifolium spumosum L. were suitable for summer sowing based on both hard seed breakdown patterns and subsequent seedling survival in WA. While in NSW, in addition to these legumes, Biserrula pelecinus L., T. vesiculosum Savi. and T. glanduliferum Boiss. were also suitable for summer sowing. A 1.5‐ to 10‐fold increase in herbage production was achieved relative to conventionally sown T. subterraneum L. This development represents a step change in forage legume development for renovated pastures in these environments. Importantly, the experiments revealed differences in G x E effects on seedling establishment, total herbage production and seed yield in different climatic zones. The summer sowing approach is presented as a revolutionary method for pasture renovation that overcomes significant barriers to adoption.