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Background: Pulses are cultivated across a range of soil and climatic conditions that often have many abiotic constraints to production. Whilst water stress has been identified as the greatest constraint in Australian pulse cultivation, other limitations include heat, frost, nutrient deficiency, and a variety of soil physiochemical constraints. Several studies on various pulses have examined shoot and root architecture and their ability to mitigate specific abiotic constraints. However, these studies have been conducted independently of each other, and there is a lack of amalgamated information combining both shoot and root responses that can address production constraints. Scope: This review examines the shoot and root system architecture of key pulses used for human consumption grown in Australia including chickpea, lentil, faba bean, field pea and lupin; and where possible it provides a comparison with relevant research from other crops, especially cereals. It examines research conducted on adaptations to drought, waterlogging, temperature extremes, soil chemical toxicities and high soil strength. Conclusion: The review utilises a physiological framework to identify trait combinations that define theoretical ideotypes of pulse crops that would be better able to mitigate abiotic constraints currently limiting Australian pulse productivity. This framework can be extended directly to other similar environments globally or be used to develop new ideotypes that are better adapted to a wider range of regions within Australia. [ABSTRACT FROM AUTHOR]

BACKGROUND: Understanding how climate change affects the phosphorus (P) nutrition of crops grown on acid soils is important in optimizing the management of P, and to secure future food production on these soils. This study assessed the impact of elevated CO2 (eCO2) on the P nutrition of wheat (Triticum aestivum) grown on Al3+‐toxic and P‐deficient soils or in hydroponics. The aluminium‐resistant near‐isogenic wheat lines EGA‐Burke (malate efflux only) and EGA‐Burke TaMATE1B (malate and citrate efflux) were grown under ambient (400 μmol mol−1) and elevated CO2 (800 μmol mol−1) in growth chambers for 4–6 weeks. RESULTS: Elevated CO2 enhanced shoot growth and total P uptake of both lines at P rates >250 mg kg−1, which was associated with improved root biomass allocation and thus increased root growth, but these effects were not apparent at lower P rates. Elevated CO2 decreased specific P uptake (P uptake per unit root length) at P supply >250 mg kg−1, but did not significantly affect external or internal P requirements. This effect on the specific P uptake was less for EGA‐Burke TaMATE1B than for EGA‐Burke, possibly due to the increased citrate efflux and decreased Al concentration in root tips of EGA‐Burke TaMATE1B. Compared to EGA‐Burke, citrate‐exuding EGA‐Burke TaMATE1B had greater shoot P concentration and greater specific P uptake. CONCLUSION: Elevated CO2 improved root growth, and thus total P uptake and plant production of both lines when high P alleviated Al3+ toxicity and improved P nutrition in acid soils. The decreased P uptake efficiency under eCO2 was less for EGA‐Burke TaMATE1B than EGA‐Burke. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Background and aims: Alkaline dispersive subsoils are characterised by multiple physicochemical constraints that limit plant water and nutrient acquisition. Subsoil amelioration through organic amendments (OAs) requires significant financial investment. Whereas large yield responses can result following amelioration, sometimes small or even negative yield responses can occur, resulting in a significant net financial loss for the farmer. For farmers to feel confident in investing in subsoil amelioration better prediction of the likely yield improvement is required and to achieve this an understanding of the underlying mechanisms such as nutritional and non-nutritional drivers, and the longevity of benefits are required. Our study aimed to ascertain the drivers of yield improvements from subsoil amelioration with OAs. Methods: In a controlled environment, wheat (Triticum aestivum L. cv. Scepter) plants were grown until maturity in a Solonetz amended with (i) poultry litter (PL; 20 t ha−1), and (ii) NPKS nutrients and (iii) model organic carbon (MOC) with equivalent amounts of nutrients and total carbon contained in the PL, and (iv) NPKS + MOC. Control (no amendments) and gypsum (5 t ha−1) were included as district practices. Before planting, amendments were applied as a vertical band at 20 – 40 cm depth and pre-incubated. Plant biomass, grain yield, root biomass, and physicochemical properties of the soil associated with the amendment band were quantified at harvest. Results: Compared to the control, wheat grain yield was increased by 30% for PL, 43% for NPKS + MOC, and 61% for NPKS, but no differences in yield were detected for MOC or gypsum. The lower yield increase by PL than NPKS with or without MOC was likely due to the readily available form of plant nutrients in the inorganic fertilisers vs slower mineralisation of nutrients from the OAs. Improvement in soil physicochemical properties following amelioration of alkaline dispersive subsoil resulted in better root proliferation and subsoil water use. Grain yield showed a positive correlation with root biomass in the subsoil layers. Conclusions: In the short-term (one crop cycle), organic amendments improved soil's non-nutritional physical and chemical properties but had no additional nutritional effect on wheat grain yield compared to inorganic fertiliser application. Longer-term studies are needed to determine the legacy effect of the nutritional contribution in conjunction with the improvement of soil structure from the OAs in alkaline dispersive subsoils. [ABSTRACT FROM AUTHOR]

Ideotype breeding is an essential approach for selection of desired combination of plant traits for testing in crop growth model for potential yield gain in specific environments and management practices. Here we parameterized plant traits for untested lentil cultivars for the APSIM-lentil model in phenology, biomass, and seed yield. We then tested these against independent data and applied the model in an extrapolated analysis (i) to assess the impact of drought on productivity across different rainfall environments; (ii) to identify impactful plant traits and (iii) to design new lentil ideotypes with a combination of desirable traits that mitigate the impact of drought, in the context of various agronomic practices across a wide range of production environments. Desirable phenological and physiological traits related to yield were identified with RUE having the greatest effect on yield followed by HI rate. Leaf size significantly affected seed yield (p< 0.05) more than phenological phases. The physiological traits were integrated into four ideotype designs applied to two baseline cultivars (PBA Hallmark XT and PBA Jumbo2) providing eight ideotypes. We identified a combination of genetic traits that promises a yield advantage of around 10% against our current cultivars PBA Hallmark XT and PBA Jumbo2. Under drought conditions, our ideotypes achieved 5 to 25% yield advantages without stubble and 20 to 40% yield advantages with stubble residues. This shows the importance of genetic screening under realistic production conditions (e.g., stubble retention in particular environments). Such screening is aided by the employment of biophysical models that incorporate both genetic and agronomic variables that focus on successful traits in combination, to reduce the impact of drought in the development of new cultivars for various environments. Stubble retention was found to be a major agronomic contributor to high yield in water-limiting environments and this contribution declined with increasing growing season rainfall. In mid- and high-rainfall environments, the key drivers of yield were time of sowing, physiological traits and soil type. Overall, the agronomic practices, namely, early sowing, residue retention and narrow row spacing deceased the impact of drought when combined with improved physiological traits of the ideotypes based on long term climate data. [ABSTRACT FROM AUTHOR]

Genetic progress in seed yield in lentils (Lens culinaris Medik) has increased by 1.1% per year in Australia over the past 27 years. Knowing which plant traits have changed through breeding during this time can give important insights as to how lentil yield has increased. This study aims to identify morphological and physiological traits that were directly or indirectly selected between 1993 and 2020 in the Australian lentil breeding program using 2 years of experimental data. Major changes occurred in plant architecture during this period. Divergent selection has seen the release of varieties that have sprawling to very upright types of canopies. Despite this genetic diversity in recently released varieties, there is an overall tendency of recently released varieties having increased plant height and leaf size with reduced number of branches. Increased light interception was positively correlated with year of release (YOR) and yield, and likely results from indirect selection of yield and taller plant types. There is an indication that recently released varieties have lower CO2 assimilation rate, stomatal conductance and canopy temperature depression (CTD) at high ambient temperatures (~30°C). Understanding lentil physiology will assist in identifying traits to increase yield in a changing climate with extreme weather events. [ABSTRACT FROM AUTHOR]

Genetic progress in seed yield in lentils (Lens culinaris Medik) has increased by 1.1% per year in Australia over the past 27 years. Knowing which plant traits have changed through breeding during this time can give important insights as to how lentil yield has increased. This study aims to identify morphological and physiological traits that were directly or indirectly selected between 1993 and 2020 in the Australian lentil breeding program using 2 years of experimental data. Major changes occurred in plant architecture during this period. Divergent selection has seen the release of varieties that have sprawling to very upright types of canopies. Despite this genetic diversity in recently released varieties, there is an overall tendency of recently released varieties having increased plant height and leaf size with reduced number of branches. Increased light interception was positively correlated with year of release (YOR) and yield, and likely results from indirect selection of yield and taller plant types. There is an indication that recently released varieties have lower CO2 assimilation rate, stomatal conductance and canopy temperature depression (CTD) at high ambient temperatures (~30°C). Understanding lentil physiology will assist in identifying traits to increase yield in a changing climate with extreme weather events. [ABSTRACT FROM AUTHOR]

Transpiration efficiency, the shoot biomass produced per unit of transpired water, is generally considered to be a constant property for a given crop in a given environment. To determine whether deep-banded organic amendments affect the transpiration efficiency (TE) of wheat plants and to provide a possible explanation for any changes in the TE, two-column experiments were carried out under controlled environment conditions. A Sodosol soil with physically constrained subsoils and a well-structured Vertosol were subjected to treatments including a control, fertilizer nutrients alone, and fertilizer-enriched organic amendments. The addition of fertilizer-enriched organic amendments in Sodosol consistently increased the canopy TE compared to the control and inorganic fertilizer treatments. The instantaneous TE, at the leaf level, was also increased by the organic-based amendments due to greater reductions in stomatal conductance and transpiration rates during periods of moderate water-deficit stress and the subsequent recovery from this stress. Shoot nitrogen (N) status could not explain the increases in TE following the addition of organic amendments relative to inorganic amendments. The increases in canopy TE were directly associated with increases in the absolute abundance of indigenous Bacillus (R 2 = 0.92, p <0), a well-known genus comprising many strains of plant beneficial rhizobacteria, in subsoil below the amendment band. In contrast, there were no differences in the canopy TE and instantaneous leaf TE between the organic and fertilizer amendments in the Vertosol with a well-structured subsoil. The positive effect of organic amendments on TE in the Sodosol should be attributed to their direct or indirect effect on improving the physical structure or biological properties of the subsoil. [ABSTRACT FROM AUTHOR]

Summary: Photosynthetic stimulation by elevated [CO2] (e[CO2]) may be limited by the capacity of sink organs to use photosynthates. In many legumes, N2‐fixing symbionts in root nodules provide an additional sink, so that legumes may be better able to profit from e[CO2]. However, drought not only constrains photosynthesis but also the size and activity of sinks, and little is known about the interaction of e[CO2] and drought on carbon sink strength of nodules and other organs.To compare carbon sink strength, faba bean was grown under ambient (400 ppm) or elevated (700 ppm) atmospheric [CO2] and subjected to well‐watered or drought treatments, and then exposed to 13C pulse‐labelling using custom‐built chambers to track the fate of new photosynthates.Drought decreased 13C uptake and nodule sink strength, and this effect was even greater under e[CO2], and was associated with an accumulation of amino acids in nodules. This resulted in decreased N2 fixation, and increased accumulation of new photosynthates (13C/sugars) in leaves, which in turn can feed back on photosynthesis.Our study suggests that nodule C sink activity is key to avoid sink limitation in legumes under e[CO2], and legumes may only be able to achieve greater C gain if nodule activity is maintained. [ABSTRACT FROM AUTHOR]

Application of organic amendments (OAs) combined with inorganic fertilizers or gypsum in poorly structured soils has recently received much attention as an agricultural management practice aiming to ameliorate physicochemical constraints and improving soil carbon (C) storage. Although microbial C-use efficiency (CUE) is recognized as a critical parameter in ecological models to predict soil C cycling and storage, little is known about the effects of OAs with exogenous nutrient supply (to balance the resource nutrient stoichiometry) or gypsum on microbial biomass and CUE. Here, we examined the role of OAs (C4 vegetation-derived: δ13C – 12 to − 15‰) in altering microbial biomass, C mineralization, and CUE, i.e., microbial growth relative to microbial C uptake (microbial growth + respiration + death) over the long-term, in an alkaline sodic-subsoil (C3 vegetation-derived: δ13C – 24‰). Four different OAs (sorghum stubble, sugarcane bagasse, sugarcane mill mud, and sugarcane mill mud + sugarcane mill ash) were used at 6.2 g C kg−1 soil, with and without the exogenous supply of nutrients and/or gypsum. The nutrients were added with the aim to convert OAs to stable soil organic matter (SOM) with a C/nitrogen (N)/phosphorus (P) stoichiometric ratio of 100:8.3:2. Over 90 days, the cumulative mineralization of OA-C varied across OA types and ranged between 42 and 497 mg CO2-C g−1 OA-C. The OA-derived microbial biomass C (MBC) ranged between 20 and 350 mg C kg−1 soil across the treatments, which was highest with sorghum stubble that contained the highest dissolved (labile) organic C. The mill mud with an inherently balanced C/nutrient stoichiometry had the highest CUE, i.e., 0.3–0.8, compared to the sorghum stubble and sugarcane bagasse (with imbalanced nutrient stoichiometry), i.e., 0.1–0.6. Balancing the nutrient stoichiometry of sorghum stubble and sugarcane bagasse via nutrient inputs increased MBC but not CUE. The input of gypsum to the OA-treated soil had no impact on either MBC or CUE. In conclusion, balanced C/nutrient stoichiometry and labile C content of OAs are critical properties to control their impact on C mineralization, MBC, and CUE, with implications for soil C storage upon amendment into a poorly structured sodic-subsoil. [ABSTRACT FROM AUTHOR]

Improving fertiliser nitrogen (N) use efficiency is essential to increase productivity and avoid environmental damage. Using a 15N mass balance approach, we investigated the effects of five N fertiliser management strategies to test the hypothesis that increasing uptake of applied N by wheat improves productivity and reduces loss of N in a semi-arid environment. Three experiments were conducted between 2012 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4-dimethylpyrazole phosphate, DMPP) and surface broadcast with and without urease inhibitor (n-butyl thiophosphoric triamide, NBPT) at the end of tillering plus an unfertilised control. It was found that deferring fertiliser application until the end of tillering decreased losses of fertiliser N (35–52%) through increasing uptake by the crop and or recovery in the soil at harvest, while maintaining yield except when rainfall following application was low. In this case, deferring application reduced fertiliser uptake (− 71%) and grain yield (− 18%) and increased recovery of N in the soil (+ 121%). Use of DMPP or NBPT reduced N loss where seasonal conditions were conducive to denitrification during winter (DMPP) and volatilisation or denitrification later in the season (NBPT). Their effect on grain yield was less significant; DMPP increased yield (+ 3–31%) in all years and NBPT increased yield (+ 7–11%) in 2 of 3 years compared to unamended urea. The majority of crop N uptake was supplied from soil reserves and as a result, crop recovery of applied N was not strongly related to grain yield response. [ABSTRACT FROM AUTHOR]

The potential impact of elevated atmospheric carbon dioxide concentration ([CO2]) and future climate predicted for 2050 on wheat marketing grades and grain value was evaluated for Victoria, Australia. This evaluation was based on measured grain yield and quality from the Australian Grains FACE program and commercial grain delivery data from Victoria for five seasons (2009–13). Extrapolation of relationships derived from field experimentation under elevated [CO2] to the Victorian wheat crop indicated that 34% of grain would be downgraded by one marketing grade (range 1–62% depending on season and region) because of reduced protein concentration; and that proportions of high-protein wheat grades would reduce and proportions of lower protein grades would increase, with the largest increase in the Australian Standard White (ASW1) grade. Simulation modelling with predicted 2050 [CO2] and future climate indicated reduced wheat yields compared with 2009–13 but higher and lower grain quality depending on region. The Mallee Region was most negatively affected by climate change, with a predicted 43% yield reduction and 43% of grain downgraded by one marketing grade. Using 2016 prices, the value of Victorian wheat grain was influenced mainly by production in the different scenarios, with quality changes in different scenarios having minimal impact on grain value. Increasing atmospheric carbon dioxide and climate changes are expected to affect future wheat yields and quality. The impact of these changes by 2050 were predicted for different Victorian regions compared with historical production, the Mallee region being most affected with a 43% reduction in yield and 43% of grain being downgraded owing to reduced grain protein. With present price premiums for grain quality, the reductions in grain protein had little impact on wheat value compared with the predicted changes in yield. [ABSTRACT FROM AUTHOR]

The deep-placement of nutrient-rich organic amendments in poorly-structured subsoils can improve subsoil structure and increase grain yields, but its widespread adoption by farmers is limited by the availability and cost of animal manures, the current choice of amendment. Three glasshouse experiments investigated the effectiveness of dried field pea (Pisum sativum L.) shoots (green chop), as green manure, on wheat growth in three subsoils with contrasting soil chemical and physical properties. The growth of wheat plants was greatly suppressed when the green chop was placed in Sodosol and Chromosol subsoils. In contrast, there was a twofold increase in shoot biomass in response to the addition of green chop to Vertosol. Three allelopathic compounds, pisatin, anhydropisatin, and maackian, were identified at higher concentrations in the extracts of remaining green chop residues in the Sodosol and Chromosol, compared to the Vertosol, directly supporting phytotoxicity as the cause of observed inhibitory effects of green chop in these soils. The persistence of the phytotoxicity in the Sodosol might be attributed to its poor aeration caused by poor structure or compaction. Nevertheless, pre-incubation led to microbial decomposition of the allelochemicals in the Sodosol, though at a much slower rate than in the Vertosol. Further studies are needed to determine the time period required for the disappearance of the phytotoxic effects in soils with different physico-chemical properties. [ABSTRACT FROM AUTHOR]

Background and aims: Increasing atmospheric carbon dioxide concentration ([CO2]) stimulates the leaf-level (intrinsic) water use efficiency (iWUE), which may mitigate the adverse effects of drought by lowering water use in plants. This study investigated the interactive effect of [CO2] and soil type on growth, yield and water use of canola (Brassica napus L.) in a dryland environment. Methods: Two canola cultivars (vigorous hybrid cv. 'Hyola 50' and non-hybrid cv. 'Thumper') were grown in large intact soil cores containing either a sandy Calcarosol or clay Vertosol under current ambient (a[CO2]) and future elevated [CO2] (e[CO2]), ∼550 μmol mol−1). Net assimilation rates (Anet), stomatal conductance (gs) and leaf area were measured throughout the growing season. Seed yield and yield components were recorded at final harvest. Water use was monitored by lysimeter balances. Results: Elevated [CO2]-stimulation of iWUE was greater than the effect on leaf area, therefore, water use was lower under e[CO2] than a[CO2], but this was further modified by soil type and cultivar. The dynamics of water use throughout the growing season were different between the studied cultivars and in line with their leaf development. The effect of e[CO2] on seed yield was dependent on cultivar; the non-hybrid cultivar benefitted more from increased [CO2]. Although textural differences between soil types influenced the water use under e[CO2], this did not affect the 'CO2 fertilisation effect' on the studied canola cultivars. Conclusion: Elevated [CO2]-induced water savings observed in the present study is a potential mechanism of ameliorating drought effects in high CO2 environment. Better understanding of genotypic variability in response to water use dynamics with traits affecting assimilate supply and use can help breeders to improve crop germplasm for future climates. [ABSTRACT FROM AUTHOR]

This field study assessed phosphorus dynamics (crop-P uptake, resin-extractable P in the root-zone, P mobilisation and microbial-P) in break crop-cereal rotation sequences at four Australian semi-arid field sites differing in soil P fertility. Phosphorus mobilisation (9–30 kg P ha−1) was apparent under break crops, consistently under canola and peas at three sites with low soil P fertility (i.e. pre-sowing soil resin-extractable P < 20 mg P kg−1). Enhanced biological cycling of P (i.e. increased microbial-P) was limited to a low P site in the break crop phase. Phosphorus content of break crop aboveground residues following grain removal was 1–7 kg P ha−1; P input was greater (12–18 kg P ha−1) where legumes were green/brown manured. Varied residue P input did not result in differences in resin-extractable or microbial-P in soil prior to sowing wheat. Phosphorus uptake was greater for wheat after legume break crops compared to continuous wheat (2.0–4.7 kg P ha−1) at all sites, especially where crops were green/brown-manured (3.9–5.9 kg P ha−1). Greater P uptake by wheat was associated with increased grain yield at three sites but was not significantly correlated with the quantity of P input from break crop residues at all four sites or with soil mineral nitrogen pre-sowing of wheat at three sites. Break crops can directly contribute to P resource-use efficiency by mobilising residual P from soil but the agronomic significance of P supply from break crop residues to a P uptake benefit for following wheat remains to be elucidated. [ABSTRACT FROM AUTHOR]

Stimulation of grain yield under elevated [CO2] grown plants is often associated with the deterioration of grain quality. This effect may be further complicated by the frequent occurrence of drought, as predicted in most of the climate change scenarios. Lentil (Lens culinaris Medik.) and faba bean (Vicia faba L.) were grown in the Australian Grains Free Air CO2 Enrichment facility under either ambient CO2 concentration ([CO2], ~400 µmol mol–1) or elevated [CO2] (e[CO2], ~550 µmol mol–1), and with two contrasting watering regimes (for faba bean) or over two consecutive seasons contrasting in rainfall (for lentil), to investigate the interactive effect of e[CO2] and drought on concentrations of selected grain minerals (Fe, Zn, Ca, Mg, P, K, S, Cu, Mn, Na). Grain mineral concentration (Fe, Zn, Ca, K, S, Cu) increased and grain mineral yield (i.e. g mineral per plot surface area) decreased in dry growing environments, and vice versa in wet growing environments. Elevated [CO2] decreased Fe, Zn, P and S concentrations in both crops; however, the relative decrease was greater under dry (20–25%) than wet (4–10%) growing conditions. Principal component analysis showed that greater grain yield stimulation under e[CO2] was associated with a reduction in Fe and Zn concentrations, indicating a yield dilution effect, but this was not consistently observed for other minerals. Even if energy intake is kept constant to adjust for lower yields, decreased legume micronutrients densities under e[CO2] may have negative consequences for human nutrition, especially under drier conditions and in areas with less access to food. Dry growing environments increased minerals (Fe, Zn, K, S, Cu) concentrations in grains of field grown lentil and faba bean. For Fe, Zn, P, S concentrations in grains, the elevated [CO2]-induced decrease was greater under drier growing conditions. Grain yield stimulation under e[CO2] led to dilute Fe and Zn concentrations in grains but this was not consistent for other minerals. [ABSTRACT FROM AUTHOR]

Background and aims: Legume N2 fixation is highly sensitive to drought. Elevated [CO2] (e[CO2]) decreases stomatal conductance (gs) and improves water use efficiency (WUE), which may result in soil water conservation and allow N2 fixation to continue longer under drought. Using a Free-Air CO2 Enrichment (FACE) approach, this study aimed to elucidate whether e[CO2] improves N2 fixation of Pisum sativum L. under drought.Methods: In a FACE system, plants were grown in ambient [CO2] (~400 ppm) or e[CO2] (~550 ppm) and subjected to either terminal drought or well-watered treatments. Measurements were taken of photosynthesis, soil water dynamics, water soluble carbohydrates (WSC), amino acids (AA) and N2 fixation.Results: Lower gs under e[CO2] increased water use efficiency at leaf and plant level, and this translated to slower soil water depletion during drought. Elevated [CO2] increased WSC and decreased total AA concentrations in nodules, and increased nodule activity under drought. N2 fixation was stimulated (+51%) by e[CO2] in proportion to biomass changes. Under e[CO2] a greater proportion of plant total N was derived from fixed N2 and a smaller proportion from soil N uptake compared to a[CO2].Conclusion: This study suggests that e[CO2] increased WUE and this resulted in slower soil water depletion, allowing pea plants to maintain greater nodule activity under drought and resulting in appreciable increases in N2 fixation. Our results suggest that growth under e[CO2] can mitigate drought effects on N2 fixation and reduce dependency on soil N resources especially in water-limited agro-ecosystems. [ABSTRACT FROM AUTHOR]

Background and Aims Soil acidity currently limits root growth and crop production in many regions, and climate change is leading to uncertainties regarding future food supply. However, it is unknown how elevated CO2 (eCO2) affects the performance of wheat crops in acid soils under field conditions. We investigated the effects of eCO2 on plant growth and yield of three pairs of near-isogenic hexaploid wheat lines differing in alleles of aluminium-resistant genes TaALMT1 (conferring root malate efflux) and TaMATE1B (conferring citrate efflux). Methods Plants were grown until maturity in an acid soil under ambient CO2 (aCO2; 400 µmol mol−1) and eCO2 (550 µmol mol−1) in a soil free-air CO2 enrichment facility (SoilFACE). Growth parameters and grain yields were measured. Key Results Elevated CO2 increased grain yield of lines carrying TaMATE1B by 22 % and lines carrying only TaALMT1 by 31 %, but did not increase the grain yield of Al3+-sensitive lines. Although eCO2 promoted tiller formation, coarse root length and root biomass of lines carrying TaMATE1B, it did not affect ear number, and it therefore limited yield potential. By contrast, eCO2 decreased or did not change these parameters for lines carrying only TaALMT1, and enhanced biomass allocation to grains thereby resulting in increased grain yield. Despite TaMATE1B being less effective than TaALMT1 at conferring Al3+ resistance based on root growth, the gene promoted grain yield to a similar level to TaALMT1 when the plants were grown in acid soil. Furthermore, TaALMT1 and TaMATE1B were not additive in their effects. Conclusions As atmospheric CO2 increases, it is critical that both Al3+-resistance genes (particularly TaALMT1) should be maintained in hexaploid wheat germplasm in order for yield increases from CO2 fertilization to be realized in acid soils. [ABSTRACT FROM AUTHOR]

The effects of elevated atmospheric carbon dioxide (eCO2) on belowground processes are known to occur directly and indirectly via plants. However, the long-term impact of eCO2 on biochemical properties and processes of agricultural soils in the absence of plants is unclear. The current study investigated whether residue decomposition and the subsequent 'priming effect' on soil organic C (SOC) mineralisation were altered in three contrasting soils previously exposed to either ambient CO2 (aCO2; 390 ppm) or eCO2 (550 ppm) using free-air CO2 enrichment (FACE) for 4 years. Surface soils (0-2 cm) of calcisol, luvisol and vertisol were amended (0.5% w w−1) with 13C-labelled field pea (Pisum sativum L. cv. PBA; C:N 20) or wheat (Triticum aestivum cv. Yitpi; C:N 60) residues, and CO2 derived from soil (CO2 soil) and residue (CO2 residue) were quantified over the 96-day incubation study. Field pea decomposition was not affected by soil type or CO2 history, and the decomposition of wheat was similar in all soils previously exposed to aCO2. However, wheat decomposition was increased in luvisol (14.4%), decreased in vertisol (26.7%) or not affected by eCO2 in the calcisol. The relative differences between soils were largely driven by labile N content and the potential to replenish inorganic N via mineralisation. Notably, priming was not influenced by residue type, despite their contrasting N content. In the calcisol, lower basal C mineralisation and C priming under eCO2 were not explained by lower N concentrations. A greater priming effect in field pea-amended vertisol previously exposed to eCO2 than aCO2 was likely due to overcoming the N limitation on microbial C mineralisation in this soil. Overall, the study highlighted that C mineralisation was mainly determined by soil N status, less by CO2 history and least by residue quality (C:N ratio). [ABSTRACT FROM AUTHOR]

Nitrogen (N) management is critical to the profitability of grain production systems, however careful management of fertiliser is needed to minimise environmental impacts. We investigated the effect of five N fertilisation strategies on nitrous oxide (N2O) emissions and nitrogen use efficiency (NUE) of rainfed wheat grown on a clay soil in a temperate, semi-arid environment of south eastern Australia during 2013 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4-dimethylpyrazole phosphate) and surface broadcasting of urea with and without urease inhibitor (n-butyl thiophosphoric triamide) at the end of tillering plus an unfertilised control. Daily N2O emissions were low and responsive to in-season rainfall and fertiliser addition at sowing. Cumulative emissions from sowing until harvest were highest where N was applied at sowing in 2013; 160 g N2O-N/ha, while the 0 N control emitted 28 g N2O-N/ha (over 201 days). Emissions during 2014 were 77% lower than 2013 due to dry seasonal conditions; cumulative emissions were 49 g N2O-N/ha where N was applied at sowing, with background emissions of around 0 g N2O-N/ha (over 177 days). Inhibitors showed limited scope for reducing N2O emissions in this environment, however deferring N application until the end of tillering reduced N2O emissions. Grain yield responses to fertiliser were significant; increasing grain yield by 11-31% and NUE was generally high (recovery efficiency > 68%). However, deferring N application until the end of tillering in 2014 reduced yield (− 19%) and recovery of applied N (− 74%). [ABSTRACT FROM AUTHOR]

Abstract: Increased biomass and yield of plants grown under elevated [CO2] often corresponds to decreased grain N concentration ([N]), diminishing nutritional quality of crops. Legumes through their symbiotic N2 fixation may be better able to maintain biomass [N] and grain [N] under elevated [CO2], provided N2 fixation is stimulated by elevated [CO2] in line with growth and yield. In Mediterranean‐type agroecosystems, N2 fixation may be impaired by drought, and it is unclear whether elevated [CO2] stimulation of N2 fixation can overcome this impact in dry years. To address this question, we grew lentil under two [CO2] (ambient ~400 ppm and elevated ~550 ppm) levels in a free‐air CO2 enrichment facility over two growing seasons sharply contrasting in rainfall. Elevated [CO2] stimulated N2 fixation through greater nodule number (+27%), mass (+18%), and specific fixation activity (+17%), and this stimulation was greater in the high than in the low rainfall/dry season. Elevated [CO2] depressed grain [N] (−4%) in the dry season. In contrast, grain [N] increased (+3%) in the high rainfall season under elevated [CO2], as a consequence of greater post‐flowering N2 fixation. Our results suggest that the benefit for N2 fixation from elevated [CO2] is high as long as there is enough soil water to continue N2 fixation during grain filling. [ABSTRACT FROM AUTHOR]

Through stimulation of root growth, increasing atmospheric CO2 concentration ([CO2]) may facilitate access of crops to sub-soil water, which could potentially prolong physiological activity in dryland environments, particularly because crops are more water use efficient under elevated [CO2] (e[CO2]). This study investigated the effect of drought in shallow soil versus sub-soil on agronomic and physiological responses of wheat to e[CO2] in a glasshouse experiment. Wheat (Triticum aestivum L. cv. Yitpi) was grown in split-columns with the top (0–30 cm) and bottom (31–60 cm; ‘sub-soil’) soil layer hydraulically separated by a wax-coated, root-penetrable layer under ambient [CO2] (a[CO2], ∼400 μmol mol-1) or e[CO2] (∼700 μmol mol-1) [CO2]. Drought was imposed from stem-elongation in either the top or bottom soil layer or both by withholding 33% of the irrigation, resulting in four water treatments (WW, WD, DW, DD; D = drought, W = well-watered, letters denote water treatment in top and bottom soil layer, respectively). Leaf gas exchange was measured weekly from stem-elongation until anthesis. Above-and belowground biomass, grain yield and yield components were evaluated at three developmental stages (stem-elongation, anthesis and maturity). Compared with a[CO2], net assimilation rate was higher and stomatal conductance was lower under e[CO2], resulting in greater intrinsic water use efficiency. Elevated [CO2] stimulated both above- and belowground biomass as well as grain yield, however, this stimulation was greater under well-watered (WW) than drought (DD) throughout the whole soil profile. Imposition of drought in either or both soil layers decreased aboveground biomass and grain yield under both [CO2] compared to the well-watered treatment. However, the greatest ‘CO2 fertilisation effect’ was observed when drought was imposed in the top soil layer only (DW), and this was associated with e[CO2]-stimulation of root growth especially in the well-watered bottom layer. We suggest that stimulation of belowground biomass under e[CO2] will allow better access to sub-soil water during grain filling period, when additional water is converted into additional yield with high efficiency in Mediterranean-type dryland agro-ecosystems. If sufficient water is available in the sub-soil, e[CO2] may help mitigating the effect of drying surface soil. [ABSTRACT FROM AUTHOR]

Background and aim: The long-term effect of elevated CO (eCO) on P biogeochemistry in farming systems is largely unknown. This study compared the effects of eCO on P fractions in three contrasting soils after growing crops for seven years. Methods: An experiment of free-air-CO-enrichment (FACE) was conducted with a rotation of wheat, field pea and canola grown in intact cores of Chromosol, Vertosol and Calcarosol under ambient CO (aCO) (390 ± 10 ppm) or eCO (550 ± 30 ppm). Crop P removal, soil P fractions and biochemical properties were determined. Results: Elevated CO resulted in extra 134, 91 and 93 mg P core removed as grains, compared to aCO, for Chromosol, Vertosol and Calcarosol, respectively. It decreased the concentration of NaHCO-extractable inorganic P (by 17-36%), and decreased NaOH-extractable inorganic P by 24% in Chromosol, and 77% in Vertosol but did not affect it in Calcarosol. Elevated CO also decreased NaOH-extractable organic P by 20, 12 and 7 mg kg in the three soils, respectively. Furthermore, eCO decreased soil organic carbon (by 8.2%) and increased microbial biomass carbon and respiration in Chromosol but not in other two soils. Conclusion: Long-term eCO favoured microbial mineralization of organic P in Chromosol and chemical mobilization of non-labile inorganic P in all three soils. [ABSTRACT FROM AUTHOR]

Background & aims: Elevated atmospheric CO (eCO) can affect soil-plant systems via stimulating plant growth, rhizosphere activity and the decomposition of added (crop residues) or existing (priming) soil organic carbon (C). Increases in C inputs via root exudation, rhizodeposition and root turnover are likely to alter the decomposition of crop residues but will ultimately depend on the N content of the residues and the soil. Methods: Two soil column experiments were conducted under ambient CO (aCO, 390 ppm) and eCO (700 ppm) in a glasshouse using dual-labelled (C/N) residues of wheat ( Triticum aestivum cv. Yitpi) and field pea ( Pisum sativum L. cv. PBA Twilight). The effects of eCO and soil N status on wheat rhizosphere activity and residue decomposition and also N recovery from crop residues with different N status (C/N ratio 19.4-115.4) by different plant treatments (wheat, wheat + 25 mg N kg and field pea). Results: Total belowground CO efflux was enhanced under eCO despite no increases in root biomass. Plants decreased residue decomposition, indicating a negative rhizosphere effect. For wheat, eCO reduced the negative rhizosphere effect, resulting in greater rates of decomposition and recovery of N from field pea residues, but only when N fertiliser was added. For field pea, eCO enhanced the negative rhizosphere effect resulting in lower decomposition rates and N recovery from field pea residue. Conclusions: The effect of eCO on N utilisation varied with the type of residue, enhancing N utilisation of wheat but repressing that of field pea residues, which in turn could alter the amount of N supplied to subsequent crops. Furthermore, reduced decomposition of residues under eCO may slow the formation of new soil C and have implications for long-term soil fertility. [ABSTRACT FROM AUTHOR]

Improving nitrogen (N) fertiliser uptake of crops growing in soils susceptible to waterlogging could potentially reduce fertiliser input costs and harmful losses of N to the surrounding environment. The fate of N labelled urea applied to wheat cv. Bolac was studied on brown chromosol soils at Hamilton and Tarrington, in the high rainfall zone of south western Victoria, in south eastern Australia. Wheat was fertilised with N-urea solution, either deep banded 0.1 m below the seed at sowing or top-dressed with or without the nitrification inhibitor DMPP (3,4- dimethylpyrazole phosphate or ENTEC) later in the crops development. Daily temporal topsoil (0-0.1 m) water was monitored, throughout the growing season, and at physiological maturity the recovery of N-urea in straw, grain and soil (to 0.4 or 0.6 m depth) was measured. Delaying untreated N-urea application until top-dressing at mid-tillering to first node stage of growth resulted in significantly ( P < 0.001) greater recovery of applied N than when deep banded at sowing or top-dressed shortly after crop emergence. However, top-dressing with DMPP did not significantly improve crop recovery of N-urea compared with untreated urea, except when top-dressed early in the growing season. Across all sites, between 64 and 84 % of the applied N-urea was recovered in the plant and soil at maturity when top-dressed at mid tillering to first node, compared with 7-42 % when N-urea was either deep banded at sowing or top-dressed shortly after crop emergence. The poor recovery of N-urea when applied around sowing appeared to result from wet to waterlogged soil and subsequent gaseous or drainage losses before wheat reached peak growth and demand for N in spring. Despite, the poor recovery from N-urea applied early in the growing season, wheat grain yields were the same as those top-dressed with N-urea; the former treatment compensating for low fertiliser recovery by sourcing more N from the soil. All sites had high concentrations of topsoil organic C (>2.8 %) and the potential for large rates of mineralisation during the growing season. [ABSTRACT FROM AUTHOR]

Background and Aims Additional carbohydrate supply resulting from enhanced photosynthesis under predicted future elevated CO2 is likely to increase symbiotic nitrogen (N) fixation in legumes. This study examined the interactive effects of atmospheric CO2 and nitrate (NO3-) concentration on the growth, nodulation and N fixation of field pea (Pisum sativum) in a semi-arid cropping system. Methods Field pea was grown for 15 weeks in a Vertosol containing 5, 25, 50 or 90mg NO3 -N kg-11 under either ambient CO2 (aCO2; 390 ppm) or elevated CO2 (eCO2; 550 ppm) using free-air CO2 enrichment (SoilFACE). Key Results Under aCO2, field pea biomass was significantly lower at 5mg NO3 -N kg-11 than at 90mg NO3 -N kg-11 soil. However, increasing the soil N level significantly reduced nodulation of lateral roots but not the primary root, and nodules were significantly smaller, with 85 % less nodule mass in the 90 NO3 -N kg-11 than in the 5mg NO3 -N kg-11 treatment, highlighting the inhibitory effects of NO3 Field pea grown under eCO2 had greater biomass (approx. 30 %) than those grown under aCO2, and was not affected by N level. Overall, the inhibitory effects of NO3 - on nodulation and nodule mass appeared to be reduced under eCO2 compared with aCO2, although the effects of CO2 on root growth were not significant. Conclusions Elevated CO2 alleviated the inhibitory effect of soil NO3 - on nodulation and N2 fixation and is likely to lead to greater total N content of field pea growing under future elevated CO2 environments. [ABSTRACT FROM AUTHOR]

Background and Aims: Benefits to crop productivity arising from increasing CO2 fertilization may be offset by detrimental effects of global climate change, such as an increasing frequency of drought. Phosphorus (P) nutrition plays an important role in crop responses to water stress, but how elevated CO2 (eCO2) and P nutrition interact, especially in legumes, is unclear. This study aimed to elucidate whether P supply improves plant drought tolerance under eCO2. Methods: A soil-column experiment was conducted in a free air CO2 enrichment (SoilFACE) system. Field pea (Pisum sativum) was grown in a P-deficient vertisol, supplied with 15 mg P kg-1 (deficient) or 60 mg P kg-1 (adequate for crop growth) and exposed to ambient CO2 (aCO2; 380-400 ppm) or eCO2 (550-580 ppm). Drought treatments commenced at flowering. Measurements were taken of soil and leaf water content, photosynthesis, stomatal conductance, total soluble sugars and inorganic P content (Pi). Key Results: Water-use efficiency was greatest under eCO2 when the plants were supplied with adequate P compared with other treatments irrespective of drought treatment. Elevated CO2 decreased stomatal conductance and transpiration rate, and increased the concentration of soluble sugars and relative water contents in leaves. Adequate P supply increased concentrations of soluble sugars and Pi in drought-stressed plants. Adequate P supply but not eCO2 increased root length distribution in deeper soil layers. Conclusions: Phosphorus application and eCO2 interactively enhanced periodic drought tolerance in field pea as a result of decreased stomatal conductance, deeper rooting and high Pi availability for carbon assimilation in leaves. [ABSTRACT FROM AUTHOR]

Background and Aims: Crop responses to elevated atmospheric CO are likely to be different in semi-arid cropping systems of Australia. This experiment aimed to investigate the interactive effects of atmospheric CO and nitrogen (N) fertiliser on carbon (C) and N partitioning in the soil-plant system of Wheat ( Triticum aestivum L.) and field pea ( Pisum sativum L.). Methods: Plants were grown with 40 or 100 mg N kg under ambient CO (390 ppm) or elevated CO (eCO; 550 ppm) using free-air CO enrichment (SoilFACE). Repeated CO pulse labelling was used to quantify C transfer via plant to the soil. Destructive sampling was performed at grain filling and maturity. Results: eCO increased shoot biomass of field pea (36 %) and wheat (55 %) but only increased root biomass of wheat (13.5 %) in the 25-50 cm soil layer. Total N content of both species was greater under eCO, and for field pea it indicated enhanced biological N fixation. However, eCO increased the C:N ratio of wheat even at the high N level. Greater C in soil of wheat grown under eCO indicated a minor increase in soil C via rhizodeposition. Conclusions: Increased biomass and C:N ratio of wheat could have implications for residue decomposition. eCO and low N tended to increase grain yield but the increase was highly variable and not significant. Additional N content of field pea under eCO exceeded the N that would be removed in wheat grain, albeit with lower than expected grain yield due to dry conditions. [ABSTRACT FROM AUTHOR]

Background and aims: As plants approach maturity and start to senesce, the primary sink for phosphorus (P) is the seed but it is unclear how plant P status affects the resulting P concentration and speciation in the seed and remaining plant parts of the residues. This study was established to measure how P speciation in different parts of wheat and canola is affected by plant P status. Methods: Wheat and canola grown in the glasshouse were supplied three different P rates (5, 30 and 60 kg P ha equivalent). At physiological maturity, plants were harvested and P speciation was determined for all plant parts (root, stem, leaf, chaff/pod and seed) and rates of P application, using solution P nuclear magnetic resonance (NMR) spectroscopy. Results: Phytate was the dominant form of P in seed whereas orthophosphate was the dominant form of P in other plant parts. The distribution of P species varied with P status for canola but not for wheat. The phytate content of wheat chaff increased from 10 to 45 % of total P as the P rate increased. Canola pods did not show a similar trend, with most P present as orthophosphate. Conclusions: Although minor differences were observed in P speciation across the three P application rates and plant parts, the effect of this on P cycling from residues into soil is likely to be relatively minor in comparison to the overall contribution of these residues to soil P pools. This glasshouse experiment shows the dominant P form in crop residues that is returned to soil after harvest is orthophosphate, regardless of plant P status. [ABSTRACT FROM AUTHOR]

Background and aims: Maintaining nutrient supply, including phosphorus (P), is critical to ensure the adaptation of cropping systems to future elevated CO (eCO) environments. There is much speculation about the role of sparingly soluble sources to supply plants with P so we tested the hypothesis that eCO increases plant's ability to utilise P from sparingly soluble sources via affecting rhizosphere properties. Methods: Chickpea and wheat were grown for 6 weeks in washed sand supplied with 40 mg P kg as either readily soluble Ca(HPO) or sparingly soluble AlPO (Al-P), FePO or hydroxyapatite (HAP). Half plants were exposed to eCO (700 ppm) while the others to ambient CO (380 ppm). Results: Elevated CO increased biomass production of both species but did not influence P concentration in plants, rhizosphere pH or Olsen P. Among the sparingly soluble P sources, HAP resulted in the maximum biomass and total P uptake in wheat and chickpea with wheat acquiring more P. Supply of nitrate, as compared to urea, to wheat decreased the uptake of P from HAP but increased it from Al-P. Conclusion: Elevated CO does not specifically affect plant access to P from sparingly soluble P sources. Urea facilitates P acquisition from HAP whereas nitrate facilitates it from Al-P. [ABSTRACT FROM AUTHOR]

There is increasing interest in enhancing the efficiency of P fertilizers or mobilizing fixed P from soil. Cation-complexing ligands are claimed to increase availability of fertilizer-applied or soil P through sequestration of cations (Fe, Al, Ca) that bind P strongly. We assessed the effect of ligand addition on mobility and availability of P in four soils, using a large range of cation-complexing compounds, in batch experiments without or with added P, and found only small effects of these compounds on P solubility. Selected compounds, including two commercial polymer coatings, coated on granular monoammonium phosphate (MAP) and an organic-complexed form of single superphosphate (SSP) fertilizer were tested in diffusion experiments and in a pot trial and compared with conventional MAP or SSP. The ligand treatments, at a 1% coating rate on granular fertilizers, did not significantly affect P diffusion. The only significant difference was between the MAP and SSP treatments, with a lower rate of diffusion from SSP, presumably because of enhanced Ca-P precipitation. Only at very high, commercially unrealistic coating rates (up to 100%) of a dicarboxylic copolymer did P solution concentrations close to the granule increase in an Oxisol, but not in a calcareous soil. The pot trial also showed no effect of the ligand treatments at a 1% coating rate in any of the three soils tested. These results, as well as theoretical considerations, indicate that complexation of P-binding cations is unlikely to be an economically viable process to either release P from stored forms in soil or to increase efficiency of added fertilizer P. [ABSTRACT FROM AUTHOR]

Aims: The efficient management of phosphorus (P) in cropping systems remains a challenge due to climate change. We tested how plant species access P pools in soils of varying P status (Olsen-P 3.2-17.6 mg kg), under elevated atmosphere CO (eCO). Methods: Chickpea ( Cicer arietinum L.) and wheat ( Triticum aestivum L.) plants were grown in rhizo-boxes containing Vertosol or Calcarosol soil, with two contrasting P fertilizer histories for each soil, and exposed to ambient (380 ppm) or eCO (700 ppm) for 6 weeks. Results: The NaHCO-extractable inorganic P (Pi) in the rhizosphere was depleted by both wheat and chickpea in all soils, but was not significantly affected by CO treatment. However, NaHCO-extractable organic P (Po) accumulated, especially under eCO in soils with high P status. The NaOH-extractable Po under eCO accumulated only in the Vertosol with high P status. Crop species did not exhibit different eCO-triggered capabilities to access any P pool in either soil, though wheat depleted NaHCO-Pi and NaOH-Pi in the rhizosphere more than chickpea. Elevated CO increased microbial biomass C in the rhizosphere by an average of 21 %. Moreover, the size in Po fractions correlated with microbial C but not with rhizosphere pH or phosphatase activity. Conclusion: Elevated CO increased microbial biomass in the rhizosphere which in turn temporally immobilized P. This P immobilization was greater in soils with high than low P availability. [ABSTRACT FROM AUTHOR]

Background and purpose: Rapid increases in atmospheric carbon dioxide concentration ([CO]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO] on the growth, grain yield and the recovery of N-labeled fertilizer by wheat ( Triticum aestivum L. cv. Yitpi) under controlled environmental conditions. Methods: Residue for ambient and elevated [CO] treatments, obtained from wheat grown previously under ambient and elevated [CO], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage N-labeled granular urea (10.22 atom%) was applied at 50 kg N ha and the wheat grown to maturity. Results: When residue was not incorporated into the soil, elevated [CO] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO] decreased fertilizer N recovery. Conclusions: A higher fertilizer application rate will be required under future elevated [CO] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment. [ABSTRACT FROM AUTHOR]

Nitrous oxide (NO) is a potent greenhouse gas released from high rainfall cropping soils, but the role of management in its abatement remains unclear in these environments. To quantify the relative influence of management, nitrogen (N) fertiliser and soil nitrification inhibitor was applied to separate but paired raised bed and conventionally flat field experiments in south west Victoria, to measure emissions and income from wheat and canola planted 2 and 3 years after conversion from a long-term pasture. Management included four different rates of N fertiliser, top-dressed with and without the nitrification inhibitor Dicyandiamide (DCD), which was applied in solution to the soil in the second year of experimentation. Crop biomass, grain yield, soil mineral N, soil temperature and soil water and NO flux were measured. Static chamber methodology was used to identify relative differences in NO loss between management. In the second crop (wheat) following conversion, NO losses were up to 72 % lower ( P < 0.05) in the furrows, receiving the lower rate of N fertiliser compared with the highest rate, with less frequent reductions observed in the third crop (canola); losses of NO from the beds was unaffected by N rate, perhaps from nitrate leakage into the adjacent furrow of the raised bed experiment. On the nearby flat experiment, nitrate leaching may have diminished the effects of N rate and DCD on NO flux. Furthermore the extra N did not significantly increase grain yield in either the wheat or canola crops on both experiments. The application of DCD in the canola crop temporarily reduced ( P < 0.05) NO production by up to 84 % from the beds, 83 % in the adjacent furrows and 75 % on the flat experiment. Grain yield was not significantly ( P < 0.001) affected however, canola income was reduced by $1407/ha and $1252/ha, compared with no addition of inhibitor on the respective bed and flat experiments. Although NO fluxes are driven by environmental episodic events, management will play a role in NO abatement. However, DCD currently appears economically unfeasible and matching N fertiliser supply to meet crop demand appears a better option for minimising NO losses from high rainfall cropping systems. [ABSTRACT FROM AUTHOR]

Purpose: This study investigated the residual contribution of legume and fertilizer nitrogen (N) to a subsequent crop under the effect of elevated carbon dioxide concentration ([CO]). Methods: Field pea ( Pisum sativum L.) was labeled in situ with N (by absorption of a N-labeled urea solution through cut tendrils) under ambient and elevated (700 μmol mol) [CO] in controlled environment glasshouse chambers. Barley ( Hordeum vulgare L.) and its soil were also labeled under the same conditions by addition of N-enriched urea to the soil. Wheat ( Triticum aestivum L.) was subsequently grown to physiological maturity on the soil containing either N-labeled field pea residues (including N-labeled rhizodeposits) or N-labeled barley plus fertilizer N residues. Results: Elevated [CO] increased the total biomass of field pea (21 %) and N-fertilized barley (23 %), but did not significantly affect the biomass of unfertilized barley. Elevated [CO] increased the C:N ratio of residues of field pea (18 %) and N-fertilized barley (19 %), but had no significant effect on that of unfertilized barley. Elevated [CO] increased total biomass (11 %) and grain yield (40 %) of subsequent wheat crop regardless of rotation type in the first phase. Irrespective of [CO], the grain yield and total N uptake by wheat following field pea were 24 % and 11 %, respectively, higher than those of the wheat following N-fertilized barley. The residual N contribution from field pea to wheat was 20 % under ambient [CO], but dropped to 11 % under elevated [CO], while that from fertilizer did not differ significantly between ambient [CO] (4 %) and elevated [CO] (5 %). Conclusions: The relative value of legume derived N to subsequent cereals may be reduced under elevated [CO]. However, compared to N fertilizer application, legume incorporation will be more beneficial to grain yield and N supply to subsequent cereals under future (elevated [CO]) climates. [ABSTRACT FROM AUTHOR]

Background and Aims: Phosphorus (P) mineralisation from crop residues is usually predicted from total P or carbon: phosphorus (C: P) ratios. However, these measures have limited accuracy as they do not take into account the presence of different P species that may be mineralised at different rates. In this study P speciation was determined using solution P nuclear magnetic resonance (NMR) spectroscopy to understand the potential fate of residue P in soils. Methods: Mature above-ground biomass of eight different crops sampled from the field was portioned into stem, chaff and seed. Results: The main forms of P detected in stem and chaff were orthophosphate (25-75 %), phospholipids (10-40 %) and RNA (5-30 %). Phytate was the dominant P species in seeds, and constituted up to 45 % of total P in chaff but was only detected in minor amounts (<1 %) in stem residue. The majority (65-95 %) of P in stems was water-extractable, and most of this was detected as orthophosphate. However, this includes organic P that may have been hydrolysed during the water extraction. Conclusions: This study indicates that the majority of residue P in aboveground plant residues has the potential to be delivered to soil in a form readily available to plants and soil microorganisms. [ABSTRACT FROM AUTHOR]

Background & aims: Understanding the mechanism of how phosphorus (P) regulates the response of legumes to elevated CO (eCO) is important for developing P management strategies to cope with increasing atmospheric CO concentration. This study aimed to explore this mechanism by investigating interactive effects of CO and P supply on root morphology, nodulation and soil P fractions in the rhizosphere. Methods: A column experiment was conducted under ambient (350 ppm) (aCO) and eCO (550 ppm) in a free air CO enrichment (FACE) system. Chickpea and field pea were grown in a P-deficient Vertisol with P addition of 0-16 mg P kg. Results: Increasing P supply increased plant growth and total P uptake with the increase being greater under eCO than under aCO. Elevated CO increased root biomass and length, on average, by 16 % and 14 %, respectively. Nodule biomass increased by 46 % in response to eCO at 16 mg P kg, but was not affected by eCO at no P supply. Total P uptake was correlated with root length while N uptake correlated with nodule number and biomass regardless of CO level. Elevated CO increased the NaOH-extractable organic P by 92 % when 16 mg P kg was applied. Conclusion: The increase in P and N uptake and nodule number under eCO resulted from the increased biomass production, rather than from changes in specific root-absorbing capability or specific nodule function. Elevated CO appears to enhance P immobilization in the rhizosphere. [ABSTRACT FROM AUTHOR]

Understanding nitrogen (N) removal and replenishment is crucial to crop sustainability under rising atmospheric carbon dioxide concentration ([ CO2]). While a significant portion of N is removed in grains, the soil N taken from agroecosystems can be replenished by fertilizer application and N2 fixation by legumes. The effects of elevated [ CO2] on N dynamics in grain crop and legume pasture systems were evaluated using meta-analytic techniques (366 observations from 127 studies). The information analysed for non-legume crops included grain N removal, residue C : N ratio, fertilizer N recovery and nitrous oxide (N2O) emission. In addition to these parameters, nodule number and mass, nitrogenase activity, the percentage and amount of N fixed from the atmosphere were also assessed in legumes. Elevated [ CO2] increased grain N removal of C3 non-legumes (11%), legumes (36%) and C4 crops (14%). The C : N ratio of residues from C3 non-legumes and legumes increased under elevated [ CO2] by 16% and 8%, respectively, but the increase for C4 crops (9%) was not statistically significant. Under elevated [ CO2], there was a 38% increase in the amount of N fixed from the atmosphere by legumes, which was accompanied by greater whole plant nodule number (33%), nodule mass (39%), nitrogenase activity (37%) and %N derived from the atmosphere (10%; non-significant). Elevated [ CO2] increased the plant uptake of fertilizer N by 17%, and N2O emission by 27%. These results suggest that N demand and removal in grain cropping systems will increase under future CO2-enriched environments, and that current N management practices (fertilizer application and legume incorporation) will need to be revised. [ABSTRACT FROM AUTHOR]

There are few reports on the effects of atmospheric carbon dioxide concentration ([CO]) on fertilizer N recovery by crops under open-air conditions. This study was conducted at the Australian Grains Free-Air CO Enrichment (AGFACE) facility in southern Australia to investigate the effects of elevated [CO] (550 μmol mol) on growth, N uptake and fertilizer N recovery by spring wheat ( Triticum aestivum L. cv. Yitpi) over a 2-year period. N-enriched (10.22 atom%) granular urea was applied to microplots at 50 kg N ha at varying seasonal rainfall and temperature scenarios (simulated by supplementary irrigation and late sowing) for three experimental periods [2008 normal sowing (2008NS), 2008 late sowing (2008LS) and 2009 normal sowing (2009NS)]. Elevated [CO] increased wheat biomass (27-58%), N uptake (18-44%) and amount of plant N derived from soil (20-50%) at 2008NS and 2009NS (rainfed), but the effect was not apparent at 2008LS (hotter and drier) and supplementary irrigated plots for 2009NS (above-average rainfall). Tissue N concentration and N derived from fertilizer were unaffected by elevated [CO] in any experimental period. Irrespective of [CO], grain yield and whole plant fertilizer N uptake was 37-94 and 13-609%, respectively, higher under supplementary irrigated plots than that in rainfed counterparts. These results indicate that more fertilizer N will need to be applied to this wheat production zone under future [CO] environments, and yield gains in hotter and drier climates will be lower than those in higher rainfall zones. [ABSTRACT FROM AUTHOR]

Knowledge of the capacity of a soil to supply phosphorus (P), and the variation in the ability of different crops to access soil P, is critical to successfully managing P in modern cropping systems. Isotopic dilution techniques were used to examine the capacity of three contrasting soil types (Calcarosol, Vertosol and Chromosol) to supply P, and to compare the ability of three different crop species (wheat, chickpea and canola) to access P under both low and adequate P conditions. This was achieved by measuring L values of the different crops grown for 56 days in P-labelled soils with various combinations of history of P fertilisation (native vs. cultivated soils) and recent P addition (none vs. added P). A parallel experiment used these identical soil types/treatments without plants to determine E values. The three soils studied varied in the capacity to supply P to crops. The sandy Calcarosol, on average, had higher E values than other two soils. E-values were generally constant or slightly decreased over 42 d. Adding water-soluble P enhanced E values in all 3 soils. While chickpea absorbed more P from the P-deficient native soils, wheat was superior to either canola or chickpea in acquiring both freshly applied and residual P fertilizer across the three soils. The L values were generally constant over 56 d for all the soils and plant species, although the value was lower at Day 21 compared to later harvests for some treatments. Irrespective of soil type, plant P uptake correlated well with L and E values. Interestingly, wheat and chickpea but not canola had higher L/E ratios when grown in the P-deficient native soils than in other P treatments of Calcarosol and Vertosol. It is concluded that soil type, crop species and P history all affect P acquisition from soil and applied fertilizer, and that both L and E values are reliable indicator of predicting plant-available P in soil. [ABSTRACT FROM AUTHOR]

For lentil production to expand further in Australia, adaptation to the less favourable soils of the low to medium rainfall zones is required. To improve adaptation to these regions, varieties are required with increased tolerance to soil constraints such as high concentrations of boron (B), salinity and sodicity. To evaluate the range of B tolerance in lentil germplasm, 310 lines were screened in soil with a high concentration of B and tolerance was assessed at the seedling stage. A wide range in response to high concentrations of soil B was observed in the germplasm tested. Current Australian varieties were generally very intolerant to high concentrations of soil B. High levels of B tolerance was identified in germplasm originating from Afghanistan and Ethiopia. A subsequent experiment comparing lentils with different levels of B tolerance found that tolerant accessions (ILL213A and ILL2024) produced greater above and below ground biomass than intolerant accessions. The tolerant accessions had no significant yield loss under a high B treatment (extractable B = 18.20 mg/kg) compared to the control treatment (extractable B = 1.55 mg/kg). The large improvement in B tolerance, at soil concentrations typical of those found in the target regions, suggests there is potential to improve the tolerance level of adapted varieties and expand lentil production areas to regions with higher concentrations of soil B. [ABSTRACT FROM AUTHOR]