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Atmospheric carbon dioxide concentrations [CO2] are increasing steadily. Some reports have shown that root growth in grain crops is mostly stimulated in the topsoil rather than evenly throughout the soil profile by e[CO2], which is not optimal for crops grown in semi-arid environments with strong reliance on stored water. An experiment was conducted during the 2014 and 2015 growing seasons with two lentil (Lens culinaris) genotypes grown under Free Air CO2 Enrichment (FACE) in which root growth was observed non-destructively with mini-rhizotrons approximately every 2–3 weeks. Root growth was not always statistically increased by e[CO2] and not consistently between depths and genotypes. In 2014, root growth in the top 15 cm of the soil profile (topsoil) was indeed increased by e[CO2], but increases at lower depths (30–45 cm) later in the season were greater than in the topsoil. In 2015, e[CO2] only increased root length in the topsoil for one genotype, potentially reflecting the lack of plant available soil water between 30–60 cm until recharged by irrigation during grain filling. Our limited data to compare responses to e[CO2] showed that root length increases in the topsoil were correlated with a lower yield response to e[CO2]. The increase in yield response was rather correlated with increases in root growth below 30 cm depth. [ABSTRACT FROM AUTHOR]

The name of the co-author of the article mentioned above was incorrectly presented. [ABSTRACT FROM AUTHOR]

Climate change impacts to crop production are likely to be greatest in semi-arid regions already constrained by marginal growing conditions. The response of temperate grain crops (wheat, field pea and lentil) to elevated CO2 (eCO2) (550 µmol mol-1) under semi-arid field conditions was studied over 11 years in the Australian Grains Free Air CO2 Enrichment (AGFACE) research program. This review synthesizes key outcomes and implications for crop adaptation in a semi-arid environment. Across all crops and environments, eCO2 increased mean yields (16-58%) compared to current ambient (aCO2) concentrations. Wheat yields increased by 18% and 29% under rainfed and supplemental irrigation, respectively resulting in yield increases of 6.1 (aCO2) and 14.1 (eCO2) kg ha-1 mm-1 of additional water. Wheat grain [N] declined (~ 7%) under eCO2 across cultivars, resulting in reduced grain protein and bread baking quality, and this was not reversed by additional fertilizer N. Of several tested crop traits favorable for dryland cropping of wheat under eCO2, a transpiration efficiency trait increased yields under eCO2 representing a path for adaptation in semi-arid environments. The rates and amounts of N2 fixation in legumes were increased by eCO2 but were greater under higher soil water content. Barley yellow dwarf virus incidence increased by 10.6% due to changes in epidemiology under eCO2. Results from AGFACE suggest that maximizing the advantages of eCO2 requires synergistic development of adapted management systems, innovative genetics and removing physiological bottlenecks. This systems approach will increase the potential to maintain agricultural production in new combinations of environments for longer than if changes are piecemeal. [ABSTRACT FROM AUTHOR]

The yield of rain-fed crops needs to increase to meet the requirements of a growing human population. One way to achieve this is to store more rain in the root zone of soils and increase its use by crops. This will be difficult where poorly structured, dense clay subsoils occur. These subsoils limit crop yields by reducing root growth, and the uptake of soil water and nutrients. Reduced root growth results from physical factors, such as low porosity restricting the movement of air and water, high soil strength and temporal water logging which impedes the roots. Chemical factors such as alkalinity, salinity, and sodicity may further restrict root growth in neutral pH and alkaline clay subsoils. This review will focus on the challenging task of improving structure in these dense clay subsoils and to overcome physicochemical constraints in the subsoil, in order to increase crop yields. Early attempts to ameliorate these subsoils using tillage practices, and amendments in some cases, were rarely successful. A more recent and successful approach has been to deep-band nutrient-rich organic amendments in the subsoil, and to follow with a field crop. This increased root growth in the subsoil, and was often associated with improved subsoil structure. It was able to produce substantial and prolonged increases in crop production. A key benefit was an increase in plant available water in the subsoil and the utilization of this water by the crop. The impact of the practice depends on the amount and distribution of rainfall, and this results in increased financial risk for the farm business. Specialized machinery will need to be developed to handle the amendments, while the form, rate of incorporation, and placement depth of amendments will need to be optimized to reduce high upfront costs of the practice. [ABSTRACT FROM AUTHOR]

Poorly-structured dense clay subsoils are widespread in dryland cropping regions in south-eastern Australia. They limit nutrient and water uptake from the subsoil which can limit grain yields. Recent research has shown that ameliorating subsoils with organic amendments can improve yields on these soils but the mechanisms underpinning this response remain unclear. Thus, different subsoil amelioration practices were imposed once at the high- and medium-rainfall sites followed with different crop sequences from 2018 to 2020. Both sites had poorly-structured sodic clay subsoils. The four experimental treatments assessed were 1) unamended control, 2) deep-banded gypsum, 3) chicken manure pellets applied to the topsoil, and (4) deep-banded in the subsoil. Compared to the control, both manure treatments significantly (p < 0.05) increased greenness in the upper leaves (SPAD readings), the green leaf area, and green leaf duration, and thereby delayed canopy senescence. The manures generally increased leaf N concentrations at anthesis, and at mid grain fill in all cereal crops, but not in faba bean. The manures also increased photosynthetic rates and instantaneous transpiration efficiencies (ITEs) in upper leaves of both cereal and faba bean crops, during grain or pod fill, but not in very dry years. Only one site and year combination, i.e. Tatyoon in 2018, showed an increase in grain yield. Despite the favourable effects of manures on crop canopies, unfavourable seasonal (rainfall) conditions were considered to be the major factor that limited yield increases by manured crops. Manuring in the medium-rainfall regions is likely ineffective in terms of crop productivity improvement. [Display omitted] • The manures generally increased greenness and leaf N concentrations in cereal crops. • The manures increased photosynthetic properties in crops but not in very dry years. • Unfavourable seasonal rainfall likely limited yield increases by manured crops. [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 & 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]

This study proposes Jarvis-type model parameterisations for estimating stomatal conductance ( g s ) in wheat ( Triticum aestivum L.) under ambient [CO 2 ] (a[CO 2 ], approximately 390 μmol mol −1 ) and elevated [CO 2 ] (e[CO 2 ], approximately 550 μmol mol −1 ), based on measurements collected in the Australian Grains Free Air CO 2 Enrichment (AGFACE) facility. Relationships of g s with phenological and environmental factors were evaluated using a boundary line technique. Results suggest that g s -response functions for vapour pressure deficit (VPD), volumetric soil moisture (VSM) and temperature dependence were different between a[CO 2 ] and e[CO 2 ]: VPD induced stomatal closure at approximately 3 and 2.5 kPa under a[CO 2 ] and e[CO 2 ] respectively, and optimum temperature was 2 °C lower under e[CO 2 ]. Elevated [CO 2 ] decreased maximum g s ( g max ) by approximately 35%. [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]

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]

Future productivity increases of lentil in the face of changing climates and their expansion into areas traditionally considered marginal for commercial production will require greater tolerance to a range of abiotic constraints, particularly in relation to edaphic conditions. Variation in root system architecture presents a possible means of addressing these constraints. Whilst considerable attention has been paid in the past to above-ground traits; little attention has been given to how root traits can improve adaptation to new environments and productivity. This study aimed to characterise the diversity in root traits present in the Australian lentil germplasm and how breeding may have impacted these traits. The study examined 36 genotypes of lentil registered over the past 27 years in Australia. The experiments were carried out under glasshouse conditions in 2021 and in the field in 2020 and 2021. Results showed a significant variation in both shoot and root traits. Late maturing genotypes accumulated more root biomass, which was associated with a negative impact on yield, harvest index and 100 grain weight. Root traits that varied substantially among genotypes included root biomass, length, depth, surface area, root: shoot ratio and diameter below 60 cm. Geneotypes were catergoised into two major root forms based on root length distribution, 'Shallow' and 'Deep'. Assessment of genotypes registered since the inception of the breeding program showed an indirect selection for smaller roots with early maturity and increasing yield. Lentil varieties released for broadacre cropping in Australia have been selected for shoot architecture and yield, which has inadvertently resulted in variation in root architecture. Thus, these variations and plasticity in root architectural responses can be directly targeted for the future development of climate-ready crops. • Lentil breeding has produced genotypes with early maturity and greater yields. • Breeding for better shoot and yield traits has indirectly selected smaller roots. • Genotypes differed significantly in both shoot and root traits. • Late maturing genotypes accumulated more shoot and root biomass. • Root biomass had a negative impact on yield traits under optimum conditions. [ABSTRACT FROM AUTHOR]

The association between the responses of microbial activity and residue decomposition to elevated atmospheric [CO2] under field conditions in Australian cropping systems is unknown. We measured soil CO2 emission and decomposition of wheat and field pea residues in a wheat cropping system in the field using the Australian Grains Free-Air CO2 Enrichment (AGFACE) facility in Horsham, Victoria. Elevated [CO2] (550 μmol mol−1) increased soil CO2 emission by 41%, but did not affect the percentage of the original mass or C remaining for either type of residue throughout the experimental period. Our findings suggest that the rates of residue decomposition and residue C mineralization in this semi-arid wheat cropping system were not affected by elevated [CO2] despite higher microbial activity. This has major implication for the C sequestration potential of semi-arid cropping systems under future CO2 climates. [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]

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]