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In the natural environment, soils undergo wetting and drying (WD) cycles due to precipitation and evapotranspiration. The WD cycles have a profound impact on soil physical, chemical, and biological properties and drive the development of structure in soils. Degraded soils are often lacking structure, and the effect of organic amendments and WD cycles on structure formation of these soils is poorly understood. The aim of this study was to evaluate the role of biotic and abiotic factors on aggregate formation and stabilization of sodic soils after the addition of gypsum and organic amendments (feedlot manure, chicken manure, lucerne pallets, and anionic poly acrylamide). Amended soils were incubated at 25 ∘C over four WD cycles, with assessment of soil microbial respiration, electrical conductivity, pH, sodium adsorption ratio (SAR), aggregate stability in water (ASWAT), aggregate size distribution, and mean weight diameter. Our results demonstrate that WD cycles can improve aggregate stability after the addition of amendments in sodic Vertisols, but this process depends on the type of organic amendment. Lucerne pellets resulted in highest soil microbial respiration, proportions of large macroaggregates (>2000 µm), and mean weight diameter. In contrast, dispersion was significantly reduced when soils were treated with chicken manure, whilst anionic polyacrylamide only had a transient effect on aggregate stability. When these organic amendments were applied together with gypsum, the stability of aggregates was further enhanced, and dispersion became negligible after the second WD cycle. The formation and stability of small macroaggregates (2000–250 µm) was less dependent on the type of organic amendments and more dependent on WD cycles as the proportion of small macroaggregates also increased in control soils after four WD cycles, highlighting the role of WD cycles as one of the key factors that improves aggregation and stability of sodic Vertisols.

In the natural environment, soils undergo wetting and drying (WD) cycles due to precipitation and evapotranspiration. The WD cycles have a profound impact on soil physical, chemical, and biological properties and drive the development of structure in soils. Degraded soils are often lacking structure, and the effect of organic amendments and WD cycles on structure formation of these soils is poorly understood. The aim of this study was to evaluate the role of biotic and abiotic factors on aggregate formation and stabilization of sodic soils after the addition of gypsum and organic amendments (feedlot manure, chicken manure, lucerne pallets, and anionic poly acrylamide). Amended soils were incubated at 25 ∘C over four WD cycles, with assessment of soil microbial respiration, electrical conductivity, pH, sodium adsorption ratio (SAR), aggregate stability in water (ASWAT), aggregate size distribution, and mean weight diameter. Our results demonstrate that WD cycles can improve aggregate stability after the addition of amendments in sodic Vertisols, but this process depends on the type of organic amendment. Lucerne pellets resulted in highest soil microbial respiration, proportions of large macroaggregates (>2000 µm), and mean weight diameter. In contrast, dispersion was significantly reduced when soils were treated with chicken manure, whilst anionic polyacrylamide only had a transient effect on aggregate stability. When these organic amendments were applied together with gypsum, the stability of aggregates was further enhanced, and dispersion became negligible after the second WD cycle. The formation and stability of small macroaggregates (2000–250 µm) was less dependent on the type of organic amendments and more dependent on WD cycles as the proportion of small macroaggregates also increased in control soils after four WD cycles, highlighting the role of WD cycles as one of the key factors that improves aggregation and stability of sodic Vertisols.

Soil constraints limit crop water and nutrient extraction and lead to yield loss globally. In rainfed agriculture, the selection of crop species more likely to yield well under constrained conditions is an important management tool. However, information on the most appropriate crops is often difficult to access due to its publication in a wide range of disparate sources and the various measures of crop tolerance used. This study aimed to improve our ability to identify crops for constrained areas in rainfed subtropical cropping systems by compiling published information that had assessed the grain yield response to acidic, saline, or sodic conditions of 17 cereal, pulse, and oilseed crops. This information was used to develop a ‘traffic light’ system for salinity and acidity to provide guidance on when soil pH or the electrical conductivity of a saturated soil extract (ECe) are likely to be ‘good’, ‘potentially limiting’ or ‘poor’ for grain yield. Crops were also ranked according to their likely ability to yield well under saline, acidic, or sodic conditions. For all crops, the point at which grain yield was affected by soil constraints was variable and there was often only a small amount of published information available to help guide the identification of tolerance limits and rankings, particularly for sodicity. Many studies were also conducted under experimental conditions that differed from rainfed farming, which can affect the transferability of results. Confidence in the tolerance limits and rankings is thus only moderate and further work is required to confirm their applicability.

Sodicity is a major soil constraint in many arid and semi-arid regions worldwide, including Australia, which adversely affects the ability of crops to take up water and nutrients from the soil, reducing yield. Reliable methods and tools are required for appropriate selection of traits, may provide a better understanding of crop responses to multiple stresses, especially in sodic soil. A novel strategy was developed using unmanned aerial vehicle (UAV)-thermal imaging and agglomerative hierarchical clustering-based techniques to evaluate and rank the physiological performance of 18 contrasting wheat genotypes grown on a moderately sodic and a highly sodic soil in north-eastern Australia. We obtained UAV-thermal imaging data at different times of the day (9:30, 12:00, and 15:00 hrs) close to flowering stage. Crop biophysical parameters (Leaf potassium concentration, normalized difference vegetation index, crop water uptake, stomatal conductance, plant moisture content, and aboveground biomass) were measured at close to flowering by destructive plant sampling and ground-based proximal sensing and yield was machine harvested at maturity. Canopy temperatures derived from thermal imagery between 28.9 and 35.4 degrees C were observed at the moderately sodic site, and between 36.2 and 41.0 degrees C at the highly sodic site from 9:30 to 15:00 hrs. Canopy temperature was consistently higher than corresponding ambient air temperatures indicating plant water stress at both sites. While the air temperature was not significantly different (p > 0.05) between the two sites, canopy temperature was significantly higher (p < 0.01) on highly sodic soil compared to moderately sodic soil, indicating greater water stress at the highly sodic site. This difference was most likely due to the adverse impacts of sodic soil constraints and not primarily due to environmental variations. Hence, our study revealed that sodic soil constraints can intensify plant water stress. Statistical analysis between canopy temperature (9:30, 12:00, and 15:00 hrs) and crop biophysical parameters showed close negative correlations at both moderately sodic (R-2 = 0.54 to 0.83) and highly sodic (R-2 = 0.30 to 0.89) sites. A closer correlation was observed at 15:00 hrs for both sites. Thus, high-resolution UAV-thermal imaging has potential to detect water-stressed plants on sodic soil. Agglomerative hierarchical clustering was used as an unsupervised machine learning tool for ranking of physiological performance of wheat genotypes. Results suggest that UAV-thermal imaging and AHC techniques can discriminate cultivars tolerant to sodicity. The study improves our understanding of crop physiological behaviour and can assist farmers in selection of water stress tolerant genotypes to sustain food security in sodic soil under water-limited environments.

Dispersive soils limit crop growth and significantly impact world food production. Although numerous reviews have examined soil dispersion, many focus on irrigated systems and fail to differentiate the approaches required for rainfed agriculture. This review seeks to fill this gap by focusing on the impact, identification and management of dispersive soils in rainfed areas. Dispersive soils can have large impacts on crop production because of their adverse physical, chemical and biological effects, with this impact particularly large in rainfed systems where irrigation water is unavailable to supplement crop water supply and assist with amelioration. However, the identification of these soils is challenging and tests that can reliably relate soil characteristics to crop performance are lacking. Recent work has found that first identifying consistently lower yielding locations (using yield mapping or proximal/remote sensing) and then using traditional soil testing to identify the potential cause/s of the yield loss may be a promising approach, although this requires refinement. Knowledge of the type of dispersive soil (e.g., saline/non-saline, acidic/alkaline/neutral) and where constraints occur in the profile (surface or subsoil) must also be determined during identification as this will affect management approaches, particularly where multiple constraints need to be treated together to achieve yield increase. Improved understanding of how to economically use ameliorants and combine them to achieve maximum benefit in the presence of multiple constraints is needed. Greater appreciation of how to use agronomic management to improve crop growth in the presence of dispersive behaviour is also likely to increase profitability in rainfed systems where amelioration is often impractical or uneconomical. Dispersive soils are a major challenge for rainfed cropping, and so the refinement of our management approach can help improve profitability and productivity. Highlights: Dispersive soils limit crop growth and significantly impact world food production We examine the impact, identification and management of dispersive soils in rainfed agriculture Improvements in the identification of dispersive soils are required to improve management Refinement of ameliorant use and agronomic management will improve profitability and productivity.

Conversion of land from native vegetation to long-term agricultural cropping adversely affects soil phosphorus (P) reserves. We examined surface soils (0-0.1 m) from three paired sites from four land uses (native vegetation, cropping, pasture, and plantation, up to 115 years) from subtropical Australia (a Vertisol from Warra, an Oxisol from Lamington, and an Oxisol from Kingaroy) for the changes in the total P concentrations as well as the fractionation of P in bulk soil and in aggregate fractions. Among different land uses and soil types, the conversion of the Kingaroy Oxisol from native vegetation to cropping decreased soil aggregation markedly. Across all three soils, land use change from native vegetation to cropping decreased total organic C (TOC) concentrations by 68-85% and organic P (P-o) by 55-63%. The corresponding decreases in P-o upon conversion to pasture and plantation were lower, being 12-23%. These decreases in P-o were primarily associated with a decrease in the NaOH-P-o fraction (relatively available P). Although land use change to cropping reduced the proportion of large macroaggregates, the P concentration, including NaOH-P-o fraction was similar across all aggregate sizes. Finally, although the overall contribution of the silt+clay fraction was small, the C and P-o reserves in this fraction tended to be more resilient and the C/P-o ratio remained relatively constant. This study has demonstrated the impacts of cropping on soil P reserves, but that conversion of cropping to pasture or plantation can largely reverse these adverse effects.

Filtration products containing silver nanoparticles (Ag-NPs) have been used for water purification to provide drinking water for humans. However, it is unclear if differences in water chemistry influence their effectiveness or whether the presence of Ag in the filtrate (drinking water) impacts the gut microbiome. Using water samples differing markedly in chemical properties, we have found that ≥99.89% of E. coli were killed in all cases, regardless of the water chemistry. However, in the first 25 mL of filtration, concentrations of Ag in most of the water samples (0.14–45.2 mg L−1) exceeded the limit for drinking water (0.1 mg L−1), differing depending upon water chemistry. Synchrotron-based X-ray absorption spectroscopy analysis revealed that up to 36% of the Ag in the filter paper was present as AgNO3 and 64% as Ag-NPs, with this AgNO3 likely contributing to the high Ag concentrations in the filtrate. Finally, we also examined the impacts of oral gavage of the Ag-containing filtrate on the mouse gut microbiome. It was found that Ag from the filtrate accumulated mainly in the liver and kidneys. In female mice, we also found that the Ag-containing filtrate increased the relative abundance of Bacteroidetes in the faeces, whilst decreasing that of Firmicutes. Our data indicate that although Ag-NP-containing filter products have excellent antimicrobial properties, the high concentrations of Ag in the filtrate are potentially of concern for the gut microbiome and further work is required in this regard.

Sodic soils adversely affect crop production over extensive areas of rain-fed cropping worldwide, with particularly large areas in Australia. Crop phenotyping may assist in identifying cultivars tolerant to soil sodicity. However, studies to identify the most appropriate traits and reliable tools to assist crop phenotyping on sodic soil are limited. Hence, this study evaluated the ability of multispectral, hyperspectral, 3D point cloud, and machine learning techniques to improve estimation of biomass and grain yield of wheat genotypes grown on a moderately sodic (MS) and highly sodic (HS) soil sites in northeastern Australia. While a number of studies have reported using different remote sensing approaches and crop traits to quantify crop growth, stress, and yield variation, studies are limited using the combination of these techniques including machine learning to improve estimation of genotypic biomass and yield, especially in constrained sodic soil environments. At close to flowering, unmanned aerial vehicle (UAV) and ground-based proximal sensing was used to obtain remote and/or proximal sensing data, while biomass yield and crop heights were also manually measured in the field. Grain yield was machine-harvested at maturity. UAV remote and/or proximal sensing-derived spectral vegetation indices (VIs), such as normalized difference vegetation index, optimized soil adjusted vegetation index, and enhanced vegetation index and crop height were closely corresponded to wheat genotypic biomass and grain yields. UAV multispectral VIs more closely associated with biomass and grain yields compared to proximal sensing data. The red-green-blue (RGB) 3D point cloud technique was effective in determining crop height, which was slightly better correlated with genotypic biomass and grain yield than ground-measured crop height data. These remote sensing-derived crop traits (VIs and crop height) and wheat biomass and grain yields were further simulated using machine learning algorithms (multitarget linear regression, support vector machine regression, Gaussian process regression, and artificial neural network) with different kernels to improve estimation of biomass and grain yield. The artificial neural network predicted biomass yield (R2 = 0.89; RMSE = 34.8 g/m2 for the MS and R2 = 0.82; RMSE = 26.4 g/m2 for the HS site) and grain yield (R2 = 0.88; RMSE = 11.8 g/m2 for the MS and R2 = 0.74; RMSE = 16.1 g/m2 for the HS site) with slightly less error than the others. Wheat genotypes Mitch, Corack, Mace, Trojan, Lancer, and Bremer were identified as more tolerant to sodic soil constraints than Emu Rock, Janz, Flanker, and Gladius. The study improves our ability to select appropriate traits and techniques in accurate estimation of wheat genotypic biomass and grain yields on sodic soils. This will also assist farmers in identifying cultivars tolerant to sodic soil constraints.

Irrigation with alkaline and sodic groundwater, including water extracted from coal seams (CS-water), has the potential to cause environmental harm through the degradation of soil structure. This study evaluated the effectiveness of soil amendment prior to irrigation with CS-water (pH 9.39, sodium adsorption ratio [SAR] 83) on the soil chemical properties of two soils, a Red Ultisol and a Red-Brown Ultisol. Repacked columns of soil were amended with either gypsum alone or with gypsum combined with elemental sulfur (S). These amendments were either surface applied or incorporated to a depth of 20 cm, with columns irrigated with the equivalent of 36 ML ha−1 CS-water. In the Red Ultisol, soil solution SAR was maintained in the desired range of 10–25 in amended soils, which was generally similar to that achieved in control soils irrigated with pre-treated CS-water where the alkalinity had been neutralized with H2SO4 and sodicity ameliorated by dosing with micronized gypsum prior to irrigation. In the Red-Brown Ultisol soil solution SAR values were higher. Surface-application of amendments (soil solution SAR values of 10–40) was more effective than incorporation (soil solution values of 80–120). Soil solution pH decreased with gypsum and S amendment of the Red Ultisol by up to ≤2.0 pH units, despite irrigation with alkaline CS-water. In contrast, soil solution pH was more difficult to maintain in the Red-Brown Ultisol, with pH increasing to ≈8.0 in most treatments. The results demonstrate that alkaline and sodic CS-water can be chemically ameliorated successfully within the soil profile by the addition of gypsum and S amendments, although the efficacy of chemical amendment depends upon the method of incorporation and soil properties.

With similar chemistry, Mn and Fe interact in their many essential roles in plants but the magnitude and mechanisms involved of these interactions are poorly understood. Leaves of soybean (a Mn-sensitive species) developed a mild chlorosis and small dark spots and distorted trifoliate leaves with 30 μM Mn and 0.6 μM Fe in nutrient solution (pH 5.6; 3 mM ionic strength). At 0.6 μM Fe, lower alternate leaves of sunflower (a Mn-tolerant species) were chlorotic at 30 μM Mn and had a pale chlorosis and necrosis at 400 μM Mn. A concentration of 30 and 300 μM Fe in solution alleviated these typical symptoms of Mn toxicity and decreased the concentration of Mn from >3000 to ca. 800 mg kg-1 dry mass (DM) in all leaf tissues. As expected, increased Fe supply increased Fe in leaves from

We use soils to provide 98.8% of our food, but we must ensure that the pressure we place on soils to provide this food in the short-term does not inadvertently push the Earth into a less hospitable state in the long-term. Using the planetary boundaries framework, we show that soils are a master variable for regulating critical Earth-system processes. Indeed, of the seven Earth-systems that have been quantified, soils play a critical and substantial role in changing the Earth-systems in at least two, either directly or indirectly, as well as smaller contributions for a further three. For the biogeochemical flows Earth-system process, soils contribute 66% of the total anthropogenic change for nitrogen and 38% for phosphorus, whilst for the land-system change Earth-system process, soils indirectly contribute 80% of global anthropogenic change. Furthermore, perturbations of soils contribute directly to 21% of climate change, 25% to ocean acidification, and 25% to stratospheric ozone depletion. We argue that urgent interventions are required to greatly improve soil management, especially for those Earth-system processes where the planetary boundary has already been exceeded and where soils make an important contribution, with this being for biogeochemical flows (both nitrogen and phosphorus), for climate change, and for land-system change. Of particular importance, it is noted that the highly inefficient use of N fertilizers results in release of excess N into the broader environment, contributes to climate change, and results in release of ozone-depleting substances. Furthermore, the use of soils for agricultural production results not only in land-system change, but also in the loss (mineralization) of organic matter with a concomitant release of CO2 contributing to both climate change and ocean acidification. Thus, there is a need to markedly improve the efficiency of fertilizer applications and to intensify usage of our most fertile soils in order to allow the restoration of degraded soils and limit further areal expansion of agriculture. Understanding, and acting upon, the role of soils is critical in ensuring that planetary boundaries are not transgressed, with no other single variable playing such a strategic role across all of the planetary boundaries. Refereed/Peer-reviewed

While land conversion from native vegetation to agriculture influences the concentration, speciation, and cycling of soil phosphorus (P), the nature of these changes remain poorly understood. We collected surface soils (0–10 cm) from paired sites at three locations, comparing soil from native vegetation with adjacent soils converted for cropping, pasture, and plantation for up to 115 y. The extent of organic P loss upon land use change differed between the three soils, with conversion to cropping causing the largest decreased in soil organic P as well as phosphatase activity. Using solution 31P nuclear magnetic resonance (NMR), it was found that cropping caused a pronounced decrease in organic P – both orthophosphate monoesters and orthophosphate diesters. Furthermore, cropping soils had a substantial reduction in the diester-P/monoester-P ratio, indicating the preferential degradation of the more labile orthophosphate diester-P upon conversion to cropping. Importantly, by subsequently converting cropping land to pasture or plantation, these adverse P-related changes could be reversed or at least halted. Synchrotron-based X-ray absorption near-edge structure (XANES) demonstrated that land use change had no pronounced impact on inorganic P, with sorbed P dominating in all treatments. Changes in land use also influenced bacterial diversity, with land use change effects being specific to the three soils. This study provides information on how land use changes alters P behaviour and cycling in soils, with this being important for ensuring the sustainable use of soils for food production. Refereed/Peer-reviewed

In recent years, unmanned aerial vehicle (UAV) - based thermal imaging techniques have become increasingly popular in precision agriculture, especially in monitoring crop biotic and abiotic stresses, and soil water, irrigation scheduling, and residue mapping. However, studies are limited on thermal imaging techniques in yield estimation and in-field variability assessment. Here we evaluate the potential of UAV thermal imaging techniques to assess crop water stress and predict grain yield of 18 contrasting wheat genotypes. We conducted an airborne campaign close to crop flowering to capture thermal imagery for a rain fed wheat experimental field in southern Queensland, Australia. Plot wise canopy temperatures (°C) (T canopy ) were extracted from thermal imagery to determine crop water stress index (CWSI). Wheat grain yield was significantly correlated with CWSI (R2= 0.63; RMSE= 0.34 t/ha). The results suggest potential for UAV thermal imaging techniques to measure crop water status and predict yield under water-limited environments.

Microbial activity strongly influences the stabilization of soil organic matter (SOM), and is affected by the abiotic properties within soil aggregates, which tend to differ between land uses. Here, we assessed the effects of SOM and pore geometry on the diversity and activity of microbial communities within aggregates formed under different land uses (undisturbed, plantation, pasture, and cropping). X-ray micro-computed tomography (μCT) revealed that macro-aggregates (2–8 mm) of undisturbed soils were porous, highly-connected, and had 200% more macro-pores compared with those from pasture and cropping soils. While the macro-aggregates of undisturbed soils had greater soil organic carbon (SOC) contents and N-acetyl β-glucosaminidase, β-glucosidase, and phosphatase activities, those of cropped soils harboured more diverse bacterial communities. Organic carbon was positively associated with the porosity of the macro-aggregates, which was negatively associated with microbial diversity and positively associated with enzyme activity. Thus, the biophysical processes in macro-aggregates may be important for SOC stabilization within the macro-aggregates.

Silver nanoparticles (Ag-NPs) are used in a wide range of everyday products, leading to increasing concerns regarding their accumulation in soils and subsequent impact on plants. Using single particle inductively coupled plasma mass spectrometry (spICP-MS) and synchrotron-based techniques including X-ray absorption spectroscopy (XAS) and X-ray fluorescence microscopy (XFM), we characterized the uptake, speciation, and translocation of insoluble Ag(2)S-NPs (an environmentally-relevant form of Ag-NPs in soils) within two plant species, a monocot and a dicot. Exposure to 10 mg Ag L(−1) as Ag(2)S-NPs for one week resulted in a substantial increase in leaf Ag concentrations (3.8 to 5.8 μg Ag g(−1) dry mass). Examination using XAS revealed that most of the Ag was present as Ag(2)S (>91%). Furthermore, analyses using spICP-MS confirmed that these Ag(2)S particles within the leaves had a markedly similar size distribution to those supplied within the hydroponic solution. These observations, for the first time, provide direct evidence that plants take up Ag(2)S-NPs without a marked selectivity in regard to particle size and without substantial transformation (dissolution or aggregation) during translocation from roots to shoots. Furthermore, after uptake, these Ag(2)S-NPs reduced growth, partially due to the solubilisation of Ag(+)in planta, which resulted in an upregulation of genes involved in the ethylene signalling pathway. Additionally, the upregulation of the plant defense system as a result of Ag(2)S-NPs exposure may have contributed to the decrease in plant growth. These results highlight the risks associated with Ag-NP accumulation in plants and subsequent trophic transfer via the food chain.

The accumulation of Ag2S in agricultural soil via application of Ag-containing sludge potentially affects the functioning of soil microorganisms and earthworms (EWs) due to the strong antimicrobial properties of Ag. This study examined the effects of Ag2S nanoparticles (Ag2S-NPs) on the EW-mediated (Eisenia fetida and Pontoscolex corethrurus) soil N cycle. We used 16S rRNA gene-based sequencing and quantitative polymerase chain reaction to examine the bacterial community and nitrification/denitrification-related gene abundance. The presence of either EWs or Ag significantly increased denitrification and N2O emissions. However, the addition of Ag2S to EW-inhabited soil reduced N2O emissions by 14-33%. Furthermore, Ag2S caused a low-dose stimulation but a high-dose inhibition to N2O flux from the EW gut itself. Accordingly, an increase in Ag in the EW gut caused a decrease in the relative abundance of denitrifiers in both the soil and the gut, especially for the dominant genus Bacillus. Ag2S also decreased the copy numbers of nitrification gene (nxrB) and denitrification genes (napA, nirS, and nosZ) in EW gut, leading to the observed decrease in N2O emissions. Collectively, applying Ag2S-containing sludge disturbs the denitrification function of the EW gut microbiota and the cycling of N in soil-based systems.

Wheat production in southern Queensland, Australia is adversely affected by soil sodicity. Crop phenotyping could be useful to improve productivity in such soils. This research focused on adapting high-throughput phenotyping of crop biophysical attributes to monitor crop health, nutrient deficiencies and plant moisture availability. We conducted an aerial and ground-based campaign during several wheat growing stages to capture crop information for 18 wheat genotypes at a moderately sodic site near Goondiwindi in southern Queensland. Three techniques were employed (multispectral, hyperspectral, and 3D point cloud) to monitor crop characteristics and predict biomass and yield. Spectral information and vegetation indices (VI) such as, normalized different vegetation index (NDVI), modified soil adjusted vegetation index (MSAVI), and leaf area index (LAI) were derived from multispectral imagery and compared with ground-based agronomic data for biomass, leaf area, and yield. Significant correlations were observed between NDVI and yield (R2 = 0.81), LAI (R2 = 0.74), and biomass (R2 = 0.65). Partial least square regression (PLS-R) modelling using hyperspectral spectroscopy data provided crop yield predictions that correlated significantly with observed yield (R2 = 0.65). The 3D point cloud technique was effective with comparison to in field manual measurements of crop architectural traits height and foliage cover (e.g., for height R2 = 0.73). For, this study multispectral techniques showed a greater potential to predict biomass and yield of wheat genotypes under moderately sodic soils than hyperspectral and 3D point cloud techniques. In future, the genotypes will be tested under more severely sodic soils to monitor crop performance and predicting yield.

Silver (Ag) is released from a range of products and accumulates in agricultural soils as silver sulfide (Ag2S) through the application of Ag-containing biosolids as a soil amendment. Although Ag2S is comparatively stable, its solubility increases with salinity, potentially altering its impacts on microbial communities due to the anti-microbial properties of Ag. In this study, we investigated the impacts of Ag on the microbially mediated N cycle in saline soils by examining the relationship between the (bio)availability of Ag2S and microbial functioning following the application of Ag2S-containing sludge. Synchrotron-based X-ray absorption spectroscopy (XAS) revealed that the Ag2S was stable within the soil, although extractable Ag concentrations increased up to 18-fold in soils with higher salinity. However, the extractable Ag accounted for

The conversion of soils from conventional till (CT) to no-till (NT) management has been identified as a soil management practice with the potential to increase soil organic carbon (SOC) sequestration and help mitigate global climate change. However, the changes in SOC observed in NT systems have often been variable and dependent on a combination of factors, including climate, cropping system, soil type and crop/soil management. This had led to large variation in the rates of sequestration observed worldwide. In addition, there is concern some studies may have overestimated SOC sequestration rates due to methodological issues, with some authors concluding that once these methodological factors are considered, the potential for NT to sequester C on a worldwide scale may be limited. When the effect of NT on N2O and CH4 emissions are also considered, the benefits of NT management to mitigate climate change can be further eroded and NT may even increase net greenhouse gas (GHG) emissions - for example from fine textured and poorly drained soils where NT management increases N2O emissions. However, the potential for net C sequestration in NT systems is site specific and where site conditions/management favor SOC accumulation and lead to neutral or decreases in N2O production, significant decreases in global warming potential (GWP) can be observed. This highlights the need to consider the net GWP of NT on a soil type, site or regional basis.

No-till (NT) farming systems have revolutionized agriculture by improving erosion control, soil water storage, soil quality and, in many instances, yield and net farm income. The adoption of NT systems has increased at an exponential rate since the 1990s and they are now used on 12.5% of global croplands. However, while the development of NT systems has seen much success, there can be significant agronomic, economic and/or social challenges associated with their use that limit large scale worldwide adoption. In addition, where NT is not implemented as part of an integrated system that incorporates stubble retention and appropriate crop rotations to help manage weeds, diseases, pests and soil fertility, decreases in yield can be observed. A combination of research, education and good policy development to remove economic/institutional and social barriers to uptake are required to ensure the continued success of NT. In particular, the tailoring of NT farming systems according to individual locations and the introduction of some flexibility in approach to tillage management can provide an opportunity to manage some of the challenges of NT farming systems.

Examples of how to simulate performance of conservation agriculture (CA) and conventional tillage (CT) practices using cropping systems models are rare in the literature, and from the Eastern Gangetic Plains (EGP). Here we report a comprehensive evaluation of the capacity of APSIM for simulating the performance of CA and CT cropping practices under a diverse range of tillage (CT vs zero tillage (ZT)), crop establishment options (puddled transplanted rice vs unpuddled transplanted rice), residue, N rates, and irrigation practices from two sites in the EGP that differed in soil type, water table dynamics, and agro-climatic conditions. We followed a robust procedure of model parameterisation, calibration, and validation, then undertook statistical analyses to evaluate model performance. We have demonstrated that when different values for key model input parameters are employed (i.e. change in soil properties (Ks, BD)), crop rooting parameters (xf- root hospitality, kl- root extraction efficiency) and soil microorganism activity (Fbiom- fraction of soil organic matter present as microbial biomass and Finert- the inert fraction of soil organic matter), the model performed well in simulating the different performances of CA and CT management practices across the environments in the EGP. Model performance was markedly better in the full-N than in zero-N, but both are still considered acceptable. In addition to well-watered and fertilised treatments, the model was able to capture an observed crop failure in rainfed unpuddled transplanted rice accurately, illustrating an ability to capture crop response under a wide range of water stress environments. As demonstrated by robust statistical criteria, APSIM was able to capture the effect of cropping system, irrigation, tillage, residue, and N-application rate within the bounds of experimental uncertainty, hence is now deemed a suitable tool for scenario analyses around the relevant practices.

The distribution and concentration of nutrients and contaminants affect almost every metabolic process in plants but analytical limitations have hindered the determination of microscopic changes over time within living plant tissues. We developed a novel method using synchrotron-based micro X-ray fluorescence (μ-XRF) that, for the first time, allows quantification of the spatial and temporal changes of multiple elements in the same area of living leaves. The utility of this approach was tested by examining changes over 48 h in unifoliate leaves of 7-d-old cowpea (Vigna unguiculata) plants simultaneously at 0.2 and 30 μM Mn in nutrient solution, with 30 μM Mn known to be toxic to cowpea and cause the formation of Mn-dense lesions. The fast X-ray fluorescence detector system reduced dwell on living leaf samples. This produced no evidence of tissue damage through repeated μ-XRF scanning, thereby overcoming previously noted experimental artifacts. This permitted, for the first time, visual and quantitative assessments of spatial and temporal changes in nutrient concentrations. By focusing on changes in Mn status, this study illustrated extension of two-dimensional μ-XRF scans to a three-dimensional geometry of Mn kinetics in the same area of leaves. The multi-element potential of this method was exemplified through the measurement of distributions and concentrations of K, Ca, Fe, Cu, and Zn within living plant leaves. This novel method and accompanying information on changes in Mn distribution showed the potential for microscopic, time-resolved, in vivo examination of changes in elemental distribution. We consider that this method will be of benefit for a wide range of studies, including functional characterization of molecular biology, examining changes in the distribution of nutrients, and understanding the movement and toxicity of contaminants.

Information on long-term yield variability is important for tailoring farming practices to the needs of crops. We present a linear mixed-effects model to predict wheat yield at a within-field scale in the northern grain-growing region of Australia. The model predicts yield as a function of Landsat time-integrated Normalized Difference Vegetation Index (iNDVI), and is trained on sparsely sampled yield-monitored data from 17 farms from 2001 to 2016. The model is flexibly parameterized, to use information from specific fields, farms or years, to capture local departures from the global yield-iNDVI relation. We estimated iNDVI numerically by integrating the area under a fitted asymmetric bell-shaped growth function, across the growing season (May to October), using NDVI time-series from April to November. We performed leave-one-out cross-validation, where data from individual farms, fields and years were omitted in a series of tests. Results showed moderate predictive accuracy at a within-field scale, with an average RMSE of 0.79 Mg/ha. The spatial pattern of within-field yield variation was adequately represented. The benefit of the mixed-effects model is that, as well as describing the general relation between wheat yield and iNDVI, it explicitly considers the spatial and temporal differences among farms, fields and years, which are related to variations in soil conditions, farm-management practices and climate. The long-term archive of Landsat imagery – combined with a growing archive of yield maps – provides potential for the model to predict yield variation across large regions and many seasons. Such information could help farmers make decisions on site-specific soil and nutrient management, and simultaneously guide policy-makers towards regional development objectives.

Soil sodicity, acidity, and salinity are important soil constraints to wheat production in many cropping regions across Australia, and the Australian agricultural industry needs accurate information on their economic impacts to guide investment decisions on remediation and minimize productivity losses. We present a modelling framework that maps the effects of soil constraints on wheat yield, quantifying forfeited wheat yields due to specific soil constraints at a broad spatial scale and assessing the economic benefit of managing these constraints. Of the three soil constraints considered (sodicity, acidity, and salinity), sodicity caused the largest magnitude of yield gaps across most of the wheat‐cropping areas of Australia, with an average yield gap of 0.13 t ha⁻¹yr⁻¹. Yield gaps due to acidity were more concentrated spatially in the high‐rainfall regions of Western Australia, Victoria, and New South Wales, and averaged 0.04 t ha⁻¹yr⁻¹ across the wheat‐cropping areas of Australia, whereas the yield gap due to salinity was estimated to be 0.02 t ha⁻¹yr⁻¹. The lost opportunity associated with soil sodicity for wheat production was estimated to be worth A$1,300 million per annum, for soil acidity, A$400 million per annum, and for salinity, A$200 million per annum. The results of this work should prove useful to guide national investment decisions on the allocation of resources and to target areas where more detailed information would be required in order to reduce the yield gap associated with soil constraints on wheat yields in Australia.