Browsing by Browse by FOR 2020 "300204 Agricultural management of nutrients"

The Macleay floodplain on the north coast of New South Wales, Australia, has surface soil concentrations of up to 40 mg kg⁻¹ arsenic (As) and antimony (Sb), due to historical mining practices in the upper catchment. The floodplain also contains areas of active and potential acid sulfate soils (ASS). Some of these areas are purposely re-flooded to halt oxidation processes, but the effect of this management on the metalloid mobility and phytoavailability of the metalloids present is unknown. This study investigated the changes to soil solution As and Sb, associations of metalloids with soil solid phases, and uptake into two common pasture species following 20 weeks of flooding in a controlled environment. The effect of an ASS subsoil was also investigated. The soil solution concentration and availability of the metalloids was in some instances higher in the floodplain soils than would generally be expected in soils with comparable contamination. There appeared to be few changes to soil solution concentrations or phase associations with flooding in this short term study, due to the high acid buffering and poise of the investigated soils. A strong relationship was found between the relative uptake of Sb into pastures and the oxalate extractable Fe in the soil, which was taken as a proxy for non-crystalline iron (Fe) hydroxides. This relationship was dependent on flooding and was absent for As. Further targeted investigations into metalloid speciation kinetics and the stability of soil solid phases with flooding management are recommended.

A tiered approach to contamination exposure assessment is currently adopted in many countries. Increasing the site-specific information in exposure assessments is generally recommended when guideline values for contaminants in soil are exceeded. This work details a Bayesian Network (BN) approach to developing a site-specific environmental exposure assessment that focuses on the simple mapping and assessment of assumptions and the effect of new data on assessment outcomes. The BN approach was applied to a floodplain system in New South Wales, Australia, where site-specific information about elevated antimony (Sb) concentrations and distribution in soils was available. Guidelines for exposure assessment in Australia are used as a template for this site, although the approach is generic. The BN-based assessment used an iterative approach starting with limited soil Sb data (41 samples ranging from 0 to 18 mg kg⁻¹ Sb) and extending the model with more detailed Sb data (145 samples ranging from 0 to 40 mg kg⁻¹ Sb). The analyses identified dominant exposure pathways and assessed the sensitivity of these pathways to changes in assumptions and the level of site-specific information available. In particular, there was a 10.8% probability of exceeding the tolerable daily intake of Sb in the case study when the limited soil Sb data was used, which increased to 26.2% with the more detailed sampling regime. There was also a 47% decrease in the probability of overexposure to Sb when the dermal bioavailability of arsenic (a similar metalloid) was used as a surrogate measure instead of a default bioavailability of 100%. We conclude that the BN approach to soil exposure assessment has merit both in the context of Australian and international soil exposure assessments.

Heavy metal soil contamination provides a danger both to human and environmental ecosystem health and is still on the rise in many developing countries. Electroremediation provides an innovative method to remedy contamination of soils by heavy metals. Fundamental to the acceptance of any soil remedial technique is proof that positive benefits outweigh the negative impacts, in terms of soil health. The environmental effect of electroremediation of heavy metals contaminated soil by some biological indicators was evaluated. A soil contaminated with Zn, Pb, Ni, and Cd was used in a laboratory experiment. Treatment was imposed with a constant voltage gradient of 0.83 V/cm for 20 days. Results indicated that the physicochemical changes caused by the electroremidiation process on the soil microbial population (actinomycetes and gram-positive and negative bacteria), soil respiration and microbial biomass were significant (p < 0.01). At the commencement of the study, soil microbial activity was reduced, due to physicochemical changes in pH, amount of moisture and the changes in the levels of heavy metals in the soil. The greatest reduction on the microbial activity was close to the cathode where high levels of heavy metal concentrations and high pH were demonstrated. The metabolic quotient index [qCO₂] was used to achieve a more refined evaluation, compared to analysis of soil respiration and microbial biomass alone. Accordingly, high amounts of qCO₂ near the cathode show the unfavorable living conditions of such microorganisms in these sections.

Deep placement of phosphorus (P) has been shown to increase the effectiveness of fertiliser application in soils with a long cropping history. This cropping history has also often depleted potassium (K) reserves. Research on co-application of phosphorus and potassium has produces variable results. Factors contributing to these variable results such as placement, pH, and K source have been investigated in a glasshouse trial. ³²P labelled P fertiliser was applied alone or mixed with four K sources (nitrate, chloride, sulfate, potassium phosphate) to test if the anion associated with K affected P and K uptake by mungbeans [Vigna radiata (L.) Wilczek]. There was no significant difference between treatments in fertiliser P recovery with either surface or deep placement. The only significant effect was higher shoot and root yield and higher fertiliser P and K recovery in most treatments compared with the zero K treatment with the highest values in the P+K₂SO₄ surface treatment. This increased uptake was not attributable to increased root growth in the fertiliser band or to a difference in band or rhizosphere pH as these were not significantly different in this treatment from the other K source treatments.

Field samples and a 9-week glasshouse growth trial were used to investigate the accumulation of mining derived arsenic (As) and antimony (Sb) in vegetable crops growing on the Macleay River Floodplain in Northern New South Wales, Australia. The soils were also extracted using EDTA to assess the potential for this extractant to be used as a predictor of As and Sb uptake in vegetables, and a simplified bioaccessibility extraction test (SBET) to understand potential for uptake in the human gut with soil ingestion. Metalloids were not detected in any field vegetables sampled. Antimony was not detected in the growth trial vegetable crops over the 9-week greenhouse trial. Arsenic accumulation in edible vegetable parts was <10 % total soil-borne As with concentrations less than the current Australian maximum residue concentration for cereals. The results indicate that risk of exposure through short-term vegetable crops is low. The data also demonstrate that uptake pathways for Sb and As in the vegetables were different with uptake strongly impacted by soil properties.

For this research, soils were collected from three long-term (16–46 years) management systems in semi-arid (Luvisol, at Condobolin, NSW), Mediterranean (Luvisol, at Merredin, WA) and sub-tropical (Vertisol, at Hermitage, QLD) environments in Australia from 0–10 cm, 10–20 cm and 20–30 cm depths. The practices at Condobolin comprised conventional (CT) and reduced tillage (RT) under mixed crop-pasture rotation, no-till (NT) under continuous cereal–cover crop rotation, and perennial pasture (PP). The practices at Merredin comprised stubble either retained (SR) or burnt (SB) under direct-drilled continuous wheat–legume rotation. The practices at Hermitage comprised a factorial combination of CT, NT, SR, SB, with either 0 (0N) or 90 kg urea-N ha-1 (90N) under continuous wheat–wheat rotation. To see soil aggregate stability, and SOC and nutrient stocks across the three long-term sites, dry and wet sieving techniques were performed to fractionate mega- (> 2 mm), macro- (2–0.25 mm), micro-aggregate (0.25–0.053 mm) and silt-plus-clay (< 0.053 mm) fractions. Further, to understand SOC and nutrient (N, P and S) mineralisation dynamics in bulk soil and soil aggregates, soils with or without crop residues were incubated for 126 days. To understand the allocation dynamics of newly assimilated C and N in a canola crop–soil system with different tillage and N fertilisation treatments, a field-based 13C15N isotopic study was performed at Wagga Wagga, NSW. The results showed that long-term management practices influenced carbon and nutrient (N, P and S) concentrations in soil aggregates, although had minimal impact on soil carbon and nutrient storage and aggregate stability. Soil organic matter was shown as a ready source of plant-available nutrients with variations across management practices. Crop stubble input in tilled (cf. no-till) systems caused a greater release of available nutrients. Further, tillage enhanced newly-assimilated carbon input into a soil system, leading a greater crop nitrogen uptake. These novel findings enhanced understanding of the impact of management practices on soil carbon and nutrient storage and nutrient availability in agro-ecosystems.

The cereal disease Fusarium crown rot (FCR), caused by the fungal pathogen Fusarium pseudograminearum (Fp), is a major constraint to cereal production worldwide. Nitrogen (N) fertilizer is estimated to be approximately 30% of the input costs for grain growers in Australia and is the primary driver of yield and grain protein levels. When targeting high yield and protein, generous nitrogen fertilizer applications are thought to result in large biomass production, which exacerbates FCR severity, reducing grain yield and quality. This research was undertaken to investigate the effect of temporal N availability in high-protein bread and durum wheat varieties on FCR severity. Laboratory and controlled environment experiments assessed the relationship between FCR and N at a mechanistic and plant level. An in vitro study demonstrated an increase in Fp mycelial growth under increased N availability, especially when N was supplied as urea compared with ammonium nitrate. Similarly, under controlled environmental conditions, increased soil N availability promoted FCR severity within infected plants. Stem N transfer efficiency was significantly decreased under FCR infection in both bread and durum wheat varieties by 4.5% and 10.2%, respectively. This new research demonstrates that FCR not only decreases yield and grain quality but appears to have previously unrecognised detrimental impacts on nitrogen-use efficiency in wheat. This indicates that the current impact of losses from FCR may also decrease N-use inefficiencies, as well as yield and quality penalties. An improved understanding of the interactions and restrictions of FCR infection may allow growers to better manage the disease through manipulation of the soil's temporal N availability.

Agricultural soils are the primary anthropogenic source of atmospheric nitrous oxide (N₂O), contributing to global warming and depletion of stratospheric ozone. Biochar addition has shown potential to lower soil N₂O emission, with the mechanisms remaining unclear. We incubated eucalypt biochar (550°C) - 0, 1 and 5% (w/w) in Ferralsol at 3 water regimes (12, 39 and 54% WFPS) - in a soil column, following gamma irradiation. After N₂O was injected at the base of the soil column, in the 0% biochar control 100% of expected injected N₂O was released into headspace, declining to 67% in the 5% amendment. In a 100% biochar column at 6% WFPS, only 16% of the expected N₂O was observed. X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N₂O and the biochar surfaces. We have shown increases in -O-C = N /pyridine pyrrole/NH₃, suggesting reactions between N₂O and the carbon (C) matrix upon exposure to N₂O. With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents. Evidence suggests that biochar has taken part in redox reactions reducing N₂O to dinitrogen (N₂), in addition to adsorption of N₂O.

According to soil scientist Dr Oliver Knox, regional nitrogen (N) fertiliser trials results continue to support the message that optimising N application rates improves profitability, reduces environmental losses, and improves nitrogen fertiliser use efficiency. The aim of these trials, conducted by the CottonInfo Regional Development Officers (RDOs) is to increase confidence in the science behind fertiliser application decisions.