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The Department of Soil and Physical Sciences has responsibility for the delivery of all undergraduate and postgraduate soil-related subjects, and many physical science subjects.
The range of research being undertaken is extensive but in recent years has increasingly focused on environmental issues, especially soil's role and influence on water and air quality.
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Item Open Access Research at the interface between Indigenous knowledge and soil science; weaving knowledges to understand horticultural land use in Aotearoa New Zealand(Copernicus GmbH, 2024-12-09) Gillespie, Julie; Payne, Matiu; Payne, Dione; Edwards, Sarah; Jolly, Dyanna; Smith, Carol; Cavanagh, Jo-AnneAddressing the complex challenges of soil and food security at international and local scales requires moving beyond the boundaries of individual disciplines and knowledge systems. The value of transdisciplinary research approaches is increasingly recognised, including those that value and incorporate Indigenous knowledge systems and holders. Using a case study at Pōhatu, Aotearoa New Zealand, this paper demonstrates the value of a transdisciplinary approach to explore past Māori food landscapes and contribute to contemporary Māori soil health and food sovereignty aspirations. Engaging at the interface between soil science and Indigenous knowledge (mātauraka Māori) in an Aotearoa New Zealand context, we provide an example and guide for weaving knowledges in a transdisciplinary context. Here, mātauraka Māori, including waiata (songs) and ingoa wāhi (place names), provided the map of where to look and why, and soil analysis yielded insight into past cultivation, soil modification and fertilisation practices. Both knowledges were needed to interpret the findings and support Māori to re-establish traditional horticultural practices. Furthermore, the paper extends the current literature on the numerous conceptual frameworks developed to support and guide transdisciplinary research by providing an example of how to do this type of research in an on-the-ground application.Publication Open Access Impact of managed aquifer recharge on nitrate concentration changes in an alluvial aquifer : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Water Resource Management at Lincoln University(Lincoln University, 2024) Teixeira, SidineiNitrate leaching poses significant challenges to agricultural environments, endangering water quality, human health, and ecosystems. Managed Aquifer Recharge (MAR) is a technology aimed at improving water quality in contaminated aquifers by dilution with high quality recharging water. This study investigates the effectiveness of MAR techniques, specifically infiltration basins and streambed channel modifications, in mitigating rising nitrate levels in the alluvial aquifers of the Hekeao/Hinds Plains (HHP), New Zealand. The research addresses four key objectives: identifying water sources contributing to groundwater recharge, evaluating biochemical processes affecting groundwater chemistry, comparing nitrate fluxes under different irrigation practices, and assessing MAR's impact on groundwater nitrate concentrations. Using chemical analyses, including isotopic signatures and major ion concentrations, alongside multivariate statistical techniques such as Bayesian mixing models, this study quantifies multiple recharge sources and their impact on nitrate pollution. The findings reveal that land surface recharge contributes 60% of groundwater recharge, with the remainder coming from water race recharge, and river recharge, collectively termed unmanaged aquifer recharge (UMAR). Oxidizing groundwater conditions were found to impede denitrification, significantly influencing groundwater chemistry and limiting natural nitrate attenuation. Areas irrigated with groundwater showed nitrate levels comparable to those irrigated with low-solute water, indicating additional influencing factors beyond irrigation water quality. Even with high-quality water inputs from abundant rain and low-solute irrigation, persistent soil solutes inevitably leach into groundwater. MAR demonstrated significant potential for nitrate dilution as far as 3 km down-gradient from the infiltration basin, with the dilution effect decreasing with distance. In one area, MAR contributed up to 52% of groundwater recharge, effectively decreasing nitrate concentrations from 26.6-30.9 mg NO3/L (start of MAR scheme operation in 2016) to 7-12 mg NO3/L (monitoring 2022). However, in areas without substantial MAR influence, the volume of MAR-influenced water was insufficient to dilute extensive nitrate plumes to below 50 mg NO3/L. This research contributes a transferable methodology for quantifying pollutant inputs in catchments with isotopically similar but chemically diverse sources. It precisely quantifies MAR's role in nitrate dilution, enhancing our understanding of sustainable groundwater management practices. The findings underscore the potential of MAR techniques as viable solutions for mitigating nitrate pollution while highlighting the need for comprehensive management strategies in alluvial aquifers. Given the oxidizing conditions that impede denitrification, effective management practices, including optimized MAR implementation, remain crucial for mitigating nitrate contamination. Keywords: Managed aquifer recharge, unmanaged aquifer recharge, heterogeneous alluvial aquifer, nitrate pollution mitigation, Bayesian mixing model, multivariate statistical techniques, stable water isotope, irrigation, groundwater chemistry, land surface recharge, Hekeao/Hinds Plains.Publication Restricted Characterisation of the hydraulic properties of soil columns via tension infiltrometer and dye tracer patterns: A dissertation submitted in partial fulfilment of the requirements for the degree of Master of Natural Resources Management and Ecological Engineering(Lincoln University, 2007) Hanzl, MarkusWater is a renewable resource, which is naturally recycled in the hydrological cycle. Surface waters have a short residence time in the hydrological cycle, while ground waters have a long residence time. This recycling renews water resources and provides a continuous supply. Nowadays, water management is becoming more and more important, especially the modification of irrigation schemes. An effective irrigation management which is similar to "drainage control" will avoid a high water outflow from an irrigated area and therefore the nutrient losses in the outflow water can be negligible. This is absolutely important because nutrients, for example nitrates and phosphorus, can lead to problems in the drinking water supply of a region with intensive irrigation.Therefore, it is essential to know as much as possible of the soil hydraulic properties and to convert this knowledge into management practices for the efficient use of water and soil resources. Tension infiltrometers have become a valuable tool for field determination of soil hydraulic properties. To estimate necessary input parameters for the Hydros-ID model (which simulates the one-dimensional movement of water and solutes through the unsaturated zone), measurements were obtained in three lysimeters (D, E, F) of: tension infiltration rates, soil water content and suction using time domain reflectometry (TDR) probes and tensiometers, installed at fixed depths. Infiltration experiments were performed under 40 mm and 0 mm suctions. Hydros was used to estimate the soil hydraulic conductivitiy K(h) at the corresponding suction values (h in cm). Water retention data measured on replicate soil cores from the 3 lysimeters and K(h) data were fitted with the Mualem-van Genuchten (MvG) equation to estimate the lysimeters' water retention curves. The resulting curves showed significant differences from the measured ones from the laboratory tension table tests. Further, dye experiments were performed to identify the flow types of the lysimeters. To stain the flow pathways, the lysimeter surfaces were flooded with a dye solution of 10 litres Brilliant Blue FCF with a concentration of 10 g/1. After a few days, the lysimeters were excavated and brought into the lab for the vertical and horizontal profile analysis. Images were taken using a digital camera (Nikon Coolpix 8800) under daylight conditions. Photographs of the soil profiles were processed by image analysis to distinguish between stained and unstained areas and to classify the stained areas into classes of dye concentrations. The flow profiles showed a logical sequence, with macropore flow along cracks for the coarser lysimeters E and F, and homogeneous matrix flow for the finer structured lysimeter DPublication Open Access Earth science field trips in the age of Covid-19: A case study of the SOSC223 virtual field trip : A thesis submitted in partial fulfilment of the requirements for the Degree of Master of Applied Science at Lincoln University(Lincoln University, 2024) Hall, LouisaUndergraduate earth science education emphasises the role of field trips in student learning and development. Thus, when the Covid-19 pandemic caused teaching to shift online, many educators developed replacement virtual field trips (VFTs) to deliver the field components of their courses. Such was the case with SOSC223, a second-year geomorphology course at Lincoln University, where the 2021 Covid-19 lockdown saw us replace the scheduled field trips with a VFT to the same locations. In this thesis, I investigate instructor and student experiences developing and learning from the SOSC223 VFT in order to evaluate what may have been lost or gained through the rapid shift from a traditional field trip (TFT) to virtual. I conducted semi-structured interviews with students and staff involved with the VFT and analysed the interview data for themes relating to 1) student and instructors’ perceptions of the VFT, 2) the strengths and weaknesses of the trip, and 3) how the VFT compared to a TFT. Thematic analysis of participants’ interview transcripts revealed different overall attitudes between the students and instructors. Instructors' reflections heavily featured the limitations and frustrations of developing the trip during lockdown. They felt the VFT was an adequate resource given the circumstance yet nevertheless saw potential benefits to VFTs as a whole. Students were apprehensive at the outset of the VFT but appreciated having the computerised replacement to the TFTs. Although most would have preferred attending a TFT, they felt the VFT benefitted their learning given the circumstances. The weaknesses of the VFT included its lack of easy interpersonal interaction, its reliance on technology like fast computers and stable internet, and the resourcing requirements to integrate multimedia and scaffold the content of the trip. Despite these challenges, the flexibility and repeatability of the VFT benefitted all participants, and the trip demonstrated clear potential for well-designed interactive multimedia to facilitate students' visual connection to place and ability to visualise complex processes. The SOSC223 VFT differed from TFTs in the logistical constraints and affordances of each and how the mode of delivery impacted students' social and physical immersion within the learning experience. Through conducting this research, it became clear that VFTs can add value to course design when thoroughly resourced and thoughtfully integrated. Whether they are used to augment or replace TFTs or incorporated into a course as standalone activities, VFTs should be designed in a way that builds on their flexibility and repeatability, minimises the impact of their lack of sociality, and builds visual connection through well-resourced, well-integrated multimedia.Item Open Access The effects of soil acidity and aluminium on the root systems and shoot growth of Lotus pedunculatus and Lupinus polyphyllus(Multidisciplinary Digital Publishing Institute (MDPI), 2024-08) Bell, LE; Moir, James; Black, AlistairLotus pedunculatus (lotus) and Lupinus polyphyllus (Russell lupin) persist in the upland grasslands of New Zealand, where soil acidity and associated aluminium (Al) toxicity impede conventional pasture legumes. This experiment investigated the response of lotus and Russell lupin to soil acidity and Al. The species were sown in 20 cm tall 1.2 L pots of acidic upland soil. A mass of 4.5 or 6.7 g lime (CaCO₃)/L was added to either the top or bottom or both soil horizons (0–9 cm and 9–18 cm), resulting in six treatments across six randomised blocks in a glasshouse. The soil pH was 4.4, 4.9, and 5.4; the exchangeable Al concentrations were 24, 2.5, and 1.5 mg/kg for 0, 4.5, and 6.7 g lime/L. At 16 weeks post-sowing, the plants were divided into shoots and roots at 0–9 cm and 9–18 cm. Root morphology, shoot and root dry matter (DM), shoot nitrogen (N), and nodulation were measured. The total plant DM and shoot-to-root DM ratio were higher, and the shoot %N was lower for the lotus plants than the Russell lupin plants for the various lime rates (13.2 vs. 2.9 g plant‾¹, 5.6 vs. 1.6, and 2.4 vs. 3.3%, p < 0.05). No response to lime in terms of total DM or total root morphology parameters was exhibited in either species (p > 0.05). Root morphology adjustments in response to acidity between soil horizons were not observed. The results indicated that lotus and Russell lupin are tolerant to high soil acidity (pH 4.4–5.4) and exchangeable Al (1.5–24 mg kg‾¹), highlighting their considerable adaptation to grasslands with acidic soils.Item Open Access Elucidating the role of earthworms on the fate of fertilizer N with synthetic and organic fertilizer application(Elsevier B.V., 2024-12) Hao, R; Wu, Y; Di, Hong; Chen, Y; Chen, W; Hu, R; Tan, WEarthworms’ activities not only increase soil nitrogen (N) uptake by crops but also lead to N losses to environment. However, it remains unclear whether earthworms’ impact on the fate of fertilizer N differs based on the type of fertilizer application. Therefore, the present pot experiment examined the transformation and fate of two types of ¹⁵N-labeled fertilizer (synthetic fertilizer urea and organic fertilizer compost applied at rate of 400 mg N/pot) with and without earthworms (Amynthas corticis) in a soil-lettuce system over three seasons of cultivation. Results showed that earthworms increased the fresh biomass of lettuce in all three seasons, regardless of the type of fertilizer used. However, the effect of earthworms on fertilizer N uptake varied depending on the type of fertilizer. With earthworms present, lettuce took up an additional 20.97 mg/pot of synthetic fertilizer N in the first season, which sharply decreased to 2.72 mg/pot and 4.63 mg/pot in the second and third seasons, respectively. In contrast, the uptake of organic fertilizer N by lettuce increased by 10.08–11.24 mg/pot throughout the entire experiment when earthworms were present. The presence of earthworms increased the percentage of synthetic fertilizer N lost to the environment by 0.8 %, due to increased N leaching, N₂O emission, NH₃ volatilization, etc. In contrast, earthworms decreased the percentage of organic fertilizer N lost to the environment by 1.9 %, primarily through reduced NH₃ volatilization, etc. This study underscores the pivotal role of earthworms in modulating fertilizer N dynamics, with organic fertilizer offering superior ecosystem services compared to synthetic fertilizer. Given that only one earthworm species was studied and nearly half of the organic fertilizer remained in the soil, future long-term experiments incorporating diverse earthworm species and changes in the soil's native N pool are essential to fully understand the role of earthworms in agro-ecosystem N cycling.Item Open Access Spatio-temporal analysis of net anthropogenic phosphorus inputs (NAPIs) and their impacts in Ningxia Hui Autonomous Region using Monte Carlo simulations and sensitivity analysis(MDPI AG, 2024-11) Ma, Hua; Liu, Xiaotong; Lei, Qiuliang; Luo, Jiafa; Di, Hong; Du, Xinzhong; Zhao, Ying; Zhang, Xuejun; Liu, HongbinThis study employed the Net Anthropogenic Phosphorus Inputs (NAPI) model to assess the impact of human activities on phosphorus input in a watershed, analyzing county-level statistical data and NAPI model parameters from 1991 to 2020. The Monte Carlo method was used for a quantitative analysis of the model parameters’ effects on each NAPI component and the overall simulation results. The sensitivity index method identified each component’s sensitive parameters. The study found that the lowest NAPI value was 454 kg/(km²·a) in 1991 and the highest was 1336 kg/(km²·a) in 2003. NAPI in Ningxia showed an overall upward trend from 1991 to 1999, a slight decrease from 1999 to 2003, and a slight increase from 2003 to 2020, with fertilizer being the main contributing factor, accounting for 77.4% of the total input. On a spatial scale, NAPI in Ningxia was significantly correlated with land use patterns, showing higher values in the northern and southern regions compared to the central part. The NAPI values derived from Monte Carlo simulations with appropriate parameters ranged from −24.83% to 31.49%. The study highlighted the net food and feed imports component as having the highest uncertainty, impacting simulation results within a range of −23.89% to 53.98%. It was observed that the larger a component’s proportion in the NAPI model, the more sensitive its parameters, with the phosphorus fertilizer (Pfer) component’s parameters being notably more sensitive than those of the food/feed phosphorus input and the non-food phosphorus input (Pnf) components. These findings can inform phosphorus pollution control policies in Northwest China, while the selection of sensitive parameters provides a useful reference for future NAPI research in other regions.Item Open Access Sulfur-doped binary layered metal oxides incorporated on pomegranate peel-derived activated carbon for removal of heavy metal ions(Multidisciplinary Digital Publishing Institute (MDPI), 2022-12) Jume, BH; Valizadeh Dana, N; Rastin, M; Parandi, E; Darajeh, N; Rezania, SIn this study, a novel biomass adsorbent based on activated carbon incorporated with sulfur-based binary metal oxides layered nanoparticles (SML-AC), including sulfur (S₂), manganese (Mn), and tin (Sn) oxide synthesized via the solvothermal method. The newly synthesized SML-AC was studied using FTIR, FESEM, EDX, and BET to determine its functional groups, surface morphology, and elemental composition. Hence, the BET was performed with an appropriate specific surface area for raw AC (356 m²·g‾¹) and modified AC-SML (195 m²·g‾¹). To prepare water samples for ICP-OES analysis, the suggested nanocomposite was used as an efficient adsorbent to remove lead (Pb²⁺), cadmium (Cd²⁺), chromium (Cr³⁺), and vanadium (V⁵⁺) from oil-rich regions. As the chemical structure of metal ions is influenced by solution pH, this parameter was considered experimentally, and pH 4, dosage 50 mg, and time 120 min were found to be the best with high capacity for all adsorbates. At different experimental conditions, the AC-SML provided a satisfactory adsorption capacity of 37.03–90.09 mg·g⁻¹ for Cd²⁺, Pb²⁺, Cr3³⁺, and V⁵⁺ ions. The adsorption experiment was explored, and the method was fitted with the Langmuir model (R² = 0.99) as compared to the Freundlich model (R² = 0.91). The kinetic models and free energy (<0.45 KJ·mol‾¹) parameters demonstrated that the adsorption rate is limited with pseudo-second order (R² = 0.99) under the physical adsorption mechanism, respectively. Finally, the study demonstrated that the AC-SML nanocomposite is recyclable at least five times in the continuous adsorption–desorption of metal ions.Item Open Access Nitrate as an alternative electron acceptor destabilizes the mineral associated organic carbon in moisturized deep soil depths(Frontiers Media, 2023-02-08) Song, W; Hu, C; Luo, Y; Clough, Timothy; Wrage-Mönnig, N; Ge, T; Luo, J; Zhou, S; Qin, SNumerous studies have investigated the effects of nitrogen (N) addition on soil organic carbon (SOC) decomposition. However, most studies have focused on the shallow top soils <0.2 m (surface soil), with a few studies also examining the deeper soil depths of 0.5–1.0 m (subsoil). Studies investigating the effects of N addition on SOC decomposition in soil >1.0 m deep (deep soil) are rare. Here, we investigated the effects and the underlying mechanisms of nitrate addition on SOC stability in soil depths deeper than 1.0 m. The results showed that nitrate addition promoted deep soil respiration if the stoichiometric mole ratio of nitrate to O₂ exceeded the threshold of 6:1, at which nitrate can be used as an alternative acceptor to O₂ for microbial respiration. In addition, the mole ratio of the produced CO₂ to N₂O was 2.57:1, which is close to the theoretical ratio of 2:1 expected when nitrate is used as an electron acceptor for microbial respiration. These results demonstrated that nitrate, as an alternative acceptor to O₂, promoted microbial carbon decomposition in deep soil. Furthermore, our results showed that nitrate addition increased the abundance of SOC decomposers and the expressions of their functional genes, and concurrently decreased MAOC, and the ratio of MAOC/SOC decreased from 20% before incubation to 4% at the end of incubation. Thus, nitrate can destabilize the MAOC in deep soils by stimulating microbial utilization of MAOC. Our results imply a new mechanism on how above-ground anthropogenic N inputs affect MAOC stability in deep soil. Mitigation of nitrate leaching is expected to benefit the conservation of MAOC in deep soil depths.Item Open Access Land use conversion to uplands significantly increased the risk of antibiotic resistance genes in estuary area(Elsevier BV, 2024-09) Shen, Jupei; Yu, Danting; Liu, Zikai; Di, Hong; He, Ji-ZhengLand use conversion in estuary wetlands may affect the transmission of antibiotic resistance genes (ARGs), while the risk rank of the ARGs and the change of clinically relevant ARGs under various land-use types are not well understood. This study used metagenomics to reveal the diversity and abundance of ARGs across five distinct land uses: reed wetland, tidal flat, grassland, agricultural land and fallow land, as well as their distribution and potential health risks. Results showed that high numbers of ARG subtypes and classes were detected irrespective of land-use types, notably higher in agricultural land (144 ARG subtypes). The most shared ARG subtypes were multidrug resistance genes across all the land uses (29 subtypes, 4.7 × 10¯²-1.5 × 10¯¹ copies per 16S rRNA gene copy). Proteobacteria and Actinobacteria were primary ARG hosts, with 18 and 15 ARGs were found in both of them, respectively. The ARG subtype mdtB was the most dominant clinical ARG detected with 90 % amino acid identity. The change of ARGs exhibited a consistent trend across land uses in terms of health risk ranks, with the highest observed in fallow land and the lowest in reed wetland. This study reveals the distribution pattern of ARGs across various land-use types, and enhances our understanding of the potential health risks associated with ARGs in the context of coastal wetland conversion in estuary areas.Item Open Access Anthropogenic N input increases global warming potential by awakening the “sleeping” ancient C in deep critical zones(American Association for the Advancement of Science, 2023-02-10) Qin, S; Yuan, H; Hu, C; Li, X; Wang, Y; Zhang, Y; Dong, W; Clough, Timothy; Luo, J; Zhou, S; Wrage-Mönnig, N; Ma, L; Oenema, OEven a small net increase in soil organic carbon (SOC) mineralization will cause a substantial increase in the atmospheric CO₂ concentration. It is widely recognized that the SOC mineralization within deep critical zones (2 to 12 m depth) is slower and much less influenced by anthropogenic disturbance when compared to that of surface soil. Here, we showed that 20 years of nitrogen (N) fertilization enriched a deep critical zone with nitrate, almost doubling the SOC mineralization rate. This result was supported by corresponding increases in the expressions of functional genes typical of recalcitrant SOC degradation and enzyme activities. The CO₂ released and the SOC had a similar ¹⁴C age (6000 to 10,000 years before the present). Our results indicate that N fertilization of crops may enhance CO₂ emissions from deep critical zones to the atmosphere through a previously disregarded mechanism. This provides another reason for markedly improving N management in fertilized agricultural soils.Item Open Access Nitrogen optimization coupled with alternate wetting and drying practice enhances rhizospheric nitrifier and denitrifier abundance and rice productivity(Frontiers Media, 2022-10-11) Abid, AA; Zhang, Q; Adil, MF; Batool, I; Abbas, M; Hassan, Z; Khan, AA; Castellano-Hinojosa, A; Zaidi, SHR; Di, Hong; Abdeslsalam, NROptimizing nitrogen (N) fertilization without sacrificing grain yield is a major concern of rice production system because most of the applied N has been depleted from the soil and creating environmental consequences. Hence, limited information is available about nutrient management (NM) performance at a specific site under alternate wetting and drying (AWD) irrigation compared to conventional permanent flooding (PF). We aimed to inquire about the performance of NM practices compared to the farmer’s fertilizer practice (FFP) under PF and AWD on rhizospheric nitrifier and denitrifier abundance, rice yield, plant growth, and photosynthetic parameters. Two improved NM practices; nutrient management by pig manure (NMPM); 40% chemical N replaced by pig manure (organic N), and nutrient management by organic slow-release fertilizer (NMSR); 40% chemical N replaced by organic slow-release N were compared. The results showed an increased total grain yield (16.06%) during AWD compared to PF. Compared to conventional FFP, NMPM, and NMSR significantly increased the yields by 53.84 and 29.67%, respectively, during AWD. Meanwhile, PF prompted a yield increase of 45.07 and 28.75% for NMPM and NMSR, respectively, (p < 0.05) compared to FFP. Besides, a significant correlation was observed between grain yield and nitrogen content during AWD (R² = 0.58, p < 0.01), but no significant correlation was observed during PF. The NMPM contributed to photosynthetic attributes and the relative chlorophyll content under both watering events. Moreover, relatively higher abundances of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) were observed during AWD, and the highest value was found after the late panicle stage. Our results suggest that the AWD–NMPM model is the best option to stimulate nitrifier and denitrifier gene abundance and promote rice production.Item Open Access Grazing weakens competitive interactions between active methanotrophs and nitrifiers modulating greenhouse-gas emissions in grassland soils(Springer Nature on behalf of Oxford University Press, 2021-12) Pan, Hong; Feng, Haojie; Liu, Yaowei; Lai, Chun-Yu; Zhuge, Yuping; Zhang, Qichun; Tang, Caixian; Di, Hong; Jia, Zhongjun; Gubry-Rangin, Cécile; Li, Yong; Xu, JianmingGrassland soils serve as a biological sink and source of the potent greenhouse gases (GHG) methane (CH₄) and nitrous oxide (N₂O). The underlying mechanisms responsible for those GHG emissions, specifically, the relationships between methane- and ammonia-oxidizing microorganisms in grazed grassland soils are still poorly understood. Here, we characterized the effects of grazing on in situ GHG emissions and elucidated the putative relations between the active microbes involving in methane oxidation and nitrification activity in grassland soils. Grazing significantly decreases CH₄ uptake while it increases N₂O emissions basing on 14-month in situ measurement. DNA-based stable isotope probing (SIP) incubation experiment shows that grazing decreases both methane oxidation and nitrification processes and decreases the diversity of active methanotrophs and nitrifiers, and subsequently weakens the putative competition between active methanotrophs and nitrifiers in grassland soils. These results constitute a major advance in our understanding of putative relationships between methane- and ammonia-oxidizing microorganisms and subsequent effects on nitrification and methane oxidation, which contribute to a better prediction and modeling of future balance of GHG emissions and active microbial communities in grazed grassland ecosystems.Item Open Access Phosphorus applications adjusted to optimal crop yields can help sustain global phosphorus reserves(Springer Nature, 2024-04) McDowell, Richard; Pletnyakov, P; Haygarth, PMWith the longevity of phosphorus reserves uncertain, distributing phosphorus to meet food production needs is a global challenge. Here we match plant-available soil Olsen phosphorus concentrations to thresholds for optimal productivity of improved grassland and 28 of the world’s most widely grown and valuable crops. We find more land (73%) below optimal production thresholds than above. We calculate that an initial capital application of 56,954 kt could boost soil Olsen phosphorus to their threshold concentrations and that 28,067 kt yr¯¹ (17,500 kt yr¯¹ to cropland) could maintain these thresholds. Without additional reserves becoming available, it would take 454 years at the current rate of application (20,500 kt yr¯¹) to exhaust estimated reserves (2020 value), compared with 531 years at our estimated maintenance rate and 469 years if phosphorus deficits were alleviated. More judicious use of phosphorus fertilizers to account for soil Olsen phosphorus can help achieve optimal production without accelerating the depletion of phosphorus reserves.Item Open Access Real-time genomics for One Health(Springer, 2023-08-08) Urban, L; Perlas, A; Francino, O; Martí-Carreras, J; Muga, BA; Mwangi, JW; Boykin Okalebo, L; Stanton, J-AL; Black, Amanda; Waipara, N; Fontsere, C; Eccles, D; Urel, H; Reska, T; Morales, HE; Palmada-Flores, M; Marques-Bonet, T; Watsa, M; Libke, Z; Erkenswick, G; van Oosterhout, CThe ongoing degradation of natural systems and other environmental changes has put our society at a crossroad with respect to our future relationship with our planet. While the concept of One Health describes how human health is inextricably linked with environmental health, many of these complex interdependencies are still not well-understood. Here, we describe how the advent of real-time genomic analyses can benefit One Health and how it can enable timely, in-depth ecosystem health assessments. We introduce nanopore sequencing as the only disruptive technology that currently allows for real-time genomic analyses and that is already being used worldwide to improve the accessibility and versatility of genomic sequencing. We showcase real-time genomic studies on zoonotic disease, food security, environmental microbiome, emerging pathogens, and their antimicrobial resistances, and on environmental health itself – from genomic resource creation for wildlife conservation to the monitoring of biodiversity, invasive species, and wildlife trafficking. We stress why equitable access to real-time genomics in the context of One Health will be paramount and discuss related practical, legal, and ethical limitations.Item Open Access Plant species identity and plant-induced changes in soil physicochemistry—but not plant phylogeny or functional traits - shape the assembly of the root-associated soil microbiome(Oxford University Press, 2023-11) Byers, Alexa; Condron, LM; O’Callaghan, M; Waller, Lauren; Dickie, IA; Wakelin, SAThe root-associated soil microbiome contributes immensely to support plant health and performance against abiotic and biotic stressors. Understanding the processes that shape microbial assembly in root-associated soils is of interest in microbial ecology and plant health research. In this study, 37 plant species were grown in the same soil mixture for 10 months, whereupon the root-associated soil microbiome was assessed using amplicon sequencing. From this, the contribution of direct and indirect plant effects on microbial assembly was assessed. Plant species and plant-induced changes in soil physicochemistry were the most significant factors that accounted for bacterial and fungal community variation. Considering that all plants were grown in the same starting soil mixture, our results suggest that plants, in part, shape the assembly of their root-associated soil microbiome via their effects on soil physicochemistry. With the increase in phylogenetic ranking from plant species to class, we observed declines in the degree of community variation attributed to phylogenetic origin. That is, plant-microbe associations were unique to each plant species, but the phylogenetic associations between plant species were not important. We observed a large degree of residual variation (> 65%) not accounted for by any plant-related factors, which may be attributed to random community assembly.Publication Open Access Nitrification inhibitor chlorate and nitrogen substrates differentially affect comammox Nitrospira in a grassland soil(Frontiers, 2024-01-01) Shah, AS; Hsu, PC; Chisholm, Chris; Podolyan, Andriy; Cameron, Keith; Luo, Jiafa; Stenger, Roland; Carrick, Sam; Hu, Wei; Ferguson, Scott A; Wei, W; Shen, J; Zhang, L; Liu, H; Zhao, T; Wei, W; Ding, W; Pan, H; Liu, Y; Li, B; Du, J; Di, HongIntroduction: Through the combined use of two nitrification inhibitors, Dicyandiamide (DCD) and chlorate with nitrogen amendment, this study aimed to investigate the contribution of comammox Nitrospira clade B, ammonia oxidizing bacteria (AOB) and archaea (AOA) to nitrification in a high fertility grassland soil, in a 90-day incubation study. Methods: The soil was treated with nitrogen (N) at three levels: 0 mg-N kg-¹ soil, 50 mg-N kg-¹ soil, and 700 mg-N kg-¹ soil, with or without the two nitrification inhibitors. The abundance of comammox Nitrospira, AOA, AOB, and nitrite oxidising bacteria (NOB) was measured using qPCR. The comammox Nitrospira community structure was assessed using Illumina sequencing. Results and Discussion: The results showed that the application of chlorate inhibited the oxidation of both NH₄+ and NO₂- in all three nitrogen treatments. The application of chlorate significantly reduced the abundance of comammox Nitrospira amoA and nxrB genes across the 90-day experimental period. Chlorate also had a significant effect on the beta diversity (Bray-Curtis dissimilarity) of the comammox Nitrospira clade B community. Whilst AOB grew in response to the N substrate additions and were inhibited by both inhibitors, AOA showed litle or no response to either the N substrate or inhibitor treatments. In contrast, comammox Nitrospira clade B were inhibited by the high ammonium concentrations released from the urine substrates. These results demonstrate the differential and niche responses of the three ammonia oxidising communities to N substrate additions and nitrification inhibitor treatments. Further research is needed to investigate the specificity of the two inhibitors on the different ammonia oxidising communities.Publication Open Access Learning by doing is more memorable: Soil judging as an educative tool(2022-07-31) Smith, Carol; Carrick, S; Nelson, J; Mazzetto, J; Penny, V; Butel, JSoil scientists are increasingly working in a multidisciplinary world where they interact with professionals from different disciplines and diverse end user groups. The ability to communicate, and to be an effective team player are just as important skills as the ability to apply practical field skills and describe soil profiles. The kinaesthetic approach embodied in soil judging allows the student to also connect with pedological theory; and it is a pedagogically aligned style of learning. At Lincoln University we first adopted innovative, experiential learning in the form of soil judging in 2016 to address these issues, and have worked collaboratively with Manaaki Whenua Landcare Research to develop this programme. Soil judging in New Zealand is in its infancy compared to other countries, but the undergraduate student soil science society and academic staff have been enthusiastic in practicing soil description skills and land use interpretation, participating in soil judging contests in New Zealand and Australia. Students report that they have become more confident in soil description and that it has stimulated their interest in learning about soil science. We designed a micro credential to recognize the academic work of the students. Several soil judging graduates have secured employment as pedologists at Crown Research Institutes or as soil resource specialists in local / regional government organisations. Soil judging may also be an effective recruitment pipeline into the discipline: offering those students with a practical and kinaesthetic aptitude who perform well at soil judging an insight into the academic side of the soil science discipline. We posit that soil judging competitions are an effective framework for students to acquire a valuable range of practical, field-based skills for a professional career in soil science or allied enterprises.Item Open Access Irrigation scheduling needs to consider both plant‐available water and soil aeration requirements(Wiley on behalf of Soil Science Society of America, 2024-05-29) Pragg, Beaulah; Deepagoda, Chamindu; Cameron, Keith; Di, Hong; Clough, Timothy; Carrick, SamGlobal food production relying on irrigated agriculture accounts for >70% of the global freshwater withdrawal. A thorough understanding of soil–water characteristics (SWCs) and critical soil–water values in the soil and subsoil is important for effective management of irrigated water. A critical soil–water “window” for plants is generally taken as the plant-available water window without considering diffusion-dominated soil aeration as a co-requisite. This study examined SWC curves in vadose soil profiles (up to 1.5-m depth) in eight pasture soils. The soil moisture measurements were made over matric potentials ranging from −1 to −1500 kPa using tension table and pressure plate apparatus. The van Genuchten model was used to parameterize the measured SWC curve, while the Millington-Quirk model was used to derive soil–gas diffusivity from measured soil physical properties. We defined critical soil–water windows considering the threshold values for both plant-available water and soil–gas diffusivity to ensure water and aeration corequisites for plant growth. The results clearly distinguished depth-dependent regimes of gravitational, plant-available, and unavailable water in selected profiles and their responses to soil structural changes across the depth. In some of the observed soil profiles, only 30%–60% of the plant-available water window was able to be utilized by plants because the remainder existed under soil conditions where soil aeration was inadequate for plant growth, emphasizing the importance of considering both the plant's water and aeration requirements during irrigation scheduling. Further, the infiltration profiles in two selected soils under simulated irrigation highlighted the importance of a priori knowledge of the soil structure in deeper soil layers for scheduling irrigation.Publication Open Access Bioavailable iron concentrations regulate phytoplankton growth and bloom formation in low-nutrient lakes(Elsevier, 2023-12-01) Dengg, M; Stirling, CH; Safi, K; Lehto, Niklas; Wood, Susanna; Seyitmuhhamedov, K; Reid, MR; Verburg, PThe growth of phytoplankton in lakes is thought to be primarily controlled by macronutrient concentrations, but the availability of trace metal micronutrients, such as iron (Fe), are increasingly recognised as important regulators of lake primary production. This study evaluates the role of Fe in regulating phytoplankton growth in lakes of different nutrient status in New Zealand. The results of this unique year-long study, combining highly sensitive trace metal concentration analysis of waters and particulates with advanced trace metal bioavailability and speciation modelling, constrains thresholds for bioavailable Fe and colloidal Fe of 0.8 nmol·L¯¹and 30 nmol·L¯¹, respectively, below which phytoplankton growth-limitation occurs. These thresholds specifically control diatom bloom formation and termination in lakes, thereby exerting a strong influence on freshwater carbon sequestration, given the dominance of diatoms in lake bloom assemblages. Importantly, potentially toxic cyanobacteria thrived only after events of bottom water anoxia, when additional dissolved Fe in concentrations ≥4 nmol·L¯¹ was released into the water column. These new thresholds for bioavailable and colloidal Fe offer the potential to manage micronutrient levels in lakes for the purpose of regulating algal bloom formation and carbon sequestration, while at the same time, suppressing the formation of harmful cyanobacterial blooms.