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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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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, C; Podolyan, Andriy; Cameron, Keith; Luo, J; Stenger, R; Carrick, S; Hu, W; Ferguson, SA; 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, B; Deepagoda, Chamindu; Cameron, Keith; Di, Hong; Clough, Timothy; Carrick, SGlobal 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, SA; 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.Publication Open Access Temporal changes in Cd sorption and plant bioavailability in compost-amended soils(MDPI, 2023-12) Al Mamun, S; Lehto, Niklas; Cavanagh, J; McDowell, Richard; Kellermann, L; Robinson, BHThe application of Cd-contaminated phosphate fertiliser has enriched concentrations of this non-essential element in many agricultural soils. Consequently, concentrations of the metal in some agricultural products exceed the Maximum Limit in foods. Composts can reduce the transfer of Cd from soil to plants; however, it is unclear how long this beneficial effect endures. We aimed to determine temporal changes of phytoavailable Cd in two market garden soils (an Allophanic Orthic Granular Soil and a Recent Silt Loam). Soils were amended with either municipal green waste compost or sawdust and animal waste compost at a rate of 2.5% w/w under three incubation regimes: at 19 °C, at 30 °C, and at 30 °C with additional N added as urea at 0.6 g urea/kg soil added over 1 year. Each replicate was sampled after 1, 5, 9, 13, 21, 31, and 49 weeks, and phytoavailable Cd was estimated through 0.05 M Ca(NO₃)₂ extraction. Seed potato (Solanum tuberosum), ‘Nadine’ variety, was grown in the Pukekohe Allophanic Orthic Granular Soil, freshly amended with municipal compost and the same soil aged for one year. The concentration of Cd in all samples was analysed using an ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometer). The C concentration in the soil—compost mixtures decreased over the year, with the greatest decreases occurring in the soils incubated at 30 °C with added N. Unexpectedly, the concentration of Ca(NO₃)₂-extractable Cd in the compost-amended soils did not increase over time and in some cases even decreased. This was confirmed through a pot experiment, which showed the Cd concentration in potato was reduced by 50% in both the freshly amended soil and the amended soil aged for one year. Cadmium immobilisation in soils might be due to both the sorption of Cd by organic matter and the occlusion of sorbed Cd by oxy-hydroxides of iron and aluminium. Over 49 weeks, soluble Cd does not increase as organic matter oxidises. The application of municipal compost to soil will reduce both plant Cd solubility and plant Cd uptake for at least one year in the soils tested.Publication Open Access Contrasting response of comammox Nitrospira, ammonia oxidising bacteria, and archaea to soil pH and nitrogen inputs(Elsevier B.V., 2024-05-10) Chisholm, C; Di, Hong; Cameron, Keith; Podolyan, Andriy; Shen, J; Zhang, L; Sirisena, Kosala; Godsoe, WilliamThis study aimed to investigate the effect of soil pH change, and nitrogen amendment on ammonia oxidiser abundance and comammox Nitrospira community composition. The experimental design used soil mesocosms placed in a temperature-controlled incubator for 90 days. A Templeton silt loam was used as its physiochemical properties are typical of the region's dairy farms. The results showed that comammox Nitrospira clade B preferred the natural (pH 6.1–6.2) soil pH with no applied nitrogen. Furthermore, synthetic urine (N700) decreased the abundance of comammox Nitrospira clade B. This may have been because the large amounts of available ammonia in the N700 treatments inhibited the growth of comammox Nitrospira. These results suggest that while comammox Nitrospira clade B are present in New Zealand dairy farm soils, but their role in nitrification in the very high nitrogen environment under a urine patch in grazed pastures may be limited. Further research is needed to confirm this. In contrast to comammox, the AOB community (dominated by Nitrosospira) responded positively to the application of synthetic urine. The response was greatest in the high pH soil (7.1), followed by the natural and then the low pH (4.9) soils. This may be due to the difference in ammonia availability. At high pH, the ammonia/ammonium equilibrium favours ammonia production. Calculated ammonia availability in the N700 treatments accurately predicted the AOB amoA gene abundance. Interestingly, the AOA community abundance (which was predominantly made up of Thaumarchaeota group I.1b clade E) seemed to prefer the natural and high pH soils over the low pH. This may be due to the specific lineage of AOA present. AOA did not respond to the application of nitrogen.Publication Open Access Thermal adaptation of soil microbial functional responses: Insights from a geothermal gradient in Aotearoa New Zealand(2023) Alster, Charlotte; van de Laar, A; Arcus, V; Prentice, E; Bååth, E; Schipper, LNatural soil temperature gradients provide an excellent proxy to study how soil microbial communities, and their associated activities, will adapt to global warming. The rate at which soil microbes adapt to warming has important implications for biogeochemical cycling and predictions of soil carbon loss. In Aotearoa New Zealand, we take advantage of a decades long geothermal gradient, ranging from 15-42°C mean annual soil temperature, to investigate thermal adaptation of soil microbial respiration (with unlimited substrate), bacterial growth, and extracellular enzyme activities (β-glucosidase, acid phosphatase, and N-acetyl-β-ᴅ-glucosaminidase). We sampled soils from across this gradient and constructed temperature response curves for each soil sample in the lab by incubating them at six or more different temperatures. Using these temperature response curves, we then estimated rates of thermal adaptation for each microbial function and compared how different microbial processes adapt differentially. Despite major changes in microbial community diversity and composition along the gradient, we found only modest shifts in thermal adaptation of the microbial functional responses. The temperature response curves for soil microbial respiration and bacterial growth increased at a rate of approximately 0.2°C per 1°C increase in mean annual temperature. In contrast, we did not find a significant relationship between mean soil temperature and the temperature response of extracellular enzyme activity, suggesting that temperature responses are highly conserved across a variety of soil microbial functions. Nonetheless, it is important to consider how these changes in microbial rates may affect predictions of soil carbon loss with global warming.Publication Open Access Quantifying soil microbial thermal adaptation(2024-04) Alster, C; van de Laar, A; Goodrich, J; Arcus, V; Deslippe, J; Marshall, A; Schipper, LThermal adaptation of soil microbial respiration has the potential to greatly alter carbon cycle-climate feedbacks through acceleration or reduction of soil microbial respiration as the climate warms. However despite its importance, the relationship between warming and soil microbial activity remains poorly constrained. Part of this uncertainty stems from persistent methodological issues and difficulties isolating the interacting effects of changes in microbial community responses from changes in soil carbon availability. To address these challenges, we sampled nearly 50 soils from around New Zealand, including from a long-term geothermal gradient, with mean annual temperatures ranging from 11-35°C. For each of these soils we constructed temperature response curves of microbial respiration given unlimited substrate and estimated a temperature optima (Topt) and inflection point (Tinf). We found that thermal adaptation of microbial respiration occurred at a rate of 0.29°C ± 0.04 1SE for Topt and 0.27°C ± 0.05 1SE for Tinf per degree of warming, demonstrating that thermal adaptation is considerably offset from warming. These relatively small changes occurred despite large structural shifts in microbial community composition and diversity. We also quantitatively assessed how thermal adaptation may alter potential respiration rates under future warming scenarios by consolidating all of the temperature response curves. Depending on the specific mean and instantaneous soil temperatures, we found that thermal adaptation of microbial respiration could both limit and accelerate soil carbon losses. This work highlights the importance of considering the entire temperature response curve when making predictions about how thermal adaptation of soil microbial respiration will influence soil carbon losses.Publication Open Access Nitrous oxide emission factors for fertiliser ammonium sulphate, diammonium phosphate, and urea(Taylor & Francis, 2023) Luo, J; van der Weerden, T; Saggar, S; Di, Hong; Podolyan, Andriy; Adhikari, K; Ding, K; Lindsey, S; Luo, D; Ouyang, L; Rutherford, AThis study determined the nitrous oxide emission factors (EF₁, the percentage of N₂O emitted as a proportion of fertiliser N applied) for fertilisers ammonium sulphate (AS), diammonium phosphate (DAP), and urea under the same field conditions. Trials were conducted on pasture soils across four sites (Waikato, Manawatu, Canterbury and Otago) in New Zealand during late autumn and spring of 2022. The average EF₁ values for urea across all four sites were 0.128% (95% C.I., 0.023% and 0.249%) in late autumn and 0.136% (95% C.I., 0.031% and 0.259%) in spring. The corresponding EF₁ values for AS were 0.125% (95% C.I., - 0.021% and 0.246%) in late autumn and 0.083% (95% C.I., 0.015% and 0.197%) in spring, while for DAP, they were 0.049% (95% C.I., - 0.044% and 0.157%) in late autumn and 0.090% (95% C.I., -0.009% and 0.205%) in spring. The mean EF₁ values across all four sites and two seasons were calculated as 0.132% (95% C.I., 0.016% and 0.269%) for urea, 0.104% (95% C.I., - 0.008% and 0.235%) for AS, and 0.069% (95% C.I., - 0.036 and 0.194) for DAP. No significant differences in EF₁ were observed between the three fertilisers (P > 0.05) at individual sites or when considering all four sites collectively.Publication Open Access Comammox bacteria and ammonia oxidizing archaea are major drivers of nitrification in glacier forelands(Elsevier, 2023-12) Yu, H; Shen, J; Zeng, J; Hu, H-W; Pendall, E; Xiao, H; Liu, Z; Zhang, H; Di, Hong; Li, Z; He, J-ZThis study investigated the abundance of comammox bacteria and canonical ammonia-oxidizing bacteria (AOB) and archaea (AOA), and their relative contribution to nitrification along a chronosequence of deglaciated forelands. The results showed that nitrification related gene abundance tended to increase with glacier retreat, with comammox bacteria and AOA appearing to be the most critical drivers for soil nitrification rates. These findings provide new evidence for the presence of comammox bacteria in glacier forelands and enhance our understanding of the niche differentiation of canonical nitrifier and comammox bacteria.Publication Open Access Factors controlling shallow subsurface dissolved reactive phosphorus concentration and loss kinetics from poorly drained saturated grassland soils(Wiley on behalf of ASA, CSSA & SSSA, 2023-03) Smith, GJ; McDowell, Richard; Daly, K; Ó hUallacháin, D; Condron, LM; Fenton, OShallow subsurface pathways dominate dissolved reactive phosphorus (DRP) losses in grassland soils that are: poorly drained, shallow, or have a perched water table in wetter months causing saturation-excess runoff. Saturated conditions can lead to anoxia, which can accelerate phosphorus (P) loss. Two scales of investigation were utilized in this study. First, at the field scale, soil cores were extracted to 2.5 m, subdivided and samples extracted using water extractable P (WEP) and sodium-bicarbonate-dithionite extractable P (NaBD-P). Second, at the laboratory scale, detailed incubation studies using field-moist grassland topsoils from sites in Ireland and New Zealand examined the kinetics of WEP under anoxic (WEPanox) and oxic (WEPox) conditions with imposed temperature and soil P fertilizer input treatments. Results from soil-core samples showed that redox-sensitive NaBD-P concentrations were depleted where artificial drainage lines were installed (100 cm deep), but WEP concentrations available to shallow flow were enriched in topsoil. The laboratory scale incubation experiment investigated the influence of temperature (3 vs. 18 °C), anoxia (designed to simulate saturation following a rainfall event), and superphosphate fertilizer (10 to 60 kg P ha¯¹ yr¯¹) on WEP concentrations over 24 h in three grassland topsoils (clay, silt, and sandy loam textures). Concentrations increased with fertilizer rate, temperature, and—in two soils—anoxic conditions. This was commensurate with nitrate (NO3¯) depletion and the reductive dissolution of iron and manganese. The release of P during anoxia was complete within 24 h. The results highlighted late winter to spring as the riskiest period for topsoil P losses in shallow subsurface flow due to wet soil conditions, increasing temperatures, and low soil NO3¯ concentrations. This knowledge highlights the necessity to consider and refine tests used to assess topsoil P loss risk, where in the landscape P losses are likely, and what strategies can be used to mitigate losses.Publication Open Access Long-term afforestation enhances stochastic processes of bacterial community assembly in a temperate grassland(Elsevier B.V., 2023-02) Chen, X; Li, H; Condron, LM; Dunfield, KE; Wakelin, SA; Mitter, EK; Jiang, NAfforestation of grassland is being promoted as a measure to mitigate climate change. While grassland afforestation influences the soil bacterial community structure and composition, the mechanisms involved and impacts of different tree species are poorly understood. In this study, we characterized the soil bacterial community to determine the phylogenetic group assembly after 19 years afforestation of unfertilized grazed grassland with radiata pine (Pinus radiata) and eucalyptus (Eucalyptus nitens). The soil bacterial community was more divergent between grassland and forest, while no differences were observed between P. radiata and E. nitens. Dominant roles of homogeneous selection and drift in soil bacterial community assembly were revealed, and comparable community assembly patterns were observed under both tree species. Afforestation increased the relative contribution of stochasticity (particularly drift) by an average of 22 % compared with grassland, and this was primarily associated with Serratia spp. (Gammaproteobacteria). In addition, the relative abundance of drift was significantly correlated with concentrations of plant-available phosphorus and sulfur in soil. These findings advanced understanding of the impact of land-use change on soil bacterial community composition and assembly.Publication Open Access Thermal adaptation of soil microbial growth traits in response to chronic warming(American Society for Microbiology, 2023-11) Eng, AY; Narayanan, A; Alster, Charlotte; DeAngelis, KM; Spear, JRAdaptation of soil microbes due to warming from climate change has been observed, but it remains unknown what microbial growth traits are adaptive to warming. We studied bacterial isolates from the Harvard Forest Long-Term Ecological Research site, where field soils have been experimentally heated to 5°C above ambient temperature with unheated controls for 30 years. We hypothesized that Alphaproteobacteria from warmed plots have (i) less temperature-sensitive growth rates; (ii) higher optimum growth temperatures; and (iii) higher maximum growth temperatures compared to isolates from control plots. We made high-throughput measurements of bacterial growth in liquid cultures over time and across temperatures from 22°C to 37°C in 2–3°C increments. We estimated growth rates by fitting Gompertz models to the growth data. Temperature sensitivity of growth rate, optimum growth temperature, and maximum growth temperature were estimated by the Ratkowsky 1983 model and a modified Macromolecular Rate Theory (MMRT) model. To determine evidence of adaptation, we ran phylogenetic generalized least squares tests on isolates from warmed and control soils. Our results showed evidence of adaptation of higher optimum growth temperature of bacterial isolates from heated soils. However, we observed no evidence of adaptation of temperature sensitivity of growth and maximum growth temperature. Our project begins to capture the shape of the temperature response curves, but illustrates that the relationship between growth and temperature is complex and cannot be limited to a single point in the biokinetic range.Publication Open Access Endophytic genera in Californian thistle (Cirsium arvense (L.) Scop.)(Springer, 2024) Kentjens, W; Casonato, Seona; Kaiser, CliveCirsium arvense is an important weed in temperate areas, causing yield losses in pasture and cropping systems. Endophytes may affect fungal biocontrol agents deployed to control C. arvense. This was the first study sampling leaves, stems, and roots of C. arvense multiple times in one growing season to determine which endophytic genera were associated with this plant species. Eighty-eight endophytic genera were isolated by culture methods and identified with molecular markers. Sixty-five of these have not previously been reported for C. arvense. This study was the first to document many genera belonging to the orders Pleosporales, Hypocreales, and Diaporthales that have not previously been identified in association with C. arvense. In addition, this study isolated more Leotiomycetes and Helothiales than previous studies on C. arvense endophytes. Information on endophytic genera in C. arvense will aid our understanding of biotic factors influencing fungal biocontrol agents and may improve effectiveness of biocontrol agents.Publication Open Access Soil carbon, erosion, and the stormflow mobilisation of sediment and nutrients in a high-country landscape : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University(Lincoln University, 2023) Provost, Shyam MichaelThis study was carried out at Mt. Grand Station, a high-country pastoral farm in the South Island of New Zealand. The landscape (400 - 1300 m altitude) supports a gradient and mosaic of native and endemic woody shrub and tussock grassland vegetation amongst more productive exotic pasture, the latter established through aerial seed top-dressing and fertilisation. In recent years several areas of the farm at higher altitudes have been converted to conservation management following Tenure Review, placing additional pressure on the remaining farmland to maximise productivity, a situation similarly faced by many other high-country farms. However, further intensification of pasture grassland would compromise existing less productive native vegetation. This research project investigated soil conservation and loss, and freshwater quality, aiming to advance existing knowledge relating to environmental sustainability of the high-country. Topsoil carbon stocks were quantified beneath various vegetation communities at different altitudes of the station to gain a better understanding of soil carbon and its dynamics. Two watershed catchments were targeted for high-frequency sampling during rainfall events, to investigate the likely significance of water flow on the mobilisation of sediment and nutrients, and to help improve the accuracy of existing run-off estimates. In addition, soil erosion was estimated from differences in residual soil 137Cs activity, which was generated from historic Pacific nuclear testing, between two of the dominant types of vegetation cover. The results revealed the potential for native vegetation to enhance soil carbon sequestration. At low - middle altitudes (450 - 850 m) of the farm, topsoil beneath a woody shrub (kānuka) vegetation cover had significantly higher carbon concentrations and carbon stocks than areas of adjacent pasture. At higher elevations (>1000 m) topsoil beneath dominant snow tussocks had significantly higher carbon, nitrogen and phosphorus concentrations, with higher carbon stocks than adjacent inter-tussock spaces. The total loads of suspended solids, nitrogen and phosphorus exported to catchment waterways were significantly larger during high-flow events in comparison to baseflow conditions, and large proportions of the high-flow loads were mobilised on the rising hydrograph following high rainfall. These findings draw attention to the significance of taking account of the early stages of rainfall events to improve accuracy when quantifying high-country catchment loads. Data for 137Cs were variable but these provisional results indicate that soil beneath kānuka is likely to have undergone lower rates of erosion over the previous 65 years in comparison to areas of adjacent pasture. The combined findings of the three parts of the experimental work in this study are interpreted as being indicative of the present and future potential for South Island high-country farming environments to make a significant contribution towards climate change mitigation through vegetation management, resultant soil building and prevention of soil erosion. It is argued that closer attention to ecological restoration is likely to have mutual benefits for conservation, the farming system and the environment. Maintenance and better-informed management of the mosaic of native and exotic vegetation can play a more important role in longer-term sustainability of this high-country land management system than is currently appreciated.Publication Open Access A global dataset on phosphorus in agricultural soils(Springer Nature, 2024-01-02) Ringeval, B; Demay, J; Goll, DS; He, X; Wang, Y-P; Hou, E; Matej, S; Erb, K-H; Wang, R; Augusto, L; Lun, F; Nesme, T; Borrelli, P; Helfenstein, J; McDowell, Richard; Pletnyakov, P; Pellerin, SNumerous drivers such as farming practices, erosion, land-use change, and soil biogeochemical background, determine the global spatial distribution of phosphorus (P) in agricultural soils. Here, we revised an approach published earlier (called here GPASOIL-v0), in which several global datasets describing these drivers were combined with a process model for soil P dynamics to reconstruct the past and current distribution of P in cropland and grassland soils. The objective of the present update, called GPASOIL-v1, is to incorporate recent advances in process understanding about soil inorganic P dynamics, in datasets to describe the different drivers, and in regional soil P measurements for benchmarking. We trace the impact of the update on the reconstructed soil P. After the update we estimate a global averaged inorganic labile P of 187 kgP ha‾¹ for cropland and 91 kgP ha‾¹ for grassland in 2018 for the top 0–0.3 m soil layer, but these values are sensitive to the mineralization rates chosen for the organic P pools. Uncertainty in the driver estimates lead to coefficients of variation of 0.22 and 0.54 for cropland and grassland, respectively. This work makes the methods for simulating the agricultural soil P maps more transparent and reproducible than previous estimates, and increases the confidence in the new estimates, while the evaluation against regional dataset still suggests rooms for further improvement.Publication Open Access Land-use suitability is not an intrinsic property of a land parcel(Springer Nature, 2023-05) Snelder, T; Lilburne, L; Booker, D; Whitehead, A; Harris, S; Larned, S; Semadeni-Davies, A; Plew, D; McDowell, RichardAgricultural production has economic, environmental, social and cultural consequences beyond farm boundaries, but information about these impacts is not readily available to decision makers. This study applied the land use suitability concept by carrying out an assessment of a region that has the potential for intensification of agricultural production, but where eutrophication of river and estuary receiving environments due to nitrogen enrichment is a significant issue. The assessment evaluated three indicators for each farmable land parcel in the region: productive potential (the inherent productive and economic potential of the parcel), relative contribution (the potential for the parcel to contribute nitrogen to receiving environments compared to other land parcels), and pressure (the load of nitrogen delivered to receiving environments compared to the loads that ensure environmental objectives are achieved). The assessment indicated that land with high suitability for land-use intensification in Southland is limited because areas with high productive potential and low relative contribution rarely coincide with receiving environments with low pressure. Existing data, methods and models can be used to calculate the indicators under different choices for regional land-use intensity and receiving environment objectives. However, the spatial resolution and accuracy that is achievable may preclude using assessment outputs to make land use decisions at small spatial scales such as individual farms. The study highlighted that land use suitability is not an intrinsic property of a land parcel because it is dependent on choices about land use elsewhere in the landscape and the environmental objectives, and that land use suitability is inherently subjective because of decisions that concern how indicators are combined and weighted.Publication Restricted Leaching losses of nitrate from undisturbed soil lysimeters under continuous and intermittent rainfall : A dissertation submitted in partial fulfilment of the requirement for the degree of Bachelor of Agricultural Science (Honours) at Lincoln College(Lincoln College, University of Canterbury, 1988) Deane, T. H.The amounts of NO₃⁻₋N leached from small undisturbed soil lysimeters (180mm diameter x 200-210mm deep) were compared under continuous and intermittent simulated rainfall conditions. Examination of breakthrough curves from both treatments indicated extensive preferential flow of solute had occurred through macropores such as earthworm burrows, plant root channels, natural structural cracks and large inter-aggregate spaces. Trends indicated that leaching of nitrate was initially less efficient under intermittent versus continuous rainfall. It was suggested that this was due to solute diffusion into intra-aggregate pores during the interval between intermittent rainfall events slowing down leaching losses. This mechanism also delayed the peak leachate NO₃⁻₋N concentrations by approximately 0 . 1 pore volume under intermittent versus continuous rainfall. Leaching losses under continuous and intermittent rain-fall of up to respectively were calculated to occur from NO₃⁻₋N fertiliser applied to the lysimeters offer 100 mm rainfall. It was suggested that fertiliser N losses would be less when several small rainfall or irrigation events immediately followed fertiliser application rather than one large rainfall/irrigation event.Publication Restricted Amounts, forms and availability of nitrogen and phosphorus in soil under conventional and organic cropping: A dissertation submitted in partial fulfilment of the requirement for the degree of Bachelor of Science with Honours at Lincoln University(Lincoln University, 2002) Horrocks, A. J.Organic farming is increasingly being promoted as a sustainable alternative to conventional farming. There is, however, a need for a greater understanding of how the organic system can function sustainably within a New Zealand agricultural setting. This study investigated the amounts, forms and availability of nitrogen (N) and phosphorus (P) in soil under conventional and organic cropping. Soil samples were taken to a depth of 70 cm from the conventionally managed Lincoln Mixed Cropping Farm (LCF) and the organically managed Biological Husbandry Unit (BHU) in Canterbury. These sites were chosen for comparison because they had the same soil type (Wakanui-fine sandy loam) and provided an opportunity to examine the effect of 25 years of contrasting management on nutrient amounts and availability. Analyses included organic carbon (C), total N and total P measurements. A 7-day anaerobic incubation was used to determine potentially mineralisable nitrogen (PMN), while isotopic exchange kinetics (IEK) was used to determine soil inorganic P availability. It was found that past management systems had not substantially affected organic C, total N and P levels of the topsoil (0-15 cm) but had significantly affected amounts of C and nutrients in the subsoil (15- 70 cm). Amounts of N, organic C and organic P were gre~ter at the BHU, which was attributed to the utilisation of deep rooting species. Inorganic P was greater in the LCF subsoil which may have been partially due to preferential leaching given the comparative lack of deep rooting species and the apparent high P fixing capacity (determined by IEK) of the subsoil. Greater pools of solution and readily available inorganic P in the BHU 0-7 .5 cm of soil indicated that the different cropping management systems had modified soil properties. The greater amounts detected at the BHU may reflect tillage regimes, intensity of production and the absence of animal grazing in the system. This study demonstrates the important role the subsoil plays regarding the nutrient fertility of cropping systems.Publication Restricted A re-evaluation of soil variability and soil fertility in relation to experimental forest plots at Bridgehill Flat, Craigieburn Research Area, Canterbury, New Zealand : A thesis submitted in partial fulfilment of the requirements for the postgraduate diploma of Applied Science at Lincoln University Canterbury, New Zealand(Lincoln University, 1994) Hassall, Leanne JaneIn 1979 Forest Research Institute (FRI) established a trial on high country forest and pastoral landuse at Flock Hill Station, in Canterbury. The soils of the trial site on a terrace, fan and hill slopes adjacent to Cave Stream, were surveyed in 1978, and in 1979 forests were planted on Craigieburn and Cass (Typic Allophanic Brown) and Castlehill (composite - Acidic Sandy Brown) soils. The area was stratified on the basis of the soil map and uneroded and eroded sites within delineations were sampled separately for soil fertility assessment in 1982 and 1984. Following the 1982 survey, the area was oversown with legumes and topdressed (300 kg ha⁻¹ superphosphate; 0.2 kg ha⁻¹ sodium molybdate). The current study (1994) includes a reassessment of soil fertility, improved definition of soil mapping units, and the analysis of soils not sampled at the time of the original survey. A Landform units map, a geomorphic surfaces map and soil map for the Bridgehill Block are all recorded. In twelve years the soil fertility under the trees is different than under adjacent grassland. In many plots available phosphorus (Bray P) levels have shown a sharper decline under grassland compared with adjacent forest, while the pH has decreased more in the soils under forest compared to those under grass.