Department of Soil and Physical Sciences
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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.
Recent Submissions
Item 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.Item 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.Item 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.Item 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.Item 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.