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Item Characterisation and potential optimisation of seepage wetlands for nitrate mitigation in New Zealand hill country : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Massey University, School of Agriculture and Environment, Palmerston North, New Zealand(Massey University, 2023) Sanwar, SuhaDiffuse nitrate (NO₃⁻) loss to pastoral waterways in hill country headwater catchments is a water quality concern in many countries with pasture-dependent economies, including New Zealand (NZ). Sheep and beef farming is the dominant land use in NZ hill country which are often located in headwater catchments. As these primary industries strive toward production growth to meet global demand for meat exports, this agricultural intensification will introduce more NO₃⁻ to its waterways. This contrasts with the recently enacted National Policy Statement for Freshwater Management 2020 (NPS-FM) which recognises the significance and calls for the protection of small wetlands in recognition of their ecosystem services including nutrient regulation, water quality improvement as well as associated social well-being. Nitrate mitigation in low-order streams in pastoral headwater catchments are important due to their proportionally large catchment coverage and major contribution to the national NO₃⁻ load to NZ rivers. Seepage wetlands in hill country landscapes can be a N-sink and, therefore, is a potentially cost-effective and natural NO₃⁻-mitigation tool for improved water quality from the pastoral headwater catchments. Seepage wetlands are features that occur along low-order streams in the low gradient of hill country landscapes. Their organic matter-rich sediment, saturated conditions and locations at the convergence of surface and subsurface NO₃⁻ rich flow pathways make seepage wetlands a unique landscape feature in terms of NO₃⁻ reduction via denitrification processes. However, denitrification is spatially and temporally variable as the process is influenced by the wetland sediment and hydrological properties. Several studies have demonstrated that seepage wetlands can be a potential NO₃⁻ sink and have quantified high sediment denitrification capacities in individual wetlands. However, variations in sediment and denitrification properties across a range of wetlands and a comprehensive study of seepage wetland hydrological characteristics that influence NO₃⁻ attenuation have not been undertaken, particularly in pastoral hill country landscapes in NZ. This thesis has examined the spatial variabilities of seepage wetland denitrification and the denitrification-influencing sediment properties across four hill country seepage wetlands within the Horizons Regional Council administrative boundary in NZ. The spatial gradients of sediment properties were examined vertically (at 15 cm depth intervals) and horizontally (within- and between- wetlands) in seepage wetland sites. Sediment physicochemical (water content (WC), pH, Eh) and chemical properties (dissolved organic carbon (DOC), NO₃⁻, NH⁴⁺, %total carbon or %TC, %total nitrogen or %TN, C:N, dissolved Fe²⁺ and dissolved Mn²⁺) and sediment denitrification enzyme activity (DEA), that represents sediment denitrification capacity, were quantified. The DEA values were highest at the surface depths across all wetland sites. Based on the wide range (560-5371 µg N₂O-N kg⁻¹ DS h⁻¹) and distinctive surface DEA values, the seepage wetland study sites were categorised into high-performing H-DEA (>3000 µg N₂O-N kg⁻¹ DS h⁻¹) and comparatively low-performing L-DEA (<1000 µg N₂O-N kg⁻¹ DS h⁻¹) sites. The H-DEA sites measured 7 to 10 times higher surface DEA values compared to the L-DEA sites. Spatial variability of denitrification in seepage wetlands was mainly driven by sediment WC, NO₃⁻, %TC, %TN, C:N, dissolved Fe²⁺ and dissolved Mn²⁺ (p≤0.05). The H-DEA site measured high WC (78%) which was above the threshold for denitrification and high sediment NO₃⁻ (15.9-18.5 mg NO₃⁻N/kg DS), in contrast to the L-DEA sites (WC 39.8-37.4%, 2.5-3.97 mg NO₃⁻N/kg DS). The heterogeneity of WC explained the heterogeneous distribution of DEA within the individual L-DEA sites. The sediment properties accounted for only 58-73% of the overall spatial variability in DEA, suggesting that additional wetland characteristics such as wetland hydrology, could have an important influence on denitrification in seepage wetlands. The seepage wetland hydrology and associated NO₃⁻ removal were characterised in detail at one of the L-DEA sites located on Tuapaka farm. During the hydrological characterisation, streamflow discharge and water quality were monitored at inflow and outflow for a 2-year period (June 2019-May 2021). Shallow groundwater quality was monitored at the 0.5, 1 and 1.5 m depths at the inflow, midflow and outflow positions in the wetland for a 1.5-year period (November 2019-May 2021). The seepage wetlands site demonstrated a stream inflow-dominated hydrology (83-87%) with small seepage contributions (8-14%) to the seepage wetland hydrology. Precipitation was found to be the major hydrological and associated NO₃⁻ removal (means attenuation) driver in the seepage wetland site. The seepage wetland was found an overall NO₃⁻ sink that on an average removed 23% of the annual NO₃⁻ inflow. Compared to the stream inflow (<0.03 mg NO₃⁻N/L), higher shallow groundwater NO₃⁻ concentrations (<0.11 mg NO₃⁻N/L) suggests that seepage is potentially an important NO₃⁻ source in these wetlands. High flow conditions, high winter precipitation and direct grazing during low flow periods are potentially major NO₃⁻ loss hot moments. In contrast, initial rapid infiltration at the onset of high precipitation events in early winter and spring and dissipated flow conditions highlighted opportunities for NO₃⁻ attenuation in the wetland and were identified as major NO₃⁻ removal hot moments. An overall dissipated flow condition driven by seasonally equivalent precipitation (22% of annual precipitation in winter) facilitated considerably higher annual NO₃⁻ removal of 40.8% (2.78 kg NO₃⁻N) in the wetland in year 2, in contrast to very low NO₃⁻ removal (0.3%, ~0.02 kg NO₃⁻N) under an erratic annual precipitation distribution (38% of annual precipitation in winter) in year 1. These findings suggest there is scope to improve NO₃⁻ removal by optimising flow conditions to slow flow in seepage wetlands to minimise NO₃⁻ loss during NO₃⁻ loss hot moments. In a follow-up laboratory-scale seepage wetland intact sediment column experiment, the effectiveness of diffuse flow, via subsurface outflow, was investigated for the optimisation of the wetland NO₃⁻ removal. During the experiment, the flow intervention altered the NO₃⁻ reduction-constraints observed in the preceding hydrological study and facilitated anaerobic conditions conducive to denitrification to capitalise on the sediment denitrification capacity, which was quantified during the preceding seepage wetland sediment characterisation study. The flow intervention involved vertical downwelling of NO₃⁻ rich (5 mg NO₃⁻N/L) pastoral surface runoff and subsequent horizontal discharge through a subsurface sediment column depth of 15 cm depth, collected from the Tuapaka seepage wetland site. The effectiveness of the subsurface drainage intervention for NO₃⁻ removal was assessed by monitoring the subsurface outflow water quality. The study showed that flow intervention achieved 50-96% NO₃⁻ removal from NO₃⁻ rich surface runoff. Based on the observations from the column study, two separate optimal operational HRTs of 2 and 13 hr are recommended to achieve large NO₃⁻ removal (50% from NO₃⁻ input of 5 mg NO₃⁻N/L) in a short period of time and large reduction in NO₃⁻ concentration at the outflow (<0.15 mg NO₃⁻N/L), respectively. The reasonably short period of HRT for such high NO₃⁻ removal efficiency (50-96%) supports the potential for the application of subsurface outflow intervention as a practical in-situ NO₃⁻ mitigation strategy, which warrants further research. This study also acknowledges the associated technical limitations of translating the laboratory-based findings to the field scale and recommends future studies to overcome these research limitations including high sediment compressions during intact sediment column samplings from the field, for example. The thesis not only demonstrates a flow intervention strategy to improve NO₃⁻ mitigation via flow regulation in seepage wetlands, but also guides future management by identifying the potential seepage wetland hot spots in the landscape (chapter 3) and the NO₃⁻ removal hot moments in the wetlands (chapter 4) and also by recommending necessary HRTs for flow intervention (chapter 5). In summary, this thesis has generated a robust dataset that improves our understanding of seepage wetland characteristics and their influences on NO₃⁻ removal at spatial and temporal scales. From an application perspective, this research provides new knowledge as to ‘where’, ‘when’ and ‘how’ seepage wetlands can be targeted to enhance their role in NO₃⁻ mitigations in hill country landscapes. This information has the potential to accelerate the integration of seepage wetlands into the toolbox of NO₃⁻ management strategies that could be used at a farm scale to improve water quality leaving NZ pastoral headwater catchments.Item Use of New Zealand native browse shrubs on sheep and beef hill country farms : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at the School of Agriculture and Environment, Massey University, Palmerston North, Manawatū, New Zealand(Massey University, 2023) Wangui, James ChegeSheep and beef cattle farming on hill country through the historic clearing of native vegetation for pasture has caused biodiversity loss and increased the risk of soil erosion. Exotic tree species such as poplar and radiata pine can be used to control erosion, but there is current interest in using native plants on the hill country for indigenous biodiversity restoration in addition to erosion control. However, there is limited information on the forage value, biomass, carbon stock, and potential economic impacts of native plants compared to exotics species. This thesis was aimed to address the lack of information available on native shrubs and their comparison to exotics trees and shrubs. The forage feeding value results revealed that native shrubs had consistent nutritional composition across seasons, higher metabolizable energy, and lower crude protein than the exotic shrub Salix schwerinii (Kinuyanagi). Findings on in vitro fermentation characteristics showed that native shrubs were highly digestible, yielded higher volatile fatty acids, microbial proteins, and greenhouse gases than S. schwerinii. Estimation of biomass revealed that the native shrubs were similar in aboveground biomass accumulation, but differed in allocation to foliage, branch, and stem. Melicytus ramiflorus (Mahoe) had lower foliage biomass while Coprosma robusta (Karamū) had lower branch biomass, among the evaluated shrubs. Estimated carbon stock accumulation was higher for Pittosporum crassifolium (Karo) due to a greater woodier portion (branch and stem) than M. ramiflorus and C. robusta but lower than exotic trees. The data from the native shrub studies was used in the bioeconomic model and showed that planting native shrubs or radiata pine on steep slopes equal to 10% of the farm area would reduce farm feed supply. This reduction would result in a decrease in sheep flock size and sheep flock net cashflow, particularly with higher planting rates and with of radiata pine. While radiata pine had a surplus overall farm net cashflow, native shrubs had negative cashflow due to high seedling costs and low carbon income, making their use on the farm currently unprofitable at the modelled prices. The study's findings suggest that replacing exotic trees with native shrubs can provide high-quality summer browse for livestock. The decision to plant native shrubs on steep hill country slopes would depend on the farmer’s financial situation and interest in biodiversity conservation and profits. However, reducing planting costs and increasing the carbon price would be necessary to make investing in native shrubs profitable and more attractive to farmers.Item Applying a landscape ecological approach and geodesign from a farmer-centric position to inform the creation of future multifunctional, sustainable agricultural landscapes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Natural Resources Management at Massey University, Palmerston North, New Zealand(Massey University, 2023) Tran, Duy XuanIn the wake of environmental challenges, it is important to improve the environmental sustainability of farm systems and landscapes whilst ensuring profitability for the farmers that manage them. This PhD study draws on theories from landscape ecology and geodesign to plan and design multifunctional agricultural landscapes from a farmer-centric position with sustainability in mind. A hill country and steep-land farm in New Zealand is used as a case study. A conceptual framework is proposed to guide landscape planning. The framework applies an ecosystem-based management approach (i.e., ecosystem services approach) coupled with geodesign at the farm scale. A comprehensive spatially explicit assessment of landscape multifunctionality and associated ecosystem services at the farm scale is carried out to understand the spatial variation of ecosystem services provision and how land use and land management goals of the landowners reflect the value and quality of landscape multifunctionality. Afterwards, spatially detailed variations in the relationship between landscape structure and the provision of ecosystem services is quantified to understand how landscape structure can affect the provision of ecosystem services in the farmed landscape. Finally, collaboration with the case farmers and application of different tools and models are carried out to generate future land use and management scenarios for the case study farm, visualise changes, and assess the impacts of future land use on landscape multifunctionality and the provision of associated ecosystem services and economic outcomes. This helps to demonstrate how the proposed approach can be applied to plan and design multifunctional agricultural landscapes that offer improved sustainability in the NZ hill country farmed landscapes. The results from the case study suggest that the proposed approach provides an effective solution for sustainable farm system design and that it can make an important contribution to advancing environmental management in New Zealand, as well as in other countries which face similar issues.Item A kānuka silvopastoral system in New Zealand hill country : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Manawatū, New Zealand(Massey University, 2023) Mackay-Smith, ThomasSoil erosion, water quality issues, low production and climate change are some of the current challenges facing land managers and farmers in New Zealand hill country. ‘Tree-pasture’ silvopastoral systems that build soil resources could be integral land management practices for mitigating these issues and improving the health and production of these systems. Silvopastoral trees are already planted in New Zealand, although primarily used as soil conservation trees. Nevertheless, there are many other potentially facilitative effects of silvopastoral systems on other under researched silvopastoral outcomes. Researching these is vital for realising the full potential of silvopastoralism in New Zealand. The native genus kānuka (Kunzea spp.) in New Zealand has the potential to form intergenerational and multifunctional silvopastoral systems that build soil resources and positively impact pasture production. This is because of the genus’s potentially advantageous bio-physical tree attributes, such as its longevity, potentially reduced competition for soil water and nutrients compared to faster-growing and more resource intensive trees typically planted in hill country, and evergreen nature, potentially influencing livestock behaviour and soil organic matter return to the soil. Despite being locally very common in New Zealand hill country, this study is the first to measure the influence of kānuka silvopastoral trees on the pastoral environment at field scale. The study begins by presenting a novel framework that links bio-physical tree attributes to a wide range of silvopastoral outcomes. Poplar (Populus spp.), the most commonly planted soil conservation tree in New Zealand hill country, and kānuka, are then reviewed as silvopastoral trees within this framework. This process clearly conveyed the complexity of silvopastoral systems and highlights that there may be potential for kānuka to positively impact many silvopastoral outcomes such as longevity, pasture production, livestock welfare, biodiversity conservation and carbon sequestration. The study then investigated the impact of kānuka on pasture production and pasture stability, soil condition and surface runoff and sediment and nutrient losses within a kānuka silvopastoral system. At two sites over two years, there was on average 107.9% more pasture production under kānuka trees compared to open pasture. This pasture production increase was associated with significantly greater Olsen-phosphorus, potassium and porosity. Soil moisture was similar between kānuka pasture and open pasture positions. The improvements to the agricultural environment were hypothesised to be because of livestock excreta deposition under the trees in the sheltered tree environment and tree litterfall. The increased pasture production under the trees was the result of trees facilitating the growth of a few dominant and competitor pasture functional groups via the mass ratio effect such as perennial ryegrass (Lolium perenne), cocksfoot (Dactylis glomerata), soft brome (Bromus hordeaceus) and barley grass (Critesion murinum). Moreover, despite reduced species richness and functional richness in kānuka pasture, there was evidence that pasture stability was maintained under the trees because functional evenness and functional dispersion was statistically similar in kānuka pasture and open pasture, and the functional groups that grew had mixed (cocksfoot) or annual (soft brome and barley grass) survival strategies. This indicates that kānuka has the potential to increase pasture production sustainably by not negatively impacting the pasture’s response to stress. There was 53.8 mm annual surface runoff in kānuka pasture and 7.5 mm in open pasture, despite the improved soil conditions in kānuka pasture. Moreover, sediment and nutrient losses were 10–100 times greater in kānuka pasture. Sediment and nutrient losses were a function of surface runoff, and these differences were hypothesised to be because significantly less pasture biomass was present under the trees, decreasing surface runoff attenuation. The pasture biomass difference was likely because of livestock preferentially grazing the pasture under kānuka because of the sheltered environment and good condition pasture. This suggests that a choice between good condition pasture under trees and poor condition pasture away from trees can lead to negative impacts in terms of sediment and nutrient management under isolated silvopastoral trees. Overall, this study shows that tree configuration is a fundamental aspect in silvopastoral systems, and gives evidence that pasture biomass under silvopastoral trees is important for mitigating surface runoff and sediment and nutrient losses. The improved pasture production and pasture species composition under kānuka, in conjunction with the other potential environmental and cultural benefits of a kānuka silvopastoral system identified in the framework, shows that this genus may have potential to transform hill country landscapes by adding economic, environmental and cultural value to New Zealand farms. Nevertheless, because of the limitations of this study, such as the potential impact of site specific conditions and compounded livestock effects, more research is required to provide a full evaluation of the potential of kānuka silvopastoral systems in New Zealand hill country.Item Quantifying the performance of silvopastoralism for landslide erosion and sediment control in New Zealand’s hill country : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Physical Geography at Massey University, Palmerston North, New Zealand(Massey University, 2022) Spiekermann, RaphaelLandslide erosion results in loss of productive soils and pasture. Moreover, sediment delivered to streams from landslides can contribute to the degradation of freshwater and marine receiving environments by smothering benthic habitats and increasing turbidity, light attenuation, and sediment-bound contaminants. Silvopastoralism is an important land management practice used to combat landslide erosion and improve the health of downstream aquatic ecosystems. Yet, the effectiveness of widely spaced trees in reducing shallow landslide erosion and sediment delivery at hillslope to catchment scales remains largely unknown. Previous studies have been limited by scale (e.g., hillslope) or method (e.g., univariate analyses). This research aims to develop spatially explicit modelling to assess the impact of differing tree species, planting densities, and individual tree location, on rainfall-triggered landslides and sediment delivery while accounting for varying environmental conditions, such as slope gradient, lithology, or soil type. As such, this thesis combines geospatial methods and statistical models to address key challenges related to erosion and sediment control in New Zealand’s pastoral hill country. First, using a study area in the Wairarapa, located in the southeast of the North Island, New Zealand (840 km2), a method was developed using open-source remote sensing products to generate high-resolution individual tree influence models for the dominant tree species. The objective was to generate a spatial explicit representation of individual trees for landscape-scaled statistical slope stability modelling. The combined hydrological and mechanical influence of trees on slopes was inferred through the spatial relationship between trees and landslide erosion. These spatial distribution models for individual trees of different vegetation types represent the average contribution to slope stability as a function of distance from tree at 1-m spatial resolution. The normalised models (0-1) largely agree with the shape and distribution of force from existing physical root reinforcement models. Of exotic tree species that were planted for erosion and sediment control, poplars (Populus spp.) and willows (Salix spp.) make up 51% (109,000) of trees located on hillslopes at a mean density of 3 trees/ha. In line with previous studies, poplars and willows have the greatest contribution to slope stability with an average maximum effective distance of 20 m. Yet, native kānuka (Kunzea spp.) is the most abundant woody vegetation species on hillslopes within the study area, with an average of 24 trees/ha, providing an important soil conservation function. A large proportion (56% or 212.5 km2) of erosion-prone terrain in the study area remains untreated. In a world-first, this allowed the influence of individual trees to be included in a statistical landslide susceptibility model using binary logistic regression to quantify the effectiveness of silvopastoral systems at reducing landslide erosion and to support targeted erosion mitigation. Models were trained and tested using a landslide inventory consisting of 43,000 landslide scars mapped across the study area. Model performance was very good, with a median Area Under the Receiver Operating Characteristic curve (AUROC) of 0.95 in the final model used for predictions, which equates to an accuracy of 88.7% using a cut-off of 0.5. The effect of highly skewed continuous tree influence models on the maximum likelihood estimator was tested using different sampling strategies aimed at reducing positive skewness. With an adequate sample size, highly skewed continuous predictor variables do not result in an inflation of effect size. Application of the landslide susceptibility model was illustrated using two farms from within the study area (Site 1: 1,700-ha; Site 2: 462-ha) by quantifying the reduction in shallow landslide erosion due to trees. Compared to a pasture only baseline, landslide erosion was reduced by 17% at Site 1 and 43% at Site 2 due to all existing vegetation. The effectiveness of individual trees in reducing landslide erosion was shown to be less a function of species than that of targeting highly susceptible areas with adequate plant densities. The excellent model performance means spatial predictions are precise, which has implications for land management as the maps provide greater certainty and spatial refinement to inform landslide mitigation. The terrain occupied by the “high” susceptible class – defined as the terrain where 80% of mapped landslides were triggered in the past – occupies only 12% of Site 1 and 7% of Site 2. This suggests there is great potential for improved targeting of erosion mitigation to these areas of the farms where landsliding may be expected in the future. To enable biological mitigation to be targeted to critical source areas of sediment, determinants of sediment connectivity were investigated for a landslide-triggering storm event in 1977. In a first of its kind, a morphometric landslide connectivity model was developed using lasso logistic regression to predict the likelihood of sediment delivery to streams following landslide initiation. An experiment was undertaken to explore a range of connectivity scenarios by defining a set of sinks and simulating varying rates of sediment generation during runoff events of increasing magnitude. Sediment delivery ratios for the 1977 event ranged from 0.21 to 0.29, equating to an event sediment yield of 3548 t km-2 to 9033 t km-2. The likelihood of sediment delivery was greatly enhanced where debris tails coalesce. Besides scar size variables, overland flow distance and vertical distance to sink were the most important morphometric predictors of connectivity. When scar size variables were removed from the connectivity model, median AUROC was reduced from 0.88 to 0.75. By coupling landslide susceptibility and connectivity predictions in a modular form, we quantified the cost effectiveness of targeted versus non-targeted approaches to shallow landslide mitigation. Targeted mitigation of landslide-derived sediment was found to be approximately an order of magnitude more cost-effective than a non-targeted approach. Compared with a pasture-only baseline, a 34% reduction in sediment delivery can be achieved by increasing slope stability through spaced tree planting on 6.5% of the pastoral land. In contrast, the maximum reduction achievable through comprehensive coverage of widely spaced planting is 56%. The coupled landslide susceptibility and connectivity predictions (maps) provide an objective basis to not only target mitigation to areas where future shallow landslides are likely to occur, but – perhaps more importantly – target future tree planting to locations that are likely to be future sources of fine sediment. In this way, the research presented in this thesis is both methodologically novel and has immediate application to support land management decisions aimed at creating a more sustainable socio-ecological landscape.Item Hyperspectral imaging of hill country farms : a thesis presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy of Agriculture and Horticulture at Massey University, Manawatu, New Zealand(Massey University, 2019) Cushnahan, Thomas AnthonyThis thesis uses hyperspectral aerial imagery, processed and classified using a Support Vector Machine (SVM) approach applied to categorise the New Zealand hill farming environment. The analysis of hyperspectral imagery presented in this thesis provides information on land use and land cover that can assist land management decision-making for hill country farming. The ability of the approach to provide a mechanism to examine complex and inaccessible environments and capture information in fine detail makes it relevant to the management of other heterogeneous environments and marginal farming systems worldwide. Precision farming techniques, used regularly in other farming sectors, hold the promise to better understand the hill farming landscape and therefore improve strategic management decisions. Pasture is the primary resource on the farm but due to the heterogenous nature of the hill farm landscape, the pasture area is currently only estimated. Aerially applied fertiliser applications represent the largest single input for these farms and are also a major source of nutrient contamination in waterways so finding ways to reduce costs and environmental damage are important. The definition of the area and various pasture groups is critical information needed to improve fertiliser efficiency via use of Variable Rate Application Technology systems. This research was able to classify pasture area to 99.59% (Kappa 0.991). Accurate base landscape information can improve management decisions, the accuracy of valuations, income expectations from lending organisations and the overall prosperity of the hill farming sector. Currently farmers and external groups must make major financial and strategic decisions with local expert opinion which is difficult to validate or question. Therefore, information derived from the hyperspectral classification is also shown to have benefits for strategic farm management decision-making and the wider farming community. This research was able to classify a number of economically valuable resources to high accuracies including;water bodies (99.97%), Thistle (98.51%), Pine (99.44%), Kanuka (89.03%) and Manuka (97.71%). By applying SVM to hyperspectral imagery the classification of pasture could be enhanced by the use of plant functional groups. The classes of High Fertility Responsive (HFR) represented sown rye varieties and had a classification accuracy of 89.06%. Low Fertility Tolerant (LFT) represented mixed swards dominated by browntop with a classification accuracy of 89.81%. The highest accuracy achieved for the legume class was 99.81%. The findings from this study represent a notable advance in our understanding of hill country farm and remote sensing research relevant to hill country farming. This is the first study to classify several key landscape components that are economically or environmentally important to the hill country farming community and this study created the most detailed map of hill farm pasture quality using plant functional groups so far. The ability to use a single hyperspectral aerial survey, to provide such a wide variety of information, useful to many industry actors, improves the potential return on investment and viability of the survey operation.Item Investigating nitrate attenuation capacity and processes in pastoral hill country landscapes : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Massey University, Palmerston North, New Zealand(Massey University, 2019) Chibuike, GraceThe presence of agricultural nutrients, particularly nitrate, in ground and surface waters is an issue of increasing concern for the degradation of water quality in New Zealand. Thus, several studies have focused on the management of pastoral agricultural systems to limit the leaching and availability of nitrate in receiving waters. Such studies, however, are rare for pastoral hill country landscapes which occupy more than 60% of New Zealand agricultural area and hence have the potential to impact on water quality. Therefore, this thesis aims to assist in filling this knowledge gap by investigating the influence of hill country landscape features on nitrate attenuation in pastoral hill country. Denitrification has, for decades, been identified as an important nitrate attenuation process in soil-water systems. Its effectiveness below the topsoil is, however, limited by the supply of dissolved organic carbon (DOC). Pastoral hill country landscape features such as soil type, topography, wet areas, land use, and climate have the capacity to impact on the availability of DOC for denitrification in both the topsoil and subsoil. This study examined the contribution of these landscape features on the dynamics of DOC, and the effect on denitrification in the soil profile (100 cm). The Massey University’s Agricultural Experiment Station (Tuapaka farm) was the case study farm used in this thesis. In order to investigate the effect of soil type and slope on DOC concentration and denitrification capacity, soil samples were collected (from three depths down to 100 cm) from the lowest to the highest elevation (50-360 m) in the farm. The sampled locations comprised of three slope classes (low, medium and high) and eight soil types (Tokomaru, Ohakea, Shannon, Tuapaka, Halcombe, Korokoro, Ramiha and Makara), grouped into three drainage classes (poorly-, imperfectly-, and welldrained). The results of the study indicated that compared to slope, soil type had a greater effect on denitrification capacity within the farm. This effect of soil type was mainly associated with soil parent material, as the Ramiha soil which had a higher carbon (C) storage capacity (due to its high content of short-range order constituents), also had the highest amount of DOC (105 mg kg⁻¹, within the 30-60 cm soil depth) and thus the highest denitrification capacity (10 μg kg⁻¹ h⁻¹). The findings of this experiment imply that farms or catchments with soil types similar to the Ramiha soil may have a greater capacity to attenuate nitrate losses to receiving waters. The contribution of hill country wet areas (seepage wetland and hillside seeps) to nitrate attenuation was assessed by first comparing the DOC concentration of the wet areas to that of an adjacent dry area. This showed that mean DOC concentration of the surface 30 cm soil depth was in the following order: seepage wetland (498 mg kg⁻¹) > hillside seep (172 mg kg⁻¹) > dry area (109 mg kg⁻¹). A subsequent more detailed examination of the seepage wetland and dry area showed that the denitrification capacity of the seepage wetland within the 0-30 and 30-60 cm soil depths was 7 and 69 times higher, respectively, than that of the dry area. The higher DOC concentration and the presence of readily-decomposable DOC in the seepage wetland contributed to its higher denitrification capacity. This contrasting nitrate attenuation capacity of the seepage wetland versus that of the dry area highlights the potential contribution of seepage wetlands to nitrate attenuation for improved water quality in pastoral hill country landscapes. Land use change from pasture to forage cropping, which is increasingly being adopted in New Zealand hill country, has the potential to influence the dynamics and leaching of DOC for subsurface denitrification. However, there is limited research understanding on the effect of land use change (forage crop establishment) on DOC dynamics and leaching in pastoral hill country. Therefore, a study was designed to investigate soil DOC dynamics and denitrification capacity as influenced by the establishment of a forage crop (swede, Brassica napobrassica Mill.) via the surface sowing technique (no cultivation). This experiment was carried out in two stages. The first stage monitored the short-term changes in DOC concentration and chemistry immediately after spraying out pasture with selected agrochemicals (active ingredients: glyphosate, dicamba, diazinon and organomodified polydimethyl siloxane). The results showed that the agrochemicals increased DOC concentration only within the surface 5 cm soil depth (by ~ 20 mg kg⁻¹) on days 1 and 6 after the agrochemicals were applied. This increase in topsoil DOC concentration was most likely due to a direct contribution of C from the agrochemical, an indirect C contribution through the displacement of adsorbed organic molecules, and the decomposition of root necromass. DOC chemistry was, however, not altered by the applied agrochemicals. These findings were further confirmed by a follow-up experiment which used δ¹³C isotope technique to measure leached DOC from an organic material (plant residue) added to the topsoil. This showed that one week after the application of organic material, only a negligible amount (≤ 5%) of C derived from the organic material was detected in the subsoil (20-60 cm depth) DOC, compared to > 20% detected in the surface 20 cm soil depth, suggesting the limited leaching of exogenous DOC (under the experimental condition studied) due to its rapid turnover in the topsoil. The second stage of the forage crop establishment experiment monitored temporal changes in DOC concentration and denitrification capacity within a year of forage crop establishment. The results indicated that DOC concentration and denitrification capacity of both topsoil and subsoil layers were generally not affected by the establishment of the forage crop. However, an increase in rainfall and soil moisture, after periods of soil water deficit, increased the DOC concentration of the soil. Forage crop establishment resulted in an initial increase (by > 55%) in the nitrate concentration of the surface 20 cm soil depth, most likely due to poor nitrogen (N) utilisation by the growing brassica forage crop. However, the higher nitrate concentrations were only detected in the topsoil and thus the risk of increased nitrate leaching was assumed to be negligible. This thesis has highlighted the variations that exist in the DOC concentration and denitrification capacity of the different soils within hill country landscapes and thus suggests that these soils require contrasting management practices for effective water quality outcomes. In addition, the potential contribution of hill country seepage wetlands to nitrate attenuation shown in this thesis suggests that management strategies that preserve and enhance these pastoral hill country landscape features should be promoted to attenuate the losses of nitrate to receiving waters. Furthermore, this thesis has demonstrated that the common land use change from pasture to a forage crop, to supplement animal feed production in New Zealand hill country, is unlikely to have any significant impact on the DOC concentration and denitrification capacity of the soil profile (100 cm), within a one-year period. The observed results suggest that this practice is also not likely to negatively impact on water quality via nitrate leaching. However, larger-scale forage crop trials would be required to validate these findings. The findings of this thesis suggest that some hill country landscape features have the potential to attenuate nitrate losses to receiving waters. This information is critical for improving hill country N management for better water quality outcomes, which could potentially credit farmers under possible N loss regulations.Item Soil water modelling in hill country, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand(Massey University, 2019) Hajdu, IstvanAs the importance of environmental sustainability and increasing market demands have expressed pressure on New Zealand’s hill country farming systems, the more effective use of available resources and additional inputs has become crucial. Pastoral hill country farms are critical components of New Zealand’s economy, and precision agriculture solutions have been increasingly utilised to improve the sectors’ financial stability and resilience, and to satisfy the elevated expectations in yield. Profitability is dependent on pasture productivity that is highly influenced by the availability of nutrients as well as the amount of soil moisture (θv, m³ m⁻³). However, high variability of soil and landscape factors that control productivity is the primary concept describing these diverse landscapes. Hence, a study was conducted on a 2600 ha dominantly beef and sheep farm in the southern east coast of the North Island of New Zealand representing typical hill country settings. Some of the specific concerns of this research were the examination of the role of accurate, calibrated θv measurements via a wireless sensor network (WSN) (1) and the spatiotemporal variability of θv (2). Furthermore, the study investigates the potential of remote sensing for the mapping of near surface θv in sloping lands (3) and the characterisation of pasture yield patterns induced by the topography (4). These primary points were addressed to better understand the complexity occurring behind the environmental factors governing pasture yield and to potentially achieve improvement in pasture growth simulations. Systematic θv measurements have been used increasingly to inform decisions regarding fertiliser applications, feed supply and stock management in non-irrigated farming systems. To assist near real time θv and soil temperature (Ts) monitoring, 400 mm capacitance-based AquaCheck (AquaCheck, South Africa) probes (four θv and four Ts sensors per probe) were installed at 20 locations (hereinafter microsites) in predominantly silt loam soils. The spatially distributed probes were arranged into a WSN to capture data from various topographical positions. The application of manufacturer-provided calibration formula resulted in a mean root mean square error (RMSE) of 0.106 m³ m⁻³, a mean bias error of -0.099 m³ m⁻³ (indicating underestimation), and a coefficient of determination (R²) of 0.58 when correlated to directly measured reference (θv values. A single custom formula, relevant to the local soils resulted in an improved RMSE of 0.039 m³ m⁻³, while microsite-specific calibrations achieved an RMSE of 0.029 m3 m−3 and R² of 0.77. The application of a sensor-specific calibration resulted in an RMSE of 0.019 m³ m⁻³ with R² = 0.9. Sensor performance and accuracy errors were observed to vary as a function of soil wetness, bulk density (ρb, gcm⁻³) clay and total organic carbon (TOC) content. These effects were significant (P value < 0.001) but eliminated by the sensor-specific custom calibration. Sensor specifically calibrated θv was utilised the examine the effect of highly variable terrain attributes such as aspect, slope angle and soil physical properties on the θv patterns, stability and distribution both spatiotemporally and along the soil profile. Non-normal θv distribution was observed in the study period. The statistical analysis confirmed that the temporal stability of θv was higher in the deeper sections in both dry and wet seasons, while the spatial variability of θv increased with decreasing mean θv, although the greatest was in the rewetting stages. The degree of temporal persistence of the θv patterns varied with soil wetness conditions and seasons. Based on the temporal stability assessment, a representative location was selected based on a north-facing and open slope with silt loam soils. The θv distribution patterns were influenced by the topographic attributes showing that north-facing steep and moderately steep slopes were characterised with the highest variation, while east- and west-facing slopes showed similar trends. Due to the significant variability, near surface θv mapping at a spatial resolution that would be useful for describing within farm heterogeneity has been challenging for researchers. The near surface θv modelling performance of a Random Forest (RF) ensemble learning method and the synergetic use of various remote sensing data with terrain attributes were investigated at 20x 20 m pixel size. The RF model was trained using a two-year reference dataset containing Sentinel-1 SAR backscatter data (i), normalized difference vegetation index (NDVI derived from Sentinel-2, Landsat 7 and Landsat 8 images) (ii), a number of landscape parameters (iii) and in situ near surface θv values obtained by the WSN (iv) as ground truth. The RF algorithm captured a significant amount of the complex relationships and the model predicted θv with a mean RMSE of 0.047 m³ m⁻³ and adjusted R² of 0.76 at the point scale as given by the repeated cross validation. The fine-tuned RF regressor was trained using 15 microsites and a series of near surface θv maps was developed. The maps were validated using the five left out microsites resulting in 0.049 m³ m⁻³ RMSE and 0.76 adjusted R² indicating good agreement between modelled and observed θv values. The general annual trend of θv was closely reflected in the developed maps. The role of near surface and root zone θv, Ts, climatic variables and topographical attributes on the spatiotemporal pattern of pasture productivity was investigated at 13 selected microsites at which pasture herbage accumulation was monitored by the moveable exclusion cage method in 2016-2018. Considerable differences were found in the stored soil water response to significant rainfall events and climatic variables influencing pasture production. On the created multitable dataset, a multiple factor analysis was executed. As a result of this analysis, the role of various environmental parameters was defined highlighting the role of slope angle as the most significant determinant of pasture growth. The effect of landscape position was found to be more significant than aspect, which showed a seasonal dependence. Additionally, the contribution of terrain attributes was not consistent during the study period and changed from year to year. Ts and θv at a soil depth of 100 mm demonstrated the strongest governing effect on pasture production among the monitored parameters. In conclusion, the outcomes of this study imply that an extended and improved version of the proposed methods have the potential to be a basis of more accurate water balance simulations in complex landscapes at the regional scale. The presented quantification and isolation of the influencing topographic factors on pasture production may assist in hill country intensification by adding value to the generation of regulatory nutrient management plans. Ultimately, these advancements will enable the better characterisation of the dynamic hill country pastoral systems, which will lead towards helping hill country sheep and beef farmers to grow more pasture and increase returns while reducing the degrading effects of fertiliser applications on the environment.Item Management aspects of phosphate fertiliser use on hill country : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in Farm Management at Massey University(Massey University, 1983) Stewart, Kenneth MFarmer decisions relating to phosphate fertiliser use greatly influence farm profitability, and Farm Advisory Officers receive many requests for assistance in making fertiliser decisions. The Cornforth/Sinclair Phosphate Maintenance Model predicts the annual loss of phosphate from grazed pasture production systems. This model is studied in this thesis and used as the basis for an investigation of phosphate use strategies on a sample of Manawatu hill country properties. Alternative management strategies on three case study farms are analysed.Item Bull beef systems for Wairarapa hill country : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University(Massey University, 1987) Journeaux, Philip RossThe purpose of this study was to investigate the viability of a number of bull beef production systems integrated with sheep, within summer dry and summer wet Wairarapa ·hill country environments. This was achieved by construction of a spreadsheet feed budget simulation model, based on representative wairarapa pasture growth and animal production data. The model balanced feed requirements over fortnightly periods, with unconsumed feed transferred between periods subject to allowances for senescence and decay. Gross margin analysis was used to investigate the financial profitability of the systems examined, including the base sheep policies used. A survey of commercial sheep/bull beef hill country farmers within the Wairarapa was carried out to verify the assumptions made in model construction and to identify practical problems/opportunities. Several off- farm factors were then considered (eg supply of bulls, availability of killing capacity, United States beef market) in terms of their on-farm impact and the outlook for bull beef, over the next 2-3 years. Following analysis of the survey and off-farm data, several farmers were re-visited individually, and then a follow-up group meeting was held, to discuss the results of the model and survey analysis. The study showed that there are a number of bull beef systems which are viable and profitable on Wairarapa hill country, and that the number of bulls farmed on hill country is likely to increase in the future. while some farmers were achieving levels of production indicated feasible by the model, many were producing below these levels. There is therefore considerable opportunity to increase meat production and profitability on these farms. There is also considerable opportunity, in terms of the supply of bulls, for the bull beef industry to expand within New Zealand, although there are some market uncertainties which could hinder this. The overall conclusion from this study is that the production of bull beef offers considerable scope to increase the profitability of North Island hill country farming, and that this industry will continue to expand.