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Item An evaluation of greenhouse gas emissions reduction potential of plantain (Plantago lanceolata L.) in pastoral dairy production systems : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agriculture Systems Management at Massey University, Manawatu, New Zealand(Massey University, 2025-05-16) Sivanandarajah, KomahanThere is increasing interest in the ability of plantain (PL) to reduce nitrogen (N) leaching losses and mitigate nitrous oxide (N₂O) emissions, while maintaining milk and pasture production. While PL’s role in lowering urinary N concentration is well established, the results regarding the effect of PL on N₂O emissions have been inconsistent. Furthermore, evidence has shown that cows fed pure PL produce less methane (CH₄) emissions compared to those fed ryegrass. However, whether this CH₄ reduction can be achieved with PL in mixed pasture, along with a clear understanding of the mechanism(s) behind those reductions, are still to be determined. This thesis evaluates PL’s potential to mitigate CH₄ and N₂O emissions through a series of in vitro and a field experiment, focusing on mixed pastures with moderate PL levels. When pastures, either a conventional ryegrass-white clover (RWC) or an RWC mix containing ~40% of PL (PLM), were collected during different seasons and tested in an in vitro rumen batch culture system, differences in their chemical composition led to significant differences in CH₄ and rumen ammonia (NH₃) production. Compared to RWC, PLM had lower fibre (neutral detergent fibre and acid detergent fibre), higher lignin, more fermentable carbohydrates (non-structural carbohydrates), and plant secondary metabolites (PSM, acteoside and aucubin) detected only in PLM, while maintaining similar digestibility and crude protein (CP) levels. Consequently, PLM produced up to 27% less net NH₃ in spring, up to 19% less CH₄ in summer, and 17% less net NH₃ in autumn compared to RWC (p<0.05) in vitro. Plant secondary metabolites found in PL, have been associated with reducing N losses from grazed pastures. However, their influence on enteric CH₄ emissions remains unexplored. Additionally, the dose-response relationship between CH₄ and NH₃ production at different concentrations of PSM needs to be established. To address this, purified compounds (>99% purity) of acteoside and aucubin were incubated with perennial ryegrass (RG) as a basal substrate, and gas and CH₄ production were measured in vitro. The addition of acteoside to RG increased gas production (GP) by up to 12%, with a similar quantity of CH₄ production, but a 5–15% lower proportion of CH₄ in gas (%CH₄), compared to the control. Aucubin addition resulted in a longer lag phase for GP and CH₄ production. On addition of aucubin, it took up to 15% more time to reach the halftime (T1/2) GP and up to 20% longer to reach the T1/2 CH₄ production. The combined treatments of acteoside and aucubin produced up to 13% greater GP with similar CH₄ production and reduced %CH₄ by around 9%. These reductions are attributed to the modification of the hydrogen utilisation pathway (less hydrogen to produce CH₄) affected by acteoside. Aucubin reduced rumen net NH₃ production by up to 46%, with a similar reduction observed when acteoside was combined with aucubin. These reductions are attributed to the possible antimicrobial activity of aucubin. These results suggest that PL influences rumen fermentation in vitro, resulting in lower CH₄ and NH₃ production. Since higher rumen NH₃ correlates with greater urinary N excretion into the environment, reducing NH₃ levels in the rumen is advantageous. Previous studies have shown that N₂O emissions from PL pastures may be reduced due to smaller N concentrations in urine and/or biological nitrification inhibition (BNI) activity. In this study, urine collected from cows fed diets containing 0% PL, ~20% PL, and diluted urine from PL-fed cows, was applied to pastures containing 0% PL, 30% PL, and 40% PL during spring. The N₂O emissions were measured over 55 days. Results indicated a trend toward lower N₂O emissions as assessed using the emission factor (EF₃) metric, with increasing PL content (p<0.09), with an average reduction of around 28% for pastures containing 30–40% PL compared to RWC pastures (p=0.03). This reduction in N₂O emissions from PL pastures was attributed to BNI activity rather than differences in urine-N concentrations per se. These results enhance our understanding of PL’s role in mitigating environmental impacts from grazing ruminants in temperate systems. This thesis concludes that medium PL pastures (30–40% PL) exhibit significant environmental benefits compared to RWC pastures in vitro, with reductions in CH₄ and rumen NH₃ influenced by PSM in PL and the seasonal variability in chemical composition. Moreover, under conditions conducive to higher N₂O emissions (in spring), maintaining 30–40% PL in the pasture could reduce N₂O emissions more effectively than excluding PL.Item Enhancing grassland nitrogen estimation : a multiscale approach through optical reflectance spectroscopy and hybrid modeling techniques : 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, 2025-01-21) Dehghan-Shoar, Mohammad HossainOptical remote sensing technology has emerged as a powerful tool for assessing vegetation characteristics, particularly nitrogen (N) concentration (N%) in heterogeneous grasslands. Accurate estimation of N% is crucial for farmers, as it directly influences grassland productivity and plays a key role in sustainable land management. Accurate N assessments optimize fertilizer use, boosting productivity, lowering costs, and enhancing environmental modeling to address impacts such as N leaching and greenhouse gas emissions. Despite significant progress, challenges and knowledge gaps remain, highlighting the need for continued research to fully harness remote sensing’s potential in agricultural management and its impact on livestock productivity. This thesis aims to advance the accurate estimation of grassland N% by integrating physically-based, empirical-statistical, and hybrid models using optical reflectance spectroscopy data. The research focuses on three primary objectives: 1. To estimate N% in grasslands using optical reflectance spectroscopy, data will be collected across multiple scales, including ground-, leaf-, canopy-, and satellite-scale observations. 2. To improve the universality and adaptability of grassland N% models through a hybrid approach that combines data from various optical sensors across multiple scales. 3. To account for and quantify uncertainties in grassland N% prediction models. The thesis addresses the challenge of uncertainty by conducting a comprehensive analysis of its sources and developing methods, such as Physically Informed Neural Networks (PINN), to account for them. Key strategies include data fusion techniques for integrating diverse data sources and improving atmospheric correction methods. A unified methodology combining empirical-statistical and physically-based approaches is proposed to enhance generalization. Machine learning algorithms play a pivotal role in feature selection and optimization, further improving model accuracy and transferability. The developed methods undergo evaluation using independent validation data collected from heterogeneous grasslands across different periods and locations. Results demonstrate that integrating physically-based and empirical-statistical approaches significantly improves model accuracy and transferability, providing a deeper understanding of the factors influencing vegetation traits. This thesis highlights the importance of advanced techniques, including machine learning, deep learning algorithms, Radiative Transfer Models (RTM), and data fusion methods, for precisely characterizing vegetation traits, contributing to more sustainable and efficient grassland management practices.Item Evaluating woodchip bioreactors for mitigating drainage nitrate levels from a municipal wastewater land treatment site : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Environmental Sciences at Massey University, Palmerston North, New Zealand(Massey University, 2024-09-23) Romero Ramírez, Stefanía YaninaWoodchips bioreactors are a well-established end-of-drain treatment technology that has been widely used to reduce nitrate (NO₃-) from agricultural drainage water. However, their application to municipal wastewater land treatment sites remains less explored, despite potential advantages. In New Zealand, land application of pre-treated wastewater is a growing practice to mitigate excessive nutrient discharges to the aquatic environment. Land treatment can prove effective when operated correctly, but challenges arise when large volumes of wastewater, and small areas available for irrigation, necessitate high application rates, which can result in NO₃- enrichment of drainage water. The Levin Wastewater Land Treatment Site (LWLTS) is an example of where relatively high annual volumes of municipal wastewater are irrigated over an under-sized application area, resulting in high application depths (4667 mm/year). Consequently, surface drains and shallow groundwater transfer NO₃- to the Waiwiri Stream continually all year. In order to reduce the impact of the LWLTS on the water quality of the Waiwiri Stream, one of its resource consent requirements involves reducing the NO₃- levels in the Waiwiri Stream, downstream from the site. The objective of this thesis was to evaluate the potential use of woodchip bioreactors for reducing NO₃- concentrations in drainage water from LWLTS, including an assessment of the ability of soluble C dosing to enhance NO₃- removal. Initial experiments used small-scale column woodchips bioreactors, which simulated similar water temperatures and NO₃- concentrations to those at the LWLTS. The effect of different water hydraulic retention times (HRT) and the use of dosing with two soluble C sources, liquid sugar, and ethanol, were assessed. Under warm temperature conditions, the column bioreactors achieved 99% NO₃- removal efficiency with a 10-hour HRT. In contrast, under cool water temperatures at the same HRT, the NO₃- removal efficiency decreased to 31%. Soluble C dosing was an effective strategy for enhancing NO₃- removal, with the choice of C source proving to be crucial. Ethanol demonstrated to be more efficient than liquid sugar. Additionally, it was determined that dosing with ethanol at a C:N dosing rate of 1.5:1 achieved high removal efficiencies of 77% under warm conditions and at a 3.3-hour HRT, and 82% under cool conditions and at a 10-hour HRT. Based on the results of the column bioreactor study, the performance of pilot-scale woodchip bioreactors at reducing NO₃- levels in drainage water were evaluated at the LWLTS under field conditions. These experiments involved quantifying the effects of different HRTs and dosing with ethanol at different C:N ratios. Operating the bioreactors, at a 10-hour HRT achieved average NO₃- removal efficiencies of 43% and 59% during the cool and warm seasons, respectively. While, at a 20-hour HRT, the removal efficiencies were 69% and 85%, respectively. The variations in NO₃- removal efficiency between both seasons demonstrated that during the cool season the bioreactors were on average about one-third less effective. When bioreactors, operating at 6.6-hour HRT in cool conditions, were dosed with ethanol at a C:N ratio of 0.75:1, the NO₃- removal efficiency improved from 24% to 93%. This result demonstrates that under field conditions ethanol dosing proved to be a higher effective strategy for enhancing the performance of woodchip bioreactors, particularly during cool periods. Based on the findings of the pilot-scale bioreactors, two woodchip bioreactor designs were proposed for the LWLTS: a non-dosed woodchip bioreactor of 645 m³ operating at a long HRT (20 hours), and an ethanol-dosed woodchip bioreactor of 197 m³ operating at a short HRT (6.6 hours). The two proposed designs provide contrasting approaches, although both are expected to achieve the same annual NO₃- load removal (1174 kg N/year) and have similar annualised NO₃- removal costs ($6.90 and $6.50/kg N, respectively). In the long term, it is expected that the NO₃- removal of the larger non-dosed bioreactor will decline at a faster rate compared to the ethanol-dosed bioreactor due to relying solely of woodchips as the C source. However, it would be less susceptible to the risk of bioclogging and has greater capacity to increase NO₃- removal. In addition, ethanol dosing could be introduced to the larger non-dosed bioreactor in the future, when a decline in NO₃- removal efficiency is observed. Therefore, the overall flexibility of the larger bioreactor design is an advantage but comes with higher initial set-up cost. The results of this research demonstrate that woodchips bioreactors are effective treatment methods for mitigating drain water NO₃- levels at a municipal wastewater land application site. Additionally, C dosing using ethanol proved to be a promising cost-effective alternative to enhance bioreactor performance, allowing the use of relatively short HRTs, especially during cool conditions. This increases the daily volume of water that can be effectively treated.Item Thin film electrochemical sensor for water quality monitoring : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering, Massey University, Auckland, New Zealand(Massey University, 2023-12-11) Lal, KartikayFreshwater is the most precious natural resource, essential for supporting life. Aquatic ecosystems flourish in freshwater sources, and many regions around the world depend on aquatic food sources, such as fish. Nitrogen and phosphorous are the two nutrients, in particular, that are essential for growth of aquatic plants and algae. However, with rising population and anthropogenic activities, excessive amounts of such nutrients enter our waterways through various natural processes, thereby degrading the quality of freshwater sources. Elevated levels of nitrate-nitrogen content, in particular, lead to consequences for both aquatic life as well as human health, which has been a cause for concern for many decades. As recommended by the World Health Organization, the maximum permissible nitrate level in water is 11.3 mg/L. These levels are often exceeded in coastal areas or freshwater bodies that are close to agricultural land. Therefore, it is essential to monitor nitrate levels in freshwater sources in real-time, which can be achieved by employing detection methods commonly used to detect ionic content in water. Hence, a comprehensive review was carried out on various field-deployable electrochemical and optical detection methods that could be employed for in-situ detection of nitrate ions in water. The primary focus was on electrochemical methods that could be integrated with low-cost planar electrodes to achieve targeted detection of nitrate ions in water. Designing resilient sensors for real-time monitoring of water quality is a challenging task due to the harsh environment to which they are subjected. There is a significant need for sensors with attributes such as repeatability, sensitivity, low-cost, and selectivity. These attributes were first explored by evaluating the performance of silver and copper materials on three distinct geometric patterns of electrodes. The experiments produced promising results with interdigitated pattern of copper electrodes that were successful in detecting 0.1-0.5 mg/L of nitrate ions in deionised water. The interdigitated geometric pattern of electrodes were further analyzed in four distinct materials namely, silver, gold, copper, and tin with real-world freshwater samples that were collected from three different freshwater bodies. The water samples were used to synthesize varying concentrations of nitrate ions. The results showed tin electrodes performed better over other materials for nitrate concentrations from 0.1-1 mg/L in complex matrix of real-world sample. The nitrate sensor eventually needs to be deployed in freshwater bodies, hence a real-time water quality monitoring system was also built that incorporated sensors to monitor five basic water quality parameters with the aim to monitor and study the quality of water around the local area.Item Crohn's Disease and environmental factors in the New Zealand context : a thesis presented in partial fulfilment of the requirements for the degree of Doctoral of Philosophy in Nutritional Science at Massey University, Manawatū, New Zealand(Massey University, 2023) Morton, HannahBackground: Inflammatory bowel disease (IBD), consisting of Crohn’s disease (CD) and ulcerative colitis (UC), are lesser-known chronic diseases of the gastrointestinal tract. The causes of IBD are unknown, although research indicates an interplay of genetic, immunological, and environmental factors. The incidence and prevalence of CD in New Zealand (NZ) are among the highest worldwide, and unlike many other Western countries, evidence suggests the incidence rate is still increasing. Objective: The objective was to investigate the involvement of environmental factors in the aetiology, pathogenesis, and symptomatology of CD in NZ. Specifically, pathogenic bacterium Mycobacterium avium subspecies paratuberculosis (MAP), vitamin D, diet, and urbanisation. Methods: Patients with IBD and controls from around NZ completed a questionnaire on environmental factor exposure. Foods implicated in symptom triggering or exacerbation, the possible mechanism(s) involved, and whether vitamin D can confer protection, were investigated using an in vitro digestion method and in vitro model of the intestinal barrier. Serum vitamin D concentrations were measured and compared in patients and controls in order to explore a possible association between vitamin D and IBD. Lastly, the incidence and prevalence of IBD in the Manawatū region was determined, and the urban and rural incidence were compared. Results: Questionnaire derived data showed significant associations between CD and exposure to rural sources of microorganisms, and a major urban birthplace (≥100,000 residents), while rainwater for drinking and cooking during childhood was protective. No associations were observed between CD and MAP exposure. Over 50% of patients implicated dietary elements in symptom onset and/or exacerbation. The in vitro investigation findings suggest this may result from tight junction damage. Vitamin D concentrations did not differ between patients and controls, however, were significantly lower in CD patients that reported recent disease activity. In the Manawatū region, the mean annual incidence and 2013-point prevalence of CD were 17.7 and 250.4 per 100,000, respectively, and urban residence at diagnosis was associated with a six-fold greater IBD incidence compared to rural residence. Conclusions: The findings demonstrate that vitamin D, diet, and urbanisation are involved in CD. A greater understanding of environmental factors, especially modifiable factors, could provide opportunities for reducing CD risk, managing symptoms, or slowing disease progression.Item Three essays on corporate finance studies in China : a thesis presented in fulfilment of the requirements for the degree of Doctor of Philosophy in Finance at Massey University, Palmerston North, New Zealand(Massey University, 2023-11-13) Yue, ShuaiThis thesis investigates three aspects of listed firms in the Chinese market. The first essay in the thesis examines the impact of state ownership on firm performance using hand collected ownership data of firms with state-private mixed ownership structures. We find a U-shaped relationship between state ownership and firm performance. At lower levels, state ownership has a negative association with firm performance, but beyond a certain threshold (e.g., 55% for ROA and 44% for Tobin's Q), state ownership becomes positively associated with firm performance. This finding indicates a trade-off between the negative effects of grabbing hand and the monitoring benefits of state owners. In addition, the introduction of strategic investors moderates the influence of state ownership on firm performance. The results show that the U-shaped impact of state ownership on firm performance diminishes after the introduction of strategic investors, implying that strategic investors may mitigate the underperformance observed around the threshold state ownership levels. The second essay focuses on the corporate information environment. It investigates the behaviour of firms with politically connected executives regarding information disclosure when subject to government inspection influences. China initiated the central environmental protection inspection in 2016. We find that while firms with politically connected executives generally exhibit lower stock price crash risk, these politically connected firms are more prone to crash risk when subject to inspection influences than firms without political connections. Further, we examine whether the inspection effect on crash risk varies based on the type of political connections developed by executives, namely achieved and ascribed political connections. Our results show that firms with executives having achieved political connections are related to higher crash risk when under government inspection influences, but no significant impact is observed for firms with executives having ascribed political connections. The final essay examines the influence of firms’ exposure to economic policy uncertainty (EPU) on environmental investment and investigates whether firm size plays a significant role in this relationship. We find that although small firms are generally associated with lower levels of environmental investment compared to large firms, there is a positive association between small firms’ EPU exposure and environmental investment, indicating that small firms are more inclined to invest in environmental initiatives when facing higher EPU exposure.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 Manipulating soil bioavailable copper as an innovative nitrate leaching mitigating strategy in New Zealand pastoral soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Soil Science, School of Agriculture and Environment, College of Sciences, Massey University, Palmerston North, New Zealand(Massey University, 2023) Matse, Dumsane ThembaUrine patches are the primary sources of nitrate (NO₃⁻ -N) leaching from pastoral dairy farms. Since NO₃⁻ -N is the product of nitrification, a clear understanding of the nitrification process is a vital step toward the development of effective and efficient mitigation approaches. The first step of ammonia (NH₄⁺) oxidation to hydroxylamine (NH₂OH) is catalyzed by the ammonia monooxygenase enzyme (AMO), and copper (Cu) is a co-factor in the activity of the AMO enzyme. Therefore, manipulating Cu bioavailability through the application of Cu-complexing organic compounds such as calcium lignosulphonate (LS) and co-poly acrylic-maleic acid (PA-MA) to soil could influence AMO activity and consequently limit the nitrification rate in soil. There are no published studies that have examined the effect of bioavailable Cu concentration changes on nitrification rate, ammonia-oxidizing bacteria (AOB) and archaea (AOA), and NO₃⁻ -N leaching. The overall aim of this thesis is to determine the significance of bioavailable Cu in the nitrification process in the context of developing novel Cu-complexing organic compounds to inhibit nitrification rate in pastoral soils. A soil incubation study was conducted to characterize the relationship between changes in soil bioavailable Cu concentration and nitrification rate. This study was conducted using three pastoral soils (Pumice, Pallic, and Recent soils) spiked with five Cu levels (0.1, 0.3, 0.5, 1, and 3 mg kg⁻¹). Treatments of Cu-complexing compounds were separately applied to each Cu level. The treatments were urea applied at 300 mg N kg⁻¹, urea + LS at 120 mg kg⁻¹, and urea + PA-MA at 10 mg kg⁻¹. Results show that increasing the added Cu concentration from 0.1 to 3 mg kg⁻¹ increased nitrification rate by 35, 22, and 33% in the Pumice, Pallic, and Recent soils, respectively. Application of LS and PA-MA significantly (P ˂ 0.05) decreased nitrification rate with the mean reduction being 59 and 56%, 32 and 26%, and 39 and 38% in the Pumice, Pallic, and Recent soils, respectively at Day 8 relative to the urea-only treatment. To further extend knowledge of the relationship between bioavailable Cu and the key nitrifying microorganisms in soils, a greenhouse-based pot trial using three soils (Pumice, Pallic, and Recent soils) planted with ryegrass and treated with synthetic urine applied at 300 kg N ha⁻¹ and three levels of Cu (0, 1, 10, 100 mg added Cu kg⁻¹) was established. Results show that AOB amoA gene abundance increased as a function of increasing added Cu from 1 to 10 mg kg⁻¹ but was inhibited at 100 mg added Cu kg⁻¹ in both Pallic and Recent soils. The effect of bioavailable Cu was not apparent in the Pumice soil. The increase in AOB amoA gene abundance positively correlated with nitrification rate in both the Pallic (r = 0.982, P < 0.01) and Recent soil (r = 0.943, P < 0.01) but not in the Pumice soil. There was no effect of increasing Cu concentration on AOA amoA gene abundance in all three soils. Results from both incubation and greenhouse pot trials provide strong evidence that Cu is an important trace element in the nitrification process and reducing Cu can reduce nitrification in soil. However, in order to definitively quantify this treatment effect, further field studies were necessary. Therefore, a field lysimeter study was conducted using Pumice soil (Manawatu climate) and Pallic soil (Canterbury climate). The following treatments were investigated to reduce NO₃⁻ -N leaching during late-autumn application; urine only at 600 kg N ha⁻¹, urine + PA-MA at 10 kg ha⁻¹, urine + LS at 120 kg ha⁻¹, urine + a split-application of calcium lignosulphonate (2LS at same rate, initial and after a month of first application), and urine + ProGibb SG (GA at 80 g ha⁻¹) + LS (GA + LS). Another set of treatment applications, urine only, urine + GA only, and urine + GA + LS, were applied mid-winter to both soils. The GA was applied to improve the effectiveness of these organic compounds during climatic periods of poor plant growth. Results showed that there was no significant reduction in mineral N leaching associated with the late-autumn application of both PA-MA and LS for the Pumice or Pallic soils. However, the application of 2LS reduced mineral N leaching by 16 and 11% in Pumice and Pallic soils, respectively, relative to urine-only. The late-autumn inclusion of GA increased the effectiveness of LS in both soils. This was confirmed by a significant reduction of mineral N leaching by 35% from both Pumice and Pallic soils. Mid-winter application of GA + LS significantly reduced mineral N leaching only in the Pumice soil (by 20%) but not in the Pallic soil relative to urine-only. In both late-autumn and mid-winter treatments application of the different Cu-complexing treatments did not have negative effects on pasture dry matter yield in either Pumice or Pallic soils. In this lysimeter study, the mechanistic effect of PA-MA and LS on reducing bioavailable, nitrification rate and AOB/AOA amoA gene abundance was not investigated. A second field lysimeter experiment was established using the Recent soil in Manawatu to explore the mechanism of Cu manipulation through the application of LS and PA-MA on nitrification rate, AOB/AOA amoA gene abundance, and mineral N leaching. The effect of combining organic inhibitors with GA on reducing mineral N leaching was also investigated. This study evaluated the same treatments used in the first lysimeter study and applications were again conducted at two different seasonal periods (late-autumn and mid-winter). The results showed that the effect of PA-MA and 2LS on bioavailable Cu corresponded with a reduction in nitrification rate and AOB amoA gene abundance. The effect of PA-MA and 2LS was associated with reduced mineral N leaching by values of 16 and 30%, respectively, relative to urine-only. The reduction in mineral N leaching induced by PA-MA and 2LS increased N uptake by 25 and 7.8% and herbage DM yield by factors of 11 and 8%, respectively, relative to the urine-only. The LS treatment did not induce a significant change of either bioavailable Cu or nitrification rate which corresponded to no significant effect on mineral N leaching. The late-autumn combination of GA + LS reduced mineral N leaching by 19% relative to urine-only, but there was no significant difference in mineral N leaching observed for the mid-winter application relative to urine-only. The overall results of this research show that bioavailable Cu is a vital trace element in the nitrification process and for AOB functioning in soil. Therefore, reduction in bioavailable Cu through the application of Cu-complexing compounds can inhibit nitrification. In this doctoral study, the application of Cu-complexing compounds (LS and PA-MA) showed potential to inhibit nitrification rate and subsequently reduce mineral N leaching in pastoral systems, but their efficacy depends on soil characteristics. Future work is recommended to investigate the effect of LS and PA-MA application on nitrous oxide emissions. Further research is recommended to investigate the short and long terms effects of these treatments on non-target soil microbiota.Item Modelling the long-term impact of modernized irrigation systems on soil water and salt balances, and crop water productivity in semi-arid areas under current and potential climate change conditions : integration of agrohydrological model, geographical information system, remote sensing, and climate change model : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand(Massey University, 2022) Khan, Muhammad HamedIrrigated agriculture plays a key role in ensuring food security and rural livelihoods across semi-arid and arid regions, like in the Indus basin of Pakistan. However, the Indus basin irrigation system of Pakistan is facing serious threats of low crop yields and increasing water scarcity, waterlogging, soil salinity, and overexploitation of groundwater. Considering the irrigation water-management issues, water managers and policymakers in Pakistan are looking into the modernization of the irrigation practices by introducing sprinkler and drip irrigation systems with the intent to save water and enhance crop water productivity. However, such intervention if adopted at a larger scale could seriously affect regional soil water and salt balances, solute leaching, and recharge to groundwaters in semi-arid and arid regions. Therefore, a robust assessment of the long-term potential impacts of modernised irrigation systems, particularly under the potential climate change scenarios, is essential for improving productivity and sustainable irrigated agriculture in semi-arid and arid regions. Field experiments are practically difficult to quantify the long-term impacts of modernised irrigation practices on soil water and salt balances and crop growths, especially under projected climate change conditions. This thesis developed a modelling framework using local field experiments, and geographical and remote sensing information, combined with a spatially distributed agrohydrological model and climate change projections to analyse the potential impacts of different irrigation application scenarios at the field and canal command scales. This methodology is applied to evaluate the potential impacts of current and proposed modernized irrigation systems on soil water and salt balances, soil salinity build-up, percolation to groundwaters, crop yield and crop water productivity of irrigated crops under long-term contemporary climate (1987-2017) and potential climate change (2070-2099) scenarios. The main irrigated crops of wheat, rice, and cotton were studied in the Hakra branch canal command as a case study. The Hakra branch canal (HBC) command, located in the Indus basin irrigation system of Pakistan, covers 0.21 million ha and is characterised by the typical problems of canal water scarcity, poor groundwater quality, waterlogging and soil salinity, and less-than-optimal crop production. The information collected from local field-scale experiments during the years 2016-2017, GIS, remote-sensing techniques and global climate models are integrated to parametrise, calibrate, and validate the agrohydrological Soil-Water-Atmosphere-Plant (SWAP) model application at both field- and canal command- scales. The SWAP model simulated soil water and salt balances, percolation to groundwaters, and water- and salt-limited crop yields and crop water productivity values of main irrigated crops of wheat, rice, and cotton from field- to canal command- scales in the study area. The modelling assessment of current irrigation practices revealed significant variation in canal water supplies and over-exploitation of groundwater, resulting in high spatial variability in soil water percolation and salt build-up in the soil at the spatial scale of the head, middle and tail reaches of the canal command. The canal water-inflow is about 19% and 42% higher at the head reaches than at the middle and tail reaches, respectively. The significant seepage from the canal network and the cultivation of high water-consuming crops such as rice are the potential cause of waterlogging at the head reaches. Whereas limited canal inflow and use of poor-quality groundwater (> 3 dS m⁻¹) appear to be potential causes of soil salinity at the tail reaches of the HBC command. The detrimental effects of limited canal inflow and the use of marginal to poor groundwater causes considerable spatial variation in simulated water and salt-limited crop yields. The simulated water and salt-limited crop water productivity values are not only different for the different crops of wheat, rice and cotton, but also for the same crop across the study area. The field- and canal-command scale modelling was applied to simulate and assess the potential impacts of the proposed modernized irrigation scenarios, such as • sprinkler irrigation is defined as a high-efficiency irrigation system with leaching fraction (HEIS_LF) and without leaching fraction (HEIS_noLF), and • precision surface irrigation system (PSIS) for cotton-wheat cultivation under contemporary climate (1987-2017) and potential climate change (2070-2099) scenarios RCP 2.6 (low emission) and RCP 8.5 (high emission or business-as-usual). The long-term simulation results suggest a saving of about 40% in irrigation water under the HEIS_noLF scenario. However, this irrigation water-saving under the HEIS_noLF scenario resulted in the risk of an increase in soil salinity due to reduction in soil percolation and its associated salt build-up in the soil profile. Under the HEIS_noLF scenario for cotton-wheat cultivation, the soil salinity is simulated to increase from 2.6 to 8.0 dS m⁻¹ at the field-scale, and from 2 to >12 dS m⁻¹ at the canal command scale, affecting crop yields due to salt stress. The high salt build-up is simulated to reduce crop yields by 38% for cotton, and 48% for wheat under the contemporary climate (1987-2017) at the canal command scale. The soil salinity is simulated to get even worse in poor-quality groundwater areas, resulting in wheat failure of < 1 ton/ha with HEIS_noLF under the RCP 8.5 scenario of potential climate change (2070-2099) conditions. The modelling analysis suggests a significant leaching fraction is required to maintain acceptable soil salt balance for successful crop production. This leaching fraction could be achieved by a pre-sowing irrigation of 60 mm depth at the start of the season, followed by an additional 10 mm depth with each irrigation interval using a high-efficiency irrigation application, simulated as HEIS_LF. The HEIS_LF scenario resulted in 50 to 65% higher average water- and salt-limited crop water productivity values (kg/m³ ET) of 0.5 for cotton, and 1.87 for wheat. This is compared to the HEIS_noLF scenario of 0.25 for cotton, and 0.65 for wheat under potential climate change (2070-2099) conditions. However, the PSIS irrigation scenario resulted in similarly favourable soil water and salt balances, water and salt-limited crop yields and crop water productivity values for the cotton - wheat cultivation. Under the PSIS irrigation scenario, the average water-and salt-limited crop water productivity values (kg/m³ ET) are simulated as 0.50 for cotton and 2.79 for wheat under the contemporary climate (1987-2017), and 0.50 for cotton and 1.92 for wheat in potential climate change (2070-2099) conditions. The modelling analysis simulated the average soil percolation rate as 10 to 20% higher, resulting in the leaching of 20 to 30% more salts from the soil profile under the PSIS scenario than the HEIS_LF under potential climate change conditions. The key findings of this modelling assessment suggest that modernisation of irrigation systems as higher-efficiency (HEIS) irrigation applications, with no appropriate leaching fraction, would compromise salt build-up in the soil profile. This would potentially reduce crop yields and crop water productivity in the long-term, especially under potential climate change (2070-2099) conditions. There appears very limited scope for real irrigation water savings using a high-efficiency irrigation system for long-term sustainable crop production in areas making conjunctive use of limited canal water supplies and marginal- to poor-quality groundwaters. Hence, proposed initiatives for implementing high-efficiency irrigation systems should be carefully evaluated in terms of their long-term potential impacts on regional soil water and salt balances, crop yields and crop water productivity values in areas such as the Indus basin irrigation system in Pakistan, particularly under potential climate-change conditions.