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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 The long-term effects of elevated CO₂ on soil organic carbon sequestration, partitioning and persistence in a grazed pasture : a thesis presented in partial fulfilment of the requirements for the degree of Doctor in Philosophy in Soil Science at Massey University, Manawatu, New Zealand(Massey University, 2024-03-04) Gonzalez Moreno, Marcela AngelicaThe increased concentration of atmospheric carbon dioxide (CO₂) is a significant driver for climate change and also influences the cycling of soil organic carbon (OC) in ecosystems. Despite the importance of grassland soils as a sink for CO₂, the effect of long-term exposure to elevated CO₂ (eCO₂) on OC sequestration, partitioning and persistence in grazed grassland soils is poorly understood. This thesis aimed to investigate the effect of eCO₂ on soil OC stocks, the partitioning of OC in soil fractions and persistence in a grazed legume-based pasture at the New Zealand (NZ) Free Air CO₂ Enrichment (FACE) facility. The NZ-FACE, established in 1997, is the only FACE experiment worldwide that includes the influence of grazing practices on the above- and below-ground components of the OC cycle. The effect of eCO₂ on soil OC persistence and stability was assessed by measuring changes in soil OC stock, in the distribution of soil OC in the soil fractions by wet fractionation analysis and in the soil OC decomposition pathways by determining the molecular composition of soil organic matter (OM) by pyrolysis analysis followed by gas chromatography/mass spectroscopy (GC-MS) and thermally assisted hydrolysis methylation-GC-MS (THM-GC-MS) analysis to a soil depth of 250 mm. In Chapter 3, we assessed OC storage and persistence in the soil fractions in a grazed legume- based pasture exposed to eCO₂ for 22 years on Pukepuke soil (Mollic Psammaquent) at three soil depths. Our study revealed that after 22 years of exposure to eCO₂ there were no significant changes in the stocks of OC and N as well as the partitioning of OC within different soil fractions in the Pukepuke soil. Interestingly, in the last 10 years at the NZ-FACE facility, there has been a sharp reduction of OC and N stocks in the Pukepuke soil, independent of the CO₂ treatment. We suggest that in the sandy Pukepuke soil under conditions of warmer temperatures and a wetter system, the deficiency that has emerged in soil nutrient availability, the environmentally enhanced plant growth and the larger amounts of fresh OM input has caused a positive priming effect, mainly in the labile fraction. Even though eCO₂ did not change the soil OC stocks nor OC content in the soil fractions in any soil layer, it did modify the soil nutrient status (phosphate in particular) and did increase polysaccharides and aliphatic proportions in the coarse particulate organic matter and micro-aggregates indicating that the priming was further enhanced in eCO₂ soils with this effect being especially prominent in the 50 – 150 mm soil layer (Chapter 3). In Chapter 4, the hypothesis that grazing animals, by returning nutrients in urine, dung, and plant litter trampled into the soil surface, would contribute to an increase in soil OC and N stocks under eCO₂ was investigated and rejected. Despite not finding any interaction effect between eCO₂ and defoliation treatment on the soil OC stocks and partitioning in the soil fractions, the presence of an interaction effect in the soil OM molecular composition suggests that distinctly different OC decomposition pathways exist depending on pastures management under eCO₂. Our study showed that under grazing there was an accumulation of lignin-derived OM, which reveals a higher proportion of shoot-derived rather than root- derived OC under eCO₂. In Chapter 5, the influence of the inherent properties of a soil – which might enhance or limit the effects of eCO₂ on soil OC persistence and stability – was examined in two contrasting soils (Pukepuke and Stratford; a Entic Dystrandept) in mesocosms installed at the NZ-FACE in May 2005 and extracted after 15 years. Our results showed that over the course of the mesocosm study, OC and N contents and stocks (to 150 mm soil depth) in the Pukepuke soil declined by 16 t ha-1 under ambient CO₂ atmosphere, possibly as a result of soil disturbance during the establishment of the mesocosms. In the Stratford soil, with the ability to strongly preserve OM through mineral associations, the decline in soil OC was much smaller (5 t ha-1). Elevated CO₂ interacted with soil type and after 15 years of exposure to eCO₂, the Pukepuke soil had 6.5 t ha-1 more OC stocks, compared to the same soil under ambient CO₂ conditions, while no differences were found in the OC stocks of the Stratford soil (Chapter 4). These findings indicate that in the Pukepuke soil the eCO₂ treatment might have (i) helped overcome the impact of disturbance by favouring plant growth and generating a larger plant detritus input to the soil that enabled the partial replenishment of the OC loss at the time of mesocosm establishment, or (ii) limited the impact of disturbance, as eCO₂ often improves soil aggregation. It is crucial to consider that (i) the Stratford soil was subjected to ~50% less precipitation at the NZ-FACE compared to its original location and (ii) the mesocosm might have introduced new variables due to physical barriers. Thus, extrapolating the findings to field conditions at the NZ-FACE facility and elsewhere requires cautious interpretation. The findings presented in this thesis contribute significantly to enhancing our understanding of the mechanistic processes underlying the influence of eCO₂ on the stabilization and mineralization of soil OM. These insights have direct implications for the development of sustainable agricultural management practices in response to a changing environment.Item Improving weed control options for ryegrass/clover pastures that contain plantain (Plantago lanceolata) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Plant Science at Massey University, Manawatū, New Zealand(Massey University, 2023) Shrivastav, NidhiThe inclusion of narrow-leaved plantain (Plantago lanceolata) in the traditional pasture system of perennial ryegrass (Lolium perenne) and white clover (Trifolium repens) is preferred by many New Zealand farmers nowadays to assist with nitrogen loss mitigation and to improve summer production. Control of weeds using selective herbicides becomes more difficult after adding extra species to a grass/clover sward. The work in this thesis investigated weed control options for ryegrass/clover pastures in New Zealand that contain plantain. This included determining the tolerance of plantain to different herbicides and identifying the herbicide options most effective for weeds. There has been some breeding of phenoxy herbicide tolerance into the Agritonic cultivar of plantain in New Zealand. In this thesis, the level of tolerance in Agritonic plantain was compared with Tonic plantain to MCPB, MCPA, MCPB/MCPA mix, 2,4-D and 2,4-DB in two glasshouse experiments. The tolerance generally appeared to be 1.3 to 3.4-fold, so not large but potentially useful. The thesis also investigated the tolerance of plantain, white clover and perennial ryegrass to a range of herbicides applied to a mixed sward of these species at an early stage of establishment in spring. The effectiveness of the herbicides was also assessed for controlling weeds that established within the swards using two field trials. Half of the recommended rate of MCPB was less damaging to both cultivars of plantain than the recommended rates of MCPB and MCPB/MCPA, but could not control most of the weeds present. The recommended rate of MCPB/MCPA had very little detrimental effect on young clover or Agritonic plantain and gave good weed control. Flumetsulam was fairly safe to use in the plantain-based pasture though it suppressed plantain initially, which recovered after 3-6 months in each trial. Bentazone was safe for the plantain, ryegrass and clover and suppressed most of the weeds, but only if there was no rainfall in the hours after herbicide application. Mowing after each harvest controlled redroot, black nightshade and fathen and also suppressed docks temporarily. The most effective weed control strategy that was also selective involved a combination of bentazone + half rates of MCPB/MCPA followed by mowing which gave useful control of weeds including docks for many months. The mechanism of tolerance of Agritonic plantain to 2,4-D was investigated using radiolabeled herbicide (¹⁴C-2,4-D) in two experiments. Absorption/translocation and metabolism of the herbicide was studied in both this cultivar and Tonic plantain for comparison. The tolerance to 2,4-D in Agritonic plantain appeared to involve reduced translocation of the herbicide, though reduced absorption may have also contributed. Two glasshouse experiments were conducted to test the tolerance of mature plantain plants (both Agritonic and Tonic) to application of some herbicides suitable for use in weed wipers (glyphosate, clopyralid, aminopyralid, dicamba, picloram and triclopyr) to the seed-heads, simulating potential contact during wiper application to pasture weeds. Aminopyralid and a low rate of glyphosate were found to be the least damaging treatments and should be safe to use for weed wiping within swards containing plantain. A high rate of glyphosate and a glyphosate/metsulfuron mix caused the most damage to plantain, and this damage was greater following simulated rainfall after application.Item Leaf regrowth stage as a morpho-physiological indicator of Bromus valdivianus and Lolium perenne mixed pasture defoliation in New Zealand grazing system : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University, Manawatū, New Zealand(Massey University, 2022) García Favre, Javier HoracioBromus valdivianus Phill. is a perennial grass species native to the South of Chile. Its better fitness for growing under low water availabilities compared with Lolium perenne L. has been assessed in field and glasshouse studies. However, Bromus valdivianus morpho-physiological attributes, such as root development under field conditions, and competitive ability are likely to manifest differently under contrasting defoliation criteria based on leaf regrowth stage. In addition, Lolium perenne and B. valdivianus growth can be complementary throughout the year under rainfed conditions. Therefore, the objective of the present thesis was to determine defoliation criteria based on leaf regrowth stage of mixed pastures (50/50% L. perenne and B. valdivianus) and consequences for species succession and functional traits development of the species. Four studies were developed in the thesis, two glasshouse and two field studies. The first glasshouse study evaluated the growth response and water-soluble carbohydrate (WSC) accumulation of B. valdivianus at three different defoliation frequencies. The results suggested that B. valdivianus increased herbage mass production and root biomass at low defoliation frequency (i.e., at 3.5–4.0 leaf regrowth stage). This was related to a higher WSC accumulation in the tiller base. In addition, under low soil water availabilities (20–25% of field capacity) WSC increased by ~20%, which indicated a drought resistant strategy of this species. The second study proved the growth enhancement (mainly root length and biomass) of B. valdivianus under competition with L. perenne compared with intraspecific competition when soil water shifted from high to low availabilities. In field studies, B. valdivianus mixed with L. perenne increased ~15% accumulated herbage mass compared to the species monocultures, which supported higher production during dry periods. This was due to the niche complementarity and asynchrony in herbage growth between the species, with B. valdivianus capable to maintain a steady tiller population throughout the year and root biomass accumulation at depth. Whereas L. perenne grew more than B. valdivianus under low level of oxygen in the soil and under optimal growth conditions and presented a higher nutritive value than B. valdivianus during winter, spring and autumn. The latter supports the partial grazing preference for L. perenne shown by sheep during part of the year, as measured in the second field study. This lower nutritive value (less energy) of B. valdivianus monocultures was overcame in the mixture, with a good overall value for high animal production. Regarding the mixture defoliation criterion, it was shown that it can be based on the optimal leaf regrowth stage of either species, as herbage mass production was similar between defoliation frequencies based on optimal leaf regrowth stage of either of the species. However, under defoliation based on optimal leaf regrowth stage of B. valdivianus, root biomass accumulation at depth increased ~45%. Overall, the results of the present thesis evidenced that Bromus valdivianus can successfully grow alongside L. perenne and, therefore, the mixture can increase forage production of New Zealand farming system in the event of climate change.Item Linking soil functional biodiversity and processes to soil ecosystem services : biochar application on two New Zealand pasture soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Ecology at Massey University, Manawatu, New Zealand(Massey University, 2020) Garbuz, StanislavSheep and beef farming and dairying are an important part of the New Zealand economy, occupying about 40% of land area used for the livestock. Maintenance of that land is an essential part of sustainable agriculture. For a long time, biochar has been used and considered as a multifunctional soil amendment adding to the natural capital stocks of the soils and contributing to a wide range of soil ecosystem services, provision of nutrients (soil fertility) through the increasing nutrient availability, neutralising acidity through liming, and mitigating climate change through carbon (C) storage. In this thesis I investigate the effects of biochar, made from willow at 350°С and added as an amendment, on soil ecology and biochemistry-based processes within an ecosystem services modelling framework. In the literature review (Chapter 2) I draw links between the importance of soil ecosystem services, including soil biodiversity and human needs. The potential role of biochar application in improving soil productivity and mitigating the negative impact of land management are also discussed. To evaluate the impact of biochar, added as an amendment, on the chemical and biological properties and processes in soil as it influences soil processes underpinning ecosystem services, and to explore any synergistic interactions between biochar, soil, functional groups of soil fauna and plants, two experiments were conducted: (i) a six-month mesocosm experiment in the glasshouse and (ii) a field-based mesocosm experiment that ran for 12 months. In both experiments two contrasting soils were used – an Andosol (Allophanic) and a Cambisol (Brown). Both soils cover extensive areas of New Zealand. In the mesocosm experiment in the glasshouse (Chapter 3) biochar had a significant positive effect on clover growth and biomass, and this effect was more pronounced in the presence of earthworms and in one soil type. On their own, biochar and earthworms increased clover growth more in the Cambisol, while the positive synergistic effect of biochar and earthworms on soil biochemical processes and clover growth was more evident in the Andosol The synergistic effect of biochar and earthworms was also observed in an increase in the abundance of Collembola and in soil fungal biomass. The field mesocosm experiment investigated how adding biochar as an amendment to a grazed pasture affects the soils biological and physico-chemical properties. The experiment was conducted at four locations with different livestock systems (dairy and sheep) and soils (Andosol and Cambisol) under contrasting management practices (two pastures, with or without dairy shed effluent addition on the Andosol, and two pastures with either low or high phosphorus (P) fertilizer input in the Cambisol) over 12 months. The three treatments were: (i) willow biochar produced at 350 °C (1% w/w); (ii) lime, added at the liming equivalence of the biochar application (positive control); (iii) no amendments (negative control). Results of the field experiment are reported in three chapters. Chapter 4 reports how adding biochar affected biological and physico-chemical properties and the plant root biomass at each of the four grazed pasture locations on Andosol and Cambisol. Biochar addition had a positive (P<0.005) effect on total nitrogen (N), organic C, Olsen P contents, bacterial (Cb) and fungal (Cf) C biomass, and Collembola abundance, compared with the control and lime treatments 12 months after addition. At all four locations, the increases in N, C and P in the biochar treatment were greater than the amount of N, C or P added in the biochar. On average, root biomass was 6.9 Mg ha-1 higher (P<0.005) in all four soils to which biochar was added, when compared with the other two than the other two treatments. Biochar addition also lowered (P<0.005) the bulk density of the soil, on average by 7% across the four sites, compared with the control. Earthworm abundance in lime-treated soils was higher (P<0.01) than in the negative control. In the presence of biochar, earthworm abundance was only higher (P<0.05) than the control in the Andosol without effluent. In biochar-amended soils, Collembola abundance was higher (P<0.005) than the controls in all soils, while there was no effect on Oribatida and Gamasina populations. Chapter 5 investigated the effect biochar addition had on the biochemical activity (soil enzymes) in the soils after 12-months. Dehydrogenase activity, which is strongly correlated with soil microbial biomass, was higher in the soils to which biochar had been added. Cellulase activity was also higher in the soil to which biochar had been added, reflecting the increased amounts of plant detritus entering the soil, from the greater root biomass following biochar application. When the geometric mean of all the enzyme activities was summed, biochar had a more pronounced effect than lime. An exception was peroxidase, which in contrast to dehydrogenase and cellulase, had higher activity in the soil treated with lime (positive control) and was positively correlated with earthworm abundance, which also was higher in the lime-treated soil. Biochar had less of an effect on both pH and earthworm abundance. There was a positive correlation between nitrate reductase and earthworm abundance, as earthworms increase nitrate concentration in soil. In Chapter 6 I attempted to assess the long-term impact of biochar on soil potential to provide ecosystem services and investigated the influence of the biochar application on the time dynamics of physicochemical and biological properties. Soil samples were collected at 6 and 12 months after the start of the field experiment. Except for mineral N (NO3--N and NH4+-N), the effect of sampling time was similar across sites. Biochar had a long-term positive effect on OC, TN and Olsen P in all sites. Reduced by biochar, soil acidity and BD remained at the same level after 6 and 12 months in all four sites. The effect of biochar on mineral N was not constant in time, and mostly depended on the soil order and management practices rather than on treatments. Soil biological and biochemical properties had patterns which can be interpreted as seasonal. Biochar increased bacterial and fungal biomass as well as abundance of arthropods and earthworms; these changes in soil biota were reflected in soil enzymatic activities. It was shown that biochar has a persistent effect on soil natural capital stocks and functions and showed itself as an effective amendment able to enhance the soil over time. In the Chapter 7 the results of the analysis of the effects of biochar and lime addition on soil physicochemical and biological properties (Chapter 4) and enzymatic activity (Chapter 5) were used to semi-quantify the effects and potential benefits of biochar and lime amendments application for the delivery of specific soil ecosystem services. In comparison with the control treatments, there was a significant positive impact of biochar on soil properties, including soil microflora, earthworms, OC, soil BD, pH and overall soil enzyme activity, associated with C sequestration. In comparison with control and lime, biochar increased components of soil natural capital stocks responsible for food and fibre production ecosystem service. There was also significant positive impact of biochar on soil properties associated with fertility maintenance. Biochar and lime had similar positive effect on water regulation and disease and pest control services. The thesis shows that application of willow wood biochar produced at low temperature has a significant positive effect on a number of the chemical and biological properties and processes in soils (up to 12 months) that extend to the rooting characteristics of the plant, and this might contribute to the productivity of pasture land, while increasing health and resilience to the impact of land management. Biochar, through its effect on soil properties contributes to dynamic interactions between soil, plant and functional groups of soil biota. As a result, biochar positively impacts on the dynamical links between components of soil natural capital and ecosystem services provided by the soil. In summary, biochar produced from willow wood at low temperature may be an effective tool in the pasture systems/soils investigated here as a part of sustainable farming practices, which can increase plant productivity, improve soil physical properties and fertility, reduce disease and pest risks, and at the same time might be used as an instrument to mitigate climate change.