Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
3 results
Search Results
Item An investigation of soil carbon fluxes and pools in the thermo-sequence of Mt. Taranaki forest : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Manawatu, New Zealand(Massey University, 2023) Siregar, Idri HastutyUnderstanding the relationship between temperature and soil carbon (C) pools and fluxes is a key aspect in determining the feedback of the global C balance to rising temperature. The overall objective of this thesis was to investigate the influence of rising temperature in the net change of soil C stocks and fluxes in a thermo-sequence of Mt. Taranaki and explore the mechanisms underlying this change if any. Taranaki region has a ca. 3.2°C mean annual temperature (MAT) gradient with identical parent material, moisture (constant plant-available moisture), and vegetation type. The soil type under this study is alu-andic Andosol, which is the mineral soil group with the largest C content worldwide and characterised by its abundance in aluminium (Al)-organic matter (OM) complexes (e.g., Al³⁺-OM and allophane-OM complexes). Yet, there is considerable uncertainty as to how rising temperatures will affect the stability of organo-mineral complexes and their formation. Together with the unique thermo-sequence available across the Taranaki slope, they offer an excellent benchmark for investigating the potential responses of soil C storage to long-term warming. Firstly, we hypothesised that: (i) temperature rise influences the forms of reactive Al (i.e., short range order (SRO) constituents vs. organo-Al complexes), with a greater abundance of SRO constituents at warmer elevation sites as opposed to organo-Al complexes at colder elevation sites, where the weathering rate is slower; (ii) in warmer conditions, microbial-derived C is favoured, while in cooler conditions, plant fingerprints are more evident; (iii) as a result, the C preservation mechanism along the transect differs, with SRO constituents (and microbial-derived C) being more prevalent at warmer elevation sites and Al cations (and plant-derived C) being more abundant at colder elevation sites. To reveal how climatic and geochemical properties regulate soil C preservation, we conducted a field survey to investigate the changes in: (i) soil geochemical properties including; soil pH, reactive Al and Fe (i.e., SRO constituents and organo-Al complexes); (ii) total C content, stocks, and fractions, as well as composition of OM along the gradient, in which soils at four elevation sites were sampled down to 85 cm depth. Four sampling sites were selected, with elevations ranging from 512 to 1024 m above sea level (asl) and and a mean annual temperature (MAT) of 7.3, 8.2, 9.1, and 10.5 °C ( referred to as T7, T8, T9, and T10, respectively). The results showed that: (i) at colder elevation sites (T7 and T8), soil profiles were richer in well-preserved plant material and in organo-Al complexes, as opposed to (ii) warmer elevation sites (T9 and T10), which had a more microbial processed C and a higher fraction of protected C forms, along with a greater abundance of SRO Al constituents. The results revealed that climate (particularly temperature rise) and soil geochemistry interacted to regulate soil C preservation. While the study has revealed that the mechanisms that protect OM (particularly at depth) differ across the thermogradient, C stocks do not change with temperature., models projecting soil C changes over time under various climate scenarios should also consider the existing interaction with soil geochemistry (Chapter 3). After understanding the interaction between soil geochemistry and temperature rise in relation to the soil C preservation mechanism, we investigated the long-term effect of rising temperatures on the soil C fluxes (input and output) in a mature native forest along the thermo-sequence in Mt. Taranaki. We used specific molecular markers to monitor the changes in soil C abundance and composition (i.e., carbohydrates) in order to gain a deeper understanding of the effect of temperature rise on the turnover of soil C. We hypothesised that, in the absence of a water shortage, an increase in temperature would increase forest productivity and litterfall, which in turn would increase soil C inputs; this increase in organic substrate along with higher temperatures would, in turn, generate an additional soil CO₂ efflux; however, no net C loss would occur as the increased in soil C input would offset the increased soil CO₂ efflux. To test this, soil C pools, plant biomass C pools, soil C fluxes, and soil OM composition (i.e., carbohydrate abundance and composition), at four elevation sites along the Taranaki thermo-sequence were quantified. The outcome of this investigation demonstrated that above- and below-ground biomass C increased ca. 32% (significant at P <.05) when temperatures rose (from T7 to T10). This led to an increase in aboveground litterfall (29%), belowground C input (15%), soil respiration rate (16%, significant at P <.05), and decay intensity (as inferred from the carbohydrate preservation index (CPI)). The study showss that the increase in temperature along this quasi-thermo-sequence at Taranaki increases plant C input through enhanced net primary production, which counteracts soil C loss, resulting in no apparent detrimental effect on soil C storage (Chapter 4). This study highlights the importance of considering plant C input of an entire ecosystem along with soil OM decomposition when investigating the response to temperature rise. To understand the effect of warming on the temperature sensitivity (Q₁₀) of soil organic matter (OM) decomposition rate along the Taranaki thermo-sequence, we collected soils from four distinct elevation sites with four different depths and incubated them in the laboratory at temperatures of 5, 15, 25, and 35°C for 330 days (Chapter 5). The incubation data were then fitted with a three-component model to generate three C pools with distinct decomposition rates, followed by the calculation of their respective Q₁₀ values. Using multivariate analysis, these values were then combined with a complete set of soil geochemical characteristics and OM molecular composition data to gain mechanistic insights into the biogeochemical causes of Q₁₀ variations. The results of this study revealed that: (i) Q₁₀ of soil OM decomposition is inclined to attenuate over a centennial scale under elevated MAT; and (ii) Q₁₀ values of the bulk soil OM and the distinct C pools were differentially regulated by soil C availability, OM molecular composition, and OM-mineral interactions (Chapter 5). These results suggest that temperature affects the distinct C pools differently; with Q₁₀ values having a trend to decrease as temperature increases.All the results obtained in this thesis contribute to provide a mechanistic understanding about the effect of rising temperatures on soil C fluxes, and stocks as well as the underlying mechanism governing them, in order to accurately anticipate soil C dynamics in response to global warming.Item An investigation on the stability of biochar-C in soils and its potential use to mitigate non-CO₂ greenhouse gases using near-infrared (NIR) spectroscopy : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Manawatu, New Zealand(Massey University, 2020) Mahmud, Ainul FaizahThe global interest in using biochar for C sequestration-climate mitigation and soil improvement has driven rapid expansion in biochar research to understand its properties and application impacts. The potential for biochar application to increase soil organic carbon (SOC) stocks and its potential agronomic and additional environmental benefits, such as reducing soil nitrous oxide (N₂O) emission, are determined by its stability in the soil, which is dependent on its intrinsic properties and the soil conditions. The inherent properties of biochar are highly influenced by feedstock type and pyrolysis temperature hence, the use of various types of feedstock and pyrolysis technologies leads to uncertainties in predicting the effect of biochar addition to soils. Previous research has established a general assumption that biochar stability is strongly influenced by the type of feedstock used and maximum pyrolysis temperature. Research is required, however, to produce practical and reliable techniques that can be used to verify the reported maximum pyrolysis temperature, regardless of the type of feedstock used and predict the likely stability of the biochar. In addition to the pyrolysis process, the final particle size of the biochar and the method of incorporation into the soil may also influence the ability of the biochar to moderate soil properties and function. With previous research, there is general lack of attention given to these potentially influential parameters when assessing the impact of biochar application to soil. Therefore this thesis evaluates (i) the use of near-infrared (NIR) spectroscopy technique for predicting the maximum pyrolysis temperature of biochar as it is a well-known, non-destructive, and rapid technique for analyzing organic material; (ii) the effect of biochar application, with special attention to biochar particle size and depth of placement, on N₂O soil emission and SOC stocks; and (iii) the integrated use of NIR spectroscopy for SOC measurement. In the first study, we hypothesized that NIR spectroscopy can be used to predict the maximum pyrolysis temperature achieved during biochar production. Eighty-two carbonized materials produced from various feedstock types and pyrolysis conditions with the reported pyrolysis temperature ranged between 220 to 800 °C, were scanned using NIR spectrometer and were used as the calibration set. The NIR calibration model was built by correlating the NIR spectral data with the reported pyrolysis temperature using partial least squares regression (PLSR). A separate sample set (n=20) was compiled using laboratory-produced biochar made from pine wood at pyrolysis temperature ranged from 325 to 723 °C. The calibration model validated using (i) leave-one-out cross-validation (LOO-CV) and (ii) the prediction set, yielded good accuracy (LOO-CV: r²=0.80 and RMSECV:48.8 °C; prediction: r²=0.82 and RMSEP: 57.7 °C). Results obtained in this study have shown that NIR spectroscopy can be used to predict the maximum pyrolysis temperature of biochar and has the potential to be used as a monitoring tool for biochar production. In addition to the first study, the predictive ability of the NIR model was evaluated further. We hypothesized that the variation in feedstock types and pyrolysis processes may affect the predictive performance of the NIR model in predicting the maximum pyrolysis temperature of biochar. Therefore, three sample sets were generated from a total of 82 carbonized materials and its subsets (Set A: n=82; Set B: n=68; Set C: n= 48) and were used for developing three calibration models. The selection of samples for Set B and C was made by reducing the variability associated with production conditions and feedstock type i.e. Set B consist of samples produced by slow pyrolysis and using the same pyrolyzer unit, while for Set C (a subset of Set B), samples produced from “processed feedstocks” were excluded. A separate sample set (n=18) consists of samples produced from animal manure, crop residue, and woody materials were used as the prediction set. This biochar was produced using the slow pyrolysis technique in a laboratory or under relatively high production controlled conditions at temperature ranged from 250 to 550 °C. These calibration models were validated using (i) leave-one-out cross-validation (LOO-CV) and (ii) a prediction set, with the model based on set C gave the best prediction (R2: 0.941; RMSEP: 27.3 °C), followed by the model based on set A (R2: 0.896; RMSEP: 35.6 °C), and set B (R2: 0.928; RMSEP: 37.3 °C). These results indicate that feedstock types have a considerable effect on the performance of the NIR model while the effect of pyrolysis conditions was less pronounced. Thus, data variability from samples needs to be taken into account in developing the NIR calibration model for predicting the maximum pyrolysis temperature of biochar. Before studying the effect of biochar on N₂O soil emission and SOC stocks, the maximum pyrolysis temperature of biochar to be used in the experiment was predicted using the NIR spectroscopy technique. The estimated pyrolysis temperature – after scanning the 3-year old pine wood biochar and using the NIR model developed – was 500 °C, while the reported temperature was 550 °C. A controlled glasshouse study was conducted to investigate the effect of biochar particle size and the impact of soil inversion (through simulated mouldboard ploughing) on N₂O emissions from soils to which cattle urine was applied. We hypothesized that the application of biochar may (i) affect N₂O emissions through changes in soil physical properties, specifically soil aeration and water retention; and (ii) the effects of biochar addition on these properties may differ depending on their particle size (e.g., a larger particle size may increase soil aeration whereas a smaller particle size may clog pores), and their placement in soil (e.g., the incorporation of a large particle size-biochar at depth may promote water movement from the top layer and increase the overall drainage of the soil). Pine biochar (550 °C) with two different particle sizes (<2 mm and >4 mm) was mixed either into the top soil layer at the original 0–10 cm depth in the soil column or at 10–20 cm depth by inverting the top soil to simulate ploughing. Nitrous oxide emissions were monitored every two to three days, up to seven weeks during the summer trial, and measurements were repeated during the autumn trial. The use of large particle size biochar in the inverted soil had a significant impact on increasing the cumulative N₂O emissions in the autumn trial, possibly through changes in the water hydraulic conductivity of the soil column and increased water retention at the boundary between soil layers. Thus, the importance of the role of biochar particle size and the method of biochar placement on soil physical properties and the implications of these on N₂O emissions was highlighted. In the same glasshouse study, the effect of biochar particle size and depth of placement was further evaluated in relation to soil organic C. We hypothesized that (i) the large-particle size biochar may affect soil aeration and accelerate soil C decomposition rate with increased oxygen availability, and this effect is greater when biochar is incorporated at depth due to the more compacted soil at deeper layer with poorer aeration compared to the surface layer; and (ii) the NIR spectroscopy technique can be used to predict the SOC concentration and SOC stocks in biochar-amended soil. Carbon stocks were estimated using NIR spectroscopy coupled with partial least-squares regression analysis (NIR/PLSR) and direct organic C measurements using an elemental analyzer. The NIR spectra of the soil were acquired by scanning intact soil cores using the NIR spectrometer. By the end of the glasshouse trial (327 days), the large-particle size biochar applied at depth had induced significant soil C loss (9.20 Mg C ha⁻¹ (P < 0.05), possibly through the combination of enhanced soil aeration, and the interrupted C supply from new plant inputs at that depth due to soil inversion. This C loss did not occur in the treatment with the small-particle size biochar. Near-infrared (NIR) spectroscopy was able to predict the SOC concentration, however, the prediction accuracy may be negatively affected by an increasing biochar particle size and soil inversion, thus may affect the subsequent SOC estimates. The information obtained in this thesis will inform the future use of biochar and contribute to the knowledge of possible factors affecting soil N₂O emission from biochar-amended soil, the mineralization of native SOC, and the changes in SOC stocks over time, particularly in the pastoral soils of New Zealand. Also, based on this study, the use of NIR spectroscopy technique may potentially be integrated as part of the methodology for SOC estimation.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.