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    Designing Technosols to reduce salinity and water stress of crops growing under arid conditions : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy of Applied Science in Soil Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2021) Kong, Chao
    Salt- and plant-water stress are widely considered to be major abiotic stresses threatening crop production in dry areas. Innovative methods to alleviate salt and plant-water stress that are both practical and economically efficient are in great demand. While the most common reclamation strategy for salt-affected soils is to flush the salts out of the root zone with low salinity/sodicity water, this is challenged by the fact that water is commonly scarce in areas affected by salt stress. The use of specific soil amendments or a combination of them in such areas may well solve some of these problems. Biochar has, in fact, been shown that, in some instances, it is able to effectively reduce salt stress to plants. Other porous materials, such as pumice, have not yet been considered although pumice has been reported to contribute to water retention under arid conditions. Further potential amendments include organic residues, as they can produce beneficial impacts on plant growth by improving soil functions. To date, however, limited research has attempted to unravel (and compare) the effects of either pumice and/or biochar in alleviating salt and plant-water stress. There is also scant information on (i) how to minimise the impact of biochar on the salinity of soils in dry regions; (ii) the underlying mechanisms explaining how the use of either pumice or biochar amendments can decrease soil salinity under arid conditions; and (iii) whether individual or combined additions of either pumice and/or an organic amendment, algae, to a sandy soil alleviates salt and water-stress on plant growth. Therefore, my objective in this study is to investigate whether these amendments can be used in the formulation of Technosols specifically designed to reduce salinity and water-stress of crops growing under arid environments. A quantitative review of the literature was carried out to evaluate what type of biochar and under what conditions its use is suitable in dryland soils. For this, a meta-analysis of 40 studies published between 2013 and 2020 using pairwise comparisons was carried out to evaluate the short-term effect of biochar on the salinity using electrical conductivity (EC) as the proxy for soils under dry environments (Mediterranean, arid, semi-arid climates, or under simulated dry and saline conditions). The results indicated that in terms of the risk of biochar increasing soil salinity, (i) biochars made from high-ash material should not be applied to soils in dry regions; and (ii) the addition of biochars made from relatively low-ash ligneous material at application rates ≤ 20 t ha-1 is suitable as an amendment to soils under dry environments. The use of a leaching fraction is recommended. Water-borne salt transport in soils under arid conditions is strongly related to the influence of amendments on the soil’s mobile-immobile water fractions. For this, the influence of the porosity and pore-size distribution of pumice and biochar (produced from willow wood chips at a highest heating temperature of 350 °C) on the mobile-water content when added to a sandy soil were investigated. Pumice and biochar (of 1.5-, 3-, and 6-cm Ø) were characterised using Scanning Electron Microscope (SEM) technology. The fraction of mobile-water present in these amendments, previously added to a sandy soil at different application rates and particle sizes, was determined using a tracer (Na+) technique. The results showed that the overall larger contribution of pumice to the water mobility than that of biochar under near-saturated conditions could be related to its relatively higher levels of macro-scale plus meso-scale porosity, and this increased as the pumice particle size increased. Both pumice and biochar had a predominance of pores with a Ø < 30 μm and relatively high total porosity, which are expected to contribute to water retention dilution of salinity when these amendments are added to salt-affected sandy soils. In order to evaluate the effects of pumice and biochar amendments on water retention and salinity of a sandy soil under simulated arid conditions, pumice and biochar of different particle sizes (1.5-, 3-, and 6-cm Ø) were separately added at different rates (3, 6, and 12%, v/v basis) to the soil. This was drip irrigated with an artificial saline water under non-draining conditions. Pebbles applied at identical rates and sizes as pumice and biochar, were used as positive controls, whereas no amendment was the negative control. Treatments underwent 10 wetting and drying cycles at 35 ℃ at the end of which, the residual soil was separated from the amendments. We found that (i) the EC of the residual soil followed the order pumice < biochar < positive control = negative control, with differences where existing, being significant at p < 0.05; (ii) the smallest EC and sodium adsorption ratio (SAR) values of the residual soil were achieved when applying 12% pumice, regardless of the particle size; the opposite pattern (12% > 6% > 3%) was observed in the pumice when analysed separately from residual soil; (iii) pumice and biochar treatments retained an increasing amount of water in the soil after each drying cycle (significant at p < 0.05); and (iv) at the end of the experiment, the EC values of the leachates indicated that salts retained in pumice were more slowly mobilised than those in the biochar. The application of either pumice or biochar can contribute to a decrease soil salinity, but pumice could additionally serve as a tool to remove salts from salt-affected soils. In order to investigate whether individual or combined additions of either pumice (PU) and/or algae (AL) to a sandy soil could alleviate the impact of irrigation with saline water on the growth of lucerne (Medicago sativa L.) under simulated semi-arid conditions. A plant growth chamber study was conducted that included six treatments that received saline water (6.4 dS m-1): T1 (sand – positive control), T2 (sand + 3% (v/v basis) PU), T3 (sand + 12% PU), T4 (sand + 3% PU + 2% AL), T5 (sand + 12% PU + 2% AL), T6 (sand + 2% AL). A seventh treatment was T7 (sand – negative control), to which deionised water was added. All treatments underwent 14 cycles of irrigation wetting and drying events (at 27 ± 1 ℃/ 16 ± 1 ℃ day/night). Results showed that, at the end of the experiment and compared with the positive control (T1), the two treatments with the largest application rate of PU (T5 and T3) showed the largest (significant at p < 0.05) reduction in soil EC, SAR, and water-extractable ions among those treatments receiving saline water (T1-T6). Lucerne in treatments T1-T6 always had a smaller (p < 0.05) biomass, leaf dry weight (DW), and relative growth rate than the treatment receiving deionised water (T7) (DW: 2.3 g m-2), but values for treatment T5 (DW: 1.7 g m-2) were significantly larger (p < 0.05) than for treatments T1-T4 and T6 (DW < 1.1 g m-2). Overall, the results obtained suggest that, if proven feasible at a field scale, the combined addition of PU (12%), by reducing salinity and contributing to water retention, and AL (2%), by adding nutrients and/or bioactive compounds, could be used to mitigate salt stress and improve plant growth in sandy soils under arid conditions. The information obtained in this thesis supports the use of pumice and algal amendments as ingredients of Technosols designed to reduce salinity and water-stress of crops growing under arid conditions. Both materials are easily available (if to be used in areas close to a volcanic region and at the seaside), low cost, and their use in agriculture may open new doors to deal with the current problems faced in dry regions.
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    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 Faizah
    The 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.
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    Glyphosate displacement from New Zealand soils and its effect on non-target organisms : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Agricultural Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2019) Jimenez Torres, Jesus Adalberto
    Glyphosate (GlyP) is the most commonly used herbicide worldwide; it is retained in the soil and is decomposed by soil microorganisms. The main degradation product of GlyP is Aminomethyl-phosphonic acid (AMPA). Phosphorus and GlyP are antagonistic anions that compete for the soil’s reaction sites; P accumulation in the soil can increase GlyP translocation through the environment and increase its bioavailability. Residual GlyP and AMPA accumulation in the soil has generated concerns about their potential toxicity to non-target organisms such as crops and soil microorganisms. GlyP in situ remediation has therefore emerged as an option to reduce the residence time of the herbicide in soil. Laboratory experiments were carried out in order to elucidate the effect of the interaction between soil chemical and physical properties, and phosphorus addition on GlyP sorption to soil surfaces. The results of the GlyP-AMPA batch adsorption- desorption experiment demostrated that the Kd and fixation of GlyP and AMPA in the soil was proportional to the Al-Fe oxy-hydroxides content of the soil, in the following order Allophanic>Brown>Pallic. In another experiment, phosphorus addition to soil reduced GlyP adsorption, which demonstrated that phosphate will occupy the same soil reaction sites as GlyP. These results suggest that due to the stability of the bond formed between Al oxy-hydroxides and P, Al oxy-hydroxides will fix GlyP; while the higher reactivity of Fe oxy-hydroxides will facilitate the exchange of phosphate by GlyP. A column leaching experiment demonstrated that the interaction between the physical and chemical characteristics of the soil will influence water infiltration and solubilisation of GlyP. Phosphorus addition to the columns enhanced GlyP’s vertical displacement through the soil and AMPA detection in the leachate. The Pallic soil with a poor physical structure had reduced GlyP vertical displacement. In contrast, the free- drained Brown soil had higher AMPA percolation regardless of the P addition. The Allophanic soil had the lowest GlyP percolation risks, despite the fact that P addition increased AMPA detection at the bottom of the column. However, AMPA was undetected in the Allophanic soil’s leachate. A soil induced respiration (SIR) experiment demonstrated that GlyP (variable doses) did not affect soil microorganism respiration, while Agave amendments were used as an exogenous source of carbon and triggered soil respiration (Agave applied had 0.382 mg TC/g soil and control C applied was 1.25 mg C/g soil). The SIR ratio values observed in the soils were as follows Allophanic>Pallic>Brown, and were inversely proportional to the total dissolved carbon concentration in soil extracts. These results demonstrate that the greater Al- Fe oxy-hydroxide content of the Allophanic soil protected organic matter from mineralisation enabling greater microbial activity over the GlyP molecule. The P adsorption-desorption experiment using Agave powder demonstrated that Agave constituents desorbed phosphorus from soil surfaces, which might help in the desaturation of P from soil, while increasing its bioavailability. Glasshouse experiments using Roundup doses and Agave amendment applied to the soil of white clover potted plants were carried out in order to elucidate the potential for GlyP degradation in soil and the biochemical responses of white clover plants. The results demonstrated that Agave amendment attenuated the translocation of GlyP to white clover shoots for a Roundup dose of 90 kg a.i./ha. The chemical constituents of Agave, 12 hrs after GlyP application to the soil, enhanced GlyP degradation to AMPA in soil at the 15 kg GlyP treatment. A similar improved GlyP degradation was observed during three days of evaluation at the 7.5 kg dose. The biochemical responses of white clover shoots demonstrated an increase of gallic acid and tartaric acid accumulation proportional to the increasing Roundup doses. This suggested that Roundup alone, and in combination with Agave amendments, exerted oxidative stress on the plants. Alternatively, the herbicide could have affected the EPSPS enzyme disrupting the carbon cycle. These results demonstrate that the white clover metabolic disruption caused by the Roundup treatments of 7.5 and 15 kg/ha, expressed through tartaric acid and gallic acid, was alleviated at the third day of evaluation. The results of this thesis can support decision-making for the implementation of strategies which could mitigate glyphosate and AMPA displacement from New Zealand farmland; as example, it may encourage the prevention of phosphorus accumulation in the farmland. In addition, these results can encourage the development of further research related to the potential use of Agave amendments for glyphosate remediation, and help in the understanding of the effects of the herbicide on the metabolism of non-target organisms.
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    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, Stanislav
    Sheep 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.
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    Cadmium management in New Zealand's horticultural soils : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management, Massey University, Palmerston North, New Zealand
    (Massey University, 2017) Thompson-Morrison, Hadee
    Cadmium (Cd) is a heavy metal trace element which presents risks for the horticultural industry in New Zealand (NZ). This element is added to soils through phosphate fertiliser application, and once there may be available for plant uptake and food chain transfer. When food products exceed international standards for Cd concentrations, these products may be excluded from international markets upon which NZ relies to maintain its economy. This presents a reputational risk for NZ’s horticultural exports. Soil pH and organic matter (OM) content are the two key drivers influencing Cd’s bioavailability, and field trials are currently being undertaken in four horticultural sites throughout NZ – Pukekawa, Manawatu, and two adjacent sites at Lincoln – to test the efficacy of the use of lime and compost amendments to influence these soil variables and thus reduce Cd plant uptake from soils. Potatoes are grown at all sites while Lincoln also includes wheat. This research aimed to characterise these soils, including total and plant-exchangeable Cd concentrations, pH, OM content, cation exchange capacity, total and plant-exchangeable Zn concentrations, aluminium and iron oxide content, total phosphorus and total nitrogen content. Findings indicated that total Cd concentrations varied among sites, with the highest (0.52 mg kg-1) at Pukekawa, followed by Manawatu (0.26 mg kg-1) and Lincoln Wheat and Potato sites (both 0.13 mg kg-1). Exchangeable Cd concentrations were low at all sites (0.01-0.02 mg kg-1) indicating little risk of plant uptake from these soils. The mitigation strategy tested in this work focuses on pH as a key soil variable that can be readily changed to restrict Cd uptake. However, the effectiveness of amendment rates to effect target pH values is dependent on soil chemistry and rates will vary across sites. Incubation experiments were conducted to determine amendment rates for lime and sulphur, and to compare the pH of amended soil in a laboratory situation with the in-field situation. Incubation and field situations were found to be similar, with no significant differences between pH values after a period of 274 days in the incubator and 169 days in the field. The accuracy of the calculated amendment rates at achieving target pH values was assessed with extended incubation experiments. The results here varied between soils, with the sulphur application rate proving more accurate in the Pukekawa soil, however too high for the Manawatu and Lincoln potato soils. The calculated liming application rate similarly resulted in a higher-than-target pH, however after a period of 231-274 days the pH reduced and approached the target value. A cost-benefit analysis was undertaken to determine the economic viability of the proposed mitigation strategy at each potato site. Results proved the strategy to be a viable option, which would remain viable in the face of varying uncertainty and reductions in potato yields. Practical considerations including timing and weather conditions, and compost availability were considered. Implementation of this strategy within NZ’s current framework of the Tiered Fertiliser Management System, which focuses on total rather than exchangeable Cd concentrations, may present difficulties, and thus there is a clear need for risk-based, soil and crop specific guidelines for Cd management within a NZ context. Considering the apparent difficulties in designing pH amendments strategies, a model to convert pH buffer curve-generated lime application rates which can be derived in as little as 24 hours, to field applicable application rates which target a specific soil pH was developed for the Pukekawa soil. A similar model was not achieved for the Lincoln Wheat soil, and thus the development of such a model is not possible for all soil types. Where possible, the development of this model would be an innovative and useful tool for farmers with which to accurately and quickly determine required lime application rates to achieve a targeted soil pH. This would be of great benefit in the implementation of a Cd mitigation strategy using lime amendments, and would allow greater control over, and management of, soil pH in a horticultural context.
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    Investigation on the effect of biochar addition and the use of pasture species with different rooting systems on soil fertility and carbon storage : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy (MPhil) in Soil Science at the Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand
    (Massey University, 2015) Wisnubroto, Erwin Ismu
    There is a potential to increase soil carbon (C) sequestration in New Zealand pastoral soils, especially in the subsoils where the soil C stocks have been reported to have a greater C saturation deficit than the topsoils. Selecting pasture species with deeper root systems will enhance soil formation at depth and mineral weathering, thus enhancing the potential for soils to stabilize organic matter (OM). Moreover, the addition of biochar may increase the stable C pool of soils and provide other additional benefits. Up to the present time few studies have investigated the potential of biochar to promote root growth and allocation of plant C to the subsoil. A glasshouse study was carried out to examine the effect of adding a nutrient-rich biochar at various dose (0, 1.5, 5 and 10 Mg ha–1 without nitrogen (N) fertiliser; 0, 1.5, 10 and 20 Mg ha–1 with N fertiliser at a dose of 113 kg N ha–1) to a sandy soil on plant growth (aboveand below-ground). The results indicated that, in the absence of N limiting conditions, biosolids-derived biochar could improve plant biomass yield as a result of the addition of available P and K. This amendment also caused an increase in plant root length. Subsequently, a 2-year lysimeter trial was set up to compare changes in C stocks of soils under deep- or shallow-growing pastures as well as to investigate whether biochar addition below the top 10 cm could promote root growth at depth. For this: i) soil ploughing at cultivation for pasture establishment was simulated in two different soils (a silt loam soil and a sandy soil) by inverting the 0–10 and 10–20 cm depth soil layers, and biochar was mixed at a rate of 10 Mg ha–1 in the buried soil layer, where appropriate; and ii) three pasture types with contrasting root systems were grown. Distinctive biochars were selected for these two soils so that soilspecific plant growth limitations could be overcome. In the silt loam, soil inversion resulted in a net loss of native organic C in the buried horizon under shallow-rooted species, but not under deep-rooted species. The addition of a C-rich pine biochar (equivalent to 7.6 Mg C ha–1) to this soil resulted in a net C gain (6–16% over the non-biochar treatment, calculated up to 30 cm; P < 0.05) in the buried soil layer under all pasture treatments; this overcame the net loss of native organic C in this horizon under shallow-rooted pastures. In the sandy soil all pasture species were able to maintain soil C stocks at 10–20 cm depth over time. In this soil, the exposure of a skeletal and nutrient-depleted soil layer at the surface may have fostered root growth at depth. The addition of a nutrient-rich biosolids biochar (equivalent to 3.6 Mg C ha–1) to this soil had no apparent effect on total C stocks. In this 2-year study, none of the biochar amendments affected either pasture yield or root growth. More research is needed to understand the mechanisms through which soil C stocks at depth are preserved.
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    Application of biochar technologies to wastewater treatment : 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, 2013) Hina, Kiran
    A review of wastewater treatment options and the properties of biochar (charcoal made from biomass with the intention of carbon sequestration in soil) indicated the potential application of biochar for removal of ammonium-N (NH4+-N) and various organic and inorganic pollutants from wastewaters. This thesis investigates (i) the capacity of alkaline activated and non-activated Pine and Eucalyptus biochars to retain N and P from wastewaters, and (ii) the potential use of these nutrient-rich materials as slow-release fertilisers in soil, thus assisting the recycling of nutrients from waste streams. The retention of NH4+-N on different materials, pine bark, pine biochar (produced from wood chips at 550 °C) and zeolite was investigated. When shaken with a 39 mg NH4+-N L-1 influent solution, Zeolite proved to be the best sorbent of NH4+-N, followed by pine biochar and pine bark; 0.71> 0.38 > 0.27 mg NH4+-N g-1 sorbent, respectively. Ways of increasing the CEC (cation exchange capacity) and NH4+-N sorption capacity of biochar were investigated by (i) alkaline activation by tannery waste or (ii) physical activation using steam as pre and post treatment of biochars, respectively to increase their CEC. Washed alkaline activated biochars (Pine and Eucalyptus) showed a significant (p < 0.05) increase in the NH4+-N sorption capacity over corresponding non-activated biochars. Steam activation increased the internal surface area of biochars but did not prove increased retention of NH4+-N. The efficiency of NH4+-N removal from synthetic NH4+ solutions and urban and dairy wastewaters by alkaline activated and non-activated Pine and Eucalyptus biochars was evaluated and compared using batch and column studies under different flow rates and retention times. Greater NH4+-N sorption was observed in alkaline activated Pine biochar from both the synthetic solution and urban wastewater in column studies @ 2.40 mg N g-1 and 2.17 mg g-1 NH4+-N biochar, respectively. Inclusion of Okato tephra with alkaline activated pine biochar proved effective in removing both P and N from urban wastewater. Finally, the activated pine biochar and tephra loaded with N and P from wastewater treatment were incorporated into two soils (Kiwitea and Manawatu) and the bioavailability of N and P was tested by growing ryegrass in an exhaustive Standford and Dement bioassay. The recovery of N and P was very low and this indicated that it was not economical to use biochar in wastewater treatment for subsequent use as a fertiliser.