Massey Documents by Type

Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294

Browse

Filters

2017 - 201912020 - 20211

Settings

Subject: search.filters.subject.Liming of soils

Search Results

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    An investigation on the effects of lime and/or phosphorus fertilizer applications on soil organic matter preservation : 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, 2021) Li, Yang
    The poor understanding of the mechanisms through which soil organic matter (OM) is lost with ongoing land-use intensification hampers the development of food security and climate-smart agricultural management practices. The overall objective of this thesis was to investigate the effect of lime and/or phosphorus (P) amendment on OM preservation in a volcanic soil classified as an Andosol – the mineral soil group with the largest organic carbon (OC) content worldwide and characterised by its abundance in aluminium (Al)-OM complexes (e.g., Al³⁺-OM and allophane-OM complexes). Special attention was paid to the response of OM stabilisation and mineralisation with depth to these amendments. Firstly, we hypothesised that (i) lime and P application has an impact on OM stabilisation through different mechanisms, and (ii) their effect is synergic. To have a direct understanding of the effect of lime and/or P application on OM preservation in the Andosol under study, we conducted a batch of water extractions. We extracted the bulk soil and its heavy fraction (>1.6 g/cm3, indicative of the presence of OM-mineral associations) with added lime and/or P to reveal the individual and combined influence of lime and P amendments on water-extractable OM (WEOM), which has been deemed to be an indicator of OM destabilisation. The results obtained from quantitative analyses of WEOM showed that adding lime and/or P significantly increased the WEOM, along with a decrease in its carbon (C)/nitrogen (N) ratio (C/N) and an increase in its aromaticity. The chemical composition of WEOM measured by pyrolysis-gas chromatography/mass spectrometry suggested that lime and P addition (at high application rate) caused an enrichment in WEOM in the poly- and monophenolic, and nitrogenised fraction, as well as in plant-derived polysaccharides. If we consider the effect on the heavy fraction, the increase in WEOM was still consistent with that observed in the bulk soil when lime was applied, but the response to P addition alone was smaller. These findings indicate that lime and P amendment to soils rich in Al-OM complexes cause destabilisation of OM, but through different mechanisms. Phosphate was found to mainly impact Al³⁺-OM complexes (partly present in the removed free particulate OM) by outcompeting organic ligands for Al³⁺, whereas alkalisation was able to disrupt both the Al³⁺-OM and allophane-OM complexes, and the stability of aggregates. These could be hastened by combined lime and P addition, as made evident by the larger impact of combined lime and P amendments than that of either P or lime addition alone (Chapter 3). After confirming the occurrence of OM destabilisation in the Andosol upon lime and/or P application, we hypothesised that the response of OM preservation (OM stabilisation and mineralisation) to these amendments varies with soil depth. We conducted a 6-month incubation experiment to have an in-depth understanding of the influence of these amendments on OM preservation in soil at different depths. A topsoil (rich in Al³⁺-OM complexes) and a subsoil (with a greater abundance of allophane) of an alu-andic Andosol was incubated with/without inorganic amendments (either lime, phosphate or lime+phosphate) in the presence or absence of an organic amendment (¹³C- and ¹⁵N- labelled barley, Hordeum vulgare L.). By conventional chemical analyses of the bulk soil, we showed an increase in WEOM in both topsoil and subsoil samples that received amendments, particularly of lime (with/without P). However, through a nano-scale secondary ion mass spectrometry analysis of OM-mineral associations in soil microaggregates, we noted that lime amendments decreased OM coverage (particularly plant-derived OM) on the mineral surface in topsoil, but increased it in subsoil (with enhanced coverage of plant-derived OM). These suggested that at these two soil depths with different biogeochemistry, lime addition resulted in OM destabilisation through different mechanisms associated with (i) the displacement of OM from inorganic surfaces in microaggregates in the topsoil, and (ii) the release of OM previously protected within macroaggregates in the subsoil. The total cumulative carbon dioxide (CO₂) emissions and stable C isotopic signature (δ¹³C) of CO₂ showed that lime amendments caused an increase in OM decomposition in the subsoil from both inherited OM (priming) and OM newly formed from barley litter decomposition, but not in topsoil. The increase in OM mineralisation observed in the subsoil (a harsher environment for microbes, with limited bioavailable OM) is consistent with the fact that more favourable conditions were generated by the lime and P addition, which caused an increase in WEOM (Chapter 4). To further understand the distinct responses in OM mineralisation with depth to lime and/or P amendments, we investigated soil bacterial and fungal community composition and their functional profile through high-throughput sequencing analysis. A shift in bacterial and fungal community composition and their functional composition was found in the limed topsoil but not in the limed subsoil. Through structural equation modelling analysis, it was found that in the topsoil, microbial properties, particularly the fungal community composition and functional profile, had a significant relationship with OM mineralisation (with a relatively greater positive or negative coefficient value than other factors). However, in the subsoil, OM mineralisation was only significantly correlated with labile OM in the subsoil. These findings suggested that in the Andosol, the key regulator controlling the response of OM mineralisation to lime and/or phosphate addition shifted with depth from microbial composition and functionality to bioavailable C substrate (Chapter 5). All the results obtained in this thesis contribute to providing a mechanistic understanding of the effect of lime and/or P amendments on OM stabilisation and mineralisation, and have implications for designing climate-smart agricultural management practices of soils with abundant Al-OM complexes.
  • Thumbnail Image
    Item
    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.