Date of Award

3-2024

Document Type

Doctoral Thesis

Degree Name

Doctor of Philosophy

Department

Biological and Pharmaceutical Sciences

First Advisor

Patrick Quille

Second Advisor

Eoin McCarthy

Third Advisor

Dr. Eilish Broderick, and Dr. Brendan O’ Donnell

Abstract

Soil pH plays a pivotal role in agricultural productivity and environmental sustainability, influencing various soil processes crucial for plant growth and ecosystem functions. It is a master variable that affects the biological, chemical and physical properties of soil. Maintaining a correct soil pH – generally through the addition of a liming product - is central to sustainable and productive agriculture and therefore accurate determination of soil pH is a vital piece of information that is central to any soil lab test. However, the accuracy of any soil pH test will be dictated by a number of soil properties such as texture, organic matter content, cation exchange capacity and exchangeable cations.

In Ireland the standard method for determining soil pH for over 50 years is the Shoemaker-McLean–Pratt (SMP) buffer method, however there are environmental and health concerns around this buffer as it contains two known carcinogens in para-nitrophenol and potassium chromate, prompting an urgent need to find a suitable replacement for Irish soils. It is important that any alternative tests to potentially replace the SMP buffer test needs to be calibrated and validated across a range of soil types and from various soil management facilities.

This study investigates the accuracy and comparability of soil lime requirement (LR) prediction methods for a range of Irish soils and examines how soil traits affect the predictability of soil pH. The study evaluates various alternative tests to potentially replace the SMP buffer test, including the Modified Mehlich (MM) buffer method, Sikora buffer method, the Santa Maria (TSM) buffer method, RothLime model, and Ca(OH)2 titration, aiming to provide a more tailored and potentially accurate method of soil pH prediction.

Key findings from the study highlight the effectiveness of various lime prediction methods across different soil types. In grassland mineral soils, the SMP buffer method demonstrated significant accuracy (r² = 0.497). The Ca(OH)2 titration method exhibited high reliability (r² = 0.816), and the MM buffer method also showed promising results (r² = 0.763). For arable soils, the study revealed intricate relationships between LR test accuracies and soil properties such as exchangeable aluminium (Al), iron (Fe), cation exchange capacity (CEC), base saturation percentage (BSP), and organic matter (OM). The Ca(OH)2 titration method had a strong correlation with LR (Pearson correlation coefficient of 0.893), and the MM buffer method was effective in tandem with lime incubations (r² = -0.665). Peat soils, rich in OM, showed strong relationships between LR methods such as CaCl2 pH measurement, SMP, and MM buffer methods.

Additionally, the study compared the impact of Irish Agricultural Lime and European Standard Lime on grassland soils, revealing significant differences in lime effectiveness over time. Irish grade lime was effective for short to medium-term pH corrections, while European grade lime showed potential for long-term pH stability. Based on these findings, the MM buffer method emerges as a recommended alternative to the SMP method for LR determination, offering comparable accuracy across soil types and promising correlations with key soil components. This research contributes to the development of a decision chart, providing a pathway to a more customized approach to determining lime requirements for Irish soils, ultimately enhancing soil management and agricultural sustainability.

Access Level

info:eu-repo/semantics/openAccess

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