Degree Name

BSc Adv Hons


School of Earth & Environmental Sciences


Tim Cohen


Competing interests shared between agricultural sectors, environmental authorities, and the public community can be reconciled through maintaining sustainable agricultural practices. As the Australian dairy industry continues to intensify, the need to improve farm sustainability is mounting, as higher inputs of phosphorus (P) raise a number of concerns pertaining to environmental, economical, as well as ethical agendas. To address this issue, improved nutrient management strategies must be implemented to minimise losses of farm P to the environment.

Alluvial landscapes are often utilised for agricultural production, but, they are frequently mismanaged due to the inherently variable nature of alluvial soils. Thus, this study was designed to investigate the influence of variable alluvial soils on P dynamics, and assess what implications this might have for improving P management strategies. A case study approach was adopted for this study, focusing on one large scale dairy operation, located on the Manning River, on the mid-north coast of New South Wales (NSW). The study investigated variations in soil properties between four major alluvial units present within the study site, including, a modern floodplain (MF) unit and three abandoned terrace units (T1- T3) with increasing height (and inferred tentative age) above the existing channel. This was carried out by extracting a number of soil cores and collecting subsamples at various depths, which were then analysed for a range of parameters.

Soil properties revealed to have the greatest influence on P dynamics were those most strongly correlated with the phosphorus buffering index (PBI); namely, clay content (rs =0.680; p = < 0.001), sand content (rs = -0.831; p = < 0.001), mean grain size (rs = -0.698; p = < 0.001), and oxalate extractable aluminium content (Alox) (rs = 0.822; p = < 0.001). Variations in these parameters between major alluvial units were discovered to be influencing the cumulative PBI (including all depth ranges sampled) in the following pattern: MF < T1 < T2 ≤ T3. This suggested that paddocks containing two or more alluvial units of variable height are highly susceptible to (P) fertiliser use inefficiencies, which may potentially be resulting in increased P losses. The main finding of this study, therefore, is that P fertiliser management strategies should take into account soil variations between major alluvial units of differential height, as this may have implications for improving fertiliser use efficiencies, in turn, minimising losses of P to the environment.



Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.