Phosphorus Distribution in Soils from Australian Dairy and Beef Rearing Pastoral Systems

Samuel Adeloju,Benjamin Webb,Ronald Smernik

doi:10.3390/app6020031

Samuel Adeloju, Benjamin Webb + Show 1 more

Open Access

https://doi.org/10.3390/app6020031

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Abstract

The influence of soil type and management practices on P distribution in soils from Australian dairy and beef rearing pastoral systems has been investigated by chemical measurements and phosphorus-31 (31P) nuclear magnetic resonance (NMR) spectroscopy. The amount and forms of P within the soil profile varied with soil type, with the acidic red Ferrosols containing relatively high orthophosphate concentrations, averaging 72.2% compared with 66.8% for Dermosols, under similar management conditions. Soil from Sodosol sites which received less fertiliser P addition had the lowest orthophosphate concentration with only 57.6%. In contrast, relatively high proportions of organic P were found in soil samples from unfertilised Sodosol sites. On average, soil from Sodosol sites contained 37.5% organic P (combined monoester P and diester P), while those from Dermosol and Ferrosol sites contained 31.7% and 25.8%, respectively. Of these, the highest monoester phosphate proportions of 44.6% (site M3) and 46.4% (site M4) were found in Sodosol sites with no recent P inputs, but the highest proportion of diester phosphate (5.7%) was found in an unclassified grey sandy loam Dermosol. The higher organic P concentrations in soil from Sodosol sites may be associated with more regular moisture input from both rainfall and boarder-check (flood) irrigation. The highest level of pyrophosphate (8.5%) was also found in a grey/yellow Sodosol. Overall, the results indicate that P speciation in the Australian soils is strongly influenced by soil type, fertiliser P application rate and timing, and moisture variations.

Highlights

Phosphorus (P) exists in soils in both inorganic and organic forms [1,2]
The organic P content of soil depends on a number of factors, including soil drainage, soil pH, the inorganic content of parent material and cultivation [6]
By removing fertiliser variables, such as timing and rate, some clear differences can be seen between soil types

Summary

Introduction

Phosphorus (P) exists in soils in both inorganic and organic forms [1,2]. Many agricultural areas have relatively high soil total P concentrations compared to background environmental levels [3].these high concentrations are often sub-optimal for agricultural practices, as most of the soil P is not readily available to plants because it is bound in insoluble inorganic and organic forms, such as calcium, iron and aluminum phosphate, inositol hexakisphosphate, and phytate. Phosphorus (P) exists in soils in both inorganic and organic forms [1,2]. Many agricultural areas have relatively high soil total P concentrations compared to background environmental levels [3]. These high concentrations are often sub-optimal for agricultural practices, as most of the soil P is not readily available to plants because it is bound in insoluble inorganic and organic forms, such as calcium, iron and aluminum phosphate, inositol hexakisphosphate, and phytate. A proportion of this is converted into insoluble forms [4,5], which accumulate, raising overall soil P concentrations.

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