
TY  - JOUR
A1  - Wong, M. T. F. 
A1  - Harper, R. J. 
T1  - Use of on-ground gamma-ray spectrometry to measure plant-available potassium and other topsoil attributes
JF  - Soil Research
JO  - Soil Res.
Y1  - 1999
VL  - 37
IS  - 2
SP  - 267
EP  - 278
KW  - 40K, Colwell-K, precision agriculture, soil survey, clay, organic matter.
UR  - https://doi.org/10.1071/S98038 
N2  - The incidence of potassium (K) deficiency is increasing in crops, pastures, and forestry in south-western Australia. Although soil K can be measured using soil sampling and analysis, &#947;-ray spectrometry offers a potentially cheaper and spatially more precise alternative. This could be particularly useful in precision agriculture, where inputs are applied according to need rather than by general prescription. In a study of topsoils near Jerramungup, Western Australia, strong relationships (r2 = 0&#183;9) were found between on-ground counts of &#947;-rays derived from 40K (&#947;-K) and both total K and plant-available K. The success of &#947;-ray spectrometry in predicting available K relied on a strong relationship (r2 = 0&#183;9) between total K and available K which may not hold in all areas. Although the relationship between &#947;-K and available K held over the range of 36&#8211;1012 mg/kg, crop response to K fertilisers is only expected when the available K content is &#60;100 mg/kg. Estimates of available K from &#947;-K were unreliable at this lower end of the regression curve. Separate analysis with a subset of the data with available K &#60;100 mg/kg showed a poor relationship between &#947;-K and available K (r2 = 0&#183;05; d.f. 11). The usefulness of &#947;-ray spectrometry may therefore be restricted to defining areas where response to fertiliser K may occur, and where further soil sampling and analysis are required to predict the fertiliser requirement. Strong relationships (r2 = 0&#183;9) were also found between &#947;-K and a range of other soil attributes, including clay, silt, and organic carbon content. These relationships depended on the locally strong relationship between total K and these soil attributes. Since such relationships do not hold everywhere, the utility of &#947;-ray spectrometry will likewise be limited. Site-specific calibrations are required if &#947;-ray spectrometry is to be used for soil property mapping. 
ER  -

