
TY  - JOUR
A1  - Falkiner, R. A. 
A1  - Polglase, P. J. 
T1  - Fate of applied phosphorus in an effluent-irrigated <emph type="2">Pinus radiata</emph> plantation
JF  - Soil Research
JO  - Soil Res.
Y1  - 1999
VL  - 37
IS  - 6
SP  - 1095
EP  - 1106
KW  - desorption, isotherm, mineralisation, sorption.
UR  - https://doi.org/10.1071/SR99014 
N2  - We examined the fate of applied phosphorus (P) in a young Pinus radiata plantation in south-eastern Australia, spray-irrigated with secondary-treated municipal effluent. Measurements included changes (before irrigation, and after 5 years) in total P, total organic P, total inorganic P, labile P, and sorption and desorption characteristics. During the first 5 years a total of 363 kg/ha of P was applied at an average concentration of 5.4 mg/L. Irrigation changed the forms and distribution of P throughout the profile (0&#8211;1 m). Increases in labile inorganic P (membrane-exchangeable, bicarbonate-extractable, and in soil solution) were confined mostly to the 0&#8211;0.5 m horizon, and wholly within the 0&#8211;0.7 m horizon. In addition, large amounts of organic P (204 kg/ha) were mineralised within the surface 0.7 m, due to stimulation of decomposer activity by increased soil water. Mineralisation, therefore, provided a significant and additional input of inorganic P to soil. Irrigation and P additions changed both the placement and curvature of soil sorption isotherms. Retention capacity (0&#8211;0.5 m), calculated from P sorption isotherms, decreased by 180 kg/ha. Desorbable P, determined by sequential extraction with dilute acid, increased by 184 kg/ha. Thus, these 2 independent methods of measuring the changes in exchangeable P gave the same result. Of the total inorganic P added to the soil (in effluent and mineralised), 25% remained in the exchangeable form; the rest was retained unavailable for short-term exchange and migration through soil. After 5 years, fluxes (kg/ha) of P in the 0&#8211;0.7 m horizon were: input in effluent less storage in vegetation (323), change in total organic P (&#8211;204), change in total inorganic P (517), net change in total P (313). Thus, 97% of the net amount of P added in effluent was recovered in the surface 0.7 m. Results have implications for the way in which P retention capacity is calculated under effluent irrigation. 
ER  -

