New Zealand Journal of Agricultural Research abstracts
The potential for phosphorus loss in relation to nitrogen fertiliser
application and cultivation
R. W. McDowell
R. M. Monaghan
AgResearch Limited
Invermay Agricultural Centre
Private Bag 50 034
Mosgiel, New Zealand
Abstract The amounts and forms of dissolved phosphorus
(P) leached from undisturbed and cultivated soil in lysimeters were measured
from sites that had received N fertiliser at 0, 200 or 400 kg N ha-1
yr-1 for 4 years. Soil in mini-lysimeters, 18 cm i.d. by 25 cm
depth, was leached at monthly intervals over autumn and winter (500 mm total
drainage) to simulate a relatively wet autumn-winter for eastern Southland
(typical drainage, c. 350 mm yr-1). The major form of P leached
was dissolved organic P (DOP), which represented 67 and 80% of total dissolved
P (TDP) losses in the undisturbed and cultivated soil treatments, respectively.
Historical N inputs had little effect on the amounts of dissolved reactive
P (DRP), DOP or TDP leached from the undisturbed soils. However, DRP, and
to a lesser extent TDP, losses decreased as historical N fertiliser inputs
increased in the cultivated soil treatment. Significantly greater losses
of DRP were observed from undisturbed compared with cultivated soils. The
lower DRP losses in cultivated soil were attributed to greater sorption of
P during matrix flow. These results suggest that, although DRP losses are
of little concern following cultivation of pastoral soils, the greater mobility
and loss of DOP in drainage, in both undisturbed and cultivated soils, represents
a potential risk to water quality and loss of P from the plant rooting zone.
Further study to examine the bioavailability of DOP is warranted to determine
its potential risk to surface water.
Keywords phosphorus; subsurface flow; cultivation;
dissolved organic P; dissolved reactive P; nitrogen application
A02017 Received 11 March 2002; accepted 16 August 2002; published 9 December
2002
New Zealand Journal of Agricultural Research, 2002, Vol. 45: 245-253
0028-8233/02/4504-0245 $7.00/0 © The Royal Society of New Zealand
2002
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