New Zealand Journal of Agricultural Research abstracts
Measurement and modelling of runoff and phosphate movement from seasonally dry hill-country pastures
A. G. Gillingham
Research Consultant
92 Waicola Drive
RD1
Palmerston North, New Zealand
a.gillingham@xtra.co.nz
M. H. Gray
Maurice Gray and Associates Ltd
1 Aotea Crescent
Havelock North, New Zealand
Abstract In seasonally dry hill pastures on a
Waipawa stony loam (Pallic Soil) in Hawke’s Bay, a range of
methods was used to measure phosphorus (P) movement and losses in
runoff water. Measurements with a rainfall simulator and micro-plots
showed that dissolved reactive P (DRP) and total dissolved P (TDP)
concentrations in surface runoff were directly related to soil Olsen P (R2 = 0.93 and R2 =
0.90 respectively) status. The distance that surface runoff travelled,
as measured by P fertiliser transport, was about 5 m when rainfall
in autumn had not occurred for 12–22 days, but decreased sharply
in subsequent rainstorms. Over a 12-month period most natural surface
runoff occurred mostly during early summer to late autumn and was
inversely related to soil moisture content (R2 =
–0.38 for all data). Most (55–84%) of total P (TP) losses
occurred in three of 12 storms measured, with the majority as DRP from
low P (60–85%) and high P (70–93%) soils. Continuous flows
from twin catchments of 12.6 ha (north, with low soil P status),
and 12.8 ha (south, with a moderate to high soil P status) were
recorded. For the north catchment, total flow ranged from 18 to 26% of
annual rainfall, and for the south catchment from 18 to 21%, over 2000
to 2002. About half of this occurred in July–August. Over a
7-month period, surface runoff was equivalent to only about 3% of
rainfall. The difference in soil P status of the two catchments
provided an approximate index of the difference in TP export. The DRP
and TDP concentrations in catchment flow were about 10-fold less than
those recorded in surface runoff from associated pastures. The TOPMODEL
runoff simulation model accurately estimated total flow from two
catchments (R² = 0.89 and 0.87 for north and south catchments respectively), but not the contribution by surface runoff.
Keywords phosphate runoff; hill country; catchment flow; surface runoff; P loss
A05073; Received 14 December 2005; accepted 18 May 2006; Online publication date 4 July 2006
New Zealand Journal of Agricultural Research, 2006, Vol. 49: 233–245
0028–8233/06/4903–233 © The Royal Society of New Zealand 2006
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