New Zealand Journal of Agricultural Research abstracts
The 'critical' ESP value: does it change with land application of dairy
factory effluent?
K. C. Cameron
H. J. Di
M. R. Anwar
Centre for Soil and Environmental Quality
P.O. Box 84
Lincoln University
Canterbury, New Zealand
J. M. Russell
J. W. Barnett
Fonterra Research Centre
Private Bag 11 029
Palmerston North, New Zealand
Abstract Decisions about the tolerable loading of sodium
during land application of dairy factory effluent (DFE) are often based on
the risk of exceeding a “critical” exchangeable sodium percentage (ESP) in
the soil. The concept of a “critical” ESP value is based on overseas research
that investigated the effects of saline irrigation water on soil structure,
rather than on experimental evidence based on research using DFE. The problem
is that sodium may degrade the structural stability of the soil and eventually
cause surface ponding and effluent run-off. The aim of this investigation
was to determine the effects of land treatment of DFE on key soil physical
properties and to establish if a single “critical” ESP value is appropriate
for these situations. Intact soil cores (200 mm diameter x 200 mm deep) were
collected from three sites at the Clandeboye dairy factory in Canterbury
covering two periods of application (4, 10 years) of land treatment of DFE,
plus an adjacent control site that had not received DFE. The soil at the
Clandeboye land treatment sites was a Lismore stony silt loam with a mixture
of perennial ryegrass (Lolium perenne) and white clover (Trifolium
repens). The results show that the soil from DFE land treatment sites
had greater wet aggregate stability than soil from the control site. Treatment
of the soil cores in the laboratory with a sodium solution decreased the
wet aggregate stability and the hydraulic conductivity of the soil. The greatest
reduction in hydraulic conductivity occurred in the control soil with a smaller
decrease in the hydraulic conductivity in the soil from the DFE treatment
sites. A decrease of 50% in hydraulic conductivity occurred at an ESP value
of 3 in soil from the control site, whereas in soil from the DFE sites this
50% reduction did not occur until an ESP of 13 was achieved. These results
show that the “critical” ESP value may change following the application of
DFE to soil, and that the use of a single ESP value in land-use decision
making is therefore too simplistic.
Keywords dairy factory effluent; hydraulic conductivity;
saline; sodium; wet aggregate stability
A02057 Received 21 August 2002; accepted 28 March 2003; published 30 June
2003
New Zealand Journal of Agricultural Research, 2003, Vol. 46: 147-154
0028-8233/03/4602-0147 $7.00/0 © The Royal Society of New Zealand
2003
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