Managing our Land and Water Resources
A research perspective
Dr Bill Cotching
Tasmanian Institute of Agricultural Research
Tasmanian catchments
are different
Landuse
Rainfall
Elevation
Relief or Topography
Soil types
River channel length
Drainage
Geology
Roads & tracks
Irrigation
Riparian zone extent
Society’s perception has grown
of the relationship between
agricultural activity and
the quality of the environment
Landscape Logic
Soil and water nutrients research
3 Scales of investigation
Catchment
Farm/paddock
Plot
Catchment scale nutrient generation to waterways
in Northern Tasmania
Irrigated pastures (dairy)
Cropping
Perennial horticulture
Grazing improved pastures
Forestry (plantation)
Total Phosphorus
Forestry (native)
Conservation
0
10
20
30
Nutrient generation rate
(kg/ha/yr)
Landscape Logic
Catchment scale nutrient generation to waterways
in Northern Tasmania
Irrigated pastures (dairy)
Cropping
Perennial horticulture
Grazing improved pastures
Forestry (plantation)
Total Phosphorus
Total Nitrogen
Forestry (native)
Conservation
0
10
20
30
Nutrient generation rate
(kg/ha/yr)
Landscape Logic
Fertiliser application rates in 2003/04
in one Tasmanian catchment
dominated by dairy farming
Average
(kg/ha)
Nitrogen
Phosphorus
116
44
Range
(kg/ha)
9 - 392
16 - 76
Average loss to
waterways
(kg/ha/yr)
25
10
Farm / paddock scale
Nutrient losses in runoff
from Togari experimental site 2004 – 2006
(Greg Holz)
Total P losses in runoff (kg/ha/yr)
Total N losses in runoff (kg/ha/yr)
Total K losses in runoff (kg/ha/yr)
Average
10
23
43
75% of P lost was in the dissolved form.
Up to 98% of P was lost as dissolved P in November 2004
due to P losses following fertilizing.
This one event amounted to 30% of P lost in the year.
Range
6 - 12
13 – 29
25 - 54
Each grazing event was followed by a period of elevated
concentrations of P, NH4 and K.
The principal driver of the loads of nutrient loss
at this site is the volume of runoff.
Lucy Burkitt and Jessica Coad
5200 ha
28 dairy farms
~ 9000 milking cows
1444 paddocks
Togari
Britton’s
Swamp
Olsen P concentration (0–75 mm) of milking
paddocks across Togari and Brittons Swamp
2005/2006
Summary of Montagu soil nutrient data

Results show high soil phosphorus and sulphur
levels (mean Olsen P = 52, range 4 – 161)

highlights need for nutrient budgeting

Uneven nutrient distribution within farms

Each catchment likely to have unique set of
issues
New project with dairy industry
in Duck catchment
to map soil nutrients
and
use farm nutrient budgets
Plot scale
Pasture growth response to soil Olsen P levels
Mean annual (2007/08) dry matter pasture yield
at the Montagu experiment site.
Pasture growth (kg dry matter/ha/yr)
22000
20000
18000
Current catchment average
16000
14000
0
20
40
60
Soil Olsen P (mg/kg)
80
100
What happens in the estuary ?
Monatagu estuary
Nitrogen concentrations
were no higher than those recorded
from the Black or Detention estuaries
Phosphorous levels were only marginally higher.
High tidal exchange
restricts the accumulation of nutrients
limiting the potential risk of eutrophication
Montagu estuary
Biological sampling found species
adapted to stressed environments,
particularly in the upper reaches of the estuary.
Dairy farming is a nutrient leaky system
Tasmanian proverb
Planting many fence posts
Will not stop soluble nutrients
from feeding fat oysters