Dr Bill CotchingTasmanian Institute of Agricultural Research
Managing our Land and Water Resources
A research perspective
Tasmanian catchmentsare different
LanduseRainfall ElevationRelief or TopographySoil typesRiver channel lengthDrainageGeologyRoads & 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
0 10 20 30
Conservation
Forestry (native)
Forestry (plantation)
Grazing improved pastures
Perennial horticulture
Cropping
Irrigated pastures (dairy)
Nutrient generation rate (kg/ha/yr)
Total Phosphorus
Catchment scale nutrient generation to waterways in Northern Tasmania
Landscape Logic
Catchment scale nutrient generation to waterways in Northern Tasmania
0 10 20 30
Conservation
Forestry (native)
Forestry (plantation)
Grazing improved pastures
Perennial horticulture
Cropping
Irrigated pastures (dairy)
Nutrient generation rate (kg/ha/yr)
Total PhosphorusTotal Nitrogen
Landscape Logic
Fertiliser application rates in 2003/04in one Tasmanian catchment dominated by dairy farming
Average Range Average loss to (kg/ha) (kg/ha) waterways
(kg/ha/yr)
Nitrogen 116 9 - 392 25Phosphorus 44 16 - 76 10
Farm / paddock scale
Average RangeTotal P losses in runoff (kg/ha/yr) 10 6 - 12Total N losses in runoff (kg/ha/yr) 23 13 – 29Total K losses in runoff (kg/ha/yr) 43 25 - 54
Nutrient losses in runoff from Togari experimental site 2004 – 2006
(Greg Holz)
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.
Each grazing event was followed by a period of elevatedconcentrations of P, NH4 and K.
The principal driver of the loads of nutrient loss at this site is the volume of runoff.
5200 ha
28 dairy farms
~ 9000 milking cows
1444 paddocks
TogariBritton’s Swamp
Lucy Burkitt and Jessica Coad
Olsen P concentration (0–75 mm) of milking paddocks across Togari and Brittons Swamp
2005/2006
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
Summary of Montagu soil nutrient data
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
14000
16000
18000
20000
22000
0 20 40 60 80 100
Soil Olsen P (mg/kg)
Past
ure
grow
th (k
g dr
y m
atte
r/ha/
yr)
Mean annual (2007/08) dry matter pasture yield
at the Montagu experiment site.
Current catchment average
What happens in the estuary ?
Monatagu estuaryNitrogen 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 postsWill not stop soluble nutrients from feeding fat oysters