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