Idenitifying the fit for perennial forage options in a crop-livestock system: use of a whole-farm optimization model. Marta Monjardino

Identifying the fit for perennial forage options
in a crop-livestock system: use of a whole-
farm optimization model

Marta Monjardino,
R. Llewellyn and A. Bathgate
5th World Congress of Conservation Agriculture
Brisbane, 26-29 September 2011

Background

• Major economic and environmental challenges in low rainfall
zones of southern Australia;
• Forage shrubs may help fill the long feed gap in the Mallee and
provide other benefits;
• But are they profitable?
• Use of a bio-economic tool to help identify where in the
landscape and at what level of production/quality they might be
profitable.

CSIRO. Identifying the fit for forage shrubs in a crop-livestock system: use of a whole-farm optimization model

Forage shrubs in the Mallee

• Old Man Saltbush (Atriplex nummularia) the most widely
available commercial shrub species;
• Low % of farmers adopting shrubs and only <1% of farm area
with shrub plantings due to relatively low quality/production;
• Opportunities to identify/develop new OMS and other shrub
types, arrangements and mixes for higher performance;
• Whole-farm model needed as perennials will always be a niche
land area, but have whole-farm impact via livestock, etc;
• Whole-farm considerations to help shape R&D strategies.


MIDAS

• Model of an Integrated Dryland Agricultural System;
• Whole-farm optimization model;
• Based on LP technique;
• Deterministic model;
• Annual equilibrium structure;
• Interactions between enterprises;
• Thousands of input parameters;
• Detailed model output;
• Software: EXCEL spreadsheets + LINDO algorithm;
• Good coverage of southern Australia agro-ecological regions
with several model versions in 4 states.


Mallee MIDAS overview

• Typical 3000 ha crop/livestock farm;
• Average annual rainfall: 250-350 mm (80% in winter);
• Average summer max daily temp. >30ºC;
• 7 LMUs with ≠ prod. potential in typical dune-swale land system;
• Crops: wheat, barley, triticale, canola, lupins, range of legumes;
• Options for fallow and cereal grazing;
• Merino/crossbred sheep dominant livestock for wool and meat;
• Grazing on annual (medic), perennial (lucerne), vol. pastures;
• Woody perennial options: forage shrubs, tree alleys;

70
Rainfall
Rainfall (mm) & temperature ('C)

60

50 Temperature

40

30

20

10

0
v
n

n

l

c
g
p
r
ar
b

ct
ay

Ju
Ap

No
Ja

Ju

Au
Se

De
Fe

O
M

M



• Over 200 crop-pasture rotations + inter-rotational effects;
• Ten pasture growing periods/year;
• Ten major feeding periods/year;
• Five supplementary feeding options;
• Over 80 sheep classes;
• Different management options/class;
• Different energy and intake volume/class;
• Deferment of pasture grazing between growing periods, and
degeneration of feed over summer;



• Several grain, stubble and wool quality classes;
• Soil N balance and fertilization options;
• Chemical control of diseases, pests and weeds;
• Groundwater recharge and surface water run-off;
• Loss of top soil by erosion;
• Machinery specifications;
• Labour requirements;
• Farm finance.


Validation

• Difficult validation of optimization models;
• Extensive process of verification;
• Expert assessment of input parameters and k.p.i. (e.g. whole-
farm profit, crop/pasture %, SR, rotations/LMU);
• Comparison with actual farming practice;
• Many issues analyzed with MIDAS/MUDAS over 3 decades, e.g.:
• New crops in rotation, e.g. lupins, canola;
• Saltland pastures;
• Trees and shrubs;
• Soil management, e.g. deep ripping;
• Impact of agric. policies, e.g. salinity tax, C price;
• Livestock breeds, e.g. Awassi, Dorper;
• Livestock management, e.g. time of lambing;
• Impact of grain quality;
• Machinery changes;
• Conservation strategies, e.g. stubble retention.


Modelling shrub-based systems

• Biological traits
• Productive life of the stand
• Shrub density
• Shrub growth rate/biomass production
• Re-establishment period
• Nutritive value and anti-nutritional effects
• Proportion of understorey pasture
• Animal impact
• Liveweight gains due to permanent feed on offer
• Increased lambing rate from extra shade and shelter
• Environmental impact
• Groundwater recharge
• Top soil loss by erosion
• Costs
• Establishment /maintenance of shrub stand

Land management units

LMU Main soil type Description W yield Shrub U/s medic
potential potential pasture
potential
1 Sandy loam Reliable, ↑ yields 2.0 100% 100%
2 Sandy Same, but fert req. 1.8 70% 67%
3 Calc, stony ↓ yld, wears mach. 0.4 50% 10%
4 Interm. Soils Med yields 1.6 90% 67%
5 Deep sands Erosion, ↓ yields 0.8 50% 17%
6 Lo o/ clay (w/ ssc) ↓↓ yld in dry spring 0.6 65% 40%
7 Lo o/ clay (no ssc) ↓ yld in dry spring 1.4 90% >100%


2000

1500

Shrub area (ha)
LMU 7
LMU 6
1000
LMU 5
LMU 4
LMU 3
LMU 2
500 LMU 1

0
0 10 20 30 40 50 60

Shrub %

Area of shrubs allocated to each LMU as they increase on the farm.


Standard output

Crop area (% of farm) 56
Pasture area (% of farm) 44
Shrub area (% of farm) 0
Stocking rate (DSM/ha of farm) 2.4
Supplementary grain feed (kg/DSE/yr) 65
Groundwater recharge (mm/ha/yr) 174
Topsoil loss by erosion (m3/ha/yr) 90
Profit ($/ha/yr) 129


Key model parameters

Parameters Std
Saltbush density (plants/ha) 1500
Saltbush nutritive value (MJ ME/kg DM) 7
Saltbush biomass production (kg DM/plant) 1
Saltbush anti-nutritional effects on intake (%) 3
Saltbush establishment cost ($/plant) 0.4
Price of wheat ($/t ASW) 280
Price of wool (c/kg clean WMI) 900
Price of prime lamb ($/kg DW) 4


Key model parameters - SA

Parameters Min Std Max
Saltbush density (plants/ha) 1500 3000
Saltbush nutritive value (MJ ME/kg DM) 7 10
Saltbush biomass production (kg DM/plant) 1 3
Saltbush anti-nutritional effects on intake (%) 0 3
Saltbush establishment cost ($/plant) 0.2 0.4
Price of wheat ($/t ASW) 180 280 480
Price of wool (c/kg clean WMI) 700 900 1100
Price of prime lamb ($/kg DW) 3 4 6


600000

Whole-farm profit ($/year) 400000

200000

0
0 10 20 30 40 50 60

Shrub %

Change in whole-farm profit with increasing % saltbush shrubs.


600000


<10% shrub area =>
200000
small decline in profit;
>10% shrub area =>
sharp decline in profit
0
0 10 20 30 40 50 60

Shrub %

Change in whole-farm profit with increasing % saltbush shrubs.


Impact of different saltbush plant density levels and establishment
costs on whole-farm profit with higher % shrubs.


600000


3 kg DM/plant
2 kg DM/plant
1 kg DM/plant
200000 0.5 kg DM/plant

0
0 10 20 30 40 50 60

Shrub %

Impact of different saltbush biomass production and nutritive value
levels on whole-farm profit as % shrubs increases on the farm.


800

600

Units//ha/yr

400
Deepflow
Erosion

200

0
0 10 20 30 40 50 60

Shrub %

Impact of prime lamb price change on whole-farm profit for a range of
shrub areas.


800

600

Units//ha/yr

400
Deepflow
Erosion

200

0
0 10 20 30 40 50 60

Shrub %

Impact of wheat price change on whole-farm profit for a range of
shrub areas.


800
800

600
600

Units//ha/yr
mm//ha/yr

400
400
Deepflow
Erosion

200
200

0
0
0
0 10 10 20 30
20 40 30 50 60
40 50
Shrub %Shrub %

Changes in ground water recharge (mm/ha/yr) with an increasing
shrub area on the farm.


Conclusions

1. At current production/quality levels, shrubs are marginally
profitable at up to 10% of farm, i.e. shrubs in the Mallee can
be introduced on small farm areas (≤ 10%) with minimal loss
in profit.


Conclusions

in profit.
2. Profitability of forage shrubs depends on opportunity cost of
giving up other farm enterprises in the poorer farm soils;


Conclusions

in profit.
2. Profitability of forage shrubs depends on opportunity cost of
giving up other farm enterprises in the poorer farm soils;
3. The current profit shortfall may well be made up through:
• R&D to improve increases in shrub quality/production, as well
as more effective shrub mixes/arrangements;
• Lower shrub establishment costs;
• Capturing of other benefits such as GHG emissions reduction
(C seq. and lower CH4 via bioactive compounds), animal
health/performance, improved soil condition, biodiversity, labour
management, and spread of farm risk.
• A change in market prices, e.g. lower grain and higher animal
prod. prices.

Photo source: Enrich project


CSIRO Ecosystem Sciences Acknowledgements
Dr. Marta Monjardino Future Farm Industries CRC
GRDC
Phone: 61 (0)8 8303 8413
Email: marta.monjardino@csiro.au
Web: www.csiro.au/ces

Thank you!
Contact Us
Phone: 1300 363 400 or +61 3 9545 2176
Email: enquiries@csiro.au Web: www.csiro.au

Idenitifying the fit for perennial forage options in a crop-livestock system: use of a whole-farm optimization model. Marta Monjardino

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Idenitifying the fit for perennial forage options in a crop-livestock system: use of a whole-farm optimization model. Marta Monjardino