5.2: Crop Rotation - Factors Affecting

Purpose of Crop Rotations

- Maximise interactions between crop, soil and climate
- Spread workload
- Maximise money
- Sustainability

Agronomic Risk Management

- Disease management
- Herbicides
- Nitrogen fertility
- Soil structure
- Soil biology

Economic risk management

- Highest profit
- Diversification of products
- Diversification of markets
- Work-flow management

Order the Victorian crop profile

- Cereals
- Oil seeds
- Pulses

List the traditional rotations

- Wheat-wheat
- Fallow-wheat
- Fallow-wheat-peas-barley
- Pasture-canola-wheat-barley

Fallow: Meaning

Rest period where land is uncultured

Longerenong Rotation: Legumes

- Add N
- Break disease cycles

Longerenong Rotation: Canola

- Breaks disease cycles
- Opens subsoil

Longerenong Rotation: Pasture

- Improves N fertility
- Improves soil struture

Longerenong Rotation: Result

- Reduced weeds
- Reduced disease hosts
- Conserve water
- Mineralise N

Seasons impact on continuous wheat

- Dry conditions: Little detrimental effect
- Wetter conditions: Detrimental effect

Problems with Continuous Cereal Cropping

- Soil-borne and stubble-born diseases
- Herbicide weeds development
- Increased fertiliser usage
- Reduced soil biological diveristy

List the soil-borne diseases

- Cereal cyst nematodes
- Root-lesion nematodes

List the stubble-borne diseases

- Crown rot
- Yellow leaf spot

Take-all: Pathogen name

Gaeumannomyces graminis

Take-all: Symptoms

- Poorly defined patches of poor growth in direction of cultivation
- Darken crowns
- White heads

Take-all: Management

- Crop rotation
- Reduce stubble
- No volunteers
- Fertiliser fungicide

Take all: Infects

- Wheat
- Barley
- Oats
- Grasses

Cereal Cyst Nematode: Pathogen name

Heterodera avenae

Cereal Cyst Nematode: Symptoms

- Yellow or pale green patches causing blotching
- Shallow knotting roots with many small laterals

Cereal Cyst Nematode: More common in

Sandier soils

Cereal Cyst Nematode: Management

- Resistant varieties
- Crop rotation
- No volunteers
- Improve nutrient status

Cereal Cyst Nematode: Infects

- Wheat
- Barley
- Oat
- Grasses

Rhizoctonia: Pathogen name

Rhizoctonia solani AG-8

Rhizoctonia: Symptoms

- Sharply defined bare patches in crop with stunted plants
- Spear shaped root tips

Rhizoctonia: Management

- Tillage
- No volunteer weeds
- Improve nutrient status
- Avoid SUs on high pH soils

Rhizoctonia: Infects

- Wheat
- Barley
- Oats
- Grasses
- Non-grasses

Root Lesion Nematodes: Pathogen name

Pratylenchus thornie and P. neglectus

Root Lesion Nematodes: Symptoms

- Unthrifty stunted plants
- Few lateral roots
- Yellowing of lower leaves

Root Lesion Nematodes: Management

- Resistant cultivars
- Crop rotation
- No volunteers
- Improve nutrient status

Root Lesion Nematodes: Infects

- Wheat
- Barley
- Oats
- Grasses
- Non-grasses

Plant-back Periods of Residual Herbicides: Definition

Time between the application of a residual herbicide and the planting of a new crop in the same treated area

Sulfonyl ureas: Plant-back Periods of Residual Herbicides and crop impacts

* 2 - 3 years
* Cereals

Simazine: Plant-back Periods of Residual Herbicides and crop impacts

* 9 months
* Pulses

Flumetsalam: Plant-back Periods of Residual Herbicides and crop impacts

* 2 years
* Pulses

Imazethapyr: Plant-back Periods of Residual Herbicides and crop impacts

* 3 years
* Pulses

Purpose of Plant-Back Periods

Does not harm subsequent crop cultivars

Plant-back Periods: Determined by

Rate of breakdown by microorganisms

Estimation of nitrogen per tonne of dry matter

25 - 40 kg

High Nitrogen Crops

- Canola
- Oats

Moderate Nitrogen Crops

- Wheat
- Triticale

Low Nitrogen Crops

- Barley
- Safflower

Nitrogen Not Important Crops

- Pulse Crops
- Pastures

Why is nitrogen taken up by cereal?

- Yield
- Protein

Nitrogen Demand \______ times N removal

2 - 4

Returns on Crops: Measurement

Gross Margins

Less variable costs: List

- Fertilisers
- Sprays
- Seeds

Variable costs: list

- Machinery
- Overheads

Why would someone grow peas or lupin when canola returns so much more?

- Soil fertility
- Weed Management

Risk Aversion: Reasons why it happens

- Variability of yield and prices
- Variability of returns