AGSY102 Agronomy Review Notes - Lecture (4-9)

Global Agriculture Trends (Lecture 4)

• Developed countries’ output plateauing; developing output still rising.
• Commodity stand-outs $1960\text{–}2020$:
– Beef: rapid growth in $\text{China},\, \text{Brazil},\, \text{Russia}$.
– Lamb: $\text{Australia}$ & $\text{NZ}$ dominate; growth in Africa/Asia.
– Cotton: spike in $\text{Australia}$ after GM adoption $\sim2000$.
– Wheat: strong rises in $\text{Canada},\, \text{China},\, \text{India},\, \text{Russia}$.
• Emerging food gap: demand ↑ (population) > supply ↔ ⇒ widening deficit.
• Food-system framework: drivers → supply chain, food environment, individual factors → outcomes (food security, diet, low env. harm).

Australian Agriculture Snapshot

• Land: $55\%$ of $426\,\text{M ha}$ in ag; $80\%$ grazing; $9\%$ certified organic.
• Water: $74\%$ of national use = $9{,}981\,\text{GL}$.
• Exports: $10.8\%$ of goods/services ($\$71.5\,\text{B}$).
• Employment: $5.9\%$ rural, $2.2\%$ national (≈ $315{,}600$ people).
• Main farming systems: rainfed dryland ($200\text{–}500\,\text{mm}$), irrigated, rangeland.

Soils (Lecture 5)

• Composition: $45\%$ minerals, $25\%$ air, $25\%$ water, $5\%$ OM.
• Formation factors: $\text{CLO RPT}$ (Climate, Organisms, Topography, Parent, Time).
• Key horizons: $A<em>1$ (organic), $A</em>2$ (leached), $B$ (clay/Fe/Al), $C$ (weathered rock).
• Texture: sand–silt–clay % ⇒ water-holding & CEC; clay ↑ = nutrients ↑.
• Structure: granular > blocky > prismatic > platy (permeability ↓).
• Chemistry: CEC ↑ with clay/OM; pH optimal $4.0\text{–}8.5$; acid soils ⇒ Al toxicity (lime to fix).
• Salinity: high soluble salts; sodicity: excess $\text{Na}^+$ ⇒ dispersion; manage via water balance & tolerant species.
• OM & microbes: drive WHC, structure, nutrient cycling; retain stubble, reduce tillage.

Crops (Lecture 6)

• Regions: West (winter rain), North (dual seasons), South (spring rain).
• Main winter crops: wheat, barley, canola; summer: sorghum, cotton.
• Key management: align phenology to climate; sustain soil health (cover, low disturbance, diversity); integrated pest/weed/disease control.
• Major constraints: salinity, erosion, acidity, nutrient imbalance.

Irrigation (Lecture 7)

• Accounts for $\sim60\%$ of irrigated area & $73\%$ of national water use in MDB.
• Top irrigated land uses $2020\text{–}21$: pastures, cereals, cotton, fruit & nuts.
• Water-quality limits: salinity < $700\,\mu\text{S cm}^{-1}$, \text{SAR}<3, pH $5.5\text{–}8.5$.
• WUE ranges: surface $60\text{–}90\%$, sprinkler $65\text{–}90\%$, drip $75\text{–}95\%$.
• Cost hierarchy (capital): surface < sprinkler < drip; drip gives highest precision.
• Key constraints: weeds $\$4.8\,\text{B yr}^{-1}$, diseases $\$2.7\,\text{B}$, pests $\$1.5\,\text{B}$, soil limits.

Pastures (Lecture 8)

• Pastures cover $\sim70\%$ ($400\,\text{M ha}$); crops $24\,\text{M ha}$.
• Types: shrublands, native C$<em>3$/C$</em>4$ grasslands, sown/improved (tropical & temperate).
• Growth phases: $1$ establishment → $2$ vegetative ★ (best graze) → $3$ reproductive → $4$ senescence.
• Northern systems: extensive, C$_4$ natives; southern: intensive, improved temperate spp.
• Selection factors: climate, soil pH/fertility, species traits.
• Benefits of mixed pastures: N fixation, soil C ↑ ($0.5\text{–}1.0\,\text{t C ha}^{-1}\,\text{yr}^{-1}$), erosion ↓, biodiversity ↑.

Grazing (Lecture 9)

• Zones: wheat–sheep $32\,\text{M ha}$, rangelands >$200\,\text{M ha}$, high-rainfall $27\,\text{M ha}$.
• Nutrient principle: lowest-supply nutrient limits animal performance.
• Carrying capacity: extensive $0.2\text{–}2\,\text{DSE ha}^{-1}$, intensive $15\text{–}25\,\text{DSE ha}^{-1}$.
• Grazing systems: continuous (low input) → rotational → cell → strip (high mgmt/intensity).
• Species diet: cattle-grass, sheep-forbs, goats-browse; mixed grazing can boost capacity $15\text{–}20\%$.
• Key management: match stocking to carrying, monitor pasture phase, maintain soil fertility.