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Lecture 10: Comparison of Agroecosystems to Natural Ecosystems

• Agroecosystems

  • Defined as systems managed to produce food, fiber, fuel, or other agricultural products.

  • Comprise over 40% of Earth’s land, indicating their significant role in land use.

  • Characterized as simplified systems that rely heavily on technology and external inputs for productivity.

  • Examples of Agroecosystems:

  • Corn-soybean rotation

  • Animal-based agroecosystems

• Ecosystems

  • Defined as natural systems where living organisms (biotic) and their environment (abiotic) function collectively.

  • Components:

  • Biotic: Living components (plants, animals, microorganisms)

  • Abiotic: Non-living components (water, soil, climate)

• Human Influence on the Environment for Crop Production:

  • Crop Residues: Influence soil temperature and moisture retention.

  • Fallow: Refers to land in rotation that is not cropped for one season.

  • Tile Drainage: Used to remove excess soil water.

  • Irrigation Methods:

  • Surface irrigation

  • Sprinkler irrigation

  • Subsurface irrigation

Lecture 11: Cropping Systems

• Types of Cropping Systems:

  • Continuous Cropping: Planting the same crop for two or more consecutive years on the same field.

  • Strip Intercropping: Alternating multiple rows of one crop with multiple rows of another crop.

  • Monoculture: Planting a single cash crop in a field.

  • Polyculture/Intercropping: Planting multiple cash crops in the same field during one growing season.

  • Double Cropping: Taking advantage of the environment to produce two crops within one growing season.

• Conservation Options in Agroecosystems:

  • Conservation Reserve Program (CRP): Converts highly erodible cropland to vegetative cover to prevent erosion.

  • Grass Waterway: Designed to limit soil erosion, slow down water velocity, anchor soil, and prevent nutrient loss to water bodies.

  • Riparian Buffers: Use of trees to prevent loss of soil and protect waterways.

  • Shelterbelts: Rows of trees planted to minimize wind erosion.

• Allelopathy:

  • Defined as a phenomenon where one plant releases toxins into the soil, inhibiting the growth of competing species.

  • Examples of Allelopathic Plants: Rye and walnut.

Lecture 12: Soil Formation Factors

• Five Soil Forming Factors (CLORPT):

  • Climate

  • Organisms (Vegetation)

  • Relief (Topography)

  • Parent Material

  • Time

  • Not all in-depth questions will focus on these, but foundational understanding is beneficial.

• Water Boundaries in Soils:

  • Influenced by factors like soil texture, structure, and presence of organic matter.

Lecture 13: Soil Properties and Fertility

• Bulk Density:

  • A measure used to determine soil compaction.

  • Compaction Problems:

  • Root restriction

  • Water restriction

  • Depleted oxygen and gas exchange

  • Lowered soil biological activity

• Cation Exchange Capacity (CEC):

  • Primarily involves clay and organic matter in soil.

• Carbon to Nitrogen Ratio (C:N):

  • Affects decomposition and nutritional cycling.

  • Low C:N: Fast decomposition

  • High C:N: Slow decomposition, can lead to nitrogen immobilization.

  • Typical Ratios:

  • Wheat: 80:1

  • Corn: 60:1

  • Cover crop: <30:1

  • Ideal Microbial C:N Ratio: 24:1

• Soil Texture Triangle:

  • Understand its use in determining water storage, nutrient holding capacity, and appropriate planting depth.

Lecture 14: Fertilizer Calculations and Plant Requirements

• Fertilizer Grade Components:

  • N-P2O5-K2O

  • Be prepared to complete calculations for a single nutrient.

  • Note: Calculators will be provided; phones are not permitted during the exam.

• Importance of Soil pH:

  • When pH dips below approximately 5.5, phosphorus ties to aluminum, becoming unavailable to plants.

  • When pH exceeds around 7, phosphorus ties to calcium, also rendering it unavailable.

• Nutrient Deficiencies in Corn:

  • Nitrogen Deficiency: Pale yellowish-green leaves in the middle of the plant.

  • Phosphorus Deficiency: Dark green leaves with reddish to purplish margins.

  • Potassium Deficiency: Yellowing along leaf edges.

Lecture 15: Herbicides and Weeds

• Herbicide Resistance:

  • Defined as the tolerance of previously susceptible weed species to herbicides.

• Weed Seed Bank:

  • Total dormant and non-dormant seeds accumulated in the soil.

• Competition of Weeds in Agroecosystems:

  • Weeds compete for light, water, and nutrients, affecting crop yields.

• Application Timing Options for Herbicides:

  • Pre-plant

  • Pre-emergent

  • Post-emergent

  • Post-harvest

Lecture 16: Plant Pathogens and Disease Management

• Common Plant Pathogens:

  • Categories include fungi, bacteria, and nematodes.

• Historic Diseases:

  • Wheat stem rust as a notable example.

• Disease Prevention Methods:

  • Examples include planting later so soil is warmer.

  • Understand how insect vectors spread plant diseases as they transfer pathogens from one plant to another.

• Disease Triangle:

  • Comprises disease, a susceptible host, and a conductive environment.

  • Breaking any component of the triangle can limit disease prevalence.

Lecture 17: Nematodes and Insect Management

• Soybean Cyst Nematodes:

  • Microscopic roundworms that feed on plants using their stylet.

  • Ideal soil temperature for survival: 75 °F

  • Lifecycle completion in approximately 4 weeks

  • Cysts can persist in soil for up to 10 years.

• Symptoms of Infestation:

  • Symptoms include stunting, wilting, chlorosis, necrotic lesions, and root malformations.

  • Management strategies include crop rotation, resistant varieties, or use of fumigants.

• Types of Metamorphosis in Insects:

  • Holometabolous: Complete metamorphosis

  • Hemimetabolous: Incomplete metamorphosis

• Lifecycle and Management Considerations:

  • Specific to corn rootworm and aphids, methods include scouting, management practices, and crop rotation.