Agronomic Crops Exam 2 Info

Corn ideal planting date

Earlier than May 1st for best yield.

Corn yield trend after May 15th

Yields begin to decline after May 15th.

Corn yield decrease rate after May 15th

About 0.5 bushels per acre per day.

Corn yield decrease rate after June 1st

About 2.5 bushels per acre per day.

Yield loss by June 1st planting

Planting by June 1st can reduce yield by ~30%.

U.S. corn production leadership

The U.S. is the world leader in corn production and corn is its highest value crop.

U.S. corn export percentage

About 15% of U.S. corn is exported.

Main U.S. corn export markets

Mexico, Southeast Asia, and the Middle East.

Brazil corn production

Brazil is the second largest corn producer after the U.S. and a major exporter.

Other major corn exporters

China, Argentina, and Ukraine.

Soybean day-length sensitivity

Soybeans are short-day, photoperiod-sensitive plants.

Soybean flowering trigger

Triggered when nights get longer and days get shorter.

Soybean flowering factors

Influenced by day length, plant stage, and temperature.

Corn vs soybean flowering difference

Corn flowering is based on growing degree days (GDD), not day length.

Nitrogen fixation and bacteria

Only bacteria can break the triple bond in N₂ to fix nitrogen.

Legume-bacteria symbiosis

Bacteria fix N₂ for plants; plants provide carbon in return.

Soybean root nodules

Nodules are nitrogen-fixing structures on roots.

Active vs inactive nodules

Red nodules = active; green nodules = inactive.

Nitrogenase function

Enzyme that breaks the N₂ triple bond for nitrogen fixation.

Soil nitrogen effect on nitrogenase

High soil N prevents nitrogenase formation.

Soybean nitrogen fertilization

Soybeans should not be fertilized with nitrogen; they fix their own.

Seed inoculation purpose

Ensures the correct Rhizobia bacteria form symbiosis with legumes.

Seed inoculation species-specific

Legume-Rhizobia relationships are species-specific.

Seed inoculation timing

Seeds must be planted quickly after inoculation because bacteria don't survive long on seeds.

Haber-Bosch process definition

Industrial method to convert N₂ gas into ammonia (NH₃).

Haber-Bosch reaction

N₂ + H₂ → NH₃ under high heat, pressure, and the presence of a catalyst.

Purpose of Haber-Bosch process

Used to make synthetic nitrogen fertilizers.

Nitrate formation from ammonia

Nitrates are synthesized from ammonia and are more available to plants.

Energy use of Haber-Bosch process

Highly energy-intensive and linked to environmental issues.

Spring wheat definition

Planted in spring, harvested same year; used where winters are too severe.

Winter wheat definition

Planted in fall, overwinters, harvested in summer; yields higher.

Spring wheat main region

Mostly grown in North Dakota.

Spring wheat growing season is

shorter

Winter wheat share of U.S. production

~75% of total U.S. wheat production.

Spring wheat planting and harvest

Planted April-May, harvested mid-August-mid-September.

Winter wheat planting and harvest

Planted mid-August-October, harvested mid-May-mid-July.

Virginia winter wheat schedule

Planted mid-October-mid-November, harvested mid-June-mid-July.

Wheat growth staging scales

Feekes and Zadoks systems.

Feekes scale

Used in U.S.; simpler.

Zadoks scale

Used internationally; more detailed.

Test weight definition

Weight of grain per bushel compared to an industry standard.

Importance of test weight

Measures grain quality, fill, and market value; key for small grains.

Seed drill calibration importance

Ensures proper seeding rate for accurate planting due to variance in grain seed sizes

Effect of poor calibration on wheat yield

Improper calibration limits yield potential.

Double cropping definition

Growing two crops on the same land within one season.

Typical double-crop combo

Wheat followed by soybeans in the southern U.S.

Benefits of double cropping soybeans and WW

Year-round growth, soil health, and higher yield with lower cost.

Trend of double cropping in Virginia

Declined due to low wheat prices.

Pasture definition

Usually composed of introduced forage species.

Range definition

Composed of native species or treated as such. (American term)

Tall fescue use

Best for cattle pasture; highly persistent.

Kentucky bluegrass use

Best for horse pasture; dense sod (rhizomes + stolon), and tolerates close grazing.

Orchardgrass use

Ideal for hay; high-yielding but intolerant of short grazing.

Native warm-season grasses examples

Big bluestem, eastern gamagrass, indiangrass, switchgrass

Traits of native warm-season grasses

Drought-tolerant, productive in summer (C4), improve soil health, low fertilizer needs

Challenges of NWSGs

Slow to establish and poor competitors but valuable once grown.

Silage moisture range

60-80%.

Haylage moisture range

About 60%.

Baleage moisture range

40-60%.

Hay moisture range

Less than 20%.

Optimal corn silage harvest stage

R5 (½ milkline near early dent)

Why is r5 optimal for corn silage harvest

Ensures that enough starch has been deposited in the kernel

Hay conditioning purpose

Speeds drying by squeezing forage between rubber rollers.

Effect of conditioning on drying

Shortens drying time by 1-2 days, especially for stems.

Harvesting equipment

Usually have conditioning rollers attached

Goal for hay

Lose moisture as quickly as possible

Outdoor hay storage conditions

No vegetation, no soil contact, sunny and well-drained area

Haystack arrangement

Rows 3 ft apart, oriented north-south, dense and flat-ended.

Hay storage slope requirement

Gentle slope for drainage, away from lightning risk.

Importance of crop growth staging for management

Essential for fertilizer, pesticide, irrigation, testing, and stress decisions.

Examples of staging importance

Corn, soybean, and wheat management rely on stage timing.

Corn critical stage V12-V15

Ear size and kernel number determined; stress must be minimized.

Corn critical stage VT (tasseling)

Main reproductive parts exposed; leaf loss cannot be replaced, damage reduces yield.

Corn critical stage R2 (blister)

Kernels may abort if sugar/protein supply is low.

Corn critical stage R5 (dent)

Kernel weight accumulation; stress reduces yield by reducing kernel weight

Soybean critical stage R4

Full pod; young pods sensitive to stress and quick to abort, impacts yield

Soybean critical stage R5

Beginning seed; seeds start forming, still sensitive.

Soybean critical stage R6

Full seed; seeds are forming/filling; stress impacts yield; yield depends on rate and duration of accumulation of dry matter and nutrients

When to apply insecticide to soybean

R6

Wheat critical stage Feekes 2-3

Tillering; determines yield potential and winter survival. Apply nitrogen here. Weeds can hinder tiller production

Wheat critical stage Feekes 4-5

Determines spikelet number which affects number of seeds plant produces; nitrogen and weed control important.

Physiological maturity definition

Plant is fully grown; growth complete.

Harvest maturity definition

Crop is dry enough to harvest safely with minimal loss.

Corn seeding rate

About 30,000 seeds per acre.

Corn row spacing

30-33 inches (spacing important for high yield)

Soybean seeding rate (single crop)

80,000-100,000 seeds per acre.

Soybean seeding rate (double crop)

140,000-200,000 seeds per acre.

Soybean seeding with double cropping systems

Seeding rates cannot be cut

Soybean spacing importance

Uniform spacing increases yield, though less critical than in corn.

Wheat seeding rate

1-1.3 million seeds per acre.