Transcript Unit 7: Major Agronomic Crops

Unit 7: Major
Agronomic Crops
Chapter 17
Unit 7: Major Agronomic Crops
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Unit 7 Objectives:
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Genetic and environmental factors affecting
production of corn, soybeans, etc.
Growth requirements
Understand the importance of crop rotation
and its implications
Identify pests and the need for their control
Unit 7: Major Agronomic Crops
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Corn
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A.k.a Maize
Several varieties of corn
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Key factors of a successful system
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Dent, sweet, popcorn, etc.
Recognize and understand the types of interactions
that occur among production factors, and what limits
yield
Develop management systems that maximize the
benefits of those interactions
Knowledge of growth and development factors
is essential
Unit 7: Major Agronomic Crops
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Temperature
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Can survive brief adverse temps
 Low ~32, high ~112
 Growth decreases when temps are <41 or >95
 Optimal range 68 – 73
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Planting Date
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Recommended planting date – mid-April to mid-May
100-150 GDD’s needed for emergence
Seed treatments and seed vigor may survive up to 3
wks if soil conditions are not excessively wet
50º temp at ½ to 2” depth indicates enough warmth
for planting
 Germination is very slow at lower temps
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Latest planting date without much reduced yield June
15th to July 1st
Plant only in dry conditions
 “Mudding in” will decrease yield greater than waiting
for dryer conditions
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No-till can be planted at the same time as
conventional
Plant long-day varieties first
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Spread workload
Reduce widespread disease risk
Increase chance of pollination of some varieties
Increase harvest window
Unit 7: Major Agronomic Crops
 Planting delays or replanting may necessitate a change
in variety selection
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Seeding Depth
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Varies w/ soil and weather conditions
Normal conditions
 ½ to 2” depth provides frost protection, allows for
adequate root development
 Shallower planting – poor root development
 Early planting – no deeper than 1 ½” depth
because of increased moisture
 As evaporation rates increase and soil warms can plant
deeper
Unit 7: Major Agronomic Crops
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Row Width
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Most perform well in 30” rows
15-20” rows can increase yields by 3-5%
 Both in moderate and high planting populations
 Both high and moderate yields
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Must match equipment to row spacing
Plant Populations and Seeding Rate
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Grain production
 20-30,000+ plants/ac depending on hybrid and
environment
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Corn silage production
 May increase another 2-4,000 plants/ac
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Newer varieties may require >24,000 to reach yield
potential
Unit 7: Major Agronomic Crops
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Seed companies usually recommend seeding rates
Higher seeding rates only recommended for sites w/
high yield potential, high soil fertility, high waterholding capacity
Uneven spacing & emergence may reduce yield
potential
 Uniform spacing is critical
 Crowding will result in too much competition and
barren ears, lodging
 Taller plants cause difficulties for smaller plants
 Reasons for delayed emergence
 Soil moisture variability
 Poor seed-to-soil contact
 Malfunctioning planter
 Soil temp variability
Unit 7: Major Agronomic Crops
Soil crusting prior to emergence
 Herbicide injury
 Insect or soilborne disease pressure
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Replanting
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10-15% usually fail to establish healthy stands
 Number increases as season progresses w/ insects,
weather, etc.
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Corn is very able to grow out of damage
 Growth point is below ground until ~6 leaf stage
 If leaf growth resumes, plant will produce as normal
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Making the decision
 Planting date and stand
 Earliest possible replant date and stand
 Cost of seed & pest control
Unit 7: Major Agronomic Crops
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Pests
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Insects
 Earworm, corn borer, aphids, cutworm, etc.
 Controlled by insecticides from tassel emergence
through grain drying
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Diseases
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Southern leaf blight, northern leaf blot, diplodia rot
Select disease resistant varieties
Improve management
May use fungicides
Unit 7: Major Agronomic Crops
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Fertilizer Requirements
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Vary according to soil tests
Corn removes:
 N, P, K, micros
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Must be supplied in a fertilization program
Crop Rotations
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Corn-SB most common rotation in the Midwest
Many advantages over growing each continuously
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More weed control options
Fewer difficult weed problems
Less disease and insect buildup
Less N fertilizer use
Corn following SB typically yields 10% more than
continuous corn
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No-till corn is better following SB than other crops
 More pronounced advantage in droughty years
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Soybeans
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Planting Date
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Has more effect on yield than any other production
practice
 Delayed planting can decrease yields from ¼ to 1
bu/ac/d
 Depends on row width, date, plant type
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Canopy should develop by flowering or end June
(whichever comes first)
 Regardless of planting date, row width, plant type
 Row width <15” if planting in early May to canopy by
June 30
Unit 7: Major Agronomic Crops
 Early canopy increases grain yield
 More sunlight converted to grain production
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Vigorous stands difficult to establish if planting too
early
 Seed treatments, good seed-soil contact, reduced
seeding depth may help
 Herbicide must control weeds longer
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Row Spacing
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Average row width <12
 For any planting date, variety, or seeding rate:
 Yields increase as row width decreases b/c of early
canopy formation
 1/3 bu/ac increase/inch of row reduction below 30”
Unit 7: Major Agronomic Crops
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Grain drills are as effective as bean planters
 Must remove wheel tracks if tillage is used
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Seeding Rate
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Not very responsive to changes in seeding rates
>250,000/ac
 Tall plants
 Weak stalks
 Lodging
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<60,000/ac
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Short
Many branches
Pods too close to soil surface
High harvest losses
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Seeding rates producing a harvest population of 80140,00/ac adequate if planting is before May 15
Delayed planting shoot for 100-160,000/ac
Uniform spacing is critical
 Yield losses can be 5% if spacing is not proper and
uniform
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Rapid growth early in the season critical for high
yields
 Height doesn’t increase after flowering
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Planting Depth
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1-1 ½” ideal when tillage is used
¾ to 1” for no-till
 Better for later planting times also
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No large clods in the soil
Unit 7: Major Agronomic Crops
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Deeper planting increases the risk of soil crusting and
reduced emergence
Combined pressure of many plants needed to emerge
 If hypocotyl breaks, seedling will not emerge
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Variety Selection
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Most varieties have genetic yield potentials well over
100 bu/ac
Environment & production system sets the yield
 Select a variety that matches the system rather than
just selecting for yield
 Smaller seeds if using a grain drill will improve
metering and stand uniformity
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Each 10d delay planting in May decrease maturity by
3-5d in the fall
Unit 7: Major Agronomic Crops
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Disease Control
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Phytophthora root rot is a major problem anywhere
SB are planted
 Most susceptible in the seedling stage
 Saturated soils w/ temps >60 increase risk
 Don’t grow susceptible varieties in wet or poorly
drained soils
 Use seed treatments for control, or resistant varieties
w/ seed treatment
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Pythium & Rhizoctonia
 Damage greatest on poorly drained soils and high
rainfall seasons
 Controlled by fungicide seed treatments
Unit 7: Major Agronomic Crops
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Sclerotinia stem rot
 Severe if wet weather during flowering
 No known resistance, some varieties more suscpetible
 Water soaked lesions, cottony growth, black irregular
shaped sclerotia
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Brown stem rot
 Can severely reduce yield
 Enters through roots and grows through xylem w/ plant
 Interferes w/ water flow
 Symptoms develop after flowering
 Internal browning of the stem in August
 Foliar symptoms are rare
 Leaves may wilt and stay attached to the plant
Unit 7: Major Agronomic Crops
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Phomosis seed rot
 Occurs when rainfall is intermittent during dry-down
and harvest
 Incidence increases as grain remains in the field after
ripening
 Use varieties that will increase the timeliness of harvest
 Can be decreased w/ crop rotation
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Soybean Cyst Nematode
 Found in the south in early 1950’s
 Has migrated to the Canadian border
 Symptoms
 Can be easily confused w/ other problems
 Usually circular patterns of stunted yellow plants
 Evident in July or August when drought stressed
Unit 7: Major Agronomic Crops
May see symptoms under normal conditions if SCN
population is high
 May increase in size in the direction of tillage each
yr.
 Laboratory analysis required for identification
 Roots may be stunted and have few rhizobium
nodules
 Detection of SCN
 Sample suspect soils
 May see females on roots, but must identify larvae
in soil samples
 Many nematodes exist, not all are bad
 Sample from top 4” of soil
 Follow sampling recommendations on suspect fields
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Unit 7: Major Agronomic Crops
 Control of SCN
 No control method will eradicate SCN completely,
just decrease yield loss risk
 Prevent introduction of SCN – SCN can only move
few inches/yr on their own, may only move long
distances on equipment
 Crop Rotation – nonhost plants can decrease SCN
population – high risk, 3yrs. Nonhost between SB
 Resistant Varieties
 Nematicides – only one has proven effective
 Fertility – good fertility will decrease yield losses
from SCN
 Planting Date – Early planting can reduce yield
losses, roots develop before SCN becomes active
Unit 7: Major Agronomic Crops
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Tillage
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Soil should be smooth, somewhat fine to promote
quick emergence
Avoid compaction that restricts root growth
Type and amount of tillage has little effect, end result
is key
Rhizobium Inoculation
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Can help fix nitrogen more quickly
Should be inoculated at planting time
Consider if SB have not been planting in >5 yrs.
Unit 7: Major Agronomic Crops
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Wheat
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Variety Selection
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Should be based on winter hardiness, standability,
disease resistance, yield potential
Planting date has the greatest effect on winter
survival
Yield potential usually >150 bu/ac
 Usually not approached because of short grain fill
period during high air temps in June
 Ideal air temp at grain fill 68-76º
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Disease must be controlled to get high yields
 Use resistant varieties and fungicides
Unit 7: Major Agronomic Crops
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Seeding Date
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Never seed prior to “fly-safe date”
 Possible severe damage by the Hessian fly
 Best time is 14d period after fly safe date
 Provides for ample growth before winter
 Reduces likelihood of disease infections
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Seeding Rate
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Too heavy will increase lodging and disease
 Decreases seed size
 Increases harvest lodge
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Rates should be based on seeds/ft. of row rather than
lbs/ac
 13-20 seeds/ft of row recommended at normal seeding
date
Unit 7: Major Agronomic Crops
 1-1.5 m seeds/ac is ideal seeding rate
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Row Width
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7” is common
May be 10” to allow for residue movement
>10” will decrease yields
Lodging Control
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Serious deterrent to high yields
Apply proper N rates
Select lodging resistant varieties
 Increased lodging will increase incidence of disease
 Reduces straw quality
 Slows harvest
Unit 7: Major Agronomic Crops
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Disease Control
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Usually major limiting factor in yield potential
 Losses can be 30-50% if no disease controls are used
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Correct diagnosis is key
Select resistant varieties
Plant well-cleaned, disease-free seed, treated w/
fungicide
Plant in well-prepared seedbed after fly-safe date
Rotate crops, never continuous wheat
Plow down diseased residues
Well-balanced fertility program
 Top-dress N in the spring
Unit 7: Major Agronomic Crops
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Control grass
Use fungicides only when necessary
 Scout from flag leaf through flowering
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Head scab is a risk when no-tilling after corn
 Same pathogen causing stalk rot and head scab
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Seed treatment should be used
 Controls many diseases
 Protect young seedlings as they establish themselves
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Fertilization
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N
 Important step to high yields
 As N increases, risk for lodging and disease increases
 N needs may vary greatly depending on previous crop,
etc.
Unit 7: Major Agronomic Crops
 Each 1% organic matter provides 8-12 lbs N/ac
 Previous SB crop can provide 30-40 lbs N/ac
 Spring N should be applied between Mar. & Apr. 15
 Should be applied before spring growth starts to
stimulate tillering and promote larger head growth
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P
 Soil P should be 90 lbs/ac or higher
 1:4:2 ratio should provide good starter fertilizer
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K
 Maintain soil level of 275 plus 5x the CEC for optimum
yields
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No-till Wheat
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Smoot seedbed, proper seeding depth and date,
absence of carryover herbicides, proper seed
treatment
Unit 7: Major Agronomic Crops
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Normally follows SB in rotation
Doesn’t grow well in poorly drained soils, especially
during wet conditions
Major cause of stand loss is standing water
Don’t no-till in fields that were harvested (SB) wet
Spread soybean straw and chaff evenly so as not to
interfere w/ seeding
Place seed 1” deep through residue
 Seeds must be covered
 Slit must be closed
 Exposure will decrease stands, disease, and injury
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Don’t drive too fast
 Never exceed 5 mph
Unit 7: Major Agronomic Crops
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Disease severity decreases when tillage is removed
from the production scheme
Reduces production costs, retains soil moisture
Management
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Determined by three factors
 Varieties genetic potential
 Management practices
 Environment or weather
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All must be optimized to get maximal yields
Steps to increased wheat yields
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Highly productive and fertile soils
High yield potential varieties
Proper seeding time
Proper seeding rates and stiff straw varieties
Unit 7: Major Agronomic Crops
 Adequate nutrient presence
 Control disease
 Scout weekly from April - June