Unit 7: Major Agronomic Crops
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Transcript Unit 7: Major Agronomic Crops
Unit 7: Major
Agronomic Crops
Chapter 17
Unit 7: Major Agronomic Crops
Unit 7 Objectives:
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
Corn
A.k.a Maize
Several varieties of corn
Key factors of a successful system
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
Temperature
Can survive brief adverse temps
Low ~32, high ~112
Growth decreases when temps are <41 or >95
Optimal range 68 – 73
Planting Date
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
Unit 7: Major Agronomic Crops
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
No-till can be planted at the same time as
conventional
Plant long-day varieties first
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
Seeding Depth
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
Row Width
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
Must match equipment to row spacing
Plant Populations and Seeding Rate
Grain production
20-30,000+ plants/ac depending on hybrid and
environment
Corn silage production
May increase another 2-4,000 plants/ac
Newer varieties may require >24,000 to reach yield
potential
Unit 7: Major Agronomic Crops
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
Replanting
10-15% usually fail to establish healthy stands
Number increases as season progresses w/ insects,
weather, etc.
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
Making the decision
Planting date and stand
Earliest possible replant date and stand
Cost of seed & pest control
Unit 7: Major Agronomic Crops
Pests
Insects
Earworm, corn borer, aphids, cutworm, etc.
Controlled by insecticides from tassel emergence
through grain drying
Diseases
Southern leaf blight, northern leaf blot, diplodia rot
Select disease resistant varieties
Improve management
May use fungicides
Unit 7: Major Agronomic Crops
Fertilizer Requirements
Vary according to soil tests
Corn removes:
N, P, K, micros
Must be supplied in a fertilization program
Crop Rotations
Corn-SB most common rotation in the Midwest
Many advantages over growing each continuously
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
Unit 7: Major Agronomic Crops
No-till corn is better following SB than other crops
More pronounced advantage in droughty years
Soybeans
Planting Date
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
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
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
Row Spacing
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
Grain drills are as effective as bean planters
Must remove wheel tracks if tillage is used
Seeding Rate
Not very responsive to changes in seeding rates
>250,000/ac
Tall plants
Weak stalks
Lodging
<60,000/ac
Short
Many branches
Pods too close to soil surface
High harvest losses
Unit 7: Major Agronomic Crops
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
Rapid growth early in the season critical for high
yields
Height doesn’t increase after flowering
Planting Depth
1-1 ½” ideal when tillage is used
¾ to 1” for no-till
Better for later planting times also
No large clods in the soil
Unit 7: Major Agronomic Crops
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
Variety Selection
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
Each 10d delay planting in May decrease maturity by
3-5d in the fall
Unit 7: Major Agronomic Crops
Disease Control
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
Pythium & Rhizoctonia
Damage greatest on poorly drained soils and high
rainfall seasons
Controlled by fungicide seed treatments
Unit 7: Major Agronomic Crops
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
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
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
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
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
Tillage
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
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
Wheat
Variety Selection
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
Disease must be controlled to get high yields
Use resistant varieties and fungicides
Unit 7: Major Agronomic Crops
Seeding Date
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
Seeding Rate
Too heavy will increase lodging and disease
Decreases seed size
Increases harvest lodge
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
Row Width
7” is common
May be 10” to allow for residue movement
>10” will decrease yields
Lodging Control
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
Disease Control
Usually major limiting factor in yield potential
Losses can be 30-50% if no disease controls are used
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
Control grass
Use fungicides only when necessary
Scout from flag leaf through flowering
Head scab is a risk when no-tilling after corn
Same pathogen causing stalk rot and head scab
Seed treatment should be used
Controls many diseases
Protect young seedlings as they establish themselves
Fertilization
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
P
Soil P should be 90 lbs/ac or higher
1:4:2 ratio should provide good starter fertilizer
K
Maintain soil level of 275 plus 5x the CEC for optimum
yields
No-till Wheat
Smoot seedbed, proper seeding depth and date,
absence of carryover herbicides, proper seed
treatment
Unit 7: Major Agronomic Crops
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
Don’t drive too fast
Never exceed 5 mph
Unit 7: Major Agronomic Crops
Disease severity decreases when tillage is removed
from the production scheme
Reduces production costs, retains soil moisture
Management
Determined by three factors
Varieties genetic potential
Management practices
Environment or weather
All must be optimized to get maximal yields
Steps to increased wheat yields
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