Numerous states: yield-goal approach - 1.2 pounds of N per bushel for corn following corn, with credits given when corn follows a legume or where manure is applied

Nebraska and Colorado: expected yield approach - based on expected yield, the amount of residual soil nitrate-nitrogen, and soil organic matter.

Indiana, Ohio, and Michigan: yield potential and previous crop

Corn yields in the U.S. increased substantially between 1950 and 1970 for several reasons

Increased use of fertilizer, particularly N
Better hybrids
Improved technology and management
Earlier planting
Better equipment
Higher plant populations, etc

Fertilizer applications should be balanced according to SOIL FERTILITY levels.

Applications are influenced by:

RECENT CROPPING HISTORY
Grain Harvest versus Silage Harvest
SOIL TYPE
SOIL MOISTURE
SOIL pH (6.0-7.0 is desirable) pH affects nutrient availability
1. Intensive farming gradually lowers soil pH, so soils in many parts of the Midwest are limed every 4-5 years
2. Liming improves soil microbial activity, which
3. Increases nutrient availability
4. Reduces plant diseases
5. Aids in decomposition of crop residues
6. Reduces herbicide carryover problems
7. Liming also adds Ca and Mg

Levels of fertilizer elements (N, P, and K) needed for optimum yields

Corn

160-190 lbs available N/a
- Amount of N mineralized from OM in the soil:
- (% OM) (20) = lbs N mineralized/a/yr
- EX: (3.0% OM) (20) = 60 lbs N mineralized/a/yr
60-80 lbs P2O5/A
280-300 lbs K2O/A

Crop Nutrient Removal
Crop	Quantity	N	P2O5	K2O	Yield	N	P2O5	K2O
Corn grain	100 bu	90	36	26	150 bu/A	135	54	39
Corn silage	1 ton (~65% moisture)	7	24	7	20 T/A	140	48	140
Soybeans	100 bu	355	82	100	50 bu/A	178	41	50
Wheat	100 bu	125	53	31	70 bu/A	88	37	22
Alfalfa	1 ton (dry hay)	50	11	45	5 T/A	250	55	225
adapted from "The Fertilizer Handbook", The Fertilizer Institute, 1982 derived from Hoeft et al., 2000

Soil Testing

Soil tests: Field sampling of soil (5 acres/composite sample)

Tissue tests: Measures N, P and K in cell sap

Apply MANURES: Manure is often spread at a rate of 5-10 tons/a

Commercial Fertilizers

Nitrogen

Forms of N fertilizer

GAS
LIQUID
SOLID (Granular)
SUSPENSIONS

GAS - Anhydrous Ammonia (82+% N)

Advantages

High analysis of N (82%)
Doesn't leach (NH3 form)
Traditionally the least expensive type

Disadvantages

Difficult to apply
Must be knifed 6-8" into the soil
Soil conditions should be ideal
Shouldn't work the soil for 5-7 days after applying anhydrous
Anhydrous requires expensive equipment
It is stored under pressure as a LIQUID and VAPORIZES when pressure is released, so it is a GAS when it is deposited in the soil
Anhydrous is dangerous. Can burn skin critically and cause blindness. When applying, a person should wear goggles and gloves and cover all skin
Do not apply on SANDY soil

LIQUID N - Nitrogen solution (28-0-0 or 10-34-0)

Not as dangerous as anhydrous

Is incorporated, either as preplant or as starter, but not incorporated as deep as anhydrous

Is expensive, so use in Wisconsin has been somewhat localized

Useful in reduced tillage systems, as liquid starter can be placed closer to the seed than granular - important when planting early in heavy, cold soil

DRY (Granular)

AMMONIUM NITRATE (NH4NO3) 33% N

NO3 form leaches readily
Easy to handle, but difficult to store because it absorbs moisture and hardens
Requires considerable energy to produce, is expensive, and has dropped in popularity in the 1980's

UREA CO(NH2)2 46% N

N is in the ammonia form, so it doesn't leach as readily as ammonium nitrate, but can VOLATILIZE (should incorporate or be rained in within 1-2 days)
Is blended with other grades of fertilizer
Many areas have switched from ammonium nitrate to urea
Urea has a higher analysis of N
Urea is not as dusty
Urea is easier to store-doesn't absorb much moisture

Dry fertilizer at Coop's

Sold in bag or bulk form
Broadcast and incorporated or banded at planting
Most coop's keep four grades of dry fertilizer on hand
- UREA: 46-0-0
- POTASH: 0-0-60
- Triple Super Phosphate (TSP): 0-46-0
- Diammonium Phosphate (DAP): 18-46-0
These are mixed in various formulations eg. 9-23-30 is made by mixing equal amounts of 18-46-0 and 0-0-60

SUSPENSIONS

Combinations of liquid and granular

A certain amount of solid (undissolved) material is suspended in a liquid medium

Advantages

Suspensions can hold a higher analysis of N, P, and K than liquid fertilizer
(Liquid fertilizer can salt out fairly easily)
Almost any level of micronutrients can be added to suspensions

TIME TO APPLY N

FALL PLOWDOWN
SPRING PRE-PLANT
STARTER
SIDEDRESSING OR TOPDRESSING

Fall plowdown

Traditionally, many CORN BELT farmers who apply large amounts of N for corn (150-200 lbs/a) apply ½ to 2/3 of it in the fall
N should be in the NH3 form, so anhydrous or granular forms are used
Best to apply when soil temp at 2-4" depth is 50 F or cooler
NH3 will not convert to nitrate until the soil warms above 50 F the following year
NITRIFICATION INHIBITORS used if soils have high N loss potential
SANDY SOILS: Fall application of N should be avoided

Advantages of fall application

Availability of equipment is usually good
Avoids ‘spring rush', which can delay planting if the following spring is wet
Anhydrous may be cheaper in the fall

Disadvantages

Some N may be lost (Groundwater)
Although anhydrous may be cheaper, paying 6 months interest can make it more expensive

Spring pre-plant incorporated

As anhydrous, liquid, granular, or suspension
In Wisconsin, most fertilizer is applied at this time. Normally there is plenty of time between thawing and 50o soil temp's. This may not be true in areas of the corn belt that warm more rapidly in the spring.

Starter

Usually little response to starter fertilizer in Wisconsin, even in fertile soils
- exception is full season hybrids planted late
- most WI fields have had high manure rates
Growers who use starter usually apply 150 to 300 lbs/a
Placement near SEMINAL root system is necessary because plants may have difficulty absorbing nutrients from the soil early in the season
Seminal root system is small
Soil and air temp's usually are cool
Soil may be too moist for rapid root growth
Not as popular in areas of the corn belt that warm more rapidly in the spring and where farms are larger in size

EFFECT OF STARTER FERTILIZER in tillage systems

Usually have a better response to starter fertilizer as the number of tillage operations is reduced

Especially true in heavy soils
May not be true in lighter soils

Response to starter fertilizer usually decreases as fertility level increases

Sidedressing or topdressing

Sidedressing of anhydrous is usually done 2-4 weeks after emergence
Sidedressing was decreasing in the Midwest until the mid-1980's. When interest rates are high and farmers use lower rates of N to be more cost efficient, sidedressing increases in popularity

FACTORS AFFECTING TIME OF N APPLICATION


N-cycle	Ammonification and Nitrification	Nitrification	Denitrification

Form of N

NH3 - many possibilities
NO3 - during or after planting
Soil type
- Heavy versus light
- Soil type and soil temp are closely associated
- Heavier soils warm more slowly, so conversion to NO3 occurs more slowly

Amount of N applied

If applying low rates of N, time of application can have a substantial effect on yield response.
If applying high rates of N, time of application usually does not influence yield response

Soil fertility level

Soils that are low to medium in fertility may have a significant yield response when starter and/or sidedressing are used

Nitrification

Inhibitors - make timing of N application less critical

Nitrification inhibitors reduce N losses because nitrification (conversion of NH3 to NO3) is delayed
Activity of Nitrosomonas bacteria is suppressed
Most often used with anhydrous, but can also be used with liquid or solid forms of N
Most often used with fall-applied anhydrous
Results with nitrification inhibitors have been somewhat inconsistent
Usually more effective in wet years than in dry years
Response has been consistent when used on irrigated sandy soils

Slow release compounds

Supposed to improve N efficiency by reducing losses from LEACHING and DENITRIFICATION

Denitrification

Loss of oxygen and conversion to N2 gas
Occurs in water-logged soils; can lose 10 lbs N/a/day

PHOSPHORUS

Is extremely immobile in the soil

Frequently bound up and unavailable

Mineralization is slow: Only 10-20% of the P2O5 applied is used by plants in the year of application

Virtually all starter fertilizer that is applied to corn has some in it

Purpling of plants

Corn grown in wet, heavy soils that test high in P may have temporary P deficiency symptoms until soils warm enough for some mineralization to occur. Symptoms usually disappear by early June.

POTASSIUM

Soils vary in their ability to supply K depending on area of origin and rainfall

Prairie soils - tend to be high in K

Forest soils - tend to be low in K

Normally applied as KCL (= muriate of potash or potash) and K2SO4

Nutrient Management

legume crediting
manure crediting
fertilizer selection
organic nutrient amendments
application timing
application method
equipment maintenance and calibration

Soil and Water Management and Conservation

irrigation scheduling
irrigation systems
irrigation maintenance and calibration
pesticide selection
riparian zones/buffer strips "bio-curtains"
soil pH
soil quality
tillage systems

Don't apply nitrogen to soybeans. Well nodualted soybeans will fix all the nitrogen they require. It is better to inoculate the seed with Rhizobium bacteria than to apply nitrogen fertilizer.

Nutrient Requirements and Uptake by Plants

Soybean plants (as well as the symbiotic bacteria associated with them) require all of the following nutrient elements:

nitrogen (N),
phosphorus (P),
potassium (K),
sulfur (S),
calcium (Ca),
magnesium (Mg),
iron (Fe),
boron (B),
manganese (Mn),
zinc (Zn),
copper (Cu), and
molybdenum (Mo).

Most nutrients are absorbed from the soil; however part of the N is obtained from bacterial fixation in the nodules and some S is absorbed (primarily as SO2 and H2S) from the air. Soil nutrients are absorbed into the plant roots with water and move up into the plant to the leaves and other vegetative plant parts.

The amounts of nutrients available vary with

soil type,
soil test,
depth of soil, and
tillage practices.

They are influenced by soil temperature and moisture conditions.

Roots will not grow into dry soil and moisture must be present for roots to absorb nutrients from the soil. However excess moisture in the soil limits aeration, and roots also require air (oxygen).

The amounts of nutrients taken up by the plants early in the season are relatively small because the plants are small. However the nutrient concentration in individual leaves of well nourished plants are as high during this period as individual leaves later in the season. Uptake and accumulation of some nutrients in the leaves continues throughout the season until maturity; uptake of others is completed by stage.

Redistribution of mineral nutrients from older plant parts to newer growing parts is a primary source for some nutrients. Some nutrient elements are very mobile in the plants and are readily translocated from older to newer plant parts. Redistribution of N, P, and S is a primary source of these nutrients for growth of the beans and results in severe depletion of these elements in the leaves, petioles, stems, and pods during the late seed-filling period. However, some nutrients such as calcium are very immobile in the plants and there is little redistribution of these elements from older to new plant parts. Late season redistribution of mobile materials that have accumulated in leaves and other plant parts without redistribution of Ca results in increased Ca concentration in the leaves late in the season.

Redistribution of other elements in the plant generally is intermediate between the extremes for very mobile N and immobile Ca. P and S are very similar to N. K is redistributed from the vegetative plant parts to the developing seeds, but is not redistributed from the pods. Zn and Cu are redistributed but not to the same degree as N. Mn, Mg, Fe, B, and Mo are relatively immobile but not as immobile as Ca. Very marked differences in mobility of Fe have been observed among different soybean varieties.

Fertilizer Use and Fertility Management

When the soil cannot supply the plant nutrient requirements, fertilizers and/or manure can be added to supplement the nutrient supply. Uptake of nutrients added to soils is not always an efficient process. Under good conditions, the recovery in the year of application ranges from 5 to 20 percent for phosphorus and 30 to 60 percent for potassium. However, additional nutrients are recovered in future years.

Nutrients Most Commonly Deficient:

Nitrogen is fixed and made available to the plants by the bacteria in the nodules on the roots. Where soybeans have not been grown previously, inoculation is needed to supply the desired bacteria. Liming of acidic soils is usually beneficial. By making conditions favorable for N-fixation, the need for N fertilization is reduced or eliminated.
The availability of phosphorus and potassium in many soils is not adequate for optimum yields so fertilizers and/or manure to supply these nutrients should be applied where needed. Depending on soil pH, lime also may be needed.
Applications of some of the other nutrients are desirable on some soils where deficiencies exist. S, Fe, B, Mn, or Zn are the elements that are occasionally deficient.

Foliar fertilization micronutrients: Mo, Fe, Cu, B, Zn, Cl, Mn

Foliar fertilization may be effective, particularly if the soil is low in availability of one or more micronutrients

Effectiveness usually depends on soil pH. Soil pH has a major effect on availability of micronutrients reduced examples: available availability iron (fe) & below ph 6.5 above 7.0 other micronutrients molybdenum (mo) above 7.0 below 6.0.

Iron chlorosis (deficiency)

widespread in prairie soils of midwest (Iowa, Illinois, Minnesota)
frequent in high lime (calcareous) soils, particularly in cool, wet weather and poorly drained soils
infected plants are light green to yellow in color
plants may recover later in the season, but yields will be reduced
best control is resistant varieties
foliar application of sequestrene (iron chelate) is usually helpful

Molybdenum

the micronutrient that is required in the smallest amounts for plant growth
more likely to get a response if ph is < 6 because mo is tied up (unavailable) in acid soils. It differs from the other essential micronutrients in this respect.
Symptoms are light green leaves
usually applied foliarly when a deficiency occurs
molybdenum is difficult to apply with granular fertilizer because it is required in such small amounts that uniform distribution is difficult.

Soil Fertility

Yield Goal v. Yield Potential