Fertilizer Forms and Placement

Chapter 6 in Lecture Manual

Fertilizer grade definition

the legally guaranteed minimum analysis of a nutrient present in the material

Fertigation Definition

the application of soluble fertilizer materials through an irrigation system

What does the the three number designation for fertilizer grade mean?

N-P-K

N = % total N by weight

P = % available P2O5 by weight

K = % water soluble K2O by weight

Called the grade of fertilizer

Explain the nutrient expression vs. actual available nutrient forms.

The nutrient form expressed on the label isn’t the plant available form.

• On label: N - P2O5 - K2O

• Plant available:

  • NO₃⁻ or NH₄⁺

  • H₂PO₄⁻ or HPO₄²⁻

  • K+

Explain the basic nutrient formula calculation with components.

NA = W*G

NA - Nutrient Applied, refers to the actual nutrient you are needing (N, P2O5, K2O)

W - weight, refers to the amount of material you are applying (MAP, DAP, UAN, Urea)

G - grade, decimal form of the %, refers to the amount of nutrient in the material

Also commonly use W = NA/G

Explain transformation of fertilizer materials after application

Nitrogen: hydrolysis, ammonification, nitrification, volatilization, leaching, denitrification

Phosphorous: Dissolution, adsorption (fixation), precipitation, microbial immobilization

Potassium: Dissolution, cation exchange, fixation, release, leaching

Explain mobility of nutrients in soil and how this influences placement strategies

Broadcast

• Incorporation is necessary for fertilizer applications of nutrients that move by diffusion (P,K,micros)

• Top dress relies on leaching for effectiveness. Use with N, Cl, or S.

Concentrated Placement

• Side dress after emergence, relies on leaching to reach root zone, effective for split applications of Nitrogen and Sulfur

• Concentrated placement includes strip till, 2×2, diffusion subsurface placement, and seed placed fertilizer application methods

Explain the density conversions of liquid fertilizers

1. Calculate weight units using NA = W*G

2. Convert calculated weight to volume units by using density conversions

Example: We figured we need 74lbs of 10-34-0 fertilizer. Take 74/ 11.6 = 6.4 gallons needed

• 11.6 is the given conversion factor in the situation

Explain effective fertilizer application methods and crops/systems for which they are appropriate

• Broadcast pre-plant: good for narrow row crops and establishing forage and hay systems

• Broadcast top dress: applied to a standing crop, used on legume and grass pastures and hay crops

• Concentrated placement side dress: applied to crops in wide rows during the growing season, good for split apply

• Diffuse Subsurface placement: good for cereals and soybeans grown in tilled fields

• 2×2: most effective for nutrient that move by diffusion, protects the seed

Explain the differences in starter fertilizer methods and advantages

Diffuse subsurface Placement: can apply all nutrients, no restriction on fertilizer quantity, shovel places fertilizer 1-3” deep and 2-4” horizontally

2×2: avoids direct contact between seeds and fertilizer, most effective for nutrients that move by diffusion, fertilizer is placed 2” below the seed and 2” to the side

Seed placed fertilizer: low fertilizer rates can be applied, may harm seedling, fertilizer is placed in seed trench

Explain the risk factors associated with a seed-placed fertilizer application

Fertilizer’s high salt content may pull moisture away from the seeding and damage the young plant.

Explain effective timing of fertilizer and amendment types and conditions

Rainfed Crops (dry land): apply limestone in the fall when possible, apply nutrients that move with diffusion in the fall or early spring, apply Nitrogen fertilizer in the Spring (split application recommended for row crops)

Irrigated Crops: split apply N fertilizer in the spring (2 or 3 applications), soluble fertilizer can be applied when needed

Explain how marketing claims and burden of proof need to be compared

Marketing claim are designed to get you to buy the product, may not be as good as it sounds. Don’t rely on personal testimonies or eye catching slogans.

Burden of Proof is data from reputable, replicated trials repeated over several years to establish economic efficacy

Use the burden of proof data when thinking about buying a product based on marketing claims.

Fertilizer grade of Urea

46-0-0

Fertilizer grade of Anhydrous Ammonia

82-0-0

Fertilizer grade of Urea ammonium-nitrate (UAN)

28-0-0

Fertilizer grade of potash

0-0-60

Fertilizer grade of monoammonium-phosphate (MAP)

11-52-0

Fertilizer grade of diammonium-phosphate (DAP)

18-46-0