AGVISE Phosphorus Fertilizer Guideline Options

In this current climate of high production costs for land, seed, fertilizer, fuel and equipment, it is important for growers to examine where they could decrease their costs without decreasing yield in the short term. One area that’s been written on extensively is banded phosphorus fertilizer and the importance of soil testing. Both over and under fertilization reduce grower profits. While trying to build your soil P test level may not be a good idea for 2009, you also need to make sure you are applying enough P fertilizer to achieve high yields.

AGVISE Laboratories provides four different P & K fertilizer guidelines for our customers to choose from. (See charts and tables.) Below is a short description of these guidelines and how following each guideline will affect your P soil test levels over time. Hopefully this information will help you choose which AGVISE P fertilizer guideline is best suited to your grower’s equipment and management.

AGVISE Band: The AGVISE Band guideline will build the P soil test to the medium range over 7-10 years if the initial soil test levels are in the very low or low category. If the soil test level is in the high or very high range initially, then the Band guideline rate will be less than crop removal and the P soil test will drop to the medium range over a 7-10 year period.

AGVISE Band/Maintenance: The AGVISE Band/Maintenance guideline is the same as the band guideline if the P soil test level is medium or lower. The Band Maintenance guideline will build the P soil test to the medium range over 7-10 years if the initial soil test levels are in the very low or low category. If the P soil test level is in the high or very high range initially, then the Band/Maintenance guideline rate will be calculated based on the amount of P that will be removed from the field in the harvested grain. Over time, the Band Maintenance guideline will keep the soil test level in the medium range. The soil test level will not drop because you will always be applying P at a rate equal to crop removal (to maintain the test level).

AGVISE Broadcast: The Broadcast guideline is designed to build the soil test level to the high range over a 5-10 year time frame. High pH fine textured soils will take longer to build than sandy soils and it may not be economical even at lower fertilizer prices. At low soil test levels the Broadcast guideline fertilizer rate will be about two times as high as the Band guideline. If the P soil test is in the high range initally, the Broadcast fertilizer guideline rate will be less than crop removal.

AGVISE Broadcast/Maintenance: The Broadcast/ Maintenance guideline will build the P soil test level to the high range over a 5-10 year time frame (the same as the Broadcast guideline). At low soil test levels, the Broadcast/Maintenance guideline fertilizer rate will be about two times as high as the Band guideline. If the P soil test is in the high range initially, the Broadcast/Maintenanc fertilizer guideline rate will be equal crop removal (Maintenance) based on the yield goal provided by the grower. The P soil test level will not drop over time if crop removal rates of phosphorus are applied.

University Broadcast: The University Broadcast guideline is based upon the Tri-State University fertilizer guidelines from ND, SD and MN. The University guideline is designed to supply enough broadcast phosphorus fertilizer to achieve your yield goal for that year. This is known as the “sufficiency” approach. If the P soil test is very low, the University Broadcast guideline will increase the P soil test to the medium range over many years. The P soil test will increase slowly because the University Broadcast rate is higher than crop removal. If the P soil test level is in the high or very high range initially, then the University Broadcast guideline will be less than crop removal and the P soil test will decline over time. If the P soil test is very high, the University Broadcast guideline will drop to 0, but a P starter of 10-15 lb/acre of P2O5 is still recommended for small grains and corn by University specialists. If you have a high P soil test initially, the P soil test will decline to the medium range over time following the University Broadcast guideline.

University Researchers recommend reducing the “University Broadcast” guideline rate by 50% if you can apply the phosphorus fertilizer in a band with or near the seed (seed safety should always be considered). A starter rate of 10-15lb/ac P2O5 is always recommended for small grains and corn.

AGVISE Phosphorus Fertilizer guidelines - 1 AGVISE Phosphorus Fertilizer guidelines - 2

Small Grains Strategies

NDSU Extension Soils Specialist, Dr. Dave Franzen states in a recent article “Phosphate-To Build or Not to Build” that at current P prices ($1/lb of P2O5) it would not be economical to build P soil test levels, even if wheat is $8/bu. If P costs drop to $0.50/lb, then it would be profitable to build the soil to 10 ppm (medium) (Olsen P test). He also states that University research shows that for wheat, banded P has a 2 to 1 efficiency over broadcast P. His recommendation is to reduce the University Broadcast recommendation 50% when banding P near the seed at planting (If the P soil test is medium or lower.). N + K20 should not exceed 25-30 lb/acre when placed in direct contact with the seed when row spacing is 6 or 7 inches.

Corn Strategies

Even with the higher gross returns of corn compared to small grains, corn growers can band lower rates of P in years of high cost fertilizer and not sacrifice yield, if the P soil test is medium or higher. Dr. George Rehm, retired U of M Extension Soil Scientist states that University Broadcast rates can be cut in half if P fertilizer is banded with or near the seed at planting without losing yield. The band must be no more than 2 inches away from the seed to get the starter affect. Maximum N + K20 in a band in contact with the seed at planting should not exceed 10-15 lb/acre. Rates of 7-8 gallons of 10-34-0 with the seed will not to cause emergence or stand establishment problems, unless the soil becomes dry and is a light sandy texture. If a shortage of 10-34-0 develops this spring, you should prioritize which fields get the higher rates of 10-34-0. The first priority should be corn on corn followed by corn on soybean situations. He also states that research has shown that when applied in equal amounts of nutrients/acre, liquid and dry P fertilizer products perform the same. The choice for liquid or dry is based upon the growers’ planter equipment.

Comparison of P Fertilizer Guideline Rates
Corn Yield Goal of 160 bu/a

Soil Test level
Soil Analysis
Method
V Low
P soil test
Low
P soil test
Medium
P soil test
High
P soil test
Very high
P soil test
Very high
P soil test
Olsen P test method 0-3 ppm 4-7 ppm 8-11 ppm 12-15 ppm 16-19 ppm >19 ppm
Bray 1 P test method 0-5 ppm 6-10 ppm 11-15 ppm 16-20 ppm 21-25 ppm >25 ppm
P fertilizer
Guideline choice
P2O5 lb/acre
University Broadcast **100 **70 40 15 *15 *15
AGVISE
Band
85 65 50 35 *15 *15
AGVISE
Band/Maintenance
85 65 65 65 65 65
AGVISE
Broadcast
145 120 95 75 50 *15
AGVISE
Broadcast/Maintenance
145 120 95 75 65 65

* = To be applied as a starter, with or near the seed   ** = can be reduced by 50% if banded near the seed

Comparison of P Fertilizer Guideline Rates
Wheat Yield Goal of 60 bu/a

Soil Test level
Soil Analysis
Method
V Low
P soil test
Low
P soil test
Medium
P soil test
High
P soil test
Very high
P soil test
Very high
P soil test
Olsen P test method 0-3 ppm 4-7 ppm 8-11 ppm 12-15 ppm 16-19 ppm >19 ppm
Bray 1 P test method 0-5 ppm 6-10 ppm 11-15 ppm 16-20 ppm 21-25 ppm >25 ppm
P fertilizer
Guideline choice
P2O5 lb/acre
University Broadcast **55 **40 25 15 *15 *15
AGVISE
Band
50 40 30 25 *15 *15
AGVISE
Band/Maintenance
50 40 35 35 35 35
AGVISE
Broadcast
95 80 60 45 30 *15
AGVISE
Broadcast/Maintenance
95 80 60 45 35 35

* = To be applied as a starter, with or near the seed   ** = can be reduced by 50% if banded near the seed