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Extension > Agriculture > Manure Management and Air Quality > Manure Application > Eliminate starter phosphorus fertilizer on fields with elevated soil test P - beef feedlot

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Eliminate starter phosphorus fertilizer on fields with elevated soil test P - beef feedlot

Case study: beef feedlot

The purpose of this study is to demonstrate the economic and environmental value of eliminating phosphorus (P) from starter fertilizer when soil test P is excessive on a beef finishing operation.

Farm description:

This Minnesota beef finishing operation feeds out about 800 heads of Holstein steers/year from about 500 pounds to finish, with an average of 352 Animal Units. Housing for all the animals is in a mono-slope barn. This farm has 555 harvested and 551 tilled acres with Loam type soils. All cropland is dry-land production. They routinely sell some soybeans, corn grain, and alfalfa hay each year.

Mono-slope barn

Phosphorus import-export analysis:

This farm purchases feed supplements and the total phosphorus (P) in the lactation ration is 0.39%. The phosphorus fertilizer used is 5.25 gal/acre of a 10-34-0 liquid corn starter. Other fertilizers used are urea, potash, ammonium sulfate, and some 18-46 for alfalfa establishment. All manure produced on the farm is applied to the fields based on nitrogen needs and no manure is imported or exported. Most of the farm's soil tests are greater than 70 ppm Bray 1-P, however current P imports exceed exports by only 3.6 lb. P/harvested acres and 5.1 lb. P/Animal Unit (see table below). This indicates that the net imports were at one time much higher, given the very high soil test values. When soil test values are this high or higher, there is a risk of significant levels of P in runoff, so stabilizing or reducing them is desirable. This case study will demonstrate the effect of eliminating P fertilizer applications as one strategy for balancing P imports with exports.

Phosphorus Balance

Phosphorus (lb.)

Ratios

P Source Imports Exports Excess Harvested acres Animal units Ratio
Animals 2937 5886 555 124 4.5
Forages 0 2153
Grains 0 1776 Excess P (lb.) Harvested acres Ratio
Protein/Minerals 5386 0 2009 555 3.6
Starter Fertilizer 3105 0
Other Fertilizer 396 0 Excess P (lb.) Animal Units Ratio
Total P 11,824 9815 2009 2009 392 5.1

Corn starter P background:

Adequate soil P is important for proper growth and production of agronomic crops. University of Minnesota research indicates that when soil P levels are less than 21 ppm Bray 1-P, corn yield may respond to additional P fertilizer1. Past work has also indicated that in a cold wet spring, plant uptake of soil P may not be adequate. Utilizing starter fertilizer containing P may get the corn off to a better start and result in a higher crop yield2 when soil test P is not excessive. University of Minnesota P guidelines indicate that no phosphate fertilizer is suggested in starter or other applications if the soil test for P is higher than 25 ppm Bray 1-P.

Using P starter on high P testing soils:

In 2012, 2013 and 2014 farm trials were conducted in Central MN on fields testing greater than 100 ppm Bray 1-P. Results are shown in the table below. A statistical analysis across all trials indicated no advantage to applying starter fertilizer containing P. 2013 and 2014 were both very cool and wet in May. At not point in any of these field trials was there any visual or measurable height difference between treatments.

Corn Silage Yield, tons/acre

Farm A

Farm B
Year 2012 2013 2014 2014
Starter 29.4 20.9 17.4 15.4
No Starter 29.4 24.3 16.9 14.3
Starter 27.4 20.3 17.4 16
No Starter 24.3 22.9 15.4 16
Starter 19.7 16
No Starter 16.3
Starter 15.1
Starter Ave 28.4 20.3 17.4 15.6
No Starter Ave 26.9 23.6 16.2 15.5

Effect of removing the P in the corn starter on the import/export imbalance:

This farm applies 5 gal/acre or 58.4 lb./acre of liquid 10-34-0 starter. This is 19.9 lb./acre of P2O5, which is 8.6 lb./acre of actual P. Elimination of the corn starter would change the total annual net import of 2009 lb. P to a next export of 1096 lb., or 2.0 lb./harvested acre, which is very near net zero. While the very high soil tests would not significantly decline at this rate, they would be closer to stabilization.

Phosphorus Balance without P Starter Fertilizer

Phosphorus (lb.)

Ratios

P Source Imports Exports Excess Harvested acres Animal units Ratio
Animals 2937 5886 555 124 4.5
Forages 0 2153
Grains 0 1776 Excess P (lb.) Harvested acres Ratio
Protein/Minerals 5386 0 -1096 555 -2.0
Starter Fertilizer 0 0
Other Fertilizer 396 0 Excess P (lb.) Animal Units Ratio
Total P 8719 9815 -1096 -1096 392 -2.8

Economic analysis:

By eliminating the corn starter fertilizer, we save this farm $6697 or $18.15/acre when using a 10-34-0 priced at $630/ton. In addition, there would also be savings of the associated costs for labor and maintenance of the liquid starter storage and application equipment.

Conclusions:

  1. Phosphorus is needed for crop production.
  2. When soil P levels are below 21 ppm Bray 1-P, UM guidelines suggest P fertilizer in a conventional crop program.
  3. When soil P levels are above 25 ppm Bray 1-P, no P fertilizer is recommended.
  4. Eliminating P in the corn starter when soil tests are above 25 Bray 1-P will save input costs.
  5. Eliminating or reducing P in the fertilizer on this farm would come closer to stabilizing the high soil test P and reduce the risk of P in runoff.

References:

  1. Kaiser, Lamb, Eliason, 2011, "Fertilizer Guidelines for Agronomic Crops in Minnesota", University of Minnesota Extension.
  2. Rehm, Randall, lamb, Eliason, 2006, "Fertilizing Corn in Minnesota", University of Minnesota Extension
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