Eliminate starter phosphorus fertilizer on fields with elevated soil test P - dairy farm
Case study: dairy operation
The purpose of this case study is to demonstrate the economic and environmental value of eliminating phosphorus (P) from starter fertilizer when soil test P is excessive.
This dairy farm in Central Minnesota has 360 head of Holstein cows with a DHIA Rolling Herd Average of 26,000 pounds on 2X milking. The milking cows, replacement heifers, and a few steers give them an average of 752 Animal Units. The cows, older heifers, and far-off dry cows are housed in sand bedded freestalls; the younger heifers and close-up cows are on conventional bedding packs. This dairy farm has 562 harvested and tilled acres with mostly Sandy Loam and some Loamy Sand type soils, of which 305 acres are under center pivot irrigation. They purchase their alfalfa and grass hay, wheat straw, and some of their corn needs. This dairy has a two-stage earthen liquid manure pit and also has a sand lane for separating sand from the manure.
Phosphorus import-export analysis:
Feed supplements are purchased, and the total phosphorus (P) in the lactation ration is .41%. The only P fertilizer used is 2.5 gal/acre of a 10-34-0 liquid corn starter. 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. The farm has an annual excess of P imports over exports of 19.8 lb. per acre or 14.8 lb. per animal unit as shown on following table. That annual excess is the equivalent of 45 lb. per acre of phosphate (P2O5), which has the effect of increasing already very high soil test P. It is likely that several strategies will be needed to Sand Lane reduce the P import/export imbalance, however the focus of this case study is discontinuation of application of P fertilizer.
|Animals||0||2311||Harvested acres||Animal Units||Ratio|
|Protein/Minerals||16,819||0||Excess P (lb.)||Harvested acres||Ratio|
|Manure||0||0||Excess P (lb.)||Animal Units||Ratio|
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 no point in any of these field trials was there any visual or measurable height differences between treatments.
Corn Silage Yield, tons/acre
|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 2.5 gal/acre or 29.13 lb./acre of liquid 10-34-0 starter. This is 9.9 lb./acre of P2O5 which calculates to 4.26 lb. actual P/acre. The table below shows import/export balance when the P in corn starter is eliminated. The net effect is to lower the P balance by 2.9 lb. P/Acre and 2.2 lb. P/animal unit.
Phosphorus Balance without Starter Fertilizer P
|Animals||0||2311||Harvested acres||Animal units||Ratio|
|Protein/Minerals||16,819||0||Excess P (lb.)||Harvested Acres||Ratio|
|Manure||0||0||Excess P (lb.)||Animal Units||Ratio|
The 2.5 gallons/acre of 10-34 liquid corn starter on this farm is lower than many farmers use. A more normal usage rate is probably 5 gallons/acre and some farmers use up to 7.5 gallons/acre, which would have further increased the excess total P applied. Additional strategies will need to be employed on this farm to lower the P balance enough to prevent continued escalation of soil P.
By eliminating the corn starter we save this farm $3670 or $9.36/acre of corn when the price of 10-34-0 is $630/ton. In addition, there are associated costs savings such as labor, cost of maintaining and operating the liquid starter system, and storage of the liquid starter.
- Phosphorus is needed for crop production.
- When soil P levels are below 21 ppm Bray 1-P, UM guidelines suggest P fertilizer in a conventional crop program.
- When soil P levels are above 25 ppm Bray 1-P, no P fertilizer is recommended.
- Eliminating P in the corn starter when soil tests are above 25 Bray 1-P will save input costs.
- 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.
- Kaiser, Lamb, Eliason, 2011, "Fertilizer Guidelines for Agronomic Crops in Minnesota", University of Minnesota Extension.
- Rehm, Randall, lamb, Eliason, 2006, "Fertilizing Corn in Minnesota", University of Minnesota Extension