Risk Management can be defined as either taking steps to prevent losses from happening or mitigating the risk through insurance or other means. On a dairy farm, phosphorus risks take two forms: Animal health and environmental.
From the animal health perspective, you can easily modify the animal's phosphorus (P) intake with a combination of forage analysis and ration balancing. If high P forages are common on your operation, then it may be time to look at some cropping management strategies to reduce this level. These include, but are not limited to:
! Feed segregation. Identify which fields produce high P forages, and store these forages in a different bunker, bag, or silo from the rest. Mix with lower P forages to make ration balance.
! Rent low soil test P fields. If all of your fields produce high P forages, then it may be time to look at renting land with lower P soil test values.
! Read the tag. Mineral supplements, feed additives and other products may have a small amount of phosphorus. Ignoring this small amount may cause problems if you are trying to fine-tune your system.
This type of open loop cycling is not considered efficient, as the potential for nutrient losses (particularly nitrogen and phosphorus) are very high. Combined with a farming practice of applying commercial fertilizers equal to or exceeding crop removal, this has led to a significant buildup of both phosphorus and potassium in the soils of livestock farms around Wisconsin. (Combs, 1996).
Since 1974, soil test phosphorus levels in Wisconsin have been on the increase. From 1974 until 1990, average soil test P levels in Wisconsin increased by 1 ppm per year. Between 1990 and 1994, the rate of increase fell to only 2 ppm/year. Statewide, soil test P levels average 50 ppm. (Combs)
This increase is evident here in NE Wisconsin as well. Looking at the data from two local counties, we see a significant increase in both P and K levels over the past 25 years.
1974 - 1977 1990 - 1994 % Increase
County P K P K P K
Outagamie 25 90 45 135 56% 67%
Brown 27 87 38 124 71% 70%
Since it takes ~8 lbs of actual P to increase soil test P by 1 ppm (this figure can vary based on soil type), it is readily apparent that overapplication (and overfeeding) is occurring statewide.
Current P Management Strategy
From a P perspective, one major flaw in the Wisconsin strategy is that manure applications are guided by the nitrogen need of the subsequent crop. Since crop need for nitrogen is 300-400% higher than the need for phosphorus while manure N concentrations are only 200% of P concentrations, excess P is deposited in the soil. Over time, a significant buildup can occur.
Crop Removal Chart (actual Nutrients)
Crop N P K
Corn, 140 bu 154 24 29
Corn Silage, 20 ton 154 37 104
Alfalfa, 4 ton 240 23 166
Soybean, 40 bu 115 15 33 (Kelling)
Manure, 16,000 gal 160* 99 336
* figure reflects 1st year availability. Actual application is 420# of Nitrogen. P and K are total nutrients in manure application.
Note that a 16,000 gallon manure application applies 4 times the total P that the corn (grain) crop will need and 11 times the K application. This excess of P and K has not been an agronomic concern in the past, as the nutrients will be removed by subsequent non-manured alfalfa crops.
Work by Kelling and Bundy has shown that it would take 26 years of continuous corn (grain) to draw soil test phosphorus levels from 100 ppm down to 26 ppm.
The regulatory strategy followed by USDA, EPA and DNR until recently has encouraged applications on a nitrogen removal basis. For a dairy operation, this means that a dairy farm could get a county permit (manure storage) by having a minimum of 1 acre per milking animal. From a P management perspective, applying manure to meet P removal would increase the acres needed by 130%.
Environmental Concerns: Unlike nitrogen which can be lost to the groundwater or denitrified (atmospheric losses) very quickly and easily, phosphorus does not tend to move once in the soil. Most P losses are through soil erosion.
Once in surface water, P becomes a significant environmental concern. The size of the algae bloom is directly related to the amount of P in the water. (Algae is a plant requiring N, P and K.) Since there is already adequate supplies of N and K in the water, P becomes the limiting nutrient.
When the available P is used up, the algae die-off begins. The bacteria breaking down the dead algae remove oxygen from the water, causing fish kills. (This same principal is at work when manure spills into a creek--the bacteria’s oxygen demand (BOD) removes almost all the oxygen that kept the fish alive.)
Managing Your Risk.
If you plan on farming ten years from now, you should plan on farming under some form of environmental regulation. Any changes you can make now in your operation will decrease the impact of those regulations when they are implemented. You will need to tailor these to your particular farming operation -- not all will work for all farms, and there may be better solutions you find in the meantime.
Employ common sense. Sounds simple, yet there are too many farmers who don’t. Don’t stack manure next to a stream, don’t empty the pit on the same field each year, etc.
Strive to keep soil test P below 65 ppm. If you are at or above this level, reduce P applications by totaling up crop removal over the rotation, and applying less P (manure and fertilizer) than crop removal.
Use soil conservation methods. Since most P entering surface water is attached to sediment, cutting erosion is the easiest way to reduce P losses. Reduced tillage, different rotations, cover crops are all good tools that make a difference.
Create a mass balance. This means sitting down with a worksheet and adding up all sources of P entering the farm and all sources leaving. Once you have the total pounds entering and leaving, you can determine how much excess is remaining on the farm. Shoot for less than 3 pounds P per acre per year excess.
Allocate your manure. Based on soil tests, spread manure on fields with lower P soil tests.
Change your fertilizer. Having the co-op or dealer blend a lower P fertilizer is a cheap (and often cost-saving) alternative. On fields with high or excessively high P values, 100# of a 10-20-20 is all the corn starter you need. Same goes for ANY field that received manure.
Incorporate manure whenever possible and avoid runoff zones. Common sense once again, but don=t daily haul in areas where runoff or standing water will carry off nutrients. Your LCD can create a hazard map with areas to avoid highlighted.
References Cited
Combs, Sherry and Scott Bullington: "Twenty Years of Wisconsin Soil Test Data" in the New Horizons in Soil Science series, UW-Madison Soil Science Department, October 1996.
Erb, Kevin A. "Final Report: Application of the CLM Nutrient Yardstick on dairy farms in the Duck-Apple-Ashwaubenon Priority Watershed", Grant summary prepared by the UW-Madison NPM Program, March 1998. 3 pages.
Nevius, Monica and D. Jackson-Smith. Do Large Farms Pose Greater Environmental Risks? Livestock Intensity and Manure Management on Wisconsin Dairy Farms" UW-Madison Program on Agricultural Technology Studies, Madison WI, 1998, 6 pgs.
Wisconsin Ag Statistics Service, Wisconsin Ag Statistics, DATCP, Madison WI, 1989-1997
Zemenchik, R.A. and N Wollenhaupt, A Bosworth and A Gallagher, "The Relationship Between Soil Test P and Bioavailable Phosphorus in Runoff." in the Proceedings of the 1995 Fertilizer, Ag Lime and Pest Management Conference, Madison WI, January 1995. Pgs 56-62.