Winter Manure Application on a High-Phosphorus Field
A 150-cow dairy plans to apply lagoon manure to a 40-acre field in late December. The field has a 6% slope, a 150-ft buffer to a perennial stream, and is currently covered by 4 inches of snow; soil temperature is 35 degrees F. The lagoon holds about 500,000 gallons, and the farm has only 30 days of storage left. The field's phosphorus index is already rated high. The manure analysis is 12 lb N per 1,000 gal, 5 lb P2O5 per 1,000 gal, and 8 lb K2O per 1,000 gal. The farm's nutrient management plan calls for applying in spring before corn, but the lagoon is near capacity. The owner wants to apply at 6,000 gal/ac now and disk it in. A neighbor has complained about muddy runoff.
1. Evaluate the proposed winter application. Identify the highest-risk factors and whether the plan's spring timing should be changed.
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The proposed application is high risk. The field has a 6% slope, a stream buffer of only 150 ft, snow cover, and frozen soil, all of which increase runoff and phosphorus loss. A high phosphorus index means the field should not receive more manure phosphorus without a specific plan exception. Applying 6,000 gal/ac over 40 acres would use 240,000 gal, delivering about 1,200 lb P2O5, or 30 lb P2O5/ac. Disking frozen ground does not reliably incorporate manure and may leave it exposed to snowmelt. The spring timing in the nutrient management plan should not be abandoned just because storage is short; the farm should first look for lower-risk alternatives. If application cannot be avoided, it should be on the lowest-risk fields, not this one.
2. Recommend at least three alternatives and describe how to choose fields if application cannot be avoided.
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Alternatives include arranging emergency storage or a temporary berm, hauling manure to a neighboring farm with a valid nutrient plan, reducing the immediate herd or milking string, and applying to a lower-phosphorus field with gentler slope and greater stream setback. The farm could also cover the lagoon to reduce added water and conserve storage. If land application is unavoidable, choose fields with low phosphorus index, less than about 3% slope, no snow or ice, soil temperature above freezing, and a setback well beyond the minimum. Apply at a reduced rate, inject or incorporate on thawed ground, avoid areas that drain directly to the stream, and keep equipment out of wet spots. Document why the emergency application was necessary.
3. What records and follow-up should the farm keep to protect itself and improve the nutrient plan?
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Keep the manure analysis, application date and time, field and setback map, application rate and total gallons, weather and soil conditions, equipment calibration, incorporation method, and photos of the field before and after. Record the phosphorus index and the nutrient management plan basis for any exception. Note any neighbor notification, runoff observations, and corrective actions. After application, monitor the field and stream buffer for ponding, erosion, or runoff, and sample soil and manure again before the next application. The records should show that the farm evaluated lower-risk alternatives and did not apply to snow-covered or saturated ground unless a genuine emergency existed. Use the results to revise storage capacity, setbacks, and application timing for the next plan.