Phosphorus Kyle Minks Land and Water Resources Scientist Land Conservation Division
Overview Phosphorus 101 Phosphorus transport What is legacy phosphorus How phosphorus is managed to reduce environmental impacts Total Maximum Daily Load (TMDL) Nutrient Management Plan Phosphorus in agricultural systems Current Dane County strategies to mitigate phosphorous impacts
Importance of phosphorus Phosphorus is an element Most commonly found as phosphate minerals in nature Phosphorus is essential for all living organisms In animals it is used for bone, cell, and tissue growth. In plants it is used for photosynthesis, respiration, cell and tissue growth. Within agricultural systems it is one of three primary (macro) nutrients. Nitrogen (N), Phosphorus (P), & Potassium (K). Within freshwater aquatic systems it is the limiting nutrient for algal and aquatic plant growth.
Phosphorus Forms Dissolved within solution Dissolved inorganic phosphate form that plants take up Particulate bound to organic and solid particles Organic phosphorus phosphate bound to a carbon molecule (plant or animal tissue) Inorganic phosphorus phosphate not associated with organic material (minerals) Total = Dissolved + Particulate
Phosphorus Measurements - Stream Aquatic systems Elemental P Total Phosphorus (mg/l) Includes all forms of phosphorus organic, inorganic, dissolved and particulate Dissolved Phosphorous (mg/l) Sometimes called soluble phosphorus Filtered to remove particulates Includes some phosphorus removed from particulates by extractants Orthophosphate (mg/l) Dissolved inorganic phosphorus Highly reactive/plant available Particulate Phosphorus (mg/l) Calculated by subtracting dissolved phosphorus from total phosphorus
Phosphorus Measurements - Field Agronomic systems Use Phosphate (P 2 O 5 ) Soil test (mg/kg) Bray 1 Method NOT the same method as total phosphorus or orthophosphate Elemental phosphorus calibrated to crop response for developing fertilizer recommendations Soil buffering capacity Takes approximately 18 pounds of P 2 O 5 to change soil test phosphorus by 1ppm or 8 pounds of elemental P to change soil test phosphorus by 1 ppm
Measurements Phosphorus Cycle Biosolids/organic byproducts Field (P 2 O 5 )? Plant & algal uptake Plant & algal release Stream (TP, DP)
Phosphorus transport
Phosphorus Concentrations in the Environment Plant Available: 10-100 ppm Runoff: 0.10-10 ppm Algae: 0.03-0.1 ppm Soil: 100-1000 ppm Waterbody: 0.01-2 ppm
Measurements Accumulation Phosphorus Cycle? Biosolids/organic byproducts Field (P 2 O 5 )? Plant & algal uptake Plant & algal release Stream (TP, DP)?
Legacy phosphorus Phosphorus that has accumulated in the environment as a result of previous (decades to century old) phosphorus applications and management. Sources Legacy phosphorus in soils Legacy phosphorus in stream sediments
Managing phosphorus to reduce environmental impacts 1. Watershed level Total Maximum Daily Load (TMDL s) 2. Field level Nutrient Management Plan (NMP s)
1. Rock River TMDL Sets the maximum amount (load) of a pollutant that can be discharged to a waterbody and still allow attainment of water quality standards. Two pollutants identified Total suspended solids Total phosphorus Load allocations assigned based on two primary source categories Point sources (Waste Load Allocation) Nonpoint sources (Load Allocation)
TMDL Phosphorus Sources & Calculations Background Load Naturally occurring from wetlands, forests Nonpoint Runoff from soil, manure, fertilizer, biosolids, compost TMDL Waste Load Allocation Municipal Wastewater Industrial Wastewater Stormwater (MS4s) Load Allocation Waste Load Allocation + + Margin of Safety
2. Nutrient Management Plan (NMP) Field level phosphorus management using Phosphorus Index (PI) Rotational P 2 O 5 balance
WI Phosphorus Index (PI) Purpose: To guide field management to protect water quality Is an estimate of the average phosphorus delivery from field to surface water Calculated as elemental phosphorus in pounds/acre/yr
Components of the PI
Rotational P 2 O 5 balance Accounts for P 2 O 5 applied from all nutrient sources Manure Compost Fertilizer Biosolids Grazing Subtract the applied amount from the amount needed for crop production (-) negative value means P 2 O 5 is being drawn down (+) positive value means P 2 O 5 is building up
Amount of phosphorus in agricultural nutrient sources Starter (9-23-30) ~ 100 lbs/acre 23 pounds P 2 O 5 10 pounds of elemental P DAP (0-46-0) ~ 100 lbs/acre 46 pounds P 2 O 5 20 pounds of elemental P Manure (beef/dairy) ~ 10,000 gal/acre 60 pounds P 2 O 5 26 pounds of elemental P Biosolids ~ 6,800 gal/acre *220 pounds of elemental P *Not all immediately plant available
Phosphorus uptake by agricultural crops Crop P 2 O 5 pounds removed/acre Acres Dane County P 2 O 5 pounds removed Yahara Watershed Acres P 2 O 5 pounds removed Corn Grain 69.8 128,647 8,979,560 34,627 2,416,964 Corn Silage 90.0 55,134 4,962,060 31,243 2,811,870 Soybeans 44.2 85,661 3,786,216 25,827 1,141,553 Wheat 39.9 13,859 552,974 5,271 210,312 Alfalfa 46.2 66,535 3,073,917 20,603 951,858 Total 349,836 21,354,727 117,571 7,532,559
Yahara watershed 2017 NMP evaluation Evaluated 1,083 fields for average values Soil test phosphorus of 63 ppm Range 8 to 348 ppm Phosphorus Index (PI) of 2.7 Range 0 to 23 Rotational P 2 O 5 balance of -258 Range -690 to 761 30 fields with a positive P 2 O 5 balance Average soil test phosphorus of 39 ppm Range 11 ppm to 145 ppm
Current LWRD phosphorus strategies 1. Reduce phosphorus runoff risk Nutrient Management Plans Cropland conservation practices Winter spreading permits Manure storage permits 2. Reduce direct phosphorus discharges Barnyard/feedlot conservation practices 3. Promote redistributing phosphorus to where it is needed Community manure storage Nutrient Management Plans 4. Promote phosphorus removal technologies and exportation out of the watershed Community digesters/nutrient concentration Instream legacy phosphorus removal
Summary Phosphorus is critical for plant and animal survival Phosphorus is found in dissolved, particulate, organic, and inorganic forms of which dissolved inorganic is the primary source for plants Phosphorus is measured differently in aquatic and agricultural systems Agronomic phosphorus needs are 10-100 times greater than algal phosphorus needs Phosphorus is managed in agricultural systems using either the WI Phosphorus Index (PI) or rotational P2O5 balance County strategies for reducing phosphorus include reducing runoff, eliminating discharges, redistributing phosphorus where it is needed, and promoting removal technologies and exportation out of the Yahara watershed
Resources Understanding Soil Phosphorus: An Overview of Phosphorus, Water Quality, and Agricultural Management Practices. http://ipcm.wisc.edu/download/pubsnm/understandingsoilp04.pdf Methods of Phosphorus Analysis for Soils, Sediments, Residuals, and Waters. https://sera17dotorg.files.wordpress.com/2015/02/sera-17- methods-for-p-2009.pdf Phosphorus: Sources, Forms, Impact on Water Quality - A General Overview. https://www.pca.state.mn.us/sites/default/files/wq-iw3-12.pdf
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