uring the June Iowa Environmental Protection Commission (EPC) meeting, the EPC board voted 5-2 to adopt regulations proposed by Iowa Department of Natural Resources staff to implement the Phosphorus Index. The Phosphorus Index is a tool used to assess the potential for phosphorus to move from agriculture fields to surface water. When phosphorus is lost from fields it can increase algae growth in surface waters. This results in eutrophication, or excessive algae growth. Eutrophication is a main cause of impaired surface water quality. Since most phosphorus adheres to soil particles, factors that affect soil erosion are critical to phosphorus movement. The Phosphorus Index is required by Iowa law to be based on the USDA NRCS Phosphorus Index and to apply only to farmland that is included in a manure management plan that has been submitted to the DNR. According to the recent results of the Census of Agriculture, 26,500 Iowa farmers treat 2.33 million acres with livestock manure, out of 23,994,343 total Iowa acres used to grow corn, soybeans and other harvested crops. The Phosphorus Index is required on a phased in schedule based on the first time the manure management plan has been submitted to the DNR. Original manure management plans that were submitted prior to April 1, 2002 have until August 25, 2008 to comply. Manure management plans submitted on or after April 1, 2002 but before October 24, 2004, have until August 25, 2006 to incorporate the Phosphorus Index. A manure management plan submitted on or after October 25, 2004 will be required to meet the Phosphorus Index at that time. If a manure management plan for new construction is submitted prior to October 24, 2004, the operation will not be required to meet the Phosphorus Index for another 22 months, even if the new construction occurs after the date when a Phosphorus Index is required. Information needed for the NRSC office to run the Phosphorus Index 1.   FSA photo with fields outlined 2.   Soil map -- large enough to determine where first three dot stream is located 3.   Erosion rates by field (RUSLE2 in ton/acre/year can be acquired from Conservation Plan) 4.   Any conservation practices installed and marked on the map (i.e. terraces, no-till, mulch till, buffers, etc.) 5.   Location within the state (i.e. section 34 T80 R47). 6.   Current soil test results in PIP and type of test used (i.e. Bray P-1) 7.   Application rates in pounds of 8.   Is field tiled? For more information on the Phosphorus Index or RUSLE 2, or to access the Iowa Phosphorus Index Calculator, visit www.ia.nrcs.usda.gov. What is RUSLE2? Released in 2003, Revised Universal Soil Loss Equation 2 (RUSLE2) is a software model that predicts long-term, average-annual erosion by water. RUSLE2 estimates soil loss from rill and interrill erosion caused by rainfall on cropland. RUSLE2, like its predecessors, RUSLE and USLE, is used to predict the long-term average rate of rill and interrill erosion for several alternative combinations of crop system and management practice. It also considers specified soil types, rainfall patterns, and topography. When these predicted losses are compared with soil loss tolerances, RUSLE2 provides specific guidelines for effective erosion control. What is rill and interrill erosion? Rill and interrill erosion is the removal of layers from the land surface by the action of rainfall and runoff. Erosion begins with the impact of raindrops, detaching soil particles and moving them across the surface. This process causes interrill erosion (sometimes called sheet erosion). Runoff from interrill erosion will collect and form rills across the hill slope. Sediment from rill and interrill erosion is transported down slope to where it slows enough to be deposited on the land surface or deposited directly into concentrated flow channels. Where do I find more information on RUSLE2? Contact your county NRCS office to find more information on the RUSLE2 or to visit with a field staff about running the RUSLE2 software program for your manure management plan. The Phosphorus Index Iowa NRCS Fact Sheet What is the Phosphorus Index? The Phosphorus Index is a tool used to assess the potential for phosphorus to move from agricultural fields to surface water. It uses an integrated approach that considers soil and landscape features as well as soil conservation and phosphorus management practices in individual fields. These characteristics include source factors such as soil test for phosphorus; total soil phosphorus; rate, method, and timing of phosphorus application from commercial fertilizer, manure, and other organic sources and erosion. Transport factors include sediment delivery, relative field location in the watershed, soil conservation practices, precipitation, runoff, and tile flow/subsurface drainage. Erosion, runoff and drainage factors for a site or field are used in a mathematical equation to determine whether the phosphorus movement risk is very low, low, medium, high or very high. Why was the Phosphorus Index developed? Phosphorus is an essential element for plant and animal growth. But when phosphorus is lost from fields it can increase algae growth in surface waters. This results in eutrophication, or excessive algae growth. Eutrophication is a main cause of impaired surface water quality. Since most phosphorus adheres to soil particles, factors that affect soil erosion are critical to phosphorus movement. If soil erosion is controlled, loss of phosphorus is less severe. The index accounts for that. NRCS began the effort to develop the index to be used as part of its revised nutrient management standard. Who developed the Phosphorus Index? The Phosphorus Index was developed by Iowa State University, the National Soil Tilth Lab and Natural Resources Conservation Service. The Index is based on soil and water quality research in Iowa and other Midwest area states. Natural Resources Conservation Service, USDA, Des Moines, Iowa Summary of the Iowa EPC rules on the Phosphorus Index The DNR rule on manure management plans, including the Phosphorus Index, was adopted by the Environmental Protection Commission and is scheduled to go into effect on Aug. 25, 2004. The Phosphorus Index is required by law to be based on the USDA NRCS Phosphorus Index and applies to farmland that is included in a manure management plan submitted to DNR. Manure management plans must meet either the Phosphorus Index or nitrogen requirements, whichever is most limiting on manure and other crop nutrient application rates. The Phosphorus Index rating (Very Low, Low, Medium, High, Very High) is not the same as soil test levels for phosphorus. The Phosphorus Index has 3 components: Erosion ­ potential phosphorus delivered to surface water with sediment Runoff ­ potential phosphorus delivered to surface water in runoff Subsurface drainage ­ potential phosphorus delivered to surface water with subsurface drainage. Soil test levels are a factor in all three components of the Phosphorus Index, but are not the only factor in determining the Phosphorus Index. To properly understand the effects of the Phosphorus Index, the soil test level of phosphorus cannot be confused with the Phosphorus Index rating. If phosphorus-based application rates are required under the Phosphorus Index, phosphorus applications cannot exceed crop uptake of phosphorus over a four-year period. Thus, unlike nitrogen, phosphorus from manure or other sources can be applied to land in a manure management plan at more than annual crop uptake levels, but cannot exceed the four-year total. The Phosphorus Index is required on a phased-in schedule based on the first time manure management plan is submitted to DNR: Original manure management plans submitted before April 1, 2002 - a manure management plan using the Phosphorus Index is first required four years after Phosphorus Index rules go into effect (August 25, 2008). Original manure management plans submitted on or after April 1, 2002 and before 60 days after Phosphorus Index rules go into effect (Oct. 24, 2004), a manure management plan using the Phosphorus Index is first required two years after the Phosphorus rules go into effect (August 25, 2006). An original manure management plan submitted on or after 60 days after Phosphorus Index rules go into effect (October 25, 2004) must meet the Phosphorus Index at the time it is submitted. The Federal AFO/CAFO rule deadline for total phase-in of phosphorus-based Comprehensive Nutrient Management Plans is December 31, 2006. Note: A manure management plan for new construction submitted on or after October 25, 2004 will be required to meet the Phosphorus Index at that time. If a manure management plan for new construction is submitted before that date, the operation will not be required to meet the Phosphorus Index for another 22 months ­ even if the new construction occurs after the date when a Phosphorus Index is required. The details of the new rule for manure management plans include: 1.   Manure application rates under the Phosphorus Index (PI) a.   Very Low (PI 0-1) and Low (PI greater than 1 - 2). Manure may be applied at nitrogen-based rates in current rules. b.   Medium (PI greater than 2 - 5). i.   Manure may be applied at nitrogen-based rates if current and/or planned soil conservation and phosphorus management practices predict the Phosphorus Index will not exceed the medium category at the next Phosphorus Index determination. ii.   Manure cannot be applied in excess of two times the phosphorus removed over the crop rotation c.   High (greater than 5-15) i.   (greater than 5-10) Until December 31, 2008, manure may be applied at phosphorus-based rates if practices will be adopted to reduce the Phosphorus Index to medium before the next Phosphorus Index determination. ii.   (greater than 10-15) No manure application. d.   Very High (PI more than 15). No manure application. Phosphorus-based rates for manure application. If the Phosphorus Index requires phosphorus based manure application rates, the following apply:     e.   Phosphorus applications over the crop schedule cannot be more than the phosphorus removed by crops during that time unless additional phosphorus is recommended by soil tests and ISU Extension publication PM-1688 "General Guide for Crop Nutrient Recommendations in Iowa."  f.   A single manure application cannot exceed the amount of phosphorus for the expected crop removal from the next four anticipated crops in the crop schedule.  g.   A single manure application cannot exceed the nitrogen-based rate for the next crop.  h.   Crop phosphorus removal rates are determined by multiplying the optimum crop yield by phosphorus removal rates for each crop (.375 pounds P/bu. of corn, or other credible sources for phosphorus uptake).  i.   Phosphorus removal for the crop schedule is determined by totaling the phosphorus crop removal for each crop in the crop schedule. 2.   Fields. The Phosphorus Index must be calculated for each field in the manure management plan and the plan must include the factors used in the calculation of the Phosphorus Index or the NRCS "detailed report." a.   Fields must be contiguous and cannot be separated by a public road, river, creek, drainage ditch, etc. b.   In calculating the sheet and rill erosion rate for the Phosphorus Index, the soil type used in the calculation shall be the most erosive soil map unit that is at least 10% of the total field area. 3.   Soil sampling and testing. a.   Each field must be soil sampled at least once every four years. Each sample must be analyzed for phosphorus and pH. b.   Each soil sample is limited to 10 acres (fields up to 15 acres may have one sample)(if the Phosphorus Index is Very Low, Low or Medium and manure is applied at phosphorus-based rates, each sample may cover up to 20 acres). c.   Each soil sample is required to have at least 10 soil cores from the sampling area. Each core must include at least the top six inches of soil. d.   Soil samples must be analyzed at a lab certified by the Iowa Department of Agriculture. e.   The average soil test phosphorus of a field is used in calculating the Phosphorus Index. 4.   Manure application rates under the Phosphorus Index (PI) a.   The Phosphorus Index must be updated every four years, unless inputs to the Phosphorus Index change before that and then the Phosphorus Index is updated at that time and submitted to DNR with the next four-year complete manure management plan. b.   If new land is added to a manure management plan, the Phosphorus Index must be calculated before manure is applied and submitted to DNR with the next 4-year complete manure management plan. c.   The rule allowing crop yield and nutrient usage rate for corn to be used for legumes in the crop rotation has been deleted. d.   The rule allowing manure applications above nitrogen crop usage rates (not more than the lesser of 1.5 times or the level providing the recommended level of phosphorus or potassium) if soil test levels for phosphorus or potassium levels are below recommended levels has been deleted. e.   The rule allowing manure management plans to be kept offsite if arrangements are made with DNR to make a copy available within two working days has been deleted. Instead, the manure management plans must be kept at the owner or operator's residence or office within 30 miles of the site. f.   Beginning August 25, 2005, manure management plan records must include dates and application rates of commercial nitrogen and phosphorus on fields receiving manure. This includes land farmed by someone else where manure is applied under a manure application agreement.

Top of page

Return to Resources and Information