Spring 2007

Your Phosphorus Index Manure Management Plan


By Angela Rieck-Hinz, Department of Agronomy, Iowa State University

If you have a confinement feeding operation with more than 500 animal units, or if you have an open lot with more than 1,000 animal units (or designated as a Concentrated Animal Feeding Operation or CAFO), state law requires you to implement the Iowa Phosphorus (P) Index as part of your manure or nutrient management plan. This requirement is not new, yet implementing this particular part of the manure or nutrient management plan seems to cause livestock producers many headaches. Why is this so? Mainly because the process of the nutrient management planning has become so complicated that few producers have the time, skills or knowledge to run the software programs it takes to develop the plan. 

What is a P Index Plan?

A P Index plan requires that you run the P Index software on each field in your plan that receives manure. This software calculates the potential risk of loss of phosphorus (P) from a field. Depending on your risk rating, it will allow you to continue to apply manure on a nitrogen-based rate or will require that you implement some type of P management plan to reduce that risk of loss of P from the field. A P management plan could include but is not limited to, reducing the manure application rate to supply enough P for the crop rotation, applying manure less frequently, applying no manure to a field,  implementing soil conservation practices on the field, reducing the amount of P in the manure by addressing feed management issues and so forth. Because erosion is the primary factor determining loss of P from fields, the P Index software uses the Revised Universal Soil Loss Equation (RUSLE2) to calculate soil loss. This software is quite complex to use and should be used only by people who have been trained to use it.

Confinement Feeding Operations

If you need to develop your P Index manure management plan, please don’t ignore any letters you receive from the Iowa Department of Natural Resources (IDNR). Some letters are being sent six months in advance of when your P Index plan is due. The IDNR is no longer granting extensions to the monthly deadlines, so please heed the letter. With fieldwork and planting season nearly upon us, please be advised your plans are still due in a timely fashion, regardless of how busy you are in the field. If you plan to develop your P index plan on your own, start early. Make sure your soil samples are recent and have been taken according to the rules. Seek training to ensure that you are capable of using the P Index Calculator and the RUSLE2 software, and have your data organized and readily available. Collect the necessary information from your neighbors who may receive manure as part of your manure easement or agreement. You will have to include P Index calculations and have the required soil samples on those fields as well as your own.

Open Feedlots

Feedlots over 1,000 animal units must develop nutrient management plans as part of their National Pollutant Discharge Elimination System (NPDES) permit. These nutrient management plans will be required to go through a public notice. Nutrient management plans, just like manure management plans for confinement feeding operations, will require the implementation of the P Index. Please see the information under “What is a P Index Plan” earlier in this article for additional information about the P Index. At this point in time, nutrient management plans for feedlots must be completed and submitted to IDNR by July 31, 2007. 

If you are a feedlot producer and you plan to develop your own nutrient management plan please make sure you use the appropriate forms, be sure to meet the soil and manure sampling requirements, start early on the development of the P Index or seek training to ensure you can adequately run the software. 

Hiring a Consultant

ResourcesIf you don’t plan to develop the P Index plan yourself, you should plan to contact a consultant who can help  prepare your plan. Please note, in Iowa, consultants are  not required to be certified to develop manure or nutrient management plans for IDNR. Please see box below for a link to a list of consultants. If you do plan to hire a consultant, you should start this process early, perhaps two to three months in advance of when your plan is due. If you need to meet the soil sampling requirements, you may need to start that process six to nine months in advance of when your plan is due. Make sure you have copies of all of the needed information. Take the time to find the right consultant for your operation. You should consider asking them questions such as:

  • How many P Index plans have you developed?
  • Have you developed plans for my type of operation?
  • Have you had plans rejected by the IDNR? If so, why?
  • Have you been trained to develop these plans?
  • How do you keep current on regulations?
  • Will you just develop my plan or will you also provide recordkeeping assistance?
  • What kind of follow-support do you provide for my plan?
  • Will you teach me how to read and implement the plan?
  • What do you charge and what services will I receive for this charge?

You manure or nutrient management plan should work  for you regardless of what the regulations require you to do. Your plan should be more than an application rate. Your plan should allocate nutrients to a field based on  what crop will be grown and the nutrients needed to grow those crops. You should understand how the plan was developed and how changes to your daily operation may affect your plan. Manure is a valuable nutrient resource so manage it wisely.


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