The Illinois P-index and how it affects pork producers
Ted Funk
ph. 217-356-1304
What's all the fuss about phosphorus and manure application? Phosphorus is widely recognized as a troublesome surface water pollutant, and is regulated. Manure can contribute both particulate and soluble forms to runoff from crop fields. For many years, Illinois livestock producers have participated in training about the practices that reduce phosphorus pollution from application fields, but due to the lack of definitive research on phosphorus loads to surface water, our state agencies have until now resisted adopting a numeric standard, or phosphorus index, to define more stringent constraints on the applications of phosphorus-containing nutrient products (including manure).
National and regional pressures have challenged Illinois' recalcitrance in the move toward a P-index, and last year the national NRCS required the state NRCS office to assemble a committee of stakeholders to revise the state's 590 standard, Nutrient Management, so that it includes a nitrogen (as nitrate) risk index as well as a numeric phosphorus risk index. The 590 standard comes into play if you participate in various conservation programs, especially those involving the Comprehensive Nutrient Management Plan 102. This means you must get on board soon if you want to sign up for a conservation program contract such as the Environmental Quality Incentive Program (EQIP) for the 2014 fiscal year, which starts October 1, 2013.
How did we evaluate fields for phosphorus risk before this? In Illinois we used to have what we called the Phosphorus Risk Assessment, which was a qualitative low-medium-high indicator that served to “nudge” producers to adopt practices to reduce pollution loadings and risks. The new P-index is better than the old risk assessment, in terms of quality, only if you and your technical service provider walk the fields and evaluate all the factors fairly. But the bottom line is, neighboring states developed their phosphorus indexes and Illinois was told to go through the same exercise.
The Illinois P-index is not some guarded secret, and it’s not difficult to understand. It's published as an Excel spreadsheet, and you can download it from the Illinois NRCS e-fotg website, . Click on Illinois, go to Section IV, and scroll down to the Nutrient Management 590 standard. Look for “Illinois Phosphorus Index,” the spreadsheet. There are other documents in that folder that are useful and informative, too.
What are the factors for the Illinois P-index? If you have the spreadsheet handy, please follow along. Each factor gets a point weighting, and the points are added up to give a range of low, medium, or high. The range then governs the practices that are recommended and allowed for land treatment(which involves manure applications)on the field being evaluated.
Sheet and Rill erosion (via RUSLE2): Expect your Technical Service Provider (TSP) to make judgments on what part(s) of the field is the dominant vs. the critical area of the field for the erosion number. This determination recognizes that most of the phosphorus runoff from a field comes from the critical area, which may be a small proportion of the field—but professional judgment is still involved. The person updating your nutrient management plan has to walk the fields to find the critical areas and justify them, in some cases with notes in the CNMP. TSP's are being trained about how to interpret the RUSLE2 application.
Leaching potential: Tile drained or not—this is a big factor that's either on or off, depending on whether the field is at least 50% pattern drained. Tile drains provide easy conduits to surface water, so the presence of pattern drainage is a big deal for both phosphorus and nitrate movement.
Distance to surface water: This is another factor that requires a trained eye and walking the field. More distance is better (lower points) but distance points can be tempered by having application setbacks and/or vegetative buffers. Slopes matter, too.
Source factors include the median soil P test (Bray P1 or Mehlich 3). Several things you need to know about phosphorus soil tests: the ranges and how they affect the P-index, new thresholds and how they are used, multi-year phosphorus applications, and soil sampling patterns. Range: if a field has a P test lower than the maximum for optimum crop production (less than 70 lb/acre), you get a low (safe) rating for that source factor. On the other end of the scale is a “very high” rating if the P test is over 300 pounds per acre. So the fields where you have traditionally spread a lot of manure may have a high P-test and that will be a target for a phosphorus drawdown land treatment. Multi-year phosphorus applications are still allowed in some situations, but the annual average application rate governs and produces a low to very high rating. Of course, how you apply manure makes a difference—injection, or sprinkle irrigation throughout the growing season, are best; and manure surface-applied without incorporation in the spring is the highest risk.
Soil sampling has to be kept up to date. Sampling should generally be done in 2.5 acre grids, but there are some fields where sampling by management zones makes more sense. You need to work with your technical service provider to determine the best method. The new Illinois Agronomy Technical Note No. 23, “Soil Sampling Guidelines for Immobile Plant Nutrients,” contains useful details for lots of situations including some special considerations for banding nutrients, for pastures, etc. The Note is in the e-fotg under the 590 Standard tab.
The Illinois P-index is here to stay, and it will affect landowners who access publicly-funded conservation programs. Stakeholders met with NRCS state office staff over a period of many months to hash out the factors and the point weightings. The P-index reflects the best compromise that crop and livestock producers, fertilizer industry, NRCS and other agency representatives, technical service providers, university agronomists, and environmental groups could hammer out. In general, every field in your comprehensive nutrient management plan that is used or could be used for manure applications needs to be re-evaluated on the new P-index grid. There is no better time than after harvest to walk the fields and get your fields evaluated for the new 590 standard. For that matter, it's pretty tough to update the RUSLE2 factors with a standing corn crop.
Is your CNMP in an EQIP contract in the current fiscal year? If you have an existing EQIP contract, it will be carried out with the previous version of the NRCS 590 standard (Nutrient Management). But if you either (1) have no EQIP application in the pipeline or (2) have an application that did not get funded last year but is still in the pipeline for Fiscal Year 2014 (which starts October 1, 2013), your CNMP needs to be updated to reflect the new P-index. The new 590 standard includes both the P-index and the new Nitrate Loss Potential tool. The Nitrate Loss Potential tool is a topic for another day (it’s in the e-fotg tab under the Nutrient Management standard also, listed as “Illinois Nitrogen Management Guidelines), but it is much easier than the P-index to evaluate for a given field.
Let's look at some of the factors and how they impact manure application. With a “low” P-index you can apply manure at crop nitrogen needs (same as with the LMFA). Once your P-index reaches “medium” risk, you must apply at phosphorus limited rates. With a “high” number, you can only apply manure in a cropping system with a phosphorus drawdown strategy. And if your field comes up to a “very high,” you really have to lay off the manure applications until you get conservation practices in place to reduce the number. No phosphorus applications can take place if the soil test phosphorus is greater than 400 pounds per acre. So you say, “What happened to the old 300 pound per acre phosphorus application limit in the LMFA?” It's in there—the “high” rating loads up points at that threshold.
It’s a good idea to get all your fields re-evaluated this fall under the new Illinois phosphorus index, the “p-index.” You only need to do it once unless conditions change for a field, and your nutrient management plan isn’t complete without the new p-index numbers.
Where to get help: If you have trouble accessing the 590 standard via the internet, your local NRCS office should also be able to help you get a copy and go over the factors with you. You may also contact the author of this article at .
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