Bay Journal

NY Phosphorus Index may not be perfect, but has served state well

  • By Karl Czymmek, Quirine Ketterings, Larry Chase & La on November 01, 2010
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Sales data were assessed on a fertilizer year basis (July of previous year through June of the assessment year). To convert pounds of phosphorus per acre to fertilizer equivalent (P2O5), multiply by 2.3. Source: New York State Department of Agriculture and Markets, as archived with the Association of American Plant Food Control Officials

There have been several recent media references to the shortcomings of phosphorus runoff management tools and how these tools allow the continued degradation of the Chesapeake Bay. We wish to set the record straight from a New York state perspective.

Contrary to some generalized statements made about phosphorus indices in the public press, the New York phosphorus index does not allow the unlimited application of manure. The index, introduced in 2001, is an indicator of phosphorus loss potential and allows for the ranking of fields for risk of loss of both particulate and soluble phosphorus forms, reflecting the predominant pathways for phosphorus runoff.

The New York index requires phosphorus application restrictions if the runoff potential is high, as well as the elimination of phosphorus application - manure or fertilizer - where the runoff risk is very high. Where phosphorus sources - soil, manure or fertilizer - and phosphorus transport risk potential are both high, the New York index requires farms to change the management of a field to reduce the risk of phosphorus loss or to apply the manure elsewhere. The index and related guidance continue to undergo changes as insights into phosphorus movement in our landscapes are developed, but we are confident that the index is an effective and appropriate tool for environmental protection.

Planners use the index on all of the state's concentrated animal feeding operations and many animal feeding operations in New York to provide information for decisions regarding the rate, timing and method of manure and/or fertilizer application to farm fields. The index is not infallible, but its implementation has led to numerous benefits, including a greater producer awareness of the need for phosphorus management, the better coordination of livestock and cropping operations and a better balancing of the cycle of nutrient flows from crops-to-feed-to-manure-to-fields.

New York's education and outreach partnership for the comprehensive nutrient management planning program involves producers and producer organizations, planners, the land grant university and state and federal agencies. It has contributed to a greater awareness of phosphorus issues. As a result, New York farmers have implemented numerous soil and water conservation and other management practices to reduce soil erosion and phosphorus losses. The index has been relatively easy to implement and the net result of phosphorus index assessment on every field of regulated farms in New York has delivered benefits to both water quality and farm economics.

Consider the following points:

  • New York producers have made huge strides in reducing fertilizer and feed use of phosphorus the last 10 years. The amount of fertilizer phosphorus used on farms decreased from 35.1 million pounds in 1997 to 28.1 million pounds in 2002 to 23.2 million pounds in 2006. Combine these statistics with conservative estimates for the reduction in feed phosphorus use by dairy farms (23 percent), amounting to a reduction of approximately 9 million pounds of phosphorus per year, (About half of this reduction is due to smaller dairy cow population, the other half is due to active decisions by farm managers to reduce ration phosphorus levels.) and it becomes evident that New York producers have reduced phosphorus use by tens of millions of pounds per year in the last decade. While doing that, New York farms have improved overall productivity as shown by an increase in the average crop yields and milk production over the same time period. These changes mean significantly less phosphorus is being brought into the state, thus reducing the amount to be lost.
  • The reductions in phosphorus use in crop production and dairy rations have changed New York from a phosphorus-excess state just 10 years ago to one that is now in approximate balance for agricultural phosphorus sources. This means that all of the fertilizer and manure phosphorus managed by New York farms equals the amount of phosphorus removed by crops. This does not mean that every field is in perfect phosphorus balance, but it clearly shows that we do not have significant phosphorus excesses in this state.
  • While New York is in statewide phosphorus balance, we need to continue to work on phosphorus distribution within the state (i.e. within farms and regions), as is evident when we look at the distribution of soil test phosphorus among counties and within farms. The harvest of crops removes phosphorus (e.g. A 20-ton crop of corn silage is expected to remove about 32 pounds phosphorus/acre.) and this phosphorus needs to be replenished to maintain soil levels in optimum ranges over time. State soil test records show that 50-55 percent of New York crop fields need additional phosphorus for optimal crop growth, while 35-40 percent are classified as optimal/high (where phosphorus fertilizer recommendations are limited to a small starter only). Only about 10 percent of fields fall into the very high soil test phosphorus category, meaning that the crop's response to extra phosphorus fertilizer is unlikely. This does not mean further additions to any soil classified as very high soil test phosphorus necessarily leads to unacceptable environmental losses, but the risk of loss may be higher and the phosphorus index assessment will guide management.
  • New York State animal agriculture is dominated by dairy cows, and their feeding programs are dominated by homegrown forages. Homegrown forage typically includes hay, hay crop silage and corn silage or the like. The typical dairy cow gets about one-half or more of her total diet from forage. Forage is bulky and heavy (often 60-70 percent water), so it is usually produced relatively close to where the cows are located. This means that most New York dairy farms tend to have a fairly large land base (resulting in a relatively low animal density of 0.43 animal units per acre) that allows farmers to produce low-cost feed nearby and to use manure as the nutrient source for those crops in a reasonably balanced fashion, reducing the need for fertilizer.
  • Increasingly, New York dairy producers are conserving ammonia-nitrogen by the spring incorporation of manure as new and more affordable technologies emerge. When manure is incorporated in the spring, the ratio of nitrogen to phosphorus in most liquid dairy manure tends to be reasonably well-aligned with crop removal for both nutrients, making for a sustainable nutrient balance year-in and year-out. Aerator incorporation of manure is gaining popularity and producers are considering various forms of injection as well, exploring technologies that are practical given constraints—stony ground, soil moisture, work load. Mixing manure with the soil through various incorporation methods reduces phosphorus runoff loss. While not all manure can be incorporated in a timely fashion for a variety of reasons, the earlier data clearly show that New York farms have worked hard to obtain and maintain a good land-to-manure balance and this has reduced losses into the environment.
  • Larger New York dairy and livestock farms are closely regulated. In the state's portion of the Chesapeake watershed, about 42 percent of the total animals units are regulated under the New York Concentrated Animal Feeding Operation permit. They have had nutrient management plans, developed by a certified planner, for approximately 10 years. These plans, at a minimum, must be balanced for crop nitrogen needs in accordance with Land Grant guidelines and, if the New York phosphorus index score becomes high, or very high, phosphorus applications from manure or fertilizer must be limited (high) or cease altogether (very high). Each field on these farms needs to be evaluated for the index and these assessments have often stimulated both redistribution within the farm and collaborative agreements between dairy farmers and their cash grain - or vegetable-producing neighbors.

A combination of applied research, educational programming, economics and environmental regulation has resulted in significant changes in how manure and fertilizers are used in New York over the last 10 years. Producers continue to find innovative ways to feed cows and crops with less waste. Additional progress is needed with solutions focusing on finding economic ways to better distribute phosphorus resources over cropland. Regional differences within and between livestock types, the nitrogen to phosphorus ratio of the manure or litter, and production arrangements or industry organization can substantially impact manure nutrient recycling.

The index has served the state's needs well the last 10 years. Its implementation has resulted in a diversion of manure from higher risk sites to lower risk areas and in farm decisions that include the recognition of the need for a land base to manage sustainably. In short, the phosphorus index, properly designed to include both source and transport risk assessments is a practical and a much more scientifically defendable option than limits based on soil test phosphorus or phosphorus saturation thresholds. The index will continue to evolve with sound science while we work with farms to develop and implement best management practices that result in better farm-gate nutrient balances.

To summarize, while we agree that the New York phosphorus index is not the final answer to the long-term sustainability of dairy farming in New York, it does not deserve the recent criticism leveled at phosphorus indices in general. We welcome any feedback and discussion on the topic.

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About Karl Czymmek, Quirine Ketterings, Larry Chase & La

Karl Czymmek, Quirine Ketterings, Larry Chase are with the Cornell University Department of Animal Science and Larry Geohring is with the Cornell University Department Biological and Environmental Engineering.

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