A new Phosphorus Index for NY: Part 1. What farmers need to know.

In the past 20 years, more than 600 dairy and livestock farms in NY have come under regulations and invested millions in best management practices. Annual fertilizer phosphorus purchases have been cut substantially and many dairies have made large reductions in phosphorus (P) fed to cows which reduces P in manure. Many other farms have made environmental improvements through state programs and their own initiative as well. Combined, these changes have resulted in millions of pounds less P applied to land annually and as a result, soil test P across NY is no longer increasing. Yet, in spite of the improvements, we have seen an increase in occurrences of Harmful Algal Blooms (HABs) in NY, a trend that is also being experienced across the US and around the world. No one is certain exactly what is going on. It is likely there are multiple causes. What we do know is that in the 60’s, 70’s and 80’s, phosphorus tended to accumulate in the environment resulting in “legacy phosphorus” in fields, stream banks and beds, and in lakes. We also know that annual rainfall is increasing, and storms have been getting more intense. More rain means more runoff and more runoff means more nutrient loss. It appears that some aspects of water quality have gotten worse, though many farmers have made significant improvements over the past decades. This tells us we have more work to do. The NY P Index (NY-PI) sits at the heart of this issue and is designed to help farmers implement practices related to manure and fertilizer phosphorus management that reduce the risk of phosphorus loss from fields and farms.



The first NY-PI was released in 2001 and like many things 18 years old, was in need of change. The updated version (NY-PI 2.0) incorporates new science and does a better job of addressing phosphorus loss risk while still giving farm managers options for recycling manure nutrients on crop fields. The process of updating the NY-PI was a broad partnership among faculty and staff in the Nutrient Management Spear Program (NMSP), PRO-DAIRY, and the Department of Biological and Environmental Engineering at Cornell University, along with NY Departments of Agriculture (NYSDAM) and Environmental Conservation (NYSDEC), and the Natural Resources Conservation Service (NRCS). Feedback from certified nutrient management planners and farmers was sought multiple times along the way.



The team tested the new NY-PI with field information from more than 300 NY farms across 40 counties, representing more than 33,000 fields. Some important facts: 90 percent of the fields had a Cornell Morgan soil test P (STP) below 40 pounds per acre, where additional P is recommended for crop growth. Fields with extremely high STP levels, represented by only a small fraction of the fields in the database, are a result of many years, in many cases, decades ago, where phosphorus loads to fields exceeded crop phosphorus removal. In a separate assessment of 18 dairy farms for which whole farm data were available, analysis showed that almost all fields on these farms were able to receive manure, though many fields needed some combination of risk reduction practices. Next month, we will explore how the P index works.

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