Agronomy Fact Sheet Series Fact Sheet 11

The New York Nitrate Leaching Index

The Nitrate Leaching Index (LI) is an indicator The Percolation Index is a function of the of the potential for nitrate to reach annual average precipitation and soil groundwater. Nitrate, because it is water hydrologic group. Hydrologic group “A” soils soluble (see agronomy factsheet #2: Nitrogen have the greatest percolation potential and cycle – the basics), moves downward as water soils of hydrologic group “D” have the least percolates through the soil. The extent of percolation and lowest risk of leaching. The percolation depends on permeability, pore-size Seasonal Index is based on the annual distribution, soil depth to a restrictive layer, precipitation and the sum of the fall and winter artificial drainage, and precipitation amount precipitation (October through March). When and distribution over the year. For a given the factors are combined, the LI ranks the well precipitation pattern, excessively well drained drained soils in areas of high rainfall with a soils such as Howard, Adams, Hoosic and higher potential for leaching. Tunkhannock, or even well drained soils such as Madrid, Palmyra, Honeoye and Ontario have Fortunately, no calculations are necessary to a significantly greater leaching potential than rate a field. Appendix A of the New York less well drained soils such as Vergennes, Nitrate Leaching Index supplies the hydrologic Swanton, Rhinebeck, Lordstown or Volusia. soil groups and Appendix B provides the LI The current LI rates leaching potential based scores for each hydrologic group in each NY on soil hydrologic group (Table 1) and 10 year township. average precipitation data from weather stations around NY. Until recently, rainfall data Management Implications were county-based. The latest version of the LI An LI below 2 indicates that the potential for uses township-based precipitation data, which nitrate leaching below the root zone is low. An more accurately reflects precipitation patterns. LI greater than 10 indicates that the potential for nitrate leaching below the root zone is high Table 1. Soil Hydrologic Groups. while LI’s between 2 and 10 are considered Soil Infiltration Leaching intermediate. In order to meet the N leaching Hydrologic Type Capacity / Potential Group Permeability requirements of the NRCS Nutrient Management Standard (590), producers are Deep, well-drained A High High sands and gravels. expected to implement best management practices (BMP) if the LI score for a field is Moderately drained, high (>10) and to consider the same practices B moderately fine to Moderate Moderate if the LI score for a field is intermediate (2- moderately coarse 10). The following BMPs exist for soils with texture. medium to high N leaching indices: Impeding layer, or o Unless the New York Phosphorus Index C moderately fine to Low Low fine texture. (agronomy factsheet #10: How to calculate the New York Phosphorus Index) identifies Clay soils, soils D with high water Very Low Very Low the need for P based fertility management, table. manure and fertilizer application rates should be based on Cornell guidelines for Calculating the LI meeting crop N needs. The Nitrate Leaching Index is calculated by o For corn, pre-plant (other than starter multiplying the Percolation Index and the fertilizer) and early post plant broadcast Seasonal Index for a particular location: applications of commercial nitrogen without the use of nitrification inhibitors are not LI = Percolation Index * Seasonal Index recommended.

Department of Crop and Soil Sciences 1 College of Agriculture and Life Sciences o Sidedress applications should be made hardy cover crops. Applications should after the corn has at least four true leaves. generally not exceed the greater of 50 o If starter N must be broadcast (e.g., for lbs/acre of first year available N or 50% of small grains or new seedings of grass), the expected N needs of next year’s crop. apply fertilizer as close to expected o Frost incorporation/injection is acceptable planting date as possible (ideally within 3 when soil conditions are suitable, but days or less). winter applications should be made in o For row and cereal crops, including corn, accordance with the NY Phosphorus Index. maintain starter fertilizer N rates below 50 o Manure N application on legumes is lbs/acre actual N under normal conditions. acceptable to satisfy agronomic o Manure and fertilizer applications should be requirements when legumes represent less adjusted based on information provided in than 50% of the stand. When legumes “Nitrogen Recommendations for Field Crops represent more than 50% of the stand, in New York” (see additional resources). manure application should be limited to no o Evaluate the need for sidedress N more than 150 lbs of available N/acre. applications based on PSNT or other soil nitrogen tests (see agronomy factsheet#3: Other Considerations Pre-sidedress nitrate test). In addition to the fields identified with a high o Sod crops should not be incorporated in the leaching potential by the LI, the best fall. Chemical sod killing may be carried out management practices should also be applied when the soil temperature at four-inch to fields with any of the situations, below: depth is approaching 45oF. Depending on o Soils, of any drainage, that are less than location, this will not likely take place until 40 inches deep over limestone bedrock. early October. o Glacial outwash and some well drained o Minimize fall and/or winter manure alluvial soils, especially over aquifers. application on good grass and/or legume o Soils, of any drainage, that are less than sod fields that are to be rotated the 20 inches deep over other bedrock types. following spring. These cases can be identified with a soil survey o Appropriate ammonia conservation is and local knowledge and aim to capture those encouraged. Losses can either be reduced fields with a thin layer of soil over fractured by immediately incorporating manure or bedrock and course textured soils over eliminated by directly injecting manure as a aquifers. sidedress application to growing crops. o Plant winter hardy cover crops whenever Additional Resources possible, especially when fall manure is o The New York Nitrate Leaching Index: applied (e.g., rye, winter wheat, or nmsp.css.cornell.edu/publications/nleachingindex.asp. o Nitrogen Recommendations for Field Crops in New interseed ryegrass in summer). York: nmsp.css.cornell.edu/nutrient_guidelines o Cornell University Agronomy Fact Sheets #2 (Nitrogen cycle – the basics), #3 (Pre-sidedress nitrate test), #4 (Nitrogen credits from manure), and #10 (How to Calculate the New York Phosphorus Index) nmsp.css.cornell.edu/ publications/factsheets.asp.

For more information

Figure 1: Plant winter hardy cover crops where/when possible to reduce N leaching. Nutrient Management Spear Program http://nmsp.css.cornell.edu o Manure may be applied in the fall where Karl Czymmek, Quirine Ketterings, Harold van Es, there is a growing crop. Judicious amounts Stephen DeGloria, and Greg Albrecht

of manure can be applied to or in 2005 conjunction with perennial crops or winter

Department of Crop and Soil Sciences 2 College of Agriculture and Life Sciences