Phosphorus Index for Alabama

AGRONOMY TECHNICAL NOTE

U.S. Department of Agriculture AL- 72 Natural Resources Conservation Service

Auburn, Alabama January 2013

Phosphorus Index for Alabama A Planning Tool to Assess & Manage P Movement

Non-point source phosphorus (P) pollution of and vegetation growth in surface water surface waters is a complex set of brought about by excessive nutrients. processes that involves P application, its Because of this concern, proper buildup in soils, and its transport to surface management of P in fertilizers, manures, waters. High P application in the form of and the soil is paramount in preventing fertilizers or manures can increase the risk nonpoint source pollution. of P transport to surface waters, but unless there is loss in runoff, the risk is minimal. P INDEX CONCEPT Extremely high soil test P also increases the risk of P enrichment, but there must be The P index is a tool to assess the site and detachment and/or dissolution and transport management practices for potential risk of of P before there is an environmental phosphorus movement to water bodies as concern. Excessive P in surface waters is the result of additional P applications. The an environmental concern. ranking of the P index identifies fields where the risk of phosphorus movement is PHOSPHORUS CONCERNS IN relatively higher than that of other sites. THE ENVIRONMENT When the parameters of the index are analyzed, it will become apparent that Eutrophication can be caused by the nutrient individual parameters could be influencing enrichment of a water body. Nutrient the index disproportionately. These movement in runoff and erosion from identified parameters should be the basis for agricultural nonpoint sources is a resource planning corrective soil and water management concern. The movement of conservation practices and management phosphorus in runoff from agricultural land to techniques. surface water can accelerate eutrophication. The result of eutrophic conditions and The P Index uses specific field features and excessive plant growth is the depletion of management practices to obtain an overall oxygen in the water. This is due to the rating for each field. Not all field features and heavy oxygen demand by microorganisms management practices have the same as they decompose the organic material. influence and input because research has Phosphorus is generally the limiting nutrient shown that relative differences exist in the in fresh water systems and any increase in P importance of each to P loss. Assigned to usually results in more aquatic vegetation. each of the field features and management Society is concerned about maintaining practices are weighted factors of 1, 2, or 3. clean drinking water. This concern has Also, assigned to each of the field features forced the inclusion of a cost for removing and management practices are value the color, turbidity, taste, and odor ratings of VERY LOW / LOW (0 points), associated with the high trophic condition MEDIUM (1 points), HIGH (2 points), VERY HIGH (4 points), and EXTREMELY HIGH (8 points). Multiplying the weighed factor high. by the value rating yields points for that specific field feature or 2. Phosphorus Application Rate is the management practice. Based on a application rate of organic phosphorus summation of the points, the field will and/or phosphate fertilizer in pounds per fall into an overall category rating of acre per year of P2O5 that is applied to the LOW, MODERATE, HIGH, or VERY site. The phosphate application rate HIGH. includes all sources of phosphorus whether from organic sources such as animal Currently, these weighted factors are manure, compost, poultry litter or based on research as well as commercial fertilizer. Research indicates professional judgment. As more that the application rate plays a significant research becomes available, the P Index role in determining the phosphorus loss will be periodically reviewed and potential. When applications of phosphorus updated. are made with equipment that is capable of precision application the “weighted factor” is Field Features, Management Practices, reduced from 3 to 2. Precision application & Weighted Factors Used in the P Index equipment must be used on all applications Field Feature and/or Mgt. Weighted of phosphorus and must utilize GPS Practice Factor guidance, a rate controller and automatic section control in order to take this 1. Soil Test P 1 reduction. If any phosphorus application Traditional 2. Phosphorus 3 are made to the field with traditional Application Application Rate equipment the “weighted factor” of 3 Precision should be used for determining the P index. Application 2 3 Nutrient Application 3. Nutrient Application Method considers 3 Method the manner that phosphate fertilizer or 4. Grazing Animals 1 organic P is applied to the site and the 5. Subsurface amount of time that the P fertilizer or organic Drainage & 3 P is exposed on the soil surface. Injection Underground implies that the fertilizer P is buried below 6. Erosion Rate 3 the soil’s surface at a minimum depth of two Common inches. Incorporation is the mixing of the P 7. Hydrologic Soil Soil Health 3 into the surface portion of soil. Surface Group Improved applied manure or litter that has been Soil Health 2 treated with chemicals to reduce P solubility or the field has applications of gypsum at 8. Field Slope 1 the same time as the manure/litter 9. Distance to Water 3 application should be considered as 10.(f t.)Filter Strip Width 2 incorporated. Both chemical treatments 11.(f t.)Impaired or and gypsum application should be done in Outstanding 3 accordance with Alabama Cooperative Waters Extension Systems recommendations for DESCRIPTION OF FIELD reducing P solubility. FEATURES AND 4. Grazing Animals considers the effect of MANAGEMENT animals to cause excessive movement of P PRACTICES into streams and other surface waters. Surface waters include streams, springs, 1. Soil Test P Value considers the branches, lakes, sinkholes, wetlands, or extractable P concentration for surface other related waterbodies. Farm ponds soils (0 – 3 inches in sod crops and depth contained within the tract that do not have a of plow layer in cultivated crops) based continuous water flow are not considered on the double acid (Mehlich 1) or unless the producer considers the farm pond Mississippi extract procedures, to be sensitive and important. Large depending on the soil. Research number of animals with unlimited access to indicates that high soil test P levels may waterbodies or feeding animals in sensitive only play a small role in determining the areas such as drainage ways, concentrated amount of P in runoff unless soil erosion flow areas, or adjacent to a stream can be a and sediment movement into water is contributor to excessive P in waterbodies. group have a moderate infiltration rate when thoroughly wetted. They are moderately deep to deep, moderately 5. Terrace Tile Outlets and Subsurface well drained to well-drained soils that Drains With Open Inlets may convey runoff have moderately fine to moderately water directly to a waterbody, ditch or coarse textures. They have a moderate drainageway without the treatment effect of rate of water transmission. vegetation and can be major way for dissolved P to enter a waterbody. Systems C - Moderate high runoff potential. with open inlets should empty onto a grass The soils of this group have a slow filter or vegetative outlet. infiltration rate when thoroughly wetted. They usually have a layer that impedes 6. Soil Erosion considers the risk of downward movement of water or have movement of sediment bound P in runoff. moderately fine to fine texture. They RUSLE II and the gully equation are used to have a slow rate of water transmission. estimate the total soil erosion. Field information needed to determine the erosion D - High runoff potential. The soils of this rate includes dominant soil type; type of crop group have a very slow infiltration and cover; soil hydrologic group; soil erodibility; thus a high runoff potential. They slope length; slope and information on chiefly consist of clay soils that have contouring, ridge heights, and terracing; and high swelling potential, soils that have a gullies. permanent high water table, soils that have a claypan or clay layer at or near the surface and shallow soil over nearly 7. Runoff Class (Hydrologic Soil Group) impervious material. They have a very considers the runoff potential of the site. The slow rate of water transmission. soils of Alabama are in four hydrologic soil groups. These groupings are based on When more than one hydrologic soil group runoff-producing characteristics of the soil. occurs in the field, use the predominate Research indicates that soil management can group. If a soil is assigned to two also have a significant effect on runoff hydrologic groups, the first letter is for potential. Generally, as soil health improves drained fields only. runoff and P loss will decrease on the same soil. If a producer has implemented BMP’s 8. Field Slope, the inclination of the land and will continue to implement BMP’s that will surface from the horizontal, considers the improve soil health the “weight factor” for the average slope percent for the field based on runoff class will be 2, To take this reduction, on the Soil Survey Report or actual field slopes crop land the following practices must have if available. Field slope is given a weighted been adopted, residue management no-till/strip factor of 1 because slope is also considered till (mulch till for strip till peanuts only), cover in the soil erosion field feature. crops during all fallow segments of the rotation and crop rotation. On pasture land a managed 9. P Application Distance to Water rotational grazing systems that is maintaining considers the distance in feet from the minimum forage height, has proper stocking closest phosphorus application site within rates, provide sufficient recovery time to the field to surface water that receives promote the vigor of the plant community, and runoff from the field. Surface waters permit grazing only when soil moisture include streams, springs, branches, lakes, conditions support livestock traffic without sinkholes, wetlands, or other related excessive compaction must be implemented. waterbodies. These waters will be In all other cases the “weight factor” for runoff identified on the U.S.G.S. topographic class will be 3. map as blue-line waterbodies or streams. Farm ponds contained within the tract that These groupings (Hydrologic Soil Groups) do not have a continuous water flow are are: not considered unless the producer A - Low runoff potential. These soils considers the farm pond to be sensitive have a high infiltration rate even when and important. thoroughly wetted. They mainly consist of deep, well drained to excessively 10. Vegetative Buffer considers the drained sands or gravels and have a treatment effect of a vegetative buffer at all high rate of water transmission. areas where water will flow from the field. This includes the down slope edges of fields B - Moderate runoff potential. Soils of this as well as where water enters conveyance structures such as ditches or concentrated flow areas within the field. The treatment assurance of low P loss. It is a planning tool effect must be from sheet flow across the that can be used in resource management buffer. These vegetative buffers should meet planning and should direct conservation the requirements of Alabama conservation efforts. The P Index can also provide a suite practice standard filter strip (code 393) of management and conservation options and/or riparian forest buffers (code 391) for available to a farmer to reduce the risk of P the intended purpose. . If a vegetative loss. This should result in more rational, buffer is not required, then consider it as a lower cost efforts to minimize the impact of very low rating (0 points) on the P Index. intensive agriculture on water quality. It may also be useful in identifying sites, which do 11. Impaired, Outstanding Waters, or not have elevated soil test P, but which may Critical Habitat Waters considers the also be prone to loss of surface P distance in feet from the closest applications. phosphorus application site within the field to the listed segment of water that receives REFERENCES runoff from the field in the same 12-digit Hydrologic Unit Code area. Listed A Phosphorus Assessment Tool; Technical segments include segment on the 303(d), Note Engineering Series No. 1901; USDA- or TMDL list impaired by nutrients from SCS, South National Technical Center, Ft. agriculture activities, Outstanding Alabama Worth, Tx. Water (OAW), Outstanding National Resource Water (ONRW), public water Jokela, W.E., J.W.Hughes, D. Tobi, and supplies, waters designated for shellfish D.W. Meals. 1999. Managed vegetative and federally designated Critical Habitat riparian buffers to control P runoff losses waters for endangered and threatened from cornfields. Agronomy Abstracts. Amer. species. Key Cave and its source waters in Soc. of Agronomy, Madison, WI Lauderdale County and Cypress Creek and its tributaries to include all tributaries Lemunyon, J.L., & R.G. Gilbert. 1993. The upstream from the junction of Burcham concept and need for a phosphorus Creek, including Burcham Creek, but assessment tool. J. Prod. Agric. 6:483-486. excluding Threet Creek and its tributaries in Lauderdale County are federally designated Lory, J,A., and P.C. Scharf. 1999. Threshold Critical Habitat for endangered and P survey. On Web page for SERA-17, threatened species. Minimizing P losses from agriculture: http:// c e s . s oil.n cs u.edu/ s e r a17/publi c ation s / Site-Specific Application of P_Threshhold/Threshold_P_Survey_3_1_99 the P Index .htm. Within fields, components of the P Index such as slope, hydrologic soil group, and Snyder, C.S., Sharpley, A. N., Bruulsema, T. distance to watercourse may vary greatly. W., Beegle, D.B. Site-specific Use of the Thus, there may be an advantage to site- Environmental Phosphorus Index concept; specific application of the P Index, to a Site-Specific Management Guidelines- resolution as small as field equipment can SSMG-1; Potash & Phosphate Institute. manage. This can be useful in terms of avoiding manure or nutrient applications in sensitive areas of the field and applying variable rates based on soil and crop capacity to absorb and retain nutrients in other areas of the field. However, it must be kept in mind that the P Index is only a crude estimator to rank sites on the relative risk of loss of P to surface water. Therefore, while the site-specific microscale approach can have advantages, it may not be seen to have value by all users. For some, a field level application of the P Index may be more appropriate.

USE OF THE P INDEX The P Index is an approximation of risk. It was developed to rank relative risks, and its level should not be interpreted as an Alabama Phosphorus Index Value Ratings Field Features & Management Practices Low Very High Weight (0 points) (1 point) (2 points) (4 points) (8 points) Source Characteristics Very Low / Extremely 1. Soil Test P Value 1 Medium High Very High Low High Traditional 3 2. P Application Application --- < 60 lbs. 60-120 lbs. 121-180 lbs. >180 lbs. Rate (lbs. P2O5/ac/year) Precision 2 --- Application < 60 lbs. 60-120 lbs. 121-180 lbs. >180 lbs. Incorporated Surface immediately, Injected applied & Surface sprinkler applied deeper than incorporated applied, not 3. Nutrient Application Method 3 --- or surface 2” < 30 days Incorporated applied treated Unlimited Unlimited access No access to Restricted access to water access to water to water 1 water and/or not &/or fed in &/or fed in 4. Grazing Animals None &/or not fed in fed in sensitive sensitive area sensitive area area sensitive area <100 animals >100 animals Transport Characteristics Runoff passes < 30% of field > 30% of field through a of Outlets empty has outlets has outlets 5. Underground Outlet Systems 3 None grass filter strip into grass emptying into emptying into before leaving waterways drainageways drainageways or the system or waterbodies waterbodies 6. Erosion Rate (tons/ac/yr) 3 < 3 tons 3-5 tons 5-10 tons 10-15 tons > 15 tons Common Soil 3 -- A B C D 7. Hydrologic Soil Health Group Improved Soil Health 2 -- A B C D

8. Field Slope (%) 1 < 1% 1-3% 3-5% 5-8% > 8% 9. P Application Distance to 3 > 400 ft. 201-400 ft. 101-200 ft. 50-100 ft. < 50 ft. Water (ft) > 50 ft. or not 30-49 ft. 20-29 ft. 10-19 ft. <10 ft. 10. Vegetative buffer Width (ft) 2 required Receiving Water Categories

11. Impaired, Outstanding, Field not in 3 > 400 ft. 201-400 ft. 101-200 ft <100 ft or Critical Habitat Waters watershed Risk Categories for Phosphorus Loss Phosphorus Total Points Application Generalized Interpretation of P Index from P Index Rate < 65 Nitrogen Rate LOW potential for P movement from the field. There is a low probability of an adverse impact to waterbodies Moderate potential for P movement from the field. The chance of organic material or nutrients getting into waterbodies 3 x P removal by exists. Buffers, setbacks, lower manure rates, cover crops, and crop residue practices alone or in combination may crops 66 to 75 reduce impact. Moderately High potential for P movement from the field. The chance of organic material or nutrients getting to 2 x P removal by waterbodies is possible. Buffers, setbacks lower manure rates, cover crops, crop residues, etc., in combination may crops 76 to 85 reduce impact. P removal by HIGH potential for P movement from the field and an impact on waterbodies. 86 to 95 crops > 96 No P Application Very HIGH potential for P movement from the field and an adverse impact on waterbodies.