ABSTRACT Decreasing the potential delivery of phosphorus in fertilizers or animal waste to surface and groundwater requires a knowledge of phosphorus's fate and transport mechanisms. The USDA Natural Resources Conservation Service has recently mandated each state to develop an assessment tool to estimate P transport to water bodies. The objective of this paper is to describe the processes involved with P transport to surface and groundwaters that must be accounted for in practical methods used to quantify the potential for P loss. Mechanistic models to assess P loss should account for: 1) P adsorbed to eroding sediments, 2) soluble P in runoff water, 3) soluble P in leaching water, and 4) P losses related to specific P sources. With sediment-bound P, the adsorbed P content in the eroded soil mass at the field edge must be quantified, whereas runoff volume and P concentration are needed to estimate soluble P loss in runoff water. Estimating P leaching potential requires calculation of drainage water volume and P concentration. When P is applied in animal waste, the specific source influences both soluble and particulate P loss because of differences in P solubility between waste types. In addition, the effects of conservation practices and other technologies on decreasing sediment, soluble, and leached P need to be included. Using these methods, a practical, quantitative P loss assessment tool can be developed that will enable technical service providers and other practitioners to estimate potential P loss and design best-management practices for land-applied waste management systems in order to minimize P transport to surface and groundwater.
Key Words: Environment, Erosion, Leaching, Manure, Runoff, Water Quality
© 2004, by the American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2004. 82(E. Suppl.):E277-E291
Implications
Producers receiving federal commodity support payments are required to incorporate P loss assessment into nutrient management planning. Accurate estimates of P loss require methods to quantify 1) P adsorbed to eroding sediments, 2) soluble P in runoff water, 3) soluble P in leaching water, and 4) P losses related to the specific P sources. Successful methods used to quantify P loss associated with P applications must also enable producers to identify best management practices that reduce or minimize P loss. Although the accuracy of a P loss assessment is important, the relative ease of use by practitioners is essential. Thus, methods that estimate P loss related to the four mechanisms discussed should be based on established and user-friendly methods. The intended use of P loss assessment tools by practitioners routinely interacting with land managers will help ensure that P use in agricultural ecosystems will minimize the contribution of P use on surface and groundwater quality.
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1This article was presented at the 2003 ADSA-ASAS-AMPA meeting as part of the symposium Production, Management, and the Environment: Impact of Animal Feeding Operations on the Environment.
2Correspondence: P.O. Box 7619 (phone: 919-513-4411; fax: 919-515-2167; e-mail: john_havlin@ncsu.edu).
Received July 10, 2003.
Accepted September 24, 2003.
| Table 1. Soil and crop management factors that reduce annual estimated sediment loss | ||
| RUSLE parametera | Conservation practice | Relative reductionb |
| Slope length (SL) | Terraces | High |
| Vegetative filter stripsc | Medium | |
| Crop cover (CC)d | Permanent pasture | High |
| No tillage (standing residue) | High | |
| No tillage (residue removed) | Medium-Low | |
| 50% residue incorporation | Medium | |
| 75% residue incorporation | Low | |
| Practice factor (PF)e | Terraces | High |
| Contour tillage | Low | |
| Contour conservation tillage | Medium-Low | |
| Contour cropping (conventional tillage) | Medium-Low | |
| Contour cropping (no tillage) | Medium-High | |
| Contour strip cropping (conventional tillage) | Medium | |
| Contour strip cropping (no tillage) | High | |
| aRevised Universal Soil Loss Equation. The abbreviation SL represents the slope length factor, CC is the crop cover management factor, and PF represents supporting practice factor. | ||
| bRelative reduction sediment transport to the field edge as influenced by conservation practices. | ||
| cNarrow (<1 m) permanent grass strips planted on the contour. As with terraces, the steeper the slope the smaller the interval between strips. | ||
| dCrop cover relates the amount of previous crop residue left on the surface and growing crop canopy available to protect the soil surface from raindrop impact. Crop cover factor varies greatly with previous and growing crop. Increasing tillage intensity decreases surface crop residue cover and increases potential sediment loss. | ||
| ePractice factor reduces estimates of sediment loss with adoption of contour tillage, contour cropping, and contour strip cropping relative to tillage and cropping parallel with the slope direction. Terraces are also included in this factor because terraces are installed on the contour. |
| Table 2. Effect of receiving slope length on the sediment delivery ratio and proportion of particulate P delivered to the field edgea,b | ||
| Receiving slope length, m | Sediment delivery ratio | Edge of field particulate P delivery |
| 0 | 1.00 | 1.00 |
| 15 | 0.45 | 0.58 |
| 30 | 0.35 | 0.46 |
| 60 | 0.15 | 0.20 |
| 90 | 0.10 | 0.13 |
| aRatio of soil transported by erosion to sediment delivered to the receiving slope. | ||
| bEdge of field particulate P delivery reflects an increase in sediment delivery ratio of 1.3 to account for enrichment of more finely textured particles in sediment delivered to the field edge. |
| Table 3. Soil Characteristics used in the curve number method of estimating surface runoff | ||
| Soil group | Soil characteristics | Minimum infiltration capacity, cm/h |
| A | Sandy, deep, well-drained soils; deep loess; | >0.76 |
| aggregated silty soils, lowest runoff potential | ||
| B | Sandy loams, shallow loess, moderately deep | 0.38-0.75 |
| and moderately well-drained | ||
| C | Clay loam soils, shallow sandy loams with clay subsoil | 0.13-0.37 |
| layer, low-organic-matter soils | ||
| D | Heavy clay soils with swelling potential, water-logged soils, certain saline soils, shallow soils with impermeable subsoil layer | <0.12 |
| Table 4. Selected sources of animal wastes and their P contenta | ||||
| Waste source | Total Pb | Soluble fractionc | Soluble Pd | Nonsoluble Pe |
| Beef | ||||
| Lagoon liquid, kg P•ha–1•cm–1 | 15.0 | 0.80 | 12.0 | 3.0 |
| Lagoon sludge, g P/L | 2.7 | 0.60 | 1.6 | 1.1 |
| Slurry, g P/L | 1.2 | 0.75 | 0.9 | 0.3 |
| Dairy | ||||
| Lagoon liquid, kg P•ha–1•cm–1 | 15.0 | 0.80 | 12.0 | 3.0 |
| Lagoon sludge, g P/L | 1.2 | 0.60 | 0.7 | 0.5 |
| Scraped, kg P/t | 1.4 | 0.60 | 0.8 | 0.6 |
| Slurry, g P/L | 0.7 | 0.75 | 0.5 | 0.2 |
| Swine | ||||
| Lagoon liquid, kg P•ha–1•cm–1 | 10.3 | 0.80 | 8.2 | 2.1 |
| Lagoon sludge, g P/L | 2.6 | 0.40 | 1.0 | 1.6 |
| Slurry, g P/L | 1.2 | 0.60 | 0.7 | 0.5 |
| Broiler | ||||
| Fresh manure, kg P/t | 3.6 | 0.25 | 0.9 | 2.7 |
| House litter, kg P/t | 17.3 | 0.25 | 4.3 | 13.0 |
| Stockpiled litter, kg P/t | 17.5 | 0.25 | 4.4 | 13.1 |
| Layer | ||||
| Highise manure, kg P/t | 12.3 | 0.60 | 7.4 | 4.9 |
| Lagoon liquid, kg P•ha–1•cm–1 | 8.9 | 0.80 | 7.1 | 1.8 |
| Lagoon sludge, g P/L | 4.9 | 0.50 | 2.5 | 2.4 |
| Slurry, g P/L | 3.1 | 0.60 | 1.9 | 1.2 |
| Undercage manure, kg P/t | 6.9 | 0.50 | 3.5 | 3.4 |
| Turkey | ||||
| Stockpiled litter, kg P/t | 15.9 | 0.25 | 4.0 | 11.9 |
| House litter, kg P/t | 11.5 | 0.25 | 2.9 | 8.6 |
| aBarker et al. (1994), USDA-NRCS (1998), Dou et al. (2000), and Sharpley and Moyer (2000). | ||||
| bConcentration units vary with waste source. | ||||
| cWeight basis. | ||||
| dSoluble P = total P × soluble fraction. | ||||
| eInsoluble P = total P – soluble P. |
| Table 5. Soluble and insoluble P attenuation factorsa | ||
| Waste source | SPAFb | NSPAFc |
| Litter | 0.4 | 0.1 |
| Manure | 0.4 | 0.1 |
| Sludge | 0.4 | 0.1 |
| Scraped | 0.4 | 0.1 |
| Slurry | 0.3 | 0.1 |
| Liquid | 0.1 | 0.1 |
| Fertilizer | 0.1 | NA |
| aAdapted from Westerman and Overcash (1980), Westerman et al. (1983), Edwards and Daniel (1993a,b), and Tarkalson (2001). | ||
| bSPAF = Soluble P attenuation factor. | ||
| cNSPAF = Insoluble P attenuation factor. |
| Table 6. Approximate factors used to adjust P loss estimates for method of P application | |
| Application method | Factor |
| None applied | 0.00 |
| Injected | 0.01 |
| Incorporated within 48 h | 0.05 |
| Incorporated within 4 wk or less following application | 0.10 |
| Incorporated between 4 and 12 wk following application | 0.50 |
| All other surface (unincorporated) applications | 1.00 |
Figure 1. Diagram of major pathways contributing to P transport to surface and groundwater.
Figure 2. Effect of soil erosion rate on particulate P loss and P enrichment ratio.
Figure 3. Influence of rainfall, tillage direction, and residue level on soil loss. Treatments shown include the following: full till U/D = full tillage (no residue cover) up and down or parallel to the slope direction; min till U/D = minimum till (30% residue cover) up and down the slope; full till-C = full tillage on with the slope contour; min till-C = minimum tillage on with the slope contour; no till = no tillage (100% residue cover).
Figure 4. Sediment P determined by clay content and the Mehlich-3 P soil test for P (Mehlich-3 P level). Inflection point represents threshold Mehlich-3 P that produces is more than or equal to 1 mg/L of soluble P.
Figure 5. Effect of riparian buffer width on P delivery ratio in the buffer, which represents the fractional decrease in sediment P with increasing buffer width (data summarized from Peterjohn and Correll, 1984; Magette et al., 1989; Daniels and Gilliam, 1996; and Dillaha and Inamdar, 1997).
Figure 6. Dissolved P in runoff on North Carolina sand and clay soils as influenced by the Mehlich-3 soil test for P (Mehlich-3 P level).
Figure 7. Influence of Mehlich-3 P soil test (Mehlich-3 P level) and dissolved P in runoff in a Pennsylvania watershed.
Figure 8. Concentration of dissolved P as a function of Mehlich-3 soil test P level for major soil textural classes. The Mehlich-3 P levels that result in 1 mg/L dissolved P are as follows: organic soils = 50; sands = 100; loams = 200; and clays = 500.
Figure 9. Example relationship between curve number and runoff volume for Wake County, North Carolina.
Figure 10. The effect of Mehlich-3 P soil test level (Mehlich-3 P) and cropping system on dissolved P in runoff. Cropped fields represent wheat with residue incorporated with a moldboard plow and grassed fields represent native short grass pasture.
Figure 11. Influence of soil erosion rate, which increases with decreasing surface residue cover, and the P extraction coefficient, which represents the slope of the linear relationship between Mehlich-3 soil test P and dissolved P concentration in runoff water. A = native grass/pasture; B = no tillage; C = reduced tillage; and D = conventional tillage.
Figure 12. Influence of soil texture (A) and duration after surface waste application (B) on P leaching in a sandy soil.
Figure 13. Effect of total P applied as swine effluent during a 5-yr period on distribution of Mehlich-3 P soil test level.
Figure 14. Dissolved P concentrations as a function of Mehlich-3 soil test P levels at the 0.75-m depth.
Figure 15. Influence of sediment content in runoff and surface broadcast or incorporated P in manure or fertilizer on total P concentration in runoff.
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