Phosphorus Site Index Update University of Maryland Phosphorus Management Tool

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1 Phosphorus Site Index Update University of Maryland Phosphorus Management Tool Joshua M. McGrath Associate Professor Soil Fertility and Nutrient Management Specialist Laboratory for Agriculture and Environmental Studies DEPARTMENT OF ENVIRONMENTAL SCIENCE & TECHNOLOGY

2 Nutrient Management Planning The Phosphorus Management Tool (PMT) is a component of the agricultural nutrient management planning process. The PMT is an update of the P Site Index (PSI), which has been in use since 2000 and updated in The PMT is a tool for assessing relative risk for P loss from an agricultural production field. The PMT does not generate a quantitative estimate of the amount of P lost in field drainage water. The PMT assessment is site specific and management specific.

3 Nutrients Nutrients Phosphorus (P) and nitrogen (N) are different. P and N behavior in soil is different. P and N management must be different.

4 Fundamentals of P Management Phosphorus is not like nitrogen Probably less than 15% of applied P is available in the first year, especially in low P soils Reductions in rate will not improve efficiency in many situations Increases in efficiency will not result in decreases in loss The only way to decrease loss is through management of timing and placement There is a dubious (if not non-existent) relationship between P use efficiency and P loss

5 Why P management? P is essential to all forms of life on earth no known toxic effects Adequate P levels in soils are essential for production of agronomic crops In most fresh surface water bodies growth of algae or aquatic plants is limited by P availability

6 Phosphorus Losses: Source and Transport Sources Transport N P K Runoff P leaching Erosion Tile flow Subsurface flow

7 Why not to use a critical value? The best science indicates that not all fields are equal when it comes to delivering P to surface water Although not agronomically efficient to apply P to high P fields, it may be economically optimum

8 Why not to use a critical value? A threshold value could lead to application of manure to lower P fields with higher potential for runoff A threshold value is an arbitrary environmental limit that is not supported by ANY science environmental thresholds are not consistent between fields

9 Case Study: Transport overrides source P measured in surface runoff during natural storm events ( ) in a strip-cropped watershed in central Pennsylvania Upper two fields had high soil phosphorus (144 &177 mg kg -1 Mehlich-3 soil phosphorus) and received manure and fertilizer Field closest to stream was a grass buffer with no P applied (78 mg kg -1 Mehlich-3 soil phosphorus). Buda et al., 2009

10 Hydrology overwhelms soil P! 8 kg/ha/yr P runoff load 4541 L Runoff Volume Riparian zone was prone to water logging Runoff volumes were 46-fold greater than from other two fields combined If soil P threshold was used to guide P application, then P losses would have been much higher 1 kg/ha/yr P runoff load 66 L Runoff Volume <1 kg/ha/yr P runoff load 32 L Runoff Volume Mehlich-3 Soil P 78 mg/kg Mehlich-3 Soil P 144 mg/kg Mehlich-3 Soil P 177 mg/kg

11 Management over P source Total Phosphorus (kg/ha) Cumulative P load from four different tillage practices in SAME corn field at Wye Research and Education Center (2006) Soil Test P = 65 mg kg -1 4 ton/acre poultry litter 0.0 Residue: NT TT ST CHP 77% Tillage 39% 46% 11% McGrath (unpublished)

12 Substitute for critical value Agronomic soil tests are not calibrated to environmental loss Can be agronomically appropriate to apply manure even if soil test says no P is needed Nitrogen, OM, ph, micronutrients, transport cost, etc. Need tool to guide nutrient application while minimizing environmental losses

13 Agronomic Test 100 Relative Yield ( % ) Low Medium Optimum Critical Level Excessive Soil Test Phosphorus (FIV)

14 Environmental Test Relative P Transport Risk Low Medium High Critical Level Phosphorus Management Tool

15 Conventional soil-test phosphorus.. the first hurdle to clear Soil-test P (FIV) EXCESSIVE OPTIMUM MEDIUM HIGH OK 0 LOW Agronomic Environmental

16 Old Phosphorus Site Index (PSI) Final Score Interpretation P Loss Rating Interpretation 0 50 LOW potential for P movement from site. N-based nutrient management planning is satisfactory MEDIUM potential for P movement from site. Limit P applications to amount expected to be removed from field by harvest or to soil test P recs. N-based planning 1 year of 3. P-based planning 2 years of HIGH potential for P movement from site. Use P-based nutrient management planning. Limit P applications to expected crop removal or soil test P recommendations. > 100 VERY HIGH potential for P movement from site. No P should be applied to this site. Implement active remediation techniques to reduce P loss potential.

17 Maryland PSI performance : 646 fields PSI Loss Rating Low 69% Medium 19% High 8% P-based planning 2 of 3 yrs P-based planning only Very High 4% No P applications

18 Maryland PSI performance : 646 fields : 8,728 fields PSI Loss Rating Low 69% 64% Medium 19% 25% High 8% 9% P-based planning 2 of 3 yrs P-based planning only Very High 4% 2% No P applications

19 Factors evaluated in P Index assessments Soil erosion loss estimation Surface runoff potential of site Subsurface drainage potential of site P leaching potential of site Distance from edge of field to surface water Buffer type and width Receiving water body priority status Agronomic soil test P level Soil P saturation ratio P fertilizer application rate P fertilizer application method, placement, tillage & timing Manure P application rate and P solubility Manure P application method, placement, tillage & timing Old PSI X UM-PMT X X

20 Revised UM-PMT Final Score Interpretation P Loss Rating Interpretation 0 50 LOW potential for P movement from this site given current management practices and site characteristics. Total phosphorus applications should be limited to no more than one three-year crop removal rate applied over a three year period MEDIUM potential for P movement from this site given current management practices and site characteristics. Phosphorus applications should be limited to the amount expected to be removed from the field by crop harvest. > 100 HIGH potential for P movement from this site given current management practices and site characteristics. No phosphorus should be applied to this site. Active remediation techniques should be implemented in an effort to reduce the P loss potential from this site.

21 Management: Critical Source Area Old Critical Source Area Transport Source and Management

22 Management: Critical Source Area Management New Critical Source Area Transport Source

23 PSI Modifications Management Subsurface + + Management Management Transport Source Transport Source Runoff Transport Source Particulate Additive pathway factors

24 PSI Modifications Subsurface + + Management Transport Source Additive pathway factors Appropriate in areas where one pathway dominates

25 The calculation OLD PSI = (Source and Management) X Transport NEW Dissolved P = Source X Management X Transport + Particulate P = Source X Management X Transport + Subsurface P = Source X Management X Transport

26 Subsurface Drainage Subsurface Drainage Component is only calculated if artificial drainage is present (e.g. ditches, tile)

27 Subsurface Drainage Transport

28 Management Timing and method of application can decrease risk Table 3. Phosphorus application method factor for subsurface transport component (AM sub ). Application Method Value None Applied 0 Incorporated within 5 days with soil mixing (precludes straight aerator) March - Nov. Incorporated within 5 days with soil mixing (precludes straight aerator) Dec. - Feb. Surface applied and subsurface placement without soil mixing (includes banded fertilizer and injection without soil mixing) March - Nov. Surface applied and subsurface placement without soil mixing (includes banded fertilizer) Dec. - Feb

29 Subsurface Source Total P applied Solubility of P applied (PSC from old PSI) Soil P solubility (DPS = P/Fe+Al)

30 Surface Dissolved P Distance*Transport*Source Distance is a function of distance and land cover on the distance Transport is a function of permeability and slope Source is a function of soil soluble P, manure soluble P, and how the manure P was applied

31 Distance Factor Table 1. Distance from edge of field to surface water and resulting distance factor. Distance from Surface Water Distance Factor (DF) >500 feet to 500 feet to 349 feet to 199 feet 0.8 <100 feet 1.0 Surface water includes any permanent, continuous, physical conduit for transporting surface water, including permanent streams and ditches even if they only flow intermittently during the course of the year.

32 Buffer Factor Table 2. Types of buffers and resulting buffer factors that will modify the Distance Risk Factor to yield the combined Distance Buffer Factor. Type of Buffer Buffer Factor (BF) >50 feet Permanent Vegetated Buffer Meeting USDA-NRCS 0.8 Standards >35 feet Permanent Vegetated 0.9 Buffer <35 feet Vegetated Buffer or 1.0 No Buffer Permanent vegetated buffers do not receive any phosphorus applications.

33 Surface Runoff Factor Table 7. Surface runoff transport risk factor (SR) based on field slope and soil permeability class. Soil Permeability Class (inches/hour) Moderately Moderately Rapid Very Slow and Slow Slope (%) Rapid ( > 20) and Rapid (2.0 to 20) Moderate (0.2 to 2.0) (0.06 to 0.2) Very Slow ( < 0.06) Concave < > Permeability class of the least permeable layer within the upper 39 inches of the soil profile. Permeability classes can be obtained from Web Soil Survey. Area from which no or very little water escapes by overland flow.

34 RUNOFF = DBF*SR*DPR r Distance-Buffer Factor Surface Runoff Factor Dissolved P Risk Factor for Runoff Method of application (e.g. tillage, injection, timing) Amount applied (Total P in manure) Solubility of P applied (PSC from old index) Solubility of P in the soil (DPS = P/Fe+Al)

35 Application Method Surface Transport Table 4. Phosphorus application method factor for surface transport component (AM r ). Application Method Value None Applied 0 Subsurface placement or immediate full incorporation (>90% residue) 0.2 Incorporated within 5 days of application ( 50% residue) 0.4 Surface applied March - Nov. OR incorporated after 5 days OR <50% residue 0.6 Surface applied or incorporated after 5 days Dec. - Feb. 0.8

36 Particulate P Particulate P is a factor of Distance from surface water (acts as a filter reducing score) Sediment loss calculated by RUSLE2 or RUSLE Soil Test P

37 Final Calculation The three transport pathways are summed The 0.1 factor scales the transport functions from 0 1 UMPMT = 0.1* ( SUBSURFACE + RUNOFF + PARTICULATE) Where SUBSURFACE = SD * RUNOFF = DBF * SR * DPR sub DPR PARTICULATE = DBF * SED * FIV r

38 Current Efforts We will continue to evaluate the performance of the UM-PMT and assess its sensitivity to site, source and management factors We are working to calibrate the UM-PMT against a validated field P loss model to make sure it is directionally and magnitudinally correct

39 Accuracy versus Precision High Precision Low Accuracy Low Precision High Accuracy 39

40 Evaluating PMT accuracy

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