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Nutrient Reduction Strategy Phosphorus Science Team

Iowa Science Assessment of Nonpoint Source Practices to Reduce Phosphorus to the Mississippi River Basin. Nutrient Reduction Strategy Phosphorus Science Team. Nutrient Reduction Strategy Phosphorus Science Team. Jim Baker – IDALS/ISU Reid Christianson – ISU Rick Cruse – ISU

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Nutrient Reduction Strategy Phosphorus Science Team

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  1. Iowa Science Assessment of Nonpoint Source Practices to Reduce Phosphorus to the Mississippi River Basin Nutrient Reduction StrategyPhosphorus Science Team

  2. Nutrient Reduction StrategyPhosphorus Science Team • Jim Baker – IDALS/ISU • Reid Christianson – ISU • Rick Cruse – ISU • John Kovar – USDA-ARS • Matt Helmers – ISU • Tom Isenhart – ISU • Antonio Mallarino – ISU • Keith Schilling – IDNR • Calvin Wolter – IDNR • Dave Webber - ISU

  3. Approach • Establish baseline – existing conditions • Major Land Resource Areas used to aggregate conditions • Extensive literature review to assess potential performance of practices • Outside peer review of science team documents (practice performance and baseline conditions) • Estimate potential load reductions of implementing nutrient reduction practices (scenarios) • “Full implementation” and “Combined” scenarios • Estimate cost of implementation and cost per pound of nitrogen and phosphorus reduction

  4. Approach • The P evaluation primarily focused on practices that limit or control P losses from agricultural land. • Does not include known sources of P such as point sources, leaking rural septic systems, and stream bank erosion. ISU NREM USDA NRCS

  5. Approach • Stream banks are known to be a potentially large source of suspended and bedded sediments. • Estimated contributions ranging from 40 to 80% of annual sediment loads in Midwestern streams. • Accurate accounting is difficult. Isenhart et al. Unpublished

  6. Practice Review Process • Established an overall list of potential practices based on input of overall science team • Shortened the list to those expected to have greatest potential for nutrient reduction through detailed discussion of P team – reviewed by overall science team • New and emerging practices could be added in future

  7. Practice Review Process Phosphorus Reduction Strategies Excluded Due to Very Limited Impact or Not Information at this Point • Timing of phosphorus application • Living mulches (e.g. kura clover) • Green manure • No continuous soybean • Shallow drainage • Drainage water management • Bioreactors • Two-stage ditches

  8. Practice Review Process P reduction practices fall into three main groups • P Management Practices • Application • Source (commercial fertilizer, manure) • Placement • Cover crops • Tillage • Land use change • Crop choice • Perennial vegetation • Erosion Control and Edge of Field Practices • Terraces • Wetlands • Buffers • Other erosion control

  9. Practice Review Process • Extensive review of literature from Iowa and surrounding states • Used Iowa and surrounding states to try to have similar soils and climatic conditions • Reviewed and compiled impacts phosphorus concentrations and loads • Reviewed and compiled impacts on corn yield • Summarized expected practice performance

  10. Nitrogen or Phosphorus? Nitrogen moves primarily as nitrate-N with water Phosphorus moves primarily with eroded soil

  11. Phosphorus Reduction Practices • Practices were compared with a corn-soybean rotation • P needed by the two crops surface-applied once after soybean harvest in the fall before soils freeze • Tillage includes chisel plowing cornstalks after harvest and disking/field cultivating in the spring before planting soybeans • Before planting corn the normal practice is disking/field cultivating in the spring

  12. Phosphorus Management Practices Phosphorus Application Rate • P rate is less important than N rate as it affects water quality • P rate affects the STP level, so historical P application rates and current STP level are important for impacts on water quality • Application rate is of great concern when any manure type is applied at N-based rates • Load reduction was estimated using Iowa P Index comparing rates of 200 kg P2O5 ha-1 (max), and 125 kg P2O5 ha-1 (avg.) compared to the average annual removal for a corn-soybean rotation of 62 kg P2O5 ha-1. • Estimates in bracket are “worst case scenarios” in which a rainfall occurs within 24 hours of P application

  13. Phosphorus Management Practices Soil Test Phosphorus Level • Phosphorus loss can be reduced by decreasing total soil P concentration • This practice assumes limiting or stopping P application to high-testing soils until STP is lowered to agronomically optimum concentrations of 20 ppm for corn and soybean production • Load reduction was estimated using Iowa P Index for a 5 Mg ha-1 erosion rate • Maximum load reduction was estimated by comparing P loss with an STP of the two highest counties in IA (125 ppm) to the optimum (20 ppm) STP level • Average load reduction was estimated based on reducing the average STP of all counties in IA (40 ppm) to the optimum STP level • Estimates in brackets are from unpublished work by Mallarino (2011)

  14. Phosphorus Management Practices Site-Specific P Management • Site-specific management that considers the P loss risk from different areas of a field could be a beneficial practice to reduce P loss • Not well studied, but research in IA has found variable-rate fertilizer and manure P application to be effective in reducing within field variability of STP levels • The approach used to estimate P load reduction was the same as for the STP practice and used mean values from a recent unpublished study by Mallarino that included the mean proportion of IA STP classes for each field

  15. Phosphorus Management Practices Source of Phosphorus • There is little evidence of P source (i.e. fertilizer compared to manure P) effects short-term delivery from fields if the P is incorporated into the soil • In the long term, manure can reduce runoff compared to inorganic P forms by increasing soil organic carbon • If runoff-producing rainfall events occur immediately after application, less P loss occurs with solid beef and poultry manure compared with commercial fertilizer

  16. Phosphorus Management Practices Placement of Phosphorus • Subsurface banding of P or incorporation of surface-applied P fertilizer or manure on sloping ground reduces P loss significantly compared with surface application when runoff-producing precipitation occurs shortly after application • Estimates in brackets are from a report by Dinnes (2004) and are the author’s best professional judgment

  17. Phosphorus Management Practices Cover Crops • Cover crops reduce erosion by improving soil structure and providing ground cover as a physical barrier between raindrops and the soil surface

  18. Phosphorus Management Practices Tillage • Tillage practices affect soil erosion, the primary process for P delivery in IA • Tillage effects on P loss are site specific, but less P loss generally occurs with minimum or no tillage compared with conventional tillage • No-till can increase the proportion of total P lost as dissolved P, especially in tile-drained areas

  19. Land Use Change Crop Choice • There is very little P loss data for specific extended rotations compared to a corn-soybean rotation in IA Perennial Vegetation • Perennial vegetation established as energy crops or land retirement would significantly reduce soil erosion and P loss • Delivery of P to water bodies is highly affected by pasture management

  20. Erosion Control and Edge-of-Field Practices Buffers • Designed to reduce P delivery by removing particulate P from runoff through filtration and sedimentation and reducing dissolved P by plant uptake or soil binding • Riparian buffers can also stabilize stream banks Erosion Control • Designed to reduce sediment delivery • Includes sedimentation basins, drop structures, ponds, etc.

  21. Phosphorus Reduction Practices *Load reduction not concentration reduction

  22. P-Index Model

  23. P-Index Inputs for Erosion Component • Gross Erosion rate (tons/acre/yr) • Landform Region (Sediment Delivery ratio) • Distance from Stream • Buffer Distance • Enrichment Factor (Tillage/No till) • Soil Test Phosphorus content (ppm P)

  24. Gross Erosion Estimate • RUSLE model • A = R * K * LS * C * P • A = annual soil loss (tons/yr) • R = rainfall erosivity factor • K = soil erodibility factor • LS = length slope factor • C = cover factor • P = practice factor

  25. County Data from NRCS

  26. Distance Categories to NHD Stream Network • 0 – 500 ft • 500 – 1,000 ft • 1,000 – 2,000 ft • 2,000 – 4,000 ft • 4,000 – 8,000 ft • 8,000 – 16,000 ft • > 16,000 ft

  27. Data from SSURGO • K Factor (soil erodibility factor) • Slope • Slope Length

  28. Cover Factor • Use Crop Rotation information from NASS CDL • Use Tillage Practice information from CTIC • 7-8 combinations for each MLRA • Use Section I-C-1 from SCS-Iowa 1990 to obtain Cover Factor and LS Factor

  29. Practice Factor • Contour Strip Cropping • Terraces • Contour Strip Cropping and Terraces • Use Section I-C-1 from SCS-Iowa 1990 to obtain Practice Factor

  30. Gross Erosion Calculation • A = R * K * LS * C * P • Perform RUSLE calculation for each cropping rotation/tillage combination in each distance class in MLRA

  31. P-Index Model

  32. P-Index Inputs for Runoff Component • Landcover condition (crop and residue) • Dominant Soil type • Soil Test Phosphorus content (ppm P) • Fertilizer Application Rate (lb P2O5/acre) • Fertilizer Application Method

  33. Dominant Soil Type in MLRA Distance Classes • K Factor • KSat Factor (Saturated Conductivity) • Slope • Slope Length • Find Soil Type that matches all factors the closest

  34. P-Index Input for Drainage Component • Tile Drained soil • Well Drained soil

  35. Result of P-Index Model • Phosphorus loss in lbs/ac/year for each crop rotation/tillage/buffer distance combination • Sum up all combinations for MLRA to obtain total Phosphorus Loss for MLRA • Perform for each individual management practice and combinations

  36. Phosphorus Practices – Potential Load Reduction Target Load Reduction from NPS for Hypoxia Goal ~29%

  37. Phosphorus Reduction Scenarios Scenario: Not applying P on acres with high or very high Soil-Test P (RR) • This practice involves not applying P on fields where STP values exceed the upper boundary of the optimum level for corn and soybean in Iowa (20 ppm, Bray-1 or Mehlich-3 tests, 6-inch sampling depth). This practice would be employed until the STP level reaches the optimum level. • Practice limitations, concerns, or considerations • Limitation to utilization of manure-N. When manure is applied, use of the P Index (which considers STP together with other source and transport factors) to assess potential impact of N-based manure on P loss is a reasonable option considering farm economics and other issues. • Landlord/tenant contracts often require maintaining STP levels, even if higher than optimum.

  38. Phosphorus Reduction Scenarios Scenario: Inject/Band P in All No-Till Acres (IN) • This practice involves injecting liquid P sources (fertilizer or manure) and banding solid inorganic fertilizers within all current no-till acres. • Practice limitations, concerns, or considerations • For inorganic P fertilizers, it adds to the costs and does not increase (nor reduce) yield in Iowa. • Possible benefits of injecting or banding inorganic P fertilizer containing N by improving N use efficiency. • For liquid manure, this is a good practice to use manure-N efficiently. • For solid manure, there is no practical way to do it yet, but engineering advances for prototypes being evaluated could make it practical in the future.

  39. Phosphorus Reduction Scenarios Scenario: Convert All Intensive Tillage to Conservation Tillage (Tct) • This practice involves the conversion of all tillage acres to conservation tillage that covers 30 percent or more of the soil surface with crop residue, after planting, to reduce soil erosion by water. • Practice limitations, concerns, or considerations • No clear data concerning impacts of this type of conservation tillage on possible corn yield reduction compared with moldboard plowing. However, data suggests the yield reduction is minimal in most conditions. • These reduced tillage practices are significantly less efficient than no-till at controlling soil erosion and surface runoff.

  40. Phosphorus Reduction Scenarios Scenario: Convert All Tilled Area to No-Till (Tnt) • This practice involves the conversion of all tillage to no-till, whereby the soil is left undisturbed from harvest to planting except for strips up to 1/3 of the row width made with the planter (strips may involve only residue disturbance or may include soil disturbance). This practice assumes approximately 70 percent or more of the soil surface is covered with crop residue, after planting, to reduce soil erosion by water. • Practice limitations, concerns, or considerations • No-till results in lower corn yield than with moldboard or chisel-plow tillage. However, the yield reduction is less or none for other minimum tillage options that, on the other hand, are less efficient at controlling soil erosion and surface runoff. • No-till or conservation tillage does not affect soybean yield significantly.

  41. Phosphorus Reduction Scenarios Scenarios: Plant a rye cover crop on all corn-soybean and continuous corn acres (CCa) Plant a rye cover crop on all no-till acres (CCnt) • The cover crop in this practice/scenario is late summer or early fall seeded winter cereal rye. • Practice limitations, concerns, or considerations • Impact on seed industry due to increased demand for rye seed. • Row crops out of production to meet rye seed demand. • New markets for cover crop seed production and establishment. • Livestock grazing. • Corn and soybean planting equipment designed to manage cover crops in no-till. • Negative impact on corn grain yield for species with spring growth.

  42. Phosphorus Reduction Scenarios Scenario: Establishing 35 foot buffers on all crop land (BF) • Buffers have the potential to be implemented adjacent to streams to intercept overland flow and reduce P transport to receiving waters.

  43. Phosphorus Reduction Scenarios Scenario: Perennial Crops (Energy Crops) Replacing Row Crops (EC) • This scenario switches corn and soybean row crop land to energy crops at the amount equivalent to reach the total number of acres in pasture/hay in 1987 for each MLRA. Row crop acres were reduced proportionally for the corn-soybean rotation and continuous corn. • Practice limitations, concerns, or considerations • Immediate limited market for perennials as energy crops. • Market shifts in crop prices and demand.

  44. Phosphorus Reduction Scenarios Scenario: Grazed Pasture and Land Retirement Replacing Row Crops (P/LR) • This scenario increases the acreage of pasture and retired land to equal the pasture/hay and retired land acreage in 1987, which was the first time land was enrolled in the Conservation Reserve Program (CRP). Row crop acres were reduced proportionally for corn-soybean rotation and continuous corn. • Practice limitations, concerns, or considerations • Market and price shifts due to reduced row crop production. • New markets for grass-fed beef.

  45. Phosphorus Reduction Scenarios Scenario: Extended Rotation (corn-soybean-alfalfa-alfalfa-alfalfa) (EXT) • This scenario Increases the acreage of extended rotations by doubling the current amount of extended rotations (and reducing proportionally the corn-soybean rotation and continuous corn) in each MLRA. • Practice limitations, concerns, or considerations • Reduce the amount of corn and soybean produced in Iowa. • Market shift in product production (more alfalfa) and associated price for crops produced. • Increased livestock production to feed alfalfa. • Market shift as little fertilizer N is needed for corn following alfalfa.

  46. Phosphorus Reduction Scenarios Target Load Reduction from NPS for Hypoxia Goal ~29%

  47. Phosphorus Reduction Scenarios Target Load Reduction from NPS for Hypoxia Goal ~29%

  48. Combined Phosphorus Reduction ScenariosExamples!

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