Eight steps to maximize returns to phosphorus (P) in row crop production while reducing downstream contributions to streams and lakes.
- Evaluate concentrated water flows leaving a field looking for gullies and other signs of erosion. Use grassed areas, conservation tillage, and cover crops or other appropriate best management practices (BMPs). A primary way P is lost is through soil erosion.
- Replace surface water connection to tile systems with designed structures (i.e., blind inlets) to reduce soil and nutrient losses.
- No application of P containing fertilizer or organic (i.e., manure, biosolids, compost) nutrient sources to frozen or snow-covered soil unless applied to a growing cover crop and using appropriate setbacks to sensitive areas.
- Take a representative soil sample, testing for a minimum of pH, buffer pH, phosphorus-Mehlich III, and potassium for all fields where crops are harvested.
- Use soil test results to monitor soil pH (for corn, soybeans, and wheat, desired pH is 6.5–6.8) and follow next step for soil test phosphorus (STP) value in Mehlich Ill. Managing pH in this range maximizes available P.
If STP is 50 PPM or less, go to step 6. If STP is above 50 PPM, go to step 7.
- STP value of 50 PPM Mehlich III or less:
- CROP YIELD—Reduce risk of crop yield losses with nutrient application.
- A STP of 20 PPM defines the corn-soybean rotation critical level. A STP of 30 PPM defines the “critical level” when wheat and alfalfa are included in the rotation. When STP is at the "critical level" or below, the risk of yield loss increases. Annual in season P nutrient application recommended to reduce risk of yield reductions. Recommendations to build STP to "critical level" are available.
- The maintenance STP range is "critical level" to 40 PPM in corn soybean rotation and 50 PPM when wheat and alfalfa are included in the rotation. Recommended rate of P is equal to P removed in harvested crop. Annual application is not required. Risk of yield loss is low with flexibility to delay application one (or more) growing seasons, if needed.
- WATER QUALITY—The greatest risk for event P losses occur when nutrient application is followed by runoff-producing rainfall. Use the following steps to reduce P loss risk at application:
- Use an agronomic rate of no more than two years’ worth crop removal as recommended in the Tri-State Fertilizer Recommendations.
- Time fertilizer applications so predicted rainfall 12 hours after application is less than a 50 percent chance of more than 1 inch of rainfall.
- Time organic nutrient applications so predicted rainfall 24 hours after application is less than a 50 percent chance of more than 0.5 inches of rainfall.
- Subsurface placement reduces losses over surface application.
- STP value above 50 PPM Mehlich III:
- CROP YIELD—Response to fertilizer with STP greater than 50 PPM is highly unlikely.
- Do not apply additional fertilizer due to lack of economic return.
- Organic applications should be determined using P content from testing the organic source and not exceed P crop removal rate for the next two (and no more than three) crops in the rotation.
- Consider in-crop application to a nitrogen-using crop to reduce purchased N, maximizing economic return to organic application.
- Where in-crop application is not used, incorporate organic nutrients.
- WATER QUALITY—The risk of P loss increases with STP values over 50 PPM, with greater risk after 200 PPM.
- Do not apply additional fertilizer: due to lack of economic return.
- Do not make organic applications when STP is greater than 200 PPM. Use site and rate criteria from Assessing Nutrient Loss Risk in Ohio (NRCS) between 50 to 200 PPM.
- Time organic applications so predicted rainfall 24 hours after application is less than a 50 percent chance of more than 0.5 inches of rainfall.
- Use the Ohio P risk index, field scale hydrology/water quality models, or monitoring to evaluate site risk for P losses and need for further site BMPs. See step 8.
- BMPs for high-risk P loss sites: Monitor fields for P loss using the Ohio P risk index and field scale hydrologic and water quality models. For sites with predicted high P losses, consider one or more of the following water management practices based on fitness and cost effectiveness for field site:
- Production practices that increase soil organic matter to retain water on site
- Drainage Water Management (NRCS 554)
- Nutrient removal wetlands (NRCS 656)
- Phosphorus Removal Structure
- Saturated Buffer (NRCS 604)
- In-field water storage or detention basins
For more detailed descriptions and supporting data for these recommendations, visit agbmps.osu.edu.
Steve Culman, Fulford, Anthony, Camberato, James, and Steinke, Kurt. 2020. Tri-State Fertilizer Reccommendations for Corn, Soybean, Wheat, and Alfalfa.Columbus, OH: OSU Extension Publishing. extensionpubs.osu.edu/tri-state-fertilizer-recommendations-for-corn-soybean-wheat-and-alfalfa-pdf
USDA, National Resources Conservation Service. 2020. Assessing Nutrient Loss Risk in Ohio. efotg.sc.egov.usda.gov/api/CPSFile/28571/590_OH_OTH_Nutrient_Management_Assesing_Nutrient_LossPhotos by Greg LaBarge, OSU Extension, unless otherwise noted.