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Tips on Best Management Practices to Keep Phosphorus on the Field, Improve Water Quality

Growers wanting to increase crop yields while helping to improve water quality can do so using a set of best management practices when applying fertilizer to their fields this fall, according to a group of agronomists and agricultural engineers with Ohio State University’s College of Food, Agricultural, and Environmental Sciences.

The recommendations are designed to offer growers insight into some of the steps they can take now to boost farm profits while also benefiting the state’s water quality, said Greg LaBarge, an Ohio State University Extension field specialist and one of the leaders of Ohio State’s Agronomic Crops Team.

The group also includes experts from the Ohio Agricultural Research and Development Center and the U.S. Department of Agriculture’s Agricultural Research Service. OSU Extension and OARDC are the outreach and research arms, respectively, of the college.

In addition to focusing on phosphorous rate, application and timing, the recommendations look at farm and field features that, based on multiple studies, can assist in reducing phosphorous loss at the edge of field, LaBarge said.

“There are some immediate practices that people can implement this fall as they are making fertilizer applications that can help them continue to maximize yields while helping improve water quality,” he said. “Some of them can be done at no additional cost, while others can be offset through cost share programs offered through USDA’s Natural Resources Conservation Service and the Ohio Department of Natural Resources.

“Doing soil testing and following Tri-State recommendations will not add additional costs to farmers, but they result in benefits to water quality. The other recommendations may require investing in practice or equipment changes that may require some capital investment.”

The recommendations for phosphorous rate, application and timing are:

  • Avoid overloading soils. Utilize current soil tests that have been performed within three years and follow Tri-State fertilizer recommendations. Where soil test levels are above 40 ppm Bray P1 or 58 ppm Mehlich III-ICP, do not apply additional phosphorus in the corn-soybean rotation. These levels require no additional fertilizer, according to the recommendations. Fertilizing soils above these levels increases the risk of phosphorous in runoff and tile drainage.
  • Avoid winter application. Eliminate surface application of manure or fertilizer to frozen or snow-covered fields. Frozen ground is ground that is frozen to a degree that tillage is impossible. Surface-applied manure or fertilizer is subject to runoff events that may occur before the ground thaws and allows nutrients to bind to soil.
  • Avoid surface application of fertilizer or manure. Surface applications of phosphorus are subject to higher loss if runoff-producing rainfall events happen close to application. Placement of nutrients below the surface of the soil reduces loss. If tillage is planned in the crop rotation, phosphorous applications should be applied prior to the tillage, and till before a rain event. Full-width tillage has the potential to increase soil erosion and total phosphorus losses. New placement tools or strategies should be implemented that place phosphorous below the surface with minimal soil and burial of residue. Until these tools become available, use banded application or the minimal amount of tillage needed to mix nutrients into the soil.

Recommendations for farm and field features include:

  • Minimize erosion. Appropriate conservation practices should be implemented to minimize erosion. Maintain 30 percent cover as crop residue/cover crop. Filter strips, grassed waterways, water retention, wetlands and water diversion structures are appropriate tools.
  • Slow the movement of water. Surface water flows from fields directed to tile via standpipes should be converted to blind inlets. As risk of loss potential increases for a field, consideration should be given to edge-of-field treatments that control water movement, or treat water as it leaves the site. Drainage water management control structures, in-ditch treatments such as two-stage ditches, and other stream practices can reduce loading.
  • Know your field’s risk. Soil testing phosphorous, the field’s proximity to water and the soil’s hydrologic class all can impact edge-of-field losses of phosphorus. The USDA-NRCS Ohio Phosphorus Risk Index provides a risk of loss index and should be used as part of the development of a nutrient management plan to assess the individual field risk.
  • Strive to build soil quality. Soil condition is a mitigating factor. Increasing water infiltration by reducing compaction and improving soil structure will increase water retention, nutrient cycling, crop rooting capacity and crop yield. Drainage and soil pH provide a foundation for other practices such as cover crops, drainage, residue management, controlled traffic and soil amendments.

Source: Ohio State University 

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