Corn-to-Go

Managing manure application when STP >50

By Greg LaBarge

I often get questions about managing manure applications in fields where Soil Test P (STP) is above the maintenance limit of 50 parts per million (ppm) in the Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa, Bulletin 974. Be aware that the Tri-State Fertilizer Recommendations provide recommendations for the economical use of purchased fertilizer. The 50 ppm maintenance limit is the STP level where “no agronomic response, either higher yield or benefit of a higher STP, results from added fertilizer.” The Tri-State Fertilizer Recommendations only address crop agronomic needs, not P’s environmental impact. If you need to apply manure to a field with STP greater than 50 PPM, how can it be done to limit field P loss?

The publication Assessing Nutrient Loss Risk in Ohio, NRCS, 2020 provides environmental P loss criteria based on the STP in a field. You can download a copy at https://go.osu.edu/lossrisk. The guidelines suggest reducing manure application rates with the long-term goal of reducing STP, plus increasing the use of other conservation practices to minimize edge-of-field P losses. Table 1 shows the rate criteria for the Moderate, Higher, and Very High P-risk loss assessment classes.

Moderate: Risk 50-120 ppm Mehlich 3. Limit the manure application rate to planned crop rotation P removal. Future soil tests must show a decreasing STP. For example, a current soil test P of 80 ppm  should use a manure rate and frequency that results in an STP of less than 80 ppm in the future. If the future soil test shows greater than 80 ppm result, then a lower rate or elimination of manure application should occur. In addition to close monitoring of soil test levels, other conservation practices are required. Required practices include applications to fields with >30% cover or incorporation, use of sensitive area setbacks, no surface application in spring without a growing cover, and erosion control. 

Higher Risk: 120-200 ppm. Applications are to provide a limited window to facilitate operational changes, such as purchasing new fields or developing arrangements with neighboring farms to secure lower STP fields. Limit the manure application rate to 50% of planned crop rotation P removal. Required practices include applications to fields with  >50% cover or incorporation, use of sensitive area setbacks, no surface application in spring without a growing cover, and erosion control. 

Very High Risk: > 200 ppm. No P application. Drawdown P with a more intensive crop rotation that includes forages, if possible.

Table 1. Rate criteria from Ohio Phosphorus (P) Loss risk for Moderate, Higher, and Very High risk assessment classes. (Adapted from NRCS, 2020).

  Moderate RiskHigher RiskVery High Risk
RateSoil Test P (STP) PPM Mehlich 350-120120-200200+
Rate of P ApplicationLess than or equal to the P removal (annual or multiple-year crop rotation)50% of P removal  (annual or multiple-year crop rotation)No P application
STP Management StrategyDrawdown STP over timeShort-term P application to facilitate changeDrawdown STP

Manure is an excellent source of N, P, and K. Given the historically high fertilizer prices in recent years, it has more value in crop production than ever. However, continuing to build STP will only worsen P loss conditions in a field and the environmental pressure on manure use. The standards in Assessing Nutrient Loss Risk in Ohio, NRCS, 2020 are valuable guidelines regardless of where you are in the state or whether you do or do not participate in NRCS cost share programs.

Fall forage management
By Stephanie Karhoff and Kyle Verhoff, AgNR Educator, Defiance County

Fall provides a great opportunity to scout and manage forage hay fields and pastures. In established stands, final harvest or intensive grazing should already have taken place to allow a fall rest period, except if planning to frost seed legumes. If needed, there is still time to soil sample and address winter annual weed concerns. 

Soil test fields that will be seeded to forages next year. Apply lime as needed to adjust pH levels. Maintaining proper soil pH increases nutrient availability and will strengthen forage stands, decreasing their susceptibility to stresses like insects, diseases, or weed infestations. The 2020 Tri-State Field Crop Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa (Extension Bulletin 974) recommends consistently soil sampling every 3 to 4 years at no more than 25-acre samples. Lime applications are recommended when soil pH is two to three units below the desired level. In mineral soils (less than 20% organic matter) where the subsoil pH is less than 6.0, the target pH is 6.8 for alfalfa and other forage legumes. In western Ohio, or in general, where the subsoil pH is greater than 6.0, the target pH is 6.5 for alfalfa and 6.0 for other forage legumes.

Now is also the time to scout for troublesome weeds like cressleaf groundsel, poison hemlock, wild carrot, dandelion, and Canada thistle in your hay fields. Fall herbicide applications are the most effective management tool against these species. That is because winter annuals like cressleaf groundsel are at the beginning of their life cycle and more vulnerable to herbicides. Control of biennials like poison hemlock and wild carrot, and perennials like dandelion and Canada thistle, is also improved since systemic herbicides will be moved to root systems along with nutrients.

Managing these weeds now is especially important in fields recently seeded this summer or early fall. Your fall herbicide options include 2,4-DB (Butyrac), Pursuit, Raptor, and clethodim in newly established pure alfalfa stands. Velpar or a dormant application of metribuzin are both options for established stands. Grass hay and pastures have a wider range of options found in the “Permanent Grass Pastures/CRP/Grass Hay” section of the Ohio, Indiana, and Illinois Weed Control Guide (Extension Bulletin 789).

With winter approaching, producers looking to extend grazing need to be aware of a few key concerns. One concern is forage toxicity. Like some previously mentioned weeds, forages like grain sorghum and sorghum-sudangrass hybrids have a high prussic acid poisoning potential. With that in mind, harvest or the final grazing of pastures with summer annuals should occur before the first frost. That first frost is also important if you are grazing high concentrations of forage legumes is a second concern. Grazing a high concentration of forage legumes a day or two after a hard frost increases the risk of bloat, so it is best to wait a few days and supplement with dry hay.

For producers that are grazing stockpiled pastures this winter, now is the time to take samples from hay and silage to calculate the nutritive value of your winter feed and to inform any supplementation needs. While grazing stockpiled forages, leaving a forage residual of four inches and having a plan to protect the pasture from livestock damage following significant precipitation events are vital to the long-term health and production of the pasture. Access more information on managing forage hay fields and pastures at https://go.osu.edu/foragemanagement.

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