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Nutrient Management of Forage Crops Intended for Hay

ANR-0109
Agriculture and Natural Resources
Date: 
11/18/2022
Greg LaBarge, Field Specialist, Agronomic Systems, Ohio State University Extension
Lee Beers, Extension Educator, Agriculture and Natural Resources, Ohio State University Extension

A sound nutrient management plan is the foundation for productive forage stands. Nutrient management of grass, legume, or mixed legume grass hay crops begins with soil testing for pH and available nutrients. Often, soil pH, phosphorus (P), or potassium (K) levels limit hay yields in Ohio.

Knowing what plant species are in a forage field sets the soil test target ranges for pH, P, and K. The Ohio Agronomy Guide provides species selection and site considerations for a successful forage stand.

A soil fertility plan requires knowledge of what plant species are being grown along with a recent soil test. With this information farmers can develop a soil fertility plan that achieves several production goals:

  • support the desired species mix
  • creating a competitive stand that reduces weed pressure
  • increasing the hay tonnage produced

Soil Sample Collection

A fertility program should rely on a high-quality soil test result. Three things determine the test’s quality (LaBarge and Lindsey 2012) :

  1. The soil sample is collected from zones that represent the field’s production capabilities.
  2. The sample is collected using standardized collection criteria.
  3. A reputable soil test lab is used for analysis.Graphic depicting three different topographical types of land, including land at the bottom of a slope, sloped land, and level land at a higher elevation.

Multiple strategies exist to collect a representative soil sample from a field. One method that works well in hay fields is to divide the field into zones. Each zone represents plant response to nutrients, topography, or soil type (Figure 1). It is common to see changes in forage yield based on previous nutrient applications, the plants’ distance from fence rows, past field management, or soil types. Consider sampling each unique area separately to increase soil testing accuracy. A single sample should represent an area no larger than 25 acres. A good sample strategy is to collect 10–15 soil subsamples across a zone in a random zig-zag pattern (Figure 2). Mix the soil cores in a plastic bucket, put a one-cup size sample in a bag, and send it to the lab.Graphic depicting overhead view of land with three areas where soil samples should be taken, including an eroded and a low area of land, and a numbered zig-zag pattern that shows where a total of 15 soil samples should be collected.

Before sampling, determine sample collection details such as sample depth (6 or 8 inches) or the time of year (either fall or spring). Use the same depth to collect each core, and thoroughly mix the sample before bagging a subsample to send to the lab. Soil nutrient levels fluctuate throughout the year due to moisture and growing season phases. Sampling at the same time of year can provide similar conditions. Consistency with these details reduces variability in soil test results from one sample year to the next, allowing farmers to track soil fertility changes based on management practices. The frequency recommended for soil tests is every four years or fewer.

Finally, select a reputable lab that meets your needs. A listing of soil testing labs can be found at ohioline.osu.edu/factsheet/anr-0107.

Learn more about soil sample collecting at ohioline.osu.edu/factsheet/AGF-513.

Soil pH and Liming Recommendations

Fertility management decisions begin with a review of the pH reported on soil sample results. Two pH values appear on a standard soil test report:

  • soil pH
  • buffer pH (sometimes labeled as acidity)

The two values have different uses in fertility management decisions. The soil pH value should be in an acceptable range for the species being grown and identifies any nutrient availability concerns. The buffer pH (or acidity) value determines the lime application rate needed to adjust the pH to a target soil pH selected. Accurate lime application rates cannot be determined without the buffer pH (or acidity) values.

Not all forage crop species require the same pH. For example, in mineral soils, legume crops such as alfalfa, trefoil, and clover generally do well in soil pH ranges from 6.5 to 6.8. However, grasses such as timothy, orchard grass, and fescue can thrive in more acidic pH ranges of 6.0 to 6.5. Legumes require a higher soil pH than grasses due to the Rhizobia bacteria that fix nitrogen. A soil pH of less than 6.0 reduces the rhizobia bacteria’s ability to infect the root system.

The region of the state is also a factor in selecting the target pH after liming. This is due to the inherent characteristics of a soil’s parent material. For instance, eastern Ohio has acid subsoils (pH < 6.0) that require a higher target pH than western Ohio, which has an alkaline subsoil (pH>6.0). See Table 1 to determine the target soil pH for different plant species and subsoil pH levels.

A lime application is recommended when the soil pH is 0.20.3 units below the desired level. If liming is required for a new planting, the lime application should be made, then incorporated with tillage in preparation for planting. Mixing lime with the soil speeds the neutralizing reaction throughout the tillage depth. If the lime is only applied to the surface, it will need rainfall to move into the soil. In established fields, lime applications can be made with broadcast surface applications.

Table 2 (Mullen, Lentz, and Watson 2016) provides the required lime (in tons) needed to adjust soil pH to the desired target pH. See the example “Determining Amount of Lime Needed” under Table 2 that uses the information in Table 1 and Table 2 to determine a lime recommendation.

Table 1. Target Soil pH Levels for Forage Crops in Ohio.
Crop Subsoil pH<6.0 Subsoil pH>6.0
Alfalfa 6.8 6.5
Other forage legumes 6.5 6.0
Grass 6.5 6.0
Table 2. Tons of liming material with an effective neutralizing power (ENP) of 2000 lb/ton needed to raise soil pH to desired target pH for Ohio mineral soils (Mullen, Lentz, and Watson 2016)
Tons of Liming Material with an Effective Neutralizing Power (ENP) of 2000 lb/ton Needed to Raise Soil pH to Desired Target pH for Ohio Mineral Soils

Download Table 2 PDF.

Example: Determining Amount of Lime Needed with ENP of 2000 lb/ton

Soil test report has a buffer pH of 6.6. Alfalfa will be planted on a field with a subsoil pH<6.0. How much lime will be needed?

Buffer pH = 6.6 (from soil test report)

Target pH is 6.8 (from Table 1)

Tons of lime material 2000 ENP needed (from Table 2) = 2.2 tons

Lime sources differ in their effectiveness. The Ohio Lime Law measures the effectiveness of lime based on its effective neutralizing power (ENP). Table 2 recommendations are based on liming material with an ENP of 2000 lb/ton. If your lime source has an ENP less than 2000 lb/ton, the rate of lime application will need to be increased. If a lime source has an ENP greater than 2000 lb/ton, the rate of lime application will need to be reduced. Information on adjusting lime amounts based on lime source ENP and on cost comparisons of different lime sources is available at ohioline.osu.edu/factsheet/AGF-505-07.

Liming the soil to adjust pH will impact nutrient availability because most lime materials contain Calcium (Ca) and Magnesium (Mg). As a result, liming increases soil test levels of both nutrients. In forage production—especially grass hay—adequate Mg levels are vital for forage quality and animal nutrition. Adjusting soil pH can also change the availability of soil nutrients. For example, liming acidic soils (pH<6.0) increases the amount of phosphorus available to plants and can change the soil test values for phosphorus. Therefore, if a field receives lime, it is recommended that the field be resampled 12 months after liming to determine changes in soil test P values resulting from adjusting the pH. Phosphorous fertilizer needs can then be based on this new soil test result.

Phosphorous (P) and Potassium (K) Recommendations

Tri-state Fertilizer Recommendation Framework

The Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa, (2020) Bulletin 974 provides P and K recommendations for row and forage crops in the state.

The tri-state fertilizer recommendations manage soil P and K levels through a buildup-maintenance framework (Figure 3). The “critical level” is key to understanding the framework. Soil test levels that fall below the “critical level” are deficient in P or K, resulting in forage that may not reach its full yield potential. Conversely, if soil test levels for P or K are above the “maintenance limit,” there is likely no yield benefit from the added P or K applications.Table displaying the maintenance and buildup fertilizer rates needed based on soil tests showing deficient, optimal, or sufficient levels of soil nutrients.

When P and K levels fall between the “critical level” (minimum) and “maintenance limit” (maximum), the recommendation is to apply P and K fertilizer to replace the nutrients removed at harvest, commonly called the crop removal rate (Culman et al. 2020). The goal is to maintain soil test P and K between the “critical level” (minimum) and “maintenance limit” (maximum). A farmer can apply the recommended fertilizer anytime during the growing season. Avoid applying large, single applications of N and K, which can result in nutrient balances that are harmful to crops. A detailed discussion of the buildup-maintenance framework can be found in the Tri-State Fertilizer Recommendations for Corn, Soybean, Wheat, and Alfalfa, (2020) Bulletin 974, on pages 23 to 29.

The “critical level” is crop-dependent. The critical P and K levels for different forage crops are shown in Table 3 (P levels) and Table 7 (K levels).

If soil test P or K is below the critical level, additional fertilizer can be applied above the crop removal rate to build soil test levels up to the critical level. Using a buildup recommendation is an economic decision based on land tenure (rent vs. own) and the current cost of fertilizer. Livestock manure can be a good option for building up soil test levels. However, if fertilizer is used, performing buildup applications when fertilizer prices are lower can reduce the total cost.

For perennial crops, there are three strategies to manage fields with soil test P and K values below the critical level. A general description of each strategy is included below. In addition, details on implementing each strategy for P and K are included in the individual nutrient sections of this factsheet.

Strategy 1. Build up the soil test level by dividing the buildup rate recommendation into four annual applications. The recommendation tables in this factsheet show rates for this strategy. The first application of the buildup and crop removal recommended rate can be incorporated with tillage for new plantings or broadcast on established plantings without tillage. The remaining three applications can be broadcast on the soil surface.

Strategy 2. Build up the soil test level before planting. This strategy requires a large nutrient application, but the nutrient can be applied before seedbed preparation tillage. This results in the nutrient being incorporated into the soil at the depth of the seedbed preparation tillage that is used. This strategy fits best when a manure nutrient source is available to meet the recommendation.

Strategy 3. No buildup application. Using the buildup recommendation is optional. However, an annual application at a crop removal rate is recommended to reduce the risk of yield loss when soil test P or K is below the critical level.

Phosphorus Management

For forage crop production, management of plant-available phosphorus (P) in the soil is addressed first by adjusting soil pH into a suitable range for the crop being grown. If a significant change in pH occurs with lime, the recommendation is to resample the soil 12 months after liming. This resampling is used for a new soil test to determine changes in soil test P values as a result of adjusting the pH, and to reassess phosphorous fertilizer needs. Once pH is in the proper range, fertilizer applications are used to keep soil test P in the desired range to meet the demands of the crop. P management decisions should start with the P soil test results and the tri-state fertilizer recommendation tables 5 and 6.

For New Plantings

If the soil test P is below the critical level, any planned applications to build up soil test P should be incorporated with tillage before planting.

Strategy 1. Build up the P soil test level by dividing the buildup rate recommendation into four annual applications. Tables 5 and 6 show the combined crop removal and buildup recommendation for soil test values less than 30 ppm (Table 5) or 20 ppm (Table 6). The first application of the buildup and crop removal recommended rate can be incorporated with tillage.

Strategy 2. Build up the P soil test level before planting. The estimated amount of P2O5 required to raise a soil test 1 PPM is 20 pounds of P2O5 per acre. For example, if a soil test is 15 PPM, and the goal to increase the soil test to a 30 PPM critical level, a total of 300 pounds of P2O5 per acre is needed. Livestock manure can be a good option for building up soil test levels. If fertilizer is used, performing buildup applications when fertilizer prices are lower can reduce the total cost.

Strategy 3. No P buildup application. If the decision is made not to build up soil test P, then a crop removal rate of P should be applied before planting based on Table 4 removal values multiplied by the crop yield.

After Establishment

If soil test P is above the critical level but below the maintenance limit (Table 3), application rates based on crop removal are a good approach (Table 5 or Table 6). An annual application of the crop removal rate is recommended when soil test P levels are below the critical level. The annual application approach is recommended for long-term plantings in severely nutrient-deficient soils. See the example “Determine Phosphorus Removal Rate and Fertilizer Product Application Rate” under Table 6.

Table 3. Recommended Mehlich 3 soil test phosphorus (STP) levels for field crops. Source (Culman et al. 2020; Lindsey 2017).
Crop Critical Level Mehlich 3 Maintenance Limit Mehlich 3 (PPM)
Alfalfa 30 50
Grass Hay 20 40
Grass/Legume Hay 30 50
Table 4. Pounds of phosphorus removed per ton of harvested forage (Culman et al. 2020; Lindsey 2017).
Crop Lb P2O5 per ton, per acre
Alfalfa 12
Grass Hay 12
Grass/Legume Hay 12
Table 5. Phosphorus recommendations for alfalfa and mixed legume/grass hay based on soil test phosphorous (STP) (Culman et al. 2020; Lindsey 2017).
Table 5 displaying phosphorus recommendations for alfalfa and mixed legume/grass hay based on soil test phosphorous (STP).

Download Table 5 PDF.

Table 6. Phosphorus recommendations for grass hay based on soil test phosphorous (STP) (Culman et al. 2020; Lindsey 2017).
Table 6 displaying phosphorus recommendations for grass hay based on soil test phosphorous (STP)

Download Table 6 PDF.

Example: Determine Phosphorus Removal Rate and Fertilizer Product Application Rate

Soil test report has a soil test P value of 20 PPM Mehlich 3. How much P2O5 will be needed to maintain soil test value with a 5-ton annual yield?

STP=20 PPM (from Soil Test Report)

Yield=5 Ton

Pounds of P2O5 need to replace removal (from Table 5)

50 lb P2O5 (4 Ton) + 75 lb P2O5 (6 Ton) / 2 = 62.5 pounds P2O5

How much 11-52-0 is needed to supply the 62.5 pounds of P2O5 needed?

62.5 pounds of P2O5 /0.52 = 120 pounds of 11-52-0 per acre

For information on calculating P need, visit ohioline.osu.edu/factsheet/agf-0515.

For information on understanding a soil test report, visit ohioline.osu.edu/factsheet/agf-0514.

Potassium Management

For forage crop production, management of plant-available potassium (K) with fertilizer applications is needed to maintain soil test K in a range that ensures enough soluble K is available to meet crop demand. The ability of soil to hold K depends on the available holding sites in the soil, which is measured by Cation Exchange Capacity (CEC). Therefore, K management decisions should start with soil test results that show K availability and CEC.

For New Plantings

If soil test K is below the critical level, planned applications to build up soil test K should be made before planting, and then incorporated with tillage.

Strategy 1. Build up the K soil test level by dividing the buildup rate recommendation into four annual applications. Tables 9 (CEC > 5) and 10 (CEC <5) show the combined crop removal and buildup recommendation for different soil test K values. The first application of the buildup and crop removal recommended rate can be incorporated with tillage.

Strategy 2. Build up the K soil test level before planting. The estimated amount of K2O required to raise a soil test 1 PPM is 5 to 6 pounds of K2O per acre. For example, if a soil test is 100 PPM and the goal is to increase the soil test to a critical level of 120 PPM (Table 9), a total of 120 pounds of K2O per acre is needed. Livestock manure can be a good option for building up soil test levels. If fertilizer is used, performing buildup applications when fertilizer prices are lower can reduce the total cost.

Strategy 3. No buildup K application. If the decision is made for no buildup K application, then a crop removal rate of K should be applied before planting based on Table 8 removal values multiplied by the crop yield.

After Establishment

If the soil test K is above the critical level, but below the maintenance limit (Table 7), application rates that are based on crop removal are a good approach (Table 9 and Table 10). An annual application of the crop removal rate is recommended when soil test K levels are below the critical level. The annual application approach is recommended for long-term plantings in severely nutrient-deficient soils. See the example “Determine Potassium Removal Rate and Fertilizer Product Application Rate” under Table 10.

Table 7. Recommended Mehlich 3 soil test potassium levels for forage crops (Culman et al. 2020; Lindsey 2017).
Table 7 displays recommended Mehlich 3 soil test potassium levels for forage crops.

Download Table 7 PDF.

Table 8. Pounds of K2O removed per ton of harvested forage (Culman et al. 2020; Lindsey 2017).
Crop Lb K2O per ton, per acre
Alfalfa 49
Grass Hay 49
Grass/Legume Hay 49
Table 9. Potassium recommendations for alfalfa, grass, and mixed legume/grass hay with CEC>5 based on soil test potassium (STK) found on your soil test report.
Table 9. Potassium recommendations for alfalfa, grass, and mixed legume/grass hay with CEC>5 based on soil test potassium (STK) found on your soil test report.

Download Table 9 PDF.

Table 10. Potassium recommendations for alfalfa, grass, and mixed legume/grass hay with CEC < 5.
Table 10 displays potassium recommendations for alfalfa, grass, and mixed legume/grass hay with CEC < 5.

Download Table 10 PDF.

Example: Determine Potassium Removal Rate and Fertilizer Product Application Rate.

The soil test report has a soil test K value of 125 PPM Mehlich 3 with a CEC of 15. How much K2O will be needed to maintain the soil test value with a 5-ton annual yield?

STK=125 PPM (from soil test report)

CEC=15 (from soil test report)

Yield=5 Ton

Pounds of K2O need to replace removal (from Table 9)

195 lb K2O (4 Ton) + 295 lb K2O (6 Ton) / 2 = 245 pounds K2O

How much 0-0-60 is needed to supply the 245 pounds of K2O needed?

245 pounds of K2O / 0.60 = 408 pounds of 0-0-60 per acre

For more information on calculating K need, visit ohioline.osu.edu/factsheet/agf-0515.

For information on understanding a soil test report, visit ohioline.osu.edu/factsheet/agf-0514.

Nitrogen Management of Forages

Nitrogen management is vital to maintaining a productive forage stand. A nitrogen management strategy is dependent on the mix of species being grown. Forage yields of pure grass stands increase with nitrogen applications when the soil test levels are adequate for P and K. Pure or predominately legume forage stands do not need nitrogen due to their ability to fix their N. Legume stands may benefit from a small amount of N as a starter fertilizer at planting. The use of nitrogen in mixed grass/legume stands depends upon the ratio of grass to legume and if there is a need to maintain legumes in the stand.

For New Plantings

The vigor of seedlings for cool-season forages is enhanced in many Ohio soils by applying nitrogen at planting. Apply 10 to 20 pounds of nitrogen per acre for mixed grass/legume stands and 30 pounds per acre for pure grass stands. Starter nitrogen applications of 10 pounds per acre may benefit pure legume stand establishment, especially in cool conditions and when the soil is low in organic matter. A manure application incorporated before seeding can help establish forage, including alfalfa stands. Use a manure nutrient test and nutrient needs identified from the soil test to determine an appropriate manure application rate.

After Establishment

For grass forage stands, good economic returns occur with applications of 100–180 pounds of total nitrogen split into three applications. A sound strategy is a spring green-up application of 60–80 pounds followed by 30–50-pound applications after each cutting. For heavy stands of grass hay, reducing the spring green-up application may aid with drying, but may limit yields. To maintain legumes in a stand, reduce the nitrogen rates based on the percentage of the stand consisting of legume species. Another factor to consider in determining the N rate is the productivity of the stand. Table 11 shows recommended rates based on species in the stand, percentage of legume in the stand, and yield potential of the stand.

Table 11. Nitrogen rate recommendations for established perennial cool-season grass forages based on the percentage of legume in the stand (Lindsey 2017).
Table 11 displays nitrogen rate recommendations for established perennial cool-season grass forages based on the percentage of legume in the stand.

Download Table 11 PDF.

References

Culman, S., A. Fulford, J. Camberato, and K. Steinke. 2020. Tri-State Fertilizer Recommendations, Bulletin 974. Columbus: Ohio State University Extension Publications.
extensionpubs.osu.edu/search.php?search_query=974&section=product.

LaBarge, G., and L. Lindsey. 2012. “Soil Sampling to Develop Nutrient Recommendations” (AGF-513). Ohioline, The Ohio State University.
ohioline.osu.edu/factsheet/AGF-513.

Lindsey, L., ed. 2017. Ohio Agronomy Guide, 15th Edition, Bulletin 472. Columbus: Ohio State University Extension Publications.
extensionpubs.osu.edu/search.php?search_query=472&section=product.

Mullen, R., E. Lentz, and M. Watson. 2016. “Soil Acidity and Liming for Agronomic Production” (AGF 505). Ohioline, The Ohio State University.
ohioline.osu.edu/factsheet/AGF-505-07.

Originally posted Nov 18, 2022.
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