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Cooperative Extension Fact Sheet FS1295

Soil Fertility Recommendations for Producing Grass Hay

  • Joseph Heckman, Extension Specialist in Soil Fertility
Zoom in Figure 1.

Hay harvest underway on a New Jersey Farm. Photo: Zane Helsel.

Soil fertility is an important part of producing high quality grass hay to feed an estimated 50,000 horses in New Jersey. The first cutting of grass should be harvested early to ensure high quality, palatability, and nutritious feed. Hay is feed for cattle, goats, sheep, and other livestock including equine, which has an especially high requirement for hay that must be leafy, green, and free of mold, dust, and foreign materials.

Sometimes hay is produced as a mixed stand with a legume, such as alfalfa. When forage legumes are included in the mix, soil fertility recommendations should favor maintenance of the legume within the mixed stand. The presence of 25% or more legumes in a mixed forage stand means that the hay crop is essentially self-sufficient with respect to nitrogen via biological N fixation. It also means zero application of N fertilizer. In the case of alfalfa, the soil pH should be kept near pH 6.8. Soil fertility levels should be managed as outlined in Rutgers NJAES bulletin E321, "Soil Fertility Recommendations for Alfalfa."

Perennial hay crops are also especially effective in controlling soil erosion and in building soil organic matter content. While a grass hay crop can build soil organic matter content, minerals associated with soil fertility are being withdrawn with each harvest; every harvested ton of hay withdraws substantial amounts of P and K from the soil. On average, each ton of harvested hay uptakes and removes 15 lbs P2O5 and 50 lbs of K2O per acre. Over a growing season, a typical 4 tons per acre hay harvest would remove 60 lbs P2O5 and 200 lbs of K2O per acre. To sustain hay harvest productivity over a period of years, these nutrients will need to be replenished with commercial fertilizer or as applied manures. Because grass hay has such a high demand for N, P, and K, fields intended for hay production are excellent locations, as part of a long crop rotation cycle, for utilizing livestock manures.

Nutrient recommendations for grass hay production should be based on an annual or recent soil test and a realistic crop yield goal. The recommendations listed in this fact sheet are derived from the cumulative knowledge of decades of soil fertility research in New Jersey and surrounding states. They also account for the need to replenish nutrients removed by hay harvest.

The most commonly grown species for grass hay are cool season perennials such as orchardgrass, bromegrass, timothy, and tall fescue. All of these grass species have a high requirement for nitrogen (N) fertilizer. A general N fertilizer recommendation is to provide 40 lbs of N per ton of expected hay yield. Applied N fertilizer will be used most efficiently when applications are spaced out over the growing season. The first N application should be at early spring green-up. Subsequent applications should immediately follow each hay cutting.

Recommendations for P and K vary depending on the initial soil fertility test level. Soil fertility levels are based on the Mehlich-3 soil test and are defined for soil test levels: low, medium, high, or very high in Rutgers NJAES fact sheet FS719, "Soil Fertility Test Interpretation." Grass hay producers should not set unrealistic yield goals on soils that test low in P or K. Before above average yields (greater than 4 tons per acre) may be achieved on low testing soils, soil fertility levels should be improved over a period of years while growing other crops and before rotating to forage crops.

Nitrogen (N)

Perennial grasses used for hay production are very responsive to N fertility. As a general recommendation, apply 40 lbs N per ton of expected hay yield. When using commercial fertilizer, divide the total recommended N application into doses among hay cuttings over the season as described in the introduction. When using manures as an N source, the total manure N may be spread as a single application in the fall or early spring just before green-up.

Commonly used N fertilizers for grass hay production include urea, or ammonium sulfate. Urea, with 46% N, is the most concentrated commercial source but must be applied shortly before rain or irrigation to prevent significant loss of the N to the atmosphere as volatile ammonia. Volatile N loss is not a concern with ammonium sulfate. Fertilizing with ammonium sulfate or with livestock manure has the added benefit of also ensuring an adequate supply of sulfur. Producers using ammonium sulfate should be aware that this fertilizer is strongly acidifying, and need for liming may increase.

When a grass legume mix is being grown, N fertilization is not recommended. But the legume seed needs to be inoculated at time of planting with a compatible species of symbiotic of bacteria that fix atmospheric N. In the case of alfalfa, the roots are colonized by Rhizobia meliloti. Seed inoculation is recommended to ensure effective nodulation and adequate N nutrition.

Phosphorus (P)

Many soils test very high or above optimum for P due to previous years of fertilizer and manure application. Ordinarily, no P fertilizer would be recommended for crops grown on very high testing soils but 20 lbs P2O5 per acre may be applied at time of planting grass seed to ensure rapid seedling establishment. Excessive soil test levels of P can lead to crop production or feed quality problems and loss of P to water resources.

Soils that test optimum have adequate P levels for production of most field crops. However, forage crops in general have exceptionally high nutritional requirements, because hay harvest withdraws substantial amounts of minerals from soil. On soils in the optimum fertility range, a typical amount recommended annually for grass hay is about 50 lbs P2O5 per acre (Table 1A&B).

On below optimum (medium or low) testing soils, the recommended P2O5 rate is designed to build the soil test level into the optimum (high) range over time. A typical amount recommended on below optimum testing soils for grass establishment is 100 to 150 lbs P2O5 per acre and for stand maintenance, about 40 to 80 lbs P2O5 per acre (Table 1A&B). Of the total amount recommended for new seedings, 20 lbs P2O5 per acre should be applied in a band with the drill; apply the remainder of the recommended P2O5 as a broadcast to be tilled in before planting. On established grass fields, the P fertilizer should be broadcast on the soil surface before spring regrowth or be split into several applications to be broadcast shortly after each cutting.

Table 1A: Recommended P2O5 applications based on Mehlich-3 soil test P for new grass (orchardgrass, bromegrass, timothy, and tall fescue) seedings.
Soil Test Category New Seedings of Grass1
Mehlich-3 Soil Test P2 Yield Goal (tons per acre)
(lb per acre) (ppm) 1 2 3 4 5
      Recommended P2O5 per acre
Below Optimum 20 10 100 120 130 150 160
40 20 70 80 100 110 130
Optimum Range 60 30 30 50 60 80 90
80 40 20 20 30 40 50
100 50 0 0 0 0 0
Above Optimum Range >100 >50 0 0 0 0 0
Table 1B: Recommended P2O5 applications based on Mehlich-3 soil test P for maintenance of established grass hay.
Soil Test Category Established Grass
Mehlich-3 Soil Test P1 Yield Goal (tons per acre)
(lb per acre) (ppm) 3 4 5 6 7
      Recommended P2O5 per acre
Below Optimum 20 10 110 120 140 150 170
40 20 80 90 110 120 140
Optimum Range 60 30 50 60 80 90 110
80 40 20 30 40 50 50
100 50 0 0 0 0 0
Above Optimum Range >100 >50 0 0 0 0 0

1Of the total amount recommended for new seedings, 20 lbs P2O5/acre should be applied in a band with the drill; apply the remainder of the recommended P2O5 as a broadcast to be tilled in before planting

2Optimum soil test P: 60 to 100 lbs per acre, or 30 to 50 ppm (note: ppm x 2 = lbs per acre)

Potassium (K)

Hay production has a high demand for K. Each ton of hay harvested removes on average 50 lbs K2O per acre or 200 lbs K2O per acre for a typical 4 ton per acre yield. Providing an adequate supply of K for economic yields is a concern for producing grass hay on many New Jersey soils, especially on sandy soils. Applying adequate amounts of this nutrient annually to soils that test below optimum for K is essential to sustaining grass yields and stand longevity.

The amount of K to apply depends on the soil test K level and the crop yield goal (Table 2A&B). K is not recommended for soils that test above optimum (very high). Excessive soil test levels of K (greater than 400 lbs per acre or 200 ppm) can lead to feed quality problems and nutritional imbalances in livestock.

On soils that test optimum (high) for K, it is important to apply enough K to maintain this optimum level of fertility. The amount recommended varies depending on the crop yield level (Table 2A&B). Recommended amounts also differ for new plantings and already established fields.

On below optimum (medium or low) testing soils, above average yields goals are unrealistic. The recommended K2O rate is designed to build the soil test level into the high (optimum) range over time. The amount recommended for at time of planting grass ranges from 60 to 260 lbs K2O per acre and for grass maintenance from 160 to 360 lbs K2O per acre.

Sandy, low cation exchange capacity soils have a more limited supply of K than loamy soils and are more prone to K deficiency. Splitting the total annual K application into several small broadcast applications, following each grass hay cutting, helps to avoid luxury K uptake, and it encourages more effective utilization of this nutrient.  

Table 2A: Recommended K2O applications based on Mehlich-3 soil test K for new grass seedings and for maintenance of established grass
Soil Test Category New Seedings of Grasses
Mehlich-3 Soil Test K1 Yield Goal (tons per acre)
(lb per acre) (ppm) 1 2 3 4 5
      Recommended K2O per acre
Below Optimum 40 20 90 140 190 240 290
80 40 80 130 180 230 280
120 60 70 120 170 220 270
160 80 60 110 160 210 260
Optimum Range 200 100 50 100 150 200 250
240 120 40 80 120 160 200
280 140 30 60 90 120 150
320 160 20 40 60 80 100
360 180 10 20 30 40 50
400 200 0 0 0 0 0
Above Optimum Range >400 >200 0 0 0 0 0
Table 2B: Recommended K2O applications based on Mehlich-3 soil test K for maintenance of established grass
Soil Test Category Established Grass
Mehlich-3 Soil Test K1 Yield Goal (tons per acre)
(lb per acre) (ppm) 3 4 5 6 7
      Recommended K2O per acre
Below Optimum 40 20 190 240 290 340 390
80 40 180 230 280 330 380
120 60 170 220 270 320 370
160 80 160 210 260 310 360
Optimum Range 200 100 150 200 250 300 350
240 120 120 160 200 240 280
280 140 90 120 150 180 210
320 160 60 80 100 120 140
360 180 30 40 50 60 70
400 200 0 0 0 0 0
Above Optimum Range >400 >200 0 0 0 0 0

1Optimum soil test K: 200 to 400 lbs per acre, or 100 to 200 ppm (note: ppm x 2 = lbs per acre)

Liming Practice: Calcium (Ca) and Magnesium (Mg)

The target soil pH level for grass hay production is 6.5. However, if it is grown as a mixed stand with alfalfa, the target soil pH is 6.8. It is important to apply limestone to acid fields well in advance of planting perennial grasses. When corn or another crop precedes forage grasses in the rotation, apply enough limestone to the preceding crop to achieve the target soil pH for grass hay production.

Calcium and Magnesium are supplied as part of a regular liming program to maintain soil pH. Select the appropriate liming material based on its Ca and Mg concentrations and the relative soil test levels for these nutrients. The goal of the liming program is to maintain the soil fertility levels for Ca and Mg in the optimum range (about 65 to 70% Ca and 10 to 20% Mg saturation of the soil cation exchange capacity) and to maintain the desired soil pH level for crop rotation.

Soil testing should be performed regularly for grass hay production to evaluate the need for P, K, and liming. Besides production, a good balance of crop mineral uptake from soil is essential to keeping livestock healthy. Refer to Rutgers NJAES fact sheets FS903, FS904, and FS905 for additional information about liming.

Sulfur (S)

Hay harvest removes large amounts of S (5 lbs S per ton) from the soil and this increases the potential for S deficiency. Sulfur fertilization is generally not based on soil testing. Soil tests for available S can be done but the required depth of soil sampling (0 to 24 inches) discourages widespread testing for this nutrient.

The need for S fertilization can be based on soil type, field history, or plant tissue analysis (Table 3) results from previous crops. The sufficiency range for S is 0.21 to 0.25% in dry plant tissue of cool season grasses. Sandy, highly leached, low organic matter content soils are the kinds of fields most likely to need S fertilization. Soils high in organic matter content or fields that have a recent history of manure application generally supply adequate amounts of S for grass hay production.

On sandy soils, which are more susceptible to S deficiency, S should be broadcast prior to seeding and top-dressed annually on established hay fields. Sulfur recommendations may range from 20 to 40 lbs S per acre. Sulfur fertilizers (ammonium sulfate, 24% S; magnesium sulfate, 14% S; potassium sulfate, 18% S; potassium magnesium sulfate, 23% S; calcium sulfate, 24% S; or gypsum, 19% S) that supply S as sulfate is equally effective when surface applied or incorporated. Consider the soil test K, Mg, and Ca fertility levels to select the most appropriate S fertilizer source.

Manganese (Mn)

Manganese is often deficient on sandy soils of southern New Jersey but is seldom found deficient in fine textured soils of northern New Jersey. Many crops grown on sandy soils of southern New Jersey are susceptible to Mn deficiency when the soil pH is greater than 6.2. Grasses exhibiting Mn deficiency lack dark green color. When the deficiency is more severe, leaves have green veins with yellowing between the veins (intervenial chlorosis). As soil pH increases, plant availability of soil Mn decreases. On soils where Mn deficiency is a problem, frequent application of Mn fertilizer is generally necessary.

Soil testing and plant tissue analysis are useful for identifying soils where Mn deficiencies are likely to occur. The deficiency is often a persistent and reoccurring problem in certain fields. On these fields with a history of Mn deficiency, be prepared to apply Mn fertilizer as a foliar spray after each cutting when the re-growth is at about 3 inches tall. Apply the Mn at the rate of 1.0 lbs of Mn per acre for each foliar treatment. Manganese sulfate or chelated forms of Mn are equally effective as foliar fertilizers. Manganese fertilizer may also be applied to the soil as a broadcast treatment. For new plantings, broadcast 10 lbs Mn per acre to prevent deficiency during establishment. After crop establishment, foliar applications of Mn fertilizer are more effective and economical. There is very little residual benefit in subsequent growing seasons to soil applied Mn fertilizer. The recommended source for foliar and soil application is manganese sulfate (31% Mn). Rutgers NJAES fact sheets FS973, and FS632 provide additional information about Mn nutrition and correction of Mn deficiency.

Boron (B)

Where grass hay is grown as a mixed stand with alfalfa, the crop will likely need an annual application of B fertilizer. To prevent B deficiency of alfalfa, broadcast 1 to 2lb B per acre prior to seeding and 2 to 3 lbs B per acre annually after establishment. Pure stands of grass hay usually do not need annual applications of B fertilizer. Because excessive B can cause harm to other crops, be careful not to exceed the recommended rates. Rutgers NJAES fact sheet FS873 provides additional information on B.

Iron (Fe), Zinc (Zn), Copper (Cu), Molybdenum (Mo), and Chloride (Cl)

Deficiencies of Fe, Zn, Cu, Mo, and Cl are not common for grass hay production on New Jersey soils. Refer to Rutgers NJAES fact sheets FS971, FS721, FS720, FS972, and FS974 for additional information on these micronutrients.

Organic Soil Fertility Management

The soil fertility management for production of organic forage crops should be considered within the context of the overall organic crop rotation cycle and organic farm system plan. When transitioning farmland to the organic system, legumes are a better choice to begin the crop rotation cycle than non-legumes because soils under organic transition are usually nitrogen-deficient. Nitrogen fertility can be provided for production of grass hay by following a good crop rotation system, application of compost, or manures. Supplemental N fertilizer, up to 20% of the recommended N requirement, may also be applied as Chilean nitrate (also known as sodium nitrate, 15% N). Instead of attempting to grow a pure stand of grass hay and be challenged to supply enough N, organic growers may prefer to produce hay as a mixed stand of grasses and legumes. Hay produced as a mix of grasses and alfalfa is acceptable as feed for horses.

On organic farms that include livestock, manure is an important source of fertility, but if supplemental P or K is needed only raw, mined, or unprocessed fertilizer sources are approved for organic production. As a source of P, rock phosphate may be used. If K is needed, three commercial K fertilizers, langbeinite, potassium sulfate, and sylvinite may sometimes be used with certain restrictions in organic farming. When micronutrient deficiencies occur, they can be corrected as necessary for organic crop production using many of the same fertilizer materials and application practices as used in conventional agriculture. In organic farming, however, micronutrient fertilizer products cannot be routinely applied without prior soil or plant diagnostics to confirm the specific micronutrient deficiency. Always check with the organic certifier to be sure a particular product is approved for use in organic farming.

Table 3. Plant analysis nutrient sufficiency for cool season grasses. Plant tissue testing is useful for assessing the nutrient status. Sample the top 6 inches of the shoots just prior to flowering.
Nutrient Low Sufficient High
Nitrogen < 3.21 3.21 – 4.20 > 4.20
Phosphorous < 0.24 0.24 – 0.35 > 0.35
Potassium < 2.61 2.61 – 3.50 > 3.50
Calcium < 0.51 0.51 – 0.90 > 0.90
Magnesium < 0.11 0.11 – 0.30 > 0.30
Sulfur < 0.21 0.21 – 0.25 > 0.25
Boron < 8  8 – 12 > 12
Manganese < 51  51– 150 > 150
Iron < 51 51 – 200 > 200
Zinc < 20 20 – 50 > 50
Copper < 3  3 – 5 > 5
Molybdenum < 1  1 – 5 > 5

July 2018