ISSUED: 11-82
K.L. Wells, L.W. Murdock and C.T. Dougherty

There are an estimated 7 to 7.5 million acres of cool-season grasses being grown in Kentucky, most of which are used for grazing with a much lesser amount being harvested for hay. This acreage consists largely of tall fescue (about 5.5 million acres), Kentucky bluegrass (about 1 million acres), orchard grass (about 0.5 million acres), and relatively small acreages of timothy, smooth bromegrass, and perennial ryegrass.
Because of the inherent growth pattern of these grasses, they respond similarly to fertilization practices, and no distinctions are made between them in lime and fertilization recommendations. Their dominant growth characteristic is a peak of production which occurs about flowering during late spring and early summer, after which growth tapers off greatly during the hotter and drier summer weather. With the return of cooler fall weather, vigorous growth resumes, if rains occur, until the onset of winter. Generalized recommendations for nitrogen fertilization management are directly related to these growth characteristics, field history, and intended use, but are independent of such factors as soil type, slope and aspect.

Although cool-season grasses will grow over a wide range of soil acidity, soil pH levels should be kept in the 5.5 to 6.5 range, particularly for bluegrass. Lime should be applied during seedbed preparation for new seedings or as a topdressing on established fields to maintain soil pH in this range. The pH should be at the high end of this range, where fertilizer use efficiency is greater, if legumes are interseeded into the grass. Lime should be added according to soil test, preferably based on "buffer pH" since this test more precisely indicates the amount of lime actually needed for any desired pH change (Table 1).

Table 1. Generalized Lime Recommendations for Cool-Season Grasses1
Soil-Water pH 
Tons Ag-Lime/A
above 6.4
5.8 - 6.4
0 - 2 
5.2 - 5.8
2 - 4 
below 5.2
1 A "buffer pH" test will more precisely show the actual amount of lime needed.

Phosphate and Potash Fertilization
Although the cool-season grasses will survive at fairly low soil test levels of phosphorus (P) or potassium (K), growth and yields will be poor. Therefore, soil test levels should be in the medium range for good production and annual topdressings should be made on low-testing soils. Under continuous grazing, much of the P and K contained in the grass is recycled back into the soil in animal wastes. Periodic use of a chain harrow will aid greatly in spreading dung hills more uniformly over the soil and also limiting rejection of forage by grazing animals.
When managed for hay production, fairly sizeable amounts of P and K are removed from the field and annual topdressings are more important, particularly on low and medium testing soils. Application of P and K should be made just before seedbed preparation for new seedings or as topdressings on established fields. Table 2 shows recommended rates for use of P and K. Soil samples from continuous pasture fields should be taken to a depth of 4 inches. If the field is in rotation and is periodically plowed, take samples to plow depth.

Table 2. Phosphate and Potash Fertilization Recommendations1
Soil Test Range
Lb/A/Yr to Topdress2
above 60
above 300
30 - 60
185 - 300
0 - 80
0 - 40
below 30
below 185
80 - 120
40 - 80
1 Since all commonly available forms of P and K are equally effective, decisions should be made based on the least cost per acre of the amount of P and K desired.
2 Increase P2O5 by 20 lb/A and K2O by 40 lb/A if field is used for hay.

Nitrogen Fertilization
The cool-season grasses respond dramatically to nitrogen fertilization. If moisture and soil test levels of P and K are adequate (medium to high-medium levels), using nitrogen (N) greatly stimulates their growth during these peak production periods. The decision to use nitrogen on grasses should be determined by what you expect from grass in the overall feed production system. Nitrogen fertilization can be helpful in increasing total production and protein content, shifting seasonality of production, and to some extent, controlling weeds. One thing of economic importance--unless the increased production from adding nitrogen is used by livestock or sold for hay, there will be no return to the expense. The best fertilizer response, particularly from nitrogen, will be from deep, well-drained soils of high yield potential. Such fields are more likely to justify using the higher nitrogen rates. Lower rates should be used on fields with low yield potential due to shallow soil, rock outcrops, significant populations of weeds, trees and shrubs, etc.

Increasing Total Production
Research data over a period of years indicate that dry matter can be increased from about 1 ton per year with no N to about 4 tons per year with up to 200 pounds of N per acre. Tall fescue is generally more responsive to N than orchard grass, with bluegrass being much less responsive. Tables 3 and 4 show responses of tall fescue and orchard grass to N fertilization.

Table 3. Production of Dry Matter (Lb/A) by Tall Fescue
with half the N applied in early March and half applied in mid August.1
Lb N/A
Production from
March to
Early May
Production from
Early May to
Mid August
Production from
Mid August to
Mid November
1 Average of 9 site-years data from studies in Breathitt, Graves, and Franklin Counties.

Table 4. Production of dry matter (Lb/A) by Boone Orchard grass
with half the N applied in early March and half applied in mid August.1

Lb N/A
Production from
March to 
Early May
Production from
Early May to
Mid August
Production from
Mid August to
Mid November
1 Average of 6 site-years data from studies in Breathitt and Franklin Counties.

Shifting Seasons of Production

Timely applications will increase the production of grasses during particular seasons. A topdressing in late winter or early spring just before growth begins will increase growth so that grazing can begin about 2 weeks ahead of pastures receiving no N. This effect can be used as a means of lowering overwintering feed costs. Another topdressing in late spring following a grazedown or hay cut will stimulate growth that will carry over into the low production period of the summer. Another topdressing following a grazedown or clipping in late summer will stimulate fall growth, which, if properly used, will extend grazing several weeks later into the fall and winter. This is a practical means of lowering winter feeding costs by keeping animals on pasture longer.

Research in Kentucky has shown little difference among commonly used N sources for topdressing cool-season grasses during late winter and early spring. From mid-May until October, topdressed urea may not be as effective as other sources because of volatilization. N losses from urea topdressed during this time will likely be on the order of 15 to 20 percent.

When to Topdress
How much N to top-dress should be dependent on how much additional production is needed. If a total of more than 100 pounds of N per acre per year is to be used, it should be applied in split applications as shown in Table 5. No more than 200 pounds of N per acre per year should be used.

Table 5. Nitrogen Fertilizer Recommendations
Date Lb N/A per Application
Feb. 15 - March 15 up to 100
May 1 - 15 up to 50
July 15 - Aug. 151 up to 80
1 Production drops rapidly as N applications are delayed past August 15.

Grass Seed Production
For pure stands of tall fescue and bluegrass from which seed will be harvested, an additional topdressing of 60 to 70 pounds of N per acre around December 1, after grazedown, will increase seed yields the following year.

Effect on Nitrogen-Sulfur Ratios
There is concern that if the ratio between percent total nitrogen content and percent total sulfur content of forage exceeds 16, nutritional imbalances in ruminant animals may occur. (For example, fescue herbage with a total N content of 3 percent and a total S content of 0.3 percent has an N:S ratio of 3 / 0.3, or 10.) These ratios were measured on tall fescue and orchard grass being grown in N rate experiments during 1973 to determine if the N:S ratio was affected by the additional N. The N:S ratio never exceeded 16 (Table 6). In fact, at N rates which would more commonly be applied, the N:S ratio ranged from 9 to 12 for spring growth, from 6 to 7 for summer growth, and from 8 to 14 for fall growth.

Table 6. Effect of Rate and Time of N Fertilization on N:S Ratios of Forage
Species and Location Date Sampled1
--------------Lb N/A---------------
0 40 80 120
-------------N:S Ratio-------------
Tall Fescue, Breathitt Co. Early May 7.9  9.3  12.0 13.7
Mid-August 6.1 5.9 6.5 7.2
Tall Fescue, Graves Co. Early May 8.8  9.9  10.7  14.1 
Mid-August 5.2  4.3  5.7  6.5 
Tall Fescue, Franklin Co. Early May 6.1  8.9  11.0  13.1 
Mid-August 8.3  5.7  6.7  7.5 
Mid-November 7.2  6.1  8.8  11.6 
Orchard grass, Franklin Co. Early May 8.0  9.2  11.6  13.6 
Mid-August 7.5  6.7  6.8  8.4 
Mid-November 10.0  8.4  12.6  13.9 
1 Nitrogen was applied in early March for the May and August samples, and mid-August for the mid-November samples.

Grass Tetany
Tetany problems with cattle are sometimes encountered on predominantly grass pastures, particularly in spring with nursing cows where grass pasture is the only source of feed. Late winter or early spring N applications onto fields testing very high in potassium or fields that have received high rates of potassium fertilization can increase the risk of grass tetany. Tetany in such animals results from an imbalance of magnesium in their blood. Supplemental feeding of magnesium to nursing cows on such fields is recommended as a means of lowering tetany risks. See Extension publication ASC-16 for detailed recommendations.

Fertilization for Surface Mine Reclamation
Extreme acidity, very low phosphorus levels, and the need for nitrogen fertilization are commonly encountered problems in growing grass on reclaimed land. See Extension publications AGR-40, AGR-41, and AGR-89 for detailed information on liming and fertilizing for reclamation purposes.