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Nitrogen and Date of Defoliation Effects on Seed Yield and Seed Quality of Tall Fescue¹

Each year approximately 150,000 to 200,000 ha of tall fescue (Festuca arundinacea Schreb.) are havested for seed in the United States. The majority of this hectarage is utilized for fall and winter grazing as well as seed production in the spring. The objectives of this study were to examine the effects of N level and date of last forage harvest in the spring on the forage and seed yield and seed quality of tall fescue.

A sward of ‘Kenwell’ tall fescue was grown under three levels of N and five defoliation regimes at Mississippi State, Miss. on a Leeper silty clay loam (fine, montmorillonitic, nonacid, thermic Vertic Haplaquept). Nitrogen rates of 0, 67, and 134 kg/ha applied as NH₄NO₃ were applied in February of 1967 and 1968. Plots were harvested zero, one, two, three, or four times at 15 day intervals prior to seed harvest. The five defoliation treatments, by date of last forage harvest prior to seed harvest were no harvest, 15 and 30 March and 15 and 30 April. Following seed harvest the aftermath was harvested for forage. Variables measured were dry matter yield, seed yield, panicles/ m², spikelets/panicle, and florets/spikelet. Seed quality characteristics measured included germination, seedling weight, and shoot and radicle length.

Dry matter and seed yields were decreased significantly in plots defoliated later than 30 March. Reductions in seed yield appeared to be the result of decreased tiller density and the number of spikelets per panicle. Early spring defoliation (15 March) resulted in some damage to fertile tillers in the 1st year as evidenced by a reduced number of spikelets/panicle, although there was no effect on seed yield or tiller density. Seed quality was reduced for all plots defoliated after 30 March.

Dry matter and seed yields increased with increasing rates of N. Maximum forage and seed yields were attained at 134 kg/ha of N while maximum seed quality was attained with 67 kg/ha of N.

Results of this study indicate that tall fescue seed fields which are to be grazed or cut for hay should not be defoliated in the spring after tillers commence to elongate and become erect if maximum production is to be realized. Higher rates of N were required to maximize dry matter and seed yields than to maximize seed quality.

Key Words: Festuca arundinacea Schreb., • Dry matter yield • Seed production

² Associate professor and professor of agronomy, Mississippi State Univ., Mississippi State, MS 39762.

Received for publication November 23, 1981.

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