Phosphorus and Nitrogen Yields From Tifton 85 Fields Over-Seeded in Cool-Season Annual Forages.

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Tifton 85 (Cynodon hybrid) is a warm-season perennial grass grown on dairy manure application fields.� Because Tifton 85 survives the winters by lying dormant, cool season annual forages can be over-seeded in the autumn for utilization during winter and spring.� These could also be used to optimize P uptake as well as to add nitrogen (N). The effect these have upon subsequent Tifton 85 spring regrowth, however, is not well documented.� Three grasses: rye (Secale cereale L.), oats (Avena sativa L.), wheat (Triticum aestivum L.) and two legumes: hairy vetch (Vicia villosa Roth) and crimson clover (Trifolium incartnatum L.) were evaluated.� The grass plots were fertilized with 56 kg N ha^-1 on soils with 83 mg plant-available P kg^-1. Hairy vetch, oats, and rye had the greatest DM yields at least two out of the three years.� The negative effect of the cool season forage upon the Tifton 85 DM yield ranged from a 14 to 68% decrease in the first summer harvest. Cumulative P uptake increased (P ≤ 0.05) up to 41 kg ha^-1 when cool-season forages were over-seeded and rainfall was adequate, but this was not consistent among all the entries. The legumes consistently added the most N (P ≤ 0.05) to the cumulative yields, sometimes up to 173% greater than Tifton 85 alone. Over-seeding cool-season annual forages onto Tifton 85 increased net P recycled only minimally.

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