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

 

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.