Germinable seed in the soil seed bank of five bahiagrass-legume pastures

Soil in five bahiagrass (Paspalum notatum FIugge)-legume pastures in central Florida was sampled for germinable seed prior to summer rains in February 2002. Three pastures contained 1, 5, or 10-yr-old stands of Aeschynomene evenia C. Wright (evenia). A fourth pasture contained 15-yr-old A. americana L. (americana), and the fifth contained 8-yr-old Desmodium heterocarpon (L) DC (carpon). Seedlings of all plants were identified, counted, and removed from flats in a glasshouse as they emerged in 5 cycles of wetting and drying over a 20-mo period. Averaged over all pastures, there was a total 9538 germinable seed m(-2) representing 48 species plus the combined Cyperaceae and Juncaceae, which constituted the largest entity with an average 6653 seed (-2). Bahiagrass ranked 3rd in density of germinable seed with an average 566 seed m(-2) (equivalent of 17.2 kg seed ha(-1)), 98 % of which germinated in Cycle 1. Evenia seed ranked 5th in density with 52, 553, and 335 seed m(-2) in 1, 5, and 10-yr-old stands, respectively (2.8, 29.7, and 18 kg seed ha(-1)). Density of americana (rank 13) and carpon (rank 6) averaged 124 and 857 seed M-2, respectively (6.7 and 11.2 kg seed ha(-1)). Of the total americana seed, 68 and 21 % germinated in Cycles 1 and 2. Germination of evenia and carpon seed was 25 and 39 %, respectively, in Cycle 1, but it reached a peak in Cycle 2 with 47 and 57 %, respectively. Seeds of common weeds were present in all pasture soils, but did not constitute a major portion of the seed bank. These data demonstrate the importance of management to build seed reserves of forage plants. The presence of weed seed indicates the need for good management to maintain strong stands of desirable forages capable of suppressing weeds.