Bahiagrass Canopy Size, Soil Water, and Establishment of Aeschynomene

Abstract

AbstractAeschynomene americana L. is a tropical pasture legume, and in Florida, where it is usually grown with bahiagrass (Paspalum notatum Flügge), there are about 5000 ha. Limited soil water is a primary reason for stand failure of this annual. Soil water in three bahiagrass canopy sizes: small (2.2 leaf area index [LAI]), medium (4.5 LAI) and large (7.7 LAI) was measured at seeding and related to aeschynomene establishment. All canopies were clipped to a 50‐mm height when aeschynomene seedlings emerged. Soil was Eau Gallie fine sand (sandy, siliceous, hyperthermic Haplaquods). Aeschynomene was drilled into sod on 17 dates between May and July in 1981 to 1985, and seedling density was determined at emergence and periodically for 21 d. Six of the 17 seedings were failures because of drought (one because of flooding), and when failure occurred, it was in all three canopy sizes. Water potential at 75‐ and 150‐mm soil depths was analyzed from 209 dates, and canopy size affected soil water potential on 41 dates. Gravimetric soil‐water was analyzed on 42 dates, and canopy size affected (P ≤ 0.05) gravimetric soil‐water on five dates. Evapotranspiration (ET) rate was measured twice and was not different among canopy sizes on 26 June 1984 (avg. 94 mg m−2 s−1). Differences (P ≤ 0.03) in ET rate were found on 16 May 1986 when the large canopy (128 mg m−2 s−1) had greater ET rate than the small canopy (100 mg m−2 s−1), with the medium canopy (117 mg m−2 s−1) intermediate. Bahiagrass canopy size before aeschynomene emergence had little effect on the amount of soil water and resulting success or failure of aeschynomene. Only rain and soil water potential were useful for predicting aeschynomene stand success. Together, rain 0 to 8 d before seeding [descriminant value (DV) ≤ 22 mm] and soil water potential at seeding (DV ≤ −15 kPa) correctly predicted 13 out of 17 seedings.