Phenotypic Plasticity and Other Forage Responses to Grazing Management of Ecoturf Rhizoma Peanut

Abstract

Forage–livestock systems in the southeastern United States are based on N‐fertilized perennial grass pastures, with minimal legume contribution. The legume rhizoma peanut (RP, Arachis glabrata Benth.) can persist and spread in grazed mixtures with C4 grasses, and Ecoturf RP is of particular interest because it is relatively decumbent and may vary its growth habit in response to defoliation management. The objective was to quantify effects of grazing frequency and intensity of Ecoturf on herbage accumulation (HA), canopy characteristics, storage organ mass, and total nonstructural carbohydrate (TNC) concentration. Treatments were the factorial combinations of three levels of regrowth interval (RI; 1, 4, and 7 wk) between grazing events and two levels of post‐grazing stubble height (SH; 4 and 8 cm). For the 4‐cm SH, HA increased from 8.4 to 10.5 Mg ha−1 in 2015 and from 9.8 to 13.6 Mg ha−1 in 2016 as RI decreased from 7 to 1 wk. The effect of RI was less pronounced for the 8‐cm SH. When grazed to a 4‐cm SH, herbage bulk density and post‐grazing leaflet mass increased linearly as RI decreased from 7 to 1 wk in both years. Changes in root‐rhizome mass and TNC pool during 2 yr of grazing were not affected by SH or RI. Ecoturf adapted to frequent, close grazing by increasing herbage bulk density and positioning leaves close to the soil surface, allowing rapid regrowth after defoliation without depleting reserves. Ecoturf is tolerant of a range of grazing strategies, showing promise for use in pastures.

Rhizoma peanut herbage and root–rhizome responses to extended regrowth periods

“…Evidence exists, however, that more frequent defoliation may result in greater HA of some RP entries under some conditions. For example, in a grazing experiment with Ecoturf, weekly close defoliation (4‐cm stubble) resulted in greater HA than defoliating every 4 or 7 wk (Shepard et al., 2018). Likewise, in a mowing experiment with Ecoturf, frequent, close mowing was associated with greater HA, more new shoots, and a dense canopy (Rouse, Roka, & Miavitz‐Brown, 2004).…”

“…(2016b) (average of 25 cm). This may be due, in part, to Ecoturf's phenotypic plasticity, whereby it assumes a shorter canopy with greater herbage bulk density when frequently and closely defoliated (Mullenix et al., 2016b; Shepard et al., 2018). Under infrequent cutting used in this study, Ecoturf assumed a more intermediate growth habit.…”

“…This depth was chosen based on techniques used by others (Ortega‐S. et al., 1992a; Shepard et al., 2018) and because it allowed recovery of a high proportion of the root–rhizome mass used as propagation material by producers. The three samples per plot were composited and washed over a 2‐mm mesh screen to remove soil.…”

“…Of perennial forage legumes adapted to the U.S. southern Gulf Coast region, RP is among the most widely used. It has documented persistence (Hernández Garay, Sollenberger, Staples, & Pedreira, 2004; Ortega‐S., Sollenberger, Quesenberry, Cornell, & Jones, 1992b; Shepard et al., 2018), can spread in mixtures with grasses (Castillo et al., 2013a, 2013b; Mullenix et al., 2014), and has excellent nutritive value (Mullenix et al., 2016b; Shepard et al., 2018.…”

“…et al., 1992b) and up to 42 d for Florigraze, ‘UF Tito’, ‘UF Peace’, and the germplasm Ecoturf (Mullenix et al., 2016a). Nutritive value was minimally affected by defoliation frequency (Mullenix et al., 2016a; Shepard et al., 2018) but frequent, close defoliation reduced rhizome mass and TNC concentration of Florigraze (Ortega‐S., Sollenberger, Bennett, & Cornell, 1992a; Rice, Sollenberger, Quesenberry, Prine, & French, 1995) and rhizome mass of several RP entries (Mullenix et al., 2016b). Response of Ecoturf, a phenotypically plastic germplasm that adapts to close grazing by developing a short, dense canopy, was different than Florigraze, as it maintained or increased herbage HA and rhizome mass under frequent, close grazing (Shepard et al., 2018).…”