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Dry Matter Partitioning in a True vs. Facultative Annual Forage Legume

USDA-ARS, Subtropical Argric. Res. Stn., 22271 Chinsegut Hill Rd., Brooksville, FL 34601-4672
Dep. of Agronomy, Univ. of Florida, Gainesville, FL 32611
Univ. of Florida AREC, Ft. Pierce, FL 34954

^* Corresponding author.

Differential partitioning of photosynthate has been suggested as the reason for low early-season (8 to 12 wk post planting) dry matter (DM) yield of ‘Savanna’ stylo [Stylosanthes guianensis (Aubl.) Sw.], a facultative annual over much of its Florida range. In a 3-yr field study (1991–1993), the effect of planting date (April vs. June) on root-to-shoot ratio (g g^–1), leaf-to-stem ratio (g g^–1), and total plant weight (g) of Savanna stylo was compared with common alyceclover [Alysicarpus vaginalis (L.) DC.], a true annual, for 16 wk post planting. Only time post planting consistently affected root-to-shoot ratio, which declined as time post planting increased. Within years, leaf-to-stem ratio also declined with increasing time post planting, but, on average, Savanna stylo had a higher leaf-to-stem ratio than alyceclover. There was a planting date x legume x year x time post planting interaction for total plant weight. This was because total plant weights, although similar regardless of planting date or legume in 1991 and 1993, differed in 1992, when April-planted Savanna stylo plants had greater total plant DM than June-planted Savanna stylo or either planting date of alyceclover. Across the 16-wk post-planting period, there was a consistent legume x planting date interaction each year for total plant weight. This was because both Aprilplanted legumes were vegetative for the full 16-wk post-planting period (April–August) and total plant weight remained similar, but only Savanna stylo remained vegetative for the full 16-wk post June-planting period (June–October). Total plant weight of June-planted alyceclover was lower due to flowering and leaf loss in the later part of the 16-wk post-planting period. These data indicate that the lower early-season DM yield of Savanna stylo compared with alyceclover is not due to physiological differences associated with perennial and annual growth habits.

Received for publication September 5, 1994.