DRY-MATTER PARTITIONING IN A TRUE VS FACULTATIVE ANNUAL FORAGE LEGUME

Differential partitioning of photosynthate has been suggested as the r eason for low early-season (8 to 12 wk post planting) dry matter (DM) yield of 'Savanna' stylo [Stylosanthes guianensis (Aubl.) Sw.], a facu ltative 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-sh oot ratio (g g(-1)), leaf-to-stem ratio (g g(-1)), and total plant wei ght (g) of Savanna style was compared with common alyceclover [Alysica rpus vaginalis (L.) DC.], a true annual, for 16 wk post planting. Only time post planting consistently affected root-to-shoot ratio, which d eclined as time post planting increased. Within gears, leaf-to-stem ra tio 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, diffe red in 1992, when April-planted Savanna stylo plants had greater total plant DM than June-planted Savanna style or either planting date of a lyceclover. Across the 16-wk post-planting period, there was a consist ent legume x planting date interaction each year for total plant weigh t. This vias because both April-planted legumes were vegetative for th e full 16-wk post-planting period (April-August) and total plant weigh t remained similar, but only Savanna style remained vegetative for the full 16-wk post June-planting period (June-October). Total plant weig ht of June-planted alyceclover was lower due to flowering and leaf los s in the later part of the 16-wk post-planting period. These data indi cate that the lower early-season DM yield of Savanna style compared wi th alyceclover is not due to physiological differences associated with perennial and annual growth habits.