Harvest Management Based On Leaf Stage of a Tetraploid Vs. a Diploid Cultivar of Annual Ryegrass.

The act of defoliation creates a major encumbrance on pasture plants with its impact being dependent on the timing and severity of defoliation.  A 2-yr study was conducted at Raymond, MS to quantify forage production, morphological characteristics and nutritive value between a tetraploid vs. a diploid annual ryegrass cultivars harvested at three different leaf stages and two stubble heights.  Treatments were two annual ryegrass cultivars ‘Maximus’ a tetraploid and ‘Marshall’ a diploid, three different leaf stages (2-, 3-, and 4-leaves per tiller^-1), and two residual stubble heights (5- and 10-cm RSH) arranged in a 3 × 2 × 2 factorial combinations in a randomized complete block design experiment with four replications for each treatment combinations.  Responses were considered different at P < 0.05.  In 2011, there was a linear increase in forage harvested as defoliation increased from 2- (7.3 Mg DM ha^-1) to 4-leaf stage (8.8 Mg DM ha^‑1) and in 2012, there was a quadratic response of forage harvested to defoliation interval.  At 5-cm RSH forage harvested (7.9 Mg DM ha^-1) tended to be greater than at 10-cm RSH (7.5 Mg DM ha^-1).  Tiller density was not different (P = 0.394) among the three defoliation intervals but tiller density was less for Maximus (1191 tillers m^-2) than Marshall (1383 tillers m^-2).  In both years, at 5-cm RSH there was a linear increase in stubble water‑soluble carbohydrate (WSC) content from 2- (4.8 mg tiller^-1) to 4-leaf stage (6.9 mg tiller^-1) and at 10‑cm RSH there was a quadratic response of stubble WSC content to defoliation interval.  Water-soluble carbohydrate content of stubble was greater for Maximus (7.9 mg tiller^-1) than Marshall (6.2 mg tiiler^-1).  The responses of leaf blade proportion to defoliation interval were mostly a quadratic decreased from 2- to 4-leaf stage and greater for Maximus by 9% than Marshall.  In 2012, at 5-cm there was a linear increase in whole plant WSC concentration from 2- (84.1 g kg^-1 DM) to 4-leaf stage (133.4 g kg^-1 DM) however, whole plant WSC concentration was not different between Maximus and Marshall.  There was a linear (2011) and quadratic (2012) decrease in digestibility from 2- (801 g kg^-1 DM) to 4-leaf stage (729 g kg^-1 DM) but digestibility was not different between Maximus and Marshall.  There was a dichotomy in forage response in terms of forage harvested and nutritive value to defoliation intervals based on leaf stage and stubble height of annual ryegrass.  Harvesting at 5-cm RSH did not result in less forage harvested than at 10-cm for Maximus and Marshall annual ryegrass. Therefore, the choice of cultivar, defoliation interval and intensity should be made in the context of farmer’s production system and location.