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Forages

Nitrogen Partitioning and Estimates of Degradable Intake Protein in Wilting Orchardgrass and Bermudagrass Hays Damaged by Simulated Rainfall

^a Dep. of Animal Science, Univ. of Arkansas, Fayetteville, AR 72701 (current address: 126 Jessie Dunn, Northwestern Oklahoma State Univ., Alva, OK 73717)
^b Dep. of Animal Science, Univ. of Arkansas, Fayetteville, AR 72701
^c Dep. of Animal Science, Univ. of Arkansas, Fayetteville, AR 72701 (current address: North Carolina State Univ. Mountain Res. Stn., Waynesville, NC 28786)
^d Dep. of Crop, Soil, and Environmental Sciences, Univ. of Arkansas, Fayetteville, AR 72701
^e USDA-ARS, National Soil Tilth Lab., Ames, IA 50011
^f Animal Science Section, Arkansas Coop. Ext. Service, Little Rock 72203. Contribution of the Arkansas Agric. Exp. Stn

^* Corresponding author (coblentz{at}uark.edu)

Received for publication March 28, 2005. This study investigated the effects of simulated rainfall on N partitioning and concentrations of degradable (DIP) or undegradable (UIP) intake protein for wilting orchardgrass (Dactylis glomerata L.) and bermudagrass [Cynodon dactylon (L.) Pers.] hays. Orchardgrass forage was wilted to 674, 153, or 41 g kg^–1 of moisture (WET-O, IDEAL-O, and DRY-O, respectively) in the field before applying the simulated rainfall (0, 13, 25, 38, 51, 64, or 76 mm). For WET-O, DIP (g kg^–1 crude protein [CP]) increased cubically (P = 0.020) with simulated rainfall, but the overall range of response was small (653–673 g kg^–1 CP). Estimates of DIP (g kg^–1 CP) for IDEAL-O and DRY-O decreased by 46 and 25 g kg^–1 CP, respectively, between the 0- and 76-mm rainfall increments; for IDEAL-O, these decreases occurred in a linear (P < 0.0001) pattern, whereas quadratic (P = 0.009) and linear (P = 0.029) effects were observed for DRY-O. Bermudagrass forage was field wilted to 761, 400, or 130 g kg^–1 of moisture (WET-B, MID-B, and IDEAL-B, respectively) and evaluated similarly. For WET-B and MID-B, DIP (g kg^–1 CP) was not affected (P > 0.05) by simulated rainfall. In contrast, quartic (P = 0.019) and linear (P = 0.002) effects were observed for IDEAL-B, but these responses were confined primarily to changes between the undamaged (0-mm) control and the initial 13-mm rainfall increment. On a practical basis, concentrations of DIP were, at most, altered only moderately in response to simulated rainfall and relatively little when forages were still too wet to bale.

Abbreviations: AIRDRY, forages air-dried in wire cages for 48 h after application of simulated rainfall • ANOVA, analysis of variance • CP, crude protein • DIP, degradable intake protein • DRY, orchardgrass subjected to simulated rainfall at 41 g kg^–1 of moisture • DM, dry matter • IDEAL, forages subjected to simulated rainfall at ideal moisture concentrations for baling (153 and 130 g kg^–1 of moisture for orchardgrass and bermudagrass, respectively) • MID, bermudagrass subjected to simulated rainfall at the approximate midpoint of dehydration (400 g kg^–1 of moisture) • NDIN, neutral detergent insoluble N • OVENDRY, forages oven-dried at 55°C after application of simulated rainfall • UIP, undegradable intake protein • WET, forage subjected to simulated rainfall immediately after mowing (674 and 761 g kg^–1 of moisture for orchardgrass and bermudagrass, respectively)