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

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 21 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 21 crude protein [CP]) increased cubically (P 5 0.020) with simulated rainfall, but the overall range of response was small (653–673 g kg 21 CP). Estimates of DIP (g kg 21 CP) for IDEAL-O and DRY-O decreased by 46 and 25 g kg 21 CP, respectively, between the 0and 76-mm rainfall increments; for IDEAL-O, these decreases occurred in a linear (P , 0.0001) pattern, whereas quadratic (P 5 0.009) and linear (P 5 0.029) effects were observed for DRY-O. Bermudagrass forage was field wilted to 761, 400, or 130 g kg 21 of moisture (WET-B, MID-B, and IDEAL-B, respectively) and evaluated similarly. For WET-B and MID-B, DIP (g kg 21 CP) was not affected (P . 0.05) by simulated rainfall. In contrast, quartic (P 5 0.019) and linear (P 5 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.