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

Abstract

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.