|Scarbrough, Dean - NORTHWESTERN OKLAHOMA|
|Ogden, Robin - UNIVERSITY OF ARKANSAS|
|Turner, Jim - NORTH CAROLINA STATE UNIV|
|Humphry, J. - UNIVERSITY OF ARKANSAS|
|Coffey, Kenneth - UNIVERSITY OF ARKANSAS|
|Daniel, Tommy - UNIVERSITY OF ARKANSAS|
|Jennings, John - UNIVERSITY OF ARKANSAS|
|Kellogg, D. - UNIVERSITY OF ARKANSAS|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 2005
Publication Date: January 2, 2006
Citation: Scarbrough, D. A., W. K. Coblentz, R. K. Ogden, J. E. Turner, J. B. Humphry, K. P. Coffey, T. C. Daniel, T. J. Sauer, J. A. Jennings, and D. W. Kellogg. 2006. Nitrogen partitioning and estimates of degradable intake protein in wilting orchardgrass and bermudagrass hays damaged by simulated rainfall. Agronomy Journal. 98:85-93. Interpretive Summary: Hay producers are frequently frustrated by rainfall events that may occur while hay crops are wilting prior to baling; however, the physiological changes that occur within wilting forage plants during these uncooperative weather events are poorly understood. Rainfall simulation techniques were used to assess the effects of simulated rainfall on protein fractions within wilting orchardgrass and bermudagrass hays. Concentrations of ruminally digestible intake protein (DIP) exhibited the greatest changes when forages were dry enough to bale at the time simulated rainfall was applied. Within this context, responses were diverse across forages; DIP decreased in response to simulated rainfall for orchardgrass forages, but increased for bermudagrass. However, the magnitude of these changes was relatively small, and the difference between the 0- and 3-inch rainfall increments was < 5% of the total protein pool for any forage dry enough to bale at the time rainfall was applied. In contrast, forages that were relatively wet when simulated rainfall was applied exhibited remarkably consistent concentrations of DIP across rainfall increments. On a practical basis, concentrations of DIP were, at most, altered only moderately in response to simulated rainfall, and not at all when forages were still too wet to bale. Based on these and previous findings, forage grasses are resistant to reductions in nutritive value if they are still well hydrated at the time the rainfall event occurs, but damage is maximized when forages are dry enough to bale.
Technical 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 41g kg-1 of moisture (WET-O, IDEAL-O, and DRY-O, respectively) in the field prior to applying the simulated rainfall (0, 13, 25, 38, 51, 64, or 76 mm). For WET-O, DIP (g kg-1 CP) increased cubically (P = 0.020) with simulated rainfall, but the overall range of response was small (653 to 673 g kg-1 CP). Estimates of DIP (g kg-1 CP) for both 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, while 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) increases 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.