Submitted to: Crop Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/27/2008
Publication Date: 11/25/2008
Citation: Coblentz, W.K., Jokela, W.E. 2008. Estimating Losses of Dry Matter from Wetted Alfalfa-Orchardgrass Mixtures Using Cell Wall Components as Internal Markers. Crop Science. 48:2481-2489. Interpretive Summary: Previous methodologies to measure recoveries of dry matter (DM) from experimental hays following natural or simulated rainfall events often have relied upon gravimetric (weight-change) techniques, resulting in questionable estimates of DM recovery. Our objective was to determine if insoluble cell-wall constituents could be used as internal markers to indirectly estimate recoveries of DM from alfalfa and alfalfa-orchardgrass mixtures damaged by simulated rainfall. Among the cell-wall components evaluated, neutral-detergent fiber appears to be the most suitable marker for experimental use because i) it comprises a greater proportion of the total DM pool than other fiber components, ii) procedures for quantification are relatively rapid, inexpensive, and do not require multiple analytical or digestion steps, iii) relationships between predicted and actual recoveries of DM were generally superior to those obtained with other markers, and iv) NDF is determined as part of nearly all routine forage testing procedures. Cell-wall components that require multiple digestion steps are probably less acceptable as internal markers, largely because their quantification procedures are more tedious, and they are analyzed less consistently in forage research projects. Generally, this research approach appears viable, but it remains contingent on complete recovery of all shattered leaf particles prior to conducting laboratory analysis.
Technical Abstract: Methods previously used to measure recoveries of dry matter (DM) from forages following natural or simulated rainfall often have relied upon simple gravimetric techniques, which yielded inconclusive estimates of DM recovery. Our objective was to evaluate insoluble cell-wall constituents as internal markers for estimating recoveries of DM from alfalfa (Medicago sativa L.) or alfalfa-orchardgrass (Dactylis glomerata L.) mixtures subjected to simulated rainfall. Forage mixtures consisted of 1000, 750, or 500 g kg-1 alfalfa with the balance comprised of orchardgrass. Regardless of the forage mixture, concentrations of all cell-wall constituents increased (P = 0.053) in response to wetting (0, 70, 140, 280, 420, 560, or 840 mm at 70 mm h-1) under a rainfall simulator. Following treatment, recovery of all cell-wall constituents was high (=901 g kg-1). Generally, losses were smallest for neutral-detergent fiber (NDF) markers regardless of analysis method (with alpha-amylase, sodium sulfite, neither or both), acid-detergent fiber (ADF), and cellulose, and largest for hemicellulose and lignin. Linear regressions of recoveries of DM by internal markers on values determined gravimetrically were good (r2 = 0.775) when NDF was used to estimate recovery. In all of these cases, neither slopes (P = 0.103) nor intercepts (P = 0.083) differed from one and zero, respectively. Fiber components appear to be suitable internal markers for measuring recoveries of DM following wetting, but this approach depends on complete recovery of shattered leaf particles prior to conducting laboratory analyses.