Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/14/2014
Publication Date: 10/17/2014
Publication URL: http://handle.nal.usda.gov/10113/59707
Citation: Coblentz, W.K., Muck, R.E., Borchardt, M.A., Spencer, S.K., Jokela, W.E., Bertram, M.G., Coffey, K.P. 2014. Effects of dairy slurry on silage fermentation characteristics and nutritive value of alfalfa. Journal of Dairy Science. 97:7197-7211. Interpretive Summary: Dairy producers frequently ask questions about the risks associated with applying dairy-manure slurry to growing alfalfa. To address these questions, dairy slurry was applied to alfalfa in the following ways: 1) no slurry; 2) slurry applied directly to stubble immediately after the preceding harvest; 3) slurry applied after 1 week of regrowth; or 4) slurry applied after 2 weeks of regrowth. All harvested forage was packaged in large-rectangular bales that were ensiled as wrapped balage. Each bale was sampled on a pre- and post-storage basis for evaluation of silage fermentation characteristics and nutritive value. Generally, dairy-slurry application strategies had little effect on fermentation products and nutritive value. Counts of clostridial bacteria, which can cause poor fermentation in silage, suggest that applications of dairy slurry onto stubble are preferred (and less risky) compared to delayed applications on growing alfalfa. Furthermore, crop damage from salt burn, wheel traffic, or smothering is much less likely when dairy slurry is applied immediately after harvest, rather than after regrowth has been initiated. Our visual observation of plots would suggest that delayed applications of slurry onto alfalfa regrowth should only be considered as a last resort, such as when manure-storage reservoirs are full. Should this be absolutely necessary, producers might be well advised to select application sites on old alfalfa stands, rather than risk damage to recently established plants, thereby reducing their productive life.
Technical Abstract: Dairy producers frequently ask questions about the risks associated with applying dairy slurry to growing alfalfa (Medicago sativa L.). Our objectives were to determine the effects of applying dairy slurry on the subsequent nutritive value and fermentation characteristics of alfalfa balage. Dairy slurry was applied to 0.17-ha plots of alfalfa; applications were made to the second (HARV1) and third (HARV2) cuttings during June and July of 2012, respectively, at mean rates of 42,400 ± 5271 L/ha and 41,700 ± 2397 L/ha, respectively. Application strategies included: i) no slurry; ii) slurry applied directly to stubble immediately after the preceding harvest; iii) slurry applied after 1 week of regrowth; or iv) slurry applied after 2 weeks of regrowth. All harvested forage was packaged in large-rectangular bales that were ensiled as wrapped balage. Yields of DM harvested from HARV1 (2477 kg/ha) and HARV2 (781 kg/ha) were not affected (P = 0.193) by slurry application treatment. By May 2013, all silages appeared to be well-preserved, with no indication of undesirable odors characteristic of clostridial fermentations. Clostridium tyrobutyricum, which is known to negatively affect cheese production, was not detected in any forage on either a pre- or post-ensiled basis. On a pre-ensiled basis, counts for Clostridium Cluster 1 were greater for slurry-applied plots than for those receiving no slurry, and this response was consistent for HARV1 (4.44 vs. 3.29 log10 genomic copies/g; P = 0.002) and HARV2 (4.99 vs. 3.88 log10 genomic copies/g; P < 0.001). Similar (P < 0.001) responses were observed on a post-ensiled basis; however, post-ensiled counts also were greater for HARV1 (5.51 vs. 5.17 log10 genomic copies/g; P = 0.018) and HARV2 (5.84 vs. 5.28 log10 genomic copies/g; P < 0.001) when slurry was applied to regrowth compared to stubble. For HARV2, counts also were greater following a 2-week application delay compared to a 1-week delay (6.23 vs. 5.45 log10 genomic copies/g; P < 0.001). These results suggest that the risk of clostridial fermentations in alfalfa silages is greater following applications of slurry. Based on pre- and post-ensiled clostridial counts, applications of dairy slurry on stubble are preferred (and less risky) compared to delayed applications on growing alfalfa.