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United States Department of Agriculture

Agricultural Research Service

Title: Enumeration of Lactic Acid Bacteria on Harvested Alfalfa at Long and Short Wilting Times

Authors
item Pitt, R - CORNELL UNIVERSITY
item Muck, Richard

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 27, 1995
Publication Date: N/A

Interpretive Summary: Bacterial inoculants are the most common silage additives in the U.S., supplying lactic acid bacteria for an efficient silage fermentation. However, research on their use in making alfalfa silage has shown that these products are not always effective. Failure of these products is normally caused by high natural populations of lactic acid bacteria that overwhelm those being applied. Earlier studies found that the natural population of lactic acid bacteria on alfalfa at ensiling could be predicted under Wisconsin conditions by knowing the average air temperature during field wilting, the wilting time, rainfall during wilting and the moisture content of the alfalfa at ensiling. Using this information, a farmer can determine if use of an inoculant would be profitable. In the current study, counts of lactic acid bacteria on alfalfa grown under New York conditions were measured and predicted using the Wisconsin equations to determine if these equations would work in the Northeast U.S. For situations similar to those reported in Wisconsin studies (primarily 1 to 3 day wilting times with little rainfall during wilting), the predictive equations worked well. However, these equations predicted counts that were too high for direct-cut alfalfa and alfalfa wilted greater than 3 days. A new equation was developed from the New York data for long wilting times and successfully predicted Wisconsin data. This equation indicates that for long wilting times, silage inoculants are profitable if the average wilting temperature is less than 20 C and if there is no rainfall. With increasing rainfall, the maximum temperature for profitability decreases. For direct-cut alfalfa, inoculation is profitable if average temperatures in the 24 h prior to harvest are less than 23 C with no rainfall.

Technical Abstract: Preservation of alfalfa as silage relies on the presence and activity of lactic acid producing bacteria (LAB) at ensiling. Counts of LAB were determined on standing, mowed and harvested alfalfa for two growing seasons under Northeast conditions. These data were used to test the prediction equations based on Wisconsin data and to modify the equations as needed. Wilting times, rainfall quantites and wilting temperature were outside the range of the Wisconsin data in 61 of 71 trials. The equations performed well when conditions were in the range of the original data, but extrapolation of the equations outside of those conditions produced unrealistically high LAB predictions. For short wilting times, the inoculation associated with chopping was assumed to be affected by rainfall and wilting time only up to 4 mm and 72 h, respectively, and to be unaffected beyond that. A new regression equation was formed for the LAB counts at wilting times greater than 72 h, with the best predictors being average ambient temperature and rainfall during wilting. Criteria for cost effective use of inoculants suggest that inoculation of direct cut alfalfa is worthwhile when the average air temperature of the 24 h prior to harvest is less than 23 C with no rainfall. For long wilting times, average wilting temperature must be less than 20 C for inoculants to be profitable, but the maximum temperature for profitable use of inoculants decreases with increasing rainfall.

Last Modified: 7/31/2014
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