Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 12, 1999
Publication Date: N/A
Interpretive Summary: In the U.S., crops are frequently stored in silos without proper sealing to keep out air or oxygen. As a consequence a substantial spoiled layer may develop at the top of the silo prior to the start of emptying. In other instances such as on small farms with one silo per crop, the farmer may feed out of a silo immediately, before an adequate fermentation that helps preserve the crop occurs. The goal of this study was to help determine 1) how far below a surface open to air does a normal silage fermentation occur and 2) how deep must one go to find a silage that should be relatively stable when put in a feedbunk. Alfalfa and corn were ensiled in two-foot tall plastic pipe silos with tops left open to air. Over 4 weeks, measurements were made periodically of the gas and silage composition at 2, 8, 14 and 20 inches below the surface. At 2 in., there was some evidence of fermentation, but the crop soon began to spoil and heat within the first 1 to 2 days. At 8 in., the crop underwent a normal-looking fermentation and drop in pH for the first week. Later, however, shifts in fermentation products and pH indicated the effects of oxygen on silage quality at this depth. By 4 weeks, the silage at this depth was beginning to spoil. Silage at the lower depths appeared to ferment normally, but the levels of spoilage microorganisms were higher than in a well-sealed silo. These results indicate that a normal silage fermentation can occur close to an open face. However, the silage even at 20 in. below the surface is much more susceptible to spoilage than silage made with proper sealing. Therefore, farmers will find that sealing a silo well not only reduces losses but also produces silage that is more likely to remain cool in the feedbunk, improving palatability.
Technical Abstract: The effect of a surface open to air on ensiling was investigated in 15 x 60 cm PVC silos in four trials, three of alfalfa (30, 41 and 49% dry matter (DM)) and one of corn silage (35% DM). Silos were sampled after 1, 2, 5, 7, 14 and 28 d ensiling at 5, 20, 35 and 50 cm from the face. At 5 cm, little fermentation occurred as oxygen contents were at 10% or higher, and spoilage microorganisms rapidly developed causing 37 to 55% DM loss by 28 d. At 20 cm and lower, oxygen levels were initially at 1% or lower. This permitted lactic acid bacterial fermentations during the first week that appeared typical of fermentations under anaerobic conditions. After one week, the levels of fermentation products at 20 cm began to differ from those at 35 and 50 cm. In general at 20 cm, lactic acid decreased, and acetic acid either increased or decreased relative to concentrations at lower depths. By 28 d at 20 cm, noticeable spoilage was beginning to occur as evidenced by increasing pH and elevated populations of one or more groups of spoilage microorganisms. At the end of the trials, spoilage microorganisms were also elevated at 35 and 50 cm relative to those normally expected in silages made under strictly anaerobic conditions.