Corn Silage Harvest Management

Harvesting corn silage at the right time is critical to obtain a high yield and quality product. Moisture content of the silage is the most important consideration, but how the silage is chopped is also important. Monitoring throughout the harvest helps to ensure a good quality silage product.

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A timely harvest is necessary to obtain the highest quality silage. Deciding on the harvest date can be a challenging management decision. It can be difficult to properly time harvest with other workload considerations and because of the interactions between genetics and environment with forage yield and quality.1 While dry matter yield is a major criteria in selecting a corn silage product, grain (or starch) content of the silage should also be a primary consideration. The grain content of silage can vary from less than 20% to over 60% on a dry matter basis, depending on harvest timing and the corn product. A corn product that has a high dry matter yield potential may produce a low percentage of grain in the silage. Grain can be more digestible than the stover portion of the silage, and producers should time the harvest to maximize the digestible starch content. Harvesting too early can result in silage with reduced starch content. Harvesting too late can result in silage with more starch content, but lower in digestibility. Harvesting at the right time provides the best whole plant digestibility with the energy coming from the starch.

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Harvesting at the proper moisture content is the main goal during silage harvest. Ideally, corn silage should have 60-70% moisture content (30-40% dry matter) at harvest. Ensiling corn at the proper moisture level sets the stage for effective fermentation and helps to minimize losses from heating and seepage. Substantial seepage and storage losses often occur with silage containing 75% moisture or more. If silage is packed too wet, seepage can remove nutrients and could damage the storage unit. However, silage packed too dry can have air pockets preventing an anaerobic environment and allowing molds and spoilage.

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Figure 1

Figure 1. Pictured is the milk line, the border between the dark yellow hard starch layer and the light milky dough layer. At 1/2 milk line, corn is at full dent (R5 stage), kernel moisture is about 40%, total plant moisture is about 60%, and over 90% of the normal yield of grain can be expected.

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The kernel milk line is a common visual tool used to estimate the moisture content (Figure 1). The milk line represents starch content of the grain. After corn dents, the starch layer, or milk line, progresses from the top to the bottom of the kernel. Break an ear and look at the milk line on the developing kernels. As a general rule, when the starch spans 1/2 to 3/4 of the kernel, it is ready for silage harvest. Kernels with no milk are physiologically mature and should have a fully developed black layer. Corn with little or no milk remaining in the kernel, or which has reached black layer, is generally too dry for optimum silage harvest. In most situations, silage harvest should begin prior to black layer development when kernels have reached at least 1/3 milk line.2 The milk line should be used as a guide to begin accurate testing of moisture content using a microwave oven, drying oven, or a commercial forage moisture tester.

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Harvesting drought-stressed corn too soon can result in silage with excess moisture, poor fermentation, and reduced feed value. The moisture level of drought-stressed corn can be much higher than it may appear upon field inspection. Even though it may appear quite dry with many or most of its leaves turning brown, it still may contain over 70% moisture. The nitrate levels of drought-stressed corn silage should also be checked prior to ensiling and feeding to livestock.

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Corn silage is traditionally harvested at a height of 4 to 8 inches above ground level, which helps maximize yield potential and milk production per acre. Increasing the cutting height improves forage quality because the lowest portion of the corn stalk is typically higher in fiber and lower in digestibility. Toxic nitrate levels in the lower stalk may be elevated if corn has grown in drought conditions. In this situation, cutting the corn up to 8 inches higher may be warranted to avoid harvesting the nitrate rich stalk. The majority of nitrates are found in the bottom 1/3 of stalk.

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Good chopping practices should be followed when harvesting corn silage. Well-maintained harvesters with sharp knives is essential. Corn silage should be cut into 1/2 to 3/4 inch pieces for good packing. Kernel processing while harvesting can also be important for obtaining high quality corn silage.3 Processing occurs through the use of rollers which further processes the silage after it has gone through the knives. The primary function of the processor is to crack or break open the kernels contained in the silage. In addition, the cob sections will be broken into smaller pieces. The benefits of crop processors is greatest when there are drier, harder kernels resulting from delayed harvest or drought. Processing is especially important when plant maturity has gone beyond the 2/3 to 3/4 milk line.

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Monitoring should take place throughout harvest to ensure a quality silage.1 Settings for length of cut and roller openings for kernel processing should be checked and adjusted during harvest. Dry matter and moisture content should also be checked periodically.