Planting and Growing Considerations
Seeding Rate
Graph 1.Seeding rates are routinely adjusted for corn produced for grain to optimize yield potential. Increasing grain yield with higher seeding rates also increases overall silage tonnage up to a point, but simultaneously reduces quality. The increased plant biomass from additional plants tends to dilute starch contributed from grain, resulting in higher fiber levels. As a result, milk per acre of silage can be increased with higher seeding rates, but milk per ton will decrease (Graph 1). Increasing seeding rates 2,000 to 4,000 over normal corn grain seeding rates will typically maximize both yield and quality.
Planting Date
Planting date has minimal impact on silage yield unless delayed into late May or June. It is common to see tonnage loss of 1 ton per week if planting after the last week in May, however, reasonable yield can still be achieved with June plantings. Energy levels are likely to reduce in later planted silage as a result of lower starch levels from reduced grain fill.
2 Ways Fungicides Improve Silage
Graph 2. Managing disease in silage corn can be just as important as it is in grain. Previous research has illustrated how fungicides can improve silage yield potential and quality before harvest and during the ensiling process (Graph 2).
Pre-Harvest Benefits
Fungicide applications can prevent fungal diseases in the field, which can preserve leaf area to improve tonnage and possibly reduce the number of fungal pathogens ensiled with corn. Fungal diseases have also been known to cause a plant defense mechanism in which cell walls increase lignin content after being infected by pathogens, resulting in lower silage quality. Fungicide applications have shown the ability to minimize this lignin increase and improve silage quality with neutral detergent fiber (NDF) reductions and increased neutral detergent fiber digestibility (NDFd) and starch content.
Ensiling Benefits
Previous research has shown increased levels of lactic acid during the ensiling process when corn received foliar fungicide applications. Lactic acid is important for lowering pH levels to preserve silage for feeding later. Reducing fungal pathogens with foliar fungicides likely increased the lactic acid content and the fermentative quality of corn silage.
Harvest Adjustments
Harvest Timing and Moisture Content
Graph 3. One of the most important management factors is aligning harvest timing to maximize nutrient value and deliver silage moistures that best fit the storage type. Ensiling at moisture higher than the target will cause poor fermentation and nutrient loss, whereas too dry of silage will pack poorly, causing mold and spoilage. Recommended moisture contents are 65-70% for horizontal silos, 63-68% for conventional tower silos, 55-60% for limited-oxygen silos and 65% for silo bags. Milkline is often referenced for targeting correct harvest moisture. However, weather and hybrid variations make this a poor indicator, as illustrated in the graph comparing 3 hybrids with different kernel drying characteristics (Graph 3). Forage moisture testers or microwave ovens can be used to determine harvest moisture quickly. If testing shows moisture is above ideal, use the dry down rate of 0.5-0.75% moisture drop per day to estimate the best chopping dates.
Cutting Height
Graph 4. Cutting heights ranging from 2-3” in some areas to 8-10” in other regions are utilized for a variety of reasons, including changing the quality or simply to avoid equipment damage from stones. However, a 6-8” cutting height is most common. Increasing cutting height is a management practice that can increase energy content and NDFd by reducing total stover while maintaining grain content. Previous studies have shown adjusting 6” cutting heights to 18” can increase starch and NDFd levels by 2-3% points (Graph 4). Tonnage reductions are the trade-off for increasing quality. Increasing cutting height may be appealing if hay or haylage in storage is known to have lower fiber digestibility or if you have more acres dedicated to silage than needed.
Chop Length
Longer cut lengths will make it more difficult to achieve a good pack, allowing more space for air between forage particles during the ensiling process which affects the fermentation process. However, shortening the cut length will reduce physical fiber and its effectiveness. Finer chop will improve packing in all silo types and is especially important in upright silos where there is less opportunity to adjust pack methods. The recommendation for the theoretical cut length of unprocessed silage ranges from 3/8” to 3/4” in length and 3/4” for silage processed with 1-2 mm. roller clearance.
Kernel Processor
As kernels begin to mature, a starch-protein matrix forms that make it harder to digest. Kernel processors installed on choppers smash kernels to increase starch digestibility. The value of processing kernels may not be observed with corn in early milkline stages, but typically provides nutritional advantages if harvested when milkline is halfway down the kernel or later stages.
Agronomic Silage Hybrid Selection Characteristics
Relative Maturity (RM)
Planting a hybrid with a RM up to 10 days longer than an adapted full-season grain hybrid can offer yield advantages and typically still reach harvest before fall frost risk in most areas. If fields may be utilized for grain harvest, you may not be able to increase RM as much. RM selection also needs to account for planting date spreads and the capability to harvest fields in a given time.
Root Strength
Hybrid root strength is important to ensure plants are standing well to chop at an efficient speed.
Disease Tolerance
Many silage acres will often be in a continuous corn rotation, resulting in a higher risk of potential disease presence. Hybrid selection and placement should consider tolerance to diseases such as gray leaf spot, northern corn leaf blight and other regionalized diseases such as tar spot. In addition, foliar fungicide applications can also help reduce disease risk in fields.
Insect Trait Selection
Due to ground limitations and feed needs, silage acres often lack crop rotation. Consecutively planting multiple years of corn greatly increases the risk of insect populations and potential damage from insects. Trait selection should consider potential risk of damage from both below- and above-ground insects as well as disease that can supervene insect damage.
Graph 5. Corn rootworm risk increases with each consecutive year of corn rotations. Agrisure Duracade® traited hybrids and Force® 6.5G insecticide may help mitigate risk.
Ear-feeding insects such as western bean cutworm (WBC) and corn earworm can reduce grain and starch in feed rations. Selecting hybrids containing the Agrisure Viptera® trait, the only insect trait registered for WBC, can play an important role in mitigating ear feeding.
Mycotoxins can occur for a variety of reasons but are often associated with pathogen infection of grain following insect feeding damage. Ear protection with insect traits can indirectly help reduce the potential risk of silage mycotoxin contamination, as shown in Graph 5.
Stay-green
Hybrids with good late-season health or “stay-green” are known to better maintain green leaf area for a longer period of time. Stay-green can help widen harvest windows and ensure proper plant moisture to minimize poor silage pit packing and spoilage or mold damage associated with it. Utilizing stay-green for expanding the harvest window should not be heavily relied on. Some hybrids will rapidly lose kernel moisture while leaves remain healthy, creating a starch-protein matrix that is harder to digest. Kernel processors can help improve starch digestibility once grain moisture starts to drop.
Hybrids with good stay-green can help widen harvest windows and optimize plant moisture for packing. Photo source: Syngenta.Test Weight
Test weight is a measure of corn grain bulk density that is sometimes associated with kernel texture. Test weight tends to increase as grain becomes drier. Test weight is loosely related to kernel hardness, which is also known to influence livestock feed to gain ratio in feeder cattle. However, as silage is harvested at a higher moisture content, it is not as great of a predictor for silage quality.
Increased starch digestibility is known to improve energy availability for dairy cows. Photo source: Syngenta.Approaches to Characterizing Hybrid Quality
Fiber Digestibility
Due to the relatively large amount of silage being in the form of stover, understanding fiber digestibility is very important where corn silage is the largest portion of feed rations. The relative fiber digestibility of a hybrid is largely dependent on how much lignin is present in silage. Lignin is an indigestible fiber that has no energy value to animals and helps compose the total fiber content of forage, expressed as NDF. Corn silage with a low NDF is desirable. NDFd measures the amount of NDF that can be digested, and larger values are more desirable. Hybrids vary significantly in quality due to fiber content and digestibility.
Starch Digestibility
Increased starch digestibility is known to improve energy availability for dairy cows, thereby improving milk production and/or feed efficiency. Besides hybrid differences, multiple management practices such as harvest timing, kernel processing and length of time in storage can greatly affect starch digestibility. Short-stature hybrids or raising chopping height can quickly reduce stover to grain ratio resulting in higher starch content as well.
Whole-Plant Digestibility
Total digestible nutrients (TDN) describe the energy content of feed as the sum of the digestibility of different nutrients. TDN is often based on calculations using acid detergent fiber (ADF), which is a low-cost and rapid turnaround method to predict energy content. Significant variations in digestibility of fiber often cause inaccuracies in ADF values and TDN values tend to underpredict forage feeding values.
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