Ash in forage comes from two sources:
1. Internal minerals in alfalfa – calcium, magnesium, potassium, phosphorus
2. External sources – dirt from the field and storage
Average mineral content of alfalfa is 8%, the remainder of ash is dirt contamination.
Why is ash a concern?
1. Each additional 1% ash is 1% less carbohydrates – ash provides no nutrition and replaces nutrients
2. Ash is a buffer that prevents pH drop in fermentation – promotes spoilage and formation of butyric acid
High ash content lowers forage quality and can promote catastrophic spoilage loss in storage.
What is a goal for ash content?
Keep ash content to a minimum, 10% or less is a good goal for alfalfa silage.
Strategies for prevention of high ash:
Cutting height: Alfalfa can be cut at 4 cm for highest yield, but higher cutting lowers ash and raises forage quality. Cut at 7-10 cm for lower ash and higher nutritional quality. The higher stubble holds windrows off the ground for better drying and results in less ash.
Wide swath: Increases drying rate and reduces need for mechanical handling operations resulting in less ash.
Knife shape: Flat knives on a disc mower pick up the least dirt, like knife on the left.
Knives with angled blade or curved shape are designed to pick up downed hay, but also create suction and pick up the most dirt, especially when the soil is dry.
Rake: Keep rake tines from touching the ground as much as possible. Rotary rakes that are power driven can be operated without touching the ground and these collect the least ash. Wheel rakes that are ground driven collect the most ash and should be adjusted with maximum float that will still turn the wheels. If a cloud of dust raises when raking 1-3% ash is being added.
Horizontal movement: Minimize moving hay horizontally to reduce ash. It is better to move two swaths on top of a third in the middle, rather than move all three to one side.
Merge: Using a windrow merger will result in less ash than a rake, since hay is moved by a conveyor rather than rolled across the ground. Merging results in 1-2% less ash than a rake.
Harvest: Adjust tines on chopper head to pick up hay without scraping the ground. Avoid raising dust with all equipment. Deliver forage to bunker silo on clean concrete pad without dirt from roads.
Storage & Handling: Store on concrete or asphalt to minimize ash contamination during feedout. Use a properly constructed and drained storage facility.
Forage testing: A high quality forage test is the only way to know the exact ash content of your silage.
Based on Extension information from University of Wisconsin, USA