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Managing grass for silage

Miner Institute Farm Report Published on 20 June 2011

If you applied nitrogen or manure to your grass fields last month they should be starting to look thick and lush.

The profitability of your grass crop will be determined by your harvest management in the coming few weeks: Grass harvested in the boot stage (no heads emerged) is “high group” cow feed, with very digestible fiber.

Grass harvested after heading is “low group” and “heifer” feed since grass digestibility plummets after heading. (“When you see the head, the quality is dead.”)

Some grass species – orchardgrass, for instance –  decline in quality faster than others (Have I mentioned lately that I hate orchardgrass?), but none hold quality very well after heading.

The last half of May is prime time to harvest grass in most of the Northeast. Our practice at Miner Institute has been to harvest first cut grass as fast as possible once it reaches the boot stage, ensiling the entire crop.

We continue to harvest grass until our alfalfa is in the late bud stage, at which time we stop grass harvest and start alfalfa-grass, beginning with the stands that have the greatest percentage of grass.

We have enough acres of grass that we seldom get all of it harvested before it’s time to harvest alfalfa, so our grass silage tends to be either very good, or not so hot (for milk cows, at least).

However, this late-cut grass, stored in a separate silo, works just fine in our heifer ration; fed right it’s just the ticket to prevent them from getting fat.

Mowing height: Unlike alfalfa, the nutrients for the next cut of grass are stored in the bottom few inches of the aboveground portion of the plant, so leave about four inches of stubble.

If you’ve been “shaving” fields to two-inch stubble height with your disc mower-conditioner you may be amazed at how the combination of early harvest and a four-inch stubble height makes the second cut really take off.

Post-harvest management: Second-cut grass needs N for maximum yield and quality, but at lower application rates than first cut because yields are almost always lower.

Commercial N is quick to apply – I prefer about 50 lbs of actual N as UAN or a 50-50 blend of urea and ammonium sulfate – but manure is a good option and by the time first cut is finished many manure storages are full – at least.

The recommended application rate depends on the nutrient content of the manure, and to a great extent that’s determined by solids content. Rates have to be very heavy indeed to “smother” grass; I can’t remember ever seeing this happen.

The sooner you apply the manure the better. And as long as you apply manure to your grass fields once each year there’s little chance you’ll need to apply P or K fertilizer for the life of the stand.

Manure application will make it difficult if not impossible to produce low-potassium grass for prefresh cows, so you might designate a field or two for these animals and use commercial N instead of manure on this land.

If you apply N fertilizer instead of manure, second cut is almost always lower in potassium than in first cut. And the potassium in dry hay is less bio-available to cows than it is in silage, so if you’re going to bale any cutting, make it the second cut and do a forage analysis (wet chemistry, not NIR) to see if it’s suitable for prefresh cows.  FG

—Excerpts from Miner Institute Farm Report, May 2011