Beef producers who choose to manage their pastures by rotating cattle through paddocks have control over when they start grazing in spring. When to start grazing varies between years, where in Wisconsin you are located, and from producer to producer. Pasture research from the Dairy Forage Research Center here in Wisconsin demonstrates that if we turn cows loose when grass is 4” tall in spring versus waiting until we’re closer to a 12” level, reduces the total seasonal yield of that paddock by a quarter ton of forage. With current hay market prices in $100-120/ton for beef hay, we’re losing $25-30/acre in lower forage production from turning out too early, either in fewer days grazing or lower stocking rates.
When pastures get to a 12” height is influenced by location, what species are present in your pasture, and how you managed your pastures the previous fall. Fall is the season when grasses are developing buds for next spring. If we grazed tight and forced cattle to “clean up the pasture” down to a 1.5” or less of grass in fall, we may be grazing next spring’s dormant buds. This will delay the average 12” date by about two weeks (May 11th rather than April 28th) in southern Wisconsin. That’s an additional quarter ton of feed we will need to supply or fewer head our pasture can carry.
Life begins at 40. Pasture forage uses nitrogen from decomposition of soil organic matter as a result of soil biology. Soil biology does not “wake up” until around 41F and increases with rising soil temperatures. A strategic application of nitrogen (N) early in the spring before soil N is widely available can stimulate additional grass growth in some situations. How do we decide?
Research by the late Dennis Cosgrove at UW-River Falls demonstrated the grass response rate of three different grass species to different spring nitrogen applications.
In orchard grass and smooth brome dominated pastures, spring response rate to N application was 20 lbs. or more per pound of N applied (20:1). As the soil temperature warms, the nitrogen response rate drops. If you choose to invest in a pound of N @ $0.60/lb., you grow 20 pounds of additional grass on dry matter basis. With hay values @ $120/2000 lbs. (ton) or $0.06/ lb. of hay, a 20 lb. response rate results in $1.20 in forage value produced. Think about this example – invest $0.60 in N and get back $1.20 in feed. Not a bad return on your investment.
Bluegrass pastures were also fertilized and response rates were measured as 5 lbs. of additional forage/pound N, (5:1). Coming off the drought of 2012 and spring 2013 with hay prices still hovering around $250/ton it “paid” to fertilize bluegrass dominated pastures. That’s the first time in my memory that fertilizing bluegrass paddocks has paid off.
The amount of nitrogen to apply depends upon the level of legume content you want to maintain in your paddock. Nitrogen and legumes exist in an antagonist relationship – as you increase the level of applied nitrogen the level of legumes decreases. In high legume paddocks, we can apply up to 50 units of N per SEASON and not have significant impact on clover percent in the pasture.
Managing this bounty of grass in spring is great problem to have. The thumb rule of “take half and leave half” is pretty sound advice. When 50% of the grass is grazed, only 2-4% of the roots stop growing; at 60% grazed, 50% of the roots stop growing. As we get above 75% defoliation, 100% of the roots stop growing. What we do in spring will impact the grass growth into summer; what we do in summer impacts fall growth. One management decision follows another.
More grass, more beef, more money. . . . It’s your choice.
Written by Gene Schriefer, UW Extension Ag Agent, Iowa County, and recently published in The Wisconsin Agriculturist