MT. VERNON, Ill. — Legumes in pastures improve forage quality, increase animal gains and reduce fescue endophyte effects.
“The clover dilemma is if there is enough clover in the field for high yields and if there are broadleaf weeds in the pasture should they be sprayed to kill them,” said Jimmy Henning, University of Kentucky Extension professor.
“Clover can extend grazing over grass alone and often times it gives you more yield in the summer,” Henning said during a presentation at the Heart of America Grazing Conference. “And it will reduce the nitrogen fertilizer cost though nitrogen fixation.”
It is important for graziers to determine how much yield they need from their pastures for their livestock before deciding if they have enough clover to withhold nitrogen fertilizer.
Henning discussed research that evaluated yields from forage and the nitrogen transfer in mature alfalfa and grass pastures. “In five- to six-year pastures, the yields increased as the alfalfa increased from 11 to 55%,” he added.
“The yield is going to be more correlated to the legume content of last year,” he said. “There is not much direct transfer of nitrogen in season from the legume to the grass.”
A study in Virginia compared the dry matter yield of three systems — fescue and nitrogen, fescue and red clover and fescue and alfalfa.
“They were able to duplicate the yield with fescue and clover and increase the yield with fescue and alfalfa,” Henning said. “We can make fields of grass and clover yield like grass and nitrogen, but it takes a lot of legumes to do that.”
How long the clover has been in a pasture impacts yield. When comparing a newly seeded grass and clover pasture to a long-term stand of grass and clover, Henning said, for the long-term stand, the yields peak out at about 30% legume, however with the new stand, yields continue to increase all the way to 80% legume.
“Actual yield tonnage depends on the productivity of the legume,” he noted.
“You may choose to apply moderate rates of nitrogen in the spring even if the stand has clover in it,” Henning said. “It doesn’t kill the clover but the clover will take a break and when the nitrogen goes away the clover will start the factory again.”
But, the speaker added, don’t put nitrogen down at the same time clover is being established.
With a grazing system, the clover, grass, livestock, roots, nodules are all interacting and the nitrogen flows throughout the system.
“The legume is pulling the nitrogen out of the air and there is the decay of leaves, dead roots and sloughing of nodules,” he said. “The majority of the nitrogen is going through the cow and coming out its back end, so feeding the grass nitrogen from legumes takes time.”
Alfalfa can fix 150 to 300 pounds of nitrogen per acre per year and both white and red clover are similar, Henning reported. “From 80 to 90% of that is excreted through the animal as manure and urine,” he added. “The manure contains nitrogen and phosphorus and the urine is nitrogen and the majority of the potassium.”
About 50% of urinary nitrogen is lost through volatilization, Henning said.
“From 14 to 22% of the area of the pasture is covered with manure and urine so the grazing system is going to have a great impact on the ability of getting nitrogen flowing through the system. With continuous or low stocking rates, more nitrogen is concentrated around the loitering areas like the fence, shade or waterers.”
When a rotational grazing system is utilized, the nitrogen distribution in the pasture is improved. The goal, Henning said, is higher stocking rates with shorter grazing duration. “The No. 1 pathway of nitrogen transfer from legumes to grass is through grazing livestock,” he added.
“The increase in yield in mixed stands comes from the legume,” Henning stated. “For high yields we need 25 to 30% legume by weight in the pasture, year after year.”