August 22, 2008

Clovers not a 'silver bullet' for high nitrogen costs

But they can reduce dependence on expensive inputs

By: Robert Burns, 903-834-6191  
Contact(s): Dr. Ray Smith, 903-834-6191,
g-smith@tamu.edu  
OVERTON – Forage legumes can provide livestock producers some relief from the skyrocketing cost of applying nitrogen fertilizer to their pastures, said a Texas AgriLife Researchscientist.

But there is a lot of "hype" surrounding forage legumes such as crimson or arrowleaf clovers, said Dr. Ray Smith, AgriLife Research legume breeder based in Overton.

"They're not a ‘get-out-of-jail card.’ They're not a silver bullet, but they do offer some valuable alternatives to high-cost nitrogen," Smith said.

Smith has long advocated the use of clover and ryegrass winter pastures to offset winter feeding costs and supply nitrogen for warm-season grasses.

Given enough moisture, it has always been an economically sound investment for cow/calf and stocker operations, he said. Now, with nitrogen costing 80 cents per pound, it has become not just an option but a necessity so East Texas forage-based cattle operations can remain profitable.

"A healthy stand of arrowleaf or crimson clover over-seeded on warm-season perennial grass pasture in East Texas will provide a nitrogen input of up to 100 pounds of nitrogen per acre per year," Smith said. "However, this is only accomplished through a grazing system with the recycling of animal waste. You've got to be thinking in terms of (recycling through) animal grazing."

About 80 percent of the Earth's atmosphere is nitrogen gas, but it's not in a form plants can use. However, forage legumes such as clovers have a symbiotic relationship with rhizobium bacteria that live in small nodules on the plant's roots, Smith said. They take nitrogen gas in the air and convert it into a form of nitrogen that plants can use.

The nitrogen-fixing abilities of legumes is a fact, Smith said, but many myths persist about the practice.

For example, one piece of misinformation that continues to circulate is that if one grows clover with ryegrass then no applied nitrogen will be needed for the ryegrass.

"Wrong!" Smith said. "Clover will not directly provide nitrogen for the ryegrass in a ryegrass-clover mixture. It will provide nitrogen to the warm-season grass (that comes later) through recycling."

Also, the amount of nitrogen fixed from the air by legumes is dependent upon the amount of nitrogen already in the soil. It is common practice to plant a clover-ryegrass mix to extend the winter grazing period, Smith said. However, ryegrass needs nitrogen before the clover can provide it. The problem can be solved by correct timing of a nitrogen application. "The clover-rhizobium symbiosis is regulated by the amount of nitrogen available in the soil," Smith said. "The sandy, acid soils of East Texas are low in soil nitrogen, but soil nitrogen increases if nitrogen fertilizer is applied. If a clover-ryegrass mix is planted and fertilized, then the nitrogen-fixation process will be slowed or turned off. The ryegrass will do great, but the clover will not contribute very much to the mix."

Smith said the solution is to not apply nitrogen fertilizer at planting. These mixtures of clover and ryegrass are generally planted in October. "This will give the early advantage to the clover, which will start fixing nitrogen," he said. "A low rate of N -- 50 to 60 pounds per acre – can be applied to the clover-ryegrass mix in late December or January. This will increase the ryegrass growth and allow the mix to efficiently fix and use nitrogen."

Another myth, Smith said, is that clovers can cause animal health problems, but this is also erroneous. There are no animal-health problems associated with clovers grown in East Texas, except for some problems with bloat, which can be easily managed.

"Bloat can be a problem, but it is not limited to clovers," Smith said. "Any fast-growing cool-season forage – ryegrass, wheat, clover – can cause bloat."

It's easy to prevent bloat, he said. Don't turn hungry cattle into lush pastures. Feed hay with winter pastures, and put out anti-bloat blocks.

Bigger issues that face producers this year are seed, fertilizer and other production costs, Smith said.

Seed costs for ryegrass and clovers are going up for the same reason as other agricultural commodities: fertilizer, fuel, and the attraction of growing other more lucrative crops, such as wheat, Smith said. See related story: http://agnews.tamu.edu/showstory.php?id=663

Fall seed costs for clover will range from $14/acre for white clover to $22/acre for Apache arrowleaf clover to $44/acre for crimson clover. More seed cost information can be found at http://aggieclover.tamu.edu .

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