LACOMBE, Alta. – A symbiotic relationship exists between soil, bacteria and plants to convert nitrogen into nutrients that plants can use.
“There is air in the soil and that air is 78 percent nitrogen. Unfortunately the plant can’t use it,” said Arvid Aasen of the Western Forage/Beef Group during a recent pasture school in Lacombe.
One solution for grassland managers is to add legumes to the pasture mix and practice intensive grazing, but it takes time before real benefits are seen from manure or alfalfa.
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“It takes a few years of this intensive grazing to really optimize that yield,” said Vern Baron of the forage group.
Soil depleted of organic matter and fertility is less able to hold or retain soil nutrients. Poor soil also results in unhealthy, low producing forages and cattle that do not gain well.
To receive more benefit from manure, producers must move their cattle around a field rather than allow them to deposit feces and urine around gathering places such as water troughs.
Little nitrogen moves from the dung to the soil in the year it is applied, but urine tends to run into the ground more quickly and converts to the nitrate form, which plants can use. It is not uncommon to lose 20 to 80 percent of urine nitrogen to volatilization, which is a conversion of nitrogen to gas. Adding alfalfa or clover has
longer-term benefits.
Fixing takes time
Aasen said legumes use the nitrogen available in the soil before they start fixing their own.
“In a stand of grass and legumes, the excess nitrogen is going to be minimal because the grass is going to sweep up as much as it can to grow and the legumes will use what it can to establish,” he said.
Alfalfa produces 80 percent of the nitrogen it needs during the growing season and can also use last year’s nitrogen in the soil to get started in the spring.
Legumes fix nitrogen in root nodules but that is not a benefit until the following year, when plants and root hairs are decomposing. Nodules do not leak nitrogen but instead provide nutrients when they break down.
Field assessments shows alfalfa could leave 70 to 190 pounds of nitrogen per acre, cicer milkvetch up to 140 lb., red clover 60 to 115 lb., white clover 115 to 180 lb. and bird’s foot trefoil 44 to 100 lb.
Legumes are also nutritious animal fodder, but Baron said it is important to remember they are biological systems. Their survival is affected by water, weather, plant composition and management.
Commerical fertilizer is more reliable but more expensive than traditional methods. As well, the goal is to produce plenty of grass for cheap feed so manure and legumes can help cut feed expenses.
“We are in the business of producing dry matter at the least cost we can,” Baron said.
