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Little River, TX | Every time you harvest alfalfa an equal weight of roots will die back. Even 2 tons/A is really a small percentage of the total root tonnage though. These roots will put nitrogen into the soil, and be available to grass and weeds.
Kill off a good stand and the roots will put 200 or more pounds of nitrogen into the soil.
Trick is only about 25% of this nitrogen is available in the short time. The roots do have to break down to release the nitrogen. After killing off a stand you can expect a reasonable amount of nitrogen to be returned each year for 3 or 4 years.
In todays agriculture we can not depend on legumes to provide all the nitrogen required to produce a good corn crop or a big grass yield. Try grazing and you can get much more nitrogen effect, simply becouse the animals return close to 50% of the nitrogen they graze off.
So your Cargill man is correct but onlly partially.
Yu are also correct in that as the feeder roots die off, with harvesting the tops, that organic matter will release nitrogen.
As for the alfalfa it's self the bacterial riding in the nodules on the roots will take free nitrogen from the air, using carbohydrates from the alfalfa plant to form protein. The alfalfa plant will use this protein. The plant will be roughly 3% nitrogen but in the form of a protein. Take off 2 tons of hay, there will be 2 tons of root die back, which will release 3% of 2 tons of root OM to slowly to the soil. Operative word is slowly. | |
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Alfalfa, putting N back in, When?
