Farmers don't usually apply nitrogen to alfalfa since its roots can fix nitrogen from air, but Utah State University soil scientist Phil Rasmussen found that adding nitrogen immediately after harvest significantly increased yields.
Growers in California reported their yields increased when they added small amounts of nitrogen (10 to 15 pounds per acre) immediately after alfalfa was cut. The lack of foliage after cutting inhibits the alfalfa plant's ability to fix its own nitrogen.When Rasmussen added 20 pounds of ammonium sulfate (21-0-0) or ammonium nitrate sulfate (30-0-0) after cutting, yields increased by more than one ton per acre during 1989 and 1990. When alfalfa was valued at $100 per ton, the nitrogen increased profits by $70 to $100.
Rasmussen also tested responses to liquid calcium ammonium nitrate and ammonium nitrate, but the results were not as consistent or profitable. He attributes part of the larger increase in yield achieved with the ammonium sulfate compounds to possible sulfur deficiencies at the test plots.
Another technique - applying phosphorus with no-till drills to established alfalfa stands - does not appear as promising, he said.
Most of alfalfa's roots are close to the surface, so farmers have usually top-dressed phosphorus where roots can easily take up the nutrient. However, several farmers reported that yields on established stands increased when they used no-till drills to deep-band phosphorus.