The Effect of Fall Harvest Timing and Cutting Frequency On the Yield of Alfalfa in Northern California.

The number of alfalfa harvests in a season, as well as the timing of the final cutting of the season, has a profound effect on alfalfa yield and vigor.  In years when environmental conditions favor haymaking, producers in Northern California often cut as late as possible in the fall in an attempt to capture as much of the fall growth as possible.  While this may increase total yield that year, alfalfa vigor and yield in subsequent years may be affected.  A series of three trials were initiated in 2009, 2010 and 2011 at the Intermountain Research and Extension Center in Tulelake, CA.  A three-cut schedule was compared with three different four-cut schedules.  The first three cuttings were the same for the four-cut schedules but the date of the final cutting varied, occurring in mid-September, early October, or mid October.  The subsequent year each treatment was harvested three or four times to determine whether alternating the number of cuttings from four one year to three the next can help overcome the negative effects of an inappropriately timed fourth cutting.  All treatments were harvested for a single uniform cutting the third year.  Delaying the last cutting until mid-October typically resulted in the highest yield that year.  The effect of cutting schedule carried over into the subsequent year, when yield was highest for the treatments that were only harvested three times in the previous year or when the forth cutting occurred in mid October.  This suggests that alfalfa should be cut early in the fall leaving sufficient time for the plant to regrow and replenish root reserves or delay cutting until late in the season when there will be minimal regrowth after cutting.