I have long recommended harvesting alfalfa in the fall following a killing frost, but an observation in 1999 lead to the hypothesis that maybe alfalfa could be harvested anytime in the fall if the plant was ready. By ready I mean reaching 40 to 50% bloom or regrowth initiating (regrowth structures at least 2 to 3 inches in length). We established this experiment to further test this hypothesis.
A bulk alfalfa field was seeded May 5, 2005 with a double-disc-opener drill with spacing of 6 inches into a prepared seedbed at Fargo, ND. The cultivar used was AmeriStand 201 +Z, which was seeded at 13 lb/acre. The soil is a Fargo clay primarily. Treatments (listed in Table 1) were initiated in 2006 and were laid in the field utilizing a RCBD with four replicates. Plots were 5 by 22 feet while the harvest plot was 38 inches by 18 feet. Forage was harvested with a Carter flail harvester at a stubble height of about 2 inches. A dry matter sample was taken from each plot.
Forage quality was determined on two replicates of all treatments. All quality samples were taken by hand following mechanical harvest for yield determination. Samples were ground to pass a 1-mm screen in a Wiley mill, mixed thoroughly, subsampled, and stored in glass bottles until quality components were determined. Stored samples were submitted to the Animal and Range Sciences Department Forage Quality Lab at North Dakota State University for determination of crude protein (CP), acid-detergent fiber (ADF), neutral-detergent fiber (NDF), neutral-detergent fiber digestibility (NDFD), and in vitro dry matter digestibility (IVDMD) by standard wet chemistry methods. Hemicellulose was calculated as NDF-ADF, and relative feed value (RFV) by the standard formulas.
Table 1 presents the harvest dates in 2006. Forage yield ranged from 5.55 to 6.05 tons/acre for the three 4-cut systems while the yields ranged from 4.87 to 5.29 tons/acre for the two 3-cut systems (Table 2). Forage yields of the second and third harvests were less than normal from the almost total lack of rainfall during these growth periods. The fall harvest was taken October 19 when regrowth was initiating from the crown.
Forage quality of all treatments relative to maturity stage was very high in 2006 (Table 3). Crude protein in the second cut was low compared to the ADF and NDF levels, and IVDMD seemed unusual relative to the maturity stage. Forage quality of the third and fourth cuts followed what would be expected with the maturity differences of the treatments.
Table 4 presents the harvest dates in 2007. The 26” harvest treatment was equal to the mid-bud growth stage in 2007 so all treatments were harvested on the same date. The third harvest was delay to 50% bloom for Treatment 2 and the fourth harvest of Treatment 5 was delayed until more regrowth had initiated in 2007.
Forage yields ranged from 6.12 to 7.23 tons/acre in 2007 (Table 5). Forage yield of fall-harvested treatments ranged from 6.85 to 7.23 tons/acre while non fall-harvested plots ranged from 6.12 to 6.48 tons/acre in the second production year. Delaying the third harvest of Treatment 2 tented to increase the forage yield compared to other treatments. Results in 2007 were very similar to second-year results of previous experiments.
Forage quality was not significantly affected by over wintering residue or the differences in maturity in the first three harvest in 2007 (Table 6). Forage quality of the first-harvest forage was exceptionally high in 2007; likewise, third-harvest forage was higher in quality than normal. All components of forage quality measured except hemicellulose were significantly lower for alfalfa harvested in the fall after a killing frost compared with the other fall-harvested forage even though no leaf loss occurred after the killing frost. Crude protein was significantly less probably indicating some translocation of protein to the root system during the fall-hardening process.
Harvest dates for 2008 are presented in Table 7. The maturity stage for the 26” treatment was similar to the mid-bud treatment as a result of the very cool, wet spring delaying early season growth. Second-harvest treatments were as targeted. Since the third harvest was quite late compared to previous years, the third harvest of Treatment 5 was harvested early at 10% bloom to differentiate Treatments 1 and 5. Unlike previous years, Treatments 1 and 5 were harvested following a killing frost since regrowth did not initiate prior to the killing frost.
Forage yields in the third production year of AMF-06 in the first harvest were unaffected by fall harvesting in 2008 (Table 8). Three-cut treatments yielded the same or slightly greater than four-cut treatments, which was similar to the second production year (Table 5). Forage yield in the second harvest of Treatment 3 (3-cut) is hard to understand in than it had and extra week of growth, but it had significantly lower yield than other treatments. One of four plots of this treatment had significant winter injury, which was interesting considering none of the four-cut treatments had even close to the injury of that plot. Forage yield in the third harvest was significantly less when harvested at 10% bloom rather than one-week latter at 30% bloom (Table 8). Forage yield of Treatment 3 was the greatest in the third harvest contrasting its production in the second harvest. Fourth-harvest yields averaged 1.24 tons/acre, significantly greater than in 2006 (Table 2) and in 2007 (Table 5). As a result, forage yields of the fall-harvested treatments were significantly greater than non-fall-harvested treatments again in 2008 (Table 8).
Forage yields of fall-harvested treatments have averaged 0.87 tons/acre greater/year over the three years of this experiment than non-fall-harvested treatments (Table 9). Experiment 1, WKA-04 that was terminated this year, averaged 0.79 tons/acre during its first three years of production, very similar to this experiment. Both of these experiments were harvested when regrowth, about 2 to 3 inches, was initiating in the fall. Therefore, our data suggest that alfalfa can be harvested anytime during the fall if regrowth is initiating and expect to have the stand over-winter in fine shape in most years. This is NOT to say that you will never see winter injury from the fall harvest. In fact, WKA-04 experienced some delay of growth this past spring. Even then, forage yield was greater from fall-harvested than non-fall-harvest plots.