Cutting Alfalfa in Late-Autumn Increases Annual Yield, Doesn’t Hurt Stands, But is Unlikely to Increase Profit

Alfalfa growers wanting to maximize annual yields are often tempted to harvest during or just after the "critical late-autumn period". Recommendations vary by region with southern data showing that harvesting alfalfa in late-autumn has little effect on stand persistence or yields in following years and northern areas recommending it only when certain favorable conditions are present. Recommendations in the lower Midwest are that if an additional late-autumn harvest is desired, that it be taken in early November. Our objective was to determine the cumulative effects of the practice over several years on the same field.

Materials and Methods

‘Pioneer 5373’ alfalfa was seeded on 1 April 1994, at 15 lb/acre at the Southwest Missouri Research Center, near Mt. Vernon, MO on a Huntington silt loam soil. Soil fertility was monitored annually and nutrients were applied at recommended levels for alfalfa. Weeds and insects were controlled chemically. Plots were harvested three times during the seeding year, the last harvest being on 15 September 1994.

There were six treatments consisting of three harvest frequencies during the growing season (28, 35, or 42 days between harvests) as main plots and two late-autumn management regimes (either not harvested or harvested an extra time in late-autumn) as sub-plots. The dates of initial and subsequent harvests for each harvest frequency were staggered so that the final harvest for each treatment was on 15 September (± 2 days) each year. September 15 is the currently recommended date for a final harvest during the growing season in Missouri. By harvesting all plots on 15 September, there were an equal number of growing days in late-autumn to measure the residual effects of previous harvest frequencies. Late-autumn harvests were taken in late October or early November each year following a hard freeze. Late-autumn harvest treatments began in 1995 and continued through 1999.

Yields were measured by cutting a 2.7 ft. x 15 ft. strip from the center of each plot with a flail-type harvester set to leave a 3-inch stubble. A sample was dried and ground for use in forage quality analyses.

Crude protein, acid detergent fiber, and neutral detergent fiber were determined for samples collected in the late-autumn of 1995, 1997, 1998, and 1999 using near infrared reflectance (NIR) spectroscopy calibrated from chemically-derived data.

Stand density was determined by counting the number of plants and stems in four, randomly placed, 1.0 sq. ft. quadrats within each plot. Stand density was measured in June and in December of the establishment year (1994). Thereafter, stand density was measured immediately after harvest in May and September each year.

Grower returns were analyzed using partial budgeting. Partial net returns for a lateautumn harvest were calculated as additional gross returns minus additional costs. Gross returns were calculated as additional yield/acre (or "net yield") times price/ton. We used a price of $90/ton, a long-term average for ‘dairy quality’ hay in Missouri (Brees, 2003).

Results

Late-autumn forage yields and its impact on the following year

Harvesting alfalfa less frequently during the growing season nearly always led to greater yields in late-autumn (Fig. 1, top panel). Averaged over all years, plots harvested every 28 days during the growing season yielded only 0.28 tons/acre in late-autumn, compared to 0.44 and 0.56 tons/acre when harvested every 35 or 42 days, respectively. Since all treatments had the same number of days to regrow before the late-autumn harvest, the residual effects of previous harvest frequency were evident. It appears that stress from harvesting frequently during the growing season substantially reduces the regrowth of alfalfa in late-autumn. The years with the largest yields in late-autumn were associated with accumulated rainfall during September and October.

We also measured the impact of a late-autumn harvest on forage yield the following year. Yield change at the first harvest the following spring of plots harvested in late-autumn when compared to plots not harvested in late-autumn is shown in Fig. 1 (middle panel). No significant yield loss due to a late-autumn harvest occurred in the spring of 1996, 1997, or 2000. In the spring of 1998 and 1999, however, plots harvested in late-autumn showed yield reductions of 0.25 to 0.61 tons/acre. Harvest frequency during the growing season had no effect on the relative yield reduction the following spring, except for the spring of 1999. There was no effect of a late-autumn harvest on the second or subsequent harvests each year.

Net alfalfa yield (autumn yield minus the change in yield at the first harvest in spring) varied substantially by year, with the largest net yields recorded in 1996-1997 (Fig. 1, bottom panel). Net yield for 1996-1997 was 0.28, 0.61, and 0.94 tons/acre for alfalfa harvested every 28, 35, or 42 days during the growing season, respectively. Averaged over all five years, net yields were 0.11, 0.24, and 0.40 tons/acre for harvest frequencies of 28, 35, and 42 days, respectively. The low net yields for all treatments and the variation between years for net yield make it difficult to predict when a late-autumn harvest might be most productive.

Forage Nutritive Value

Nutritive value for alfalfa harvested in late-autumn was generally high for all treatments but was greatest (low detergent fiber and high crude protein) from plots harvested 28 days throughout the growing season and lowest when harvested every 42 days. However, the differences between harvest frequencies were small and it is doubtful that they represent any meaningful biological differences or economic opportunities for producers. Sheaffer et al. (1985) also reported the high nutritive value of alfalfa harvested in late-autumn, noting that it provided some of the best quality forage of the entire growing season.

Except for the spring of 1997, forage nutritive value at the first harvest the following spring was generally equal or greater for plots harvested in late-autumn than plots not harvested in late-autumn. After the first harvest in spring, there was no difference in forage quality between late-autumn harvest treatments (data not shown).

Stand Persistence

Stand persistence was unaffected by harvesting in late-autumn or by harvest frequency. Over the life of the study, the number of stems per square foot declined from 61 stems/sq. ft. in 1995 to 36 stems/sq. ft. by 2000. This shows that alfalfa can be harvested in late-autumn without sacrificing stand density in the lower Midwest.

Economic Returns

Averaged over all years, harvesting alfalfa in late-autumn can increase or decrease net returns but depends strongly on harvest frequency during the growing season (Table 1). For alfalfa harvested every 28 or 35 days during the growing season, an additional harvest in late-autumn reduces net returns by $16.07/acre and $7.52/acre, respectively. This is primarily due to low net yields and harvest costs that are insensitive to yield (for example, the cost to mow and condition is the same regardless of yield). Net returns are $1.63/acre if a 42-day harvest frequency is used.

The overall low net yields from a late-autumn harvest are not likely to substantially increase profits compared to other management decisions such as pest management, cultivar selection, and harvest frequency. Additionally, there are several factors that make a late-autumn harvest risky in the lower Midwest, notably, variable net yields from year to year and unfavorable weather conditions for haymaking. Other low-cost harvesting methods, such as grazing, might offer more consistent or greater economic returns.

Conclusions

1. Autumn yields are greatest when the stand is harvested infrequently during the growing season and rainfall is adequate in September and October.
2. Forage nutritive value of alfalfa in late-autumn is typically high and is best when stands are harvested frequently during the growing season.
3. In 2 of 5 years, taking an extra harvest in late-autumn reduced forage yields the following spring. Yield loss at the first harvest the following season can make net yields low and the residual effect of a late-autumn harvest is unpredictable prior to making a harvest decision. This makes it difficult to advise producers as to which years this practice might be most effective.
4. If alfalfa is harvested every 42 days during the growing season, then a late-autumn harvest can increase profits but the net returns are likely to be small even in this case. A majority of producers in the lower Midwest use a 28- to 35-day harvest frequency during the growing season; when harvesting this frequently during the growing season, net returns are reduced by taking a late-autumn harvest.

References

Brees, M. 2003. Alfalfa production and alfalfa establishment budgets of southern

Sheaffer, C.C., J.V. Wiersma, D.D. Warnes, D.L. Rabas, W.E. Lueschen, and J.H.

Table 1. Partial budget showing additional gross returns, costs, net returns and break even cost/ton for alfalfa harvested an additional time in late-autumn.