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 September 26, 2002

###  Consider Cutting Alfalfa in October

#####  Paul Peterson, Extension Agronomist - Forages and Craig Sheaffer, Professor, Agronomy and Plant Genetics

 

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| What a growing season it has been! Most of the state has had rainfall |
| well above average, and one or more rainfall events that has caused   |
| some significant flooding. Where fields have not been flooded out,    |
| the ample precipitation has translated into lots of forage            |
| production. Unfortunately, however, this has not led to an ample      |
| supply of high quality forage in the silo or barn. The high humidity  |
| and frequent rainfall have made it difficult to put up high quality   |
| hay and haylage throughout much of Minnesota this summer, and thus    |
| many livestock producers are facing a shortage of high quality forage |
| as we head into fall and winter. Many will compensate by feeding more |
| corn silage this winter, but keep in mind that we still have an       |
| opportunity to conserve more high quality alfalfa this year.          |
|                                                                       |
| Thanks to continued warm weather and precipitation through mid        |
| September, alfalfa and other forages generally have continued to grow |
| rapidly. Many fields thus have an abundance of September growth that  |
| we could harvest. Traditionally, we've been cautious about cutting    |
| alfalfa in the fall due to concerns that it will increase the risk of |
| winter injury to the stand. This was a good general recommendation 25 |
| years ago, but our increased understanding of genetic and management  |
| factors affecting winter survival enable us to now be much less       |
| conservative about fall cutting, especially when we face the prospect |
| of a shortage of high quality forage and high prices for hay          |
| purchasing.                                                           |
|                                                                       |
| The two main reasons that fall cutting has traditionally been         |
| discouraged are 1) a concern about sending alfalfa into the winter    |
| with limited energy reserves in the roots, and 2) a desire to         |
| maintain more material on the field to catch insulating snow cover.   |
| This is sound logic and still applies today, but this conservative    |
| approach should no longer dominate our fall management                |
| decision-making. We now know that there are a number of other         |
| controllable factors that influence an alfalfa stand's potential for  |
| winter injury:                                                        |
|                                                                       |
| -   **Stand age**: younger stands are less susceptible to winter      |
|     injury than older stands                                          |
|                                                                       |
| -   **Variety selection**: modern, winter hardy, multi-disease        |
|     resistant varieties are less susceptible to winter injury than    |
|     are older varieties                                               |
|                                                                       |
| -   **Soil pH**: alfalfa in soils with pH 6.5 to 7.0 is less          |
|     susceptible to winter injury than when grown at pH 6.0 or less.   |
|                                                                       |
| -   **Soil K**: high soil K levels reduce the likelihood of winter    |
|     injury                                                            |
|                                                                       |
| -   **Soil drainage**: winter injury is less likely in well drained   |
|     versus poorly drained fields or fields that are very wet in fall. |
|                                                                       |
| When the above conditions are in the \"low risk\" category, the       |
| chances of fall cutting causing winter injury are low. In essence,    |
| healthy, well-managed alfalfa plants with good genetics are not very  |
| susceptible to winter injury when cut in the fall, especially if that |
| cutting comes close to the time of the first killing frost (early to  |
| mid October). The risk is further reduced if stands have not been cut |
| frequently earlier in the season. In other words, if the fall cut is  |
| only the 3^rd^ cutting of the season, the risk of a winter injury is  |
| minimal.                                                              |
|                                                                       |
| Table 1 shows data from a cutting management study with variable fall |
| cutting dates conducted in Minnesota in the mid 1980's. The data      |
| represent 3 years of cutting treatments on 3 alfalfa varieties        |
| averaged over 2 experiments (total of 6 years of data). Note that     |
| within 3- or 4-cut systems, treatments with September 15 or October   |
| 15 harvest dates did not have reduced yield compared to treatments    |
| with the last cut September 1. In addition, the minimum single season |
| yield obtained for each harvest regime over the 6 years of testing    |
| (as shown by the yield range) never occurred during the final year of |
| cutting. In fact, maximum yields were sometimes obtained during the   |
| final (3 ^rd^) year of cutting. This further indicates that fall      |
| cutting was generally not detrimental to long-term yields or stands.  |
| Interestingly, a 4-cut system with the final two cuttings on          |
| September 1 and October 15 produced among the highest total season    |
| yields. This cutting schedule seems particularly relevant this year,  |
| with first cutting generally being late statewide due to an unusually |
| cool May. It is important to note, however, that within that system,  |
| alfalfa was allowed to mature to flower at two of the four cuttings;  |
| this compromised quality to some degree, but allowed plants to        |
| accumulate a high level of carbohydrate reserves prior to two of the  |
| four cuttings. Nevertheless, the data clearly show that fall cutting  |
| was not detrimental to yields of stands that were subjected to        |
| cutting treatments for 3 consecutive years.                           |
|                                                                       |
| **Table 1. Influence of cutting frequency and timing on total season  |
| yield and season average forage quality of alfalfa at Rosemount, MN   |
| (average of two 3-year experiments).**                                |
|                                                                       |
|   ----                                                                |
| ----- ---------------- ------------ --------- ------------ ---------- |
|   **                                                                  |
| Cuts    **Avg. Cutting   **Avg. Total **Yield   **Season     **Season |
|   per                                                                 |
|        Dates**          Season       Range**   Avg.         Avg. CP** |
|   Year**                     Yield**                Digestible        |
|                                                     DM**              |
|                                                                       |
|                              Tons DM/acre           \% DM             |
|                                                                       |
|   3         6/4, 7/14, 9/1   4.9          3.9-6.2   59           18   |
|                                                                       |
|             6/4, 7/14, 9/15  4.7          3.5-5.7   57           18   |
|                                                                       |
|             6/4, 7/14, 10/15 4.8          3.5-5.8   54           17   |
|                                                                       |
|   4         5/24, 6/25, 8/4, 4.1          2.9-5.4   65           21   |
|             9/1                                                       |
|                                                                       |
|             5/24, 6/25, 8/4, 4.4          2.9-5.9   64           20   |
|             9/15                                                      |
|                                                                       |
|             5/24, 6/25, 8/4, 4.5          3.2-5.3   60           19   |
|             10/15                                                     |
|                                                                       |
|             6/4, 7/14, 9/1,  5.1          3.9-6.2   60           19   |
|             10/15                                                     |
|                                                                       |
|   *LSD                       *0.4*                  *2*          *1*  |
|   (0.05)*                                                             |
|   ----                                                                |
| ----- ---------------- ------------ --------- ------------ ---------- |
|                                                                       |
| Source: Sheaffer, C.C., and G.C. Marten. 1990. J. Prod. Agric.        |
| 3:486-491.                                                            |
|                                                                       |
| Depending upon harvest frequency, under good September growing        |
| conditions, a producer can expect to harvest about a ton of dry       |
| matter per acre of high quality alfalfa in October. Having drying     |
| conditions adequate to produce hay can be a challenge (preservatives  |
| may be an option), but appropriate moisture for haylage is generally  |
| not difficult to achieve. Grazing is another option, as long as bloat |
| precautions are taken.                                                |
|                                                                       |
| [Summary Points]{.underline}                                          |
|                                                                       |
| Where you have a foot or more of growth in October of a modern,       |
| winter hardy, multi-disease resistant alfalfa variety on a good       |
| alfalfa soil with adequate potassium; consider harvesting at least    |
| your older alfalfa stands to provide more high quality forage for     |
| this winter. Alfalfa stands typically begin to lose yield potential   |
| after their third year anyway, so where high quality forage is a      |
| priority, concerns about damaging stands more than 3 years old should |
| generally not weigh heavily in the decision of whether or not to cut  |
| in the fall.                                                          |
|                                                                       |
| One potentially high risk factor this fall is soil moisture. Fields   |
| that are very wet going into the winter have a higher risk of winter  |
| injury if a fall cutting is taken.                                    |
|                                                                       |
| If you're of a conservative bent and/or in an area where snow tends   |
| to blow off fields with short stubble, you may wish to leave strips   |
| of uncut alfalfa to help catch snow.                                  |
|                                                                       |
| It's still preferable to avoid cutting in the \"heart\" of the fall   |
| critical period (i.e. mid-late September). Better to target early     |
| (northern MN) to mid (southern MN) October, near the time when a      |
| killing frost is likely and thus continued growth unlikely.           |
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