Alfalfa Cutting Height to Maximize Forage Yield and Quality

 

Daniel W. Wiersma - Assistant Superintendent

 Marshfield Agricultural Research Station

University of Wisconsin-Madison

 

 

Current recommendations regarding cutting height of alfalfa are designed to maximize yield while maintaining high quality forages and stand longevity. Forage growers frequently cut forages at a height of 3-inches or more. However, recent reports indicate that there may be an advantage to cutting alfalfa closer, leaving an inch or less of stubble height (@griculture Online, 1999). Research indicates that dry matter yields and nutrient yields are higher for shorter cutting heights as compared to leaving taller stubble (Sheaffer et al., 1988). Obtaining higher yields requires that the plants are healthy and that carbohydrate root reserves are adequate for plant regrowth following harvest. Early Wisconsin studies using Vernal alfalfa showed that forages harvested three or four times per season produced more total forage when cut at a 1-inch height versus cutting at 3 inches or more (Kust and Smith, 1961, Smith and Nelson, 1967). North Dakota research looking at cutting height since the mid-1960s shows similar results where shorter cutting height leads to higher yields.

 

One of the reasons for leaving taller stubble is to improve the quality of the forage harvested. The lowest sections of the alfalfa plant are typically higher in fiber and have fewer high quality leaves present. If growers raise their cutting height to leave these high fiber basal stem sections in the field, they may increase forage quality.

 

Research was initiated at the Marshfield Agricultural Research Station during 1999 to explore the relationships among cutting height, forage yield and forage quality. This paper will discuss the influence of cutting height on yield and quality of alfalfa.

 

Materials and Methods

 

During the summer of 1999, two research trials were conducted at Marshfield, WI that evaluated the effects of cutting height on alfalfa yield and quality. One trial was harvested using small-plot equipment (Small-Plot Trial) and a second trial was harvested using a self-propelled haybine (Field-Scale Trial).

 

Each of the trials were replicated three times and had the following cutting height treatments applied to them:

1)      2-inch height for all cuts during the season,

2)      2-inch height for the 1st cut, 3-inch height for 2nd and 3rd cuts,

3)      3-inch height for all cuts during the season,

4)      6-inch height for all cuts during the season.

 

While we had hoped for our lowest cutting height to be 1-inch, the lowest our equipment and soil conditions would allow was about 2-inches. Actual cutting height was determined by measuring stubble height from 35 random locations within each harvested plot. Data will be reported based on actual cutting height for these studies. For the first two harvest periods, the field-scale plots were harvested 7-10 days earlier than the small plots. This allowed us to measure forage quality changes among the various cutting heights at early and late harvest times within a cut.

 

Small-scale plots measuring 3-ft wide by 25-ft long were established on in an existing alfalfa field. These plots were harvested using a small-plot harvester and electronic weighing system. On each harvest date, a subsample was taken from each plot to determine forage quality. Harvest dates for these plots were June 8, July 13, and August 16.

 

Field-scale plots measuring 12-ft wide by 150-ft long were established in an existing alfalfa field (1996 seeding, weed free stand). Cutting height treatments were made using a self-propelled haybine and forage was immediately chopped and weighed after cutting. Electronic pad scales were used to weigh each plot and a 1-lb subsample was taken from each plot for quality analysis. Harvest dates for these plots were May 25, July 1, and August 20.

 

RESULTS AND DISCUSSION

 

            Results from the small plot and field-scale trials were similar for both forage yield and quality. Measurement of forage yield and quality from the field-scale trial was more variable, while trial precision was highest for the small-plot trial. Yield and quality trends and levels of differences were similar between the two trials.

 

Forage Yield

 

            For each cutting, forage yield increased as cutting height was reduced (Figures 1-2). The largest differences among cutting height treatments were measured in the first cut of the season. Significant yield differences were measured for each harvest, however the smallest differences tended to be in the third cut. On average, total alfalfa yield for the season increased by 0.5 tons/acre for each 1-inch reduction in cutting height. This is similar to the findings of researchers in North Dakota.

 

Forage Quality

 

            Forage quality was compared using relative feed value (RFV). In general, as cutting height was reduced, forage quality decreased (Figure 3-4). Overall, for each 1-inch reduction in cutting height forage quality decreased an average of 4-7 units RFV. These differences were present in each cutting, but most pronounced with first and second cut forages. Forage quality (RFV) differences among cutting height treatments were very slight for alfalfa harvested in August (3rd-cut). Cutting dates between the field-scale trial and the small-plot trial were staggered by 7-10 days (cuts 1 and 2) to see if the quality trends were the same at different stages of alfalfa maturity. While we could not compare them statistically, the trends and magnitude of forage quality changes with cutting height are similar for the two cutting times.

 

 

 

Milk Yield Per Acre

 

            Combining forage yield and quality into a single measure is accomplished by using the Milk95 spreadsheet that generates an estimate of milk yield per acre (Undersander, et. al., 1995). For each harvest, the potential milk yield per acre increased as cutting height decreased (Figures 5-6). Totaled over the three-cut season, milk yield increased by 800-940 lbs/ac with each 1-inch reduction in cutting height. In the small-plot trial, milk yield trends were identical for each cut, and only differed in magnitude. The field-scale trial exhibited very large changes in milk yield for first cut, and only small differences for second and third cuts. This was likely due to the reduced level of precision in the field-scale trial.

 

SUMMARY

 

            This preliminary research from Marshfield, WI indicates that alfalfa yield and milk yield is highest when cutting at the lowest possible height. While forage quality declines with lower cutting heights, forage yield increases significantly. These initial studies were done on healthy, weed-free stands of alfalfa and soil moisture conditions were adequate during most of the growing season. Additional studies will be conducted in Wisconsin during 2000.

 

Current recommendations for alfalfa cutting height in Wisconsin include the following:

1)      Cut healthy, non-stressed alfalfa fields at 1-2 inch heights to achieve maximum dry matter and nutrient yields,

2)      In fields where plants are experiencing moisture or flooding stress, or where the crop has been cut early and frequently, root carbohydrate reserves may be low and cutting height should be adjusted upward to avoid additional stress or plant death.

3)      Adjust cutting height to avoid injuring plants, contaminating the forage with soil, or picking up rocks.

4)      If harvesting forages in the fall, growers should leave a 4-inch or greater stubble to help capture snow.

 

REFERENCES

 

@griculture Online, 1999. Cut it close for best performance in alfalfa. http://www.agriculture.com, April 9, 1999.

 

Kust, C.A., and Dale Smith. 1961. Influence of harvest management on levels of carbohydrate reserves, longevity of stands and yield so hay and protein from Vernal alfalfa. Crop Sci. 1:267-269.

 

Sheaffer, C.C., G.D. Lacefield, and V.L. Marble. 1988. Cutting schedules and stands. P. 411-437. In A.A. Hanson et al. (ed.) Alfalfa and alfalfa improvement. Agron. Monogr. 29. ASA, CSSA, SSSA, Madison, WI.

 

Smith, Dale and C.J. Nelson. 1967. Growth of birdsfoot trefoil and alfalfa. I. Responses to height and frequency of cutting. Crop Sci. 7:130-133.

 

Undersander, D. J., T. Howard, R. Shaver, 1995. MILK95: Calculating Forage Milk Per Ton of Dry Matter and Per Acre. Univ. of Wis., Madison, WI.

 

Figures 1 and 2

Forage yield of alfalfa at various cutting heights in small-plot (Fig. 1) and field-scale (Fig. 2) trials at Marshfield, WI during 1999.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Figures 3 and 4

Relative feed value (RFV) of alfalfa at various cutting heights in small-plot (Fig. 1) and field-scale (Fig. 2) trials at Marshfield, WI during 1999.

 


 

 

 

 

 

 

 

 

 

 

Figures 5 and 6

Milk yield per acre of alfalfa at various cutting heights in small-plot (Fig. 1) and field-scale (Fig. 2) trials at Marshfield, WI during 1999.