LOVELOCK - 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. This article will discuss the influence of cutting height on yield, quality, and persistence of alfalfa.
How does cutting height effect yield?
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 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). A tall stubble height was needed to maintain high yields only when cutting frequencies increased to five or six times per season.
In a North Dakota two-year study using three- or four-cut systems, annual alfalfa yields were reported to be 1.6 tons per acre higher when cut at 1-in compared to 5-in heights (@griculture Online, 1999).
Research conducted in 1999 demonstrated a reduction of a half-ton of dry matter per inch as cutting height increased from 2 to 6 inches above the ground when combined across three harvests for the year (Wiersma, 2000).
Follow-up studies in 2000-2001 evaluated cutting height in mid-May, late-May, early-June and mid-June. An average yield reduction of 0.13 tons of alfalfa occurred for each inch increase of cutting height during the first harvest. These yield reductions were consistent across the four spring harvest dates.
These studies clearly show that there is a forage yield benefit to cutting at shorter heights when alfalfa plants are not under stress or low in root carbohydrate levels.
How does cutting height effect quality?
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. This change in quality would most likely be greatest for spring growth alfalfa since the proportion of stems to leaves is highest at this time.
Buxton et al. (1985) showed that the digestibility of stem sections decreased with increasing maturity while leaves did not. The lower stem portions (bottom two thirds) decreased in quality at a faster pace than did the upper portion of the stem. This occurs because the lower stem sections have been growing for the longest period of time and tend to be more fibrous and woody compared to the less mature upper stem sections.
On-farm research in Wisconsin confirmed quality diminishes modestly when alfalfa is harvested closer to the soil surface. Crude protein was reduced by less than 1 percent of dry matter when cutting height was increased from 2 inches to 6 inches. Depending on location and year, Relative Feed Value increased from 0.9 to as much as 7 units per inch increase in cutting height.
Milk per acre summaries from these before mentioned locations indicates the most milk per acre is generated at lower cutting heights. The quality improvement obtained by increasing the cutting height is not enough to offset the yield reduction. The amount of quality gain must be weighed against the yield loss due to leaving taller stubble. If growers are harvesting in a timely manner, there should be no reason to forego yield for a slight quality increase due to leaving taller stubble.
How does cutting height effect stand longevity?
When changing alfalfa management practices, growers want to be certain that stand longevity is not jeopardized. Cutting alfalfa shorter can reduce stand life if other stress factors exist. Frequent cutting of alfalfa at very early maturity stages often depletes root carbohydrate reserves. When carbohydrate reserves are low, energy for stem regrowth is low and results in poor plant recovery after harvest.
Cutting height research shows that early plant decline or death does not occur for alfalfa when proper crop management practices are used. When plants are healthy and not under stress, it appears that short cutting heights will not reduce stand longevity.
However, when harvesting alfalfa in the fall, increased cutting heights may be warranted for the purpose of catching snow. Longer stubble catches snow and may help keep the snow cover for a longer period of time. Adequate snow cover can help to protect alfalfa plants from cold temperature extremes or fluctuating late winter temperatures.
Recommendation:
• Cut healthy, non-stressed alfalfa fields at 1-inch heights to achieve maximum dry matter and nutrient yields.
• 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.
• Adjust cutting height to avoid injuring plants, contaminating the forage with soil or picking up rocks.
• If harvesting forages in the fall, growers should leave a 4-inch or greater stubble to help capture snow.
Source: "The Long and Short of Alfalfa Cutting Height", by Daniel Wiersma, Mike Bertam, Ron Wiederholt and Nick Schneider
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