Abstract: Forage yield, quality, and stand persistence are all major considerations in the development of a profitable harvest management program. Sufficient time must be allowed for alfalfa to build energy reserves before winter. This is an important aspect of winter survival and stand persistence. A shortened alfalfa growing season in northern regions will make it necessary to combine calendar dates and stage of development into harvest strategies. Timing of harvest, and the harvest process are both critical to obtaining hay of a desired quality. High quality alfalfa hay will not be obtained if harvest is delayed or if leaves are lost during the hay drying process. Adverse weather will greatly lower quality and may dictate the use of either or both hay drying agents and hay preservatives. Principles of hay making and strategies for coping with adverse weather are discussed.
To maximize benefit from forage crops one must understand the interrelationships of forage yield, forage quality, and forage crop stand persistence. Maturity stage at harvest is the most important factor influencing forage quality. As forage crops mature, forage quality declines and fiber content increases. If harvest is delayed for maximum yield in alfalfa, then forage quality will deteriorate and fall below that needed for optimal animal performance. Adequate forage quality is essential for animal weight gain, high levels of milk production, reproduction efficiency, and farm profits.
A quality forage has the potential to produce a desired animal production response. Thus, a forage that is adequate for one animal group may be inadequate, or more than adequate to another animal group, since the nutritional need of animals depends on species, age, sex, and production status. Factors that influence quality are palatability (will animals eat the forage), intake (how much will they eat), digestibility, nutrient content, and anti-quality factors. Maturity at harvest influences animal intake, because intake drops dramatically as fiber increases, and as fiber increases, digestion also slows.
When producing forages, especially legumes, if the goal is the highest quality this will tend to shorten stand persistence and decrease yield. Maximum yield of alfalfa is achieved at the stage of full flowering, whereas quality is highest prior to flowering. For the first cutting in spring, forage quality may change 4 to 5 points in relative feed value (RFV) per day. Any delay in spring harvest will then result in reduced forage quality. Also, if all forage is ready to harvest on the same day, then harvesting over several days will result in a gradual decline in forage quality. Planting a range of varieties, including some very high quality varieties, will help to spread the harvest period while helping to preserve forage quality.
In deciding on the harvest management strategy for alfalfa, one can aim for high quality, for high yield and high quality, or for maximum persistence. For high quality, the first cutting would be taken at the early bud stage and remaining cuttings taken at mid-bud. Repeated early cutting at the early bud stage to maximize quality, will reduce stand persistence. Usually there will be 28 to 33 days between 1st and 2nd cuttings, and then 30 to 35 days between remaining cuttings. Because of rapid changes in quality, especially for the first cut, the forage must be harvested during a 3-4 day time period. Also, no late fall cutting is recommended because alfalfa needs to build reserves prior to winter.
Allowing alfalfa to build energy reserves before winter is an important aspect of winter survival and stand persistence. After the third or fourth harvest, there should be a non-harvest period of 5 to 8 weeks prior to the first killing frost. There must be sufficient time for plant recovery prior to a killing frost and onset of winter dormancy. This relationship of fall management has been shown to be associated with the level of total non-structural carbohydrates (TNC - sugars and starches) in alfalfa roots and crowns. Root TNC provides energy for plant survival during the dormant season, early spring growth, and regrowth after each harvest.
If the management is for high yield and high quality, then the first cutting should be at the bud stage (May 20-25), the second cutting 28 to 33 days after first, and the third (and 4th) cutting 38 to 55 days after second or at the 10 to 20% bloom stage. Since forage quality changes rapidly early in the season, the cutting interval for all fields should be short. In summer, quality changes more slowly which allows a 7-10 day harvest window. An additional cutting after the second can be taken if a 6 to 8 week rest period is maintained prior to killing frost. Taking a late-fall cutting after killing frost can shorten stand life and the yield next spring.
If the management is for maximum persistence then the first cutting is between 1st flower and 25% flowering, and then approximately 35 to 40 days between subsequent cuttings. In this strategy, the emphasis is placed on high yield. This management allows a slightly wider harvest period than when cutting for high quality, however, the quality will often be below that required for high levels of production.
While maturity of alfalfa determines potential forage quality, the yield and the quality are also influenced by the harvest process and storage conditions. Harvest management and environmental or weather conditions both interact, influencing losses from mechanical action and biological activity. Most hay losses are associated with mechanical handling processes and weather related damage in the field, whereas for silage more losses occur during storage and feeding. Leaves, are highly digestible and protein rich, and are more prone to losses than stems. For alfalfa hay, almost all mechanical handling will result in some leaf loss. Cutting alfalfa early in the morning will allow a full day’s drying, thereby maximizing drying time, minimizing respiration losses, and the time exposed to any impending adverse weather.
Respiration occurs in living cells and is a process that uses plant sugars. Cell respiration losses continue until the hay dries. With the loss of plant sugars, the proportion of fiber (NDF and ADF) increases, and the digestibility of the hay decreases. Rain damage on hay prior to baling washes out soluble carbohydrates (sugars) and proteins. Both NDF and ADF increase, and hence digestibility decreases. The drier the hay crop before baling, the more damage will result from rain. Wet weather can also cause a delay in harvest, resulting in an over-mature hay crop, higher in fiber and lower in crude protein.
Use of a mower-conditioner with full width conditioning rollers to crush alfalfa stems will speed up the drying process. Conditioning is essential to reduce leaf loss since without conditioning leaves will dry, become brittle and shatter long before stems are dry enough for hay to be baled. Moisture content of topsoil will also influence the drying rate of alfalfa. If the ground is wetter than the cut hay, moisture evaporating from the soil will be absorbed by the hay. Always try to cut hay when the soil surface moisture is below 45%. If the ground is wet, allow hay to dry until it reaches the moisture level of ground, then move the hay crop carefully to drier ground, and to expose the hay to new air, rather than the saturated air that becomes trapped around swaths or in wind rows.
The normal cutting height for healthy, non-stressed alfalfa for maximum yield is 3-5 cm. This should be adjusted upwards for fields under stress (i.e. water stress, fields cut early, and fields cut frequently throughout the season). Also, adjust cutting height upwards according to field conditions, (for example fields with stones), and in the fall use a minimum cutting height of 10 cm for greater winter survival and ability to catch snow. In wet conditions a taller stubble will aid the drying of the lower part of hay, by keeping it off the ground and allowing better aeration. To improve drying, avoid deep, dense wind rows, instead use wide, thin wind rows to expose more of the hay to sunlight and drying winds.
Raking and inverting may be necessary, to aid drying or to combine wind rows, but it should be kept to a minimum. Raking can be the cause of the greatest loss of leaves in the hay making process. Leaf shatter increases in alfalfa with less than 50% moisture, and increases greatly as the hay dries. It is recommended not to rake alfalfa hay if moisture content is below 40%. If raking is necessary when the hay is below 40% moisture content then gently rake early in the morning before the dew has completely evaporated.
The recommended time to bale hay is based primarily on moisture content of the hay. It is recommended to bale alfalfa when moisture is between 18 and 20%. Baling at a lower moisture will result in excessive leaf loss, while baling at a higher moisture may result in spoilage form mold and heat unless a preservative or artificial drying is used. Medium square (360 to 450 kg) bales are denser than small square and large round bales and thus need to have 2 to 3% less moisture at time of baling to avoid molding. Recommended bale moisture levels for storage with minimal losses may be difficult to attain in humid weather conditions, and may require a preservative for good bale storage. Risk of fire also increases in stored high moisture hay.
The main thing farmers can do to speed the drying process is to use a well adjusted mower conditioner, so that stems are completely crushed and hay is laid down in a wide, loose swath. Also important, is to cut hay early so that as much as possible is on ground by midday, when drying conditions are best. There is some research that suggests late afternoon cutting will increase soluble sugar levels in alfalfa compared to early morning cutting, when most sugars have been converted into storage products. However, the increased nutritional value is small and may not be worth the extra time needed to dry hay with late afternoon cutting compared to morning cutting. Further, cell respiration losses may be increased because of a delay in drying, especially in summer harvests with warmer night temperatures.
Sometimes so-called hay drying agents or desiccants have been used to increase hay drying rate. These chemicals are applied at the time of cutting and reduce field drying time by increasing the rate of water loss. They do not directly dry the hay crop, but rather break down the waxy layer (cuticle) on alfalfa stems. Mechanical conditioning is a physical process that breaks this waxy layer. Drying agents are most effective during good drying conditions such as warm weather, low humidity, dry soil, and light wind. Also, they are better when alfalfa stems are small and with wide thin wind rows left by the mower conditioner. Drying agents are less effective in the U.S. in spring when conditions for good drying are less likely to occur. Compared to mower-conditioner alone, chemical conditioning may reduce curing time ½ to 1/1/2 days. Chemicals used are potassium carbonate (K2CO3) and sodium carbonate (Na2CO3) with K2CO3 being more effective than Na2CO3. Drying agents have no effect on grasses, there will be little benefit in long periods of good drying conditions, and drying agents will not work on hay laying on wet soil, they may make it worse. Economics to consider are costs of chemical, and increased labor and added fuel. Mixing and handling spray material may increase mowing time by 10-20%.
On occasions, often too frequently, hay does not seem to dry fast enough to avoid approaching adverse weather. On these occasions, use of hay preservatives allows hay to be baled at a higher moisture content (25-30%) , and may be profitable, especially if the alternative is rained-on hay. Use of preservatives permits baling earlier in the morning and later into the evening or at night. Often baling can begin 12-24 hours earlier, and studies have shown harvest yields averaged 140- 300 lbs/ac (165 to 345 kg/ha) more due to less leaf loss and exposure to adverse weather. Typically, hay is treated and baled at 25-30% moisture. Products used in North America are acids or acid derivatives (propionic acid, acetic acid/sodium diacetate), or combination of sulfur salts and enzymes to limit cell respiration, and to reduce both development of mold and heating. The preservative must be applied uniformly and at the correct amount, based on yield and moisture content, or heating and mold can still develop. Hay preservatives may be used in combination with hay drying agents (chemical conditioners) in same hay harvest. Benefits from using both will be additive. There is no need for a preservative when hay moisture is below 20%. Another alternative for baling at higher than optimal moisture (18-20%) is bale wrapping. Wisconsin research has shown that wrapping medium bales with plastic at 21-38% moisture adequately preserved them, although some browning of hay occurred. However, there was no increase in ADF.
An understanding of the hay making process and careful attention to details will help ensure quality hay is harvested and this will increase animal production and farm profits.
Dr. Stephen J. Herbert
Professor, Dept. of Plant and Soil Sciences
University of Massachusetts
Amherst, MA 01003, USA