• 2019/08/25 00:47:47
  • in Alfalfa Management
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  • modifi date: 2019/08/28 10:47:41

Harvest

Harvest

The final step to profitable alfalfa production is to set goals for forage quality and use the appropriate harvest techniques to minimize field losses and maximize tonnage of high quality forage. This recognizes that high quality forage is profitable to animals that can use the quality but that tradeoffs exist between forage quality, yield, and stand life.



Forage quality

Alfalfa is superior to other forage crops because it is high in crude protein and energy, reducing the need for both types of supplements in rations. The superior intake potential allows for greater use in rations of high-producing dairy cows.


What quality forage is needed?

The nutrient need of an animal depends primarily on its age, sex, and production status (Figure 19). Maximum profit results from matching forage quality to animal needs. Lower-than-optimum quality results either in reduced animal performance or increased supplement costs. Conversely, feeding animals higher quality forage than they need wastes unused nutrients that were expensive to produce and may result in animal health problems.

Quality standards are presented in Table 11. (Forage quality terms are defined at the end of the Harvest section.) Use the RFQ index to allocate the proper forage to the proper livestock class (Figure 19). Performance of high-producing dairy cows is most limited by intake of digestible dry matter and prime hay or haylage is recommended. An RFV or RFQ of 151 or higher is recommended for dairy cows after the first trimester, heifers, and stocker cattle.

Forage quality needs of cattle and horses.
Figure 19. Forage quality needs of cattle and horses.

Quality standards for legume, grass, and grass–legume mixture
Table 11. Quality standards for legume, grass, and grass–legume mixture


 

As shown in Figure 20, ADF is a poor estimate of energy in feedstuffs. In response, the National Research Council Nutrient Requirements for Dairy Cattle (2001) recommended estimating energy from total digestible nutrients (TDN). TDN is the sum of digestible components (nonfibrous carbohydrates, crude protein, fatty acids, and digestible fiber). If NDFD is not reported on lab analyses, TDN was likely estimated from ADF only and is much less accurate.

RFQ was designed to use the new analyses that better predict animal performance. It is based on energy intake estimates relative to a standard just like RFV was. The only differences are that intake is adjusted for digestible fiber and that energy is calculated as TDN using digestible fiber. This calculation allows more meaningful comparisons between alfalfa, alfalfa–grass mixtures, and grasses.

Comparison of ADF to in vitro digestibility of alfalfa.

 

 

Figure 20. Comparison of ADF to in vitro digestibility of alfalfa.



 

Plant growth and forage quality

Understanding how alfalfa grows and its relationship to forage yield, forage quality, and carbohydrate root reserves is critical to production of high quality hay. Alfalfa is a perennial plant that stores carbohydrates (sugars and starches) in the crown and root. Plants use these carbohydrate reserves for regrowth both in the spring and after each cutting. When alfalfa is 6 to 8 inches tall, it begins replacing carbohydrates in the root (Figure 21). This cycle is repeated after each cutting.

Carbohydrate content of alfalfa roots
Figure 21. Carbohydrate content of alfalfa roots.

 

High levels of carbohydrate reserves encourage rapid regrowth after cutting and winter survival. Regrowth begins with buds either on the crown or at the base of old shoots (after first cutting). Alfalfa regrowth for second and later cuttings begins while growth from the previous cycle is beginning to flower. Cutting at late maturity can remove shoots for the next cutting and delay regrowth.

Forage growth is most rapid until early flowering (Figure 22). Forage growth continues until full flower, but often leaf losses from lower stems slow yield increase after first flower. Alfalfa forage quality is greatest in early vegetative stages when the leaf weight is greater than stem weight; however, by first flower, and sometimes earlier, stem proportion exceeds that of leaves. Higher alfalfa yields after early flower can be attributed mainly to more low-quality stems. As cutting interval increases or as plants are harvested at later stages of maturity, yield per cutting increases but quality of the forage harvested decreases. Temperatures during growth affect forage quality. Alfalfa grown during cool weather tends to produce higher quality forage than alfalfa grown during warm periods, assuming all harvests are equally weed-free and at the same maturity stage.

Forage quality is also influenced by the time of day alfalfa is cut. Plants convert sugars and starches to energy in a process called respiration. Respiration after cutting lowers forage quality and is stopped only by drying the forage. Therefore, the best time to cut alfalfa is in the morning to speed drying and capture sugars and starch for higher quality hay and haylage.

Forage yield relative to quality at different growth stages
Figure 22. Forage yield relative to quality at different growth stages.

 



Harvest management

Forage yield, quality, and stand persistence are all major considerations in the development of a profitable harvest management program. Increased awareness of the nutritional value of high quality alfalfa in terms of potential savings of energy and protein supplements has caused many to re-evaluate current harvest strategies.


Cutting schedule

Selection of a harvest schedule begins with the decision on quality of forage desired. Growers desiring all high quality alfalfa will shorten stand persistence and decrease yield. Harvest schedule decisions include number of cuts per season, date of cut, stage of maturity, interval between cuts, and cutting height. The link between the stage of maturity and yield, quality, and persistence makes it apparent why growth stage is frequently used to decide when to harvest alfalfa. Keying harvests to specific stages of development also takes into account the varying effects of changing environments and variety maturity rates. A shortened growing season in northern states dictates combining calendar dates and stage of development into harvest strategies.


 

Maximum persistence

If harvesting for maximum persistence, cut alfalfa between first flower and 25% flower. This is approximately 35 to 40 days between cuttings (Figure 23). The system has a slightly wider harvest window and longer cutting interval than when cutting for high quality because the emphasis is on high yield.

Cutting schedules for different management goals
Figure 23. Cutting schedules for different management goals.

 


High quality

When harvesting for high quality the first cutting should be taken by an early calendar date appropriate for the region. The remainder of cuttings should be taken at midbud, generally 28- to 33-day intervals early in the season and longer near the end of the season (Figure 23). Cutting for high quality forage means that forage must be harvested within a 3- to 4-day period. No late-fall cutting should be taken in northern states, although it should be taken in regions where needed to decrease insect overwintering. Yield of the late fall cutting is generally low, and removal of this forage will increase winterkill and decrease first cutting yield the next spring.

 

High yield and high quality

For harvest schedules to provide the highest yield of high quality forage, the first two cuttings must be timely. During this time forage quality changes most rapidly and short delays mean low quality forage (Figure 24). Take the first cutting at bud stage or between May 15 and 25 in Minnesota and Wisconsin, and earlier farther south. Take the second cutting 28 to 33 days after the first cut or midbud, whichever is earlier, and take subsequent cuttings at 38- to 55-day intervals or at 10 to 25% bloom. An early first harvest followed by a short cutting interval gives a high yield of quality forage (Figure 23) while

letting one cutting mature to early flower will increase root reserves and stand persistence. The forage quality of alfalfa does not change as rapidly in later cuttings as in earlier cuttings so later cuttings maintain quality to later maturity stages (Figure 24). This slower quality change allows a harvest window of 7 to 10 days. Additional cuttings may be taken if time permits before the required 6- to 8-week rest period prior to the first killing frost. In northern regions, delaying the third cut often results in alfalfa flowering during the 6 weeks before the first killing frost (between September 1 and October 15 in northern states). To prevent loss of persistence, delay harvest until mid- to late October, regardless of the stage of maturity. However, this late-fall cutting will shorten stand life and decrease yield the next spring, so should be cut high (at 6 inches) or not harvested if adequate forage is available. Minnesota researchers found that highest yields came from three cuttings during the growing season with a late-fall cutting. Using this cutting schedule, the percentage of total yield cut at "prime standard” (>150 RFV index) ranged from 32 to 75%.

Dry matter yields increase with longer intervals between cuttings while forage quality rapidly declines, particularly during first and second cuttings
Figure 24. Dry matter yields increase with longer intervals between cuttings while forage quality rapidly declines, particularly during first and second cuttings.

 


Fall management


Fall management of alfalfa involves assessing the risk of winter injury and the need for additional forage. The risk of winter injury to alfalfa depends on uncontrollable environmental factors (snow cover, temperature, and soil moisture) and controllable factors (variety, soil fertility, seasonal cutting strategy, stand age, and cutting height).


Uncontrollable environmental factors

Extended periods of cool temperatures are required in the fall for alfalfa to develop resistance to cold temperatures. Sudden changes from warm to cold reduce hardening.

A snow cover of 6 inches or more protects alfalfa plants from severe cold. During winters without snow cover, soil temperatures can fall below 15°F, injuring or killing plants.

Even hardy varieties can be injured or killed by 2 weeks or more of temperatures below 5° to 15°F.

Warm fall weather (40°F or higher) and midwinter thaws cause alfalfa to break dormancy and have less resistance to freezing.

Excessively moist soil in the fall reduces hardening and predisposes alfalfa to winter injury. Excess surface and soil moisture can lead to the formation of ice sheets. Ice sheets smother plants by freezing the soil before the plant has hardened. Also, high concentrations of toxic substances—such as carbon dioxide, ethanol, and methanol—accumulate beneath the ice. Ice sheeting frequently occurs in conjunction with midwinter thawing and is more prevalent in poorly drained soils.

 

Controllable factors

Select alfalfa varieties with good winterhardiness and moderate resistance to several diseases. These varieties will better tolerate late-fall cuttings.

Soil fertility management is vitally important for maintaining productive alfalfa stands. Potassium (potash) is particularly important for developing plants that have good winter survival.

Greater harvest frequency and stand age at harvest increases the potential for winter injury when fall cuttings are taken. When the interval between previous cuttings has been 35 days or less, avoid harvesting during the critical fall period 6 weeks before the first killing frost (between September 1 and October 15 in northern states, later in southern states). This allows plants to enter winter with higher root carbohydrates (Figure 21).

Young alfalfa stands survive winters better than older stands due to lower disease infestation and less physical damage.

Stem and leaf stubble remaining in the late fall catch snow and insulate the soil. Alfalfa harvested in October should have a 6-inch stubble left and uncut strips to reduce risk of winter damage.

 

Making the decision to cut in the fall requires using the above factors to estimate the risk of winter injury to alfalfa and weighing it against the need for forage. The questions in Table 12 will help you assess the risk of winter injury.

Harvesting the late-fall cutting will increase tonnage for the season and may be more profitable in areas where risk potential is low (see Table 12) and good snow cover is likely and in areas with less severe winters. Minnesota research shows that taking a fourth cutting after October 15 is more profitable than three cuts by September 1 (6 weeks before killing frost) or four cuts by September 15 with no fall cutting for a 4-year-old alfalfa stand. In five-cut systems, the first cutting yield the next spring was lowered by approximately the same amount as the yield from the fall cutting. Root rot was increased and, therefore, stand life was also shortened.

Calculate your risk of alfalfa winter injury. Enter the score for answers that describe your situation.
Table 12. Calculate your risk of alfalfa winter injury. Enter the score for answers that describe your situation.


 


Hay and silage management


Hay-making and silage-making differ in how the moisture content of alfalfa is employed as a strategy in preservation. Fresh alfalfa contains about 80% moisture. Soluble sugars and proteins are dissolved in the forage liquid. When concentrated through wilting, this "juice” provides an ideal medium for the growth of yeasts, molds, and bacteria and for rapid activity of plant enzymes. Appropriate bacterial growth can result in fermentation that produces lactic acid and preserves the material as silage. When forage is dried to hay before harvest, water in the forage evaporates, resulting in a higher concentration of nutrients in the remaining liquid where cell growth and enzyme activity are restricted.


Losses

Each step in the preservation process—mowing, raking, chopping, baling, storing, and unloading—causes a loss of forage dry matter (Figure 25). Some losses result from mechanical action; others are biological processes. Total losses from cutting to feeding are 20% to 30% of the standing crop dry matter in typical hay and silage systems. In hay-making, most of the losses result from mechanical handling and weather damage in the field. In silage-making, most losses occur during storage and feed out.

Dry matter losses during harvest and storage relative to forage moisture content at harvest
Figure 25. Dry matter losses during harvest and storage relative to forage moisture content at harvest.

 


Quality changes

Most of the dry matter lost from forage during harvest and storage has high nutritional value. More leaves than stems are lost during hay-making, and most protein- and energy-rich nutrients are concentrated in the leaves. Biological processes in silage-making use the most readily available nutrients, such as plant sugars. Thus, in both hay and silage systems, the changes that occur are often detrimental to the quality of the final product.


Minimizing losses

Dry matter losses and quality changes cannot be eliminated in hay preservation, but they can be minimized by using good management practices. The practices for good hay-making are summarized in Table 13.

Summary of good hay-making practices.
Table 13. Summary of good hay-making practices

 



Quality losses during hay-making

Respiration uses plant sugars, a process that increases NDF and ADF and decreases digestibility.

Rain on hay before baling leaches soluble nutrients (protein and carbohydrates). NDF and ADF increase; digestibility and crude protein decrease. Additional quality is lost from leaf shattering.

Rainy weather causes delays in harvest. NDF and ADF increase; digestibility and crude protein decrease.

 

Good hay preservation depends primarily on handling and harvest management. The drying rate, mechanical handling of the forage, and the moisture content at baling all affect the quality of the hay. With proper management, little or no deterioration takes place in the hay during storage.

 

Quality losses during silage-making

Dry matter loss increases ADF and NDF; decreases digestibility and dry matter intake by animals.

Loss of leaves decreases crude protein.

Soluble protein can increase in silage during fermentation. Animals on high-performance diets (dairy or growing beef) need insoluble protein, so performance is lowered.

Acid detergent fiber crude protein is protein made insoluble through the heating during fermentation. Up to 14% is beneficial; more than 14% reduces protein availability to the animal.

 

Unavoidable losses include those due to field losses, plant respiration, and primary fermentation. Avoidable losses occur from effluent, anaerobic fermentation, and aerobic deterioration in storage structure. Estimates of unavoidable dry matter losses range from 8% to 30%; avoidable losses range from 2% to 40% or higher. The importance of quickly achieving and maintaining oxygen-free conditions has led to improved equipment and techniques for precision chopping, better compaction, rapid filling, and complete sealing. Alfalfa is more difficult than corn to ferment properly because alfalfa contains fewer soluble carbohydrates relative to protein. For an outline of good silage management practices see Table 14 on the next page.

Summary of good alfalfa silage practices.
Table 14. Summary of good alfalfa silage practices.

 


Feeding considerations of hay and haylage

A widely used rule of thumb in formulating rations for lactating dairy cattle is that one-third of the diet be forage, one-third concentrate, and the remaining one-third either forage or grain, depending upon the quality of the forage fed. By feeding high quality alfalfa in place of lower quality forages, dairy producers can decrease the amount of concentrates that must be fed and can increase the utilization of forage. The lactation study in Figure 26 shows concentrates cannot supply the energy required at high production levels when the quality of the forage is too low.

How alfalfa is harvested and preserved has been the focus of many research studies, but no clear advantage in animal performance has been demonstrated for harvesting and storing alfalfa either as hay or haylage. Harvesting alfalfa at higher moisture contents will decrease field losses but will increase storage losses unless forage is kept in airtight silos or silage tubes.

Fat-corrected milk (FCM) yield as influenced by change in alfalfa maturity and concentrate level.
Figure 26. Fat-corrected milk (FCM) yield as influenced by change in alfalfa
maturity and concentrate level.


 

Advanced Techniques

Drying agents, preservatives, and silage inoculants

To speed drying, use a drying agent in addition to mechanical conditioning. These products, either sodium or potassium carbonate, should be applied to alfalfa as it is cut. They will shorten drying time by 5 to 24 hours. Drying agents do not work on grasses. These products cost $2 to $6 per acre and require large volumes of water for application.

Preservatives allow hay to be baled at higher moisture contents than can normally be stored:

above 14% for bales larger than 31⁄2' × 31⁄2'; 16% for 21⁄2' to 31⁄2' square bales or round bales; and 20% for small square bales. These products are only cost effective if their use prevents rain damage, so apply only when rain is imminent. Propionic acid is the most effective chemical preservative. Ammonium propionate is less caustic than propionic acid and equally as effective per unit of propionate. Acetic acid is only half as effective as propionic acid as a preservative. In all cases the amount needed for preservation is in relation to the moisture content of the hay (Figure 27).

Propionic acid needed to preserve hay
Figure 27. Propionic acid needed to preserve hay.


 

Silage inoculants provide the lactic acidforming bacteria required for good haylage or silage fermentation. These products (either microbial or enzyme formulations) are beneficial when naturally occurring populations of lactic acid-forming bacteria are low and plant carbohydrate levels high. In the northern United States, these conditions occur on all early- and late-season cuttings when the drying time has been less than 2 days (Figure 28). Bacterial inoculants must be stored in cool places and contain 106Lacto-bacillus plantarum colony forming units (cfu) per gram. To be effective, the inoculant must be uniformly mixed throughout the forage. A liquid applicator on the chopper or on the blower is the preferred method of application.

Conditions for profitable use of inoculant on silage. Shaded areas indicate profitable conditions.
Figure 28. Conditions for profitable use of inoculant on silage. Shaded areas indicate profitable conditions.

 


Forage quality terms


Acid detergent fiber (ADF)
is the percentage of highly indigestible and slowly digestible material in a feed or forage. This fraction includes cellulose, lignin, pectin, and ash. Lower ADF indicates a more digestible forage and is more desirable.

Neutral detergent fiber (NDF) is the percentage of cell walls or fiber in a feed that is digested in a specified time (usually 24, 30, or 38 hours). NDFD is inversely related to animal intake and the energy that an animal can derive from a feedstuff.

Neutral detergent fiber digestibility (NDFD) is the percentage of the NDF that is digested by animals in a specified time period (usually 24, 30, or 48 hours).

Total digestible nutrients (TDN) is the sum of digestible crude protein, nonfibrous carbohydrate, fat (multiplied by 2.25), and digestible NDF minus 7.

Relative forage quality (RFQ) is an index used to rank forages by potential intake of digestible matter where 150 is considered milking dairy quality feed and lower indices are needed for other categories of animals (Figure 19).

 

Relative Forage Quality Calculations for Legumes

1. Calculate digestible dry matter of forage (% of Dry matter)

TDN = (NFC × .98) + (CP × .93) + (FA × .97 × 2.25) + (NDFn × (NDFD/100) − 7

where:

CP = crude protein (% of DM)

EE = ether extract (% of DM)

FA = fatty acids (% of DM) = ether extract − 1

NDF = neutral detergent fiber (% of DM)

NDFCP = neutral detergent fiber crude protein

NDFn = nitrogen free NDF = NDF − NDFCP, else estimated as NDFn = NDF × .93

NDFD = 48-hour in vitro NDF digestibility (% of NDF)

NFC = non fibrous carbohydrate (% of DM) = 100 − (NDFn + CP + EE + ash)

2. Calculate dry matter intake of forage (% of body weight)

DMI = 120/NDF + (NDFD − laboratory average digestibility for alfalfa) × .374/1350 × 100

3. Calculate Relative Forage Quality

RFQ = (DMI, % of BW) × (TDN, % of DM)/1.23

 

Crude protein (CP) is a mixture of true protein and nonprotein nitrogen. It is determined by measuring total nitrogen and multiplying this number by 6.25. Crude protein content indicates the capacity of the feed to meet an animal’s protein needs. Generally, moderate to high CP is desirable since this reduces the need for supplemental protein. Forage cut early or with a high percentage of leaves has a high CP content.

 

Rumen undegraded protein (also called bypass protein) is that portion of the protein not degraded in the rumen. Some bypass protein is needed for high producing dairy animals.


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