Forage Considerations for Fall

Forage Considerations for Fall

Mark Marsalis, Extension Forage Specialist, Los Lunas, (505) 865-7340, marsalis@nmsu.edu

Small grains planting

As with any crop, success at wheat harvest begins with proper variety selection and using high-quality seed at planting. This is true whether the crop is grown for grain or forage (grazing, hay, silage) purposes. When choosing a wheat (or other small grain) variety, select a well-adapted variety that has performed well over multiple years. But do not overlook criteria such as seed size, germination and seedling vigor. For wheat, a test weight of 56 lb/bu and 85% or greater germination are recommended as minimums for proper establishment. Minimum acceptable test weights for triticale, barley, rye and oats should be 50, 48, 56 and 32 lb/bu, respectively. Large, heavy seed is preferred over lighter, smaller seed. Although cheaper seed is appealing, it can cost you more in the long run and can mean the difference between a healthy stand and complete crop failure. There is quite a bit of variation among wheat and triticale forage yields, and producers should understand the differences between these species and select a variety that has consistently high yields. NMSU conducts small grain tests at the Clovis Agricultural Science Center. Results from these tests can be found at: http://clovissc.nmsu.edu/variety-trials.html. Small grains planted for forage (grazing, hay or silage) production should be planted at rates about 25-30% higher than what would be planted for grain.  For example, if a typical seeding rate for irrigated wheat grain in your area is 90 lb/ac, then the corresponding forage rate would be about 100-120 lb/ac. For all of the small grains, typical seeding rates range from 30-60 lb/ac for dryland and 75-120 lb/ac for irrigated crops. Very little improvement in grain yield has been observed with planting rates greater than 90 lb/ac or greater than 100 lb/ac for forage. Always plant into good soil moisture and a well-prepared, firm seedbed. If planting into dry soil conditions, irrigate immediately after planting and maintain adequate moisture in the seedling zone through establishment. Seeding rates will need to be increased if planting under less-than-optimum conditions. Another important factor to consider is pest control. Although early-planted (e.g., August) small grains produce more fall growth for grazing, push roots deeper, and have a greater ability to utilize available soil moisture better than late-planted stands, they are particularly susceptible to damage caused by various insects (e.g., wireworms, white grubs) and soilborne diseases (e.g., seedling blight). If grazing is not part of the program, it is recommended that planting be delayed until soil temperatures are low enough to reduce soil insect populations (Sept-Oct). Using seed treated with insecticides and fungicides will greatly reduce the risk of damage from soil insects and soil- and seedborne pathogens that affect seedling plants. Several products are available for seed treatment and many are effective on multiple insects and diseases (See Seed Treatment Decisions for Use on Winter Wheat, https://agrilifecdn.tamu.edu/amarillo/files/2010/11/WheatSeedTreatmentsAug2008.pdf; Texas Coop. Ext., for a list of products to use). 

Extension Circular 630 Small Grain Forages for New Mexico was recently updated. For more information on growing small grains for forage access Circular 630 at: http://aces.nmsu.edu/pubs/_circulars/CR630.pdf.

Managing last cuts on alfalfa

As the alfalfa growing season starts to wind down, it is important for producers to understand how the last cuttings of their stands may affect winter survival and yields in subsequent years.  Some growers may choose to have a frequent cutting interval during spring and summer in order to maximize forage quality of the hay. Others may choose to wait a little longer (first flower to 25% flower) between cuttings to improve stand persistence and longevity. Whichever the case, proper fall management is critical for future productivity. Alfalfa must build root reserves prior to going into the winter, and cutting at frequent intervals and at certain times in the fall can negatively impact these root reserves, subsequently reducing plant persistence and yield the following spring. Longer intervals should be allowed for late season cuttings for root reserve accumulation. In fall, either of two approaches should be taken: 1) alfalfa may be cut so early (last full cut) that enough regrowth occurs to replenish root carbohydrate reserves prior to first frost (in this case, the last ‘clipping’ may occur at or just after a dormancy-inducing frost which means little or no regrowth or ‘waste’ of stored carbohydrates will occur) or 2) the last full cut should be taken so late that regrowth is minimal enough to not exhaust root reserves before freezing. General recommendations for fall management are to let plants rest for 6 to 8 weeks between the last regular harvest and the first freeze (27°F for 4 hrs). The 6 weeks leading up to first frost is critical for root reserves and plant survival. Also, leaving a 6-inch stubble will help insulate the soil and protect plants. Alfalfa producers thinking of making a late harvest should consider their need for extra forage and market demand contrasted with the possible risk of losing part of the alfalfa stand due to winterkill. In areas where winter temperatures may warm enough to break dormancy, less dormant alfalfas (e.g., Fall Dormancy 6 or above) may grow only to get shut down by a freeze and this, too, wastes stored carbohydrates and is a reason to be cautious about planting less dormant alfalfas—even if they are winter hardy—because this process is not desirable for the alfalfa stand. Factors that increase the risk of winter injury are:  stand > 3 yrs old, variety with high winter hardiness number, low soil fertility – particularly potassium (K), poor soil drainage/excessively wet soil, and fall cutting at inappropriate time. 

In general, we do not recommend to harvest alfalfa planted in the fall (late-summer really) in the same calendar year. Often there is not enough growth to warrant cutting. Alfalfa should be in bloom before it is considered established after planting. In some locations in NM, one cut may be possible when alfalfa is seeded in mid-August to mid-September. If absolutely necessary to harvest, this cutting should occur late enough that very minimal regrowth occurs. Even then, enough stubble should be maintained to help insulate the new plant crowns.

A note about spring-planted alfalfa: The proper fall management mentioned above is particularly critical for 1^st year alfalfa that was planted in the spring. Most producers will have harvested the spring-planted alfalfa at least twice, perhaps as many as 4 times, in the establishment year, depending on how early it was planted and location. While this is understandable, it is stressful on the new plants still trying to develop an adequate root system, and first harvest should be delayed as long as possible (80+ days after planting, or 50% bloom). It is tempting to get as many cuts as growth will allow in the establishment year, but too many and cutting too early can severely damage the stand. Oftentimes, this isn’t noticeable until the following spring or summer after dieback due to weakened plants succumbing to drought or heat stress. Grazing in fall/winter of the seeding year only exacerbates the stresses put on the plants in summer after a spring plant.

Sorghum forage toxicities in the fall (Sorghum x sudan hybrids, sudangrass, etc.)

(Excerpt from: NMSU Guide A-332, Sorghum Forage Production in New Mexico, available at: http://aces.nmsu.edu/pubs/_a/A332/)

Sorghum grasses have the potential to be very toxic to animals consuming them, particularly late in the year. These include sudangrass, sorghum x sudangrass hybrids, forage sorghum, grain sorghum, and Johnsongrass. Two concerns that producers should be aware of are nitrate toxicity and prussic acid (hydrogen cyanide; HCN) poisoning. Both of these conditions can develop rapidly without much warning, and many times it is too late by the time the problem has been diagnosed. As a general rule, anything that suppresses or disrupts growth of leaves relative to root absorption (i.e., drought, overcast days, frost, low temperatures, shading, herbicide damage, hail, disease) could contribute to increased levels of nitrates and HCN in the plant. Excessive nitrogen fertilization may result in toxic forage as well, especially when combined with drought stress. As temperatures cool and as we experience frosts, growers need to be aware that sorghum forages pose a significant risk.

Nitrates, when converted to nitrites in the rumen of cattle, interfere with the ability of red blood cells to carry oxygen, and animals can die from asphyxiation. Symptoms of nitrate toxicity appear as rapid/labored breathing, staggering and collapse, muscle tremors, diarrhea and frequent urination, and a distinct chocolate-brown coloration to the blood. Caution is warranted when nitrate levels in forage exceed 2,500 ppm (0.25%) on a dry matter basis (Table 2). In general, nitrate levels are higher in the stems than in leaves, especially the lower stem. Nitrate toxicity is more likely if stocking rates are such that cattle are forced to graze stalks or when cut or chopped forage is cut low to the ground.

Table 2. Nitrate Concentrations and Respective Management

Nitrate level (ppm, DM basis)	Status	Comments
0 - 2,500	SAFE	Generally considered safe to feed.
2,500 - 5,000	CAUTION	Generally safe when fed with a balanced ration. Limit to 1/2 of total dry ration for pregnant animals. Do not feed with other non-protein nitrogen supplements. Caution with young animals.
5,000 - 15,000	DANGER	Limit to 1/4 of ration. Possible reproduction problems and milk losses.
Over 15,000	TOXIC	Do not use in free choice feeding program. Should be ground and limited to 15% of total ration.
Source: Ball et al. (2001).

Prussic acid is formed from naturally occurring cyanogenic glycosides in the plant and is readily absorbed in the bloodstream, leading to respiratory problems and eventual death if high enough concentrations are consumed. It is extremely fast-acting and toxic in low levels. To complicate matters, HCN poisoning is characterized by symptoms similar to nitrate poisoning and, in some situations, both conditions may be present at the same time. However, they are different conditions. Blood taken from an animal with only HCN poisoning will not be brown, but will instead be a bright cherry-red color. Prussic acid exceeding 600 ppm (0.06%) on a dry matter basis should be fed sparingly (Table 3). Young, tender growth often contains more HCN than mature growth, and plants must be at least 18 inches tall before turning animals out on pasture. Prussic acid levels tend to be greatest in leaves.

Table 3. Prussic Acid Concentrations and Respective Management

Prussic acid content (ppm)		Comments
As fed basis	Dry matter basis
<200	<600	Safe to feed.
200 - 600	600 - 1,800	Potentially toxic. Should be fed at a restricted rate.
>600	>1,800	Potentially very toxic. Dry, ensile, allow to mature prior to feeding or grazing. Retest before feeding.

Waiting at least seven days after a stressful environmental condition (e.g., drought or frost) before allowing animals to graze is recommended; sorghum forages should be tested before any type of grazing or feeding. In the fall when light freezes followed by warmer days is common, grazing should be delayed after the last green plant material has been frosted (at least a week after heavy freeze event). Haying toxic forage will not reduce nitrate levels, but because HCN converts to a gas, it will deteriorate as hay is dried down. As a result, prussic acid poisoning is more of a problem in grazing situations. Nitrates, on the other hand, will persist in hay and greenchop, and high-nitrate hay should be limited in the animal's diet (Table 2). Ensiling forages will reduce nitrates by about 30 to 50%. Hungry cattle should not be given potentially toxic hay or turned out to graze suspect pastures.

It is recommended to not allow horses to graze any of the sorghums on pasture as prussic acid poisoning and urinary tract problems (cystitis) are likely to develop. Although HCN breaks down in hay, feeding sorghums to horses is discouraged. Due to the difficulty of drying thick stems, sorghums are often baled moist, leading to mold production and subsequent respiratory problems in horses. For more information on nitrate toxicity and prussic acid poisoning, consult Cooperative Extension Service Guide B-807: Nitrate Poisoning of Livestock and Guide B-808: Prussic Acid Poisoning in Livestock, both available at http://aces.nmsu.edu/pubs/_b/. Contact your local Cooperative Extension Agent for information on sampling and testing procedures for sorghum forages.

 

____________________________________, Mark Marsalis, Extension Forage Specialist—New Mexico State University is an equal opportunity employer. All programs are available to everyone regardless of race, color, religion, sex, age, handicap or national origin, New Mexico State University and the U.S. Department of Agriculture cooperating.