Fed hay builds soil fertility

Mike Rankin

MAKING hay is an expensive process these days. Harvest costs are up because of the current high cost of diesel fuel, labor, equipment repairs, and machinery costs. The price of fertilizer has also risen substantially over the last couple of years. When hay is harvested, we are taking off a relatively large volume of nitrogen and soil minerals. Hay typically removes more than 80% of the minerals in the above-ground portion of the plant.

If we just think in terms of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S), each ton of hay removed contains 30 to 50 pounds of N, 5 to 7 pounds of P, 30 to 70 pounds of K, and 4 to 5 pounds of S. Using current commercial fertilizer prices, the value of N-P-K-S in one ton of hay is $85 to $90. Add in the calcium, copper, cobalt, zinc, and other minerals, and we find about $15 added value based on livestock mineral supplement prices. For the first time in my life, a ton of hay contains over $100 of N-P-K-S and mineral value.

While that is a scary number from the cost of production standpoint, there are some other considerations of value.

In the eastern half of the U.S., as of September 2022, there are still many areas where a ton of hay can be purchased for less than $100 per ton. Think about that for a minute. If you purchase hay at that low price, you are bringing in $100 worth of livestock feed, but you are also bringing in $100 worth of fertility for your farm. You are either getting your feed for free or your fertilizer for free.

In the western half of the U.S., it is hard to find hay for less than about $150 per ton and much is selling for $200 to $300 per ton. Using hay for fertility building in the West is not nearly the bargain that it is in the East. When we decide to buy hay to feed our livestock, we need to be factoring the fertility value it brings to our farm or ranch.

To capture that fertility value, make sure you are feeding it in a strategic way. I have long advised my consulting clients to get into a soil testing routine whether they ever plan to buy an ounce of fertilizer or not. We use soil testing as a tool to guide where hay should be fed out. Feeding hay only has fertilizer value if it is fed in an area that will benefit from the added nutrients.

There is also the consideration of how much hay should be fed across an area for proper nutrient management. Because of the high N-P-K content of hay, we need to have target feeding amounts to avoid nutrient overload. I have seen many bale-grazing situations where excessive amounts of nutrients are being applied through nonplanned feeding regimes.

It is important to understand the N and mineral content of the hay you are feeding and how the animal retains or excretes those nutrients. Nitrogen excretion is greater than 90%. Almost all other minerals are greater than 90% with K excretion being around 99%. Very little of the mineral nutrients contained in any kind of feed is actually retained in the animal’s body.

When the protein content of the feed is appropriate for the animal’s requirement, N excretion is split evenly between urine and feces. If the protein content exceeds the requirement, all excess N passes through urine. A 14% crude protein hay contains about 45 pounds of N. If N retention is 10%, that equates to 40 pounds excreted. Based on the animal’s requirement, there may be an equal urine-feces split, or there may be somewhat higher urinary output. Remember, urinary N is highly soluble and almost immediately available for plant uptake. Fecal N is a slow-release source of N.

What is a reasonable available N application rate in the winter months?

That is a serious consideration from a nutrient loading standpoint. Let’s say our target is 100 pounds of N per acre. Knowing our hay is providing 20 pounds per ton of urinary N tells us we should be feeding no more than 5 tons per acre. If our bales weigh 1,000 pounds each, feed no more than 10 bales per acre.

If bale grazing with bales set on 40-foot centers, that would result in 27 bales per acre being placed, or nearly three times our maximum number to avoid N overload in the feeding area. This is why we really need to feed hay in a thoughtful and planned way. While we should be trying to manage nutrients in a way that does not harm the ecosystem, we also should be motivated to get that fertility put on as many acres as possible. That is where the value of the nutrients in the hay is optimized. •

JIM GERRISH

The author is a rancher, author, speaker, and consultant with over 40 years of experience in grazing management research, outreach, and practice. He has lived and grazed livestock in hot, humid Missouri and cold, dry Idaho.

LTHOUGH we’re heading into the winter months, looking ahead to spring and being prepared to ward off potential pasture problems is something that should be on every producer’s mind. In particular, the following three issues can be tough to recognize unless you know what to look for.

Also called grass staggers, grass tetany develops from an imbalance of magnesium and potassium. Rapidly growing grasses take up potassium and other nutrients from the soil quickly. If the balance of potassium (high) to magnesium (low) becomes too great and cattle are unable to mobilize magnesium stores from their skeletal system, they may develop grass tetany.

In many cases, cattle are found dead with signs of convulsions. Less severely affected animals may become ill over two to three days, exhibiting lower milk output and appearing uncomfortable and nervous. They may stop grazing, stagger, and develop twitches in their face, ears, and flank. If aroused, cattle act erratically and run with an altered (staggered) gait — hence, “grass staggers.” Eventually, they will collapse and suffer convulsions, facial twitching, foreleg paddling, and death within a few hours. Older animals, especially in early lactation, are most susceptible, although any animal can be affected. Blood samples will indicate low serum magnesium.

If caught early, cattle can be treated with an injection of calcium and magnesium. There is a risk of causing heart failure if this treatment is administered incorrectly, so it’s best performed by a veterinarian.

Grass tetany can be prevented by supplementing cattle with extra magnesium during potential danger periods. This is accomplished through providing a high-magnesium lick or switching temporarily to a high-magnesium mineral supplement. Magnesium boluses are available, although they are more labor intensive.

Magnesium, in some forms, can be bitter and unpalatable, so make sure that the form being used is consumed by the cattle. Start providing magnesium before the first rapid growth of grass begins and continue providing it until growth slows. Finally, grass tetany is rarely seen in pastures that include legume species.

There are several plant species known to accumulate high levels of nitrate under stressed conditions. These include johnsongrass, pigweed, kochia, lambsquarters, and some crop species such as sorghums and sudangrass. Plants naturally take up nitrogen from the soil and utilize it during photosynthesis. Anything that disrupts that normal cycle puts plants at risk for accumulating high levels of nitrate.

Young, growing plants are most likely to accumulate nitrates, especially if subjected to a stress event such as a late frost. The highest concentrations of nitrate are typically found in the lower one-third of the plant stalk. Drying the forage for baling does not reduce the level of nitrates significantly, although ensiling may cause a 30% to 60% reduction, if allowed to go through a full fermentation.

When consumed by cattle, nitrates (NO3) are converted to toxic nitrites (NO2) in the rumen. These nitrites are absorbed into the bloodstream where they bind hemoglobin (the compound in the blood that carries oxygen), turning it into methemoglobin. As a result, cattle are unable to get adequate oxygen to their tissues or organs and essentially suffocate.

Common signs of nitrate toxicity include blue-tinged membranes, excessive salivation, urination, and difficulty breathing, as well as the characteristic chocolate-colored blood. As poisoning progresses, cattle become weak. Moving cattle around may exacerbate symptoms or cause death because the movement of muscle requires oxygen. Pregnant cattle may abort even at low, nonlethal doses of nitrate.

Poisoning from nitrate can occur quickly, and often cattle are simply found dead. If cattle are diagnosed early, they may be treated with methylene blue.

Plants or forage suspected of being high in nitrate can be tested, as can water sources. Labs may report nitrate levels in different ways, as nitrate (NO3), nitrate-nitrogen (NO3-N), or potassium nitrate (KNO3). Be sure to look at the correct recommendation of safe levels for your lab’s reporting method. Horses, as hind gut fermenters rather than ruminants, are less susceptible than cattle to nitrate toxicity.

Also known as hydrogen cyanide (HCN), prussic acid is similar to nitrate poisoning in that it is usually preceded by some sort of plant stressor, such as a frost or drought, and it affects the cattle’s ability to utilize oxygen. Rather than preventing hemoglobin from binding oxygen (as is the case with nitrites), HCN — formed in the rumen from cyanogenic glycosides present in the plant — acts to prevent tissues from utilizing oxygen.

Cattle exhibit difficulty breathing, foam at the mouth, and become progressively weakened, but they are most often found dead. The blood of affected cattle is a bright cherry red color as it becomes saturated with oxygen that the tissues cannot uptake. The rumen is noted to release a smell similar to bitter almonds. Treatment is possible with sodium nitrate and sodium thiosulfate; however, a veterinarian should be consulted to ensure a differential diagnosis from nitrate toxicity.

Johnsongrass and other sorghums are the most likely plants to produce HCN under stressed conditions, especially when there is a high nitrogen-to-phosphate ratio in the soil Unlike nitrates, prussic acid does break down when forages are dried, so hay is rarely a concern for prussic acid poisoning. •

ASHLEY WRIGHT

The author is an area assistant livestock agent with the University of Arizona based in Cochise County.

Alan Franzluebbers

WE’VE reached the time of crisp fall mornings, and the grass is green all around — well, as long as it’s been raining in your neck of the woods! Throughout much of the eastern U.S., cool-season forages are back to life, and you might be offering succulent grass for the herd. But what about your winter forage needs? Winter grazing requires deferment in the fall so that cool-season forages can be stockpiled. Fresh, grazed forage is often more cost-effective than feeding hay throughout the long winter. Stockpiling for winter grazing is easy on the pocketbook but requires some planning.

Preparing for winter grazing means evaluating the condition of pastures at the end of summer. Is tall fescue a major component of your pasture? Have summer annual species overtaken the pasture? Has the pasture been adequately fertilized and limed in the past? Answers to these questions might determine whether the pasture is a good candidate for fall stockpiling.

You’ll know if tall fescue will be present in the fall even if it was not visible at the end of the summer. Just think back to last fall or spring. Tall fescue can go dormant in the summer with the heat and extended dryness. If the pasture is overgrown with crabgrass or other smothering forages, then a late summer clipping will help expose the young tall fescue shoots to the sun and help them get a good start.

Many agricultural advisers will tell you that you need to fertilize the pasture with 40 to 100 units of nitrogen per acre to stimulate growth in the early fall. However, if there is insufficient moisture during a dry fall, that nitrogen may be wasted because conditions aren’t conducive for growth. Another reason why nitrogen might be wasted is because the soil may be providing enough nitrogen for abundant fall growth from the decomposition of organic matter.

Decomposition occurs daily but gets rejuvenated following the hot and dry summer when bright sunshine still heats the ground and precipitation becomes more frequent to energize the microorganisms living in soil. Those soil bacteria and fungi get to work consuming the roots, plant residues, and feces that were deposited in and on soil. They release the carbon fixed in plants back to the atmosphere as carbon dioxide to complete a natural cycling.

In the process of decomposing these organic carbon compounds, soil microorganisms also release mineral nitrogen contained in these protein-rich plant materials. Mineral nitrogen is composed of ammonium and nitrate — the very elements that forages need to make abundant growth when there is sufficient moisture and a suitable temperature.

How would you know if there’s sufficient nitrogen to satisfy plant growth requirements? Well, you could get a soil test. If you need 100 units of nitrogen, and a soil test indicates only 10 units are available at the time of sampling, then you might logically think you need to apply 90 units of nitrogen fertilizer. But this is only a part of the story.

If you asked for a soil test to determine the total amount of nitrogen, including both inorganic (mineral) and organic nitrogen, then you might be surprised if you get the report with 1,000 units of total nitrogen present per acre. Fortunately for us, not all of the organic nitrogen is available to plants in our lifetime, so that we can savor this ecosystem reserve of nitrogen for longer.

But your most important question to ask might be: “How much nitrogen will be available during the fall stockpile period?”

Soil testing labs would have to incubate a soil sample for several weeks to determine the actual amount of mineral nitrogen released by those microorganisms consuming organic matter in soil. This process is called nitrogen mineralization, or the conversion of organic nitrogen into mineral nitrogen (ammonium and nitrate).

Fortunately, we’ve discovered a quick method to estimate the amount of nitrogen mineralized from soil. This is from the flush of carbon dioxide released during a three-day period following rewetting of a dried soil. The burst of soil microbial activity following rewetting of dried soil, also known as soil-test biological activity, gives a fairly accurate snapshot of the long-term rate of soil microbial activity.

Soil microbial activity is strongly associated with nitrogen mineralization potential. Different soil types can have different inherent nitrogen miner-

Figure 1. Comparison of two fields with different management histories

Forage yield @ 15% moisture (lb/acre)

5,000

4,000

3,000

2,000

1,000 Soil-test biological activity = 150 mg/kg/3d

2,331 2,830 3,070 3,185

Economically optimum N rate of 69 lb N/acre Baseline cost of N fertilizer

0

0 40 80 120

Nitrogen fertilzer rate (lb N/acre) Forage yield @ 15% moisture (lb/acre)

5,000

4,000 3,234 3,377 3,465 3,519

3,000

2,000

1,000

0

0 Economically optimum N rate of 0 lb N/acre Baseline cost of N fertilizer

Soil-test biological activity = 517 mg/kg/3d

40 80 120

Nitrogen fertilzer rate (lb N/acre)

alization potential, but importantly, historical management can also greatly influence the nitrogen mineralization potential of a soil (see graphs).

Crude protein in fall stockpile is often more than adequate for pregnant beef cows in winter. Soil microorganisms are providing a service to you and your cattle herd by recycling nitrogen in the pasture back to this stockpiled forage. Are you ready to appreciate and take advantage of this process? • For information on how soil-test biological activity can influence the amount of nitrogen needed to optimize economic return of fall-stockpiled tall fescue, refer to bit.ly/HFG-Nrate.

ALAN FRANZLUEBBERS

The author is a soil scientist with the USDA Agricultural Research Service in Raleigh, N.C.

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Mike Rankin

FORAGES are the main ingredients used in dairy cattle diets. Producing high-quality forages is vital for dairy profitability and sustainability. As such, many research trials about this topic are presented yearly during the annual meeting of the American Dairy Science Association, and this year was no different. The objective of this article is to describe and discuss some of the forage research presented. For full disclosure, these are only a few of the many research trials presented and were hand-picked to represent different areas within forage research.

analysis: Regardless of your role within the forage industry, you’ve probably had to submit samples for nutrient analysis or made decisions based on those results. Many farmers and nutritionists submit samples for analysis routinely. But when it comes to forage analysis, turnaround time, costs, and the reliability of the methodology used are all key factors in determining how to analyze forage samples. It is undeniable that analyzing forage samples via near-infrared spectroscopy (NIRS) is faster and cheaper than by wet chemistry methods. However, forage growers, dairy producers, and nutritionists always wonder “Is NIRS analysis as accurate as wet chemistry?” or “Can we rely on NIRS analysis for this specific crop or conditions?”

Researchers from Canada conducted a three-year study trying to answer these questions for first-cut legumegrass silage. Briefly, 202 samples were collected from Canadian dairy farms between 2018 and 2020, and subsamples were sent to a commercial laboratory for NIRS and wet chemistry analyses. No differences between methods were observed for crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and fat, but ash was slightly higher (1.6 percentage units) for wet chemistry than NIRS. The authors concluded that NIRS is sufficiently accurate for nutrient analysis of first-cut legume-grass silage.

Keep in mind that regardless of which method you pick, analyzing samples with the same method and laboratory allows for an apples-to-apples comparison and ensures the decision-making process is based on accurate information.

silage processing: Sorghum silage has been growing in popularity and is being fed by more and more dairy operations. But losing grain in the feces has been one of the biggest, if not the main, challenge faced by producers. A survey collected 53 sorghum silage samples from commercial farms between January and February of 2022. Samples were analyzed for berry processing score (the equivalent assay to kernel processing score widely used for corn silage but adapted for sorghum) and nutrient composition. Berry processing score (percent of starch passing through a 2.36-mm sieve) averaged 20% and ranged from 7.2% to 54.8%. These values highlight berry processing has been minimal in commercial operations. Although we cannot determine which factors are associated with these results, the most common factors impairing processing are maturity at harvest, harvester settings, and lack of monitoring.

Sorghum berry size is another factor compromising processing in sorghum silage. Because berries are small, even forage harvesters set with adequate chop length and kernel processors (based on corn silage standards) struggle to achieve high berry processing scores.

Research conducted in West Texas evaluated processing and starch digestibility of two sorghum hybrids, one with larger berry size and another with smaller berry size. Even though berry processing was slightly lower for the larger berry hybrid, starch concentration and digestibility were identical. Because berries were much larger for the larger berry hybrid, as expected, these results suggest perhaps larger berries were broken into more pieces to reach a similar score and starch digestibility. More research is required to better understand if larger berries will help achieve adequate processing.

size: Despite being available for several years, the undigestible NDF (uNDF) assay remains the new kid on the block regarding forage research and analysis. This method measures the amount of NDF undigested after a certain period (240 hours is the most common) of incubation in rumen fluid and is often used as a replacement for lignin.

Researchers from New York compiled data from seven feeding trials for a total of 22 diets to determine

the relationship between uNDF and performance. Forages included in those diets were corn silage, haycrop silage, timothy hay, and wheat straw. Increasing amounts of uNDF in the diet moderately lowered intake and energy-corrected milk production. But predictions of intake and energy-corrected milk were improved when physically effective fiber was combined with uNDF and used in predictions, highlighting the importance of fiber particle size in dairy rations.

A study from Brazil evaluated the physical effectiveness of corn silage particles. Researchers sieved corn silage through a Penn State Particle Separator (19 millimeters [mm], 8mm, and pan) and added particles coarser than 19 mm, between 8 and 19 mm, and finer than 8 mm to a basal diet. This study revealed particles between 8 and 19 mm were more effective at stimulating an adequate rumen environment than other fractions. This is because cows sorted against particles coarser than 19 mm. When formulating diets based on the 19 mm screen, evaluating sorting routinely is recommended. This study also confirmed the effectiveness of corn silage particles finer than 8 mm, but these particles were still less effective than coarser particles.

fermentation: Raising chop height is a well-known harvesting practice to achieve greater nutritional value at the expense of yield. When forage inventory permits, increasing chop height reduces lignin, NDF, and uNDF concentrations while lowering starch concentration and NDF digestibility. But raising the chop height also reduces moisture, which could affect fermentation.

Two studies evaluated this effect. The first study, conducted in Illinois, harvested brown midrib corn silage at 12 or 22 inches of chop height. Even though increasing chop height improved nutritive value, the lower cut silage had improved fermentation. A similar study, conducted in Wisconsin, compared conventional corn silage harvested at 10 or 25 inches in height. Nutritive value improved with higher chop, but total acids concentration was reduced. Both studies also evaluated different microbial inoculants and observed improved fermentation with inoculation.

Combined, these studies underscored that increasing chop height remains a great tool to improve nutritive value of corn silage when forage inventories permit. However, fermentation will be slightly less pronounced compared with lower cut silage and the use of a research-proven microbial inoculant is advised. •

LUIZ FERRARETTO The author is an assistant professor and ruminant nutrition extension specialist at the University of Wisconsin-Madison.

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by Gonzalo Ferreira

SEVERAL scientists have contributed enormously to the dairy industry during the past 50 years, and Dave Mertens might be at the top of the list. If you still need convinced of this reasoning, I invite you to consider the following question: Have you ever submitted a forage sample to a commercial laboratory to be analyzed? If the answer is “yes,” then it is likely Mertens’ work on forage analysis and dairy cattle nutrition helped guide which forage quality metrics are on the report and how they are derived.

During the 2022 annual meeting of the American Dairy Science Association, a symposium was held to recognize the contributions of Dave Mertens to the dairy industry. The following are some highlights of his influence on feed analysis.

The concentration of digestible energy of a feed is mainly determined by the concentration of fiber in the feed. This means that forages containing greater concentrations of fiber have less energy than forages containing lower concentrations of fiber. This relationship is explained by the fact that fiber is incompletely and nonuniformly digested by cattle. Conversely, the nonfibrous components of a feed are almost completely and uniformly digested by cattle. The message here is that the more fiber the forage has, the lower its energy content.

Before we get into the specific contributions of Mertens, it is important to offer some definitions. Let’s start by describing “fiber.” From a botanical perspective, fiber includes the structural components that support and give strength to the plants, and these components include pectin, hemicellulose, cellulose, and lignin, which are all contained in the cell walls.

From a ruminant nutrition perspective, fiber includes the structural components of the cell walls that are slowly digested in the rumen of the animal and only by the action of microorganisms in the rumen. These components include mostly hemicellulose, cellulose, and lignin of the cell walls (pectin is excluded). These three components are included in a term known as neutral detergent fiber, or NDF. Putting the pieces together, the next take-home message is that when the NDF concentration of a forage increases, the energy concentration typically declines.

In a forage laboratory, there are two major types of analytical procedures: theoretical and empirical. For theoretical procedures, a pure standard of the analyte exists — for example, a mineral like calcium or a specific molecule like glucose. In these theoretical procedures, you can subject a known amount of pure standard to analysis and assume success on the technique when the laboratory measures or “recovers” the total known amount.

In contrast, a pure standard does not exist for empirical procedures. The NDF procedure is an empirical method subjected to differing or misleading results depending on how the analysis is performed. There is no way to determine if a laboratory is running the analysis properly. This problem led to the challenge of developing a procedure by which laboratories can ensure they are performing the NDF analysis correctly.

In the early 1990s, no official method had been approved for determining the concentration of NDF in animal feeds, and this void gave laboratories license to modify the method arbitrarily, resulting in great variability in NDF concentration among labs. In addition, the lack of an official method was impeding commercial laboratories to obtain certification.

To directly tackle this problem, Mertens developed a research program at the USDA-ARS Dairy Forage Research Center in Madison, Wis., and fine-tuned the NDF procedure to reduce variability among laboratories. This procedure, known as the amylase neutral detergent fiber (aNDF) method, later became the reference method utilized by the National Forage Testing Association to certify commercial laboratories in the U.S. and around the world.

Mertens’ procedure was later accepted by AOAC International (formerly, the Association of Official Agricultural Chemists) as the official method to determine the concentration of fiber in all types of animal feed. In 2003, Mertens was awarded the Collaborative Study of the Year Award by AOAC, which stated, “This study is deserving of this award for its complexity and impact on the international agricultural community. The method truly deserves to become the much-awaited international standard for the determination of neutral detergent fiber.”

Mertens’ impact on the dairy industry is truly remarkable. Any ruminant nutritionist knows that at least two things are needed to formulate a ration, and these are knowing the nutritional requirements of the animals to be fed and knowing the nutritional composition of the feeds. The latter means that thousands of farmers and millions of cattle have been directly impacted by Mertens through forage testing for feed evaluation or in the ration formulation process.

To add further perspective, two of the commercial laboratories certified by the National Forage Testing Association have reached more than 8,683 stakeholders within the U.S. and 1,820 stakeholders throughout 49 countries since 2015. Also, through his work with the National Forage Testing Association, Mertens has contributed to the certification of at least 99 laboratories within the U.S. and 38 laboratories around the world.

Mertens has dedicated a great part of his career to improving laboratory techniques that have a direct impact on ruminant nutrition and cattle farming systems. For those who believe that being a scientist and working in a laboratory might be too far from having impacts on the farm, I invite you to remember Dave Mertens the next time you submit a forage sample for analysis. •

GONZALO FERREIRA

The author is an associate professor and dairy management extension specialist with Virginia Tech University.

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