Where we’d cut the grass before this season it was knee high, but the untouched areas were 5′ tall. That was a new experience for me, because if I cut more than half the brush-hog width at a time it would stall my tractor. You know the grass is too tall when it stalls a 20hp-at-the-drawbar about-100x-more-powerful-than-your-average-riding-lawn-mower tractor.

We made a lot of progress with the grass. If it stopped raining now, we’d be set. Ha! If! Anyway, I thought it was kind of funny to find so much grass wrapped around the PTO shaft of my tractor. The safety instructions on tractors tell you to never get off with the PTO running, or wear loose clothing around it or you can get snagged. Obviously, the grass wasn’t following the instructions.

Class started with a reminder that the 6th class would be held at the annual meeting of the Oregon Forage and Grassland Council at Benton County Fairgrounds on April 7th. The OFGC is a new group that brings together local representatives of the university extension, seed companies, forage producers, and ranchers for mutually beneficial discussion. Anyone who attends the Wednesday session (or shows up after 5pm for the trade show) can attend the 6th class. Follow the link above for details.

Manure and soil

One should not underestimate the value of animal manure as a fertilizer. Although less concentrated than chemicals, they are applied in larger volumes. As a fertilizer source, manures are generally examined on a “dry basis” to remove the effects of water on the values. Cow manure is 86% water, so a ton of cow manure contains 280 lbs of dry matter (DM). Of this, 11 lbs are nitrogen (N), 3 lbs are phosphorus oxide (P₂O₅), and 10 lbs are potash (K₂O). This works out to a fertilizer value of 4-1-4 (on a dry matter basis). Unlike purchased fertilizers, most the N, P, and K will actually be tied up in organic forms that must be broken down by microorganisms before they can be used by plants. This makes it “slow release”. Manure also adds organic matter to the soil, further boosting fertility. We also considered sheep manure, which is dryer at only 68% water. The fertilizer value when worked out would be 3-2-1. Sulfur and other trace minerals will also be found in manure. A common factor across manures is the relatively low N-P-K numbers (under 5%), with N generally being the most plentiful.

Soil science often concerns itself with soil types, studying the quantities of sand, silt, and clay in the soil structure and determining the effects of soil type upon productivity, water permeability, supported animal life, and so forth. You can find this information for your property on the USDA soil site. Our focus in pasture management is on soil fertility, so we can largely ignore the soil type for a simple reason: proper management can increase the land’s productivity by 4x making the effects of soil type largely negligible.

Handouts covered taking soil samples properly. We are going to turn in samples of our soil for the 7th class, to be available about a week later. Robin and I plan to also sample her mom’s garden soil, which has had high levels of horse manure applied to it for over 20 years. We want to test a theory about nutrient concentration in overly manured/composted soils.

Here’s an interesting note about soil tests. Soil tests are performed by first checking the pH, and then mixing the soil into liquid with the same pH. The nutrient levels reported are those which can enter the solution at its current pH. Even though there are certainly much higher total levels of various nutrients present in the sample, the only ones we are interested in are those that are immediately available to plants. This differs significantly from forage tests, which take a sample of vegetation, break it down, and report the exact amounts of various elements present in the sample.

Ruminant digestion

One third of all plant material on earth is cellulose, and none of it can be digested directly by any mammal. Among monogastric species (those having only one stomach: humans, cats, dogs, etc), cellulose is often referred to as “dietary fiber” as it passes through their digestive tract unchanged. Since cellulose is composed of tightly linked glucose molecules, any animal that could break it down for energy would obviously have a competitive advantage. Unsurprisingly, most common grazing species are such animals: cattle, goats, sheep, alpacas, llamas, bison, deer, and giraffes. These are collectively called “ruminants”.

Ruminants have multiple stomach-like organs and can regurgitate partially digested food and chew it further to improve digestion. Most ruminants have four organs responsible for initial digestion: the reticulum, the rumen, the omasum, and the abomasum. The rumen is the key to cellulose digestion, being a large fluid filled sac with a headspace of gas. Within this organ, large colonies of beneficial bacteria, protozoa, and fungi drive anaerobic fermentation of consumed vegetable matter. Enzymes produced by these microorganisms can tear apart the chains of cellulose, extracting maximum energy from fiber. The reticulum is a small pouch off the rumen that works in conjunction with it during rumination (cud chewing). The omasum receives the fermented food that leaves the rumen, and is a poorly understood organ with baffles involved in the absorption of water, certain minerals, and fatty acids. From the omasum, digesta (food being digested) travels to the abomasum which is a true stomach as found in other mammals. Here a highly acidic environment breaks down proteins (in both plant material and bacteria from the rumen), preparing it for the small intestines where amino acids and additional compounds will be extracted. Thus, ruminants achieve extremely efficient digestion both by absorbing the byproducts of bacterial fermentation and by digesting bacteria lost in the process.

Horses eat grass, so are they ruminants? No. Horses have a normal stomach and small intestines, but a greatly enlarged large intestines where bacterial fermentation occurs. This allows them to derive energy from cellulose in forage, but they do so less efficiently as they cannot chew their cud nor can they further digest the bacteria involved in the fermentation (it simply exits). This also makes horses more susceptible to toxins in their food (such as molds), because they do not have the initial fermentation stage which neutralizes many harmful compounds.

Total Digestible Nutrients (TDN)

The study of ruminant nutrition is really the study of how animals derive energy, protein, vitamins, minerals, and water from forage. The first of these is energy, and the unit most commonly used to measure the energy level in feeds is TDN. This is an old metric, which roughly corresponds to the percentage of food by weight that “disappears” into the animal during digestion. If an animal eats 100 lbs of food and produces 28 lbs of manure, then the food has a TDN value of 72%. This is not how it’s calculated of course. In fact, it’s best not to think of it as a percentage. It’s just a score of relative nutrient value. Since TDN is based on the energy value of proteins and carbohydrates, and fats have 2.25 as much energy per gram, it’s possible to have TDN values well above 100. Pure vegetable oil, for example, would have a TDN value of 225. Here is a table of feeds and their TDN value:

From this table we can see that Oregon pastures in March/April are an extremely high quality feed. Pastures at this time of year can be hugely productive: cattle can gain 3 lbs a day and lambs can gain 3/4 lb per day. Finally, note that TDN is intended to report the actual energy that a ruminant can extract from the food. This is different from “gross energy”, which is the theoretical value of the feed as it is consumed (which, incidentally, is all that human nutrition measures). TDN applies to ruminants. Horses will have a different TDN score for the same feed.

Protein

Protein content is often listed for hay and other animal feeds. Measuring the exact protein content is difficult as there are literally 1000’s of different proteins present in most living things. Instead, a shortcut is used. Since all proteins are about 16% nitrogen (N) by weight, it is much simpler to just measure the N content of a substance and multiply by 6.25 (which is the same as dividing by 0.16). (Side note: Many seed meals intended as animal feed can be used as an organic fertilizer to supply nitrogen. Just divide the listed protein content by 6.25. A 30% protein animal feed is about 5% N.) Protein levels determined by measuring N instead of actual protein are known as “crude protein”. Here’s a table of feeds and their percentage protein:

Looking at this table raises the question: if the grass is 25% protein in April, why is it 9% protein when we’re making hay in June?

Pasture nutrition vs time

All of the above leads us to one of the most important diagrams in forage management. I’ve recreated it here to save myself from trying to describe it in words:

As the season progresses, forages convert more and more of their structure into lignin, which is indigestible even to ruminants. There is a knee point as the plants start to work toward setting seed. After this point (shown here in May), nutritional value drops precipitously at a rate of approximately 0.5 TDN per day. Protein levels drop at a similarly increased rate. So, if you experience an equipment failure in early June and have to postpone hay making by 3 weeks, the nutritional value of your crop falls by 10.5 TDN. That’s a huge decrease in value.

So, how do we work with this? There are many ways.

Cut the grass. The biggest impact can be had by cutting the grass (either by mowing, making hay, or grazing). Notice from the graph that the regrowth loses value much more slowly, by about 0.1 TDN per day. The regrowth produces more leaves and converts to lignin more slowly. So, that same 3 week equipment failure on the regrowth only causes a nutritional drop of 3 TDN. Much less significant. You often hear people make distinctions between first, second, and third cuttings. The cuttings are not intrinsically different, but often are from a practical standpoint. Late spring rains and rapid TDN/protein loss conspire to make the first cutting lower on both metrics. Similarly, drier weather and slower loss of TDN/protein means someone has to go out of their way to make bad hay on a second cutting. The third cutting behaves similarly.

Improve fertility/genetics. Another way to preserve nutrition is to delay the knee point. Improving the soil fertility reduces plant stress and can delay when they set seed. A more effective way is to select improved pasture species which go to seed much later. Paying for improved genetics is almost always worth the cost.

Grow more legumes. Increasing clover and alfalfa populations will improve late nutrition. The graph has a dotted line for legumes. Nitrogen fixing crops have a late season advantage and will generally not fall below 11-12% protein.

Grow a vernalized annual. Planting an annual in the spring such as Italian Ryegrass lets you break the rules for the first season. As it has no immediate plans to set seed, the TDN value of Italian Ryegrass remains constant for the first year. It will still dry out over the summer without irrigation, but will bounce back from dormancy in the fall at the same nutritional level.

Make balage. Making a fermented stored forage such as balage in May allows you to capture the higher TDN values available earlier in the season without having to wait for dry conditions to work.

Finally

Wow, that was an exhausting summary to write and I still have one more pending! The reading for next week is taken from Greener Pastures on Your Side of the Fence: Chapter 2 and Chapter 4.

This is of course but a short list of invasive species. All of these were brought to the U.S., either by accident or intent, where they found ecosystems that were poorly adapted to control their proliferation. Eventually, we can expect the populations of such exotics to balance out. Some local plants will develop a resistance to their attacks, and some local predators will develop a taste for them. Unfortunately, natural balancing is a slow process by human standards, so other solutions are attractive. One such solution is to intentionally import another species which will keep the exotic species in check. This is called a biological control.

Wait a minute … isn’t that how we got into this trouble in the first place?

Most scientists are understandably wary of biological controls. Ecosystems are big complex things, and it’s hard to be certain that there will be no unwanted side effects. In a recent post, I’ve mentioned the blackberry rust which is spreading across Oregon. Our forages class covered another case of biological control in Oregon, and a few days later we found an example on our property.

This is Tansy Ragwort:

It is a biennial plant native to Europe. Tansy contains high levels of alkaloids which cause irreparable liver damage and death in horses and cattle, but have no effect on sheep. It was first found in Oregon in 1922, and by the 1970s it was causing heavy losses in the beef and dairy industries. Sheep were used as a limited control, as they will readily eat the foliage, but a more effective solution was sought. From among the 60 insect species that feed on Tansy in it’s native ecosystems, 3 were approved for import into Oregon as biological controls. Of these, two have been extremely effective. The Cinnabar Moth and the Tansy Flea Beetle. The larvae stage of the Cinnabar Moth is the most high profile of the two, feeding exclusively on Tansy during the summer. You can at times barely see the plant for all the orange and black striped caterpillars. But if the moth larvae weakens the plant while it is trying to set seed, the Flea Beetle larvae truly kills it. The larvae stage of these beetles feed on the root systems of Tansy, killing many plants outright. Those that survive then become a food source for the adult form of the Flea Beetle. Both of these insect controls work well, because Tansy is their exclusive food source.

When we found this specimen of Tansy Ragwort growing in the disturbed soil of the chicken coop tracks, we looked at it very closely and …

Have at it little guys. This plant is for you.

Grass Identification

The first portion of class focused on identifying grasses based on unique attributes of their leaves, stems, ligules (collar that extends behind the shoot at a joint), and auricles (tiny arms that reach around the front of the shoot at a joint). We passed around small potted grasses and examined handfuls of recently cut grass. Class handouts include diagrams to identify many grasses based on their joint areas. All commercially available identification guides rely on the inflorescence (seed head) for identification.

Fertilizer

There has been a renewed interest recently in more efficient use of fertilizers. One driver of this was the 400% increase in fertilizer costs that occurred in 2008. This was caused by many factors including: increased price of oil, increased demand from India and China, and a China-imposed excise tax on urea exports of 100%. Although prices have fallen since then, many of these same driving factors are still present. (i.e. Expect fertilizers to continue to rise.)

Fertilizer concepts between chemical and organic farming are the same.

There are four core nutrients most considered by fertilizers: nitrogen (N), phosphorus (P), potassium (K), and sulfur (S). Of these, N and S most rapidly leach out of our soils. For forage crops and pasture improvements in western Oregon, amendments are generally made as follows. In late summer, while the ground is still dry and the grass dormant, lime may be added to raise the pH (up to 2 tons / acre). Elemental sulfur is generally added at this time too. Active pastures need about 30 lbs / acre of S each year. In early fall, when the grass is starting to awaken from the first rains, phosphorus and potassium are added (as needed based on soil tests). In Oregon, P and K do not run off our soil. The Midwest is known for P runoffs, but confined animal systems in that area have raised soil levels of P to 300 ppm or higher. Pastures in Oregon are doing well if they can reach 20 ppm. Nitrogen is the most volatile of fertilizers and applications of chemical N (such as triple 16 or urea) last only 60 days. Thus, N must be applied as a series of smaller doses that correspond with periods of greatest grass growth. These times are: October for fall growth, February for early spring growth, April for late spring growth, and July for late summer growth if irrigation is available.

Timing the first N application of the year is important to maximize growth. The T-SUM 200 method of determining this application date was developed in Great Britain and found to work well in our maritime climate. One of the students in our forages class has developed a web based calculator for this date, which you can find here. In Oregon, the T-SUM 200 date generally corresponds with the first Daffodil bloom.

Organic Matter

Soil is comprised of two broad categories of particles: minerals and organic matter. Minerals are bits of clay, silt, and sand derived from rocks. Organic matter is less well understood, but it is primarily much smaller carbon-based particles derived from the remains of living things. Adding compost and manure slowly increases the organic matter. Soil tests will report an organic matter (OM) percentage, and in western Oregon this number will be in the 5% to 20% range. (This is much higher than is typical for most of the U.S.) Since nutrients available to plants are found on the surface of soil particles, soils with smaller particles (and thus greater surface area) tend to support greater fertility. Soil tests and most soil research is based on low OM levels. Soils with greater than 6% OM tend to break the rules.

In addition to the fertility storage, organic matter provides growth surface for large populations of beneficial bacteria, fungus, and protozoa. The greater the organic matter content, the more this living mass alters the soil behavior. Tests in southern Oregon in high OM soils showed that grass still had boosted growth rates from nitrogen fertilizer a full year after it was applied. (See previous declaration that N only lasts 60 days in the soil.) In this case, high bacterial populations were being fed by the nitrogen and holding it for plants. Even rules about pH requirements for certain plants become less certain as OM levels increase.

Annual Ryegrass

Lolium multiflorum has the potential for explosive growth in winter and early spring. It’s an aggressive seeder and responds well to fertility improvements. Annual Ryegrass is often recommended as a first step in improving lost pastures. Applying 40 to 50 lbs per acre in the spring can produce a thick 18-month stand of grass on which the skills of pasture management can be learned without committing to a particular species mix. Woody suggests this might not be a bad long term strategy either.

Annual Ryegrass comes in two genetic forms: Diploid and Tetraploid. Tetraploids have twice as many chromosomes, which physiologically produces larger leaves, more sugars, fewer tillers, and higher moisture levels. Although sometimes used as a selling point, neither form is “better” than the other. They just provide more options.

Generic Annual Ryegrass found in unimproved pasture mixes is called ‘Gulf’. It is a non-certified variety that will set seed much sooner than modern certified varieties. (Class 4 explains why this is important.) Annual Ryegrass also comes in two forms regarding it’s behavior in setting seed: Westerwold and Italian. Westerwold varieties are a true annual. They will set seed in mid-summer regardless of when they are planted and thus provide only about 8 months of forage growth (if planted the previous fall). Italian varieties must experience vernalization (discussed in class 1) to start setting seed. If planted in the spring, they will produce vegetative growth during the summer and winter, and set seed during the next summer. This is the better variety for spring planting when maximum forage production is desired.

Finally

The reading for next week is taken from Chapter 7: pages 195-206.

Continue to class 4

Soil Acidity (pH)

The primary focus of this class was a review of soil fertility concepts, predominantly focusing on pH. Soil acidity, pH, is one of the most common factors which will be listed on a laboratory soil test. Two metrics will be provided, soil pH and pH buffer. Soil pH is the present acidity, literally it stands for “concentration of hydrogen (H)”. pH uses a logarithmic scale, which means that a change of 1.0 on the scale indicates a 10x change in acidity. So a pH 5.0 soil is 10 times as acidic as a pH 6.0 soil and 100 times as a pH 7.0 soil. Other commonly used scales that are logarithmic (10x per increment based) include audio decibels (dB) and the Richter scale. The pH scale ranges from a low of 1.0 to a high of 14.0. Neutral acidity is 7.0, which represents distilled water. Stomach acid is quite acidic, with a pH of 3.0. Lye (used in making soap) is very “basic” (the opposite of “acidic”) with a pH of about 13.0.

Rain water is somewhat acidic, usually about pH 5.7. From this we can immediately guess that areas with high rainfall (Oregon west of the Cascades) will have acidic soils and areas with low rainfall (Oregon east of the Cascades) will have basic soils. Most western Oregon soils have a pH between 4.8 and 6.0. Unfortunately, most pasture plants prefer a soil pH of 6.0 to 7.0.

Next we looked at a chart which showed how common soil nutrients are affected by pH. In general, most nutrients (nitrogen, phosphorus, potassium, sulfer, calcium, magnesium, iron, manganese, …) become less available as the soil moves away from a neutral pH (7.0) in at least one direction. Phosphorus is especially effected by pH. Changing the soil from 5.0 to 6.0 will double the availability of phosphorus to plants. This doesn’t “add” any phosphorus the ground, but at a more neutral pH more of the existing phosphorus will enter solution where it can be used by plants. If you tell a soil scientist that you only have $100 to spend on fertilizer, he will tell you to spend it on lime to fix the pH first!

There are other important minerals affected by pH. Molybdenum availability decreases with pH. This is indirectly important for sheep. Sheep are easily affected by copper toxicity, but uptake of molybdenum in their diet ties up the copper in their gut, preventing harm. As the pH goes down, they are more at risk from copper. (Molybdenum is a key element in an enzyme used by nitrogen fixing bacteria, so legumes do worse as pH goes down also.) Minerals don’t just become less available as pH changes. Some become too available. Manganese, for example, becomes more plentiful with lower pH, so many plant problems from low pH are caused by manganese toxicity.

What followed was a rather involved chemistry explanation for soil acidity and how it is neutralize by lime. The short answer is that lime (calcium carbonate or CaCO₃) raises the pH by means of a chemical reaction which produces water, carbon dioxide, and free calcium. Since calcium is a useful soil mineral, this is a simple and non-toxic way to fix pH problems, but how much do you apply?

pH buffer

As mentioned above, there are two pH-related metrics on a soil test. The second is “buffer index”, or “pH buffer”. This number is an indication of how resistant the soil will be to changes in pH. Sandy soils change pH easily. Clay soils respond slowly. Given a pH buffer value, you can consult a table and determine how many tons of lime are required per acre to raise the pH of the top 6″ of soil to a certain goal level. Note that pH changes are unfortunately not permanent, but should be considered a 4-6 year investment in pasture productivity. Rain will eventually return the soil to its original pH. Generally, no more than 2 tons of lime should be applied per year, and soil tests performed every 2-3 years to monitor the pH level. Lime is generally applied in the fall so that the reaction can work over the winter and the boosted pH be available for spring growth. Animals can still graze pastures after liming, as the mineral is often used as a calcium supplement in their feed.

In western Oregon, our goal should be to raise soil pH into the 6.0 range, but productive pastures can still be grown at lower levels. Many grasses, plaintain, and chicory will grow in soils as low as pH 4.9. Some legumes, such as red clover, can handle pH 5.5. Don’t plan on growing much alfalfa, which prefers a pH of 7.0 to 7.5.

Fertilizer concepts

Most people are familiar with the NPK numbers on the side of a bag of commercial fertilizer. For example, “triple 16″ available here in Oregon is written 16-16-16-6. The 6 is for sulfur, and is sometimes omitted. These numbers do not represent the percentage of each of those elements available in the fertilizer by weight. This is a common misconception. The “N number” does represent “percentage of nitrogen”, and the “S number” does represent “percentage of sulfur”, but the remaining two are different. The “P number” is actual “percentage of phosphorus oxide”, which is P₂O₅. Phosphorus comprises only 44% of phosphorus oxide by weight. The rest is oxygen. Similar, the “K number” is “percentage of potash”, which is K₂O. Potash is only 83% potassium.

Note that these definitions are by U.S. law, rooted in the history of how nutrients were once calculated, and no doubt kept in place by the fertilizer industry who wouldn’t want to rewrite 16-16-16-6 as 16-7-13-16-6. (Not very catchy is it?) Unfortunately, most topics in animal and plant nutrition will talk about actual weights of nitrogen, phosphorus, and potassium, while the fertilizers deal in these compounds containing the desired elements. To get around this ambiguity of expression, farmers will use the phrase “unit of”. A “unit of N” is a pound of nitrogen, and a “unit of P” is a pound of potassium.

Finally, a word of warning about fertilizers. Many chemical fertilizers can have an acidifying effect on the soil. This can drive down the pH, potentially lowering the availability of other minerals. Such fertilizers will be labeled with “equivalent acidity”. This value is the number of pounds of lime that should be added for every 100 pounds of fertilizer, to neutralize the acidifying affect. For example, adding 100 pounds of anhydrous ammonia (a highly concentrated nitrogen fertilizer used on factory farms) requires 148 pounds of lime to neutralize the acidity.

Mining the soil

Finally, we considered some numbers to reinforce the point, first presented last week, that selling hay off a field without restoring equivalent fertility was literally mining it’s nutritional value and reducing it’s future productivity. An average field might produce 2 tons of hay per acre. As the truck leaves your property with 2 tons of hay (3600 pounds of dry matter), it’s taking with it approximately:

• 72 pounds of nitrogen
• 8 pounds of phosphorus
• 36 pounds of potassium
• 8 pounds of sulfur

In general, the cost of replacing these minerals with fertilizers will exceed the profit from selling the hay. Famous pasture farming advocate Joel Salatin uses this to his advantage. His pasture-raised chickens are also fed a grain suppliment. Much of the nutritional value of this grain is then distributed onto the pasture in the form of chicken manure. This results in a net import of nutrients to his farm. Even if you aren’t importing feed, grazing animals are predominantly nutrient recyclers, not consumers. However, proper management is still needed to prevent animals from redistributing nutrients to areas of tree cover (where they rest and fertilize after grazing).

Finally

There was lots more I didn’t cover: grass characteristics, diversity of commercially available cultivars, lime sources, lime score, and use of selenium additives in Oregon. The reading for next week is taken from Greener Pastures on Your Side of the Fence: Preface, Chapter 1, and Chapter 3.

Continue to class 3

Well, quite a lot, actually. I’ve been interested in management intensive grazing ever since I read Gene Logsdon’s inspiring book All Flesh Is Grass. We only have about 3 acres on which we plan to raise sheep, and we’d like to maximize our pasture productivity for the health of our animals, to save money on purchased feed, and improve the long-term viability of our land. The ideas presented in that book showed me how much I didn’t know.

So, when I heard about a course being taught by Woody Lane Ph.D., a nationally known specialist in livestock nutrition and forage management, I signed us up. The class runs 10 weeks, every Wednesday night, and will feature some pre-class pasture tours and a weekend farm tour of 4 sites. It will cover plant identification, nutrition, growth habits, livestock grazing, storage (hay and silage), problems, and more. The information will be Western Oregon specific based on local research and trials, and that’s something we definitely can’t get from a book.

I’m taking extensive notes along with reading all the provided material and assigned chapters in the class reference, Greener Pastures on Your Side of the Fence, which I fortunately already own. I thought I would write up a summary of each class on our blog, for the benefit of those interested. I’ll include links to additional information where appropriate. This will not be a transcript of the class. I recommend reading the books cited in this post and looking for a similar course taught in your area.

Disclaimer: These posts are based on my notes. Although I strive for accuracy, there may be mistakes. Please verify information before using it to make important decisions.

Here’s a complete list of our class-related posts. I’ll update it as more are added:

• Class 1 : Pasture plants (this post)
• Class 2 : pH and fertilizer
• Class 3 : Fertilizer and organic matter
• Class 4 : Forage nutrition

We aren’t the only blog that’s posted notes from a Woody Lane pasture management session. Over at Collie Farm Blog, workingcollies has posted notes from a lecture at the KHSI Expo. You might want to check out her notes for a different perspective. I’m providing the links here, as I had a hard time finding them in sequence:

• What I Learned About Grass at the KHSI Expo: Part I
• What I Learned About Grass at the KHSI Expo: Part II
• What I Learned About Grass at the KHSI Expo: Part III
• What I Learned About Grass at the KHSI Expo: Part IV
• Last KHSI Notes on Grass: RCG in the Northwest

Class 1

Here’s the highlight from March 3rd.

The chemistry of plants

At their most basic form, plants use water, carbon dioxide, and sunlight to produce carbohydrates, specifically glucose. They combine glucose with nitrogen to produce amino acids. Amino acids are used to produce proteins, and proteins are used to grow the plan bigger to capture more water, carbon dioxide, sunlight, nitrogen, and so forth. Pastures are like vast solar panel factories. A well managed pasture is a solid mass of green, teeming with energy, but few of us have seen pastures like that. One problem is nutrition.

Plants need a variety of minerals to grow. The big three are potassium (k), phosphorus (P), and nitrogen (N), but sulfur (S), iron (Fe), copper (Cu), magnesium (Mg), manganese (Mn), and other elements are also needed. These must be present in the right proportions. Too much can be poisonous. Too little can affect the efficiency of growth. Most pasture plants have 6″ deep roots, so if the the minerals are deeper than that, they effectively don’t exist. Rain drives minerals such as nitrogen and sulfur deeper into the ground. Also, taking products off the land without paying back reduces the available nutrition. Consider this: every ton of hay removed from a field removes 40 lbs of potassium.

Types of pasture plants

There are three important groups of pasture plants: grasses, legumes, and forbs. Grasses are familiar to most people: perennial rye, timothy, orchard grass, johnson grass, bermuda, etc. Legumes are nitrogen fixing broadleaf plants such as: alfalfa, clovers, vetch, peas, beans, etc. Forbs are broad leaf plants that don’t fit in the other categories: brassicas, chicory, plantain. Yes, brassicas–radishes, turnips, rutabagas, and so forth–can be used as forages. Plantain apparently does very well in Oregon, with it’s deep tap roots and high levels of growth during the cloudy months of January and February.

Two types of grass

Grasses are divided into two types based on the first carbohydrate molecule they produce during photosynthesis. Most grasses produce a 3-carbon molecule, and are called C3 grasses (or cool season grasses). These have shallow roots and prefer cooler temperatures, with most growth occurring in the spring. They are easily stressed by lack of water, and generally go dormant in the summer. All the grain crops (wheat, barley, oats) are C3 grasses, as are most of the common lawn and pasture grasses.

The other group of grasses uses a modified chemical reaction to supercharge photosynthesis in hot weather, producing a 4-carbon molecule. These are called C4 grasses (or warm season grasses), and they are capable of producing explosive summer growth. These grasses are generally very water efficient, and can be properly timed in Oregon to fill in the dry summer months with useful forage production. Corn is the most famous of the C4 grasses, but also the least water efficient. Other species include sorghum-sudangrass, millet, and … wait for it … crab grass. Yes, crab grass can be a useful forage crop and has been tested in the Roseburg area of Oregon quite recently. Unlike most C4 grasses, it actively self-seeds (just ask anyone trying to keep a monoculture lawn), but has the potential to run-amuck without a well developed management technique. Warning: planting crab grass might get you tarred and feathered if you live in an area of grass seed production (much of Linn and Lane counties).

Some people will tell you that the grass only grows in Oregon for 4 months and then you have to feed hay the rest of the year, but this is entirely species and management dependent. The Oregon climate lends itself to forage production 365 days of the year.

Nitrogen fixation

As mentioned above, legumes have the unique ability to fix nitrogen. They do this forming a symbiotic relationship with soil dwelling rhizobia bacteria. The bacteria form in colonies called nodules, which are tiny white bumps on the plant’s roots. These colonies capture N₂ from the air, break the powerful triple bonds, and convert it to soluble nitrogen forms that the plant can use. This gives legumes a distinct competive advantage over other plants, as they can sustain growth in low nitrogen soil by tapping into the 78% nitrogen content of the air.

There are many species of rhizobia bacteria, and a specific species can partner only with specific legumes. If the right bacteria is not present in the soil, legumes will still grow just fine but they will use existing soil nitrogen instead of fixing it from the air. This eliminates the greatest advantage of planting them. When seeding with legumes, be sure to buy pre-inoculated seed or coat with the appropriate inoculant before seeding. Also, you should occasionally pull up plants to ensure that the nodules are present on the roots. Note that nitrogen fixed by a legume is not immediately available to other plants growing in the pasture. When the upper potion of the legume is cut or grazed, the roots will die back proportionally, leaving high-nitrogen plant material underground where it can break down and be absorbed by grasses and forbs.

Well, that’s all for my summary of the first class. We discussed many other things (basic grass identification features, the commonly misidentified rushes and sedges, yearly growth patterns, vernalization, classic varieties vs. cultivars, use of scientific names, and mycorrhiza), but I want to keep these posts to a reasonable length. Robin says she didn’t know there was so much to learn about grass. In reality, these 30 hours of instruction will only scratch the surface.

Continue to class 2