This is the third of a ten part series of posts chronicling core concepts from a class we are taking. Further details and links to walk through the series can be found on the class 1 post.
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.
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.
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.
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.
The reading for next week is taken from Chapter 7: pages 195-206.