by Joel Bagg, Forage Development Specialist & District Sales Manager, Quality Seeds Ltd
New forage seedings are underway as weather permits, and some farmers are finished. Alfalfa and other forage species have generally over-wintered very well. There are only scattered reports of alfalfa winterkill, winter injury and alfalfa heaving, mostly on older stands. Minimal winterkill issues (<10%) have been reported in the normally higher risk area of the Ottawa Valley. There has been some alfalfa winter injury in fields that broke dormancy in December and early spring. While this does not necessarily kill alfalfa plants, new crown buds have to be formed, resulting in uneven growth and reduced yields. Some fields harvested in late-fall are showing delayed green-up and growth this spring.
Spring Forage Fertlity Considerations
1. Nitrogen Application To Grass Stands
Nitrogen can dramatically increase the yield of grass stands, as well as forage protein levels. In pure grass stands or in injured mixed stands that have good grass content, an application of nitrogen can easily paying for itself. Optimum rates depend on the cost of nitrogen, anticipated value of the hay, thickness of stand, moisture conditions, and whether it is pasture or hay. A thumb rule is to apply 45 lbs/acre of nitrogen for every tonne of expected dry matter forage yield. The first application of nitrogen for hay should be made at green-up, as soon as possible in the spring when soil conditions are suitable.
Figure 1 - Orchardgrass response to nitrogen - no N applied (bottom left) versus N applied (top right)
2. Sulphur Deficiency In Alfalfa
There are more and more situations where there are yield responses from applying sulphur (S) to alfalfa. Some field trials have had quite dramatic yield increases, but there are others that have shown no response. S deficiencies are more likely to occur on low organic matter soils, and soils that have not had a recent manure application. S deficient plants will be spindly and light-green. Tissue testing of alfalfa (at mid-bud to early-flower stage) is a diagnostic to determine S deficiencies.
A general thumb rule for S application on alfalfa is 5 lb/ac per ton of dry matter yield. Sulphur must be in the sulphate form to be taken up by the plant. Sulphate-S should ideally be applied in the spring at green-up to improve plant utilization, minimize losses due to leaching, and receive the first-cut yield boost. Common sulphate fertilizers used include ammonium sulphate (34 - 0 – 0 – 24), sulphate of potash magnesia (Sul-Po-Mag or K-Mag) (0 – 0 – 22 – 20) and calcium sulphate (gypsum) (0 – 0 – 0 – 17). Elemental sulphur (0-0-0-90) consists of finely ground sulphur that has been pelletized. It is much cheaper than sulphate, but must be slowly converted by oxidation to sulphate by soil bacteria before plants can utilize it. Applying elemental-S bulk blended with other fertilizer in the summer or fall, rather than sulphate in the spring, provides a cheaper, longer term S source, but it is not immediately available to the plant. (Sulphur On Alfalfa http://www.qualityseeds.ca/blog/7-sulphur-on-alfalfa)
3. Spring P & K Application?
Managing forage phosphorus (P) and potassium (K) fertility by soil testing, and commercial fertilizer or manure application is important to both higher yields and stand longevity. If a soil test is below 120 ppm K, you can expect a yield response from top-dressing potash on established stands. Topdressing of P and K (and possibly boron) is usually done when soils are fit in the summer or early fall immediately following a cutting in order to stimulate regrowth and increase winter hardiness. Spring applications of P and K on alfalfa are usually not recommended in order to avoid luxery consumption of K and physical damage to alfalfa crowns, and also because research suggests there is no yield benefit over summer or fall applications. The exception may be where P and K soil tests are very low and the fertility limitations outweigh the risk of stand damage with spring application.