Forage Fertility

Forage fertility is often a much neglected side of agriculture. Typically, forages are grown on marginal land, and often the goal for fertility is guided by how much the grower has spent each year on fertilizer in the past, or worse, “what Dad did.” Obviously, this has little to do with the requirements of the plants being fertilized, or what production goals may be. However, there are several reasons why it’s worth it to spend a little more time managing the fertility of forages.

  • Better yield
  • Better longevity of stand
  • Better feed quality
  • Better stand consistency of grass: legume
  • Better $$$ in your bank account!

Maintaining fertility in forage production means growers will spend less on mineral supplements for their cattle. Higher quality feed commands higher prices from buyers, if a grower is selling hay off the farm. Keeping phosphate and potash levels up in the soil will ensure that the stand doesn’t die out prematurely, and will thus provide more profitable hay production for more seasons. In addition, proper fertility management will maintain the desired ratio of legume:grass in mixed hay stands.

Often in northwest Sk, we see hay fields lose most of their productivity after 5-7 years of production. In most cases, a soil test will confirm that the fields are severely deficient in phosphorus and potassium. These deficiencies are the main contributing factor for loss of forage production in our area. If we look at crop removal rates, it’s not hard to see why. One tonne of alfalfa (dry matter basis) removes 14 lbs of phosphate, and 60 lbs of potassium per acre in a season. Comparatively, a 60 bu/ac spring wheat crop removes 36 lbs of phosphate, and 63 lbs of potassium. Most growers wouldn’t hesitate to apply 20-30 lbs/ac of each nutrient in the spring for a wheat crop. Yet most annual hay fertility programs are only applying around 15 lbs/ac each of phosphate and potash, without the addition of manure. Deficiency, in this system, is guaranteed.

This creates a problem: if the field is to be taken out of forage production, a significant expense must be incurred to bring soil fertility levels back to where they can support a crop. An approach that maintains good fertility levels throughout the lifespan of the forage stand spreads costs over more years, and thus makes it more manageable. At the same time, growers are able to make more profit by growing higher yielding, higher quality feed each year, instead of seeing a steady decline in their production.

When determining fertility rates for forages, there are two things that should drive your decisions. A soil test, and the desired ratio of grass: legume in the stand should be the basis of forming a fertility plan. The higher grass content in the field, the more nitrogen fertilizer should be applied. As legumes dominate the stand, the focus for nutrition should shift more to phosphorus, potassium and sulfur. Generally, when legumes constitute more than 35% of the total plants in the field, nitrogen fertilizer is not required.

A soil test is a great starting point. With this information, you are able to make the best plan possible. Soil testing is especially important on manured land. Manure tends to get spread closer to where it is produced (ie. Fields close to the corrals), so far away fields tend to be lower in fertility. Soil testing helps identify fields where fertility is higher, and thereby may be able to save on synthetic fertilizer costs. Since manure is quite variable in composition, and is commonly applied to forage acres, a soil test is often the only way to determine what value manure has as a fertilizer. Whenever possible, test the manure itself to determine nutrient composition.

Legume plants have a higher requirement for phosphorus, potassium, and sulfur than grasses. In areas where soil fertility requirements and yield are high, the annual phosphorus and potassium application can be split to avoid salt toxicity. Under these circumstances, the first application should go on after the first cut of forage is made, and the remainder should be applied in early fall, just before root carbohydrate reserves are being built up for the winter.

A good practice is to band fertilizer ahead of seeding forages to ensure that the proper nutrition is in the  root zone in the year of establishment. Phosphorus and potassium move very slowly downward in the soil profile, so it’s important to make sure plants have access to these nutrients during early growth. Research has shown that following the initial sub-surface fertilizer with an annual broadcast fertilizer application is most beneficial.

Sulfur is an important constituent of plant proteins in legumes. It is also normally quite low in the grey-wooded and black soil zones. Sulfur in the sulfate form (Ammonium sulfate) is plant available, while elemental sulfur forms (0-0-0-90, for example) require some time to breakdown and convert to plant available forms. Generally, supplying some sulfur as ammonium sulfate, combined with elemental sulfur in the seeding year gets forage seedlings off to a good start. Thereafter, elemental sulfur applications can be made annually, and are generally more economical.

This is all well and good from a philosophical standpoint, right? So let’s put it to the numbers test. Without accounting for soil test levels, the average removal rate of 1 dry matter tonne (2204 lbs) of 100% alfalfa is 58 lbs N, 14 lbs P2O5, 60 lbs K2O, 6 lbs S. A mixed or 100% grass crop would have slightly lower removal rates. Assuming that alfalfa produces its own N, the fertilizer blend would be 8-14-60-6. At today’s fertilizer prices, that blend would cost $30/acre. The going rate in the area for a 1500lb grass/hay bale is around $60.  Applying that fertilizer blend should give you an extra 2204lbs/ac yield. That equates to an extra 1.46 bales/ac, for the cost of half a bale.



Fertility for Perennial Stands.$foragebeef/frgebeef.nsf/all/frg90 Accessed Feb 8, 2017.

Flore, Norm. Fertility Management in Forages. PDF article on Accessed  Feb 7, 2017

Bruulsema, Dr. T.W. 2000. Managing P and K Fertility for Forages. New & Views Publication published by Potash & Phosphate Institute and Potash & Phosphate Institute of Canada.


Written By: Amber Bernauer