Wondering if your forage stand could use an application of fall fertilizer this year? Government of Manitoba Land Management Specialist Marla Riekman has some tips for diagnosing your field.
N-P-K-S #
When looking at fertilizing your forage stand, you’ll largely be looking at amounts of nitrogen (N), phosphorus (P), potassium (K), and sulphur (S). Different soil types have different nutrient needs — Riekman noted that sandier soils will likely need more K and S than other soils.
Keeping an eye out for deficiency symptoms (chlorosis or yellowing of plants for an N deficiency, stunted plants for a P deficiency, small white spots on plants for a K deficiency, and pale green to yellow discolouration of plant leaves for an S deficiency) is a good way to know when a fall fertilizer application may be needed.
Soil Testing #
If you think your field may be in need of nutrients, the best way to know for sure is with a soil test. Regular soil testing is the number one way to know what your field needs and when. Riekman said “regular” doesn’t mean testing every year — a soil sample every two to three years will help you to determine what your crop removal rates are and if your expected fertilizer application matches that or not. A test will also come back with recommendations from the lab, so you can combine those with the results to make a plan.
Some general fertilizer recommendations for forages from the Government of Manitoba are:
- Nitrogen: Apply 90 to 110 lb/acre to established stands when forage price is high and soil moisture is sufficient.
- Phosphate: Apply 20 to 30 lb/acre to established stands.
- Potassium: Apply 30 to 60 lb/acre to established stands on sandy-textured or organic soils.
- Sulphur: Apply 15 lb/acre on well-drained soils and grey wooded soils.
Riekman said the general recommendations are just a guideline, and growers should compare them to the results from their soil tests to figure out their exact rate. Regular soil tests also allow growers to monitor their field’s levels on an ongoing basis, which helps to understand field history and future.
Factors to Consider #
When it really comes down to it, figuring out your fertilization rate depends on your nutrient removal or uptake rate.
Field history plays a large role in determining which nutrients your field may need. Understanding the field’s crop removal rates will help growers to stay on top of their crop needs.
If the field has a mixture of legumes and grasses, that can also affect nutrient needs. Legumes can fix their own N, so they don’t require nitrogen fertilizer. If you’re spreading manure on the field, it’s likely getting plenty of nutrients from that, and will end up needing a lesser application as a result.
When harvesting hay you’re removing whole plants from the field rather than just the seed, so more nutrients will be needed in the field in its entirety as all uptake is now gone. Riekman said this can also require a higher rate of fertilization for matching that removal rate.
“If you’re fertilizing every fall, you may be doing a blanket application rate based on your best estimation as to what that crop requirement will be,” she said. “But having that check-in (soil test) is really important because you’re then able to monitor targeting that maintenance ability.”
Weather conditions can also affect your nutrient needs. Drier soils, as much of Western Canada has seen in recent years, may mean lack of soil moisture, which can induce deficiencies in certain nutrients. Riekman said if you’re seeing patches with deficiency symptoms, the best practice is to take tissue tests from the poor plants and good ones and then take corresponding soil samples from each area to determine why you’re seeing those symptoms and what you can do about them.
