Fall fertilizer questions for 2018

September 26, 2018 – Issue 26

Question: After a couple of bad years, cash flow is tight. How can a farm reduce fertilizer costs while still keeping the door open for a good rebound yield?
Answer: (1) Soil sampling is often more valuable after a bad year because reserves could still be high. A soil test may show higher than expected carryover. Note that after a dry year, soil nutrient reserves may be concentrated a little deeper so test to at least 12” and probably to 24”. (2) With dry conditions, mineralization may have been reduced, so it could happen that soil test results are lower than expected. However, this means more nutrients may be available for mineralization with the return of moisture. (3) An in-crop top dress could be one way to reduce fertilizer application rates at seeding while waiting to see how the year shapes up. (4) Growers short on cash for fertilizer could also take advantage of the CCGA-administered Cash Advance Program, which provides advances of up to $100,000 interest free and up to $400,000 in total.

Question: A lot more fields were baled this year because of an overall shortage of feed. What will this mean for nutrient carryover?
Answer: Make sure soil test labs know that the straw has been removed. Knowing that nutrients from the residue will not be returned to the soil will influence fertilizer recommendations. Removal of residue might help with the availability of applied nitrogen because residue can tie up nitrogen as it breaks down. Removal of residue will reduce the amount of available potassium as most potassium (75%) taken up by the plant remains in the residue.

Question: What do soil test results tell me?
Answer: Soil tests provide a scorecard for most of the basic nutrient building blocks required to grow a crop. Tracking macronutrients like N, P, K,and S can help predict the levels of added fertilizer needed to meet your yield goal. Regular soil testing can also track trends and can indicate whether current practices are depleting the soil. Additional information available through the soil test on soil properties like pH, electrical conductivity (EC), cation exchange capacity (CEC), organic matter and micronutrients assist the grower in identifying soil limitations that may need to be addressed. Reading a soil test is a bit of an art, and definitely requires practice, so take advantage of the skills your fertilizer dealer, consultant or local agronomist have developed over time.

Question: Ammonium sulphate (21-0-0-24) can create challenges for handling and drill function (gumming). Do I have options for fall application of sulphur?
Answer: One option is elemental sulphur which should be applied in the fall because it needs time and moisture to breakdown and become available for next year’s canola crop. However, conversion rate to the available sulphate form is difficult to predict, so while more concentrated, elemental sulphur is a less predictable form of sulphur for canola cultivation. Read more about sulphur options and timing.

Question: I want to apply nitrogen in the fall to reduce the amount of fertilizer handled at the time of seeding. What is the best practice?
Answer: Apply fall nitrogen as close to freeze up as possible to balance two objectives: (1) allow soil to seal over the band (frozen soil may not seal) and (2) reduce losses due to high microbial activity in warm soils. Band urea at least 2” deep. For NH3 banding depth, Manitoba Agriculture soil fertility specialist John Heard recommends increasing the depth of the band if you are seeing a lot of gas or if you can still smell the gas strongly after applying it.Note that banding in wet soil conditions will increase ruts, and wet soils can also increase losses if the soil does not close well over the band. And banding in dry soils can also increase gassing-off losses because soil does not provide a proper seal on the band. Read more.

Have other fall fertilizer questions? Send them our way and we’ll try to answer them. The Canola Encyclopedia section on Fertilizer Management has lots of detail on products and timing.

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