Corn Nitrogen Questions 2022April 5, 2022 | Category: Agronomy |
There are a lot of wheels in motion this year when it comes to nitrogen management in corn. Here are some of the key questions: Question 1. If I have unlimited nitrogen supply, should I reduce N rates on corn regardless, because of high nitrogen prices? Answer 1: High nitrogen prices alone, are not a good reason for reducing N rates. Why? Because it is the ratio of corn price to nitrogen price that drives the N rate recommendation, not either of those price components individually. Table 1 outlines a case study to give some background on this question. Table 1. Case Study – Steghulk Farms: corn after wheat (straw removed), clay loam soil, 3000 CHU, 3.6 % soil organic matter, corn yield expectation = 212 bu/ac. All nitrogen applied as UAN, via preplant streamers then incorporated plus some additional UAN on the planter. Table details: Impact of corn and nitrogen prices on the most economical nitrogen rate recommendation. Table 1 points out that if corn prices remain flat at $7.50 and nitrogen prices spike upwards, then a reduction in nitrogen in the range of 25-40 lbs/acre is a good move. If you anticipate corn prices to surge in 2022 to $10, then even with high nitrogen prices the pullback in N rates might be better left in the 15-25 lbs per acre range. Question 2. If I have restricted nitrogen supply, how much yield will I surrender by applying less than the optimum economical N rate? Answer 2: My esteemed colleagues Ken Janovicek (University of Guelph) and Ben Rosser (OMAFRA) and I have all attempted to respond to this question. Fortunately, we have all approached the question from different angles. I won’t bore you with the details, but the good news is that we all came up with similar findings for yield reductions based on shaved N rates. In Table 2, the approximate loss in yield from various N rate reductions, below the optimal rate, are displayed. Table 2: Case Study – Birdsclaw Farms: corn after soybeans, loam soil, 3000 CHU, 3.6% organic, matter, corn yield expectation 220 bu/ac. Corn price: $7.50; UAN price: $700/MT. 60 lbs N/ac applied with herbicide immediately after planting, 3 lbs N applied with in-furrow fertilizer on planter, remainder side-dressed in mid-June. Table Details: Impact on corn yields and economics when N rates are reduced because of limited supply. Table 2 illustrates that if your N supply is limited, then pulling back N rates by 40 lbs/acre would cost the grower about $45 per acre in net returns. In many situations corn profits, even with a $45 per acre trim because of restricted N supply, could still be financially superior to growing additional acres of soybeans. Question 3. How do fields experience nitrogen loss and what factors impact these losses? Answer 3. There are three key loss mechanisms for nitrogen: urea volatilization, gaseous N losses from denitrification and leaching losses. Table 3 reviews these three risks and outlines some contributing factors. Question 4. Where does a corn grower employ nitrogen stabilizers most effectively and with the best chance of a return on investments? Answer 4. The following situations represent the greatest likelihood of a positive impact from nitrogen stabilization products:
- Use of volatilization inhibitors when urea N sources are surface-applied, or where incorporation is very shallow and when soil surfaces are damp, and temperatures are warm (May – June temps riskier than April temps).
- Growers who are generally applying more N than is recommended or needed by the crop are much less likely to experience financial gain from N stabilization use. If a grower typically applies 200 lbs per acre and his optimal N rate is 175 then reducing N loss by using N stabilizers will be less likely to pay. If in 2022 that grower decides to shave N rates down to 170 because of nitrogen costs, then nitrogen stabilization will be more likely to provide a payback.
- If nitrate does not leave your field via denitrification or leaching, then why would it matter if you had a large pool of nitrate (no stabilizers) or a small pool of nitrate (stabilizers) on June 15? This is why it will be much more difficult to get a return on investment on nitrogen stabilizers on well-structured, well-drained loam soils compared to sands or clays.
- Following the Ontario N Calculator or Maizex N Tracker will generally mean you apply somewhat less than you normally feel comfortable with; in many cases this can move you in a good direction even if you don’t follow them exactly. These recommendations will also mean often applying less on loams and silt loams and applying more on sands and clays. Some reduction in nitrogen loss can be obtained by keeping the planting time N rates to modest amounts i.e., 60-80 lbs per acre and then side-dressing the remainder.
- Corn growers with significant manure or legume nitrogen sources will find more advantage under high N prices to increasing the N credit they apply to their fields. If you are concerned about being too aggressive with N credits and underapplying, consider this example: Estimated N credit is 80 lbs per acre, but the grower usually reduces N rate by only 50 lbs. 2022 is the year to take the full 80 lb reduction and then do soil nitrate sampling to ensure that the N supply is adequate. If not, then you can top up later.
- At one time, the golden ticket to generating 70 lb of nitrogen for your corn crop was simply under-seeding red clover into winter wheat in the previous cropping year. Some growers can still make that happen and this could mean a $100 per acre advantage in reduced N costs in 2023. In other situations, 110 bu/ac wheat seems to snuff out even the best red clover intentions. This year, the challenge will be for those growers to see if they can drill in something (Red Clover, Crimson Clover, Vetch, etc.) immediately after wheat harvest and generate some of those high N carryover situations. My experience would suggest trying to get 50 plus lbs of N credit out of oats, peas, oilseed radish, etc. as a summer-seeded cover crop is a real longshot.