Critical Management Period for CornMay 16, 2016 | Category: Agronomy |
You are in the process of planting your highest yielding corn crop. How high can you aim for? Hopefully the most important rule of planting corn was obeyed – plant only when fit. Your next actions to come will greatly influence your success in obtaining that yield number you were wishing to achieve.
There is no magic nitrogen rate that provides maximum yield other than simply overapplying, which is not economically viable or environmentally responsible. Most economical rates will be a function of general factors (previous crop, yield expectations, etc.) and in-season factors (rainfall, soil nitrate supply, etc.). N application timing has also received much more attention lately, emphasizing the advantages of applying nitrogen closer to the time that the corn plant will use it.
What we do know about nitrogen in 2016 so far:
- Pre-plant N if not in the nitrate form (i.e. urea) will be slower in converting to plant available nitrate due to cold soil temps. The same may be true for organic N sources as soil organic matter, legumes and manures may be lagging this season in terms of their contribution to the available nitrate pool.
- It is critical that the corn plant has adequate supply, so if you applied low rates of N upfront you may not have enough N to carry the crop to a late sidedressing or high clearance application. Some earlier N (i.e. steamer nozzle UAN at 3 leaf corn) might be in order.
- Soil nitrate testing can help quantify the nitrate supply in the soil. The OMAFRA PSNT recommendations are designed for soil samples taken in soil that has not received fertilizer N upfront. If you apply all of your N upfront, a soil nitrate test can help you verify that the total nitrate pool is adequate for a high yielding crop. Research has indicated that a threshold level of 36ppm was quite a reliable indicator that no additional N is required. Take a first sample at about 6 leaf stage corn and follow up with another sample a week or ten days later to assess your nitrate levels. Be sure to contact you Maizex representative if you would like assistance in interpreting your soil N test results.
As herbicides are applied, it is crucial to stage your corn properly. Your corn plant goes through some rapid growth stages and there are some very key times at which certain herbicides are very detrimental.
- 5-7 leaf stage: the number of potential ear shoots are determined
- 7-10 leaf stage: the number of potential kernel rows are determined
- 10 leaf to just before tasseling: the number of potential kernels per row are determined
Actions that impact the health/metabolism of corn leading into these critical time frames can be very large. Creating an unwanted stress coupled with a second stress can lead to a major reduction of bushels. For example, spraying a hormonal spray combined with cold night time temperatures can really disrupt the metabolism of the corn plant. With a population of 32,000 plants/acre, a reduction of 2 kernel rows or pulling ear length back by 5 kernels in length might represent a yield reduction of 25-30 bu/ac!
I have found a simple way to keep track of your stage is to use a permanent marker and number the leaves as they come out of the whorl. Remember that as corn gets older the 1st leaves senesce and disappear, so start numbering by the time corn reaches 4-5 leaf to make much easier.
It’s too early to determine exactly which diseases will be the hot topics for 2016, however, for the past few years Northern Corn Leaf Blight has been increasing in both the areas impacted and the size of the yield reduction. Put scouting high on your priority list and keep an eye on new fungicide products and timings to prevent yield loss.
Kirk Van Will, CCA-ON, Maizex Seeds Territory Manager, West Middlesex & Lambton Counties
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