Wet Soils, Yellow Crops and Options for Midseason Applications of Nitrogen Fertilizer

With the large rainfall events across many parts of Manitoba recently, some farmers are noticing yellowing in their crops and wondering if they should top up their fields with some more nitrogen fertilizer. Unfortunately, there are no easy rules to follow or large experimental datasets to refer to for making this type of decision.

The attached article by Dr. Don Flaten, University of Manitoba, and John Heard, Manitoba Agriculture, outlines some principles if considering midseason application of nitrogen fertilizer.

Wet Soils, Yellow Crops and Options for Midseason Applications of Nitrogen Fertilizer – June 2016

And remember….the first issue to consider is whether the crop yellowing is from N deficiency or simply flooding stress due to excess water. Applying N fertilizer onto crops that are suffering primarily from flooding stress could be a poor investment.

Submitted by: John Heard, Crop Nutrition Specialist, Manitoba Agriculture

Visit Manitoba Agriculture website at http://www.gov.mb.ca/agriculture/crops/soil-fertility/ for more information on soil fertility.


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Apply your Nitrogen Stamp – Assess Losses and Sufficiency for Your Crop

Submitted by John Heard, Crop Nutrition Specialist, Manitoba Agriculture

With the excessive rainfall and standing water in some Manitoba fields, some agronomists may be asked to assess possible N losses. If applied N had already converted to nitrate (NO3) form it is subject to leaching on sandy soils and denitrification on poorly drained and heavier textured soils.

In many cases it is not too late to apply your “Nitrogen Rich Strip” or N Stamp” that can serve as a reference when one wants to assess potential losses and yield penalties. Nitrogen Rich Strips are usually applied with field equipment and run across the field to encompass a range of soil types, drainage, etc. Simple differences in colour and growth between the field and this strip usually indicate a lack of N for field yield potential. When applied before or at seeding such strips should be 150-200% of the base field N rate. A number of devices and sensors (like chlorophyll sensors, NDVI or GreenSeeker) can be used to quantify such a difference and estimate in-season N applications for a variety of crops.

Nitrogen Ramp Calibration Strips or N Stamps can be simply applied by hand after seeding into fields. Details on applying the N Ramp Calibration Strip are available at: http://www.gov.mb.ca/agriculture/crops/soil-fertility/nitrogen-ramp-calibration-strips-in-manitoba.html

N Stamps are simpler – generally 30, 60 and 90 lb N/ac hand applied within a 20ft x 20ft (6m x 6m) cells. We are applying these in several wheat fields to test the abilities of UAVs or drones to detect N differences in fields. To try this out simply weigh 258, 517 and 775 g of urea into bags and hand apply to the 20’ x 20’ plot. We treat our urea with NBPT to minimize losses to volatilization. Observe differences in colour and growth. If none are seen mid-season, then the applied N was likely sufficient for yield.



20 ‘

 20’ 0 N check


30lb N/ac          =  258 g urea


60lb N/ac            = 517 g urea

90lb N/ac          = 775 g urea



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GOT YELLOW CORN? Using Tissue & Soil Analysis to Confirm Nutrient Deficiency

Not only are soybeans turning yellow in Manitoba, but corn is as well.   So how do you confirm a nutrient deficiency is causing the yellowing?

John Lee of AGVISE Laboratories provided MAFRD staff last year (2013) with the below information on how to properly determine if nutrient deficiencies are playing a role in the ‘yellowing’ corn seen across Manitoba.   It is a great article so thank you to John Lee!

Using Tissue and Soil Analysis to Confirm Nutrient Deficiency in Corn

A cool, cloudy spring with excessive moisture has affected many areas.  One effect of these conditions has been yellow corn from Manitoba to South Dakota.  Using plant tissue analysis along with soil analysis can help determine if the yellow corn is a result of sulfur or nitrogen deficiency.

AGVISE staff recently worked with a local grower to help him determine why one of his corn fields was yellow while the adjacent neighbor’s field was dark green.  Tissue and soil samples were collected from the yellow corn field and also from the adjacent corn field planted the same day.  The concentration of sulfur in the plant tissue from the yellow corn field was well below the sufficiency range established for sulfur at this stage of growth.  The nitrogen concentration in the yellow corn was good and in the middle of the sufficiency range for this stage of growth.  A tissue sample from the adjacent corn field with dark green color was also tested and found to have sulfur and nitrogen levels well within the sufficiency ranges (see tissue and soil test results and pictures of corn at http://www.agvise.com/wp-content/uploads/2013/06/S-defcorn-AGVISEExample20132.pdf).  There were also a large difference in the soil nitrate and sulfate sulfur levels in the soil samples from the yellow field and the adjacent green field.

The soil type in these fields is a sandy loam which is subject to leaching of sulfur and nitrogen with excessive rainfall like this spring.  The yellow field did not have sulfur fertilizer applied this spring while the adjacent dark green corn did have sulfur fertilizer broadcast and tilled in before planting.  The grower was planning on sidedressing the yellow corn with nitrogen fertilizer, but but now with the additional information from the tissue and soil tests, he is going to include some sulfur fertilizer in the sidedress application as well on this sandy loam soil.

This is just one example of how using tissue analysis along with soil analysis in season can help figure out if symptoms are being caused by a nutrient deficiency and which nutrient is the main cause of the symptoms.

Note:  If agronomists/producers send suspected nutrient deficiencies to MAFRD’s Crop Diagnostic Lab, please send samples for tissue and soil analysis simultaneously to an appropriate laboratory.  Then follow up with Crop Diagnostic Lab on the results from the tissue and soil analysis.

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