The Indiana Certified Crop Adviser panel includes Betsy Bower, Purdue Extension senior research associate, West Lafayette; Abby Horlacher, Nickel Plate Consulting, Sheridan; Brian Mitchem, Farmer 1st Agronomy Consulting Services, Decatur; and Dan Quinn, Purdue Extension corn specialist, West Lafayette. 

 

I’ve already applied all my nitrogen in corn at planting, but heavy rains are making me wonder if my corn will be deficient. Should I make a rescue application? How should I apply it? How much should I apply?

 

Bower: Applying a rescue nitrogen application should be a well-thought-out plan and not a gut feeling. Consider nitrogen source, soil type, rainfall timing, nitrogen application methods, nitrogen stabilizer use, and current health of the crop. 

 

There are three main mechanisms of nitrogen loss: volatilization of ammonia, leaching of nitrate and denitrification of nitrate in saturated soils. Volatilization can occur in any soil type when urea-based fertilizers and manure are surface-applied. While leaching of nitrate can occur in any soil type, the potential for a large magnitude for loss is on sandier soil types. Denitrification is most associated with poorly drained soils. 

 

Nitrogen stabilizers will buy some time to get at least half an inch of rain to incorporate urea into the soil and protect it from volatilization. The impact of rainfall on nitrogen loss immediately after planting is typically not as devastating as compared to four to six weeks after planting. Sources of nitrogen can also differ in potential nitrogen loss. Anhydrous ammonia has a little advantage, compared with urea or UAN. 

 

In a nutshell, with nitrogen applied at planting, losses would be more of a concern with unstabilized nitrogen in excessively and poorly drained soil four or more weeks after planting. One tool I used a lot when my customer and I were unsure of potential nitrogen loss was to take a soil nitrogen test. Take several cores at 12 inches deep to

determine the nitrogen concentration. By knowing the nitrogen concentration in the upper foot and stage of crop, you can then understand if you have any nitrogen deficiency. 

 

There are several ways to apply nitrogen. The first tool is a Y-drop applicator. Although it does place a band of nitrogen close to the corn row, there still needs to be some rainfall to put the nitrogen in play in the soil. The Y-drop applicator is an improvement over a sprayer with drops that put a band in the middle between two rows. But I certainly would use a sprayer with drops over waiting to find an available Y-drop applicator. Some aerial applicators have spreaders that can apply urea. 

 

Horlacher: Nitrogen rates and timing are always challenging decisions, especially this year with heavy rainfall and periods of stalled crop growth that raise questions about nitrogen availability and loss. One useful tool is the pre-sidedress nitrate test, which measures nitrogen in its nitrate and ammonium forms. For accurate results, sample at least three representative areas within the field to gain a better understanding of overall field conditions. 

 

When looking at how to apply, consider equipment. Is there a way to get nitrogen on with the tools you have in your shed? If not, then does your local fertilizer dealer have the tools to apply? If your crop is too tall and no one can get nitrogen on, consider flying on urea with a plane. 

 

Mitchem: Soil that has been saturated with water is subject to nitrogen loss. Losses can vary with length of time the soil was saturated, the soil temperature and the form of nitrogen at the time of the water event. Warmer soils lose more nitrogen, and the primary form of nitrogen that is lost is nitrate. 

 

Warm and saturated soils can lose 4% to 5% of the nitrate each day the soil is waterlogged, so losses can accumulate rapidly. Urea converts to nitrate in 10 to 20 days. Anhydrous ammonia converts to nitrate in three to eight weeks. 

 

Start with a current best estimate of the lost nitrogen. If that number is more than 10% of the applied nitrogen, then look for visual symptoms of nitrogen deficiency. Examine lower leaves for signs of yellowing, starting in the center and moving outward. Another option is to collect tissue samples from at least three different areas of a field and send them to a lab for analysis. Once results are returned, you can use that information as a guide to decide if additional nitrogen is needed. Ear leaf tissues are the most accurate to test. The ear leaf will be between the 12th and 14th nodes on the plant. Remember, the first three leaves are no longer present. 

 

Application of mid- to late-season nitrogen using a high-clearance sprayer with a Y-drop system has been effective at providing nitrogen. An effective rate is typically 15 gallons per acre of solution with Y-drop systems. 

 

Quinn: If you had heavy rainfall after applying most or all your nitrogen at planting, some loss may have occurred through denitrification or leaching, depending on soil conditions and fertilizer source. Denitrification is most common in saturated, poorly drained soils where nitrate is converted to gaseous forms and lost to the atmosphere, while leaching is more common on sandy soils where nitrate moves below the root zone. 

 

Evaluate field conditions, crop appearance and estimated nitrogen loss. Factors such as fertilizer source, application timing, use of nitrification inhibitors, soil temperature and the number of days soils remained saturated all influence how much nitrogen may have been lost. Visual deficiency symptoms, especially yellowing of lower leaves prior to pollination, are a strong indicator that supplemental nitrogen may be needed. 

 

If significant nitrogen loss is suspected, rescue applications made before pollination or just after can help preserve yield potential. Supplemental nitrogen should ideally be applied in a liquid form and only to affected areas using a high-clearance application method with either Y-drops or drop tubes to avoid any potential plant injury. A supplemental application of 40 to 60 pounds of nitrogen per acre is often adequate for yield preservation in many Indiana environments.