Managing Nitrogen Loss

Spring has presented many challenges when it comes to crop production. It seems like it rains every other day. Now that a majority of the crop has been planted, we can switch gears and insure nutrient requirements are adequate for maximum yield. One of the biggest challenges that growers face as a result of a wet spring is potential nitrogen loss. Heavy rains have the potential to leach nitrogen deeper into the soil profile and below the plant root zone.

Several factors can drive the severity of leaching. Soil type, structure, and subsoil recharge are just a few. Sandy soils are more prone to leaching due to low water holding capacity. Water is able to move through course textured soils more quickly, thus increasing leaching potential. The large quantities of precipitation have left the subsoil saturated. With the soil being completely saturated, it is unable to hold onto water molecules, allowing water and nitrates to move deeper in the soil profile. Denitrification is another form of nitrogen loss; often affecting saturated soils and areas of ponding the most. Denitrification occurs in oxygen limiting areas where soil bacteria consume the nitrates in order to break down organic matter. Losses from denitrification can vary depending on the ponding severity and temperature. Figure 1 illustrates the potential losses.

Figure 1.

Table 5.1. Denitrification rates from saturated soil

Table courtesy of USDA.

What can we do to manage our nitrogen loss and make sure the crop does not run out? Soil nitrate tests can be a valuable in season tool to measure the amount of nitrogen that is available to the plant. Tests should be taken before a potential sidedress application when plants are 6”-12” tall. Nitrate tests are taken at a 12” depth and sent to a reputable testing lab for results. Research has shown that the critical value for corn is 25ppm. Tests under this value should be sidedressed. Normalized Difference Vegetation Index (NDVI) is another tool that can be used to analyze and assess crop health within a field. Stressed corn plants that are nitrogen deficient will show up on an NDVI image. Figure 2 shows an example of a strip trial that shows plant stress in the yellow and red areas.

Figure 2.

Photo courtesy of On-Farm Network

Managing nitrogen can be a very tough task for any farmer. Applying nitrogen in the spring and fall, even with N stabilizers, does not guarantee it will all be available when the plant needs it. Managing nitrogen with an in-season test and sidedress application is the best tool for maximizing your yield. Several options are available when it comes to spoon feeding nitrogen to your crop; applying UAN with Y drops, side dressing UAN or anhydrous ammonia with a knife or coulter, or applying urea by spreader or plane are all options to supplement nitrogen. f you need help determining your crops nitrogen needs, please contact us at Harvest-Max Associates.

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