With over 5 inches of rain in the last 7 days (Burton Extension office) one of the questions being asked is how much of my corn nitrogen supply is being lost due to the heavy rains. There are several precise ways to know what your loss potential might be. You can use PSNT soil test to determine loss and a chlorophyll meter. The newest one on the market and one that is very intriguing is Green Seeker by Trimble. More on this tool in a later post.
The two primary ways to lose N this time of year are de-nitrification and Leaching. Both require a significant rain fall resulting in soil saturation for a period of time. Denitrification occurs after an ammonium form of nitrogen is converted to nitrate. Let’s consider the nitrogen cycle works. Using Anhydrous Ammonia as a nitrogen source, Ammonia NH3 enters the soil and is converted to Ammonium NH4 Ammonium which o converts to nitrites N02 and eventually to Nitrates N03 which is used by the plants. Actually plants can use both the ammonium and the nitrate form of nitrogen. This process is carried out by bacteria and is called nitrifications. When soils become waterlogged and oxygen disappears anaerobic bacteria absorb the nitrogen and convert it back into a nitrogen gas which is released back into the atmosphere.
This process can result in significant nitrogen loss. However, for this to happen, you need to have certain environmental conditions. The soil needs to be saturated to the point where Oxygen levels are reduced for a specific amount of time. Also the soil temperature needs to be above 75F degrees for the loss to accelerate. When soil temperatures early in the season are between 55 and 60F you can go up to 5 days with saturation and only experience 10% loss and 10 days with only 25% loss. Raise the temperature to 75 to 80F and you can lose 60 % of your N in 3 days and 75% in 5 days. Soil type and drainage also plays a critical role the finer the soils with poor drainage will retain water for a longer period of time. This increases your chances for nitrogen loss. Sandy, well drained soils are less likely to hold water and to denitrify. There must also be converted nitrate in the soil. The length of time that it takes for a nitrogen fertilizer to convert to Nitrate depends on the source. Most of our in row starters such as MAP and DAP and 10-34-0 take 1 to two weeks to convert to nitrate. Anhydrous Ammonia takes 3 to 8 weeks primarily because it lowers the pH of the soil slowing the process. Urea must be hydrolyzed by the enzyme Urease before it converts to Ammonium. It takes Urea 1.5 to 2.5 weeks to convert to nitrate and UAN 1 to 2 weeks. Usually denitrificatrion impacts pre-plant applied nitrogen the most. This nitrogen has been in the soil long enough to convert to the nitrate form. Recently applied side dress forms of N may not be impacted because the conversion to nitrate has not been completed. Also the use of Nitrogen Loss inhibitors such as Nutrisphere-N and Agrotain can help to slow down the nitrification process and protect the N that is applied. Leaching is primarily a problem on sandy or gravel soils. These soils usually hold around 1 inch of water per foot of soil as compared to medium or fine textured soils that holding 2.5 inches of water per foot of soil. Once again the amount of loss from leaching is dependent on the amount of rain during a specific period of time and how much of the fertilizer has been converted to the nitrate form.
Once you have determined that you may have lost N or that the addition of supplemental Nitrogen would be beneficial then you can go back in and apply N with several application techniques. The best would be dribbling a concentrated band of UAN on the surface with application tubes on your sprayer. This directs N away from the leaves to avoid burning. You can broad cast Urea but only up to 8 collar. The rule is to limit the application rate to 90# N up to 5 collar and 60# N up to 8 collar. If you use Urea you do not want to apply urea this time of year without the addition of an inhibitor to slow volatilization.
A Nitrogen management plan should not only contain the amount of N to applied but but how and when to apply the N. In reality we are developing a Nitrogen management plan that uses the 4R approach to Nutrient management. Right Rate, Right Source, Right Place and Right Time The closer you can apply the N to the primarily N Uptake period, this is usually after pollination and during ear kernel set and grain fill period the better utilization you will get. To read the entire article on Potential For Nitrogen Loss Following Heavy Rain by the University of Wisconsin go to; http://www.npketc.info/?p=180
Crop Progress Report
Corn: V-5 to V-7, corn is starting to yellow in some areas due to excessive moisture. There has been some flooding and ponding in poor drainage area and areas along creeks and rivers. Other than these problems the main concern will be getting Nitrogen on and weed control.
Soybeans are everywhere from V-E to V-3 and above. Some of the early planted fields are starting to canopy. Soybeans do not like excess moisture and there have been multiple reports across the state with root and stem problems from too much moisture.
Wheat; Still looks good and is turning fast. In high humidity conditions get ready to harvest the crop as quickly as you can to avoid grain quality issues. Be prepared to use bin drying as conditions require.
Forages: first cutting is a mess with very little harvested and wet field conditions; the quality for the most part will range from fair to poor. Be on the lookout for Potato Leaf Hopper in recently harvested Alfalfa fields
Source : neohiocropweather