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Agronomic Crops Network

Ohio State University Extension


Look Out for Nitrogen Loss Due to Heavy Rains

The recent heavy rainfall events have implications on the fate of applied nitrogen (N). In the past two weeks, Ohio has received rainfall ranging from about 1.5 inches in the northwest to 6 inches in the central-eastern counties. Year to date, we are experiencing 2 to 8% higher rainfall than normal. Nitrogen loss is exacerbated under such excessive rainfall scenarios via three pathways: runoff, leaching, and denitrification.


The amount and intensity of rain received in the past week may have caused substantial soil erosion. Fields with no cover or residue are more susceptible to N runoff. If N fertilizer was applied recently in such fields, especially without incorporation into the soil, there is high likelihood of N fertilizer being eroded out of the field.


The nitrate form of nitrogen is liable to leach down the soil profile. Leaching is more prevalent in coarse textured soils than fine textured soils. In addition to the amount of rain, the amount of N loss via leaching will depend on:

Type of fertilizer used: Leaching loss of N depends on the amount of nitrate present in the soil. Fertilizers that contain N in the nitrate form such as UAN increase the chance of leaching loss because a large portion of UAN exists as nitrate form. According to Havlin et al. (1999), most of the anhydrous ammonia gets converted to nitrate in about 3 to 8 weeks whereas 25% of UAN is in nitrate form on day 1 of application and 100% of it is converted to nitrate within 1.25 to 2.5 weeks. Enhanced efficiency fertilizers that either include nitrification inhibitors or protective covering reduce the leaching potential by slowing the conversion of the source to the nitrate form.

Crop stage: If the field was bare, nitrate leaching potential could have been substantial. The presence of a cover crop or wheat during this time of the year can reduce nitrate leaching. The N uptake of wheat during the dormancy or early green up stage is minimal, thus making nitrate liable to leach down. If wheat was in stem elongation phase, nitrate leaching is less likely due to increased N uptake and prolific rooting system of wheat at this stage.


When soil is saturated with water during or after the rain event, N can be lost to atmosphere via denitrification process. The denitrification process refers to the conversion of nitrate form into gaseous forms (NOx or N2). The amount of N loss depends on how long soil stays saturated and soil temperatures during waterlogging, with warmer temperatures accelerating denitrification losses. Table 1 shows the potential loss of N due to denitrification under saturated soil conditions for different periods in days and soil temperatures.

Table 1. Potential loss of nitrogen due to denitrification based on days of saturated soil conditions and soil temperature. (

Time (days)

Soil Temperature (degree F)

N loss (percent)












If any of the above N loss mechanisms occurred in your field, especially after an N fertilizer application was made, it is important to supplement N to growing/upcoming crop to avoid yield losses. You can follow below given strategies:

Estimate the N loss: The amount of N loss can be estimated based on the fertilizer type, time of application, crop growth stage, and soil water content. Lentz and Culman (2015) outlined a procedure in this article: Concerns for N Loss in Corn from Recent Storms

Determine N in the soil: Pre-Sidedress Nitrogen test (PSNT) can be done to quantify the status of nitrogen in the soil. LaBarge (2022) outlined the procedure to decide if additional N would be needed in this article: Estimated and Soil Test Methods to Determine Supplemental N need after Flooding

Look out for plant N deficiency symptoms: Yellowing of lower leaves or inverted yellow V pattern on leaves could be a sign of N deficiency in crops. If such symptoms persist after soils are no longer waterlogged and temperatures are not on cooler end, it might be worthwhile to consider side-dressing N. You could also utilize sensors to determine NDVI to calculate N fertilizer requirement. The description of some Apps is outline by Logan et al. (2018) in this article: Crop Nutrition Apps


Havlin, J.L., J.D. Beaton, S.L. Tisdale, and W.L. Nelson. 1999. Soil Fertility and Fertilizers. An Introduction to Nutrient Management. 6th ed. Prentice Hall. Upper Saddle River, NJ.

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C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.