Nitrogen Loss Assessment Tool (N-LAT) for Nebraska: Background and Users Guide

This publication provides the basis and procedure for using N-LAT to estimate average nitrogen (N) loss over several years for corn and soybean production to leaching, volatilization, denitrification, and nitrous oxide emission for specific field-management situations. The effects of alternative management practices can be assessed. N-LAT is not intended for short-term, in-season management decisions.

Charles S. Wortmann, Nutrient Management Specialist
Jim A. Jansen, Extension Educator
Michael W. Van Liew, Hydrologic Computer Simulation Modeler
Richard B. Ferguson, Soils Specialist
Gary W. Hergert, Nutrient Management and Soil Quality Specialist
Charles A. Shapiro, Soil Scientists – Crop Nutrition
Tim M. Shaver, Nutrient Management Specialist

Nitrogen is an essential nutrient for crop growth. Soil N chemistry and the N cycle are complex with numerous transformations and several pathways for loss, including leaching, volatilization, denitrification, nitrous oxide (N2O) emission, runoff, and soil erosion. In comparison, phosphorus loss from crop land, excluding removal in harvests, is nearly all through runoff and soil erosion.

All N losses have economic and environmental significance. Leached nitrate-N often contributes to contamination of ground water. Some volatilized ammonia is deposited in N-sensitive water bodies or natural ecosystems, contributes to acid rain, and reacts in the atmosphere to form N oxides and ammonium salts. Denitrification results in N loss but also contributes, together with the nitrification process, to the emission of N2O. Nitrous oxide is a greenhouse gas and contributes to ozone depletion. Transport of N through soil erosion and runoff results in contamination of surface waters. Nitrogen losses are difficult to measure and vary greatly from year to year. The Nebraska N Loss Assessment Tool (N-LAT) quantifies these losses and the effects of alternative management practices considering precipitation, soil properties, and management practices.

N-LAT is a decision-aid and was developed to be used on either a whole field or sub-field basis for making pre-plant decisions. In many fields, risk of N loss may be considerably greater for one sub-field compared with other sub-fields due to differences in soil properties including pH, organic matter content, hydrology, and drainage.

The Structure of N-LAT


The Worksheets

N-LAT was developed as Excel® spreadsheets to ease calculations. Tabs of two worksheets are found at the bottom of the screen.

  1. All data are entered into the Data Entry worksheet where the results are presented. The results also can be saved in the Report worksheet.
  2. Report contains the summarized records for up to five N-LAT simulations. The records are numbered from one to five and coincide with the run number at the top of the Data Entry worksheet.

The Components

N-LAT has components for denitrification, leaching, volatilization, and N2O emission. N-LAT does not estimate runoff and erosion losses of N, most of which would be in organic form and not necessarily available in the short term. All losses are estimated in pounds per acre per year (lb/ac/yr) of N. N-LAT was developed considering information from diverse sources, including simulations conducted with the Nitrogen Loss and Environmental Assessment Package (NLEAP; Delgado et al., 2010) and the California N-index (Delgado et al., 2008), but with final determination based on the consensus of the authors.

Functions were developed considering properties of soil and climate, and of inorganic N supplied from fertilizers and organic materials such as

Nitrogen mineralization rates from corn and soybean residue of previous crops were estimated at 0.11 and 0.97 lb/bu of grain harvested, respectively. Therefore, for each 100 bu/ac of corn or 50 bu/ac of soybean harvested the previous season, N available to the current crop from decomposing crop residue was estimated to be 11 and 48.5 lb/ac, respectively.

Estimated N from soil organic matter (SOM) mineralization was 40 lb/ac/yr for each 1 percent soil organic matter. Therefore total N availability (TN), not considering leaching and N2O emission loss, was:

TN = 56 + %SOM x 40 + IrrN (ac-in x ppm x 0.225) + (0.11 x bu of previous corn crop) or (0.97 x bu of previous soybean crop) + FertilizerN + ManureN – volatilization loss – denitrification loss.

Corn N uptake (Nu) was estimated as 1.2 x bu/ac grain yield. Soybean N uptake was estimated as 5 x bu/ac yield. The difference of total N available and corn N uptake (TN – Nu) was used in calculating NO3--N leaching loss. Manure N availability was determined according to information in the NebGuide, Determining Crop Available Nutrients from Manure (G97-1335).

Fertilizer use efficiency products intended to reduce N losses were considered in N-LAT (Table I). These included fertilizer additives such as nitrification or urease inhibitors for reducing leaching and volatilization losses, respectively, and controlled release fertilizers. Some products also affected denitrification and N2O emission. The N-LAT drop-down list does not include all of these products but has options for “Other nitrification inhibitor” and “Other urease inhibitor.”

Table I. Fertilizer use efficiency products available in the United States.

Chemical or Compound Nitrogen Products* Common Product Names Process Affected
Dicyandiamide (DCD) Guardian® Nitrification
2-chloro-6 (trichloromethyl) pyridine (Nitrapyrin) N-Serve®, Instinct® Nitrification
N-butyl-thiophosphoric triamide (NBPT) Agrotain® N volatilization
Malic + itaconic acid co-polymer with urea Nutrisphere® Nitrification, N volatilization
Polymer-coated urea (PCU) ESN®, Polyon®, Duration® N release
Sulfur-coated urea (SCU) SCU N release
Polymer + SCU Tricote, Poly-S® N release
Urea formaldehyde Nitroform® N release
Methylene urea Nutralene®, CoRoN®, NFusion® N release
Triazone N-Sure® N release
NBPT + DCD Agrotain®Plus, SuperU® Nitrification, N volatilization
Methylene urea + triazone Nitamin®, Nfusion® N release
Triazone + NBPT N-Pact® N release, volatilization
*Mention or omission of a commercial company or trade name does not imply endorsement or censure by the authors or the University of Nebraska–Lincoln.

The N Loss Processes


Denitrification is mostly affected by soil aeration, N availability, and source. The denitrification rate used by N-LAT for N available from sources other than fertilizer and manure was 5.5 percent on a soil of better than “somewhat poor drainage” and hydrology class B, according to USDA-NRCS Soil Survey soil descriptors. Exceptions for other fertilizers and manure were:

The calculated sum for all fertilizer and manure N was then multiplied by one or more of the following, if these apply:

Denitrification decreased as sand content of the soil increased. The adjustment for sand content was to add lb/ac N to the denitrification loss estimate according to (percent sand – 10) x -0.06.


Ammonia loss was affected by the total N supply, the ammonium and urea N application rate, the ammonia volatilization constant for the N source, fertilizer placement, soil pH, and whether a urease inhibitor was used. The volatilization rate used for N available from sources other than fertilizer and manure was 2 percent. The N-LAT equations to estimate a base loss of NH3-N to volatilization on a neutral soil pH are given in Table II. The loss factor for each treated urea (including urea in UAN) application event was adjusted by multiplying by:

The loss factor for each fertilizer and manure application was then multiplied by the following one or more factors if applicable:

Table II. Base estimates of NH3 volatilization for application rates of ammonium and urea N (AmN).

Fertilizer Product Application Method Adjustment Equations
Urea N Surface
NH3-Nv = AmN x 0.05
NH3-Nv = AmN x 0.01
Ammonium N Surface
NH3-Nv = AmN x 0.025
NH3-Nv = AmN x 0.0015
Anhydrous ammonia Injected NH3-Nv = AmN x 0.004    
Manure Surface NH3-Nv = AmN x (1.0-0.985 x power (0.65,d)); d = ≤7 days to incorporation
Manure Injected NH3-Nv = AmN x 0.008


Nitrate-N leaching is a function of water from precipitation and irrigation (TW), the difference in available N and N uptake (Ndiff), soil hydrology class, application method, use of a nitrification inhibitor, split application, cover crops, and fertilizer compared with manure N. The base leaching rate for N available from all sources was equal to 0.00005 x TW2 x (total available N – N uptake) in lb/ac/yr. The applied N leaching loss estimate for each fertilizer and manure N application event was multiplied as appropriate by one or more of the following:

The above calculated sum of products for all fertilizer and manure application was multiplied as appropriate by one or more of the following:

Nitrous Oxide

Base N2O emission with UAN surface-applied in lb/ac/yr was 0.94 + 0.015 x N + 0.15 x denitrification loss – 0.00039 x N x denitrification loss. A value of 1 percent of inches of annual precipitation plus irrigation amount was added to the base emission estimate. The base emission estimate for each fertilizer application event was then multiplied as appropriate by one or more of the following:

The above calculated sum of products for all fertilizer applications was multiplied by the following (their product if more than one applies):

Crop Rotation

N-LAT estimates losses for the current crop of corn or soybean. Much less N was applied on average for the corn-soybean rotation compared to continuous corn. To estimate N losses with corn-soybean rotation, run N-LAT for corn and then for soybean as the current crop and use the estimated losses to calculate annual average losses for the rotation. For example with the corn-corn-soybean rotation, average the values obtained for corn with soybean as the previous crop, corn with corn as the previous crop, and soybean with corn as the previous crop.

N-LAT User Guide

In the Data Entry worksheet, select:

Fertilizer type and application method are selected from a drop-down list. For each selection the user provides the rate, selects the time of application (fall, spring, or in-season), and checks a box indicating use of nitrification inhibitor, urease inhibitor, controlled release, or ammonium thio-sulfate.

Manure type is selected. A default unit of measurement is determined (t/ac, 1000 gal/ac, or ac-in/ac). Default values are given for NH4-N, organic N, and water content. Rate of application and time to incorporation is entered.

Some default values can be revised, including rainfall, soil organic matter, soil pH, and for manure, NH4-N, organic N, and water content.

The outputs are estimated N losses (lb/ac) due to:

The Data Entry sheet can be saved for a complete record of the field results. The results, with abbreviated input information, also can be transferred and saved in the Report worksheet for easy comparison of the results for different scenarios.

Report Sheet

Scenario number
Scenario name      
Soil unit      
Previous crop      
Cover crop      
N fertilizer† UreaSpSuUr150    
N fertilizer      
N fertilizer      
Manure 2012FL-Su25ON15AN4    
Irrigation Pivot-8”-3ppm    
Total N supply      
N uptake      
Denitrification N loss lb/ac      
Leached NO3-N lb/ac      
Volatilized NH3-N lb/ac      
N2O-N emission lb/ac      
Sum of all losses      


For fertilizer,

  • UreaSpSuUr150: Nitrogen fertilizer type: AmN, ammonium nitrate; Anh, anhydrous ammonia; UAN, urea ammonium nitrate
  • UreaSpSuUr150: Fa, Fe, Sp, and St are fall, fertigation, spring, and split application
  • UreaSpSuUr150: Ij, I7, and Su are injection, incorporation days after application, and surface application with no incorporation within seven days
  • UreaSpSuUr150: Co, Ni, and Ur are controlled release N fertilizer, nitrification inhibitor, and urease inhibitor
  • UreaSpSuUr150: the rate of N application in lb/ac

For manure,

  • 2012FL-Su25ON15AN4: year of application
  • 2012FL-Su25ON15AN4: FL, HP, Sl, SD, and Po are feedlot solid, feedlot holding pond, swine or dairy slurry, swine or dairy solid, and poultry solid
  • 2012FL-Su25ON15AN4: Ij, I7, and Su are injection, incorporation days after application, and surface application with no incorporation within seven days
  • 2012FL-Su25ON15AN4: Rate in t/ac for solids, ‘000 gal/ac for slurry, and ac-in for holding pond
  • 2012FL-Su25ON15AN4: Content of organic (ON) and ammonium (AN) N in lb per rate unit

For irrigation,

  • Pivot-8”-3ppm: Irrigation system
  • Pivot-8”-3ppm: Water applied, in/yr
  • Pivot-8”-3ppm: NO3-N concentration in ppm


Nitrogen Loss and Environmental Assessment Package (NLEAP) with GIS Capabilities (NLKEAP-GIS 4.2): User Guide; J.A. Delgado, P.M. Gagliardi, D. Neer, and M.J. Shaffer. 2010. http://www.ars.usda.gov/SP2UserFiles/ad_hoc/54020700NitrogenTools/NLEAP_GIS_4_2_Manual_Nov_29_2010.pdf

California N Index: A Tool to Assess N Management for Environmental Conservation. Z. Kabir, D. Chessman, and J. Delgado, USDA-NRCS and USDA-ARS. http://www.epa.gov/region9/ag/workshop/nitrogen/2013/kabir-epa-workshop-california-n-index2.pdf


This publication has been peer reviewed.


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Index: Soil Management
Issued December 2014