Urea Volatility Model Download Instructions

To download the Urea Volatility Model click on the text link or image below. A Caution dialog box will appear giving you four options.

Click on the Save File option. This will download the Volatility Model to your computer.

Download the Urea Volatility Model

Urea Volatility Model

The Urea Volatility Model is a personal computer program developed to help growers determine if AGROTAIN¨ with UAN or urea application to corn is profitable under the specific conditions of their own farms. The model requires input of information about field conditions, expected weather conditions, soil characteristics, and fertilizer and crop prices, to make 1) an estimate of how much N would be expected to be lost from the urea or UAN solution applied to those fields, 2) what the effect of the N loss would be on shelled corn yield, and 3) what would be the economic consequences of using and not using AGROTAIN¨. The model is meant to help growers decide on whether AGROTAIN¨ makes dollars and cents for them on specific fields and under specific weather conditions.

How To Use It

To run the model, click on the Assessment icon. Four indexes will come up which contain the information needed to run the model calculations. The numbers or descriptive terms in the white boxes should be changed to what the conditions in the field are at the time of sidedress application, while the lime-colored boxes contain numbers calculated by the model. Make sure that the index icon has four boxes at the bottom which say "print", "calculate", "graph", and "quit". If you do not see those boxes, raise the window so you can click on the boxes.

After the correct values have been put in all the white boxes, click to the calculate index and then the "calculate" box at the bottom. The results of the model calculations, based on the input information will appear in the lime-colored boxes. The cation exchange capacity, in units of meq/1OOg, can be changed if those values are known, otherwise the number will be estimated from the soil texture. The crop height refers to the height of the corn (in inches) at the time of the sidedressing. Enter zero for pre-plant applications. Note that the model is for applications of urea or UAN solutions which are not incorporated.

How It Works

The model works by first looking at the relationship of N application and expected yield. It is therefore very important that realistic values be entered for the normal, good yield expected with a normal rate of N application and good seasonal weather conditions. If poor data are input for these values, the model will produce poor estimates.

The model then estimates the amount of ammonia-N loss that is expected to occur under the specific soil and weather conditions, based on scientific research that has been done in the Midwest to relate wind speed, soil moisture, organic matter, pH, and other things to ammonia volatilization. Rainfall of more than about 0.25 inches stops ammonia loss by washing the urea on the soil surface into the soil. Therefore, the guess about expected rain or irrigation can greatly effect the results. Temperature, soil moisture and soil organic matter effect the rate at which urea is converted into ammonia, and if the soil surface is very dry, the conversion can be slowed and ammonia-N losses will be less

The input parameters that the grower is asked to provide all pertain to the conditions at the time of the sidedress fertilizer application. If a value is not known, the model has "default" or average values that are put in. This prevents the model from "crashing" and allows running the model with the best available information. Each parameter will remain the same until it is changed by overwriting a new value in the white boxes.

Evaluating The Results

The results of the model can be seen in graph forms by clicking on the "graph" box and then selecting the simulation desired.

Some of the input parameters, particularly the expected weather, are best guesses at the time of the sidedress application. While the model is a truthful attempt to estimate the losses of N and the effects of those losses on yield, the reliability of the guesses as well as the reliability of the model limit the reliability of the results. Obviously, if an August drought hits, the model predictions will not be correct. In addition, the scientific basis for combining the many interacting factors that effect ammonia-N losses is not perfect. The model is an attempt to estimate the effects and to help growers to make decisions that are profitable for them.