This nitrogen model predicts the pounds per acre of plant available nitrogen released with time from soil organic matter, winter cover crops, poultry litter and compost. In order to calculate the available nitrogen released from the cover crops, the user needs to provide information to the calculator about their location (for weather information), their soil, and their cover crop. The user will also provide an estimate of the pounds of dry matter of standing cover crop and then provide representative samples to the laboratory of both the cover crop and the soil (the top six inches) on which the cover crop is growing. At the laboratory, the soil and plant samples will be scanned with a Near Infrared Reflectance Spectrophotometer to provide the following information for model input. For soil, the test results will provide the % soil organic carbon, and the rate of nitrogen mineralization from soil humus. For the cover crop, the test results will provide the % nitrogen, % lignin, % cellulose, and % non-structural carbohydrates. Other information will also be required, such as the date the cover crop is killed or incorporated into the soil, and the available nitrogen in the top six inches of soil. The information required from laboratory analysis for poultry litter and compost are % mineralizable nitrogen and % nitrogen, respectively, along with inorganic nitrogen in the litter. Rates and dates of application are needed for both. Additional information will be requested on the input screen in order to complete the calculation. The results of the calculation will be both the rate of appearance of available nitrogen and the total available nitrogen released to the crop, which can be used to determine the amounts of any additional fertilizer nitrogen needed to meet the nitrogen needs of the crop.