Nitrogen application to corn is a large determinant for high yield, and rate has important implications for economic profitability and off-field movement of nitrate-N. Nitrogen rate recommendation systems have varied over time. A popular system was yield-goal based, with grain yield multiplied by a per-bushel factor and then rate adjusted for previous crop and other N inputs. Modifications of this system are still used today in some states. Seasonal (site-year) variability in economic optimum N rate (EONR) has been widely recognized. However, to date there has been no recommendation system that provides a solution to accurately predict EONR. Recently, seven states across the Corn Belt adopted the MRTN (Maximum Return To Nitrogen) recommendation approach which provides N rates based directly from analysis of large N response trial databases and maximization of return to N (Corn Nitrogen Rate Calculator; http://extension.agron.iastate.edu/soilfertility/nrate.aspx). Rate is determined from yield increase to applied N and current grain and fertilizer prices; but not yield level (Nafziger et al., 2004; Sawyer and Nafziger, 2005; Sawyer et al., 2006; Nafziger and Sawyer, 2008). The MRTN approach directly provides opportunity for user input and N rate adjustment, such as geographic location, previous crop, and price of N fertilizer (or other N inputs such as manure) and corn. The system provides a suggested N rate at the MRTN, but also provides a profitable range than can be used by producers to adjust rates based on experience, attitude toward risk, available capitol, water and air quality concerns, and local research information. The MRTN approach has some of the same limitations as other recommendation systems. It is well known there is large variability in temporal and spatial N response, which increases the most profitable RTN range and lowers certainty of getting the ���correct�۝ N rate in a given field in a given year. The MRTN approach incorporates this variability through response trial regression models, but does not solve the issue of site-specific N fertilization requirement or directly provide adjustment for yearly factors influencing N response. The MRTN approach does provide, however, a high level of confidence for achieving high yields over time within a reasonable N rate range. With new technologies, such as those used in precision agriculture, and greater available site- specific field information, producers have increased expectation of more highly refined rate recommendation systems. Of great interest is incorporation of weather data to adjust N applications, especially in years of excess rainfall. The Adapt-N (http://adapt-n.cals.cornell.edu/) is an on-line system designed to use radar-interpolated rainfall, along with soil and crop models, to estimate sidedress N fertilization need (Melkonian et al., 2008; Moebius-Clune et al., 2011). The system uses a budget approach, with adjustments from an initial yield-based rate. Input information for running the models include geo-referenced location, soil, rooting depth, slope, sod or soybean previous crop, soil organic matter, tillage system, corn hybrid maturity, planting date, plant population, expected yield range, any manure or fertilizer application date and placement, and season end date (date of recommendation run or in-season N application date). North Central Extension-Industry Soil Fertility Conference. 2013. Vol. 29. Des Moines, IA. Page 61 For full information about Adapt-N, go to http://adapt-n.cals.cornell.edu/. Expected yield is used to determine the base N rate for budget calculations. That amount is then adjusted for N currently in the crop (when Adapt-N is run), N currently in the soil (crop available), N in soil after sidedress, soybean credit if following soybean, losses after N applications, and an uncertainty of profit correction. The expect yield is assumed to be the economically optimum yield for the field, although as with all yield-based systems, the appropriate yield goal is nebulous. A recommended N rate and range is provided, with the range reflecting the uncertainty with post-application fertilizer losses for the remainder of the growing season. If N was applied and was in excess of the recommended amount, a negative or excess estimated amount is provided. With this recommendation system designed to be year-specific for individual fields, refined calculation of potential losses via denitrification/leaching and supply of soil N via mineralization, are of great importance. In addition, if the actual season-specific corn yield and complete-season N use efficiency does not match the entered expected yield and model assumptions, then the Adapt-N recommended rate may not reflect the actual field-specific economic optimum. The objective of this evaluation was to compare N rate recommendations from the MRTN and Adapt-N systems to site-specific determined corn N fertilization requirements.