Nitrogen recommendations for addressing weather

Iowa State University's new nitrogen fertilizer recommendations for corn (outlined in Pm-1714) are designed to help producers address uncertainty associated with weather. The exact methods used, however, depend on the management intensity of the producer. The variety of methods available is best explained by defining five levels of nitrogen management and giving examples of the methods used at each level.

Level one management

Nitrogen is applied without any objective program to evaluate and improve nitrogen management. Neither the late-spring test for soil nitrate nor the end-of-season test for cornstalk nitrate is used. Rates, times, and methods of application are selected largely on the basis of general guidelines, tradition, and/or convenience. Producers at this level often worry about N losses when above average-rainfall occurs during late April and May, but they take essentially no action to address the problem.

Level two management

This uses the late-spring test for soil nitrate and/or the end-of-season cornstalk test to check fields after fertilizers have been applied at rates used by producers at level one. At the lower end of this level, fields are sampled only when weather conditions or other factors give reason for concern that substantial losses of fertilizer N have occurred. Producers at the upper end of this level use many of the methods at management level three. Observations made at this level can be used to detect and correct major problems in N management.

Level three management

The late-spring test for soil nitrate and the end-of-season test for cornstalk nitrate are used routinely at a few sites in several fields every year. Simple records are kept relating to where the samples were taken, rates and methods of N application, and weather conditions. Some N usually is applied before corn emergence, but these rates are kept relatively low to minimize losses of fertilizer N during spring rainfall and to enable adjusting in-season fertilization rates for N supplied by the soil. Information obtained by the soil and cornstalk testing is used to continuously evaluate and improve N management practices. Information collected over several years is used to adjust rates of preemergence fertilization for weather conditions during the preceding months. Producers at this level for a few years begin to realize that they can predict nitrate concentrations each year. The soil test, therefore, is used more to improve the accuracy of their predictions, rather than to directly measure fertilizer needs at a given site in a given year. Information provided by the soil and tissue tests at this level is used to optimize N management practices one farm at a time.

Level four management

This includes all the activities in level three, but many corn producers work cooperatively to get more extensive evaluations of management practices in less time. A pilot program demonstrating this level of management has been initiated as the N-Check Program in west central Iowa. This is a cooperative effort of the Raccoon River Watershed Project, the Iowa Corn Promotion Board, the Iowa Farm Bureau, the Leopold Center for Sustainable Agriculture, and the USDA Sustainable Agriculture Research and Education Program.

As part of the N-Check Program, producers collect samples and record relevant information about soil types, management practices, and location of the test area. The information is analyzed by researchers at ISU. Producers get results for their farm and a summary analysis of all data collected. The large number of samples helps identify trends that one producer would not be able to identify. The trends enable comparison of factors such as time or method of application. They also show how these factors interact with soil types and weather. Producers can compare their results to the average of many other farms using similar or dissimilar management practices. This gives an objective basis for selecting among the many alternative fertilization practices currently available to producers.

Level five management

Management is probably done by a professional agronomist in the business of selling information to producers. A few consultants and dealer agronomists seem to be rapidly approaching this level. Activities would resemble those at level four, but sites sampled across many farms would be judiciously selected to enable effective evaluation and comparison of various management practices across a wide range of conditions.

Much more information would be collected at each site than with level four management, possibly by use of weather stations, remote sensing, yield monitoring, or information gathered in integrated crop management programs. All data would be analyzed continuously to identify the best possible recommendations, which include suggestions as to how, when, and in what form the N should be applied.

Recommendations for a specific site and year would be updated as weather events occur. Complex recommendations often would be supplied directly to computers on applicators that have the capacity to vary rates of fertilization as they move across fields. Although the exact method used to calculate the recommendations may remain the property of the professional agronomist, the producer would obtain an objective assessment of the performance of the recommendations.

Objective evaluations of alternative fertilization methods across a wide range of soil and weather conditions provide a basis for making informed decisions concerning what fertilization practices should be used. The knowledge obtained helps producers select among all alternative practices available. This same knowledge helps the fertilizer and farm equipment industry develop better alternatives. The current level of interest in "precision farming technologies" essentially ensures that major changes in N management practices will occur in the near future. These new management practices cannot be significant advances unless they address weather-induced variability in nitrogen fertilizer requirements.

This article originally appeared on pages 89-90 of the IC-478(12) -- June 9, 1997 issue.

Updated 06/08/1997 - 1:00pm