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© 2007 Plant Management Network. An Educational Program on the Proper Timing of Fall-applied Nitrogen Fertilizer George F. Czapar, P. O. Box 8199, Springfield Center, University of Illinois Extension, Springfield 62792; Jean Payne, P. O. Box 1326, Illinois Fertilizer and Chemical Association, Bloomington 61702; and Jodie Tate, P. O. Box 8199, Springfield Center, University of Illinois Extension, Springfield 62791 Corresponding author: George F. Czapar. gfc@uiuc.edu Czapar, G. F., Payne, J., and Tate, J. 2007. An educational program on the proper timing of fall-applied nitrogen fertilizer. Online. Crop Management doi:10.1094/CM-2007-0510-01-RS. Abstract Fall application of anhydrous ammonia for corn production is a common practice for Illinois farmers, but if applications are made too early, rapid nitrification can lead to increased risk of nutrient loss and water quality concerns. In 2001, educational materials and soil thermometers were sent to over 1000 producers in Illinois to encourage them to closely monitor soil temperatures before applying nitrogen fertilizer in the fall. A follow-up survey of producers in two watersheds indicated that over 70% of all respondents used the soil thermometers, and the median date of fall application occurred during the first week of November for both watersheds. Introduction Applying nitrogen fertilizer in the fall is a common practice for many corn growers in the Midwest. Although fertilizer application closer to the time of crop uptake often results in less nitrogen loss, many producers favor fall application because they have more time, and soil conditions may be more suitable for field work (5). Delaying application until soils are below 50°F and the use of a nitrification inhibitor have been suggested as practices to improve the efficiency of fall-applied nitrogen (1). Minnesota researchers reported that nitrate losses in subsurface drainage from a corn-soybean rotation can be reduced 10% by the addition of a nitritrification inhibitor with fall-applied nitrogen (6). Application of recommended nitrogen rates, the use of nitrification inhibitors with fall-applied anhydrous ammonia, and delaying application until soils cool down are common best management practices (BMPs) that have been promoted in Illinois (3). A survey of fertilizer and agricultural chemical dealers in Illinois suggested that the adoption of BMPs is viewed as an effective approach for protecting water quality (2). Although usage patterns are not readily available, it is estimated that a nitrification inhibitor is added to approximately 50% of the fall-applied anhydrous ammonia in Illinois (R. G. Hoeft, personal communication, 2006). For nitrogen that is fall-applied without a nitrification inhibitor, current Illinois recommendations are to delay applications until soil temperatures are below 50°F at the 4-inch depth (4). Further, it is recommended that fall applications be delayed until the third week of October in central Illinois, regardless of soil temperatures. The goal of this project was to evaluate the effectiveness of an educational program on proper timing of fall-applied nitrogen fertilizer in two watersheds in central Illinois. Since soil thermometers are a simple and inexpensive method of monitoring soil temperature, it was proposed that mailing producers a soil thermometer, along with educational materials, would encourage producers to follow best management practices for nitrogen application. Educational Program Producer mailing lists were obtained from the Sangamon and McLean County Soil and Water Conservation Districts for the Lake Springfield and Lake Bloomington watersheds. On 21 September 2001, a cover letter, soil thermometer, and educational brochure were mailed directly to 213 producers in the Lake Springfield Watershed and 160 producers in the Lake Bloomington watershed. The brochure outlined the importance of best management practices for fall-applied fertilizer application. This information focused on soil temperature guidelines, recommended procedures, the role of nitrification inhibitors, and an overall discussion of research supporting these practices. The total cost for printing the brochure, soil thermometers, padded envelopes, and postage was $6.11 per mailing. During the fall of 2001, soil thermometers and brochures were also sent to producers in ongoing watershed projects in five other counties. A total of approximately 1100 soil thermometers and brochures were distributed. In addition, several fertilizer dealerships requested soil thermometers and copies of the brochure to distribute to their customers. Information about the program and a copy of the brochure were posted on the Illinois Council on Best Management (C-BMP) and the Illinois Fertilizer and Chemical Association (IFCA) websites. Program Evaluation On 25 March 2002, a brief questionnaire was mailed to producers in the Lake Springfield and Lake Bloomington watersheds that had received a soil thermometer in 2001. They were asked if they used the thermometer and when they began applying nitrogen in the fall of 2001. Background information including the extent of fall-applied anhydrous ammonia, changes in crop yield and nitrogen application rates was also collected. In order to encourage producer response, the survey instrument was limited to six questions. Cross tabulations were used to compare survey responses and data were analyzed using a Pearson’s chi-square statistic to identify significant differences between watersheds. Background Information In the Lake Springfield Watershed, 91 questionnaires were returned for a response rate of 43%, while 83 questionnaires in the Lake Bloomington watershed were completed, reflecting a 52% response rate. Since producers received a soil thermometer six month earlier, they may have been more receptive to completing the survey. This might account for the relatively high response rates from both watersheds. As shown in Figure 1, over 85% of producers in these two watersheds apply at least some of their nitrogen fertilizer in the fall, and over 50% of producers in both watersheds apply all of their nitrogen using this practice. There was no significant difference in response between the two watersheds.
Respondents were asked to indicate if their corn yields have changed over the last three years (Fig. 2). Similar responses were noted between watersheds with almost 70% of both groups indicating that yields had not changed, while approximately 25% of respondents indicated their yields had increased. When asked if their nitrogen application rates had changed over the last three years, there was a significant difference (P < 0.05) in response between the two watersheds (Fig. 3). In the Lake Springfield Watershed, 28% of respondents indicated that nitrogen application rates had decreased in the last three years. In contrast, 46% of respondents in the Lake Bloomington Watershed reported that nitrogen rates had been decreased. One possible explanation is that Lake Bloomington has had elevated levels of nitrate in public drinking water supplies in the past, while nitrate levels in Lake Springfield have been much lower. As a result, several watershed and nutrient management programs have been promoted by local watershed organizations, and the focus on nitrogen management has been greater in the Lake Bloomington watershed.
Program Results Although it is difficult to measure the direct impact of this educational program on changing application practices, some observations can be made. As shown in Table 1, over 70% of all survey respondents indicated they used the soil thermometer in 2001. Also, significant differences were noted in the extent of producers that used a nitrification inhibitor in 2001. Table 1. Survey responses from producers in two Illinois watersheds.
* Significant difference in watershed response (P < 0.05) Most producers delayed nitrogen application until soils had cooled down, and the median date of application occurred during the first week of November for both watersheds. In addition, only three producers began applying anhydrous ammonia before 15 October 2001. It should be noted that other factors, such as rainfall and soil conditions, may have also affected their decision to begin field operations. Proper timing of nitrogen applications is a critical component of protecting water quality and assuring optimum utilization of nitrogen. The use of a soil thermometer to accurately schedule fall nitrogen applications is a best management practice. It will become increasingly important as nutrient issues continue to focus on proper stewardship of nitrogen inputs by the agricultural community. Acknowledgments The project was funded, in part, by the Illinois Council on Best Management Practices (C-BMP). Literature Cited 1. Bundy, L. G. 1986. Review: Timing nitrogen applications to maximize fertilizer efficiency and crop response in conventional corn production. J. Fert. Issues 3:99-106. 2. Czapar, G. F., Curry, M. P., and Brink, W. H. 2002. Pest management recommendations and water quality concerns: An Illinois Agribusiness Perspective. Weed Technol. 16:440-443. 3. Hirschi, M., Frazee, R., Czapar, G., and Peterson, D. 1997. 60 ways farmers can protect surface water. N. Central Regional Ext. Publ. No. 589, Info. Technol. and Commun. Serv., Coll. of Agric., Consumer and Environ. Sci., Univ. of Ill., Urbana-Champaign, IL. 5. Randall, G. W., and Goss, M. J. 2001. Nitrate losses to surface water through subsurface tile drainage. Pages 95-122 in: Nitrogen in the Environment: Sources, Problems, and Management. R. F. Follett and J. L. Hatfield, ed. Elsevier Science B.V., Amsterdam. 6. Randall, G. W., and Vetsch, J. A. 2005. Nitrate losses in subsurface drainage from a corn-soybean rotation as affected by fall and spring application of nitrogen and nitrapyrin J. Environ. Qual. 34:590-597. |
