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Fluid Journal : Spring 2017
10 The Fluid Journal Spring 2017 Dr. John E. Sawyer is Professor and Extension Specialist in Soil Fertility and Nutrient Management, Dr. Daniel W. Barker is Assistant Scientist, and Mr. John P. Lundvall is research affiliate, Department of Agronomy at Iowa State University in Ames, Iowa. N application. The EONR does vary by site-year conditions, which is highlighted by the EONR at individual sites. Therefore, sidedressing provides an opportunity to adjust rate or apply additional N based on input information such as springtime precipitation models, canopy sensors, or soil tests. In 2004-2006, N was applied preplant/ early sidedress (pre-sensing N) or split-applied (post-sensing N) in-season at corn V10-VT stages (SPAD meter based) across 30 fields with corn following soybean (Ruiz Diaz et al. 2008) [Table 2]. Across the 30 sites, and with a pre-sensing N application of 60 lb N/acre plus a mean 55 lb N/acre post-sensing N (total 115 lb N/acre), there was a yield increase from 141 bu/ acre (no N) to 185 bu/acre. However, the yield with 120 lb N/acre all applied early was 7 bu/acre higher than the post-sensing N (192 bu/acre vs 185 bu/acre). In some fields, response to the post-sensing N was not enough to achieve full yield potential. In other fields, yield with post-sensing N was equivalent to that with the pre-sensing N only, especially when rain was received shortly after N application. Overall, the sensor-based split N system would not be fully justified compared to applying all N early because the in-season application did not reduce the total N applied, nor did it improve yield relative to early applied N. Additionally, the in- season application would incur sensing and higher application costs. In a study conducted in 2009- 2010 (Barker and Sawyer, 2012), total N applied preplant (PP-N) or a combination of preplant plus sensor- based (PP+S-N) resulted in the same corn yield level at equivalent total N rates (Figure 2). Nitrogen response and EONR was quite different between years, with 2010 having large rainfall events and high EONR. While the yield response was the same to both timings in each year, there was potential to adjust in-season rate for the different seasons and N fertilization needs. Best in-season rate determination each year was with no N applied preplant. In two years with dry conditions (2012-2013) [Barker and Sawyer, 2016], sensor based in-season N application increased yield when preplant (PP-N) rates were deficient (Figure 3). However, the yield increase from in-season N (PP+S-N) was limited when applied to in addition to PP-N rates below the EONR. Also, the total amount of N applied (PP+S-N) at all preplant (PP-N) rates was greater than the EONR, with the sensor-based rate (total N) quite high when 150 lb N/acre or more had been applied preplant. Summing up While sidedress/split N application has appeal for yield and economic return improvement, recent research has shown it is difficult to achieve a frequent and consistent positive response in corn production. While the sidedress practice may be of frequent benefit in coarse- textured soils, with irrigation, or in geographic areas with high rainfall and poorly drained soils (eastern U.S. Corn Belt), that has not been the general case with Iowa soils and conditions. Certainly soils that are poorly drained and with high springtime rainfall periods can have positive return to sidedress or in-season N application; however that should not be an expected o occurrence on all soils or in all years. In addition, in years with dry conditions, especially after sidedress application, dry soils and lack of rainfall can result in poor crop fertilizer N uptake and reduced yield compared to preplant or early season application. In-season N application, by itself, will not improve yield unless there is deficient N in the soil system and the crop can respond. More N does not mean more yield, even if late applied. There are many opportunities for N application to be accomplished during the spring season, with options for successful preplant through midseason timing, along with tools to adjust rates. The potential frequency of soil and weather conditions that may impact optimal N timing, along with time and equipment to accomplish applications, should be considered when implementing sidedress/split N application systems. ACT NOW! Write, call or e-mail the Fluid Fertilizer Foundation Phone: 785-776-0273 E-mail: email@example.com Research and education for efficient use of fluids. The Fluid Fertilizer Foundation We need you to join hundreds of other growers, dealers, fertilizer manufacturers and other supporting industries JOIN IN THE SUPPORT OF THIS ORGANIZATION THAT DIRECTLY BENEFITS YOUR BUSINESS!