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SUMMARY

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eturn to table of contents CORN HYBRID RESPONSE TO NITROGEN FERTILIZER by Mark Jeschke, Ph.D., Agronomy Information Manager and Jason DeBruin, Ph.D., Research Scientist - Field Tech Innovation & Ops SUMMARY • Efforts to improve nitrogen (N) management efficiency have driven interest in tailoring management practices to individual corn hybrids. • Successful implementation would depend on differences in hybrid response to N being large enough and consistent enough to justify hybrid-specific management. • University studies have commonly found either no hybrid by N rate interactions or that interactions were inconsistent across locations and years. • Recent DuPont Pioneer research found that yield response to N was affected greatly by location and year and that hybrid responses were generally similar when averaged across multiple environments. • The accumulated body of research in hybrid by N management suggests little opportunity for meaningful improvements to date in efficiency and profitability relative to other aspects of N management. • Response to nitrogen (RTN) values for corn hybrids are descriptive of the data collected but do not provide an actionable N management plan for growers to follow. • Analytical approaches that dynamically adjust for environmental factors, such as those employed by Encirca SM services, may provide a better opportunity to account for differences in hybrid genetics than static hybrid ratings based on a limited number of field trials. 62

eturn to table of contents INTRODUCTION Nitrogen management is among the most uncertain and costly aspects of modern corn production. Economic pressures, along with public concern regarding offsite movement of N, have driven interest in improving the efficiency of N management in corn. Efforts to improve efficiency have often focused on application timing and varying application rates based on crop needs. The development of advanced N management tools, such as the Encirca SM Yield Nitrogen Management Service, have helped enable this effort. Growers and researchers have both explored opportunities for improving N efficiency through managing N differently for each hybrid. Some seed and fertilizer suppliers have also promoted the concept of unique N needs and application timings for specific hybrids. Genetic differences in N uptake and utilization undoubtedly exist. Other characteristics, such as plant density tolerance and drought tolerance, are known to differ among hybrids, and grower management practices are often tailored accordingly. Some seed companies and dealers currently provide nitrogen response ratings and management recommendations for individual hybrids. However, the most pertinent question for growers is whether differences described by these ratings are actually large and consistent enough to justify hybrid-specific N management. A related and equally important consideration is the capability of industry and university research methods to reliably characterize hybrid differences in a way that provides useful management guidance to growers. HYBRID BY NITROGEN RATE INTERACTIONS In order to evaluate the potential value of hybrid-specific N management, it is first necessary to define what constitutes a hybrid by N rate interaction, the different types of interactions that may exist, and the management implications of each. A hybrid by N rate interaction means that the grain yield of two hybrids respond differently across a range of N application rates. Figure 1 depicts N rate responses for two hypothetical hybrids in which no hybrid by nitrogen rate interaction results. Hybrid A is higher yielding across the entire N rate range; however, the agronomic optimum N rate would be the same for these two hybrids. Grain Yield (bu/acre) 250 200 150 100 50 Low N Hybrid A Hybrid B No Hybrid x N Rate Interaction: Similar response to N between hybrids; Hybrid A is higher yielding across all N levels. Full Nitrogen Yield Low Nitrogen Yield Response to N (RTN) Nitrogen Rate Hybrid A 200 120 0.4 Full N Hybrid B 160 80 0.5 Figure 1. Response of two hypothetical corn hybrids across a range of N application rates showing no hybrid by N rate interaction. Corn showing nitrogen deficiency symptoms. Figures 2, 3, and 4 depict different types of hypothetical hybrid by N rate interactions. In Figure 2, the two hybrids have similar yields when supplied with sufficient N, but Hybrid A has greater yield than Hybrid B at low N levels. Hybrid A, in this example, could be described as having greater yield stability under low N and would be better suited for placement in fields at greater risk for N stress. Grain Yield (bu/acre) 250 200 150 100 50 Low N Hybrid A Hybrid B Significant Hybrid x N Rate Interaction: Hybrids have comparable yield with full N; yield of Hybrid A is more stable at low N levels. Full Nitrogen Yield Low Nitrogen Yield Response to N (RTN) Nitrogen Rate Hybrid A 200 150 0.25 Full N Hybrid B 200 100 0.50 Figure 2. Response of two hypothetical corn hybrids across a range of N application rates showing a significant hybrid x N rate interaction in which Hybrid A maintains greater yield stability under low N than Hybrid B. In Figure 3, the two hybrids have similar yields under low and full N but have different responses; Hybrid A approaches maximum yield at a lower N level than Hybrid B and, therefore, would have a lower economic optimum N rate. In this scenario, a grower may be able to reduce the N rate for Hybrid A without a yield penalty. Hybrid A would also be the preferred choice for placement in fields where there is a risk of N stress. This type of hybrid by N rate interaction is the most difficult to characterize experimentally as it would require testing the two hybrids at several rates in order to determine the optimum N rate for each. 63