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United States Department of Agriculture

Agricultural Research Service

Title: In-season nitrogen recommendations for corn

Authors
item Varvel, Gary
item Schepers, James
item Wilhelm, Wallace
item Shanahan, John
item Francis, Dennis

Submitted to: North Central Extension Industry Soil Fertility Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: March 15, 2006
Publication Date: November 11, 2006
Citation: Varvel, G.E., Schepers, J.S., Wilhelm, W.W., Shanahan, J.F., Francis, D.D. 2006. In-season nitrogen recommendations for corn. North Central Extension Industry Soil Fertility Conference Proceedings. 2006 Des Moines, IA. 22:72-77.

Interpretive Summary: Making fertilizer N recommendations involves a great deal of guess work and uncertainty because much, essentially all, of the fertilizer N is applied before the crop is planted and the amount is based on estimated crop use from historical data. In addition, producers, consultants, and fertilizer dealers try to anticipate how much N might be lost because of untimely or excess precipitation or how much additional N might be required if the weather conditions are favorable. This study explored a technique for using the crop as a bio-indicator of soil N status and applying supplemental N on a variable rate basis using a locally derived algorithm. The objective of the study was to evaluate the approach for making in-season N applications and determine the wider-scale applicability of the algorithm. Chlorophyll meter readings and grain yield were collected from corn in an irrigated monoculture corn cropping system with four hybrids and five N fertilizer application rates in the Platte Valley near Shelton NE. Normalized chlorophyll meter readings (sufficiency index, SI) were calculated from data collected at three growth stages (V8, V10, & V12), during each of the ten years of study (1995-2004). Both SI and relative yield responded significantly to N fertilizer application. A single quadratic model was developed using the data from all three-growth stages to describe the relationship between N rate and SI. That relationship is: (SI = 0.8073 + 0.002(N rate) 0.0000056(N rate)2, R2 = 0.70). Using this algorithm, producers can determine if N is needed, and if so, the amount of N needed for maximum yield. In addition if SI is computed for specific areas of the field, N applications can be tailored to those areas, thereby reducing the potential of introducing more N into the system than needed to achieve maximum yield, within the constraints of the hybrid, site, and season.

Technical Abstract: Nitrogen fertilizer continues to be the major input influencing corn yield in the Midwest. Improved N recommendations should result in greater N use efficiency and producer profit while reducing surface and groundwater contamination. This study was conducted to develop a plant-based technique to detect and correct N deficiencies during the growing season. Chlorophyll meter readings and grain yield were collected from corn in irrigated monoculture corn and soybean-corn cropping systems with four hybrids and five N fertilizer application rates in the Platte Valley near Shelton NE. Normalized chlorophyll meter readings (sufficiency index, SI) were calculated from data collected at three vegetative stages, defined by thermal time accumulation after planting, during each of the ten years of study (1995-2004). Highly significant linear correlations between SI and relative yield indicated both responded similarly to N fertilizer application. Relationships between N rate and SI (at each of the three vegetative stages and combined over stages) were described by quadratic models. The combined model (SI = 0.8073 + 0.002(N rate) 0.0000056(N rate)2, R2 = 0.70) can be used to compute N needed to achieve maximum yield. This procedure gives producers the tools to determine if N is needed, and if so, the amount of N needed for maximum yield. In addition if SI is computed for specific areas of the field, N applications can be tailored to those areas, thereby reducing the potential of introducing more N into the system than needed to achieve maximum yield, within the constraints of the hybrid, site, and season.

Last Modified: 11/23/2014
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