Using canopy reflectance to monitor corn response to nitrogen and the effects of delayed nitrogen application

Daniel Joseph Emmert, Purdue University

Abstract

Nitrogen (N) fertilizer is one of the most important and expensive inputs for a corn crop. Current Indiana N recommendations are based upon yield goals. As corn yields continue to rise, N recommendations need to be reevaluated. Reflectance measurements using a crop reflectance sensor during the growing season may be useful for determining the need for additional N. The objectives of this study were to evaluate corn grain response to N in Indiana, and to evaluate a crop reflectance sensor as a management tool to assess corn N status and predict grain yield. Studies were conducted at seven Purdue University Agriculture Centers during 2006 and 2007. Plots were sidedressed with injected urea ammonium nitrate (UAN) when plants reached V3 to V5 growth stages. Treatment rates ranged from 0 to more than 200 lb N/acre in 40 or 50 lb increments dependent on location. At approximately V11, canopy reflectance was measured with a crop reflectance sensor using wavelengths of 590 (VIS) and 880 (IR) nm. The average optimum N rate was 167 lb N/acre for corn grown in rotation with soybean and 204 lb N/acre for corn grown after corn. The optimum N rate ranged from 116 to 229 lb N/acre and was not related to maximum grain yield or soil organic matter. Soil yield potential based on a modified Diderikson’s model and optimum N rate were inversely related; high yield potential soils required lower amounts of N. A strong correlation was found between the relative chlorophyll index [(IR/Vis)-1] determined with crop reflectance sensors and the relative grain yield (r2= 0.82). The crop reflectance sensor is most effective at detecting N stress during the late vegetative stages so a second study was established at three locations to determine corn response to fertilizer N application after V12 in a rain-fed environment. Three treatments were designed to induce varying degrees of N stress. All treatments received starter fertilizer (21 to 35 lb N/acre depending on location) at planting. The least N stress was obtained by sidedressing N at growth stage V3 (SIDEDRESSV3). DELAY plots received starter fertilizer at planting and sidedressed N near growth stage V13. SPLIT plots received starter fertilizer plus an additional 70 lb N/acre at planting and sidedressed N near growth stage V13. Sidedress N rates ranged from 0 to 210 lb N/acre in 35 lb increments. SDV13 treatments resulted in reduced yields at all three locations compared to SDV3 while the SPLIT treatments yielded lower at two of three locations.

Degree

M.S.

Advisors

Camberato, Purdue University.

Subject Area

Agronomy|Soil sciences

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