Evaluation of Nitrogen Recommendations for Corn Based on Soil Analysis and Optically Sensed Data.

Nitrogen fertilizer is annually applied to corn (Zea mays L.) due to losses from grain removal and to the environment.  As a result of rising N fertilizer prices and environmental concerns, it is important to identify the amount of N needed to obtain maximum economic return.  The presidedress nitrogen test (PSNT) and normalized difference vegetation index (NDVI) derived from canopy reflectance of near-infrared and red light at the V7-8 growth stage may aid in making N recommendations.  The objectives of this study were to evaluate existing optical sensing algorithms, to identify optimum N rates, and to evaluate the PSNT for managing nitrogen in corn receiving liquid swine manure applications.  The relationship between the NDVI and PSNT performance was also determined.

This study was conducted at the Western Branch of the Ohio Agricultural Research and Development Center in South Charleston, Ohio, in 2007.  A split plot randomized complete block design was used.  Three liquid swine manure preplant rates (0, 117 and 233 kg N/ha), applied April 18, were used as main plots and nitrogen applied at 5 sidedress rates (0, 57, 113, 170, and 227 kg/ha), applied June 15, were used as subplots.  The 15 treatments were replicated four times.  One-foot deep soil samples were taken for PSNT analysis, and canopy reflectance of near-infrared and red light was collected on June 14.

Treatment, plant, and grain yield data were analyzed using regression analysis and ANOVA.  Results will be presented.