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NITROGEN MANAGEMENT

Nitrogen Recommendations for Corn: An On-The-Go Sensor Compared with Current Recommendation Methods

^a USDA-ARS, Bldg. 3702, Curtin Rd., University Park, PA 16802
^b USDA-NRCS, 478 Jeffers St., Bldg. 3, Ste. D, Dubois, PA 15801
^c Dep. of Crop and Soil Sci., Pennsylvania State Univ., 116 ASI Bldg., University Park, PA 16802

^* Corresponding author (john.schmidt{at}ars.usda.gov).

Precision agriculture technologies provide the capability to spatially vary N fertilizer applied to corn (Zea mays L.), potentially improving N use efficiency. The focus of this study was to evaluate the potential of improving N recommendations based on crop canopy reflectance. Corn was grown at four field sites in each of 2 yr in Centre County, Pennsylvania. Preplant treatments included: zero fertilizer, 56 kg N ha^–1, and manure. Split-plot treatments included the following N sidedress rates as NH₄NO₃: 0, 22, 45, 90, 135, 180, and 280 kg N ha^–1, and one at-planting N rate of 280 kg N ha^–1. Light energy reflectance (590 and 880 nm), chlorophyll meter (SPAD) measurements, and the presidedress NO₃ test (PSNT) results were obtained at sidedress. The late-season stalk NO₃ (LSSN) test was determined. The economic optimum nitrogen rate (EONR) was determined based on grain yield response to sidedress N rates. Relative green normalized difference vegetation index (GNDVI) and relative SPAD were based on relative measurements from the zero sidedress treatment to the 280 kg N ha^–1 at-planting treatment. The EONR from 24 preplant treatment–site combinations was related to relative GNDVI (R² = 0.76), the PSNT (R² = 0.78), relative SPAD (R² = 0.72), and the LSSN test (R² = 0.64), suggesting that relative GNDVI was as good an indicator of EONR as these other, more conventional tests. Because relative GNDVI can be obtained simultaneously with a sidedress N fertilizer application, the potential to accommodate within-field spatial and season-to-season temporal variability in N availability should improve N management decisions for corn production.

Abbreviations: AASL, The Pennsylvania State University Agricultural Analytical Service Lab • EONR, economic optimum nitrogen rate • GNDVI, green normalized difference vegetation index • LSSN, late season stalk NO₃ • PPNT, preplant NO₃ test • PSNT, presidedress NO₃ test • SPAD, chlorophyll meter

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Received for publication December 18, 2008.