Corn Stalk Nitrate Test Spatial Variability.

The corn stalk nitrate test (CSNT) is a post-harvest plant test that can be used to identify where N application rates exceeded crop N needs, allowing for more informed decisions on adjustment N management in the following years (adaptive management process to N management for corn). Current recommendations suggest sample densities of 1 stalk acre^-1, creating a composite sample per field for analysis. The aim of this study was to: (1) analyze within-field CSNT spatial variability and its relation with silage yield; (2) evaluate yield-based, targeted, CSNT sampling; and (3) evaluate the relation between CSNT and soil Electrical Conductivity (EC). Field experiments were conducted between 2013 and 2015. Stalks were collected 1 or 2 days after corn silage harvest. Forage yields were evaluated by yield monitors and soils were scanned for soil EC using a Veris_® EC Mapper. Our results showed that higher yielding fields consistently obtained more homogenous CSNT values than low-yield fields or areas within fields. The spatial variability in CSNT was reduced by determining different yield zones and analyzing them separately. Soil EC was indirectly correlated with yield zones; high-yield zones had the lowest EC. The data suggest that a yield-based CSNT sampling protocol can improve the adaptive management process where within-field variability exists.