Using Active Canopy Sensors to Quantify Corn Nitrogen Stress and Nitrogen Application Rate
2010
Barker, Daniel W. | Sawyer, John E.
In-season corn (Zea mays L.) N sensing with active canopy sensors can provide input variables that direct variable rate N fertilizer applications. The objectives of this study were to assess corn N stress at the V10 to V12 growth stages, establish canopy indices that relate to optimum N application, and provide N rate algorithms for use in applying variable rate N fertilizer. Corn was sensed with the GreenSeeker Green 506 (GS-506) and Crop Circle ACS-210 (CC-210) active canopy sensors. Sensing was conducted in N rate trials over 3 yr encompassing 62 site-years across Iowa. The relationship between sensor indices and differential from economic optimum nitrogen rate (dEONR) was evaluated by fitting quadratic-plateau (QP) regression models between sensor values and dEONR. Sensing corn at the V10 to V12 stages resulted in statistically significant QP models relating sensor indices to corn N response. Relative canopy index models had greater adjR ² values than others, resulting in better representation between canopy index values and dEONR. These were the relative simple ratio index (rSRI), relative green difference vegetative index (rGDVI), and relative modified simple ratio index (rMSRI) for the GS-506 sensor, and relative green normalized difference vegetative index (rGNDVI), rSRI, rMSRI, and rGDVI for the CC-210 sensor. Variability in sensor prescribed N rate was greatest at slight N deficiencies (0–50 kg N ha⁻¹ deficit dEONR). Several indices relating to canopy biomass (rGNDVI) or canopy chlorophyll (rSRI, rMSRI, or rGDVI) can be used as an N rate algorithm for applying N fertilizer in-season.
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