top of page

Corn Health Management

How NDVI, NDRE, and drones can be used together to monitor corn field health and guide maintenance decisions during the growing season.

1. Understanding the Tools: NDVI and NDRE

These are vegetation indices calculated from light reflected by the crop canopy. They act as proxies for plant health, vigor, and density.  

  • NDVI (Normalized Difference Vegetation Index):

    • Calculation: Uses Near-Infrared (NIR) light (which healthy plants reflect strongly) and Red light (which healthy plants absorb for photosynthesis). The formula is typically (NIR+Red)(NIR−Red)​.  

    • What it shows: Good indicator of overall plant biomass, density, and general greenness. It's sensitive to chlorophyll content.  

    • Best Use Case: Excellent for early to mid-season monitoring when the canopy isn't fully closed or extremely dense.

    • Limitation: Can become "saturated" in later growth stages when the corn canopy is very dense. This means NDVI values might plateau even if the plant's health (like nitrogen content) continues to change, making it harder to spot subtle differences.  

  • NDRE (Normalized Difference Red Edge Index):

    • Calculation: Uses Near-Infrared (NIR) light and Red Edge light (a narrow band between Red and NIR). The formula is typically (NIR+RedEdge)(NIR−RedEdge)​.  

    • What it shows: Less sensitive to just the top layer of leaves than NDVI. Red Edge light penetrates deeper into the plant canopy. It's strongly correlated with chlorophyll concentration and nitrogen content within the leaves.  

    • Best Use Case: More effective than NDVI during mid-to-late growth stages when the corn canopy is dense. It's better at detecting stress related to nutrient deficiencies (especially nitrogen) when NDVI might already be saturated.  

    • Benefit: Can provide earlier warnings of stress compared to visual scouting or sometimes even NDVI in later stages.  

2. The Role of Drones (UAVs)

Drones equipped with the right sensors are key to collecting the data needed for NDVI and NDRE mapping efficiently and effectively.  

  • Equipment: DJI Mavic 3 Multispectral : This drone is equipped with a multispectral sensor. Standard RGB cameras (like on typical consumer drones) capture Red, Green, and Blue light, but cannot accurately measure the specific NIR and Red Edge bands needed for true NDVI and NDRE calculations.

  • Data Collection:

    • Flight Planning: Automated flight paths are programmed using software to ensure consistent altitude, speed, and image overlap across the entire field or specific management zones.

    • Image Acquisition: The multispectral sensor captures data across the necessary light bands (Red, Red Edge, NIR, etc.) simultaneously.

    • Frequency: Flights should occur regularly throughout the growing season (e.g., weekly, bi-weekly, or timed with key growth stages like V6, V10, VT/R1) to track changes and trends.

3. The Monitoring and Maintenance Workflow

Here’s how these components work together during the growing season:

  • Step 1: Data Acquisition: Sky Dog ATI has the equipment to fly repeatable missions to aquire imaging.

  • Step 2: Data Processing: Sky Dog ATI has the equipment and software to generate VI (Vegetation Maps) maps.  

  • Step 3: Analysis & Interpretation:

    • Identify Variability: Look for patterns, zones, or spots within the field showing lower NDVI/NDRE values compared to surrounding areas or established benchmarks. Lower values indicate potential stress or less vigorous growth.  

    • Compare Indices: Use NDVI for early/mid-season general health and canopy development. Switch focus to NDRE as the canopy closes to better detect potential nitrogen stress or other issues masked by NDVI saturation.

    • Track Trends: Compare maps from different flight dates to see how areas are changing over time. Is stress spreading? Are management practices having an effect?

  • Step 4: Ground-Truthing (Crucial!): The maps show where potential issues are, but not necessarily what they are. It's essential to physically visit the identified low-index areas in the field.

    • Scout these zones for specific problems: Look for signs of nutrient deficiency (e.g., yellowing patterns typical of N deficiency), water stress (wilting), pest damage (insects, lesions), disease symptoms, weed pressure, or compaction issues.

    • Soil and tissue sampling might be warranted in problem areas to confirm nutrient status.

  • Step 5: Suggested Maintenance & Targeted Actions: Based on the map analysis and ground-truthing, implement targeted management actions:

    • Variable Rate Nutrient Application: If ground-truthing confirms nutrient deficiency (often Nitrogen, correlating well with NDRE), use the maps to create prescription files for variable-rate applicators. Apply more fertilizer only to the zones that need it, saving costs and reducing environmental impact in healthier zones. This is particularly common for side-dress nitrogen applications.

    • Targeted Pest/Disease Management: If scouting reveals localized pest or disease outbreaks corresponding to low-index areas, target scouting and potentially pesticide/fungicide applications to those specific zones rather than blanket spraying the entire field.

    • Irrigation Adjustments: If low index values and ground-truthing indicate water stress, check irrigation systems in those areas for clogs or pressure issues. Adjust irrigation schedules or amounts for specific zones if possible. Conversely, very high reflectance in NIR might sometimes indicate waterlogged areas needing drainage investigation.

    • Weed Management: Identify areas with heavy weed pressure that might be impacting corn growth and target post-emergence herbicide applications or cultivation.  

    • Evaluating Practices: Use the maps to assess the performance of different hybrids planted in strips, compare tillage practices, or evaluate the effectiveness of previous interventions.

In Summary:

Using drones with multispectral sensors to generate NDVI and NDRE maps throughout the corn growing season provides a powerful way to visualize crop health variability. NDVI offers a good general overview, especially early on, while NDRE excels at detecting nutrient stress and subtle health changes within denser, later-stage canopies. Combining these map insights with essential ground-truthing allows farmers to move from whole-field management to precision agriculture, enabling targeted maintenance actions like variable-rate fertilization, spot spraying, and optimized irrigation, ultimately aiming for improved yields, reduced input costs, and more sustainable practices.

bottom of page