Delaware Agronomy Blog

University of Delaware Cooperative Extension

Author: Jarrod Miller (page 1 of 16)

Estimation of Cover Crop Nitrogen with Drones

Jarrod O. Miller, Assistant Professor and Extension Specialist, Agronomy, jarrod@udel.eduAmy L. Shober, Professor and Extension Specialist, Nutrient Management and Environmental Quality,,  Jamie Taraila, Graduate Research Assistant; 

As part of a Northeastern SARE graduate student grant, we used a drone to predict the nitrogen (N) that may be present in cover crops prior to burndown. We flew fields in Laurel, Georgetown, and Harbeson with a readily available consumer drone (Phantom4) equipped with a standard (RGB) camera. Each of the fields were flown prior to cover crop burndown (late April to late May) resulting in 25-100 images per field that had to be stitched together into one image (Figure 1a). The camera captured different wavelengths of light (i.e., red, green, blue) that were reflected by plants which were transformed into the Visible Atmospherically Resistant Index (VARI). This allowed us to estimate plant biomass by comparing VARI values to cover crop biomass that was collected in the field. We collected 10 samples per field, which were dried, weighted, and then analyzed for N content by the UD soil testing lab.

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Evaluating Cover Crop Growth with Drones

 Jamie Taraila, Graduate Research Assistant; Jarrod O. Miller, Assistant Professor and Extension Specialist, Agronomy,; Amy L. Shober, Professor and Extension Specialist, Nutrient Management and Environmental Quality,


As part of a Northeast SARE sponsored project, we evaluated cover crop growth response (biomass) to various seeding rates. We also followed cover crop growth through the winter using drone imagery. We planted NRCS recommended rates of rye (100 lbs/acre), clover (15 lbs/acre), and a rye/clover mix (40 lbs/acre rye, 10 lbs/acre clover) at the UD Carvel Research and Education Center in Georgetown following corn harvest in late September 2020. We also planted the same cover crops at reduced rates of 25, 50, and 75% the NRCS recommendation. By the time we sampled cover crop biomass in April, there was very little difference in biomass from the 25 to 100% (full) rates. In fact, the biomass response curves show that there was little increase in biomass above the 25% seeding rate (0.25) for each cover crop type, as the curve is relatively flat above this rate (Figure 1). Continue reading

Keep Stress Down During Reproductive Stages


Corn silks have pollinated kernels as they move into the R2 stage

A corn ear that has pollinated and is in the R2 ( blister) stage.

As we enter the grain fill period, with some of our fields already at R2 (blister stage) or R3 (milk stage), it is important to keep stress down. Fields still at R1 or R2 (mid-May planting dates) may have the most to lose as kernels are being pollinated and start to fill. In past field trials, we have observed that yield correlates the best between about R2-R4 (from drone imagery, see below), so while there isn’t much you can do to improve yield, you can certainly do your best to maintain it by managing irrigation wherever it is needed.

Vegetation indexes and their correlation to yield over the corn growing season.

Vegetation indexes and their correlation to yield over the corn growing season.

July Temperatures and Pollination

According to data from the last two years (, silking and pollination (R1) has occurred between 1320 and 1594 growing degree days, while VT (tasseling) occurs between 1200-1300. In many of our research fields, VT also began to occur in this range last week, followed quickly by silking. Stress during pollination can determine initial pollination and kernel set, so temperature becomes very important. Planting date is an important part of this, as corn growth will follow heat accumulation, so cooler springs will take longer to reach R1 and vice versa. Continue reading

Checking Vegetative Growth Stages

Corn at our research station is at V4, which means we will probably be sidedressing several fields next week. Anyone who planted prior to April 25th may be one leaf ahead, and plans for sidedressing should be done. If you are unsure of which stage you are at, one common method is to count leaves based on the presence of the collar (Figure 1a). While many leaves can be emerged from the whorl, only those with collars are considered fully developed. Continue reading

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