Delaware Agronomy Blog

University of Delaware Cooperative Extension

Category: Programs (page 1 of 9)

Grid Sampling Soils to Improve Understanding of Soil Variability

Jarrod Miller and James Adkins, University of Delaware

Variability in soil land landscape characteristics reduces yield response to management techniques, particularly regarding seeding rates and fertilizer additions. Yield maps provide a spatial map of yield, which can be associated with drainage issues, soil nutrient holding, or nutrient concentrations. One method to uncover soil variability and crop response is to use precision soil sampling, including either grid or zone methods. Both increase the cost of taking soil samples, and each have their value depending on the desired outcomes.

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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

Cover Crops May Protect Corn from Cooler Temperatures

The weather outlook in Georgetown includes no air temperatures (currently) in the 30s through April 21st. With that outlook, soybean and corn planting can probably start late next week. Although there can still be a random late freeze, the probability really drops after April 15th in our region.

The preferred soil temperature for corn germination is 50°F, which allows the seed to begin root and shoot growth.  Many of the weather stations on DEOS ( have soil temperature as an option, so you can track current conditions. Since April 1st, soil temperatures have ranged from 47-53°F in Newark and 47-55°F in Georgetown. Soil temperature does not change as rapidly as air temperature, so we would expect the daytime temperatures over the next week to keep soils above 50°F, even when nighttime temperatures dip into the 40s.

Figure 1: Corn on the left was planted in bare plots while corn a few inches away in a rye cover crop appears unaffected.

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Cover Crop Termination for 2021

Jamie Taraila,  Jarrod Miller,  and Amy Shober

With April and warmer temperatures finally here, it is time to think about cover crop termination. This spring, we expect lower cover crop biomass at burndown due to the cool, wet winter conditions that delayed growth, particularly small grains. Therefore, termination timing decisions are very important this year. We must recognize that there are pros and cons of early and late cover crop termination and make decisions that maximize benefits.

Figure 1: Vetch cover crop before spring corn planting.

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