Delaware Agronomy Blog

University of Delaware Cooperative Extension

Cover Crop Termination and Growing Degree Days

Cover crops respond to planting conditions and temperatures like other crops, and their growth will certainly follow winter temperatures as they accumulate growing degree days (GDD). Rather than set a solid burn down date based on a month or corn/soybean planting dates, you should scout fields to check on the current stage and biomass present. If your goal is to reduce interference with cash crop planting, then warmer winters and excessive growth may occur earlier in the spring than usual. If your goal is to build biomass for nitrogen, weed suppression, or a moisture retaining mulch layer, your potential burn down date can still vary from year to year. Additionally, our wet spring has caused variable conditions our fields, with saturated conditions killing off some cover crop growth (Figure 1).

Figure 1: A rye cover crop with variable growth. The brown colors are ponding and bare soil where the cover crop did not survive the winter.
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Soybean Planting Management in Delaware

Soybean Row Spacing and Population Studies

Modern soybean varieties can tolerate lower seeding rates and still produce good yields, providing there are no other issues with stand loss or stress. In southern Delaware two studies (2022 and 2023) observed no yield difference when planting full season beans (MG 4.2, late May planting date) when planted between 60,000 to 180,000 seeds per acre (Figure 1). You may consider dropping your seeding rates, considering your regional weather, planting date, and soil conditions.

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Corn Yield Responses to In-furrow Biological Products

James Adkins, Extension Engineer,,  Jarrod Miller, Extension Agronomist

In 2023, the University of Delaware evaluated the corn yield response to 14 biological products at 3 nitrogen fertility levels (optimum, 80%, and 50% rate).  While some of the products claimed to provide nitrogen fixation others were designed to improve plant health and root structure.  Products tested include:        

Invigorate (AMVAC)   

Ion Strike (Planet Earth Agronomy)

Zypro (Helena)   

BioGrowth (Willard Ag)

UtrishaP (Corteva)     

Source (Sound Ag)

ProveN40 (Pivot Bio)   

Blaine (Farmer 2 Farmer)

Accomplish Max (Loveland)     

Blaine with humic (Farmer 2 Farmer)

RioZyme Supreme (Schaeffer’s)   

Nexia (Innvictis)

RioZyme Plus (Schaeffer’s)     

Launch (Ag Concepts)

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Potassium Applications in Delaware Soils

Jarrod Miller, Extension Agronomist

University of Delaware recommends potassium (K) applications for low (0-70 ppm) and medium (71-140 ppm) soil test categories. However, soils in Delaware may have K that is not accounted for in a normal soil test, with minerals slowly release K over the growing season. Some of this was established by UD soil chemists in the 1980s, who observed high total K (not all plant available) in our soils, particularly in the sand fraction ( This means that some soils may need less K than is recommended by a regular soil test.

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Corn planting timing effects on yield and the relationship to deer feeding

Figure 1: Deer being allowed to eat our plots because it was part of the research.

Based on some observations in prior years, we planted irrigated corn on three different timings (April, May, and June) to observe three outcomes 1) yield, 2) nutrient uptake, 3) herbivory by deer. Average yields were all below 200 bushels, at 143, 175, and 128 bu/acre in the April, May, and June planted plots, respectively. Yield losses are potentially related to a range of factors, including deer feeding, weather, and soil nitrogen.

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