Delaware Agronomy Blog

University of Delaware Cooperative Extension

Category: Weather (page 1 of 3)

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.
Continue reading

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.

Continue reading

Soybean Yield Response to Planting Populations, Row Spacing and Irrigation

To update our recommendations for soybean population, the Delaware Soybean Board sponsored a study of five different planting populations (60, 90, 120, 150, and180,000 seeds per acre), two row spacings (15 and 30”), and included irrigated and rainfed treatments under variable rate irrigation. Overall, no differences in yield were observed by population, while 15″ rows boosted yields by 10.6 bushels and irrigation boosted yields by 25.9 bushels.

Figure 1: a) aerial image of planting populations and row spacings at our Irrigation research farm, b) rainfed plots senescing earlier under our variable rate linear irrigation field.

Project Summary

Soybeans (maturity group 4.3) were planted at the UD Warrington Irrigation Research farm in May 2022 and harvested in November 2022 with a plot combine. The results were analyzed statistically as a randomized complete block design with three factors (population*row-spacing*irrigation) with means separation by Fisher’s LDS (alpha = 0.1).

Continue reading

Exchangeable Cation Uptake by Irrigated and Rainfed Soybeans (2021-2022)

Although Ca, Mg, and K are all exchangeable nutrients that are considered plant available, soil chemistry and plant root interactions result in different uptake and bioavailability. Within the soil, Ca and Mg can move with soil water or by diffusion, while the lower K concentrations do not readily move with soil water. This results in differences in uptake for soils with adequate moisture versus those under drought stress. Understanding how concentrations of each nutrient, the soil CEC, and soil moisture content interact is important for giving future nutrient recommendations.

Irrigated and rainfed dry corners in a Delaware field.

Average Delaware Growing Degree Days (2019-2021)

The standard method used to follow and predict corn growth stages is using growing degree days (GDD). This is a calculation that uses average daily temperatures measure accumulated heat over the growing season. Using GDD works better than days from planting because cool spring temperatures slow early planted corn, while corn planted later in May can have a more linear growth pattern.

For the past three seasons in Georgetown we have followed our research plots and have these values as the average GDD for our area (Table 1). They will be similar to those found in other states, but represent averages and ranges for our region. You may find GDD values on our regional mesonet (DEOS) or through the Climate Smart Ag page at Cornell (edit the site location).

Growing Degree Days (GDD) Average Accumulation to Reach Corn Vegetative and Reproductive Stages.
Older posts