Delaware Agronomy Blog

University of Delaware Cooperative Extension

Category: Soybean (page 1 of 2)

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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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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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).

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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.

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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