Delaware Agronomy Blog

2024 Soybean Row Spacing and Population Studies for Coastal Soils

November 8, 2024 / Jarrod Miller / Comments Off

Summary: Three years of population studies have only shown little difference in population (60-180k), when planted early enough, however later planted (double crop) beans may be safer at 120k or above. Planting in 15 inch rows can increase yields 5-10 bushels.

As soybean genetics have improved, national studies in planting populations are revealing that lower populations can still provide similar yields. We have performed studies over the past few years, including 2022 (Click for link) and 2023 (Click for link). For both of those years there was a 10-bushel advantage for narrower rows (15 vs 30”), 25 bushels for irrigation, but no differences between populations of 90 to 180,000 seeds per acre.

Grid Sampling Soils for Variable Rate Lime Applications

November 4, 2024 / Jarrod Miller / Comments Off

Jarrod Miller, Extension Agronomist & James Adkins, Irrigation Engineer

One method to uncover soil variability and crop response is to use precision soil sampling, including either grid or zone methods. These maps can then be used to make variable rate applications, where application rates will change as you cross the field, and GPS helps guide the rates. For this study, soil samples were taken from the upper eight inches of soil on our irrigation research farm in Harbeson, DE. Samples were taken on a 90 by 90-foot grid in April 2022 (Figure 1).

**Figure 1:** Grid sampling points overlain onto a September 2024 image of the Warrington Irrigation Research Farm, including both center pivot and linear irrigation.

From these grids, maps of nutrients and soil properties were created, including soil pH and buffer pH (Figure 2). Soil pH is measured using water and is the pH your crop will react to. So you use the soil pH measurement to decide if you want to raise or lower your pH. The buffer pH helps figure out any acidity within the soil that will react with lime, causing the need for a higher lime rate (Figure 2b). These two pH measurements were combined using UD recommendations to create a variable rate lime map (target pH = 6.2), which was applied in 2023.

Using NDVI to Determine Early Vegetative Growth and Nitrogen Needs

November 1, 2024 / Jarrod Miller / Comments Off

Jarrod Miller, Extension Agronomist, University of Delaware

Precision nitrogen (N) management through the use sensors has been used to improve nitrogen use efficiency (NUE) for field crops by estimating corn needs during early growth stages (Aula et al., 2020; Cao et al., 2017) Indices have been developed using specific wavelengths of light, such as the normalized difference vegetation index (NDVI) to estimate plant biomass and correlate it to N needs (Holland et al., 2012; Raun et al., 2005a; Dellinger et al., 2008). The use of NDVI has allowed for reductions in N application have been performed without reducing crop yield (Barker and Sawyer, 2012; Aula et al., 2020).

Cover Crop Termination and Growing Degree Days

April 2, 2024 / Jarrod Miller / Comments Off

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.

Soybean Planting Management in Delaware

April 2, 2024 / Jarrod Miller / Comments Off

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.