Within the region, minimal differences have been observed between April and May planted soybeans, although cooler weather and disease may reduce yields with earlier planting. Another issue uncovered in recent DSB research projects is the effects of Al and Fe uptake on reducing early planted soybean yields. One way to reduce the effects of these metals is maintaining a
higher soil pH, reducing the solubility of Al and Fe. By increasing soil pH, soybean producers may find that earlier planting on our coastal soils can take advantage of a longer pre-solstice growing season and obtain greater yields.

Alternatively, higher pH may reduce the availability of other metal micronutrients, including Mn, Zn and Cu. It may also give rise to greater edge site cation exchange capacity, allowing for greater leaching of B and SO4 from the soil surface. Rather than having a net sum reduce the effectiveness of liming, we must determine the liming effects on all nutrients taken up in these
soils.

1) Lime soils at five rates to observe soybean growth and yield
2) Plant soybeans at two different timings within the lime plots to observe Al uptake.
3) Compare the effects of lime and planting timing on yield.

Using a regional farmer field, we will establish 10 by 30-foot plots to receive lime treatments as a randomized complete block design (RCBD). There will be five lime rates (0, 0.25, 0.5, 0.75, and 1.0 tons acre-1), two planting timings (April and late May), and three replications for a total of thirty combined plots. Lime treatments will be hand applied in the spring prior to soybean
planting. Soil samples will be taken prior to lime application to establish each plots baseline. Soybean tissue samples will be taken at V3 and R1 to establish nutrient uptake over the season. All samples will be submitted to the UD soil testing lab for analyses. Yield will be collected at the end of the growing season using a plot combine. Tissue nutrient content will be correlated to yield and initial soil nutrient levels. Using SAS statistical software, we will compare the plot data
as a factorial RCBD to determine treatment effects. Results will be reported to the board as well as at regional extension meetings.

Updated August 8, 2024:
A section of a rye cover crop was terminated in March 2024, plots were established and then limed followed by a turbo-tilled to incorporate into the upper 2 inches of the soil. The first soybean timing was planted in early April 2024, and the second timing was planted in late May 2024. Due to persistent deer feeding, a fence was placed around the plots for two weeks, limiting feeding to outside the plots so they could recover. At this point in the season both April and May planted soybeans have reached reproductive growth stages, so that tissue samples from both vegetative and the R2 growth stage have been sampled and placed in a drier. Pre-plant soil samples were taken in April. Soybeans have been irrigated earlier than expected due to drought conditions, and weed control has been performed to prevent herbicide resistant weeds from growing in the plots. Drone flights have been performed over the plots before and during the project duration.

Updated January 3, 2025:
All soybean plots were harvested in October 2024 for yield. Although the April planted soybean dried down earlier, randomized plots made us wait to harvest the entire field at the same time. However dry conditions sped up senescence of the May planted soybean crop, and we did not see any issued with pod shatter in the April planted soybean. Yields were not affected by lime rates, however all tissue samples for the V3 and R2 growth stages were submitted to the UD soil testing lab for analyses. Liming may still have an affect on nutrient uptake based on tissue samples.

Updated April 4, 2025:

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In the Mid-Atlantic region, soybean yields usually show little difference between April- and May-planted crops. However, earlier planting may expose soybeans to cooler temperatures and increased disease, which could lower yields. Research on double-cropped soybeans suggests that aluminum (Al) and iron (Fe) uptake negatively impacts early-planted crops. Raising soil pH with lime can reduce the solubility of Al and Fe, potentially benefiting coastal soil producers by extending the growing season. However, higher pH may reduce availability of micronutrients like manganese (Mn), zinc (Zn), copper (Cu), and increase leaching of boron (B) and sulfate (SO4).

This study aimed to evaluate the effects of different liming rates and planting timings on soybean yield and nutrient uptake using dolomitic lime. It was performed at the Carvel Research and Education Center in Georgetown, DE, with two factors: liming rate (0, 0.25, 0.5, 0.75, and 1.0 tons per acre) and planting timing (April 9, 2024 and May 29, 2024). The lime was dolomitic based on soil testing prior to application. Soil and tissue samples were collected at V3 and R3 growth stages to assess nutrient levels.

Yield results showed no significant differences among liming rates, with yields ranging from 56.27 to 64.14 bu/ac. The highest yield (64.14 bu/ac) was recorded at the 0.75 tons/acre lime rate, and the lowest (56.27 bu/ac) at 0.5 tons/acre. However, planting timing significantly affected yield, with soybeans planted in April yielding 62.67 bu/ac compared to 54.74 bu/ac in May, likely due to warmer weather conditions in April.

Soil nutrient concentrations varied with liming, showing significant changes in calcium, pH, magnesium, boron, and base saturation. Calcium and magnesium increased with dolomitic lime rates, while phosphorus, manganese, zinc, copper, iron, sulfur, and sodium did not change significantly. Aluminum (Al) and iron (Fe) decreased with lime, supporting the idea that liming reduces the solubility of these metals in coastal soils.

For leaf tissue, micronutrient availability decreased with higher lime rates, particularly for manganese (Mn), zinc (Zn), and boron (B), both in soil and tissue. In soil, Mn, Zn, and B levels declined with increasing lime rates, especially at 0.75 tons/acre (where pH > 5.8). Similarly, V3 trifoliate tissue concentrations of Mn, Zn, and B were highest at the 0 and 0.25 tons/acre lime treatments, with a steady decline as lime rates increased. Soybeans planted in May had higher Mn and Zn concentrations compared to those planted in April, while B followed a similar, but less consistent pattern. These results suggest that excessive liming reduces the availability of these essential micronutrients, potentially affecting soybean growth when soil concentrations are deficient.

From V3 to R2, nitrogen (N), phosphorus (P), and potassium (K) concentrations declined more in April-planted soybeans, while Mn and B increased more in May-planted soybeans. Iron and aluminum concentrations decreased more in May-planted soybeans. These shifts did not negatively affect early-planted soybeans, which yielded better.

Overall, soybean yield was not significantly affected by liming rate but was higher with earlier planting, due to warmer than normal conditions. Liming had minimal effects on macronutrient availability, except for increases in calcium and magnesium in the soil. Higher lime rates reduced Mn, Zn, and B availability, which may limit growth. These findings suggest that early planting remains beneficial for yield, and liming effects on nutrient uptake were relatively minor for the rates applied. A pH higher than 5.8 may have caused greater issues.

Soybean farmers will be able to apply the lime necessary for both maximum yield benefits while limiting aluminum uptake into the plant.