Updated March 25, 2021:

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Strong relationships between maturity group and nutrient uptake were not observed in this study, but potential herbicide damage, drought, and other environmental conditions may have contaminated the study. Instead the strongest relationships in Delaware for soybean yield remain to be soil type and access to adequate moisture. Soil nutrient concentrations varied by site, which is not unusual considering variation in management and natural soil variability.

However, there were some interesting relationships for nutrient uptake and sufficiency ranges. The only nutrient that did not meet the sufficiency range was leaf concentrations of Ca. When compared to yield, higher Ca levels had a weak, but significantly negative relationship with yield. Whether this means Ca sufficiency levels are high, or nutrient imbalances needed corrected is not known. A more confusing observation is that Middletown had the lowest Mg, Cu, and Fe in the soil, but the highest in the whole plant tissue. Middletown also had the lowest P concentration, but a higher leaf P, but lowest whole plant P concentration.

Some of the strongest correlations to yield included Mg, S, and Cu, which all increased in the plant with higher yield. These three nutrients were also correlated to each other by plant tissue concentrations. Higher potassium in leaf samples was actually related to lower yield though, which may indicate some kind of stress or competitive uptake with Mg or Ca.

Sodium tissue levels were similar to the 2019 statewide survey, which was also the only plant nutrient which correlated to yield. In 2019 we assumed this to be a corollary to irrigation, with higher plant levels related to irrigation water salt concentrations. In the 2020 variety trial study, Na had a negative correlation to yield as well as Mg, S, and Cu. As a monovalent cation, it would also be expected that Na would have a negative relationship with K uptake, but this was not the case. With tissue levels similar to 2019, it can be assumed that Na uptake was either in competition with other nutrients, or the result of some kind of environmental stressor. As this study was not controlling for any nutrient or variable, that cannot be known.

This study leads us to conclude that Mg uptake, and its relationship to soil and nutrient characteristics, needs further study for soybeans in Delaware. Whether it is important for increasing yields or is a corollary to other abiotic controls on soybean growth warrants further investigation.