2021
Exchangeable Cation Uptake by Irrigated and Rainfed Soybeans
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Contributor/Checkoff:
Delaware Soybean Board
Category:
Sustainable Production
Keywords:
DiseaseField management Pest
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Jarrod Miller, University of Delaware
Co-Principal Investigators:
Project Code:
PLSC43292521013/PLSCDA2113
Contributing Organization (Checkoff):
Delaware Soybean Board
$4,901
Institution Funded:
University of Delaware
$4,901
Brief Project Summary:

Most soybean nutrient recommendations are based on target yield, which vary based on a variety of factors. One factor not considered is nutrient availability based on soil type. Although Ca, Mg, and K are all considered plant available, soil chemistry and plant root interactions result in different uptake and bioavailability. This results in differences in uptake for soils with adequate moisture versus those under drought stress. This project samples irrigated and rainfed soybean fields, with a focus on dry corners in center pivot fields and compares Ca, Mg, and K uptake in the tissue to soil nutrient contents and cation exchange capacity, all to inform future nutrient recommendations.

Key Benefactors:
farmers, agronomists, Extension agents

Information And Results
Project Deliverables

Final Project Results

Updated March 12, 2022:
Final report attached.

View uploaded report PDF file

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. The objectives of this study were to sample center pivots in their dry corners and irrigated regions and compare soil nutrient levels and nutrient uptake in the leaf tissue for potential. To do that, soybean fields 10 center pivots in Delaware were sampled in irrigated and dry corners. Upper leaf tissue and soil samples were obtained at the R2/R3 growth stage and tested for soil characteristics and nutrient contents.

Irrigated soybeans had higher concentrations of N, P, Fe, and Na in the upper leaf tissue, with K and Cu being slightly higher, but not statistically significant. This is not necessarily an issue for yield, as all measured leaf tissue nutrients were within their sufficiency ranges, except Ca which was just below the 0.8% threshold in both rainfed and irrigated soybeans.

Nitrogen also had no significant negative correlations in irrigated fields, with concentrations above threshold values (5.7%), so its possible N was not limited in these scenarios and would not produce negative correlations with other elements. This was not the case in rainfed samples, where N uptake was inversely correlated to Ca, Mg, and Al uptake, potentially due to stress when moisture was limited.

Greater Na concentrations in both irrigated soil and tissue samples was most likely related to salts in irrigation water, with Na having very few relationships to other elements in leaf tissue samples. Iron was also higher in irrigated tissue samples but had more correlations to tissue nutrients in rainfed samples. This may mean that Fe uptake occurred with higher soil moisture but was not related to any other nutrient uptake. Alternatively, Al uptake in rainfed beans may also reflect excess uptake, but under stressed conditions, where it positively correlated with many other tissue nutrients, but had no positive correlations with irrigated soybeans.

All these relationships are based on 2021 rainfall, which was sufficient for most of the early summer in Delaware, and not deficient until late July. It is certainly possible to have different relationships in doughtier years, which includes greater differences (lower N, P, and K in rainfed) between regions or fields with different moisture contents.

The United Soybean Research Retention policy will display final reports with the project once completed but working files will be purged after three years. And financial information after seven years. All pertinent information is in the final report or if you want more information, please contact the project lead at your state soybean organization or principal investigator listed on the project.