2020
Nitrogen Dynamics of Soybeans & Soybean Residues in Long-term No-till Production systems
Contributor/Checkoff:
Category:
Sustainable Production
Keywords:
GeneticsGenomicsSeed quality
Parent Project:
This is the first year of this project.
Lead Principal Investigator:
Larry Cihacek, North Dakota State University
Co-Principal Investigators:
Project Code:
QSSB
Contributing Organization (Checkoff):
Leveraged Funding (Non-Checkoff):
ND State Board of Agricultural Research and Education - Soybean Committee $9,550.00
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Institution Funded:
Brief Project Summary:

Most soybeans in North Dakota are grown in rotation with spring wheat or corn and are expected to provide a portion of the following crop’s nitrogen needs. Ongoing research on nitrogen mineralization from heavy crop residue accumulations in no-till systems has indicated that more immobilization of nitrogen rather than mineralization may be taking place. This project aims learn how soybeans and its residues interact with nitrogen availability in no-till systems and how this relates to soil health. Researchers will look at nitrogen transformations in the plant and the soil around the root zone during the late maturity, plant senescence, and post-harvest.

Key Benefactors:
farmers, agronomists, extension specialists

Information And Results
Project Deliverables

Final Project Results

Nitrogen Dynamics of Soybeans and Soybean Residues in Long-term No-till Production Systems : Final Report

Larry Cihacek and Rashad Alghamdi
Soil Science Department
North Dakota State University
Fargo, ND 58108

Executive Summary

In 2017, approximately 7,050,000 acres of soybeans were harvested in North Dakota, making the state the 5th largest producer of soybeans in the nation. In the region, most soybeans are grown in a rotation with spring wheat or corn which is expected to provide a part of the N needs of the following crop. No-till conditions often result in heavy crop residue accumulation. The cooler climate and shorter growing season of the region may slow down decomposition and inhibit nitrogen availability and mineralization by plants when certain crop residues are present. Instead, an immobilization of N may be taking place in these systems. Several states in the northern U.S. have recommended that N should be added in long-term no till systems when heavy crop residues are present (Bundy, 1998; Ketterings et al., 2003; Jokela et al., 2004; Pariera Dinkins and Jones, 2019). To better understand crop fertilizer N needs, nitrogen mineralization and immobilization trends were examined taking into consideration climatic conditions such as freeze and thaw, as well as crop rotational effects. In nature, the C:N ratios of post-harvest crop residues differ by species. When crops are rotated in a field, the C:N ratios of the system may be altered resulting in soil N mineralization or immobilization values which vary from those observed by each crop on its own (Chatterjee et al., 2016). Incorporating a late season cover crop in a rotation where non-leguminous crop residue exists may alter the soil N immobilization effects of non-leguminous crops to accelerate soil or residue N mineralization. In this research, a series of soil incubations were conducted with additions of corn (C), soybean (S), spring wheat (SW), and radish (R) crop residues, to simulate common cropping systems with a 2-year, 3-year and 3-year with cover crop rotation. Cropping systems and rotations included: C-C-C, R-R-R, C-S-C, S-C-S, SW-S-SW, S-SW-S, SW-S-C, S-C-SW, C-SW-S, SW/R-S/R-C, S/R-C-SW/R, C-SW/R-S/R and S/R-C-SW/R. Soils were incubated for 12 weeks (the length of a normal North Dakota growing season), frozen for 3 weeks to simulate winter freezing and were then thawed. Samples were leached and nitrate was recorded. After thaw, the subsequent crop for the sequence was applied and the process was repeated. Nitrate mineralization and immobilization trends were recorded with the bare soil as a control and baseline standard to determine the trend. Findings of this research determined that crops were only mineralizing where the radish cover crop was incorporated for the sequence. For all other sequences, immobilization trends were evident. High C:N ratio crop residues (C:N>40) did not demonstrate N mineralization patterns over a period of time with similar climatic conditions in a field setting. Evaluation of N mineralization soybean plant residues at senescence or at harvest Showed a general trend of N immobilization for most plant parts. Results of this study indicate a need for field validation research to verify these findings and should lead North Dakota soybean farmers to reconsider N fertilizer credit recommendations for their fields with long-term no-till conditions.

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.