Update:
March 15, 2020 Report
Late-season nitrogen fertilizer applications after R5 increased seed protein concentration, supporting our hypothesis that N availability during seed fill is partially limiting protein concentration, and this may be palliated with management practices. Preliminary analysis by NIRs in harvest seed showed a significant effect of N fertilizer applications on some amino acids and fatty acids. Further analysis of seed composition by reverse phase HPLC and gas chromatography is underway. Results from aerial phenotyping of the crop N status was summarized in the report. The association between canopy greenness measured from aerial images and measured shoot N concentration suggests that aerial phenotyping may be used to assess crop N status in soybean fields.

Update:
September 15, 2020 Report
The results from a source sink manipulation study reveal that actual soybean seed size are always below the maximum achievable, but that seed growth can response to increases in assimilate supply up to the end of the seed fill phase to reduce this gap. Findings from this study have important implications that emphasize the importance of late-season soybean management recommendations. Results were summarized in a manuscript that will be submitted to a peer-reviewed journal. Sample processing from 2019 trials was delayed due to Covid, but it is now completed, and plant tissue and seed composition analyses will be completed in the next weeks. Field trials from the 2020 season are carried out according to plan, and include frequent data collection with aerial imaging at each location. Harvest of early cultivar maturities is expected to start this month.

Update:
Developing strategies that ensure that meal from U.S. soybean seeds is competitive in global markets is essential for producers. Management practices can be an inexpensive and fast-response strategy to accurately match N supply with the crop N demand. However, there is insufficient research documenting the potential of cultural practices to influence protein quantity and quality. Past regional studies and meta-analyses stressed the need of a more mechanistic understanding on the effect of cultural practices on grain protein. In this project we conducted field trials during 2019-2020 evaluating different maturity groups and cultivars across a wide range of environmental conditions (AR, KY, and MN) to: (1) quantify the potential of late season N fertilizer applications and B. japonicum inoculations to improve protein quantity and quality (amino acid and fatty acid profiles), (2) evaluate these practices in soybean grown after fallow or after a winter cereal cover crop, and (3) to quantify if aerial images can be used to detect crop N limitations and adapt inputs. Results from our study provided clear evidence that increasing late-season N availability can increase seed protein concentration, and avoid meal protein concentration below the threshold required by the food industry. Moreover, late-season N applications had a positive effect on yield that would increase net economic returns in some years and locations, making this cultural practice economical for producers. The protein quality, measured from the amino acid composition, was maintained across the different cultural practices evaluated. Spray inoculant applications of B. japonicum at R3 in previously inoculated seed and fields with soybean history did not have an effect on soybean yield or seed composition. Lastly, this project provides exciting new evidence of the potential of aerial imaging to assess in real time crop N status and the effect of cultural practices in soybean. This project generated a dataset across different environments and cultural practices that will be instrumental to improve eco-physiological and process-based soybean models for the simulation of seed protein.