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6978373 
Journal Article 
A Quantitative Method for Analyzing Nitrogen Assimilation in Soybeans 
Kakiuchi, Jin; Kobata, T; , 
2017 
Yes 
Crop Science
ISSN: 0011-183X
EISSN: 1435-0653 
CROP SCIENCE SOC AMER 
MADISON 
903-913 
WOS:000397994900037 
Seed yield in soybeans [Glycine max (L.) Merr.] strongly depends on nitrogen (N) assimilation (N-A). The N-A in nodulated soybeans is based on two N sources, soil and N fixation. Hence, the controlling N-A in soybean to increase seed yield is more difficult than in many other crops that depend on fertilizer. The objective of this study was to establish a quantitative relationship between N-A by plants and N applied via fertilizer (N F) to increase soybean seed production. The N-A was modelled as a function of N F with two parameters: amount of available soil N (N S) and maximum N assimilation (N-Amax), both to be determined experimentally, and one equation to describe fixed N (N-FIX), would be maximum under nonfertilizer conditions (N-FIXmax). It is assumed that N-A is equal to N(A)max when N F 3 N-Amax -N-S and that, below this threshold, N-A decreases in proportion with N-FIX + N-S. To obtain variable datasets, different rates of N fertilizer were applied to nodulated and non-nodulated isolines under pot and field conditions from full bloom to beginning of maturity. Seed yields were found to be highly dependent on N-A regardless of nodulation type or genotype. In non-nodulated isolines, N-A -N-F was a good estimate of N-S. In nodulated soybeans, N (FIX) could be modelled as a liner function of N-F. These results indicate that the relationship between N-A and N-F with N-S and N-FIX can be modelled in a simplified way. The relationships between N-FIX, N-F, and N-FIXmax indicate key traits for determining N-A for seed production in nodulated soybeans.