Improved Screening Method for High DI-Nitrogen Fixation in Soybean.

The rate of di-nitrogen fixation varies greatly throughout the growth cycle of soybean. Restrictions in nitrogen (N) availability suggest that N accumulation follows different patterns in plants. Therefore, information on exploitable genetic variation for high di-nitrogen fixation capacity in different growth stages of soybean is crucial for developing improved varieties. The objective of this study was to assess the value of screening for di-nitrogen fixation capacity at the early and late growth stages of soybean. A total of 22 soybean lines was evaluated in a randomized complete block design with four blocks and four replications per block under greenhouse conditions for two cycles. Leaf samples were collected at 35 d after emergence (35 DAE) and pods at the R7 growth stage. The ¹⁵N dilution technique was used to calculate the percentage of N derived from the atmosphere foreach genotype. A weak but significant correlation between the early and late di-nitrogen fixation measurements (r=0.15; p< 0.01) indicated the relative independence of evaluations throughout the growth cycle. Our results suggested that the assessment of di-nitrogen fixation capacity at the early and late growth stages was more informative than a single evaluation over the soybean growth cycle, since it allowed to identify different patterns of di-nitrogen fixation among soybean genotypes.