VARIATION IN THE PATTERN OF NITROGEN ACCUMULATION AND DISTRIBUTION INSOYBEAN

The contribution of early nodulation and dinitrogen (N-2) fixation to overall soybean [Glycine max (L.) Merr.] plant performance in the cool er northern states of the U.S. Midwest needs further investigation. In a previous growth chamber study, we identified traits associated with improved early nodulation and N-2 fixation in this crop. This study e xamined the nodulation, N accumulation, and N distribution patterns fo r the same 19 soybean lines in the field, and relates field performanc e to previous growth chamber results. The study was conducted in 1992, 1993, and 1994 at Becker, MN, in a soil with 7 to 15 kg NO3- ha(-1). The following data was recorded: nodule fresh weight (NFW), plant dry weight (PDW), anti fatal N accumulation (TNA) at 20 to 60 d after plan ting (DAP), PDW and TNA at the R3 and R6 growth stages, and gain and s eed protein yield at maturing. Differences in NFW, PDW, and TNA were f ound at most sampling dates, and were indicative of significant geneti c differences in N-2-fixing ability. Lines also differed in partitioni ng of N, with the cultivar Lambert distributing 88% of total N accumul ated to reproductive tissue at the R6 growth stage, compared with only 31% for PI 437966. Two canonical variables, one created by analyzing together the NFW data collected at 20, 40, and 60 DAP in the field, th e other derived from NFW, PDW, and nodule soluble protein data obtaine d in the previous growth chamber study each correlated with the seed p rotein yield of field-grown plants. This suggests that the measurement of early nodulation and N-2 fixation in either the growth chamber or field can serve as an indicator on which to base selection for enhance d N-2 fixation.