| Summary: | Soybeans (Glycine max L. Merr.) are a symbiont of two beneficial associations:
biological nitrogen fixation (BNF) with Bradyrhizobium japonicum, and arbuscular
mycorrhizal fungi (AMF). Within the Northern Great Plains of the USA, iron deficiency
chlorosis (IDC) of soybean is a yield-limiting factor. The effects of IDC on BNF and AMF
are not well defined. This study was conducted to determine the effects of IDC on BNF
and AMF. A laboratory study was performed to compare three methods of measuring
ureide-N, a product of BNF in soybeans. Field studies in soybean were performed at three
locations at eastern N011h Dakota. The experimental design was a factorial combination of
three cultivars and three treatments. The three cultivars, in order of decreasing chlorosis
susceptibility, were NuTech NT-0886, Roughrider Genetics RG 607, and Syngenta S01-C9
RR. The three treatments were control, Sorghum bicolor L. companion crop planted with
the soybean seed, and FeEDDHA applied with the soybean seed. Chlorosis severity was
the greatest and least for the NuTech and Syngenta cultivars, respectively. The FeEDDHA
treatment decreased chlorosis severity. Ureide levels were abnormally high in plants
severely stunted by JDC. The excess accumulation of ureides in IDC-stunted plants
suggests that plant growth was reduced more than the rate of nitrogen fixation. The AMF
population \vas at an adequate level at all locations and not affected by cultivar or
treatment, in general. In the laboratory study, the Patterson et al. method had greater ureide
concentrations due to the non-specific measuring of ammonium compounds compared to
the Vogels and Van der Drift and Goos methods. === North Dakota Soybean Council
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