Effects of genistein on yield, nodulation and nitrogen(2) fixation of field-grown soybeans planted at low soil temperatures

Soybean (Glycine max [L.] Merrill) roots produce genistein, particularly in the presence of Bradyrhizobium japonicum. This isoflavonoid also activates nod genes involved in dinitrogen (N 2) fixation. The signaling process is impaired at low root zone temperatures, so Bios Agriculture Inc. has developed Affix+ and SoyaSignal, which add genistein to activate the signaling process. The objectives of these experiments were to evaluate the efficacy of Affix+ and SoyaSignal under field conditions and to determine the seasonal patterns of N2 fixation and soil-derived N. No-till field experiments were conducted in new soybean soils during 1997 and 1998, near Rockwood ON. Similar studies were conducted in 1998 near Elora ON, using conventional tillage. At Rockwood, plant samples were taken at the V3, R1, R3, R5, R6, R7 and R8 development stages. Nodule number and biomass, above-ground biomass, plant N concentration, seed yield and protein and oil content were measured. No evidence was found at this site that the signal compound in Affix+ or SoyaSignal improved inoculant performance. At Elora in 1998, there was an increase in yield with SoyaSignal in one comparison. Overall, the signal technology produced a positive effect in only one of five comparisons and does not appear to warrant recommendation to growers. Rapid soil N uptake occurred up to R3, with a slower rate thereafter. N2 fixation was rapid from R3 to R6 in 1997. In 1998, drought delayed N2 fixation until R4 but was compensated for by continuing N accumulation during late bean-filling.