Growth, nodulation and nitrogen fixation in soybean as affected by air humidity and root temperature

Growth, nodulation and N2 fixation inGlycine max L. Merr., cv. Biison as affected by the relative humidity of air (RH) during the dark period (95 or 50 - 65 %) and day/night root temperature (Tr) (28/28, 25/25, 18/18, 22/28, 22/18 °C) were studied. The growth parameters (plant fresh and dry mass, yield), nodulation (nodule number and fresh mass) and N2 fixation abilities (total nitrogen content, nitrogenase activity) increased significantly with the increasing Tr. In addition, at the same Tr during the day all studied parameters were increased at the higher Tr during the dark period. Growth, nodulation and N2 fixation were significantly enhanced at low RH. The findings indicate that all studied parameters could be regulated by environmental factors during the dark period.