The influence of temperature and nitrate on vegetative growth and nitrogen accumulation by nodulated soybeans glycine max cultivar ransom

Jones, R.S.; Patterson, R.P.; Raper, C.D.Jr

Plant and Soil 63(3): 333-344


ISSN/ISBN: 0032-079X
Accession: 006700959

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Inoculated [with Rhizobium japonicum] soybeans [G. max (L.) Merrill] were grown in controlled environments to evaluate the relationship between temperature and applied NO3-N on growth rates, N accumulation, and acetylene reduction [N2 fixation] activity during the vegetative growth stage. Soybeans were grown at day/night temperatures of 22/ and 26/ C in sand culture with daily applications of 21.4 mM (high) and 2.1 mM (low) NO3-N in a complete nutrient solution for durations of 14, 21 and 42 days after emergence and with an N-free solution. Dry matter and N accumulation were greater at 26/ than 22/ C. In general, both increased as the level and duration of applied NO3-N was increased. These increases were attributable to an abbreviation in the interval between emergence and onset of rapid growth. The presence and assimilation of NO3-N, even at the high level, did not inhibit development of functional nodules. Neither mass nor acetylene reduction activity of nodules was reduced by high NO3-N; however, the root mass was increased by NO3-N more than the nodule mass. There was an interaction between temperature and NO3-N on specific nodule activity as measured by acetylene reduction. The specific nodule activity was unaffected by NO3-N at 22/ C, but at 26/ C the specific activity was lower in the absence of NO3-N than when NO3-N was present. Apparently, rapid early growth at 26/ C depleted cotyledonary reserves of N before nodules became active and, thereafter, the plants were unable to develop adequate leaf area to support nodule development and functioning. This result has implications in N fertilization of late-planted soybeans.