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Title: SOYBEAN CULTIVAR VARIABILITY FOR NODULE FORMATION AND GROWTH UNDER DROUGHT.

Author
item SERRAJ, RACHID - MARRAKECH, MOROCCO
item Sinclair, Thomas

Submitted to: Plant and Soil
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: A major advantage in the selection of soybean as an important crop is that it symbiotically fixes atmospheric nitrogen for its own use. Hence, soybean does not need to be fertilized with nitrogen. Nitrogen fixation occurs in the nodules that form on soybean roots. One question that has been virtually ignored is the fate of nodules and nodule formation when soil dries. This investigation, which was conducted in part by an ARS scientist at Gainesville, FL, examined the changes in nodule number and weight when different cultivars of soybean were subjected to drought. This study discovered that among the different cultivars there was a range of responses to the soil drying, including cultivars that were able to retain nodules and to continue nodule growth. These differences could be useful in the selection of parental cultivars in breeding superior soybean varieties for dryland conditions.

Technical Abstract: Both nodulation and nitrogen fixation in soybean [Glycine max (L.) Merr.] are sensitive to soil drying, which can have important negative effects on yield. An exception to this general response has been the identification of the cultivar Jackson as being drought tolerant for N2 fixation. The objectives of this research were to examine nodule formation and growth in Jackson among other soybean cultivars in response to soil drying under field. Substantial variation among soybean lines was found in two field experiments in the sensitivity of nodule numbers and dry weights to soil drying. Greenhouse experiments confirmed cultivar variation in nodulation response to soil water content. Importantly, the relative drought insensitivity of N2 fixation in cultivar Jackson was associated with high individual nodule dry weight under drought conditions, relative to well-watered plants. It was concluded that large variation in nodulation sensitivity to water deficit exists among soybean cultivars and that the response of N2 fixation rates to drought is related to nodule formation and growth.