Soil effects on nitrogen fixation in soybean (Glycine max (L.) Merr.)
1993
Mosca, G. | Bona, S. | Toniolo, L. (Padua Univ. (Italy). Istituto di Agronomia Generale e Coltivazioni Erbacee)
In 1991 four different soil types were tested (sandy, clay, organic and silty-loamy) in order to evaluate the nitrogen fixation rate of a soybean cultivar (Gemma, group I +) regularly inoculated at sowing. The soils were characterized for chemical composition and for B. japonicum viable cells with the Plant Infection Test. During the cycle measurements of nitrogen fixation rate were made using the ARA in situ (Bona et al., 1992). Nitrogenase activity was detected 47 days after sowing and resulted greater during the first part of the cycle in the soils with a greater number of rhizobia. The root distribution resulted optimal in the clay soil and nitrogenase activity was intense in the last part of the cycle because of a greater biomass that allowed the nodules to receive more assimilate for sustaining the symbiose. In the organic soil, eventhough the biomass was equivalent to the clay soil, the nitrogenase activity was perturbed by the presence of free nitrates from the mineralization. In the sandy soil as the symbiosis was the main source for nitrogen there was a high rate of nitrogenase activity since R3
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