Effect of Rhizobium Numbers on Nodulation and Dinitrogen Fixation in Groundnut

In greenhouse studies, shoot and nodule wt./plant of groundnut cv. Kadiri 71-1 increased with increase in inoculum density from 6.1 × 10² to 3.2 × 109 rhizobia/seed. In a 2nd experiment with cv. Robut 33-1 and TMV2 inoculated with 2 Rhizobium strains, number of nodules/plant increased from 6-11 at 2.7 × 10² to 143-243 at 2.7 × 108 rhizobia/seed but N2 fixation at 106 rhizobia/seed was close to that at 108. Strain 5a/70 fixed more N2 at a given inoculum density than strain NC92.ADDITIONAL ABSTRACT:In greenhouse studies, seedlings of three cultivars were inoculated with Rhizobium at four inoculum densities (102-109 rhizobia/seed). Robut 33-1 and TMV2 required 106 rhizobia/seed for maximum nodulation and nitrogen fixation, while Kadiri 71-1 required larger numbers

Efeito de diferentes herbicidas na nodulação e na atividade da nitrogenase no amendoim Effect of herbicides on nodulation and nitrogenase activity in peanuts

Em ensaio de herbicidas na cultura do amendoim (Arachis hypogaea L.), realizado em Ribeirão Preto, SP, em 1984/85, sem o uso de inoculante, não foram encontrados nódulos nos diferentes tratamentos. Como é comum sua presença em amendoim nessa região, suspeitou-se que os herbicidas utilizados pudessem ter efeito inibitório na nodulação. Avaliou-se, então, o efeito de alachlor, linuron, oxadiazon, pendimetalin e trifluralin aplicados na dose recomendada, na nodulação e na atividade da nitrogenase, durante dois anos consecutivos, usando-se sementes inoculadas e não inoculadas. Foram feitas amostragens aos 28, 42, 63, 84 e 105 dias após a semeadura, observando-se nodulação abundante, em todos os tratamentos, e reduções ocasionais na nodulação e na fixação do nitrogênio, porém não consistentes nas diversas amostragens. A atividade da população nativa de Rhizobium em geral permaneceu num nível maior do que nos tratamentos com inoculação. Embora alguns herbicidas tenham afetado a nodulação e a fixação do nitrogênio, não houve influência na produção de grãos.<br>No nodules were found in a peanut herbicide trial held at Ribeirão Preto, State of São Paulo, Brazil, during the growing season 1984/85. Since spontaneous nodulation is commom in this region, a hypotheses was raised that herbicides could have an inhibitory effect on nodulation. To test the effect of herbicides on nodulation and nitrogenase activity an experiment was carried out on two consecutive years, using a factorial design with two factors: a) five herbicides (alachior, linuron, oxadiazon, pendimethalin and trifluralin) applied in usual dosages and a control without herbicide and b) with and without Bradyrhizobium inoculation. Samples were collected at 28, 42, 63, 84 and 105 days after planting. The results showed that nodulation was abundant in all treatments. Nitrogenase activity in the non inoculated treatments persisted for a longer period than in the inoculated ones. Although some herbicides reduced nodulation and nitrogen fixation, peanut grain production was not affected