Érica de Oliveira Araújo

Effect of nitrogen fertilization associated with diazotrophic bacteria inoculation on nitrogen use efficiency and its biological fixation by corn determined using 15 N

The use of plant growth-promoting diazotrophic bacteria as an alternative to increase nitrogen (N) availability and contribute to its use by corn can be a less costly and ecologically more viable option. Thus, this study aimed to evaluate the effects of the inoculation with Azospirillum brasilense and Herbaspirillum seropedicae in association with N fertilization on the N use efficiency and its biological fixation by corn, in field conditions, using the 15N-isotope technique. A randomized-block design was used, with nine treatments and six replicates. The following parameters were evaluated: grain productivity, dry matter production, accumulated N in plant, percentage of N from the fertilizer, total N from the fertilizer, use efficiency of N applied as fertilizer and percentage of biological N fixation. Results show that N fertilization associated with A. brasilense and H. seropedicae inoculations influences positively grain productivity in corn. The inoculation with A. brasilense and H. seropedicae combined with 30 and 120 kg ha-1 of N promotes a reduction of N percentages in corn grains and shoot. The increase in N dose associated with the inoculation of A. brasilense and H. seropedicae promotes an increase in the N from the fertilizer in corn grains and shoot and reduces the N use efficiency by the crop. Using the 15N natural abundance technique, it was found that the inoculation with A. brasilense and H. seropedicae contributed, respectively, with in average 19.40% and 9.49% of the N required for the development of corn plants. Key words: Zea mays L., Azospirillum brasilense, Herbaspirillum seropedicae, 15N, biological nitrogen fixation.

Manejo do solo e adubação nitrogenada na supressão de plantas daninhas na cultura do feijão de inverno e irrigado

Objetivou-se avaliar diferentes plantas de coberturas do solo e a adubacao nitrogenada na supressao de plantas daninhas na cultura do feijao de inverno e irrigado. O delineamento experimental utilizado foi o de blocos casualizados em esquema de parcelas subdivididas, constituido por quatro blocos e quatro repeticoes. Nas parcelas foram utilizados manejos de cobertura de solo (milheto, crotalaria juncea, sem cobertura e vegetacao espontânea). Nas subparcelas utilizou-se a presenca e ausencia de nitrogenio em cobertura no feijoeiro aos 20 DAE. Foram avaliadas as massas verdes e secas das plantas de coberturas antes da incorporacao no solo. Apos 35 dias da emergencia do feijoeiro avaliou-se a massa seca, o numero de especie, numero total de plantas daninhas por m2 e a porcentagem de incidencia de plantas daninhas (observacoes visuais). Com base nos resultados o manejo do solo com crotalaria conferiu maior supressao as plantas daninhas, devido a quantidade de massa no solo. A adubacao nitrogenada em cobertura na cultura do feijao influenciou significativamente a producao de massa seca pelas plantas daninhas. A liberacao acelerada do nitrogenio pela crotalaria favorece a ocorrencia e o estabelecimento de algumas especies de plantas daninhas, conferindo alta competitividade por parte da planta daninha, e consequentemente favorecendo a producao de massa seca.