ABSTRACT The application of flumioxazin and imazethapyr can affect the interactions between rhizobia and soybean in the rhizosphere. However, it remains unclear the effect of both herbicides, even when applied in mixture, on early nodulation and biological N fixation (BNF) in soybean, mainly related to some important biochemical traits in nodules. This study assessed the effect of flumioxazin, imazethapyr and their mixture on early nodulation and BNF in rhizosphere of soybean. The plant emergence, early nodulation, growth, and N accumulation were evaluated in soybean grown in sandy and clayey soils. The leghemoglobin content and glutamine synthetase (GS) activity were also assessed in fresh nodules. Individually, flumioxazin and imazethapyr did not affect the plant emergence, nodulation and N accumulation in soybean, while the mixture decreased significantly these parameters. Also, the values of leghemoglobin content and GS activity did not decrease with the application of the herbicides individually. The application of herbicides imazethapyr and flumioxazin separately negatively influenced the growth of soybean, while they do not influence the nodulation and N accumulation. However, the use of these herbicides in mixture can negatively influence the early nodulation and N fixation by native rhizobia.

RESUMO: Este estudo avaliou a atividade de isolados de rizóbios inoculados em sementes pequenas (11 mm) e grandes (18 mm) sobre o crescimento, nodulação e fixação de N de feijão-fava. Isolados selecionados de rizóbios foram comparados com uma estirpe de referência CIAT899 e dois controles sem inoculação. Sementes grandes contribuíram para maior crescimento de plantas, nodulação e fixação de N do que sementes pequenas. Os isolados UFPI-59, UFPI-18 e UFPI-38 promoveram os maiores valores de massa seca de parte aérea e raízes. Os isolados UFPI-32 e UFPI-59 promoveram os maiores valores de número e massa de nódulos, respectivamente. Os isolados UFPI-38 e UFPI-59 promoveram maior acúmulo de N. Este estudo mostrou que o tamanho de sementes influencia o crescimento, nodulação e fixação de N em feijão-fava. Considerando os isolados de rizóbios, UFPI-59, UFPI-38 e UFPI-18 contribuíram para o crescimento de plantas, promoveram melhor nodulação e eficiência na fixação de N.

ABSTRACT: This study evaluated the activity of rhizobia isolates inoculated in large (18 mm) and small (11 mm) seeds on lima bean growth, nodulation and N fixation. Selected rhizobia isolates were compared with a reference strain CIAT899 and two controls without inoculation. Large seeds contributed for highest plant growth, nodulation and N fixation than small seeds. The isolates UFPI-59, UFPI-18 and UFPI-38 promoted the highest values of shoot and root dry weight, respectively. The isolates UFPI-32 promoted the highest values of nodule number, while UFPI-59 promoted the highest values of nodule dry weight. The isolates UFPI-38 and UFPI-59 promoted the highest accumulation of N. This study showed that seed size really influences lima bean growth, nodulation and BNF. Considering rhizobia isolates, UFPI-59, UFPI-38, and UFPI-18 contributed for plant growth, promoted better nodulation and effectiveness on biological N fixation.

RESUMO. Este estudo avaliou as propriedades do solo e a produtividade do feijão-caupi após seis anos de aplicações consecutivas de lodo de curtume compostado. Anualmente, o composto foi aplicado a 0, 2,5, 5, 10 e 20 Mg ha-1 e no sexto ano as propriedades químicas e físicas do solo e a produtividade do feijão-caupi foram avaliadas em experimento de blocos casualizados. Cr, P, K, C orgânico, pH, Ca, Na, e a capacidade de troca de cátions aumentaram linearmente após seis anos de aplicação do composto. A densidade do solo diminuiu linearmente enquanto a estabilidade de agregados aumentou após a aplicação do composto. Em consequência das mudanças nas propriedades químicas e físicas do solo, a produtividade do feijão-caupi apresentou resposta quadrática às doses de lodo de curtume compostado com máxima produtividade estimada encontrada na dose de 8,3 Mg ha-1. Em conclusão, as propriedades químicas e físicas do solo melhoraram após seis anos de aplicação do lodo de curtume compostado. Entretanto, o pH do solo, bem como os teores de Cr e Na aumentaram com aplicação do lodo de curtume compostado e estes parâmetros influenciaram a produtividade do feijão-caupi que apresentou resposta quadrática.

ABSTRACT. This study evaluated soil properties and cowpea yield after six years of consecutive amendment of composted tannery sludge. The compost was applied annually at 0, 2.5, 5, 10, and 20 Mg ha-1 and at the end of the sixth year, the chemical and physical properties of the soil were evaluated using a randomized block design. The Cr, P, K, Ca, Na and organic C contents and the pH and cation exchange capacity increased linearly after six years of compost amendment. The soil bulk density decreased linearly while the aggregate stability index increased after compost amendment. As a consequence of the changes in the chemical and physical properties of the soil, cowpea yield showed a quadratic response to the tannery rates, with an estimated maximum cowpea yield at 8.3 Mg ha-1. In conclusion, the soil chemical and physical properties improved after six years of composted tannery sludge amendment. However, the soil pH and the Cr and Na contents increased with composted tannery sludge amendment, which influenced the cowpea yield and resulted in a quadratic response to the compost.