The patterns of nitrate reductase activity (NRA) in the leaves (in vivo assay) and root nodule nitrogenase actiVity (C2H2 reduction) were investigated throughout the season in field-grown Phaseolus vulgans plants.Maximal NRA (per g fresh weight) occurred at early stages of leaf development but total activity (per leaf) was maximal when the leaf reached full size. In mature plants, most NRA was associated with the upper leaves.Nitrogenase activity was initiated about 2 weeks after sowing, reached a maximum at flowering (5 weeks after sowing) and declined rapidly thereafter. Nitrogenase activity followed the pattern of nodule development. After flowering, P. vulgans was apparently able to take up and assimilate NO5 as evidenced by the increase in NOi content of the stem and the high levels of NRA in the leaves. Total plant NRA was maximal after flowering and addition of NH4NO3 to the soil at flowering resulted in even higher levels of NRA through most of the pod-filling period, thus resulting in higher seed yields (59% over control).It is proposed that P. vulgans can benefit from both N2 fixation and NO3 assimilation and that nitrate reductase plays an important role in the assimilation of nitrogen after flowering.Biological N2 fixation and NOC-assimilation represent the major sources of reduced N for plant growth and seed yields in legume crops. Several environmental and plant factors are known to control the amount of N incorporated through N2 fLxation in Phaseolus vulgaris plants (4, 6) and attempts to supplement N2 fixation with fertilizer N have not succeeded in increasing yields (4,5,9). Nevertheless, low levels of combined N during the initial stages of development have been shown to enhance nodulation and N2 fixation (1, 5).There are no reports about the relationships between NO3 assimilation and N2 fixation throughout the season in P. vulgaris plants. The seasonal patterns of NO-uptake and reduction and the patterns of N2 fLxation in soybean plants indicate that the processes of NO3 assimilation and N2 fixation are successive events, each contributing nitrogen at defined stages of plant development (4,8,16). NO3-reduction appears to be more important in certain legumes at the preflowering stages while maximal nitrogenase activities were observed after the decline of NRA3 (4,8,16). Because NOi-is considered the primary source of N available from the soiL the characterization of NO3 uptake and reduction throughout the season in P. vulgaris plants, along with 'A preliminary report of this work was given at the annual meeting of the Society of Plant Physiologists in Madison,

RESUMORealizou-se este trabalho com o objetivo de avaliar a degradação do herbicida sulfentrazone em dois solos (Latossolo Vermelho Distroférrico típico e Neossolo Quartzarênico Órtico típico) utilizados na cultura da cana-de-açúcar, em Mato Grosso do Sul, e avaliar também a influência da temperatura, umidade e profundidade na taxa de degradação. Os experimentos de degradação foram realizados utilizando-se solos incubados em diferentes condições de umidade (50 e 80% da capacidade de campo -CC), temperatura (30 e 40 ºC) e profundidade (0-30 e 50-70 cm). Os resultados das concentrações remanescentes do sulfentrazone no solo foram, em função do tempo, ajustados aos modelos de cinética de primeira ordem (SFO) e ao de cinética de primeira ordem para multicompartimentos (FOMC). O sulfentrazone foi menos persistente em condições de maior umidade (80% da CC), temperatura mais elevada (40 ºC) e em horizontes superficiais do solo (0-30 cm). A degradação do sulfentrazone para a maioria das condições estudadas foi melhor descrita pelo modelo FOMC. Os valores de meia-vida para o sulfentrazone nas diferentes condições de umidade, temperatura e profundidades avaliadas, variaram de 34 a 116 dias. Palavras-chave: meia-vida, persistência, cana-de-açúcar, agrotóxicosDegradation of sulfentrazone herbicide in two soils of Mato Grosso do Sul State ABSTRACT This study had the aim to evaluate sulfentrazone degradation in two soils (distroferric red Latossol and orthic quartzarenic Neosol) used for sugarcane production in Mato Grosso do Sul State and also to evaluate the influence of temperature, moisture and soil depth in the sulfentrazone degradation rates. Experiments were carried out using incubated soils at different soil moistures (50 and 80% field capacity -FC), temperatures (30 and 40 °C) and depths (0-30 and 50-70 cm). Remaining sulfentrazone concentrations in soil as a function of time were adjusted to single first-order kinetics model (SFO) and also to the first-order multi-compartment kinetic model (FOMC). Sulfentrazone was less persistent in conditions of high soil moisture (80% FC), high temperature (40 °C) and in the topsoil (0-30 cm depth). Sulfentrazone degradation was best described by FOMC model. Half-life values of sulfentrazone evaluated at different conditions of moisture, temperature and soil depths ranged from 34 to 116 days.

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RESUMOObjetivou-se, neste trabalho, avaliar a persistência e a lixiviação de endossulfam no campo e sua degradação e formação do metabólito sulfato de endossulfam em condições de laboratório. Visando ao experimento da persistência e à lixiviação no campo, amostras de solo até a profundidade de 100 cm foram coletadas aos 0, 41, 74 e 125 dias após aplicação. Em laboratório amostras de solo nas profundidades de 0-30 e 50-70 cm foram incubadas a 30 ± 2 °C e 80% da capacidade de campo e os resíduos de endossulfam e sulfato de endossulfam foram quantificados em função do tempo para ajuste dos modelos de cinética de primeira ordem e do modelo bifásico. Observou-se, no campo, que o endossulfam não lixiviou para menos de 10 cm de profundidade e houve uma rápida dissipação resultando em uma quantidade remanescente no perfil do solo (100 cm) inferior a 1% da dose aplicada aos 41 dias após a aplicação. Em laboratório os valores de TD 50 para o endossulfam variaram de 17 a 26 dias e para o sulfato de endossulfam de 26 a 59 dias. O modelo de degradação bifásico mostrou-se superior ao de cinética de primeira ordem para descrever a degradação do endossulfam em laboratório. Palavras-chave: degradação, meia-vida, lixiviação, dissipaçãoPersistence of endosulfan and its metabolite endosulfan sulfate under field and laboratory conditions ABSTRACT This study aimed to evaluate endosulfan leaching and persistence in the field as well as its degradation and formation of the metabolite endosulfan sulfate under laboratory conditions. For the persistence experiment and leaching in the field, soil samples until 100 cm depth were collected at 0, 41, 74, and 125 days after application. In the laboratory, soil samples of 0-30 cm and 50-70 cm depth were incubated at 30 ± 2 ºC and 80% field capacity and endosulfan residues were quantified as a function of time for adjusting the first order kinetics and biphasic models. In the field, it was observed that endosulfan did not leach beyond 10 cm depth and there was a rapid dissipation resulting in a quantity in the soil profile (100 cm) less than 1% of the applied dose at 41 days after application. In laboratory TD 50 values for endosulfan ranged from 17 to 26 days and endosulfan sulfate 26-59 days. The biphasic decay model was superior to the first-order kinetics to describe the degradation of endosulfan in the laboratory.

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