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The purpose of this study was to evaluate, during the phenological stages of inoculated soybean crop [Glycine max (L.) Merrill], the effect of different N fertilization levels and inoculation with Bradyrhizobium japonicum on N 2 O emissions from the soil. Gas emissions were evaluated at field conditions by the static-chamber method. Nitrogen fertilization increased N 2 O emissions significantly (P< 0.05). The variable that best explained cumulative N 2 O emissions during the whole soybean growing season was the soil nitrate level (r 2 =0.1899; P=0.0231). Soil moisture presented a greater control on N 2 O emissions between the grain-filling period and the crop commercial maturity (r 2 = 0.5361; P < 0.0001), which coincided with a positive balance of the available soil N, as a consequence of the decrease in crop requirements and root and nodular decomposition. Only soil soluble carbon (r 2 =0.29; P= 0.019) and moisture (r 2 =0.24; P=0.039) were correlated with N 2 O emissions during the residue decomposition period. The relationship between soil variables and N 2 O emissions depended on crop phenological or stubbles decomposition stages.

The objective of this work was to evaluate the effect of the chemical nature and application frequency of N fertilizers at different moisture contents on soil N 2 O emissions and N 2 O/(N 2 O+N 2 ) ratio. The research was based on five fertilization treatments: unfertilized control, a single application of 80 kg ha −1 N-urea, five split applications of 16 kg ha −1 N-urea, a single application of 80 kg ha −1 N-KNO 3 , five split applications of 16 kg ha −1 N-KNO 3 . Cumulative N 2 O emissions for 22 days were unaffected by fertilization treatments at 32% water-filled pore space (WFPS). At 100% and 120% WFPS, cumulative N 2 O emissions were highest from soil fertilized with KNO 3 . The split application of N fertilizers decreased N 2 O emissions compared to a single initial application only when KNO 3 was applied to a saturated soil, at 100% WFPS. Emissions of N 2 O were very low after the application of urea, similar to those found at unfertilized soil. Average N 2 O/(N 2 O+N 2 ) ratio values were significantly affected by moisture levels (p=0.015), being the lowest at 120% WFPS. The N 2 O/(N 2 O+N 2 ) ratio averaged 0.2 in unfertilized soil and 0.5 in fertilized soil, although these differences were not statistically significant.

The use of Stevia rebaudiana Bertoni, perennial indigenous native plant from the tropical region of South America is presented, with a brief outlook on the history and uses of the wild plant by Guarani Indians, the crop domestication, and the authorization of its use as a natural sweetener in food and beverages. Other aspects considered are natural glycosides and physicochemical properties for food processing, nutritional information, medicinal properties, Stevia market and household uses. The future of this plant is promising but more research is needed to ensure use of leaves and steviosides, and also to study cultivation practices in various regions of the world.

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