ABSTRACT The need for crop rotation and profitability in lowland areas are the two main reasons for the introduction of soybean cultivation in the state of Rio Grande do Sul, Brazil. These areas have poor natural drainage, which impedes proper soybean growth. In this sense, this study aimed to assess the efficiency of using broad base ridges in comparison to the surface drainage for soybean cultivation in lowlands. The study was conducted during the 2014/2015 and 2015/2016 growing seasons in São João do Polêsine, RS, Brazil. The assessed drainage methods were the use of broad base ridges with different width dimensions (22.5, 15.0, and 7.5 m) and surface drainage. The results showed that the shoot dry matter and leaf area index have similar behavior. The broad base ridge was better than the surface drainage method for these variables. The 7.5-m broad base ridge stood out among the treatments when compared to the others, as it had the best results for the leaf area index (8.66), plant height (102.5 cm), and shoot dry matter (33.06 g).

ABSTRACT The aim of this study was to evaluate the performance of less accurate analysis methods of slope stability, in order to reduce the number of operations used by the most accurate methods available in the literature. The study evaluated four methods for calculating slope stability. Fellenius (FELLENIUS, 1936), Bishop (BISHOP, 1955), Simplified Bishop (BISHOP & MORGENSTERN, 1960) and Simplified Janbu (JANBU, 1973) were compared with the Spencer method (SPENCER, 1967), which is considered an accurate method for calculating the factor of safety (FS). The procedure was performed in scenarios with different soil groups according to the Unified Soil Classification System (USCS) (ASTM 2011), heights and slope inclinations, and under conditions of reservoir subject to fast and slow emptying. Thus, comparative analyses were made using the correlation index “r”, the accuracy index “d” (WILLMOTT et al, 1985) and the performance index “c” (CAMARGO & SENTELHAS, 1997). The methods that had optimal performance for the analyzed conditions were the Simplified Bishop, the Simplified Janbu and the Bishop methods; the Simplified Bishop method obtained a correlation coefficient of 99%. Thus, they can be used as alternative methods to replace the Spencer method in the analysis of slope stability on earth dams.