ABSTRACT Estimation of soil loss susceptibility is of great importance for the management of watersheds. Thus, several models for soil loss prediction have been proposed. This study estimated the total annual soil loss for the Santa Rita watershed, located in southern Brazil, using the Revised Universal Soil Loss Equation. In addition, a classification to soil loss index (ISL) was proposed to identify regions with critical soil loss values. Altitude, slope, land use, and soil class data were applied to the model, in addition to spatial information for 78 soil samples collected within the study area. It was found that there is an average annual loss of 35.94 Mg ha-1 year-1, with the most substantial loss occurring in areas with predominantly exposed soil and annual cropping. Furthermore, the ISL values indicated that approximately 50% of the study area is experiencing erosion estimates above the tolerable limit. Results emphasize the need for changes in conservation and application practices present in the watershed, considering land use and soil bearing capacity.

A distribuição de diâmetro do sedimento produzido pela erosão hídrica dependerá do tipo e da textura do solo. Este trabalho foi desenvolvido com o objetivo de avaliar a distribuição de tamanho de sedimentos produzidos por erosão em entressulcos, em três Latossolos do Rio Grande do Sul (Latossolo Vermelho aluminoférrico-LVaf, Latossolo Vermelho distroférrico-LVdf e Latossolo Vermelho distrófico-LVd), com diferentes classes texturais. Três repetições de chuva simulada com intensidade de 88 mm h-1 e duração de 90 min foram aplicadas sobre os solos, em parcela experimental com área útil de 0,36 m² e declividade de 0,09 m m-1. As amostras do sedimento foram coletadas em um conjunto de peneiras. A distribuição de diâmetro dos sedimentos variou conforme a textura do solo e os sedimentos produzidos apresentaram partículas e agregados de menor diâmetro que os do solo original. A maior parte dos sedimentos aportados no LVdf pertence à classe de 9,51 a 4,76 mm, enquanto no LVaf a classe predominante é a de 4,76 a 2,00 mm, os quais são os solos com maior teor de argila, carbono orgânico e óxidos de ferro e maior estabilidade de agregados em água. O Latossolo com menor estabilidade de agregados em água (LVd) foi o que apresentou sedimentos de tamanho menor (1,00 a 0,25 mm).

The sediment particle size distribution depends on soil type and texture. This study had the objective to evaluate the sediment yield by interrill soil erosion in three Oxisols of Rio Grande do Sul state, Brazil: Rhodic Hapludox (LVaf and LVdf) and a Typic Hapludox (LVd), of different textural classes, by simulated rainfall events in laboratory. Experimental plot with test area of 0.36 m² and 0.09 m m-1 slope was used. Simulated rainfall with mean intensity of 88 mm h-1 and duration of 90 min was applied in three replications on three oxisols. Sediment particles leaving the experimental plots were collected in a set of sieves. The distribution of sediment diameter varied as the soil texture. The sediment yielded by interrill soil erosion had individual particles and aggregates smaller than those in the original soil. Most of the sediment yielded by interrill soil erosion at LVdf soil was in the class diameter from 9.51 to 4.76 mm whereas in LVaf was from 4.76 to 2.00 mm and in LVd was from 1.00 to 0.25 mm. The original LVdf and LVaf soils present higher clay, organic carbon and iron oxides contents and greater aggregate water stability than the LVd soil, and this probably explains the differences among size classes of sediment yielded by interrill soil erosion.

O dano causado à soja [Glycine max (L.) Merrill] por Euschistus heros (Fabricius) parasitado por Hexacladia smithii Ashmead, foi estudado em casa-de-vegetação. Utilizaram-se plantas de soja da cultivar BR-37, cobertas com tela de filó, infestadas com dois percevejos/planta por um período de 15 dias, do final do desenvolvimento de vagens (R4) até o estádio de enchimento de grãos (R5-R6). Plantas infestadas com percevejos parasitados por H. smithii foram comparadas a plantas infestadas com percevejos sadios e a plantas livres do ataque de insetos (testemunha), com 20 repetições por tratamento. Pelos resultados obtidos, o rendimento (g/planta), o número total de vagens e o número de vagens chochas por planta foram semelhantes entre as plantas atacadas por percevejos sadios e parasitados por H. smithii, diferindo ambas da testemunha. Da mesma forma, a análise qualitativa dos grãos, através do teste visual (sementes boas, médias e ruins) e do tetrazólio (sementes picadas, sementes inviabilizadas e vigor), demonstrou que percevejos sadios e parasitados causaram danos estatisticamente iguais entre si e diferentes da testemunha. Entretanto, o potencial germinativo das sementes atacadas por percevejos parasitados foi maior do que o das sementes sugadas por percevejos sadios, demonstrando que ocorre menor dano quando os percevejos estão parasitados.

Damage on soybean [Glycine max (L.) Merrill] caused by Euschistus heros (Fabricius) parasitized by Hexacladia smithii Ashmead was studied in greenhouse. Soybean plants, cultivar BR-37, were covered with nylon screen net and artificially infested with two bugs/plant, for a 15-day period, from the stage corresponding to the end of pod development (R4) up to filled seeds (R5-R6). Plants infested by non-parasitized bugs were compared with plants infested by bugs parasitized by H. smithii and with non-infested plants (control), with 20 replicates per treatment. The yield (g/plant), total number of pods and number of failed pods per plant did not differ between plants attacked by non-parasitized as well as by parasitized bugs, but they both differed from the control. Similarly, the qualitative analysis of seeds (good, medium and bad) and the tetrazolium test (punctured seeds, damaged seeds and vigor) demonstrated the same effect. However, the germination potentiality of the seeds attacked by parasitized bugs was higher than those seeds attacked by non-parasitized ones, indicating that a lower damage was caused by parasitized bugs.

Parasitism of Euschistus heros (F.) adults was studied in Londrina, PR. Twenty males and 20 females were collected each week from November 1996 to December 1997. In the laboratory, adults were sexed and maintained in plastic box (12 x 12 cm) with humidity and soybean pods as food, and observed daily during 30 days. The encyrtid Hexacladia smithii Ash. was observed attacking the bugs, being the first register of parasitism by Hexacladia in this host. The natural incidence of parasitism varied from 0.6% to 39.5%. Higher abundance of the parasitoid occurred during December and January and it was drastically reduced (<1%) from May to September. Males and females were equally attacked by the parasitoid (14.7% and 11.9%, respectively). H. smithii is a gregarious endoparasitoid that completed its development inside the host body. Adults emerged through a hole in the ventral or dorsal surface of the abdomen. From 2 up to 39 parasitoids were observed to emerge from a single adult E. heros.