Os estresses hídrico e salino são apontados como os principais fatores abióticos que limitam a germinação e o estabelecimento da cultura de soja. Estudos que visam identificar cultivares com maior tolerância ao estresse hídrico e a salinidade são importantes para a pesquisa agrícola. A pesquisa foi conduzida com a finalidade de avaliar a tolerância de 25 cultivares de soja aos estresses hídrico e salino durante a fase de germinação e crescimento inicial das plântulas. Os estresses hídrico e salino foram induzidos pela exposição das sementes durante 10 dias a 25 ºC, em soluções com potencial osmótico de -0,30 MPa preparadas com polietilenoglicol PEG-6000 (151,403 g L–1) e NaCl (3,536 g L–1). A partir dos dados de germinação, comprimento e matéria seca das plântulas em condições não estressantes (controle) e estressantes (estresses hídrico e salino), foram calculados os índices de tolerância ao estresse (ITE). As cultivares de soja RK 8317 IPRO, TMG 2383 IPRO, TMG 7061 IPRO, TMG 7063 IPRO e ST 777 IPRO possuem maior tolerância ao estresse hídrico, e são as cultivares mais indicadas para serem semeadas em condições de baixa disponibilidade de água no solo. As cultivares de soja NS 8399 IPRO, NS 7007 IPRO, NS 7505 IPRO, RK 8115 IPRO e TMG 2381 IPRO possuem maior suscetibilidade ao estresse hídrico, e não devem ser recomendadas para o cultivo em condições de baixa disponibilidade hídrica. As cultivares TMG 2383 IPRO, 98R31 IPRO, 98R35 IPRO, ST 777 IPRO, M5917 IPRO, ST 797 IPRO e TMG 7067 são as cultivares mais indicadas para serem cultivadas em solos salinos por apresentarem maior tolerância à salinidade. Por sua vez, as cultivares NS 8399 IPRO, HO Paranaíba IPRO, HO Cristalino IPRO e BMX Foco IPRO são classificadas como suscetíveis à salinidade.
The occurrence of water restriction is one of the environmental stresses that most limit soybean grain yield. Studies that seek to identify soybean cultivars with greater drought tolerance are important for agricultural production. This study was carried out with the purpose of evaluating the response of 22 soybean cultivars grown under adverse environmental conditions (irrigated and rainfed system), aiming to determine the best selection indexes to identify drought-tolerant soybean cultivars. Two experiments were carried out under field conditions in the municipality of Cassilândia (MS) during the 2018/2019 growing season, one in rainfed conditions with water restriction and the other in an irrigation system with central pivot. A randomized block design was used, in a 2 × 22 factorial scheme with three replications. The treatments consisted of two cultivation conditions (irrigated and rainfed system) and 22 soybean cultivars. From the data of grain yield in irrigated and rainfed systems, 12 drought tolerance indexes were estimated. The identification of soybean cultivars tolerant and/or susceptible to water restriction was carried out using different multivariate analysis methods (ranking method, hierarchical cluster analysis and principal component analysis). The 98R35 IRPO, RK 8317 IPRO and RK 8115 IPRO cultivars were classified as having greater drought tolerance, and are therefore the most suitable cultivars to be cultivated in Cerrado regions with water restriction. On the other hand, the TMG 7067 IPRO, M 5917 IPR, RK 6719 IPRO cultivars were classified as more susceptible to water restriction, and should not be recommended for cultivation in the region of Cassilândia (MS) under rainfed conditions in season with high probability occurrence of water deficiency. The indices of tolerance MP, STI, GMP and HM were the most indicated to identify soybean cultivars with greater tolerance to drought and with high grain yield potential in irrigated and rainfed systems in the region of Cassilândia, State of Mato Grosso do Sul.
The silvopastoral system (SPS) stands out as an agroecological production system that has improved the soil's chemical quality. However, these chemical properties may have distinct changes with greater or lesser distances from the tree row tracks of the silvopastoral system. The objective of this study was to investigate the effects of the distance of the soil sampling points from the eucalyptus tree rows in a 2-year silvopastoral system on acidity components and oxidizable organic carbon fractions of the soil, as well as to compare these chemical properties with the conventional pasture system and native Cerrado vegetation. In the silvopastoral system (SPS), the soil samples were collected at 2.5, 5.0, 7.5, and 10 m of transverse distance from the eucalyptus tree row tracks. Soil samples collected in a conventional pasture area (CP) and a native Cerrado vegetation area (NV) were used as reference treatments. Soil samples were collected at depths from 0.0–0.10, 0.10–0.20, and 0.20–0.30 m. The acidity components (pH, Al3+ and H + Al) and oxidizable organic C fractions (F1: labile fraction; F2: moderately labile fraction; and F3: poorly labile fraction) were determined. The results showed that the lowest soil acidity level was observed at 2.5 and 10.0 m distances from the eucalyptus tree rows. However, the spatial distribution of soil sampling points to the eucalyptus tree rows in a 2-year silvopastoral system did not change the oxidizable fractions of the soil organic carbon. The 2-year silvopastoral system and native Cerrado vegetation area had the highest concentrations of organic carbon in the labile (F1) and poorly labile (F3) fractions in the soil profile compared to the conventional pasture system. A 2-year silvopastoral system in a low fertility tropical soil from the Brazilian Cerrado has not yet been able to improve the soil's chemical quality; therefore, further research should be carried out to investigate the medium and long-term effects of the silvopastoral system on the acidity components and oxidizable organic carbon fractions of the soil.
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