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The production of soybean (Glycine max L.) has doubled in the last two decades. It is now being grown on both traditional arable lands and on marginal soils, including saline soils, in various parts of the world. Most research on crop tolerance to salinity has been performed using soils with stable levels of salinity. However, there are soils that undergo sudden increases in topsoil salinity for short periods of time. The aim of this study was to compare the effect of stable salinity concentrations with peaks of salinity for their effects on soybean vegetative growth, grain yield, and the accumulation of chlorides. The response of soybean growth was evaluated in pot experiments with the following treatments: Control (non saline soil), soil salinity level of 0.4 S m -1 (0.4S) or 0.8 S m -1 (0.8S), and soil subjected to salinity peaks of 0.4 S m -1 (0.4P) and 0.8 S m -1 (0.8P). The salinity levels were obtained by application of saline irrigation water. Soybean responded differently to stable salinity levels versus peaks of salinity. When salinity was a permanent stress factor, regardless of the salinity level (i.e. 0.4 and 0.8 S m -1 ), biomass production and differentiation of reproductive organs was greatly affected. For 0.8S treated plants, they never reached the reproductive phase. Conversely, only small differences in growth data were found between 0.4P and Control treatments, although an 80% decrease in yield was associated with the 0.4P treatment. To obtain a reasonable soybean yield, a leaf chloride concentration of 1 mg g -1 of Cl -in dry matter should be considered a maximum threshold. Key words: NaCl, Glycine Max L., saline irrigation, yield loss, chloride accumulationCrescimento da soja sob salinidade estável ou em forma de pulsos RESUMO: A produção de soja (Glycine max L.) duplicou nas últimas duas décadas. Atualmente está sendo cultivada em terras aráveis tanto nos solos tradicionais quanto marginais, incluindo solos salinos, em várias partes do mundo. A maioria das pesquisas sobre a tolerância das culturas à salinidade foi realizada utilizando solos com níveis estáveis de salinidade. No entanto, há solos que são sensíveis ao aumento brusco de salinidade do solo superficial por curtos períodos de tempo. Comparou-se o efeito das concentrações de salinidade estável com picos de salinidade no crescimento vegetativo da soja, na produção de grãos e no acúmulo de cloretos. A resposta do crescimento da soja à salinidade foi avaliada em experimentos em vasos com os seguintes tratamentos: irrigação com água destilada (Controle, C), a irrigação para alcançar a salinidade de 0,4 S m -1 (0,4S) ou 0,8 S m -1 (0,8S) e irrigação com picos para alcançar a salinidade 0,4 S m -1 (0,4P) e 0,8 Sm -1 (0.8P). A soja respondeu diferentemente aos níveis de salinidade estável contra picos de salinidade. Quando a salinidade foi um fator de estresse permanente, independentemente do nível de salinidade (ou seja, 0,4 e 0,8 S m -1 ), a produção da biomassa e a diferenciação dos órgãos reprodutivos foram muito afetadas,...

Stress parameters in F treatments were less affected. Plants grown in soils enriched with P revealed a decrease in the toxic effects caused by As and F.

2 The magnitude of crop growth and yield depends on the salinity level, the toxic ions present, and the irrigation system used. In order to study the effect of saline sprinkler irrigation on soybean growth and ionic accumulation in plant tissues a pot experiment was set up. There were three irrigation water quality treatments [electrical conductivity (EC) 0, 2, and 4 dS m −1 ]. Soybean aerial biomass was 25% lower than the Control when irrigation salinity was 4 dS m −1 . Clearly salinity entering via leaves affected the grain filling stage and severely reduced soybean grain production (80% reduction) when salinity in irrigation water surpassed 2 dS m −1 . Sprinkler irrigation aggravates soybean's low salinity tolerance and restricts its cropping in such conditions. For early stages two linear relationships between leaf chloride (Cl − ) concentration (Y = 14.2-2x) or potassium (K + )/ sodium (Na + ) ratio (Y = 5.3x−3.4) and soybean grain yield were found. Both relationships may be used as diagnostic tools for soybean growing under saline sprinkler irrigation.

SUMMARYThe Proctor test is time-consuming and requires sampling of several kilograms of soil. Proctor test parameters were predicted in Mollisols, Entisols and Vertisols of the Pampean region of Argentina under different management systems. They were estimated from a minimum number of readily available soil properties (soil texture, total organic C) and management (training data set; n = 73). The results were used to generate a soil compaction susceptibility model, which was subsequently validated using a second group of independent data (test data set; n = 24). Soil maximum bulk density was estimated as follows: Maximum bulk density (Mg m -3 ) = 1.4756 -0.00599 total organic C (g kg -1 ) + 0.0000275 sand (g kg -1 ) + 0.0539 management. Management was equal to 0 for uncropped and untilled soils and 1 for conventionally tilled soils. The established models predicted the Proctor test parameters reasonably well, based on readily available soil properties. Tillage systems induced changes in the maximum bulk density regardless of total organic matter content or soil texture. The lower maximum apparent bulk density values under no-tillage require a revision of the relative compaction thresholds for different no-tillage crops.Index terms: soil organic carbon, soil compaction, soil texture. SEÇÃO I -FÍSICA DO SOLO

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