In agricultural fields soil compaction is a major cause of physical degradation. Degree of compactness (DC) is a useful parameter for characterizing compaction and the response of crops for different soils. The objectives of this study were: (1) to identify the critical DC and PR values for soybean [Glycine max (L.) Merrill] using plant growth variables and (2) to verify the relationship between DC and PR, and assess which parameter is recommended for the evaluation of soil compaction. The study was conducted in a greenhouse in a completely randomized factorial design of 4 textures × 5 compaction levels for sandy loam and sandy clay loam soils, and 3 compaction levels for the clayey and very clayey soils. Soil samples were collected from the surface of a Xantic Kandiudox from the NE region of the State of Pará, Brazil. The DC was calculated from the maximum bulk density obtained by the Proctor test, and the PR curve was determined in undisturbed samples equilibrated in different matric potentials. The growth and development of the soybean was favored in the DC range of 80 to 85%, regardless of soil texture. The critical degree of compactness for the growth of soybean was around 98% regardless of soil texture, while the critical values for penetration resistance at field capacity varied according to soil texture and bulk density and were 28.2, 5.6, 3.5, and 5.2 MPa for the sandy loam, sand clay loam, clayey and very clayey soils, respectively. The root length was the plant growth variable most susceptible to soil compaction. Change in soil penetration resistance was poorly related with change in degree of compactness showing that one parameter cannot be replaced by the other. Because PR is quickly determined in field and have a direct relationship with plant growth, for the soils evaluated in this study we recommend the use of soil PR to assess the state of soil compaction.

Viabilidade econômica da produção de couve-flor irrigada por gotejamento no Nordeste Paraense Economic viability of cauliflower production drip irrigated in Northeast Paraense Contribuição dos autores: Michel Emerson Martins Pereira conduziu o experimento, a análise estatística e a redação do artigo; Joaquim Alves de Lima Junior supervisionou e acompanhou todas as etapas, além das análises estatísticas e redação do artigo; Valdeides Marques Lima contribuiu com a revisão bibliográfica e a redação do artigo; Sérgio Antonio Lopes de Gusmão contribuiu com a revisão bibliográfica e a redação do artigo; Pedro Daniel de Oliveira colaborou com revisão ortográfica, gramatical e redação científica. André Luiz Pereira da Silva contribuiu com a redação do artigo e com a revisão ortográfica e gramatical Agradecimentos: Ao Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico (CNPq), pelo suporte e financiamento, e

Acmella oleracea (L.) R.K. is a native Amazon vegetable, known as jambu, which is widely used in regional cuisine and has aroused the interest of the pharmaceutical and cosmetic market. Thereby, this work aimed to study the effect of different soil water tensions and nitrogen rates on Jambu cultivation in the State of Pará. The experiment was conducted in a greenhouse for 30 days in 2016 testing Jamburana cultivar in a 10 × 10 cm spacing in the experiment. The experimental design was based on randomized blocks in a 4 × 4 factorial scheme with three replications. The treatments consisted of four soil water tensions (12, 18, 24 and 30 kPa) adjusted using drip irrigation, and four doses (0, 50, 100 and 150 kg ha-¹) of nitrogen. The analyzed variables were fresh mass, plant height, productivity and water use efficiency. There was no interaction between soil water tensions factors and nitrogen rates for all variables. The results showed that the best water tension in the soil and nitrogen dose that provided better development and productivity of jambu were 18 kPa and 79 kg ha-¹, respectively.

Com objetivo de fornecer informações técnicas sobre a produção da couve-flor irrigada em casa de vegetação no nordeste paraense, instalou-se um experimento na Fazenda Experimental da UFRA, no município de Igarapé-Açu, com a cultivar híbrida Desert, que apresenta adaptabilidade para o clima da região. O delineamento utilizado foi em blocos casualizados em esquema fatorial 4 x 3, com 12 tratamentos e 3 repetições. Os tratamentos foram constituídos por quatros tensões de água no solo (15, 30, 45 e 60 kPa), com indicativo no momento de irrigar e três doses de boro (0, 3 e 6 kg ha-1) aplicadas via foliar. O método de irrigação utilizado foi o gotejamento e o manejo de irrigação foi via tensiometria. As parcelas experimentais apresentaram 3,6 m2 constituídas de 8 plantas, com espaçamento de 0,8 m entre linhas e 0,5 m entre plantas. Em cada parcela, foram avaliadas 4 plantas centrais, totalizando 288 plantas. De acordo com os dados obtidos, a cultivar híbrida Desert mostrou-se promissora para o cultivo nas condições edafoclimáticas da região nordeste do Pará. A tensão que apresentou melhores resultados foi a de 37 kPa, obtendo produtividade de cabeça de 11,3 t ha-1, massa fresca de 450 g, massa seca de 31,48 g, diâmetro de 15,6 cm, circunferência de 50,99 cm e altura de 9,87 cm. As doses de boro não apresentaram diferença significativa.

The aim of this study was to evaluate the critical soil bulk density from the soil penetration resistance measurements for soybean root growth in Brazilian Amazon Oxisols. The experiment was carried out in a greenhouse using disturbed soil samples collected from the northwest of Para characterized by different texture. The treatments consisted of a range of soil bulk densities for each soil textural class. Three pots were used for soybean growth of and two for the soil penetration resistance curve. From the fitted model, the critical soil bulk density was determined considering the penetration resistance values of 2 and 3 MPa. After sixty days, plants were cut and root length, dry mass of root, and dry mass of shoots were determined. At higher bulk densities, the increase in soil water content decreased the penetration resistance, allowing unrestricted growth of soybean roots. Regardless of soil texture, the penetration resistance of 2 and 3 MPa had a slight effect on root growth in soil moisture at field capacity and a reduction of 50% in the soybean root growth was achieved at critical soil bulk density of 1.82, 1.75, 1.51, and 1.45 Mg m-3 for the sandy loam, sandy clay loam, clayey, and very clayey soil.