RESUMO -Os Tabuleiros Costeiros, com ocorrência nas regiões Norte, Nordeste e Sudeste do Brasil, apresentam solos com horizontes coesos, os quais podem ocasionar impedimentos físicos à penetração das raízes e à dinâmica da água. No entanto, a gênese desses horizontes ainda é muito questionada. Desta forma, objetivou-se avaliar a influência do material amorfo na coesão desses solos, estudando-se uma topossequência no município de Trairi -CE. Foram descritos e caracterizados (física e quimicamente) três perfis de solos com caráter coeso (P2; P3 e P4) e um perfil (P1) não coeso. Para a avaliação do efeito do material amorfo na coesão dos solos, foram utilizadas amostras dos horizontes Bt1 dos 4 perfis, com e sem extração de material amorfo. Três ciclos de umedecimento e secagem foram aplicados nas amostras e, em seguida, a resistência à penetração (RP) foi determinada. Com base nos resultados, os solos foram enquadrados, taxonomicamente, nas subordens dos Argissolos Amarelos (P1; P2 e P3) e Acinzentados (P4). A maior expressão do caráter coeso foi encontrada em P4, situado na posição mais baixa da paisagem, sugerindo a influência do relevo na intensificação do caráter coeso. Apesar dos baixos teores de argila e de destorroamento, os solos retomaram uma alta RP após apenas três ciclos de umedecimento e secagem. Após a extração de material amorfo, os horizontes coesos dos perfis P2 e P4 apresentaram uma significativa redução da resistência à penetração, indicando que estes compostos atuam na gênese de horizontes coesos. Palavras-chave:Caráter coeso. Compostos amorfos. Pedogênese. ABSTRACT -The coastal plains, in the North, Northeast and Southeast Brazil, soils with cohesive layer are common, and can cause physical impediment to root and water. However, the genesis of these horizons is still unknown. The main objective of this work was to evaluate the influence of amorphous materials on the cohesion processes with cohesive layers from a toposequence in Trairi -CE. Four soil profiles were described and characterized (physically and chemically). Three soils present cohesive layers (P2, P3 and P4) and one (P1) did not. To evaluate the effect of amorphous material in the cohesion, samples of Bt1 horizons were subjected to two treatments: with and without extraction of amorphous material. Samples (with and without extraction) were subjected to three cycles of wetting and drying and then the penetration resistance (PR) was determined. Based on the chemical and physical analysis, the soils were classified as Ultisols. The highest expression of the cohesive character was found in P4, located in the lowest position of the landscape, suggesting the influence of relief on the intensification of the cohesion. Despite the low clay content and the loosening of the soil, a high PR was achieved after only a few cycles of wetting and drying. After extraction of amorphous material, the cohesive horizons of profiles P2 and P4 showed a significant reduction of PR, indicating that these compounds act in the genesis of cohesive layers.

Cohesive horizons are widespread along the Brazilian coastal tablelands and, despite their importance to soil management under intensive cultivation, their genesis remains, in many aspects, controversial. Studies diverge and indicate the participation of different mechanisms in the formation of these soil horizons. Although clay illuviation has been considered as one of the processes determining the formation of this soil attribute, recent studies suggest a limited participation of this soil process. The aim of the present study was to evaluate the relative contribution of argilluviation and sorting of sand to the genesis of cohesive horizons in an Ultisol toposequence from a toposequence from north-east Brazil. Soil samples were collected from cohesive and non-cohesive horizons from four soil profiles. We determined bulk soil density (BD), penetration resistance (PR), particle size distribution and the percentage of different sand fractions. The sand fractionation data were treated statistically to obtain different grain size parameters, such as mean grain size, sorting and kurtosis. An additional micromorphological study was performed on cohesive and non-cohesive horizons. The lowest BD and PR were recorded in non-cohesive horizons (1.53 Mg m–3 and 0.74 MPa, respectively), whereas significantly higher values of BD (1.66–1.80 Mg m–3) and PR (2.61–7.71 MPa) were observed in cohesive horizons. Thin sections of cohesive soil horizons showed a significant reduction in void sizes and interconnecting pores compared with non-cohesive soil horizons. The higher values of BD and PR observed in the cohesive horizons are apparently related to this poorly interconnected void network. Textural pedofeatures observable with optical microscopy, which indicate argilluviation, were only found in one cohesive horizon. Sand fractionation showed a predominance of medium and fine sand fractions and indicated the dominance of poorly selected sand in cohesive horizons, probably causing the higher BD and PR values. However, the presence of textural pedofeatures (clay coatings) in one of the cohesive horizons studied may indicate a combined contribution of sand heterogeneity and argilluviation in the genesis of these horizons. Overall, the results of the present study showed that subtle variations in the distribution of basic soil components (i.e. particle size fractions) may determine the formation of cohesive horizons and thus must be taken into account in future studies aiming to predict their spatial distribution and to establish more efficient management strategies.

EFFECT OF LEACHING FRACTION DETERMINED BY TWO METHODS ON GROWTH AND YIELD OF MAIZE SUBMITTED TO SALT STRESS1     EMANUEL DIAS FREITAS2; CLAUDIVAN FEITOSA DE LACERDA3; JULIANA MATOS VIEIRA4; BRUNO GABRIEL MONTEIRO DA COSTA BEZERRA5 E AURELIANO DE ALBUQUERQUE RIBEIRO6   1Parte da tese de doutorado do primeiro autor. Projeto financiado pelo CNPq; 2 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:emanueldiasfreitas@gmail.com; 3 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:cfeitosa@ufc.br; 4 Departamento de Ciência do Solo, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:julianamatosvieira@gmail.com; 5 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:brunog768@gmail.com; 6 Departamento de Engenharia Agrícola, Universidade Federal do Ceará – UFC, CEP: 60451-970, Fortaleza, CE, e-mail:alburibeiro@gmail.com.     1 ABSTRACT   The aim of this study was to evaluate the effects of the leaching fraction determined by two methods in maize cultivated in a soil column and submitted to irrigation with water of different salinities. The experiment was conducted in the meteorological station of the Federal University of Ceará, Fortaleza - CE, in a completely randomized design, composed by four levels of irrigation salinity water (0.5, 2.0, 4.0 and 6.0 dSm-1) and two methods of determination of the leaching fraction. Each treatment had seven replicates. The plots were constituted by maize cultivated in soil columns, measuring 20 cm in diameter and 100 cm in length. The leaching fractions (LF) were defined as follows: A. Application of the LF calculated according to the formula proposed by Rhoades (1974), Rhoades and Merrill (1976); B. Application of the LF of 15% calculated from the soil water balance of the experimental plots. The results showed that plants that were irrigated with ECw of 0.5 and 4 dS m-1, the LF of 5 and15%, respectively, were able to minimize the effects of salinity. For ECw of 6 dS m-1, the LF of 15 and 92% showed no improvement in maize growth and yield.   Keywords: Zea mays L. soil columns, saline water.     FREITAS, E. D.; LACERDA, C. F. DE; VIEIRA, J. M.; BEZERRA, B. G. M. DA C. E RIBEIRO, A. DE A. EFEITO DA FRAÇÃO DE LIXIVIAÇÃO DETERMINADO POR DOIS MÉTODOS NO CRESCIMENTO E PRODUÇÃO DO MILHO SUBMETIDO A ESTRESSE SALINO           2 RESUMO   Objetivou-se com o trabalho avaliar os efeitos da fração de lixiviação determinado por dois métodos na cultura do milho cultivado em coluna de solo e submetido a irrigação com água de diferentes salinidades. O experimento foi instalado na estação meteorológica da Universidade Federal do Ceará, Fortaleza – CE, em delineamento inteiramente casualizado, composto por quatro salinidade de água de irrigação (0,5, 2,0, 4,0 e 6,0 dS m-1) e duas formas de determinação da fração de lixiviação (FL). Utilizou-se sete repetições para cada tratamentos. As parcelas foram constituídas por milho cultivado em colunas de solo, medindo 20 cm de diâmetro e 100 cm de comprimento. As frações de lixiviação foram determinadas pelos seguintes métodos: A. Aplicação das FL de acordo com a fórmula de Rhoades (1974), Rhoades e Merrill (1976); B. Aplicação de FL de 15 % calculada a partir do balanço hídrico do solo. Os resultados mostraram que as plantas que foram irrigadas com CEa de 0,5, 4 dSm-1 as LF de 5 e 15%, respectivamente, foram capazes de dirimir os efeitos da salinidade. Para a CEa de 6 dSm-1 as LF de 15 e 92% não apresentaram melhoria no crescimento e produção do milho.   Palavras-chave: Zea mays L., colunas de solo, água salina.