Abstract Atriplex nummularia L. is one of the most studied halophytes in research on phytoremediation of salt-affected soils. However, the optimization of biomass requires studies that indicate the appropriate way to evaluate the photosynthesis. The objective of this study was to investigate the photosynthetic efficiency of A. nummularia irrigated with saline water in order to indicate the best range of photosynthetically active radiation (PAR) that should be used. Plants were subjected to daily irrigations (0, 50, 100, 200, 250 and 300 mmol L-1 of NaCl). The light curves were determined at 15 and 84 days applying twenty light intensities (2000, 1750, 1500, 1250, 1000, 750, 500, 250, 200,175, 150, 125, 100, 75, 50, 25, 15, 10, 5, 0 μmol m-2 s-1 PAR). The highest values of photosynthesis rate were observed at PAR of 2000 μmol m-2 s-1 and of 800 μmol m-2 s-1 to 15 and 84 days of evaluation, independent of the NaCl concentration. The present study provides data that support the choice of the ideal PAR in evaluations of gas exchange in A. nummularia.

RESUMO Os solos afetados por sais ocupam extensas áreas em regiões áridas e semiáridas do mundo, e impactam a produção de alimentos, notadamente quando os processos de salinização ocorrem em áreas irrigadas. Nesse contexto, a possibilidade de uso de técnicas para recuperação desses solos precisa ser considerada. Entretanto, muitas dessas técnicas são inacessíveis para a maioria dos agricultores do semiárido brasileiro, face aos elevados custos, especialmente quando é necessária a instalação de sistema de drenagem subsuperficial. Há, portanto, necessidade de se avaliar outras estratégias de recuperação do solo, bem como a possibilidade de aproveitamento dessas áreas para outros propósitos. Nesta revisão são abordados tópicos relacionados à caracterização e impactos dos solos afetados por sais, a influência dos microrganismos do solo e as estratégias de recuperação, tais como o uso de condicionadores químicos e orgânicos, biodrenagem, fitorremediação e revegetação com espécies tolerantes. Os temas abordados nesta revisão indicam novas possibilidades para a recuperação e manejo dos solos afetados por sais no semiárido brasileiro. Também é apresentado um estudo de caso, que demonstra que o aproveitamento dos solos afetados por sais é definido por aspectos técnicos, sociais e econômicos.

ABSTRACT Salt-affected soils occupy extensive areas in arid and semi-arid regions around the world, and impact food production, particularly when salinization processes occur in irrigated areas. In this context, the possibility of using techniques for the reclamation of these soils needs to be considered. However, many of these techniques are inaccessible to most farmers in the Brazilian semi-arid region, given the high costs, mainly when it is necessary to install a subsurface drainage system. Thus, there is a need to evaluate other soil reclamation strategies as well as the possibility of using these areas for other purposes. This review covers topics related to the characterization and impacts of salt-affected soils, the influence of soil microorganisms, and strategies for soil reclamation, such as the use of chemical and organic conditioners, bio-drainage, phytoremediation, and revegetation with tolerant species. The topics addressed in this review indicate new possibilities for the reclamation and management of salt-affected soils in the Brazilian semi-arid region. A case study is also presented, which demonstrates that the use of salt-affected soils is defined by technical, social, and economic aspects.

Resumen La falta de cobertura es uno de los principales aceleradores de la degradación del suelo. Sin protección y expuesto a la lluvia, el suelo rompe las partículas, provocando el sellado de la superficie, dificultando la infiltración. Este estudio caracteriza el sellado superficial y la erosión hidráulica en Ultisoles de la Cuenca del Alto Ipanema. Se establecieron ocho parcelas de erosión bajo los tratamientos: suelo desnudo y suelo con mantillo de Brachiaria decumbens. Se simularon tres eventos de lluvia a intervalos de 24 horas, con una intensidad de 54,63 mmh-1. Después de cada simulación, se investigó la micromorfología de la superficie y la cantidad de suelo perdido. El uso de mantillo redujo la escorrentía en un 42% y la pérdida de suelo y la tasa de desagregación se redujo en un 70% en promedio. La infiltración se incrementó en un 242%. El mantillo fue eficaz para preservar la porosidad y la microestructura del suelo para el primer evento de lluvia simulado (0 h), pero no se observó en el segundo (24 h) y tercero (48 h) eventos de lluvia.

Abstract The lack of cover is one of the main accelerators of soil degradation. Without protection and exposed to rainfall, the soil breaks the particles, causing surface sealing, making infiltration difficult. This study characterizes surface sealing and hydraulic erosion in Ultisols of the Alto Ipanema Basin. Eight erosion plots were established under the treatments: bare soil and soil with Brachiaria decumbens mulch. Three rain events were simulated at 24-hour intervals, with an intensity of 54.63 mmh-1. After each simulation, the surface micromorphology and the amount of soil lost were investigated. The use of mulch reduced runoff by 42% and the loss of soil and the rate of disaggregation was reduced by 70% on average. Infiltration was increased by 242%. Mulch was effective in preserving soil porosity and microstructure for the first simulated rainfall event (0 h), but was not observed in the second (24 h) and third (48 h) rainfall events.

ABSTRACT Drought and soil salinity are the main abiotic stresses in semiarid regions of the world. This study aims to evaluate the effect of water tensions generated by the reduction of soil moisture and salt on the leaf water potential of cowpea (Vigna unguiculata L. Walp). The experiments were conducted in a randomized complete block design, with a 6 × 2 factorial arrangement consisted of six soil water tensions (0.025, 0.265, 0.485, 0.705, 0.925, and 1.145 MPa) and two tension sources (water deficit and salt), with four replications. Two experiments were performed with the same environmental conditions to evaluate the influence of the tensions on vegetative and reproductive stages. Water and osmotic potentials, relative water content, leaf succulence, and shoot biomass yield were evaluated. Soil water tension was not the main factor of changes on water and osmotic potentials of V. unguiculata plants; the water deficit treatments at soil water tensions of up to 1.145 MPa did not reduce the water and osmotic potentials either at the vegetative or flowering phenological stages; high correlations were found between shoot biomass yield and the leaf water potential at seven days after stress. The osmotic potential was the main indicator of stress in plants at the vegetative and flowering stages subjected to water deficit by the presence of salts in the soil solution.

RESUMO Pesquisas que avaliem o uso de cobertura morta no solo tem grande aceitação, uma vez que otimiza o manejo sustentável e melhora a qualidade do solo. Objetivou-se, com o presente trabalho, avaliar a eficiência da cobertura morta na redução das taxas erosivas do solo em cultivo de sorgo (Sorghum bicolor L. Moench) submetido à chuva simulada, bem como o incremento de carbono orgânico no solo. O experimento foi desenvolvido no período de agosto a dezembro de 2013 sob condição de campo, onde foram estabelecidos os seguintes tratamentos: sorgo com cobertura morta (CM) utilizando-se a vegetação espontânea da área e sorgo sem cobertura morta (SM), com três repetições em blocos casualizados. Foi realizada chuva simulada em três períodos distintos (nicial, intermediário e final do ciclo da cultura), utilizando-se um simulador de chuvas. Em todas as fases da cultura, o uso da cobertura morta no solo em cultivo de sorgo se mostrou eficiente por proporcionar maior retenção da umidade no solo, a qual se manteve por mais tempo entre os intervalos de chuva, resultando na ausência de perda de água, além de proporcionar maior aporte de carbono orgânico no solo.

ABSTRACT Researches evaluating the use of mulch has contributing to optimize soil management towards sustainability, and improving soil quality. The objective of this study was to evaluate the efficiency of mulching on the reduction of erosion in a soil with sorghum (Sorghum bicolor L. Moench) crops subjected to simulated rainfall and increased soil organic carbon. The experiment was carried out from August to December 2013 under field conditions, using a randomized block design with three replications. The treatments consisted of sorghum with mulch, using the local vegetation available in the area; and sorghum without mulch. Simulated rainfalls were performed in three different periods of the crop cycle (initial, intermediate, and final), using a rainfall simulator. The use of mulch in soils with sorghum crops was efficient in improving soil water retention in all phases of the crop, and maintaining soil moisture during the rainfall intervals used, resulting in the absence of plant water loss, and greater contribution to soil organic carbon.

ABSTRACT Investigations into water potentials in the soil-plant system are of great relevance in environments with abiotic stresses, such as salinity and drought. An experiment was developed using bell pepper in a Neossolo Flúvico (Fluvent) irrigated with water of six levels of electrical conductivity (0, 1, 3, 5, 7 and 9 dS m-1) by using exclusively NaCl and by simulating the actual condition (using a mixture of salts). The treatments were arranged in a randomized block design, in a 6 × 2 factorial arrangement, with four replicates. Soil matric (Ψm) and osmotic (Ψo) potentials were determined 70 days after transplanting (DAT). Soil total potential was considered as the sum of Ψm and Ψo. Leaf water (obtained with the Scholander Chamber) and osmotic potentials were determined before sunrise (predawn) and at noon at 42 and 70 DAT. There were no significant differences between the salt sources used in the irrigation water for soil and plant water potentials. The supply of salts to the soil through irrigation water was the main factor responsible for the decrease in Ψo in the soil and in bell pepper leaves. The total potential of bell pepper at predawn reached values of -1.30 and -1.33 MPa at 42 and 70 DAT, respectively, when water of 9 dS m-1 was used in the irrigation. The total potential at noon reached -2.19 MPa. The soil subjected to the most saline treatment reached a water potential of -1.20 MPa at 70 DAT. There was no predawn equilibrium between the total water potentials of the soil and the plant, indicating that soil potential cannot be considered similar to that of the plant. The determination of the osmotic potential in the soil solution should not be neglected in saline soils, since it has strong influence on the calculation of the total potential.

A adição de subprodutos orgânicos ao solo pode ocasionar mudanças na dinâmica da matéria orgânica dele, influenciando a atividade e utilização do carbono pelos microrganismos presentes nele. O objetivo deste trabalho foi avaliar a influência da aplicação de doses crescentes de subproduto da agroindústria de café nos atributos biológicos de dois solos com textura distinta, em diferentes tempos de incubação. O delineamento experimental foi em blocos casualizados, em esquema fatorial 2 × 8, sendo dois solos e oito doses de subproduto de café, com cinco repetições. Foram realizadas coletas de subamostras dos solos aos 30, 60, 90 e 125 dias após a incorporação do subproduto nesses. Nessas datas foram avaliados o carbono microbiano (C-CBM), a respiração basal microbiana (RBM) e o carbono orgânico total (COT). A adição do subproduto do café proporcionou aumentos nos valores de C-CBM, C-CO2 e COT dos dois solos utilizados. A maior atividade microbiana ocorreu no período de 30 dias, com maior liberação de C-CO2; o COT foi superior no solo argiloso por ele permitir maior proteção dos compostos orgânicos à decomposição pelos microrganismos.

The addition of organic residue byproducts in the soil may lead to changes in the dynamics of soil organic matter, influencing the activity and the use of C by microorganisms in the soil. The aim of this study was to evaluate the influence of the application of increasing rates of a byproduct from a coffee agroindustry on the biological properties of two soils with different clay contents as a function of incubation time. A randomized block experimental design was used in a 2 × 8 factorial arrangement of two solos and eight sources of coffee byproduct, with five replicates. Subsamples were collected from the soil at 30, 60, 90, and 125 days after incorporation of the byproduct in the soil. On these days, microbial biomass carbon (C-MBC), microbial basal respiration (MBR), and total organic carbon (TOC) were evaluated. Application of the coffee byproduct led to increases in the values of C-MBC, MBR and TOC in the two soils. The greatest microbial activity occurred at 30 days, with greater release of C-CO2, and the TOC was higher in the clayey soil because it provides greater protection of organic compounds from decomposition by microorganisms.

Polímeros solúveis em água caracterizam-se como eficientes agentes floculantes relacionados aos seus aspectos moleculares, cuja aplicação em solos com horizontes que apresentam problemas estruturais, como acontece com o caráter coeso, favorece a melhoria da qualidade física e, assim, amplia a aptidão agrícola desses solos. Esta pesquisa teve como objetivo avaliar a qualidade estrutural de solos com horizontes coesos dos Tabuleiros Costeiros de Pernambuco com a aplicação de Poliacrilamida (PAM) como condicionador químico. Para isso, foram avaliados três horizontes (um coeso e dois não coesos) de um Argissolo Amarelo e, para fins comparativos de horizontes coesos, foi selecionado o horizonte de um Latossolo Amarelo. Como tratamentos, foram aplicadas soluções aquosas de PAM (12,5; 50,0; e 100,0 mg kg-1) e água destilada (controle). Os aspectos estruturais dos horizontes foram avaliados pela estabilidade (massa de solo retida em cinco classes de diâmetro), distribuição de agregados por classe de tamanho (diâmetro médio ponderado - DMP, diâmetro médio geométrico - DMG) e magnitude das alterações promovidas pela PAM, medindo o índice de sensibilidade (Is). As soluções aquosas de PAM aumentaram a estabilidade de agregados na maior classe de diâmetro avaliada dos horizontes coesos e não coesos, repercutindo em maiores valores de DMP e DMG, com a solução de 100 mg kg-1 mais eficiente. O horizonte coeso Bt1, do Argissolo, evidenciou-se mais sensível à ação da PAM, onde foram encontrados maiores valores do Is; porém, o horizonte BA, do Latossolo, apresentou melhor qualidade estrutural inferida pela estabilidade e distribuição de tamanho de agregados.

Water-soluble polymers are characterized as effective flocculating agents due to their molecular features. Their application to soils with horizons with structural problems, e.g, a cohesive character, contributes to improvements in the physical quality and thus to the agricultural suitability of such soils. The purpose of this study was to evaluate the structural quality of soils with cohesive horizons of coastal tablelands in the State of Pernambuco treated with polyacrylamide (PAM) as chemical soil conditioner. To this end, three horizons (one cohesive and two non-cohesive) of a Yellow Argisol (Ultisol) were evaluated and to compare cohesive horizons, the horizon of a Yellow Latosol (Oxisol) was selected. The treatments consisted of aqueous PAM solutions (12.5; 50.0; 100.0 mg kg-1) and distilled water (control). The structural aspects of the horizons were evaluated by the stability (soil mass retained in five diameter classes), aggregate distribution per size class (mean weight diameter- MWD, geometric mean diameter - GMD) and the magnitude of the changes introduced by PAM by measuring the sensitivity index (Si). Aqueous PAM solutions increased aggregate stability in the largest evaluated diameter class of the cohesive and non-cohesive horizons, resulting in higher MWD and GMD, with highest efficiency of the 100 mg kg-1 solution. The cohesive horizon Bt1 in the Ultisol was most sensitive to the action of PAM, where highest Si values were found, but the structural quality of the BA horizon of the Oxisol was better in terms of stability and aggregate size distribution.

Devido ao avanço das áreas em processo de degradação decorrente de causas naturais e, ou, influências antrópicas, faz-se necessária a utilização de ferramentas, preferencialmente de baixo custo, que indiquem os estádios dessa degradação, a fim de viabilizar um manejo adequado e a recuperação dessas áreas. Desse modo, o objetivo desta pesquisa foi analisar a variabilidade de atributos químicos e microbianos de solos, visando a utilizá-los como indicadores de processos de desertificação, em áreas sob níveis crescentes de degradação na região semiárida do Estado de Pernambuco. Foram amostrados três ambientes: conservado, moderadamente degradado e intensamente degradado, no município de Floresta-PE. Em cada ambiente foram escolhidas quatro áreas de amostragens e efetuadas sete coletas em cada um delas, totalizando 28 pontos amostrados por ambiente. Foram coletadas amostras de solo na profundidade de 0-10 cm, nos períodos seco e chuvoso. Realizaram-se análises químicas (pH, bases trocáveis, acidez potencial, C orgânico do solo, estoque de C, P disponível e capacidade de troca de cátions) e microbianas (C da biomassa microbiana, respiração basal, quocientes microbiano e metabólico) do solo, além da caracterização física (textura e densidade do solo). Os dados foram analisados adotando-se métodos de análises de componentes principais e teste t. Verificou-se o efeito da sazonalidade para os atributos do solo, sendo essa mudança mais perceptível no ambiente degradado. Com as análises de componentes principais, foi possível destacar alguns atributos mais sensíveis ao avanço da degradação, como o C da biomassa microbiana do solo, a acidez potencial e a saturação por bases, tanto no período seco como no chuvoso. Desse modo, esses atributos podem ser utilizados como indicadores do nível de degradação do solo.

To analyze the process of degradation caused by natural or anthropogenic influences tools are required, preferentially low-cost, to indicate the degradation stages aiming the selection of techniques to reclaim degraded areas. The purpose of this study was to analyze the variability of microbiological and chemical soil properties as indicators of desertification processes in areas with increasing levels of degradation in the semiarid region of the State of Pernambuco, Brazil. Three environments were sampled: conserved, moderately degraded and heavily degraded in Floresta, PE. Seven samples were collected from four areas per environment (28 points per environment). Soil samples were collected from the 0-10 layer in dry and rainy seasons. Soil samples were used for chemical (pH, exchangeable bases, potential acidity, soil organic carbon, carbon stock, available phosphorus and cation exchange capacity), microbiological (microbial biomass carbon, basal respiration, microbial and metabolic quotients) and physical analyses (texture and bulk density). The data were analyzed using main components and t test. An effect of seasonality was observed for the soil properties, especially in the degraded environment. Principal component analysis identified microbial biomass carbon, potential acidity and percent of base saturation as most sensitive to the degradation level in the rainy and dry seasons. These properties can therefore be used as indicators of soil degradation.

A análise dos atributos físicos e da salinidade de solos em áreas irrigadas é de extrema importância para elaboração e implantação de propostas de manejo. Com o objetivo de avaliar a dependência espacial das frações granulométricas e da condutividade elétrica do extrato de saturação, foi desenvolvido um estudo em área aluvial irrigada no semi-árido de Pernambuco, em que se adotou uma malha regular de 5 x 5m, correspondendo a um total de 98 pontos amostrais, e foram coletadas amostras de solo na profundidade de 0-20cm. As variáveis foram submetidas à análise estatística clássica, seguida de análise geoestatística. A variabilidade dos dados foi classificada como média para todas as variáveis estudadas, com coeficientes de variação respectivamente de 26,08; 14,81; 16,01 e 28,00% para areia, argila, silte e condutividade elétrica do extrato de saturação. A dependência espacial foi considerada alta para as frações granulométricas e moderada para a condutividade elétrica, com alcances de 56, 50, 55 e 35m, respectivamente. A condutividade elétrica está fortemente correlacionada espacialmente com o teor de silte, apresentando alcance de 52m para o semivariograma cruzado. Os resultados ressaltam a importância da fração silte na distribuição espacial da salinidade, bem como na relevância para o manejo racional do solo estudado.

Analysis of the physical attributes and salinity of soils is important for proposing management strategies in irrigated areas. The objective of this study was to evaluate the spatial dependence of the granulometric fractions and electric conductivity of the saturation extract in an area irrigated in the semi-arid of Pernambuco State. A 5 x 5m regular mesh was adopted, with 98 sampling points collected at depth 0-20cm. The variables have been analysed through statistics and geoestatistics. The variation coefficients of the saturation extract were 26.08; 14.81; 16.01 and 28.00% for sand, clay, silt and electrical conductivity of the saturation extract, respectively. The spatial dependence was identified as high for the granulometric fractions and as moderate for the electric conductivity, with ranges of 56; 50 and 55 and 35m, respectively. The electric conductivity has a strong spatial correlation with silt content, presenting range of 52m, for the cross semivariogram. The results highlight the importance of the silt fraction in the spatial distribution of salinity in loam soils, and its relevance for adequate management of these soils.