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Este estudo teve por objetivo avaliar o efeito de doses de K2O sobre a nutrição (teores de nitrogênio, fósforo, potássio, cálcio, magnésio, enxofre, cobre, zinco, ferro e manganês) na cana-de-açúcar em cultivo de sequeiro. O delineamento experimental foi em blocos ao caso em arranjo fatorial (6x2) com 4 repetições, sendo seis doses de K2O (0, 25, 50, 100, 200 e 250 kg ha-1) e duas variedades de cana-de-açúcar (RB92579 e RB962962). A aplicação das doses de K2O não promoveu efeito significativo sobre a nutrição das variedades de cana. A variedade RB92579 apresentou maiores teores de nitrogênio, potássio e zinco, enquanto que a RB962962 apresentou maiores teores de magnésio e manganês. A aplicação de fertilizantes potássicos não é aconselhada em ambientes com alto teor de potássio trocável no solo, acima de 0,24 cmolc dm-3, pois não resulta em melhoria do estado nutricional na cana-de-açúcar.

A cana-de-açúcar possui grande importância econômica para o Estado de Pernambuco por ser matéria prima para produção de açúcar e álcool. Vários fatores afetam os seus parâmetros morfológicos (altura, diâmetro e número de colmos). Dentre esses, a fertilidade do solo possui papel de destaque, em especial, para os teores de potássio (K). O potássio é o nutriente exigido em maiores quantidades pela cana-de-açúcar. Essa pesquisa teve por objetivo avaliar a aplicação de doses de K sobre as características morfológicas de duas variedades de cana-de-açúcar cultivadas em sistema de sequeiro. O trabalho foi realizado na Estação Experimental de Cana-de-Açúcar do Carpina (EECAC/UFRPE). O delineamento experimental foi em blocos ao acaso em arranjo fatorial 6x2. Utilizou-se duas variedades de cana (RB 92579 e RB 962962) e seis doses de K2O (0, 25, 50, 100, 200 e 250 kg ha-1), na forma de KCl. As doses de K e a interação Dose x Variedade não influenciaram as características morfológicas de ambas as variedades (p>0,01). Houve efeito significativo (p

Desertification is a problem in regions with arid, semi-arid and dry sub-humid climates and is characterized by the degradation of natural resources. The influence of vegetation cover and rainfall intensity on the dynamics of water infiltration, surface runoff and soil loss was measured in situ in a Desertification Zone in the semi-arid region of Brazil. Twenty-four plots were evaluated in two areas, each with the same type of soil that is predominant in the region: 1) Luvisol with dense vegetation cover (LD) and 2) Luvisol with sparse vegetation cover (LS). Rainfall of 60 and 100 mm h was simulated with a rainfall simulator. Soil hydraulic conductivity, soil water retention curves and soil carbon and nitrogen stocks were also determined. Water infiltration was greater in the LD (53 mm h ) compared to the LS (15 mm h ), while the runoff rates were 27 mm h for the LD and 61 mm h for the LS. Rainfall intensity significantly influenced when runoff started and the runoff rate, accelerating soil loss. Vegetation cover significantly influenced the total soil carbon and nitrogen stocks, as well as the saturated hydraulic conductivity of the soil. This is the first study in the semi-arid desertification region of Brazil that used simulated rainfall to assess the effects rain intensity on soil properties. The results of this study can be used as a reference for calibrating erosion models in areas undergoing a desertification process

The energetic state of water in the soil-plant system is a relevant theme in ecosystems affected by abiotic stress. Thus, the present study aimed to investigate the water potential in soil and in s...

Osmotic adjustment is a persisting controversy in studies on the effect of salt and water stress in cowpea crops. Our hypothesis is that the osmotic potential determination method interferes with the osmotic adjustment calculation. The objective of this study was to consider the osmotic adjustment comparing results obtained by pressure-volume (P–V) curves and osmometry. The experiment was conducted in a randomized block design, with six salt water concentrations 0, 20, 40, 60, 80, and 100 mmol L−1 of NaCl in a Fluvisol. The osmotic adjustment found through osmometry were lower than those found through P–V curves. The apoplastic water fraction of the cowpea had a dilution effect, denoting overestimation of the osmotic potential by the methodology based on osmometry. This may be the source of the different interpretations of osmotic adjustment in cowpea plants. Thus, osmotic adjustment should be calculated preferably using the osmotic potential determined by method of pressure-volume curves.

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. 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.

The K is important for sugar concentration in sugarcane, but the salt effect on K fertilizer may reduce the productivity. The objective of this study was to evaluate productivity of sugarcane, to establish soil and plant K critical levels, and to determine a saline limit of the soil with maximum agronomic efficiency. The sugarcane variety RB992506 was cultivated in the field in Oxisol (Kandic) dystrophic with very sandy and low K content, mainly in subsurface. Six doses of K2O were used: 0; 25; 50; 100; 200; 250 kg ha-1. We evaluated soil and leaf K content, electrical conductivity of the saturated soil paste, productivity and technological quality of the sugarcane. The application of K promoted increase in soil and leaf K levels, increasing also both productivity and the sugar concentration. The dose of maximum agronomic efficiency was 150 kg ha-1 of K2O and production of 116 Mg ha-1. High doses of K (> 200 kg ha-1 of K2O) decreased the productivity due to elevated soil salinity by the application of K fertilizer. The critical levels of K were 0.18 cmolc dm-3 in the soil and 9.53 g kg-1 in the plant and were associated with low doses of K (< 25 kg ha-1 of K2O). The salinity limits that reduced productivity were 1.38 dS m-1 in the surface layer and 1.19 dS m-1 in the subsurface, suggesting that these critical levels and limits can be used to evaluate the fertility of sandy soils cultivated with sugarcane in tropical regions.

Hydroponic cultivation using saline waters is an alternative for agricultural production, especially in the cultivation of vegetables. Therefore, the present work was conducted with the objective of evaluating the water consumption, water use efficiency and water content, as well as dry matter partitioning of chives (Allium schoenoprasum), cv. Todo Ano Evergreen – Nebuka exposed to six levels of nutrient solution salinity (1.5, 3.0, 4.5, 6.0, 7.5 and 9.0 dS m-1), applied at two circulation frequencies (twice a day at 8 and 16 h; and three times a day - at 8, 12 and 16 h). The level in the nutrient solution reservoir, which decreased according to the water consumption by plants, was replaced with the respective saline water (Experiment I) and supply water (Experiment II). Both experiments used a completely randomized design, in a 6 x 2 factorial scheme, with five replicates. It was observed that increased circulation frequency and the use of supply water in the replacement mitigated the effects of salinity on water consumption, water use efficiency and water content in the plant. However, with the increase in nutrient solution electrical conductivity, dry matter allocation in the roots increased, to the detriment of the shoots.

Advances in soil science have enabled the development of different approaches for assessing soil physical quality related to sugarcane (Saccharum spp.) growth. The present study aimed to evaluate the medium-term influence of conventional tillage on the physical qualities of a Typic Fragiudult cultivated with sugarcane under rainfed conditions in the State of Pernambuco, northeastern Brazil. The experiment was conducted in a randomized block design with four replications. Each block was composed of two experimental units (plots), and two different tillage systems were tested: i) minimum tillage (MT) (i.e., furrowed plots) and ii) conventional tillage (i.e., chiseled, harrowed and furrowed plots). The following soil physical attributes were determined in the laboratory: bulk density, wet aggregate stability and size distribution, total porosity and pore-size distribution and saturated hydraulic conductivity; both soil water retention and penetration resistance curves also were constructed. Soil penetration resistance in the field was also determined. To obtain a better understanding of these systems, we calculated the following soil quality indicators based on our laboratory data: least limiting water range, integral water capacity and integral energy; we also calculated the S and H indexes. Furthermore, sugarcane productivity and quality were assessed. After 17 months, no evidence was obtained indicating that conventional tillage improved some structural properties of the soil, including bulk density and aggregation. On the other hand, conventional tillage increased total porosity and modified pore-size distribution. Thus, CT increased slightly the total porosity of the soil by 2.1% and as result PR values reduced around 30% at 15-20 cm depth. Consequently, there was an increase in soil hydraulic conductivity, which reduced storage capacity, increasing the hardsetting behavior but without compromising the water availability for sugarcane at the surface layer (0–30 cm). On the other hand, conventional tillage increased the least limiting water range, but this increase was not enough to indicate good physical quality, mainly due to restrictions by penetration resistance. The integral energy values were similar between tillage systems. With respect to the crop, the conventional tillage system neither improved productivity nor quality. We concluded that conventional tillage improved the physical quality of a Typic Fragiudult in the medium term. However, under rainfed conditions, stalks and sugar yields depend on rainfall amounts and distribution rather than on the applied tillage system.

Geostatistical and multivariate techniques have been widely used to identify and characterize the soil spatial variability, as well as to detect possible relationships between soil properties and management. Besides that, these techniques provide information regarding the spatial and temporal structural changes of soils to support better decision-making processes and management practices. Although the Zona da Mata region is a reference for sugarcane production in the northeast of Brazil, only a few studies have been carried out to clarify the effects of different management on soil physical attributes by using geostatistical and multivariate techniques. Thus, the objectives of this study were: (I) to characterize the spatial distribution of soils physical attributes under rainfed and irrigated sugarcane cultivations; (II) to identify the minimum sampling for the determination of soil physical attributes; (III) to detect the effects of the different management on soil physical attributes based on the principal component analysis (PCA). The study was carried out in the agricultural area of the Carpina Sugarcane Experimental Station of the Federal Rural University of Pernambuco, 7º51’13”S, 35º14’10”W, characterized by a Typic Hapludult with sandy clay loam soil texture. The investigated plot, cultivated with sugarcane, included a rainfed and an irrigated treatment in which a sprinkler system was installed according to a 12x12m grid. The interval between consecutive watering was fixed in two days, whereas irrigation depth was calculated to replace crop evapotranspiration (ETc) and accounting for the effective precipitation of the period. Daily ETc was estimated based on crop coefficient and reference evapotranspiration (ETo) indirectly obtained through a class A evaporation pan. In both treatments, the soil spatial variability was determined according to a 56x32m grid, on 32 soil samples collected in the 0.0-0.1m soil layer, spaced 7x8m, and georeferenced with a global position system. The soil was physically characterized according to the following attributes: bulk density (BD), soil penetration resistance (SPR), macroporosity (Macro), mesoporosity (Meso), microporosity (Micro), total porosity (TP), saturated hydraulic conductivity (Ksat), gravimetric soil water content (SWCg), geometric mean diameter (GMD) and mean weight diameter (MWD). The results of the descriptive statistics showed that among the studied attributes, Ksat, SPR, and Macro presented higher CV values, equal to 63 and 69%, 35 and 40%, and 32 and 44%, under rainfed and irrigated conditions, respectively. The minimum sampling, adequate to characterize the different soil attributes, resulted in general smaller in the rainfed area, characterized by higher homogeneity. Thus, the GMD, SWCg (both with 2 points ha-1), and SPR (with 6 points ha-1) were identified as the soil physical attributes requiring the lowest sample density; on the other hand, MWD and Ksat, with 14 and 15 points ha-1, respectively, required the highest number of samples. Pearson’s correlation analysis evidenced that soil BD was the most influential physical attribute in the studied areas, with a significant and inverse effect in most of the investigated attributes. The geostatistical approach associated with the multivariate PCA provided to understand the relationships between the spatial distribution patterns associated with irrigated and rainfed management and soil physical properties.

Under arid and semiarid climates, the natural process of soil formation can cause the accumulation of salts that limit plant growth and development. The Northeast region of Brazil has an extensive area under semiarid climate with drought most of the time. Additionally, the inadequate management of irrigation has promoted the accumulation of salts in soils, degrading them. Some of such areas are becoming unproductive and are abandoned. Reclamation techniques that involve drainage, use of chemical and organic conditioners, are expensive and difficult to implement. Phytoremediation of salt-affected soils is a low cost alternative. Plants adapted to the environment, which tolerate high levels of salts, can grow and produce biomass, should be studied. It is also important that the plants used are able to absorb the salts, extracting them from the soils. However, phytoremediation results are not observed in the short term. But, over time, phytoremediation promotes the return of vegetation to degraded soils, as well as the associated microbiota and protects the soil surface. This chapter reports trials in Brazil, evaluating some plant species for their ability to survive and improve soil quality.

Vesicular trichomes play a key role in excluding toxic ions from some halophyte species, preventing the essential processes and functions of plants from being altered. Thus, the present study aimed to evaluate the influence of these structures on Atriplex nummularia irrigated using waters with three levels of osmotic potential (−0.1, −1.4 and −2.7 MPa), formulated with NaCl in plants with vesicular trichomes and plants with partial removal of trichomes. The experiment was conducted in a protected environment and plants were evaluated for physiological parameters (water, osmotic and pressure potentials, relative water content, osmotic adjustment, pressure-volume curve, gas exchange), electrolyte leakage, lipid peroxidation and enzymatic activity (superoxide dismutase, ascorbate peroxidase, catalase). The results obtained made it possible to identify the strong contribution of vesicular trichomes to physiological and biochemical parameters, with indication of cell wall stiffening and maintenance of turgor. Furthermore, the evaluation of the osmotic potentials obtained in the study suggests that the contribution of vesicular trichomes to the salinity tolerance of the species is greater than that of osmotic adjustment. Furthermore, gas exchange results suggest that the presence of trichomes was able to regulate stomatal processes so that the plant maintains its photosynthetic performance. Evaluation of electrolyte leakage, together with the increase in malondialdehyde content, showed that the maintenance of trichomes reduces the probability of oxidative stress. The activity of antioxidant enzymes was efficient in eliminating reactive oxygen species, especially the activity of ascorbate peroxidase, which stood out in terms of hydrogen peroxide detoxification.

Soil water availability has a strong role on vegetation conservation and biodiversity, particularly at vulnerable environments such as archipelagos, subject to significant temporal changes of climate and rainfall, which influence soil weathering and erosion processes. Few field studies on hydrology of volcanic islands in the Atlantic Ocean have been developed focusing on soil and water temporal dynamics and conservation, mainly because such studies require data with high temporal resolution, and also due to the financial costs involved with field data acquisition at such remote places. Considering the importance of soil moisture content to several hydrological processes and islands environmental sustainability, this study aimed to investigate the soil water temporal dynamics in relation to different rainfall patterns and also the rainfall erosivity and its temporal variation, and the resulting infiltration depths, during a typical hydrological period, in an experimental plot at the main watershed of Fernando de Noronha, in the Brazilian Atlantic Coast. Rainfall was recorded every 5 min, and soil moisture was intensely monitored by 16 moisture probes, installed at 10–40 cm and 40–70 cm layers, during three years, representing the typical local hydrological regime and seasons. Rainfall bursts pattern were identified and described. Experimental data allowed a hydrological model to be calibrated and validated, providing estimates of infiltration depths, which can be valuable for water resources planning and management. Hydrological patterns were determined for each erosive rainfall, depending on the precipitation peak position, as advanced, intermediate and delayed. The soil water effectiveness was also evaluated and related to the different rainfall patterns. Soil moisture is highest from April to June, close to saturation; whilst for the other months the values were close to the residual value. The rainfall erosivity in the archipelago was identified as moderate to strong, and the most frequent rainfall pattern was the advanced. Fast wetting-drying cycles during the rainfall events were observed, due to rainfall intermittency, evapotranspiration, and to soil hydraulic conductivity. It was observed the prevalence of high moisture indexes, with percentages higher than 40% (extremely effective level) for both investigated depths within the first 70 cm of soil, essential for plant water uptake. The observed rainfall erosivity highlights the importance of defining local strategies for soil and water conservation aimed at water security in the island. Based on a simulation model, which was successfully calibrated (Nash-Sutcliffe Efficiency Index NS = 0.76) and validated (NS = 0.81) for periods in the wet season, high infiltration depths have been identified, which contributes to canopy conservation in the archipelago.

The survival of Atriplex nummularia plants in saline environments is possible mainly due to the presence of salt-accumulating epidermal vesicles. Commonly, destructive methods, such as plant material maceration and subsequent reading in osmometers, are employed in studies on water relations and osmotic adjustment and are inconvenient due to their underestimation of the total water potential inside the cells, which can cause overestimation of an osmotic adjustment that is not present. As a result, methods that preserve leaf structure, such as pressure-volume (P-V) curves, which take into consideration only the salts that compose the symplastic solution, are more adequate. Thus, the main objectives of this study were to evaluate the effect of determination methods of osmotic potential (Ψo) in Atriplex nummularia through destructive and leaf structure-preserving techniques and to determine the water relations of the species under increasing NaCl concentrations. Plants were subjected to daily irrigations, maintaining soil moisture at 80% of field capacity, with solutions of increasing NaCl concentration (0, 0.05, 0.1, 0.2, 0.25 and 0.3 M) for 84 days. Water potential, osmotic potential and osmotic adjustment were determined. In addition, P-V curves were constructed using pressure chambers. Water and osmotic potentials decreased linearly with increasing NaCl concentration in the irrigation solution. The main discrepancies observed were related to the osmotic adjustments determined through maceration and P-V curves. Based on the present research, it was possible to conclude that in studies with species that have salt-accumulating vesicles in the epidermis, such as the plants in the genus Atriplex, constructing P-V curves is more adequate than destructive methods.

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. 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.

Many researches have performed on gypsum application to correct high exchangeable aluminum content in acidic soils, especially in subsurface. Although, they have found increases in the exchangeable calcium and sulfur contents, exchangeable aluminum has not been decreased. The exchangeable aluminum buffering by organic matter may contribute to non-significant reduction in exchangeable acidity. The objective of this study was to evaluate the effect of mineral gypsum on the aluminum compartments of Hardsetting Ultisol and monitor the capacity of gypsum to provide exchangeable calcium and sulfur in subsurface. Increasing amounts of mineral gypsum (0, 2, 4, 6, and 8 Mg ha-1) were applied with broadcast at the field. The experimental design consisted of randomized block with four replicates. Aluminum compartments (Al-organic matter, Al-amorphous and Al-crystalline) were evaluated at 0 and 15 days after gypsum application and the exchangeable calcium and sulfur contents were evaluated at 0, 15, 64 and 90 days. The evaluations were performed in three different layers. Gypsum application increased the exchangeable calcium and sulfur contents in subsurface and did not reduce the exchangeable aluminum content. Al-organic matter in the surface layers decreased along the incubation time and application gypsum. Al-amorphous in the subsurface layers increased with the increased amounts of gypsum. Al-crystalline decreased as soil depth increased. The exchangeable aluminum buffering in surface layers was performed by Al-organic matter and, in subsurface, by Al-crystalline. Key words: Aluminum compartments, aluminum fractionation, soil acidity, soil pH, exchangeable calcium.

Leaf gas exchanges in plants and soil respiration are important tools for assessing the effects of salinity on the soil-plant system. An experiment was conducted with cowpea irrigated with saline water (0, 2.5, 5.0, 7.5, 10.0 and 12.5 dS m-1) prepared with two sources: NaCl and a mixture of Ca, Mg, Na, K and Cl ions in a randomized block design and a 6 x 2 factorial scheme, with four replicates, totaling 48 experimental plots. At 20 days after planting (DAP), plants were evaluated for net photosynthesis (A), stomatal conductance (gs) and transpiration (E) using the Infra-Red Gas Analyzer (Model XT6400- LICOR), and water use efficiency, intrinsic water use efficiency and instantaneous efficiency of carboxylation were calculated. At 60 DAP, the soil CO2 efflux (soil respiration) was determined with a camera (Model 6400-09- LICOR). Salinity caused reductions in A, gs and E. However, the salt source did not have significant effect on these variables. Soil CO2 efflux was reduced with the increase in the electrical conductivity, especially in the mixture of ions. RESUMO As trocas gasosas em plantas e a respiração do solo são ferramentas importantes para avaliar os efeitos da salinidade no sistema solo-planta. Com este propósito conduziu-se um experimento com feijão-caupi irrigado com seis níveis de condutividade elétrica (0; 2,5; 5,0; 7,5; 10,0 e 12,5 dS m-1) elaborados com duas fontes: NaCl e uma mistura de íons de Ca, Mg, Na, K e Cl, em blocos ao acaso e arranjo fatorial 6 x 2, com 4 repetições totalizando 48 parcelas; aos 20 dias após o plantio (DAP) foram determinadas fotossíntese líquida (A), condutância estomática (gs) e transpiração (E) com o Infra-Red Gas Analyzer (Modelo XT6400- Licor) e se calcularam a eficiência do uso da água, a eficiência intrínseca do uso da água e a eficiência instantânea de carboxilação; aos 60 DAP determinou-se o efluxo de CO2 (respiração do solo) com uma câmara de solo (Modelo 6400-09- LICOR). Observaram-se reduções de A, gs e E com o aumento da salinidade; entretanto, a fonte de sal não apresentou efeito significativo para tais variáveis; já para a respiração do solo ocorreu redução com o aumento da condutividade elétrica da água de irrigação sendo mais pronunciado quando se utilizou somente a mistura de sais.

Long molecular chain of polymers with active groups, combined with its complexity and flexibility to different environmental conditions provides an interaction of these groups with the mineral soil clays, thereby qualifying the polymers as soil flocculants effective. This study is aimed at evaluating the pore size distribution and hydro-physical properties of soils with cohesive horizons of the coastal plains of Pernambuco State, Brazil, with the application of anionic polyacrylamide (PAM). Thus, three horizons, one cohesive (Bt1) and two non cohesive (E and Bw/Bt) Ultisol were evaluated and, to compare the cohesive horizons, a BA horizon of Oxisol was selected. PAM aqueous solutions (12.5, 50.0 and 100.0 mg kg-1) and distilled water (control = 0 mg kg-1) were applied in undeformed samples by capillary. Pore volume was evaluated by diameter (macro, meso and micropores), total porosity, saturated hydraulic conductivity (Ksat), soil penetration resistance (PR) and soil-water characteristic retention curve. Polymer solutions reduced Ksat, macroporosity and total porosity of cohesive horizons (micropores dominated). More concentrated solutions increased PR of the Bt1 horizon. The excess negative charges in the system are the main factor for the negative effects of PAM on clay horizons. We hope that less electronegative PAMs may improve the hydro-physical characteristics of cohesive horizons. Key words: Polyacrylamide, coastal tablelands, soil penetration resistance, negative charges, water retention, macroporosity.

Although there has been a long tradition in plant ecology of grouping species into functional groups, there is a lack of consensus regarding both the successional status of species and the dynamics of forest recovery. Therefore, plant species are commonly classified into two groups: early successional pioneers and late successional or even climax species. Here, we aimed to answer the following question: if pioneer and late successional species have different photosynthetic characteristics, will these differences be translated to improved performance when plants are grown under similar conditions, particularly high irradiance and different water regimes? To this end, we investigated gas exchange, photoprotection, plasticity, and nutritional traits in ten native species that were subject to natural variations in photosynthetically active radiation, rainfall, and air temperature throughout the year. Our results provided evidence that photosynthesis is directly dependent on nitrogen and phosphorus. Remarkably, this characteristic increased in importance when the species were grouped into pioneer and late successional species compared with each species separately. Furthermore, principal component analysis demonstrated that physiological traits are excellent parameters for characterizing the pioneer and late successional plants growing in situ under the same irradiance. Our findings indicate that the responses of trees to seasonal variations depend on their ability to absorb nutrients to meet the mineral requirements to sustain long-term growth. We further analyzed the mechanisms that allow woody species to cope with drought stress.

The sustainable use of brackish water in agriculture demands the use of compatible cultivation systems. The objective of this study was measure differences in the water status of spinach plants (Spinacia oleracea L.), cv. Viroflay, cultivated in covered and uncovered soil and in a hydroponic floating system, using brackish water (EC = 0.8, 1.5, 3.0, 4.5, 6.0 and 7.5 dS m−1) in the irrigation of plants in soil and replacement of nutrient solution in the floating system. At 38 days after transplanting, leaf water potential and osmotic potentials of the crop and of the systems were determined, as well as the osmotic adjustment, water consumption, leaf succulence, water use efficiency, leaf sodium content and yield. The hydroponic system showed a linear increase in the fresh weight of the leaves due to the salinity increase. The use of plastic cover attenuated the effects of salinity by 16 % in comparison to the uncovered soil, but the hydroponic system was the least affected by salinity, despite having the highest water consumption, which was 58 % higher than that of the uncovered soil. The main adaptive strategies observed in Spinacia oleracea L. cv. Viroflay in response to salinity were: increase in osmotic adjustment and leaf succulence and reduction in leaf water potential. The responses, positive in general, are corroborated by the values of sodium concentration in the leaves and fresh weight, which showed the highest results in the hydroponic cultivation for both variables. It is recommended to use the plastic cover or hydroponic methods during spinach cultivation, especially when using brackish water.

Chlorophyll fluorescence is a non-destructive analysis tool to diagnose the effects of salinity on the photosynthetic apparatus and photochemical yield. The present study aimed to evaluate the photochemical yield of parsley plants, exposed to increasing levels of electrical conductivity of nutrient solutions (1.7; 2.7; 3.7; 4.7; 5.7 and 6.7 dS m−1) formulated in waters with NaCl, CaCl2, MgCl2 and KCl. The mode of water replenishment in hydroponic system was also evaluated. For this, two experiments were conducted, maintaining the same experimental configuration, and varying the water replenishment. The nutrient solution, whose volume decreases with the consumption by plants, was replenished using a public-supply water (Experiment I) and the respective saline water used to prepare the nutrient solution (Experiment II). The following parameters were evaluated: initial (Fo), maximum (Fm) and variable (Fv) fluorescence; quantum (Fv/Fm) and maximum (Fo/Fm) yield of photosystem II; and also the quantum yield of electron transport (φEo), flux absorption (ABS/RC), flux transport (ETo/RC) and dissipated energy (DIo/RC) per reaction center for the two experiments. It was concluded that replenishment with public-supply water causes less damage to chlorophyll variables and quantum yields as the nutrient solution electrical conductivity increases than replenishment with saline water, whereas on variables related to electron transfer, such effect was not noticeable. Plants cultivated under NaCl had higher tolerance to salt stress compared to other cations.

Atriplex nummularia is a halophyte widely employed to recover saline soils and was used as a model to evaluate the water potentials in the soil-plant system under drought and salt stresses. Potted plants grown under 70 and 37% of field capacity irrigated with solutions of NaCl and of a mixture of NaCl, KCl, MgCl2 and CaCl2 reproducing six electrical conductivity (EC): 0, 5, 10, 20, 30, and 40 dS m-1. After 100 days, total water (Ψw, plant) and osmotic (Ψo, plant) potentials at predawn and midday and Ψo, soil, matric potential (Ψm, soil) and Ψw, soil were determined. The type of ion in the irrigation water did not influence the soil potential, but was altered by EC. The soil Ψo component was the largest contributor to Ψw, soil. Atriplex is surviving ECs close to 40 dS m-1 due to the decrease in the Ψw. The plants reached a Ψw of approximately -8 MPa. The water potentials determined for different moisture levels, EC levels and salt types showed huge importance for the management of this species in semiarid regions and can be used to recover salt affected soils.

A avaliação de atributos solo em sistemas agroecológicos é de fundamental importância para verificar os benefícios desse tipo de manejo. Objetivou-se avaliar as características físicas, o efluxo de CO2 e o carbono orgânico em diferentes condições de manejo. A área de pesquisa pertence à Unidade de Serviços de Tecnologia alternativa, localizada na cidade de Glória do Goitá, Pernambuco, que desenvolve técnicas com base nos princípios agroecológicos, visando o desenvolvimento sustentável no ambiente rural. Três áreas foram selecionadas: Permacultura, Rotação de Cultura e Mata em Regeneração. Para cada uma das áreas foram coletadas amostras de solo deformadas e indeformadas, em duas profundidades 0-20 e 20-40 cm. As variáveis analisadas foram: granulometria, densidade e porosidade do solo, Carbono Orgânico Total (COT) e calculada a Matéria Orgânica do Solo (MOS). Realizou-se também a medição do efluxo de CO2 do solo, utilizando uma câmara específica para solo acoplada ao IRGA, modelo 6400XT. Os resultados foram analisados pela comparação de médias utilizando o teste de Scott-Knot a uma probabilidade de 5%. A permacultura e a rotação de cultura apresentaram valores de atributos físicos que se aproximaram da condição de mata. Com relação aos teores de Carbono e MOS, a área de mata obteve as maiores médias, enquanto que para o efluxo de CO2, as áreas manejadas obtiveram médias superiores, demonstrando os benefícios destes manejos para a melhoria da qualidade do solo.CO2 efflux, physical attribute and soil carbon in agro-ecological management systems Abstract: Evaluation of soil in agroecological systems is of fundamental importance to check the influence of this type of soil management. The aim of this study is to evaluate the physical, CO2 efflux and the carbon in different management conditions. The survey area belongs to Alternative Technology Services Unit, located in Gloria do Goitá, Pernambuco, which develops techniques based on agro-ecological principles for sustainable development in the rural environment. Three areas were selected: Permaculture, Culture rotation and Forest in regeneration, for each of the areas disturbed and undisturbed soil samples were collected from two layers 0-20 and 20-40 cm. The variables analyzed were: grain size, density, soil porosity, Total Carbon (TC) and Soil Organic Matter (SOM). It was also performed measuring the soil CO2 efflux, using a specific camera to soil coupled to Irga 6400XT. The results were analyzed by comparison of means using the Scott-Knot test at a probability of 5%. The permaculture and crop rotation had physical attributes values that approached the forest condition. With respect to C and MOS levels, the forest area had the highest averages, while for soil CO2 efflux, the areas managed obtained higher averages, demonstrating the benefits of these managements to improve soil quality.

Soil salinity directly affects plants, interfering in the emission of fluorescence, and promoting the degradation of photosynthetic pigments. Thus, estimating the damage to the photosynthetic apparatus caused by saline water is an important tool to detect abiotic stresses. For this purpose, sorghum plants were cultivated in a greenhouse and irrigated with two water sources (NaCl and salt mixture) with six levels of electrical conductivity (EC) (0, 2.5, 5, 7.5, 10, and 12.5 dS m-1), forming a 6 × 2 factorial in randomized blocks with four repetitions. At 60 days after sowing, the photosynthetic pigments were quantified, the chlorophyll a fluorescence parameters (initial fluorescence [F0]; variable fluorescence [Fv]; maximum fluorescence [Fm]; quantum efficiency of photosystem II - PSII [Fv/Fm]; electron flux per reaction center [ET0/CR]; quantum energy dissipation [DI0/CR] and quantum yield for heat dissipation [φD0]) were evaluated. The photosynthetic pigments were decreased with an increase in the salinity of the irrigation water, and were more expressive at higher electrical conductivities. With the wear on the photosynthetic apparatus by the increase in salinity, a reduction in the emission of the chlorophyll a fluorescence was observed, pointing to a possible photoinhibition of photosystem II.

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.

Com o objetivo de avaliar o ponto de murcha permanente fisiológico, a umidade foliar e o potencial osmótico no feijoeiro caupi, sob duas condições de estresses (salino e salino + hídrico), foram conduzidos dois experimentos em casa de vegetação na Universidade Federal Rural de Pernambuco (Recife, PE, Brasil). O delineamento experimental adotado foi o inteiramente casualizado, em arranjo fatorial 2 x 4, sendo duas classes texturais de solos (franco-arenoso e franco-argiloso) e quatro níveis de salinidade do solo, equivalentes às condutividades elétricas do extrato de saturação do solo 4, 8 e 12 dS m-1, mais testemunha, com cinco repetições. A cultura teste utilizada foi o feijoeiro caupi [Vigna unguiculata L. (Walp.)], cultivar Pele de Moça. O ponto de murcha permanente do feijoeiro caupi é menor quando determinado pelo método fisiológico do que o determinado na câmara de pressão de Richards; o incremento da salinidade do solo (CEes) até 12 dS m-1 não influencia a umidade foliar, independente da textura do solo; e o potencial osmótico foliar do feijoeiro caupi diminui com o aumento da salinidade do solo e pode ser usado como variável importante em ambientes salinizados. In order to evaluate the physiological wilting point, the moisture content and leaf osmotic potential in cowpea, two experiments were carried out in a greenhouse of the Federal Rural University of Pernambuco (Recife, PE, Brazil). Two stress conditions were evaluated: salinity and salinity + water stress. The experimental design was completely randomized, in factorial arrangement of 2 x 4, composed of two classes of soil texture and four levels of soil salinity (control, 4, 8 and 12 dS m-1), with five replications. The species cowpea [Vigna unguiculata L. (Walp.)], cultivar Pele de Moça was used as test crop. It was concluded that the permanent wilting point of cowpea is smaller when determined by the physiological method than by Richards chamber method; the increase in soil salinity (CEes) up to 12 dS m-1 does not influence the leaf moisture content, regardless of soil texture; and the leaf osmotic potential of cowpea decreases with the increasing soil salinity, which can be used as an important variable in saline environments.