Preserving isohydricity: vertical environmental variability explains Amazon forest water-use strategies.

Increases in hydrological extremes, including drought, are expected for Amazon forests. A fundamental challenge for predicting forest responses lies in identifying ecological strategies which underlie such responses. Characterization of species-specific hydraulic strategies for regulating water-use, thought to be arrayed along an 'isohydric-anisohydric' spectrum, is a widely used approach. However, recent studies have questioned the usefulness of this classification scheme, because its metrics are strongly influenced by environments, and hence can lead to divergent classifications even within the same species. Here, we propose an alternative approach positing that individual hydraulic regulation strategies emerge from the interaction of environments with traits. Specifically, we hypothesize that the vertical forest profile represents a key gradient in drought-related environments (atmospheric vapor pressure deficit, soil water availability) that drives divergent tree water-use strategies for coordinated regulation of stomatal conductance (gs) and leaf water potentials (ΨL) with tree rooting depth, a proxy for water availability. Testing this hypothesis in a seasonal eastern Amazon forest in Brazil, we found that hydraulic strategies indeed depend on height-associated environments. Upper canopy trees, experiencing high vapor pressure deficit (VPD), but stable soil water access through deep rooting, exhibited isohydric strategies, defined by little seasonal change in the diurnal pattern of gs and steady seasonal minimum ΨL. In contrast, understory trees, exposed to less variable VPD but highly variable soil water availability, exhibited anisohydric strategies, with fluctuations in diurnal gs that increased in the dry season along with increasing variation in ΨL. Our finding that canopy height structures the coordination between drought-related environmental stressors and hydraulic traits provides a basis for preserving the applicability of the isohydric-to-anisohydric spectrum, which we show here may consistently emerge from environmental context. Our work highlights the importance of understanding how environmental heterogeneity structures forest responses to climate change, providing a mechanistic basis for improving models of tropical ecosystems.

Time-domain transmission sensor system for on-site dielectric permittivity measurements in soil: A compact, low-cost and stand-alone solution.

Dielectric-based measurement techniques have been shown to be very effective in determining the properties of various materials. These techniques have been widely used in a variety of fields and applications. Time Domain Transmission (TDT) techniques have grown in popularity because they are practical, non-destructive, provide measurements in real time and produce accurate measurements that are independent of multiple reflections. TDT techniques, on the other hand, are mostly performed with specialized bulky laboratory equipment, such as a Vector Network Analyzer (VNA) which makes TDT measurements prohibitively costly and unpractical. In fact, few works in the literature have reported portable on-site TDT systems. The aim of this paper is to design and implement a dedicated, compact, and low-cost microwave Time Domain Transmission (TDT) sensor for measuring superficial soil dielectric properties on-site. Our sensor uses a time-delay measurement technique over a microstrip transmission line to estimate the dielectric properties of the soil under test. Measurement results show that the computed mean absolute error (MAE) is less than 1.2 when compared to a calibrated dielectric assessment kit (DAK) with soils containing less than 20 % of water ( ε ' r < 5.0 ), implying that our TDT sensor system can obtain on-site measurements in relatively dry soils with acceptable accuracy.

Effect of the Soil Matric Potential on the Germination Capacity of Prosopis chilensis, Quillaja saponaria and Cryptocarya alba from Contrasting Geographical Origins.

As a consequence of the megadrought in Central Chile, it is expected that most of the distribution of woody species will be narrowed in the northern limits because of restrictions imposed by soil matric potential on seed germination. In this study, we analyzed the effect of the soil matric potential on seed germination and initial recruitment of the sclerophyllous species Prosopis chilensis, Quillaja saponaria and Cryptocarya alba from contrasting geographic origins (i.e., seed sources). We evaluated the germination capacity (%) under different matric potentials (i.e., 0, -6, -33, -750 and -1250 kPa) for 100 days. Soil matric potential of -1250 kPa negatively affected the germination capacity of the three species. P. chilensis seeds stopped germinating under soil matric potential close to -1200 kPa, whereas in Q. saponaria and C. alba the complete inhibition of germination was under -1000 kPa. Seed sources also differed in their germination capacity by soil matric potential: northern seed sources of P. chilensis germinated with the lowest soil matric potential. There was no clear trend in Q. saponaria and C. alba, but in general, southern seed sources performed better than the northern ones. The results showed that Ñ°m in the soil played an important role in the germinative capacity against different seed source origins, but not in soils with a north-south gradient.

Nonlinear models for soil moisture sensor calibration in tropical mountainous soils

Electromagnetic sensors are widely used to monitor soil water content (θ); however, site-specific calibrations are necessary for accurate measurements. This study compares regression models used for calibration of soil moisture sensors and investigates the relation between soil attributes and the adjusted parameters of the specific calibration equations. Undisturbed soil samples were collected in the A and B horizons of two Ultisols and two Inceptisols from the Mantiqueira Range in Southeastern Brazil. After saturation, the Theta Probe ML2X was used to obtain the soil dielectric constant (ε). Several readings were made, ranging from saturation to oven-dry. After each reading, the samples were weighted to calculate θ (m³ m-³). Fourteen regression models (linear, linearized, and nonlinear) were adjusted to the calibration data and checked for their residue distribution. Only the exponential model with three parameters met the regression assumptions regarding residue distribution. The stepwise regression was used to obtain multiple linear equations to estimate the adjusted parameters of the calibration model from soil attributes, with silt and clay contents providing the best relations. Both the specific and the general calibrations performed well, with RMSE values of 0.02 and 0.03 m³ m-³, respectively. Manufacturer calibration and equations from the literature were much less accurate, reinforcing the need to develop specific calibrations.

Morphological, molecular and ecological characterization of a native isolate of Steinernema feltiae (Rhabditida: Steinernematidae) from southern Chile.

BACKGROUND: Steinernema feltiae is an entomopathogenic nematode used in biological control programs with a global distribution. Populations of this species show phenotypic plasticity derived from local adaptation and vary in different traits, such as location and host penetration. The aim of this work was to describe a Chilean isolate of this nematode species, using integrative approaches. METHODS: Nematode morphological and morphometric studies were conducted along with molecular analysis of nuclear genes. The symbiotic bacterium was also identified by sequencing the 16S rRNA gene. Some ecological characteristics were described, including the temperature requirements for the nematode life cycle and the effect of soil water content for optimal reproduction. RESULTS: Morphometric characterization revealed a large intra-specific variability. The isolate identity was also corroborated with the analysis of nuclear genes. Based on the 16S gene, its symbiont bacteria, Xenorhabdus bovienii, was identified. The lowest, optimal and highest temperatures found to limit the infestation and reproduction on Galleria mellonella were 10, 20 and 30 °C, respectively; the emergence from the host larvae occurred approximately 10 days after inoculation. Differences were observed in offspring, and 120 infective juveniles (IJ)/larva was the most prolific dose at 20 °C. The soil water content did not affect the number of IJ invaders, penetration efficacy and IJ emergence time or offspring per larva, but it caused a delay in achieving full mortality at the permanent wilting point with respect to saturation and field capacity. CONCLUSIONS: For the first time, a Chilean isolate of S. feltiae is described in detail considering morphological, molecular and ecological aspects. The isolate was shown to be efficient in soil containing water, with optimal temperatures ranging from 15 to 25 °C for host infestation and production of an abundant offspring; these characteristics would allow its potential use as control agents in a wide geographical area of the country.

CSRR-Based Microwave Sensor for Dielectric Materials Characterization Applied to Soil Water Content Determination.

A new and compact sensor based on the complementary split-ring resonator (CSRR) structure is proposed to characterize the relative permittivity of various dielectric materials, enabling the determination of soil water content (SWC). The proposed sensor consists of a circular microstrip patch antenna supporting a 3D-printed small cylindrical container made out of Acrylonitrile-Butadiene-Styrene (ABS) filament. The principle of operation is based on the shifting of two of the antenna resonant frequencies caused by changing the relative permittivity of the material under test (MUT). Simulations are performed enabling the development of an empirical model of analysis. The sensitivity of the sensor is investigated and its effectiveness is analyzed by characterizing typical dielectric materials. The proposed sensor, which can be applied to characterize different types of dielectric materials, is used to determine the percentage of water contained in different soil types. Prototypes are fabricated and measured and the obtained results are compared with results from other research works, to validate the proposed sensor effectiveness. Moreover, the sensor was used to determine the percentage of water concentration in quartz sand and red clay samples.

Predicting soil water content at - 33 kPa by pedotransfer functions in stoniness 1 soils in northeast Venezuela.

Soil water content is a key property in the study of water available for plants, infiltration, drainage, hydraulic conductivity, irrigation, plant water stress and solute movement. However, its measurement consumes time and, in the case of stony soils, the presence of stones difficult to determinate the water content. An alternative is the use of pedotransfer functions (PTFs), as models to predict these properties from readily available data. The present work shows a comparison of different widely used PTFs to estimate water content at-33 kPa (WR-33kPa) in high stoniness soils. The work was carried out in the Caramacate River, an area of high interest because the frequent landslides worsen the quality of drinking water. The performance of all evaluated PTFs was compared with a PTF generated for the study area. Results showed that the Urach's PTF presented the best performance in relation to the others and could be used to estimate WR-33kPa in soils of Caramacate River basin. The calculated PTFs had a R2 of 0.65. This was slightly higher than the R2 of the Urach's PTF. The inclusion of the rock fragment volume could have the better results. The weak performance of the other PTFs could be related to the fact that the mountain soils of the basin are rich in 2:1 clay and high stoniness, which were not used as independent variables for PTFs to estimate the WR-33kPa.

A New Method for Sensing Soil Water Content in Green Roofs Using Plant Microbial Fuel Cells.

Green roofs have many benefits, but in countries with semiarid climates the amount of water needed for irrigation is a limiting factor for their maintenance. The use of drought-tolerant plants such as Sedum species, reduces the water requirements in the dry season, but, even so, in semiarid environments these can reach up to 60 L m-2 per day. Continuous substrate/soil water content monitoring would facilitate the efficient use of this critical resource. In this context, the use of plant microbial fuel cells (PMFCs) emerges as a suitable and more sustainable alternative for monitoring water content in green roofs in semiarid climates. In this study, bench and pilot-scale experiments using seven Sedum species showed a positive relationship between current generation and water content in the substrate. PMFC reactors with higher water content (around 27% vs. 17.5% v/v) showed larger power density (114.6 and 82.3 µW m-2 vs. 32.5 µW m-2). Moreover, a correlation coefficient of 0.95 (±0.01) between current density and water content was observed. The results of this research represent the first effort of using PMFCs as low-cost water content biosensors for green roofs.

A method for soil moisture probes calibration and validation of satellite estimates.

Optimization of field techniques is crucial to ensure high quality soil moisture data. The aim of the work is to present a sampling method for undisturbed soil and soil water content to calibrated soil moisture probes, in a context of the SMOS (Soil Moisture and Ocean Salinity) mission MIRAS Level 2 soil moisture product validation in Pampean Region of Argentina. The method avoids soil alteration and is recommended to calibrated probes based on soil type under a freely drying process at ambient temperature. A detailed explanation of field and laboratory procedures to obtain reference soil moisture is shown. The calibration results reflected accurate operation for the Delta-T thetaProbe ML2x probes in most of analyzed cases (RMSE and bias ≤ 0.05 m3/m3). Post-calibration results indicated that the accuracy improves significantly applying the adjustments of the calibration based on soil types (RMSE ≤ 0.022 m3/m3, bias ≤ -0.010 m3/m3). •A sampling method that provides high quality data of soil water content for calibration of probes is described.•Importance of calibration based on soil types.•A calibration process for similar soil types could be suitable in practical terms, depending on the required accuracy level.

Models for moisture estimation in different horizons of yellow argisol using TDR / Modelos para estimativa da umidade em diferentes horizontes de argissolo amarelo com uso da TDR

The determination of soil moisture is very important because it is the property with the most influence on the dielectric constant of the medium. Time-domain reflectometry (TDR) is an indirect technique used to estimate the water content of the soil (?) based on its dielectric constant (Ka). Like any other technique, it has advantages and disadvantages. Among the major disadvantages is the need for calibration, which requires consideration of the soil characteristics. This study aimed to perform the calibration of a TDR100 device to estimate the volumetric water content of four horizons of a Yellow Argisol. Calibration was performed under laboratory conditions using disturbed soil samples contained in PVC columns. The three rods of the handcrafted probes were vertically installed in the soil columns. Weight measurements with digital scales and daily readings of the dielectric constant with the TDR device were taken. For all soil horizons evaluated, the best fits between the dielectric constant and the volumetric water content were related to the cubic polynomial model. The Ledieu model overestimated by approximately 68 % the volumetric water content in the A and AB horizons, and underestimating by 69 % in Bt2, in relation to volumetric water content obtained by gravimetry. The underestimation by linear, Topp, Roth, and Malicki models ranged from 50 % to 85 % for all horizons.(AU)

A reflectometria no domínio do tempo (Time Domain Reflectometry, TDR) é uma técnica indireta usada para estimar o conteúdo de água do solo (?) em função da constante dielétrica (Ka). As vantagens do uso desta técnica são, no entanto, requer calibração específica para cada tipo de solo. Neste estudo objetivou-se realizar a calibração de modelos para estimar a umidade volumétrica de quatro horizontes de um Argissolo Amarelo com uso da TDR. A calibração foi realizada em condições de laboratório utilizando amostras deformadas do solo em estudo, acondicionadas em colunas de PVC. As sondas fabricadas artesanalmente com três hastes foram instaladas verticalmente nas colunas de solo. Foram realizadas pesagens com balança de precisão e leituras diárias da constante dielétrica com o equipamento TDR. Os modelos polinomial cúbico e linear foram os que apresentaram melhor ajuste aos dados de umidade observados. Os modelos de Topp et al. (1980), Ledieu et al. (1986), Malicki et al. (1996) e Roth et al. (1990) superestimaram em aproximadamente 15% as médias de umidade nos horizontes A e AB e subestimam em aproximadamente 18% no Bt2. No horizonte Bt1 todos os modelos foram semelhantes entre si.(AU)

A Self-Powered and Autonomous Fringing Field Capacitive Sensor Integrated into a Micro Sprinkler Spinner to Measure Soil Water Content.

We present here the design and fabrication of a self-powered and autonomous fringing field capacitive sensor to measure soil water content. The sensor is manufactured using a conventional printed circuit board and includes a porous ceramic. To read the sensor, we use a circuit that includes a 10 kHz triangle wave generator, an AC amplifier, a precision rectifier and a microcontroller. In terms of performance, the sensor's capacitance (measured in a laboratory prototype) increases up to 5% when the volumetric water content of the porous ceramic changed from 3% to 36%, resulting in a sensitivity of S = 15.5 pF per unity change. Repeatability tests for capacitance measurement showed that the θ v sensor's root mean square error is 0.13%. The average current consumption of the system (sensor and signal conditioning circuit) is less than 1.5 µ A, which demonstrates its suitability for being powered by energy harvesting systems. We developed a complete irrigation control system that integrates the sensor, an energy harvesting module composed of a microgenerator installed on the top of a micro sprinkler spinner, and a DC/DC converter circuit that charges a 1 F supercapacitor. The energy harvesting module operates only when the micro sprinkler spinner is irrigating the soil, and the supercapacitor is fully charged to 5 V in about 3 h during the first irrigation. After the first irrigation, with the supercap fully charged, the system can operate powered only by the supercapacitor for approximately 23 days, without any energy being harvested.

Models for moisture estimation in different horizons of yellow argisol using TDR / Modelos para estimativa da umidade em diferentes horizontes de argissolo amarelo com uso da TDR

The determination of soil moisture is very important because it is the property with the most influence on the dielectric constant of the medium. Time-domain reflectometry (TDR) is an indirect technique used to estimate the water content of the soil (?) based on its dielectric constant (Ka). Like any other technique, it has advantages and disadvantages. Among the major disadvantages is the need for calibration, which requires consideration of the soil characteristics. This study aimed to perform the calibration of a TDR100 device to estimate the volumetric water content of four horizons of a Yellow Argisol. Calibration was performed under laboratory conditions using disturbed soil samples contained in PVC columns. The three rods of the handcrafted probes were vertically installed in the soil columns. Weight measurements with digital scales and daily readings of the dielectric constant with the TDR device were taken. For all soil horizons evaluated, the best fits between the dielectric constant and the volumetric water content were related to the cubic polynomial model. The Ledieu model overestimated by approximately 68 % the volumetric water content in the A and AB horizons, and underestimating by 69 % in Bt2, in relation to volumetric water content obtained by gravimetry. The underestimation by linear, Topp, Roth, and Malicki models ranged from 50 % to 85 % for all horizons.

A reflectometria no domínio do tempo (Time Domain Reflectometry, TDR) é uma técnica indireta usada para estimar o conteúdo de água do solo (?) em função da constante dielétrica (Ka). As vantagens do uso desta técnica são, no entanto, requer calibração específica para cada tipo de solo. Neste estudo objetivou-se realizar a calibração de modelos para estimar a umidade volumétrica de quatro horizontes de um Argissolo Amarelo com uso da TDR. A calibração foi realizada em condições de laboratório utilizando amostras deformadas do solo em estudo, acondicionadas em colunas de PVC. As sondas fabricadas artesanalmente com três hastes foram instaladas verticalmente nas colunas de solo. Foram realizadas pesagens com balança de precisão e leituras diárias da constante dielétrica com o equipamento TDR. Os modelos polinomial cúbico e linear foram os que apresentaram melhor ajuste aos dados de umidade observados. Os modelos de Topp et al. (1980), Ledieu et al. (1986), Malicki et al. (1996) e Roth et al. (1990) superestimaram em aproximadamente 15% as médias de umidade nos horizontes A e AB e subestimam em aproximadamente 18% no Bt2. No horizonte Bt1 todos os modelos foram semelhantes entre si.

Models for moisture estimation in different horizons of yellow argisol using TDR / Modelos para estimativa da umidade em diferentes horizontes de argissolo amarelo com uso da TDR

The determination of soil moisture is very important because it is the property with the most influence on the dielectric constant of the medium. Time-domain reflectometry (TDR) is an indirect technique used to estimate the water content of the soil (?) based on its dielectric constant (Ka). Like any other technique, it has advantages and disadvantages. Among the major disadvantages is the need for calibration, which requires consideration of the soil characteristics. This study aimed to perform the calibration of a TDR100 device to estimate the volumetric water content of four horizons of a Yellow Argisol. Calibration was performed under laboratory conditions using disturbed soil samples contained in PVC columns. The three rods of the handcrafted probes were vertically installed in the soil columns. Weight measurements with digital scales and daily readings of the dielectric constant with the TDR device were taken. For all soil horizons evaluated, the best fits between the dielectric constant and the volumetric water content were related to the cubic polynomial model. The Ledieu model overestimated by approximately 68 % the volumetric water content in the A and AB horizons, and underestimating by 69 % in Bt2, in relation to volumetric water content obtained by gravimetry. The underestimation by linear, Topp, Roth, and Malicki models ranged from 50 % to 85 % for all horizons.

A reflectometria no domínio do tempo (Time Domain Reflectometry, TDR) é uma técnica indireta usada para estimar o conteúdo de água do solo (?) em função da constante dielétrica (Ka). As vantagens do uso desta técnica são, no entanto, requer calibração específica para cada tipo de solo. Neste estudo objetivou-se realizar a calibração de modelos para estimar a umidade volumétrica de quatro horizontes de um Argissolo Amarelo com uso da TDR. A calibração foi realizada em condições de laboratório utilizando amostras deformadas do solo em estudo, acondicionadas em colunas de PVC. As sondas fabricadas artesanalmente com três hastes foram instaladas verticalmente nas colunas de solo. Foram realizadas pesagens com balança de precisão e leituras diárias da constante dielétrica com o equipamento TDR. Os modelos polinomial cúbico e linear foram os que apresentaram melhor ajuste aos dados de umidade observados. Os modelos de Topp et al. (1980), Ledieu et al. (1986), Malicki et al. (1996) e Roth et al. (1990) superestimaram em aproximadamente 15% as médias de umidade nos horizontes A e AB e subestimam em aproximadamente 18% no Bt2. No horizonte Bt1 todos os modelos foram semelhantes entre si.

Contrasting strategies to cope with drought conditions by two tropical forage C4 grasses.

Drought severely limits forage productivity of C4 grasses across the tropics. The avoidance of water deficit by increasing the capacity for water uptake or by controlling water loss are common responses in forage C4 grasses. Napier grass (Pennisetum purpureum) and Brachiaria hybrid cv. Mulato II are tropical C4 grasses used for livestock production due to their reputed resistance to drought conditions. However, there is scant information on the mechanisms used by these grasses to overcome water-limited conditions. Therefore, assessments of cumulative transpired water, shoot growth, leaf rolling, leaf gas exchange, dry mass production and a number of morpho-physiological traits were recorded over a period of 21 days under well-watered or drought conditions. Drought reduced shoot dry mass of both grasses by 35 %, yet each grass exhibited contrasting strategies to cope with water shortage. Napier grass transpired most available water by the end of the drought treatment, whereas a significant amount of water was still available for Mulato II. Napier grass maintained carbon assimilation until the soil was fairly dry, whereas Mulato II restricted water loss by early stomatal closure at relatively wet soil conditions. Our results suggest that Napier grass exhibits a 'water-spending' behaviour that might be targeted to areas with intermittent drought stress, whereas Mulato II displays a 'water-saving' nature that could be directed to areas with longer dry periods.

Seasonality of soil water exchange in the soybean growing season in southern Brazil

The processes of water transfer in the soil-plant-atmosphere system are strongly affected by soil use and management. Differences in the dynamics of soil water transfer between no-tillage (NT) and conventional tillage (CT) practices during a soybean (Glycine max) growing season in southern Brazil were assessed in this study. All the water balance components were analyzed during the soybean growing season (2009/2010). Rainfall, runoff, soil water storage and hydro-physical soil properties were analyzed under two tillage systems. The land-atmosphere water vapor exchanges, obtained from eddy covariance stations, were analyzed with regard to the soybean agroecosystem. Characterizations of soil water storage were also formulated in the 2006/2007 and 2008/2009 soybean growing seasons under the NT system. During the periods without rain, the soil water content under NT was greater than under CT. The soil superficial layer, more porous under NT, contributed to less runoff during rainy events. Moreover, under NT conditions the water supply was always high, between 0.2 - 0.5 m. The total evapotranspiration in the soybean agroecosystem growing season was 410.8 mm.

Seasonality of soil water exchange in the soybean growing season in southern Brazil

The processes of water transfer in the soil-plant-atmosphere system are strongly affected by soil use and management. Differences in the dynamics of soil water transfer between no-tillage (NT) and conventional tillage (CT) practices during a soybean (Glycine max) growing season in southern Brazil were assessed in this study. All the water balance components were analyzed during the soybean growing season (2009/2010). Rainfall, runoff, soil water storage and hydro-physical soil properties were analyzed under two tillage systems. The land-atmosphere water vapor exchanges, obtained from eddy covariance stations, were analyzed with regard to the soybean agroecosystem. Characterizations of soil water storage were also formulated in the 2006/2007 and 2008/2009 soybean growing seasons under the NT system. During the periods without rain, the soil water content under NT was greater than under CT. The soil superficial layer, more porous under NT, contributed to less runoff during rainy events. Moreover, under NT conditions the water supply was always high, between 0.2 - 0.5 m. The total evapotranspiration in the soybean agroecosystem growing season was 410.8 mm.(AU)

Water requirements of sugar cane grown in tropical environment / Necessidades hídricas da cana-de-açúcar cultivada em clima tropical

An accurate estimation of water consumption of cane sugar crop is important for maximum productivity with less investment. The objective of this study was to determine the water requirements of sugar cane grown in tropical environments. The field experiment was carried out in Paraiba state, during the productive cycle of sugar cane crop variety RB 92 579 irrigated by central pivot irrigation (sprinkler) from October 2009 to September 2011. The crop evapotranspiration was obtained based on soil water balance and reference evapotranspiration by Penman-Monteith method (FAO/56), using the data of air temperature, relative humidity, wind speed and solar radiation from Data Collection Platform, next to the experimental site. Soil water moisture was monitored by TDR probes (Frequency Domain Reflectometry), Model PR2/6, Delta-T. The results showed that the crop coefficients values proposed by the FAO for sugar cane are not suitable for tropical regions. The water consumption of sugar cane ranged from 2.6 mm day-1, at initial crop growth stage, to 6.38 mm day-1, with an average of 4.3 mm day-1 for all cycle. Similarly, the crop coefficient ranged from 0.56 to 1.43, with an average of 0.99 for the same development crop growth stages.(AU)

A estimativa precisa do consumo hídrico da cana-de-açucar é importante para obtenção da máxima produtividade com menos investimentos. O objetivo do trabalho foi determinar as necessidades hídricas da cana-de-açúcar cultivada em clima tropical. O experimento foi realizado no Estado da Paraíba, durante o ciclo produtivo da cultura da cana-de-açucar variedade RB 92 579 irrigada por pivô central, no período de outubro de 2009 a setembro de 2011. A evapotranspiração da cultura (ETc) foi obtido pelo método do balanço hídrico (BH) e a evapotranspiração de referência (ETo) pelo método de Penman- Monteith, utilizando-se os dados de temperatura do ar, umidade relativa, velocidade do vento e radiação solar coletados na Plataforma de Coleta de Dados próxima à area experimental. A umidade do solo foi monitorada utilizando-se sondas TDR (Frequency Domain Reflectometry), modelo PR2/6, Delta-T. Os resultados permitiram constatar que os valores dos coeficientes de cultivo (Kc) propostos pela FAO para a cultura da cana-de-açúcar não são apropriados para regiões tropicais. O consumo hídrico da cultura variou entre 2,6 mm dia-1, na fase inicial, a 6,38 mm dia-1, na fase intermediária, com média de 4,3 mm dia-1. Similarmente, o coeficiente da cultura variou entre 0,56 e 1,43, com média igual a 0,99, respectivamente, nos mesmos estádios fenológicos da cultura.(AU)

Water requirements of sugar cane grown in tropical environment / Necessidades hídricas da cana-de-açúcar cultivada em clima tropical

An accurate estimation of water consumption of cane sugar crop is important for maximum productivity with less investment. The objective of this study was to determine the water requirements of sugar cane grown in tropical environments. The field experiment was carried out in Paraiba state, during the productive cycle of sugar cane crop variety RB 92 579 irrigated by central pivot irrigation (sprinkler) from October 2009 to September 2011. The crop evapotranspiration was obtained based on soil water balance and reference evapotranspiration by Penman-Monteith method (FAO/56), using the data of air temperature, relative humidity, wind speed and solar radiation from Data Collection Platform, next to the experimental site. Soil water moisture was monitored by TDR probes (Frequency Domain Reflectometry), Model PR2/6, Delta-T. The results showed that the crop coefficients values proposed by the FAO for sugar cane are not suitable for tropical regions. The water consumption of sugar cane ranged from 2.6 mm day-1, at initial crop growth stage, to 6.38 mm day-1, with an average of 4.3 mm day-1 for all cycle. Similarly, the crop coefficient ranged from 0.56 to 1.43, with an average of 0.99 for the same development crop growth stages.

A estimativa precisa do consumo hídrico da cana-de-açucar é importante para obtenção da máxima produtividade com menos investimentos. O objetivo do trabalho foi determinar as necessidades hídricas da cana-de-açúcar cultivada em clima tropical. O experimento foi realizado no Estado da Paraíba, durante o ciclo produtivo da cultura da cana-de-açucar variedade RB 92 579 irrigada por pivô central, no período de outubro de 2009 a setembro de 2011. A evapotranspiração da cultura (ETc) foi obtido pelo método do balanço hídrico (BH) e a evapotranspiração de referência (ETo) pelo método de Penman- Monteith, utilizando-se os dados de temperatura do ar, umidade relativa, velocidade do vento e radiação solar coletados na Plataforma de Coleta de Dados próxima à area experimental. A umidade do solo foi monitorada utilizando-se sondas TDR (Frequency Domain Reflectometry), modelo PR2/6, Delta-T. Os resultados permitiram constatar que os valores dos coeficientes de cultivo (Kc) propostos pela FAO para a cultura da cana-de-açúcar não são apropriados para regiões tropicais. O consumo hídrico da cultura variou entre 2,6 mm dia-1, na fase inicial, a 6,38 mm dia-1, na fase intermediária, com média de 4,3 mm dia-1. Similarmente, o coeficiente da cultura variou entre 0,56 e 1,43, com média igual a 0,99, respectivamente, nos mesmos estádios fenológicos da cultura.

Dye tracer and morphophysical properties to observe water flow in a Gleyic Luvisol

The understanding of the preferential water flow and solute transport is important with regard to losses of nutrients and pesticides that affect the quality of the groundwater or surface water resources. Experiments using the brilliant blue dye tracer, a tension infiltrometer (TI) and a double square infiltrometer (DI) were carried out in the experimental field site located around 15 km southeast of the city of Rostock (North-Eastern Germany) on arable land in a Pleistocene lowland landscape where corn (Zea mays L.) and barley (Hordeum spp.) had been cultivated. One day after dye the infiltration, a pit was dug and vertical profiles were prepared in the TI and DI sites to assess the dye pathways in the subsoil of a Gleyic Luvisol. We wanted to examine if the mottled red and white (bleached) colour-pattern of the Gleyic Luvisol subsoil resulting from temporally stagnant water could be related to flow paths as visualized by dye tracing and if the soil colour could be related to other physical soil properties. Biogenic soil structures were the main transport routes conducting water and solutes into great depth in short time. These pathways had lower bulk density and less cone resistance than the adjacent red or white (bleached) areas of the Gleyic Luvisol subsoil. The red areas were involved in transport because their water contents increased after as compared to before infiltration. However, the measured physical soil properties did not differ between white and red areas. We assume that red areas participate in transport at least by imbibing water from the adjacent biogenic flow paths.

O fluxo preferencial de água e o transporte de solutos relacionam-se com perdas de nutrientes e pesticidas e afetam a qualidade de águas subterrâneas. Foram realizados experimentos utilizando o traçador Brilhante Blue, um infiltrômetro de tensão (TI) e um infiltrômetro com "duplos quadrados" (DI) num campo experimental localizado a cerca de 15 km a sudeste da cidade de Rostock (nordeste da Alemanha) num solo onde cultiva-se milho (Zea mays L.) e cevada (Hordeum spp.). Um dia após a infiltração do traçador, perfis de solo foram escavados no local do TI e do DI para observar o fluxo da água deixado pelo do traçador no solo. O objetivo era verificar se os mosqueados vermelhos e partes esbranquiçadas cor-padrão do subsolo do Gleyic Luvisol, resultante da água estagnada temporariamente, poderia estar relacionada ao fluxo da água visualizados pelo traçador e se a cor do solo poderia estar relacionada a outras propriedades físicas do solo. A estrutura biogênica do solo foi a principal rota de transporte conduzindo água e solutos em profundidade e em menor tempo. Esses caminhos tiveram menor densidade do solo e menor resistência do que as áreas vermelhas e esbranquiçadas adjacentes do subsolo do Gleyic Luvisol. Áreas vermelhas foram relacionadas com o transporte devido apresentarem maior conteúdo de água após o teste de infiltração. Entretanto, não houve diferenças entre as propriedades físicas do solo das áreas brancas e vermelhas. Assumiu-se que as áreas vermelhas participaram do transporte de água porque absorveram água do fluxo adjacente, ou seja, dos bioporos.

Spatial distribution of top soil water content in an experimental catchment of Southeast Brazil

Soil water content is essential to understand the hydrological cycle. It controls the surface runoff generation, water infiltration, soil evaporation and plant transpiration. This work aims to analyze the spatial distribution of top soil water content and to characterize the spatial mean and standard deviation of top soil water content over time in an experimental catchment located in the Mantiqueira Range region, state of Minas Gerais, Brazil. Measurements of top soil water content were carried out every 15 days, between May/2007 and May/2008. Using time-domain reflectometry (TDR) equipment, 69 points were sampled in the top 0.2 m of the soil profile. Geostatistical procedures were applied in all steps of the study. First, the spatial continuity was evaluated, and the experimental semi-variogram was modeled. For the development of top soil water content maps over time a co-kriging procedure was used having the slope as a secondary variable. Rainfall regime controlled the top soil water content during the wet season. Land use was also another fundamental local factor. The spatial standard deviation had low values under dry conditions, and high values under wet conditions. Thus, more variability occurs under wet conditions.

A umidade do solo é essencial para o entendimento do ciclo hidrológico, uma vez que controla a geração do escoamento superficial, infiltração de água no solo, evaporação do solo e transpiração das plantas. Este trabalho objetivou analisar os padrões espaciais da umidade superficial do solo e caracterizar a média e o desvio padrão espaciais da mesma ao longo do tempo em uma bacia hidrográfica experimental localizada na Serra da Mantiqueira, MG. As medidas da umidade superficial do solo foram conduzidas a cada 15 dias, entre Maio/2007 e Maio/2008, usando um equipamento TDR portátil, em 69 pontos amostrados na camada de 0-20 cm. Procedimentos geoestatísticos foram aplicados em todas as etapas do trabalho. Primeiramente, a continuidade espacial foi avaliada modelando-se o semivariograma experimental. Mapas de umidade do solo foram desenvolvidos com base na cokrigagem usando o padrão de declividade como variável secundária. O regime de chuvas controlou a umidade superficial do solo durante o período úmido, devido aos altos conteúdos de umidade. O uso do solo também foi outro fator fundamental na distribuição espacial da umidade do solo. O desvio padrão espacial apresentou baixos valores sob condições secas e valores mais altos sob condições úmidas.