Adolfo Posadas | World Agroforestry Centre (original) (raw)

Papers by Adolfo Posadas

Soil Science Society of America Journal, 2010

Multispectral reflectance imagery and spectroradiometry can be used to detect stresses affecting ... more Multispectral reflectance imagery and spectroradiometry can be used to detect stresses affecting crops. Previously, we have shown that changes in spectral reflectance and vegetation indices detected viral infection 14 days before visual symptoms were noticed by the trained eye. Herein we present evidence that shows that the application of multifractal analysis and wavelet transform to spectroradiometrical data improves the diagnostic power of the remote sensing-based methodology proposed in our previous work. The diagnosis of viral infection was effectively enhanced, providing the earliest detection ever reported, as anomalies were detected 29 and 33 days before appearance of visual symptoms in two experiments.

Nonlinear Processes in Geophysics, 2015

Remotely sensed data are often used as proxies for indirect precipitation measures over data-scar... more Remotely sensed data are often used as proxies for indirect precipitation measures over data-scarce and complex-terrain areas such as the Peruvian Andes. Although this information might be appropriate for some research requirements, the extent at which local sites could be related to such information is very limited because of the resolution of the available satellite data. Downscaling techniques are used to bridge the gap between what climate modelers (global and regional) are able to provide and what decision-makers require (local). Precipitation downscaling improves the poor local representation of satellite data and helps end-users acquire more accurate estimates of water availability. Thus, a multifractal downscaling technique complemented by a heterogeneity filter was applied to TRMM (Tropical Rainfall Measuring Mission) 3B42 gridded data (spatial resolution ∼ 28 km) from the Peruvian Andean high plateau or Altiplano to generate downscaled rainfall fields that are relevant at an agricultural scale (spatial resolution ∼ 1 km).

Soil Science Society of America Journal, 2010

Wetlands are valuable for their function as C sinks, water conservation and filtering, flood cont... more Wetlands are valuable for their function as C sinks, water conservation and filtering, flood control, and as a recreational landscape. In the Central and Southern Andes, peatlands (aka, bofedales) are also a source of good quality pastures for wild and domestic South ...

Soil Science Society of America Journal, 2001

1999), using the model of and , also found that three domains A particle-size distribution (PSD) ... more 1999), using the model of and , also found that three domains A particle-size distribution (PSD) constitutes a fundamental soil characterized the cumulative PSD of 19 soils. They assoproperty correlated to many other soil properties. Accurate representations of PSDs are, therefore, needed for soil characterization and ciated the power exponent in each domain with fractal prediction purposes. A power-law dependence of particle mass on dimensions defining scaling in the clay, silt, or sand particle diameter has been used to model soil PSDs, and such power-

Soil Science Society of America Journal, 2003

Spatial arrangement of soil pores determines soil structure and is important to model soil proces... more Spatial arrangement of soil pores determines soil structure and is important to model soil processes. Geometric properties of individual pores can be estimated from thin sections, but there is no satisfactory method to quantify the complexity of their spatial arrangement. The objective of this work was to apply a multifractal technique to quantify properties of ten contrasting soil pore systems. Binary images (500 by 750 pixels, 74.2 µm pixel − 1 ) were obtained from thin sections and analyzed to obtain f(α) spectra. Pore area and pore perimeter were measured from each image and used to estimate a shape factor for pores with area larger than 0.27 × 10 6 µm 2 . Mean area of the lower (MA L ) and upper (MA U ) one-half of cumulative pore area distributions were calculated. Pore structures with large (MA U > 10 × 10 6 µm 2 ) and elongated pores exhibited "flat" f(α)-spectra typical of homogenous systems (three soils). Massive type structure with small (MA U < 10 × 10 6 µm 2 ) rounded and irregular pores resulted in asymmetric f(α)-spectra (two soils). Well defined and symmetric f(α)-spectra were obtained with soil structures having elongated pores of intermediate size (1 × 10 6 < MA U < 10 × 10 6 µm 2 ) clustered around relatively small structural units (five soils). Multifractal parameters defining the maximum of the f(α)-spectra were correlated to total porosity (P < 0.01), and silt content (P < 0.05). This study demonstrates that the spatial arrangement of contrasting soil structures can be quantified and separated by the properties of their f(α)-spectra. Multifractal parameters quantifying spatial arrangement of soil pores could be used to improve classifications of soil structure.

Soil and Tillage Research, 2002

Scaling of mass within soil aggregates is characterized with a power-law model relating mass, M, ... more Scaling of mass within soil aggregates is characterized with a power-law model relating mass, M, and radius, r, of aggregates. When distribution of mass is fractal, the constants of the power-law model are the fractal dimension of mass, D m , with a value <3, and a linear constant k m . Tillage may alter mass scaling in soil by changing the internal arrangement of matter inside aggregates. Estimates of D m and k m have been made from measurements of mass contained in aggregates covering a range of sizes, but they could also be obtained by eroding aggregates of a single size class. Studies on eroded aggregates have shown that matter may be concentrically arranged in soil aggregates as a result of wetting and drying processes. The objective of this study was to estimate and compare D m and k m values from intact and eroded aggregates from wooded and cultivated sites of the same soil. Soil aggregates were sampled from the surface horizon of wooded and cultivated sites of a Typic Hapludults (Gladstone series), an Aquic Hapludults (Holmdel series), and an Ultic Hapludalfs (Ryder series) soil. A group of initially large air-dried aggregates was subjected to cycles of erosion that removed concentric layers of soil leaving increasingly smaller aggregates. Volumes of intact and eroded aggregates were measured by submerging kerosene-saturated aggregates in a 1:1 mix of water and glycerin and estimating the volume displaced by solving a balance of forces. An equivalent aggregate radius, r, was calculated as the cubic root of aggregate volume. Parameters D m and k m , and the variance of k m (lacunarity), were estimated separately from the air-dried mass and r of intact and eroded aggregates with r > 1 cm and r < 1 cm. Scaling of mass was influenced by the soil type and soil management. In general, fractal scaling of mass was consistently found only in intact and eroded aggregates ðr > 1Þ of the Gladstone and Holmdel soils. For the wooded Gladstone and Holmdel soils, mass scaling of intact and eroded aggregates was statistically characterized by the same values of D m and k m , suggesting a concentric arrangement of mass, but only within aggregates that are not subjected to tillage. The k m values of intact and eroded aggregates were correlated ðR ¼ 0:97Þ to aggregate bulk density of intact aggregates. Typically, small aggregates ðr < 1 cmÞ, aggregates from wooded sites, and intact aggregates had larger values of lacunarity than their corresponding counterparts. This study indicates that fractal scaling of mass cannot be assumed for all soils, but it can be maintained in cultivated soils despite changes in mass scaling introduced by tillage. #

Precision Agriculture, 2012

Potato bacterial wilt, caused by the bacterium Ralstonia solanacearum race 3 biovar 2 (R3bv2), af... more Potato bacterial wilt, caused by the bacterium Ralstonia solanacearum race 3 biovar 2 (R3bv2), affects potato production in several regions in the world. The disease becomes visually detectable when extensive damage to the crop has already occurred. Two greenhouse experiments were conducted to test the capability of a remote sensing diagnostic method supported by multispectral and multifractal analyses of the light reflectance signal, to detect physiological and morphological changes in plants caused by the infection. The analysis was carried out using the Wavelet Transform Modulus Maxima (WTMM) combined with the Multifractal (MF) analysis to assess the variability of high-resolution temporal and spatial signals and the conservative properties of the processes across temporal and spatial scales. The multispectral signal, enhanced by multifractal analysis, detected both symptomatic and latently infected plants, matching the results of ELISA laboratory assessment in 100 and 82%, respectively. Although the multispectral method provided no earlier detection than the visual assessment on symptomatic plants, the former was able to detect asymptomatic latent infection, showing a great potential as a monitoring tool for the control of bacterial wilt in potato crops. Applied to precision agriculture, this capability of the remote sensing diagnostic methodology would provide a more efficient control of the disease through an early and full spatial assessment of the health status of the crop and the prevention of spreading the disease.

Journal of Theoretical Biology, 2003

Grazing systems in harsh environments are common throughout the world, and animal production is t... more Grazing systems in harsh environments are common throughout the world, and animal production is the mainstay of the livelihoods of many resource-poor farmers. The energy cost of the various activities involved in the process of harvesting the pasture to transform it into animal product can be estimated through an energy balance. This cost would be the difference between the metabolizable energy intake (MEI) and the energy expenditures for maintenance (MEm), temperature regulation (MEtr), and the energy for production (MEp). Each of the ME has its own net energy (NE) and its associated efficiency (K). When MEI&amp;amp;gt;MEm+MEtr+MEp, the difference is attributable to the energy dissipated during grazing. The efficiency of converting the energy consumed into animal products depends on the magnitude of the dissipation. The inefficiency is associated with the energy spent in locomotion and the stress produced when there is low availability of energy in the pasture. This paper presents a method to quantify the dissipation of energy by grazing animals by considering it as a function of available energy. Such an understanding is required in order to develop management strategies to increase conversion efficiency.

Journal of Applied Physics, 1995

Experiments of water infiltration in a vertical plane through layered soils were carried out in t... more Experiments of water infiltration in a vertical plane through layered soils were carried out in the laboratory. We have followed the fingering dynamics by using image techniques. The fractal theory has been applied to describe the fingering phenomena. We also have simulated a modified site gradient invasion percolation model where most of the physical ingredients relevant to the problem have been incorporated. In contrast to what occurs with the standard gradient invasion percolation model, we have found the formation of many fingers. Taking into account the bond number, the number of fingers, and the wetted area of the experiments, we have fitted the parameters of our model. This opens the possibility of a theoretical prediction of the poresizedistribution of the soil. The results are then compared with the experimental data.

… 2010, held 2-7 May, 2010 …, 2010

Two dimensional (2-D) images representing pores and solids are used for direct quantification of ... more Two dimensional (2-D) images representing pores and solids are used for direct quantification of soil structure using tools that are sensitive to the spatial arrangement of pores or by grouping pores by morphological properties such as shape and size. Pore shapes and sizes are ...

Downscaling techniques aim at resolving the scale discrepancy between climate change scenarios an... more Downscaling techniques aim at resolving the scale discrepancy between climate change scenarios and the resolution demanded for impact assessments. Requirements for downscaled climate, to be useful for end users, include reliable representation of precipitation intensities, temporal and spatial variability, and physical parameters consistency. This report summarizes the results of the proof of concept phase in the development and testing of a novel data reconstruction method and a downscaling algorithm based on the multiplicative random cascade disaggregation method using rainfall signals at different spatial and temporal resolutions. The Wavelet Transformed-based Multi-Resolution Analysis (WT-MRA) was used for reconstructing the historical daily rainfall data needed as input for the downscaling methodology, using satellite-derived proxy data. Comparisons with presently used software showed that in all the cases; that is, the reconstructed, generated daily or downscaled daily data, the products developed outperformed the control test by either generating more accurate outcomes or by demanding significantly less parameterizing data.

Soil Science Society of America Journal, 2010

Multispectral reflectance imagery and spectroradiometry can be used to detect stresses affecting ... more Multispectral reflectance imagery and spectroradiometry can be used to detect stresses affecting crops. Previously, we have shown that changes in spectral reflectance and vegetation indices detected viral infection 14 days before visual symptoms were noticed by the trained eye. Herein we present evidence that shows that the application of multifractal analysis and wavelet transform to spectroradiometrical data improves the diagnostic power of the remote sensing-based methodology proposed in our previous work. The diagnosis of viral infection was effectively enhanced, providing the earliest detection ever reported, as anomalies were detected 29 and 33 days before appearance of visual symptoms in two experiments.

Nonlinear Processes in Geophysics, 2015

Remotely sensed data are often used as proxies for indirect precipitation measures over data-scar... more Remotely sensed data are often used as proxies for indirect precipitation measures over data-scarce and complex-terrain areas such as the Peruvian Andes. Although this information might be appropriate for some research requirements, the extent at which local sites could be related to such information is very limited because of the resolution of the available satellite data. Downscaling techniques are used to bridge the gap between what climate modelers (global and regional) are able to provide and what decision-makers require (local). Precipitation downscaling improves the poor local representation of satellite data and helps end-users acquire more accurate estimates of water availability. Thus, a multifractal downscaling technique complemented by a heterogeneity filter was applied to TRMM (Tropical Rainfall Measuring Mission) 3B42 gridded data (spatial resolution ∼ 28 km) from the Peruvian Andean high plateau or Altiplano to generate downscaled rainfall fields that are relevant at an agricultural scale (spatial resolution ∼ 1 km).

Soil Science Society of America Journal, 2010

Wetlands are valuable for their function as C sinks, water conservation and filtering, flood cont... more Wetlands are valuable for their function as C sinks, water conservation and filtering, flood control, and as a recreational landscape. In the Central and Southern Andes, peatlands (aka, bofedales) are also a source of good quality pastures for wild and domestic South ...

Soil Science Society of America Journal, 2001

1999), using the model of and , also found that three domains A particle-size distribution (PSD) ... more 1999), using the model of and , also found that three domains A particle-size distribution (PSD) constitutes a fundamental soil characterized the cumulative PSD of 19 soils. They assoproperty correlated to many other soil properties. Accurate representations of PSDs are, therefore, needed for soil characterization and ciated the power exponent in each domain with fractal prediction purposes. A power-law dependence of particle mass on dimensions defining scaling in the clay, silt, or sand particle diameter has been used to model soil PSDs, and such power-

Soil Science Society of America Journal, 2003

Spatial arrangement of soil pores determines soil structure and is important to model soil proces... more Spatial arrangement of soil pores determines soil structure and is important to model soil processes. Geometric properties of individual pores can be estimated from thin sections, but there is no satisfactory method to quantify the complexity of their spatial arrangement. The objective of this work was to apply a multifractal technique to quantify properties of ten contrasting soil pore systems. Binary images (500 by 750 pixels, 74.2 µm pixel − 1 ) were obtained from thin sections and analyzed to obtain f(α) spectra. Pore area and pore perimeter were measured from each image and used to estimate a shape factor for pores with area larger than 0.27 × 10 6 µm 2 . Mean area of the lower (MA L ) and upper (MA U ) one-half of cumulative pore area distributions were calculated. Pore structures with large (MA U > 10 × 10 6 µm 2 ) and elongated pores exhibited "flat" f(α)-spectra typical of homogenous systems (three soils). Massive type structure with small (MA U < 10 × 10 6 µm 2 ) rounded and irregular pores resulted in asymmetric f(α)-spectra (two soils). Well defined and symmetric f(α)-spectra were obtained with soil structures having elongated pores of intermediate size (1 × 10 6 < MA U < 10 × 10 6 µm 2 ) clustered around relatively small structural units (five soils). Multifractal parameters defining the maximum of the f(α)-spectra were correlated to total porosity (P < 0.01), and silt content (P < 0.05). This study demonstrates that the spatial arrangement of contrasting soil structures can be quantified and separated by the properties of their f(α)-spectra. Multifractal parameters quantifying spatial arrangement of soil pores could be used to improve classifications of soil structure.

Soil and Tillage Research, 2002

Scaling of mass within soil aggregates is characterized with a power-law model relating mass, M, ... more Scaling of mass within soil aggregates is characterized with a power-law model relating mass, M, and radius, r, of aggregates. When distribution of mass is fractal, the constants of the power-law model are the fractal dimension of mass, D m , with a value <3, and a linear constant k m . Tillage may alter mass scaling in soil by changing the internal arrangement of matter inside aggregates. Estimates of D m and k m have been made from measurements of mass contained in aggregates covering a range of sizes, but they could also be obtained by eroding aggregates of a single size class. Studies on eroded aggregates have shown that matter may be concentrically arranged in soil aggregates as a result of wetting and drying processes. The objective of this study was to estimate and compare D m and k m values from intact and eroded aggregates from wooded and cultivated sites of the same soil. Soil aggregates were sampled from the surface horizon of wooded and cultivated sites of a Typic Hapludults (Gladstone series), an Aquic Hapludults (Holmdel series), and an Ultic Hapludalfs (Ryder series) soil. A group of initially large air-dried aggregates was subjected to cycles of erosion that removed concentric layers of soil leaving increasingly smaller aggregates. Volumes of intact and eroded aggregates were measured by submerging kerosene-saturated aggregates in a 1:1 mix of water and glycerin and estimating the volume displaced by solving a balance of forces. An equivalent aggregate radius, r, was calculated as the cubic root of aggregate volume. Parameters D m and k m , and the variance of k m (lacunarity), were estimated separately from the air-dried mass and r of intact and eroded aggregates with r > 1 cm and r < 1 cm. Scaling of mass was influenced by the soil type and soil management. In general, fractal scaling of mass was consistently found only in intact and eroded aggregates ðr > 1Þ of the Gladstone and Holmdel soils. For the wooded Gladstone and Holmdel soils, mass scaling of intact and eroded aggregates was statistically characterized by the same values of D m and k m , suggesting a concentric arrangement of mass, but only within aggregates that are not subjected to tillage. The k m values of intact and eroded aggregates were correlated ðR ¼ 0:97Þ to aggregate bulk density of intact aggregates. Typically, small aggregates ðr < 1 cmÞ, aggregates from wooded sites, and intact aggregates had larger values of lacunarity than their corresponding counterparts. This study indicates that fractal scaling of mass cannot be assumed for all soils, but it can be maintained in cultivated soils despite changes in mass scaling introduced by tillage. #

Precision Agriculture, 2012

Potato bacterial wilt, caused by the bacterium Ralstonia solanacearum race 3 biovar 2 (R3bv2), af... more Potato bacterial wilt, caused by the bacterium Ralstonia solanacearum race 3 biovar 2 (R3bv2), affects potato production in several regions in the world. The disease becomes visually detectable when extensive damage to the crop has already occurred. Two greenhouse experiments were conducted to test the capability of a remote sensing diagnostic method supported by multispectral and multifractal analyses of the light reflectance signal, to detect physiological and morphological changes in plants caused by the infection. The analysis was carried out using the Wavelet Transform Modulus Maxima (WTMM) combined with the Multifractal (MF) analysis to assess the variability of high-resolution temporal and spatial signals and the conservative properties of the processes across temporal and spatial scales. The multispectral signal, enhanced by multifractal analysis, detected both symptomatic and latently infected plants, matching the results of ELISA laboratory assessment in 100 and 82%, respectively. Although the multispectral method provided no earlier detection than the visual assessment on symptomatic plants, the former was able to detect asymptomatic latent infection, showing a great potential as a monitoring tool for the control of bacterial wilt in potato crops. Applied to precision agriculture, this capability of the remote sensing diagnostic methodology would provide a more efficient control of the disease through an early and full spatial assessment of the health status of the crop and the prevention of spreading the disease.

Journal of Theoretical Biology, 2003

Grazing systems in harsh environments are common throughout the world, and animal production is t... more Grazing systems in harsh environments are common throughout the world, and animal production is the mainstay of the livelihoods of many resource-poor farmers. The energy cost of the various activities involved in the process of harvesting the pasture to transform it into animal product can be estimated through an energy balance. This cost would be the difference between the metabolizable energy intake (MEI) and the energy expenditures for maintenance (MEm), temperature regulation (MEtr), and the energy for production (MEp). Each of the ME has its own net energy (NE) and its associated efficiency (K). When MEI&amp;amp;gt;MEm+MEtr+MEp, the difference is attributable to the energy dissipated during grazing. The efficiency of converting the energy consumed into animal products depends on the magnitude of the dissipation. The inefficiency is associated with the energy spent in locomotion and the stress produced when there is low availability of energy in the pasture. This paper presents a method to quantify the dissipation of energy by grazing animals by considering it as a function of available energy. Such an understanding is required in order to develop management strategies to increase conversion efficiency.

Journal of Applied Physics, 1995

Experiments of water infiltration in a vertical plane through layered soils were carried out in t... more Experiments of water infiltration in a vertical plane through layered soils were carried out in the laboratory. We have followed the fingering dynamics by using image techniques. The fractal theory has been applied to describe the fingering phenomena. We also have simulated a modified site gradient invasion percolation model where most of the physical ingredients relevant to the problem have been incorporated. In contrast to what occurs with the standard gradient invasion percolation model, we have found the formation of many fingers. Taking into account the bond number, the number of fingers, and the wetted area of the experiments, we have fitted the parameters of our model. This opens the possibility of a theoretical prediction of the poresizedistribution of the soil. The results are then compared with the experimental data.

… 2010, held 2-7 May, 2010 …, 2010

Two dimensional (2-D) images representing pores and solids are used for direct quantification of ... more Two dimensional (2-D) images representing pores and solids are used for direct quantification of soil structure using tools that are sensitive to the spatial arrangement of pores or by grouping pores by morphological properties such as shape and size. Pore shapes and sizes are ...

Downscaling techniques aim at resolving the scale discrepancy between climate change scenarios an... more Downscaling techniques aim at resolving the scale discrepancy between climate change scenarios and the resolution demanded for impact assessments. Requirements for downscaled climate, to be useful for end users, include reliable representation of precipitation intensities, temporal and spatial variability, and physical parameters consistency. This report summarizes the results of the proof of concept phase in the development and testing of a novel data reconstruction method and a downscaling algorithm based on the multiplicative random cascade disaggregation method using rainfall signals at different spatial and temporal resolutions. The Wavelet Transformed-based Multi-Resolution Analysis (WT-MRA) was used for reconstructing the historical daily rainfall data needed as input for the downscaling methodology, using satellite-derived proxy data. Comparisons with presently used software showed that in all the cases; that is, the reconstructed, generated daily or downscaled daily data, the products developed outperformed the control test by either generating more accurate outcomes or by demanding significantly less parameterizing data.