In many arid countries, runoff water-harvesting systems support the livelihood of the rural popul... more In many arid countries, runoff water-harvesting systems support the livelihood of the rural population. Little is known, however, about the effect of these systems on the water balance components of arid watersheds. The objective of this study was to adapt and evaluate the GIS-based water-shed model SWAT (Soil Water Assessment Tool) for simulat-ing the main hydrologic processes in arid environments. The model was applied to the 270-km 2 watershed of wadi Kou-tine in southeast Tunisia, which receives about 200 mm an-nual rain. The main adjustment for adapting the model to this dry Mediterranean environment was the inclusion of water-harvesting systems, which capture and use surface runoff for crop production in upstream subbasins, and a modification of the crop growth processes. The adjusted version of the model was named SWAT-WH. Model evaluation was per-formed based on 38 runoff events recorded at the Koutine station between 1973 and 1985. The model predicted that the average annua...
Communications in agricultural and applied biological sciences, 2006
The toxic effects of a widely used herbicide (Stomp 330 containing 33% pendimethalin as active in... more The toxic effects of a widely used herbicide (Stomp 330 containing 33% pendimethalin as active ingredient) applied alone or in combination with three heavy elements (copper sulphate, cadmium sulphate and lead acetate) modelling the heavy metal load of the environment were studied on chicken embryos with injection treatment. The treatment was done on day 0 of incubation. Solutions and emulsions of different concentrations were made from the test materials and injected in 0.1 ml volume into the air space of eggs. The macroscopical evaluations were done on day 19 of the incubation. Summarizing the findings, it can be established that the individual administration of the 33% pendimethalin containing herbicide formulation was less toxic compared to the control group than the simultaneous administration of the pesticide and heavy elements. As compared with each other the results from the combined administrations of the 33% pendimethalin containing herbicide formulation and heavy elements the simultaneous administration of cadmium and the herbicide caused the highest embryomortality while the incidence of developmental anomalies were the highest in the interaction study of the copper and the pesticide.
In arid and semi-arid zones runoff harvesting techniques are often applied to increase the water ... more In arid and semi-arid zones runoff harvesting techniques are often applied to increase the water retention and infiltration on steep slopes. Additionally, they act as an erosion control measure to reduce land degradation hazards. Both in literature and in the field, a large variety of runoff collecting systems are found, as well as large variations in design and dimensions. Therefore,
ABSTRACT Traditionally, research on soil degradation focused on water erosion. Recent studies, ho... more ABSTRACT Traditionally, research on soil degradation focused on water erosion. Recent studies, however, point to the importance of tillage operations as a source of soil translocation in traditional animal-powered farming systems comparable to those applied in the Cuyaguateje watershed, Cuba. Together with the effect of some controlling factors, the extent of tillage erosion on a Ferralsol (Ferralítico Rojo) caused by the traditional ox-drawn mouldboard plough, the ‘arado americano’, and a harrow, the ‘rastrillo’, were studied with a tracer experiment on a Ferralsol with 30 plots on moderate slopes ranging from 4% to 16.5%. Two tillage directions were considered: (i) parallel to the contour and (ii) up and down the slope. Due to the shallow average tillage depth of tillage with the ‘rastrillo’ (3.8 cm), net mean downslope displacement could not be observed. Average tillage depth with the ‘arado americano’ was relatively shallow (11.5 cm) as well and resulted only in the up and downslope direction in a significant downslope soil flux. This downward movement showed no significant relation with the slope gradient, nor with tillage depth, tillage speed and plant cover. While the potential for tillage erosion is considerable with the ‘arado americano’, actual erosion rates in our study were low compared to previous tillage erosion studies. Single soil movements up to 44 cm were detected, but taking crop rotation and tillage frequencies into account, soil transportation rates of accumulated tillage operations only ranged from 8.78 to 26.34 kg m− 1 yr− 1. This is mainly due to the moderate slope range, the low tillage depth and the good farmers' practice of tilling alternately in opposing direction.
There are various types of the windblown sediment traps developed for wind tunnel and field studi... more There are various types of the windblown sediment traps developed for wind tunnel and field studies. One of the main supports expected from these traps is in measuring surface dust concentrations to appropriately derive flux equations. The measurement performance and accuracy of a trap is very important and depends strictly upon the physical characteristics and the behaviors of dust grains
The estimation of non available soil variables through the knowledge of other related measured va... more The estimation of non available soil variables through the knowledge of other related measured variables can be achieved through pedotransfer functions (PTF) mainly saving time and reducing cost. Great differences among soils, however, can yield non desirable results when applying this method. This study discusses the application of developed PTFs by several authors using a variety of soils of different characteristics, to evaluate soil water contents of two Brazilian lowland soils. Comparisons are made between PTF evaluated data and field measured data, using statistical and geostatistical tools, like mean error, root mean square error, semivariogram, cross-validation, and regression coefficient. The eight tested PTFs to evaluate gravimetric soil water contents (Ug) at the tensions of 33 kPa and 1,500 kPa presented a tendency to overestimate Ug 33 kPa and underestimate Ug1,500 kPa. The PTFs were ranked according to their performance and also with respect to their potential in descr...
Understanding soil spatial variability and identifying soil parameters most determinant to soil o... more Understanding soil spatial variability and identifying soil parameters most determinant to soil organic carbon stock is pivotal to precision in ecological modelling, prediction, estimation and management of soil within a landscape. This study investigates and describes field soil variability and its structural pattern for agricultural management decisions. The main aim was to relate variation in soil organic carbon stock to soil properties and to estimate soil organic carbon stock from the soil properties. A transect sampling of 100 points at 3 m intervals was carried out. Soils were sampled and analyzed for soil organic carbon and other selected soil properties along with determination of dry aggregate and water-stable aggregate fractions. Principal component analysis, geostatistics, and state-space analysis were conducted on the analyzed soil properties. The first three principal components explained 53.2% of the total variation; Principal Component 1 was dominated by soil exchang...
ABSTRACT Although there is not a sole satisfactory methodology that applies universally up to now... more ABSTRACT Although there is not a sole satisfactory methodology that applies universally up to now, aggregate stability has been proposed as an indicator of soil physical quality (SPQ). Difficulties persist when comparison of aggregate stability from different procedures are performed. The objective of this study is to evaluate appropriate aggregate stability methods that enable to distinguish the SPQ condition of both temperate and tropical medium-textured soils. Among different methods tested, results show that wet sieving using the well known fast wetting methods of Kemper & Rosenau and of Le Bissonnais rendered similar results in both environments. The mean weight diameter value of both methods for assessing aggregate stability can be considered as a dependable indicator of soil structure status for comparing soils. These aggregate stability methods are in correspondence with only one out of the eight SPQ indicators when entirely soils were used. It was concluded that the aggregate stability should be used judiciously and in concert with other indicators for an overall assessing of the SPQ condition.
In many arid countries, runoff water-harvesting systems support the livelihood of the rural popul... more In many arid countries, runoff water-harvesting systems support the livelihood of the rural population. Little is known, however, about the effect of these systems on the water balance components of arid watersheds. The objective of this study was to adapt and evaluate the GIS-based water-shed model SWAT (Soil Water Assessment Tool) for simulat-ing the main hydrologic processes in arid environments. The model was applied to the 270-km 2 watershed of wadi Kou-tine in southeast Tunisia, which receives about 200 mm an-nual rain. The main adjustment for adapting the model to this dry Mediterranean environment was the inclusion of water-harvesting systems, which capture and use surface runoff for crop production in upstream subbasins, and a modification of the crop growth processes. The adjusted version of the model was named SWAT-WH. Model evaluation was per-formed based on 38 runoff events recorded at the Koutine station between 1973 and 1985. The model predicted that the average annua...
Communications in agricultural and applied biological sciences, 2006
The toxic effects of a widely used herbicide (Stomp 330 containing 33% pendimethalin as active in... more The toxic effects of a widely used herbicide (Stomp 330 containing 33% pendimethalin as active ingredient) applied alone or in combination with three heavy elements (copper sulphate, cadmium sulphate and lead acetate) modelling the heavy metal load of the environment were studied on chicken embryos with injection treatment. The treatment was done on day 0 of incubation. Solutions and emulsions of different concentrations were made from the test materials and injected in 0.1 ml volume into the air space of eggs. The macroscopical evaluations were done on day 19 of the incubation. Summarizing the findings, it can be established that the individual administration of the 33% pendimethalin containing herbicide formulation was less toxic compared to the control group than the simultaneous administration of the pesticide and heavy elements. As compared with each other the results from the combined administrations of the 33% pendimethalin containing herbicide formulation and heavy elements the simultaneous administration of cadmium and the herbicide caused the highest embryomortality while the incidence of developmental anomalies were the highest in the interaction study of the copper and the pesticide.
In arid and semi-arid zones runoff harvesting techniques are often applied to increase the water ... more In arid and semi-arid zones runoff harvesting techniques are often applied to increase the water retention and infiltration on steep slopes. Additionally, they act as an erosion control measure to reduce land degradation hazards. Both in literature and in the field, a large variety of runoff collecting systems are found, as well as large variations in design and dimensions. Therefore,
ABSTRACT Traditionally, research on soil degradation focused on water erosion. Recent studies, ho... more ABSTRACT Traditionally, research on soil degradation focused on water erosion. Recent studies, however, point to the importance of tillage operations as a source of soil translocation in traditional animal-powered farming systems comparable to those applied in the Cuyaguateje watershed, Cuba. Together with the effect of some controlling factors, the extent of tillage erosion on a Ferralsol (Ferralítico Rojo) caused by the traditional ox-drawn mouldboard plough, the ‘arado americano’, and a harrow, the ‘rastrillo’, were studied with a tracer experiment on a Ferralsol with 30 plots on moderate slopes ranging from 4% to 16.5%. Two tillage directions were considered: (i) parallel to the contour and (ii) up and down the slope. Due to the shallow average tillage depth of tillage with the ‘rastrillo’ (3.8 cm), net mean downslope displacement could not be observed. Average tillage depth with the ‘arado americano’ was relatively shallow (11.5 cm) as well and resulted only in the up and downslope direction in a significant downslope soil flux. This downward movement showed no significant relation with the slope gradient, nor with tillage depth, tillage speed and plant cover. While the potential for tillage erosion is considerable with the ‘arado americano’, actual erosion rates in our study were low compared to previous tillage erosion studies. Single soil movements up to 44 cm were detected, but taking crop rotation and tillage frequencies into account, soil transportation rates of accumulated tillage operations only ranged from 8.78 to 26.34 kg m− 1 yr− 1. This is mainly due to the moderate slope range, the low tillage depth and the good farmers' practice of tilling alternately in opposing direction.
There are various types of the windblown sediment traps developed for wind tunnel and field studi... more There are various types of the windblown sediment traps developed for wind tunnel and field studies. One of the main supports expected from these traps is in measuring surface dust concentrations to appropriately derive flux equations. The measurement performance and accuracy of a trap is very important and depends strictly upon the physical characteristics and the behaviors of dust grains
The estimation of non available soil variables through the knowledge of other related measured va... more The estimation of non available soil variables through the knowledge of other related measured variables can be achieved through pedotransfer functions (PTF) mainly saving time and reducing cost. Great differences among soils, however, can yield non desirable results when applying this method. This study discusses the application of developed PTFs by several authors using a variety of soils of different characteristics, to evaluate soil water contents of two Brazilian lowland soils. Comparisons are made between PTF evaluated data and field measured data, using statistical and geostatistical tools, like mean error, root mean square error, semivariogram, cross-validation, and regression coefficient. The eight tested PTFs to evaluate gravimetric soil water contents (Ug) at the tensions of 33 kPa and 1,500 kPa presented a tendency to overestimate Ug 33 kPa and underestimate Ug1,500 kPa. The PTFs were ranked according to their performance and also with respect to their potential in descr...
Understanding soil spatial variability and identifying soil parameters most determinant to soil o... more Understanding soil spatial variability and identifying soil parameters most determinant to soil organic carbon stock is pivotal to precision in ecological modelling, prediction, estimation and management of soil within a landscape. This study investigates and describes field soil variability and its structural pattern for agricultural management decisions. The main aim was to relate variation in soil organic carbon stock to soil properties and to estimate soil organic carbon stock from the soil properties. A transect sampling of 100 points at 3 m intervals was carried out. Soils were sampled and analyzed for soil organic carbon and other selected soil properties along with determination of dry aggregate and water-stable aggregate fractions. Principal component analysis, geostatistics, and state-space analysis were conducted on the analyzed soil properties. The first three principal components explained 53.2% of the total variation; Principal Component 1 was dominated by soil exchang...
ABSTRACT Although there is not a sole satisfactory methodology that applies universally up to now... more ABSTRACT Although there is not a sole satisfactory methodology that applies universally up to now, aggregate stability has been proposed as an indicator of soil physical quality (SPQ). Difficulties persist when comparison of aggregate stability from different procedures are performed. The objective of this study is to evaluate appropriate aggregate stability methods that enable to distinguish the SPQ condition of both temperate and tropical medium-textured soils. Among different methods tested, results show that wet sieving using the well known fast wetting methods of Kemper & Rosenau and of Le Bissonnais rendered similar results in both environments. The mean weight diameter value of both methods for assessing aggregate stability can be considered as a dependable indicator of soil structure status for comparing soils. These aggregate stability methods are in correspondence with only one out of the eight SPQ indicators when entirely soils were used. It was concluded that the aggregate stability should be used judiciously and in concert with other indicators for an overall assessing of the SPQ condition.
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Papers by Donald Gabriels