The Experts below are selected from a list of 303 Experts worldwide ranked by ideXlab platform
Allan Walker - One of the best experts on this subject based on the ideXlab platform.
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Investigation into the effect of tillage on solute movement to drains through a heavy clay soil. I. Lysimeter experiment
Soil Use and Management, 2006Co-Authors: Colin D. Brown, Allan Walker, V. L. Marshall, A. D. Carter, D. Arnold, Russell L. JonesAbstract:. A lysimeter experiment showed a decrease in maximum concentrations and total losses of the herbicide isoproturon leached from a heavy clay soil where the topsoil had a finer, deeper Tilth than with a standard agricultural Tilth. Volumes of leachate for the first flow event of the season were also smaller and leaching of bromide was slower. The isoproturon was radiolabelled so that its movement could be assessed using a novel radio-scanning technique. Bypass flow began close to the surface as a scan at 8 cm depth showed that only 0.5% of the total soil area had an activity more than four times the nominal background level. At depths of 10–20 cm, isoproturon was preferentially retained within areas of very fine aggregates. No radioactivity was detected in the scans below 20 cm depth, suggesting little or no retention of isoproturon during transport through the subsoil to the bottom of the lysimeter. Rhodamine-B dye injected to the base of the topsoil (approximately 20 cm depth) was also used to assess flow pathways through the subsoil. The dye spread laterally across the interface between topsoil and subsoil and then penetrated the subsoil through cracks and fissures. Even within cracks, transport of dye frequently occurred through only a very small proportion of the total crack area. The macropore flow model MACRO 4.0 was used to simulate results from the lysimeter experiment. The fourfold decrease in maximum concentrations of herbicide from the finer Tilth lysimeter could be predicted by varying only a parameter describing aggregate sizes at depths of 6–24 cm, suggesting that transfer of herbicide between macropore and micropore regions was faster in the finer Tilth. Differences in concentrations of bromide could be simulated only by adjusting the soil hydraulic parameters for the fine Tilth to reflect a slight decrease in the predominance of bypass flow relative to matrix flow.
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influence of topsoil Tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil
Pest Management Science, 2001Co-Authors: Colin D. Brown, Christopher J. Fryer, Allan WalkerAbstract:Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural Tilth or a finer topsoil Tilth. The influence of topsoil Tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h−1 over a 4-week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4-week period. Leaching losses of the three herbicides were monitored for a subsequent drainage event. Analysis of covariance showed a significant effect of topsoil Tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer Tilth. However, generation of the fine Tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains. © 2001 Society of Chemical Industry
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Influence of topsoil Tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil.
Pest management science, 2001Co-Authors: Colin D. Brown, Christopher J. Fryer, Allan WalkerAbstract:Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural Tilth or a finer topsoil Tilth. The influence of topsoil Tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h-1 over a 4-week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4-week period. Leaching losses of the three herbicides were monitored for a subsequently drainage event. Analysis of covariance showed a significant effect of topsoil Tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer Tilth. However, generation of the fine Tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains.
Je Mcphee - One of the best experts on this subject based on the ideXlab platform.
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The effect of initial soil water content and tillage implement on seedbed formation
Soil and Tillage Research, 1991Co-Authors: Mv Braunack, Je McpheeAbstract:Abstract This study was undertaken to determine the effect of initial soil water content and various tillage implements in producing a suitable seedbed Tilth on a cracking clay soil (Entic Chromustert). The soil was tilled with one, two and three passes of a tined implement, a disc and a rotary hoe at three different initial soil water contents. Bulk density, aggregate size distribution and cone index were measured before and after tillage. Soil water content was measured before tillage only. Results tend to indicate that finer Tilths were produced at drier initial soil water contents and with an increasing number of implement passes. Soil bulk density and cone index were reduced after tillage. Initial soil water content appears to be the controlling factor in producing a suitable seedbed Tilth. All combinations of implement, number of passes and initial soil water contents appeared to produce reasonable seedbed Tilths over the range of water contents examined.
Colin D. Brown - One of the best experts on this subject based on the ideXlab platform.
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Investigation into the effect of tillage on solute movement to drains through a heavy clay soil. I. Lysimeter experiment
Soil Use and Management, 2006Co-Authors: Colin D. Brown, Allan Walker, V. L. Marshall, A. D. Carter, D. Arnold, Russell L. JonesAbstract:. A lysimeter experiment showed a decrease in maximum concentrations and total losses of the herbicide isoproturon leached from a heavy clay soil where the topsoil had a finer, deeper Tilth than with a standard agricultural Tilth. Volumes of leachate for the first flow event of the season were also smaller and leaching of bromide was slower. The isoproturon was radiolabelled so that its movement could be assessed using a novel radio-scanning technique. Bypass flow began close to the surface as a scan at 8 cm depth showed that only 0.5% of the total soil area had an activity more than four times the nominal background level. At depths of 10–20 cm, isoproturon was preferentially retained within areas of very fine aggregates. No radioactivity was detected in the scans below 20 cm depth, suggesting little or no retention of isoproturon during transport through the subsoil to the bottom of the lysimeter. Rhodamine-B dye injected to the base of the topsoil (approximately 20 cm depth) was also used to assess flow pathways through the subsoil. The dye spread laterally across the interface between topsoil and subsoil and then penetrated the subsoil through cracks and fissures. Even within cracks, transport of dye frequently occurred through only a very small proportion of the total crack area. The macropore flow model MACRO 4.0 was used to simulate results from the lysimeter experiment. The fourfold decrease in maximum concentrations of herbicide from the finer Tilth lysimeter could be predicted by varying only a parameter describing aggregate sizes at depths of 6–24 cm, suggesting that transfer of herbicide between macropore and micropore regions was faster in the finer Tilth. Differences in concentrations of bromide could be simulated only by adjusting the soil hydraulic parameters for the fine Tilth to reflect a slight decrease in the predominance of bypass flow relative to matrix flow.
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influence of topsoil Tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil
Pest Management Science, 2001Co-Authors: Colin D. Brown, Christopher J. Fryer, Allan WalkerAbstract:Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural Tilth or a finer topsoil Tilth. The influence of topsoil Tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h−1 over a 4-week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4-week period. Leaching losses of the three herbicides were monitored for a subsequent drainage event. Analysis of covariance showed a significant effect of topsoil Tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer Tilth. However, generation of the fine Tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains. © 2001 Society of Chemical Industry
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Influence of topsoil Tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil.
Pest management science, 2001Co-Authors: Colin D. Brown, Christopher J. Fryer, Allan WalkerAbstract:Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural Tilth or a finer topsoil Tilth. The influence of topsoil Tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h-1 over a 4-week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4-week period. Leaching losses of the three herbicides were monitored for a subsequently drainage event. Analysis of covariance showed a significant effect of topsoil Tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer Tilth. However, generation of the fine Tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains.
Benno P. Warkentin - One of the best experts on this subject based on the ideXlab platform.
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Soil Structure: A History from Tilth to Habitat
Advances in Agronomy, 2008Co-Authors: Benno P. WarkentinAbstract:Publisher Summary This chapter concentrates on the thread of the changing concepts and studies of soil structure. The chapter examines the approaches to soil structure, based on writings from five periods in the past two millennia. While the dates are somewhat flexible, periods of different thinking can be distinguished. The early concept of soil structure was soil Tilth, stirring the soil to prepare a seedbed consisting of small aggregates. Soil aggregates, aggregation, and field description of soil structure were described during 1930 to 1950. Aggregation and Tilth, soil structure and soil erosion, soil mechanics studies of soil structure, and soil compaction were described during 1950 to 1980. Structure as habitat for biota has revitalized the study of soil structure. These studies are led largely by soil biologists and landscape ecologists. Knowledge about soils was developed, in its early history, by practitioners who worked with soils. This knowledge was related to the social conditions of the times and to society's needs. With the advent of soil science laboratories, the dominant concern soon became measurement of static properties relating to Tilth and stability of structure: aggregate-size distribution, porosity, grain-size distribution, stability of aggregates, shape, and size of aggregates. The importance for soil structure of organic matter and of clay content was generally recognized. All these properties were studied in relation to cultivation and to the effects of cultivation on Tilth and yield. The concept of hierarchical arrangement of different aggregate sizes, and the bonds responsible for stability, drew attention to different void sizes and to the soil functions of each.
Christopher J. Fryer - One of the best experts on this subject based on the ideXlab platform.
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influence of topsoil Tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil
Pest Management Science, 2001Co-Authors: Colin D. Brown, Christopher J. Fryer, Allan WalkerAbstract:Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural Tilth or a finer topsoil Tilth. The influence of topsoil Tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h−1 over a 4-week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4-week period. Leaching losses of the three herbicides were monitored for a subsequent drainage event. Analysis of covariance showed a significant effect of topsoil Tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer Tilth. However, generation of the fine Tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains. © 2001 Society of Chemical Industry
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Influence of topsoil Tilth and soil moisture status on losses of pesticide to drains from a heavy clay soil.
Pest management science, 2001Co-Authors: Colin D. Brown, Christopher J. Fryer, Allan WalkerAbstract:Twelve lysimeters with a surface area of 0.5 m2 and a length of 60 cm were taken over mole drains from a Denchworth heavy clay soil and divided into two groups with either a standard agricultural Tilth or a finer topsoil Tilth. The influence of topsoil Tilth on leaching of the herbicide isoproturon and a bromide tracer was evaluated over a winter season. The effect of variations in soil moisture status in the immediate topsoil on leaching of isoproturon, chlorotoluron and linuron was investigated in the following winter season. Here, water inputs were controlled such that lysimeters received 50 mm at a maximum intensity of 2 mm h-1 over a 4-week period with herbicides applied on day 15. Three treatments received the water either all prior to application, all after application, or evenly spread over the 4-week period. Leaching losses of the three herbicides were monitored for a subsequently drainage event. Analysis of covariance showed a significant effect of topsoil Tilth and total flow on both the maximum concentrations (P = 0.034) and total losses (P = 0.012) of isoproturon in drainflow. Both concentrations and losses were c 35% smaller from lysimeters with the finer Tilth. However, generation of the fine Tilth in the field was restricted by a wet autumn and this is not considered a reliable management option for reducing pesticide losses from heavy clay soils. In the second experiment, variation in soil moisture content prior to and after application did not have any significant effect (P < 0.05) upon subsequent losses of the three herbicides to drains.
