estimating N2O emissions from soils relates N2O emis- sions to fertilizer input, that is, about 2... more estimating N2O emissions from soils relates N2O emis- sions to fertilizer input, that is, about 2% of N2O loss Experiments to document the long-term effects of clipping manage- for nitrogen added as fertilizer (Intergovernmental ment on N requirements, soil organic carbon (SOC), and soil organic nitrogen (SON) are difficult and costly and therefore few. The CEN- Panel on Climate Change,
The numerical representation of flow and solute transport is often intimidating to the introducto... more The numerical representation of flow and solute transport is often intimidating to the introductory student. Quantifying the results of simple demonstrations in chemical movement is a valuable introduction to transport modeling and parameter estimation. A solution of the convection-dispersion equation (CDE) is used to describe the solute breakthrough curves gener-ated in the demonstrations suggested in the companion paper. Estimation of the best fit model parameters (solute velocity, dispersion, and retardation) is illustrated step-by-step using the method of moments for an example data set. In addition to the model fitting exercise, the predictive merits of the CDE are demonstrated by employing secondary measurements to esti-mate the parameters. The most important of these supportive measurements is characterization of the soil-dye adsorption isotherm. The blue dye displays linear adsorption in the sand and clay loam (K o of 0.25 m 3 Mg -t and 2.19 m 3 Mg -~, respectively) while th...
Most citrus in central Florida is grown on sandy soils that have very low water holding capacitie... more Most citrus in central Florida is grown on sandy soils that have very low water holding capacities. A small change in soil volumetric water content can greatly affect available water. The purpose of this study was to determine if a moderately low cost sensor (ECH 2 O probe) can perform well in this sandy soil. Three water stress treatments (irrigated, non-irrigated, and non-irrigated with rain exclusion) were imposed on Valencia orange trees in the fall and winter (2003-2004) to determine the effects of stress on sugar accumulation in the fruit. Five ECH 2 O probes were installed in each treatment plot at depths ranging from 10 to 90 cm. Sensors were calibrated in the laboratory. Real time probe responses due to irrigation, rainfall, and water uptake by the plants were collected and analyzed. These probes were able to detect small changes in soil water content at the lower end of the soil water regime and performed well in this soil.
ABSTRACT Most soils in the Central Florida Ridge (CFR) area are Entisols that contain > 95... more ABSTRACT Most soils in the Central Florida Ridge (CFR) area are Entisols that contain > 95% sand, < 3% clay, and < 2% organic matter. Field capacity (theta(fc)) is commonly similar to 0.08 m(3) m(-3). Therefore, accurate estimation of soil water content (0,) is important in these soils. The objective of this study was to evaluate the performance of ECH2O probes when estimating theta(v) for scheduling irrigation in CFR soils. Probes were tested for (i) probe-to-probe output variability, (ii) soil Volume sampled, (iii) sensitivity to salinity, temperature, and air pockets close to the sensor surface, (iv) pockets of very dry soil close to the sensor surface, and (v) performance after installation in the field. According to the calibration, a 1% change in water content corresponds to a probe output of 17 mV Laboratory testing suggested that output variability from probe to probe can be a problem in these soils. The sampling volume of the probe was within 1.5 cm from either side of the sensor surface. Salinity induced during fertigation increased the output by about 200 mv, and for each 1 degrees C drop in temperature, the sensor output dropped by 2.3 mV. When the bulk density was changed from 1.56 to 0.94 Mg m(-3), the output decreased by 3.5 MV for each 1% drop in air-filled porosity When very dry soil lenses with < 0.01 m(3) m(-3) Ov were associated with the probe surface, the probe failed to sense the wet soil even I cm away from the sensor surface. Sensor failure was common due to water leaking into the circuit when sealing material deteriorated or casing material was damaged by insects. These issues need to be addressed before the probes can be considered reliable to estimate theta(v) or used in automated irrigation.
ABSTRACT In developing management practices to reduce chemical leaching below the root zone, till... more ABSTRACT In developing management practices to reduce chemical leaching below the root zone, tillage and irrigation management are important considerations. Two studies were performed to evaluate the movement of bromide in tilled and non-tilled soils under sprinkler versus flood irrigation. In each study, bromide was applied either with an irrigation or presprayed to the soil surface followed by periodic soil sampling to monitor the bromide movement. Tillage was observed to reduce the mean depth of chemical penetration under both irrigation treatments and reduce the spatial variation of bromide concentration under flood irrigation. For example, after 30 days of periodic flood irrigation, 25% of the applied bromide remained in the upper 0.2 m of a tilled soil while in the companion non-tilled soil virtually no bromide remained above this depth. The most rapid bromide movement was observed in non-tilled, flood irrigated soil, particularly when the solute was added with the irrigation. We speculate that the tillage effect of reduced leaching results from the alteration of pore continuity and creation of diffusional sinks and not increased evaporative water loss in the tilled soil. The Root Zone Water Quality Model was calibrated using site-specific hydraulic property measurements and used to predict the solute movement. The model predictions were fairly accurate for the sprinkler irrigated soil but less satisfactory for the flood irrigation studies. In comparing the effect on chemical leaching of the treatments imposed, we found that tillage and the timing of the chemical application had greater impact on reducing leaching than did the method of irrigation.
ABSTRACT Investigation of factors affecting leaching patterns under tilled and no-till soils are ... more ABSTRACT Investigation of factors affecting leaching patterns under tilled and no-till soils are important for successful modelling of solute leaching. There can be various other factors that may offset an anticipated tillage effect on solute leaching. A study was conducted in a Donnelly silty loam (fine-loamy, mixed frigid Typic Cryoboralf) at Dawson Creek, British Columbia, Canada, to investigate how a reactive chemical (FD&C blue#1 dye) and a conservative tracer (bromide, Br−) would leach in a no-till (NT) soil compared to a tilled (T), when high volume of water are provided discretely, at short time intervals. Three plots of 1.5 m × 1.5 m were prepared in each NT and T soil for flood irrigation. The chemicals were applied by spray using a knapsack sprayer. Soil cores were extracted from a maximum depth of 1.25 m using a truck mounted hydraulic soil sampler at 5, 19, and 55 days (S1, S2, and S3, respectively) after irrigating different amounts of water. These soil cores, sub-sampled at different depths, were analysed for water content, Br− and dye concentrations. The analyses indicated that Br− and dye moved in distinctive patterns in the two tillage systems. After irrigating with a total of 240 mm of ponded water in three applications over a period of 10 days, the centre of mass of the travel depth profiles for Br− was 0.15 m in the NT and 0.26 m in the T plots; for the dye, 0.27 m in the NT and 0.17 m in the T plots. At soil core sampling times S1, S2, and S3, the average mass recovered for Br− was 82%, 39%, and 27% in the NT and 78%, 50%, and 45% in the T plots. For the dye, mass recovery rates of 78%, 58%, and 22% were observed in the NT and 92%, 79% and 25% in the T plots. The increasing mass loss of Br− observed with increasing net water inputs in the two tillage systems was more likely due to a lateral loss with water than due to a leaching below sampling depth. The increasing mass loss of dye over time in the two tillage systems was more likely due to a high rate of degradation than to a loss through a lateral or vertical flow.
ABSTRACT,ational facilities, and other greenbelts. Turfgrass ecosys- tems provide excellent soil ... more ABSTRACT,ational facilities, and other greenbelts. Turfgrass ecosys- tems provide excellent soil erosion control, dust stabili- Soil organic C (SOC) directly affects soil quality by influencing zation, flood control, and urban heat dissipation. These aeration and water retention and serving as a major repository and reserve source of plant nutrients. Limited information is available grasslands may act as C sinks, absorbing more CO2 than concerning the long-term SOC changes in turfgrass systselection, mowing, and irrigation management. 0.83 for putting greens. Our results suggest that the CENTURY model Organic C change in soil is a slow process, and many can be used to simulate SOC changes in turfgrass systems and has the years and decades of measurements,are needed,to assess potential to compare C sequestration under various turf management C changes,as influenced,by,management,practices. conditions. Simulation results also suggest that warming temperatures Therefore, evaluation of different management options have greater degree of influence on SOC in turf systems compared with native grasslands.,relative to C sequestration is difficult to accomplish by sampling,and measuring,SOC content and C fractions over time. Simulation models,offer the opportunity,to predict long-term trends based on mathematical,repre- U nderstanding,long-term,SOC changes,in various sentations of nutrient-cycling processes in the soil–plant ecosystems,is of importance,because SOC directly systems. Predictive modeling,exercises allow significant affects soil quality by influencing the air-filled porosity insight into the ecosystem,dynamics. A number,of com- and water retention and serving as a major,repository puter models are available to evaluate SOC dynamics and reserve source of plant nutrients, especially N, P,
HortScience: a publication of the American Society for Horticultural Science
The most important worldwide problem in citrus production is the bacterial disease Huanglongbing ... more The most important worldwide problem in citrus production is the bacterial disease Huanglongbing (HLB; citrus greening) caused by a phloem-limited bacterium Candidatus Liberibacter asiaticus. The earliest visible symptoms of HLB on leaves are vein yellowing and an asymmetrical chlorosis referred to as ‘‘blotchy mottle,’’ thought to be the result of starch accumulation. We tested the hypothesis that such visible symptoms are not unique to HLB by stem girdling 2-year-old seedlings of two citrus rootstocks with and without drought stress in the greenhouse. After 31 days, girdling had little effect on shoot growth but girdling increased the relative growth rate of shoots in drought-stressed trees. Starch content in woody roots of non-girdled trees was three to 19 times higher than in girdled trees. In non-girdled trees, drought stress induced some starch accumulation in roots, but there were no effects of drought stress on root starch or sucrose in girdled trees. Girdling induced a 4-fo...
estimating N2O emissions from soils relates N2O emis- sions to fertilizer input, that is, about 2... more estimating N2O emissions from soils relates N2O emis- sions to fertilizer input, that is, about 2% of N2O loss Experiments to document the long-term effects of clipping manage- for nitrogen added as fertilizer (Intergovernmental ment on N requirements, soil organic carbon (SOC), and soil organic nitrogen (SON) are difficult and costly and therefore few. The CEN- Panel on Climate Change,
The numerical representation of flow and solute transport is often intimidating to the introducto... more The numerical representation of flow and solute transport is often intimidating to the introductory student. Quantifying the results of simple demonstrations in chemical movement is a valuable introduction to transport modeling and parameter estimation. A solution of the convection-dispersion equation (CDE) is used to describe the solute breakthrough curves gener-ated in the demonstrations suggested in the companion paper. Estimation of the best fit model parameters (solute velocity, dispersion, and retardation) is illustrated step-by-step using the method of moments for an example data set. In addition to the model fitting exercise, the predictive merits of the CDE are demonstrated by employing secondary measurements to esti-mate the parameters. The most important of these supportive measurements is characterization of the soil-dye adsorption isotherm. The blue dye displays linear adsorption in the sand and clay loam (K o of 0.25 m 3 Mg -t and 2.19 m 3 Mg -~, respectively) while th...
Most citrus in central Florida is grown on sandy soils that have very low water holding capacitie... more Most citrus in central Florida is grown on sandy soils that have very low water holding capacities. A small change in soil volumetric water content can greatly affect available water. The purpose of this study was to determine if a moderately low cost sensor (ECH 2 O probe) can perform well in this sandy soil. Three water stress treatments (irrigated, non-irrigated, and non-irrigated with rain exclusion) were imposed on Valencia orange trees in the fall and winter (2003-2004) to determine the effects of stress on sugar accumulation in the fruit. Five ECH 2 O probes were installed in each treatment plot at depths ranging from 10 to 90 cm. Sensors were calibrated in the laboratory. Real time probe responses due to irrigation, rainfall, and water uptake by the plants were collected and analyzed. These probes were able to detect small changes in soil water content at the lower end of the soil water regime and performed well in this soil.
ABSTRACT Most soils in the Central Florida Ridge (CFR) area are Entisols that contain > 95... more ABSTRACT Most soils in the Central Florida Ridge (CFR) area are Entisols that contain > 95% sand, < 3% clay, and < 2% organic matter. Field capacity (theta(fc)) is commonly similar to 0.08 m(3) m(-3). Therefore, accurate estimation of soil water content (0,) is important in these soils. The objective of this study was to evaluate the performance of ECH2O probes when estimating theta(v) for scheduling irrigation in CFR soils. Probes were tested for (i) probe-to-probe output variability, (ii) soil Volume sampled, (iii) sensitivity to salinity, temperature, and air pockets close to the sensor surface, (iv) pockets of very dry soil close to the sensor surface, and (v) performance after installation in the field. According to the calibration, a 1% change in water content corresponds to a probe output of 17 mV Laboratory testing suggested that output variability from probe to probe can be a problem in these soils. The sampling volume of the probe was within 1.5 cm from either side of the sensor surface. Salinity induced during fertigation increased the output by about 200 mv, and for each 1 degrees C drop in temperature, the sensor output dropped by 2.3 mV. When the bulk density was changed from 1.56 to 0.94 Mg m(-3), the output decreased by 3.5 MV for each 1% drop in air-filled porosity When very dry soil lenses with < 0.01 m(3) m(-3) Ov were associated with the probe surface, the probe failed to sense the wet soil even I cm away from the sensor surface. Sensor failure was common due to water leaking into the circuit when sealing material deteriorated or casing material was damaged by insects. These issues need to be addressed before the probes can be considered reliable to estimate theta(v) or used in automated irrigation.
ABSTRACT In developing management practices to reduce chemical leaching below the root zone, till... more ABSTRACT In developing management practices to reduce chemical leaching below the root zone, tillage and irrigation management are important considerations. Two studies were performed to evaluate the movement of bromide in tilled and non-tilled soils under sprinkler versus flood irrigation. In each study, bromide was applied either with an irrigation or presprayed to the soil surface followed by periodic soil sampling to monitor the bromide movement. Tillage was observed to reduce the mean depth of chemical penetration under both irrigation treatments and reduce the spatial variation of bromide concentration under flood irrigation. For example, after 30 days of periodic flood irrigation, 25% of the applied bromide remained in the upper 0.2 m of a tilled soil while in the companion non-tilled soil virtually no bromide remained above this depth. The most rapid bromide movement was observed in non-tilled, flood irrigated soil, particularly when the solute was added with the irrigation. We speculate that the tillage effect of reduced leaching results from the alteration of pore continuity and creation of diffusional sinks and not increased evaporative water loss in the tilled soil. The Root Zone Water Quality Model was calibrated using site-specific hydraulic property measurements and used to predict the solute movement. The model predictions were fairly accurate for the sprinkler irrigated soil but less satisfactory for the flood irrigation studies. In comparing the effect on chemical leaching of the treatments imposed, we found that tillage and the timing of the chemical application had greater impact on reducing leaching than did the method of irrigation.
ABSTRACT Investigation of factors affecting leaching patterns under tilled and no-till soils are ... more ABSTRACT Investigation of factors affecting leaching patterns under tilled and no-till soils are important for successful modelling of solute leaching. There can be various other factors that may offset an anticipated tillage effect on solute leaching. A study was conducted in a Donnelly silty loam (fine-loamy, mixed frigid Typic Cryoboralf) at Dawson Creek, British Columbia, Canada, to investigate how a reactive chemical (FD&C blue#1 dye) and a conservative tracer (bromide, Br−) would leach in a no-till (NT) soil compared to a tilled (T), when high volume of water are provided discretely, at short time intervals. Three plots of 1.5 m × 1.5 m were prepared in each NT and T soil for flood irrigation. The chemicals were applied by spray using a knapsack sprayer. Soil cores were extracted from a maximum depth of 1.25 m using a truck mounted hydraulic soil sampler at 5, 19, and 55 days (S1, S2, and S3, respectively) after irrigating different amounts of water. These soil cores, sub-sampled at different depths, were analysed for water content, Br− and dye concentrations. The analyses indicated that Br− and dye moved in distinctive patterns in the two tillage systems. After irrigating with a total of 240 mm of ponded water in three applications over a period of 10 days, the centre of mass of the travel depth profiles for Br− was 0.15 m in the NT and 0.26 m in the T plots; for the dye, 0.27 m in the NT and 0.17 m in the T plots. At soil core sampling times S1, S2, and S3, the average mass recovered for Br− was 82%, 39%, and 27% in the NT and 78%, 50%, and 45% in the T plots. For the dye, mass recovery rates of 78%, 58%, and 22% were observed in the NT and 92%, 79% and 25% in the T plots. The increasing mass loss of Br− observed with increasing net water inputs in the two tillage systems was more likely due to a lateral loss with water than due to a leaching below sampling depth. The increasing mass loss of dye over time in the two tillage systems was more likely due to a high rate of degradation than to a loss through a lateral or vertical flow.
ABSTRACT,ational facilities, and other greenbelts. Turfgrass ecosys- tems provide excellent soil ... more ABSTRACT,ational facilities, and other greenbelts. Turfgrass ecosys- tems provide excellent soil erosion control, dust stabili- Soil organic C (SOC) directly affects soil quality by influencing zation, flood control, and urban heat dissipation. These aeration and water retention and serving as a major repository and reserve source of plant nutrients. Limited information is available grasslands may act as C sinks, absorbing more CO2 than concerning the long-term SOC changes in turfgrass systselection, mowing, and irrigation management. 0.83 for putting greens. Our results suggest that the CENTURY model Organic C change in soil is a slow process, and many can be used to simulate SOC changes in turfgrass systems and has the years and decades of measurements,are needed,to assess potential to compare C sequestration under various turf management C changes,as influenced,by,management,practices. conditions. Simulation results also suggest that warming temperatures Therefore, evaluation of different management options have greater degree of influence on SOC in turf systems compared with native grasslands.,relative to C sequestration is difficult to accomplish by sampling,and measuring,SOC content and C fractions over time. Simulation models,offer the opportunity,to predict long-term trends based on mathematical,repre- U nderstanding,long-term,SOC changes,in various sentations of nutrient-cycling processes in the soil–plant ecosystems,is of importance,because SOC directly systems. Predictive modeling,exercises allow significant affects soil quality by influencing the air-filled porosity insight into the ecosystem,dynamics. A number,of com- and water retention and serving as a major,repository puter models are available to evaluate SOC dynamics and reserve source of plant nutrients, especially N, P,
HortScience: a publication of the American Society for Horticultural Science
The most important worldwide problem in citrus production is the bacterial disease Huanglongbing ... more The most important worldwide problem in citrus production is the bacterial disease Huanglongbing (HLB; citrus greening) caused by a phloem-limited bacterium Candidatus Liberibacter asiaticus. The earliest visible symptoms of HLB on leaves are vein yellowing and an asymmetrical chlorosis referred to as ‘‘blotchy mottle,’’ thought to be the result of starch accumulation. We tested the hypothesis that such visible symptoms are not unique to HLB by stem girdling 2-year-old seedlings of two citrus rootstocks with and without drought stress in the greenhouse. After 31 days, girdling had little effect on shoot growth but girdling increased the relative growth rate of shoots in drought-stressed trees. Starch content in woody roots of non-girdled trees was three to 19 times higher than in girdled trees. In non-girdled trees, drought stress induced some starch accumulation in roots, but there were no effects of drought stress on root starch or sucrose in girdled trees. Girdling induced a 4-fo...
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