Showing papers by "Donald Gabriëls published in 2009"

Changes of soil enzyme activities under different tillage practices in the Chinese Loess Plateau

Abstract: The effects of middle term (7 years) consistent tillage practices on the catalase (CAT), urease (URE) and invertase (INV) activities were investigated during the whole winter wheat growing period on a loess soil in Luoyang (east edge of the Chinese Loess Plateau, Henan province, China). Field plots, set up in 1999, included following tillage practices: subsoiling with mulch (SS), no-till with mulch (NT), reduced tillage (RT), and a conventional control (CT). A clear redistribution of soil organic carbon (SOC) and total nitrogen (TN) was found along the slope in RT and CT, however, no difference was observed between studied enzyme activities along different slope positions. SS had higher winter wheat yield than other treatments, which was attributed to the increased soil water content and improvement of soil fertility. Changes in soil temperature and soil moisture content influenced the magnitude of the enzyme activities, but not the ranking of the different treatments during most of the season. SS consistently had higher enzyme activities compared to other treatments. This indicated that seasonal fluctuations did not obscure effects associated with soil tillage practices and enzyme activities could reflect the effects of conversion of soil tillage practices on soil quality. Time within the growing season had a clear impact upon the enzyme activities. Comparatively higher enzyme activities were observed in the stages with vigorous vegetative growth of winter wheat than in stages with productive growth.

Residue cover and rainfall intensity effects on runoff soil organic carbon losses

Abstract: Soil cover and rainfall intensity ( RI ) are recognized to have severe impacts on soil erosion and an interaction exists between them. This study investigates the effect of rainfall intensity ( RI ) and soil surface cover on losses of sediment and the selective enrichment of soil organic carbon (SOC) in the sediment by surface runoff. A field rainfall simulator was used in the laboratory to produce 90 min rainfall events of three rainfall intensities (65, 85 and 105 mm h − 1 ) and four cover percentages (0%, 25%, 50% and 75%) on soil material at 9% slope. A strong negative exponential relation was observed between cover percentage and RI on sediment loss under 85 and 105 mm h − 1 of rain, while under RI of 65 mm h − 1 , the highest sediment loss was observed under 25% cover. Overall, higher RI and lower cover produced higher sediment and consequently higher nutrient loss, but resulted in a lower SOC enrichment ratio (ER SOC ) in the sediment. The amount of runoff sediment rather than the ER SOC in the sediment was the determinant factor for the amount of nutrients lost. The values of ER SOC were high and positively correlated with the ER values of particles smaller than 20 µm ( p

Modelling water-harvesting systems in the arid south of Tunisia using SWAT

Abstract: . 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 watershed model SWAT (Soil Water Assessment Tool) for simulating the main hydrologic processes in arid environments. The model was applied to the 270-km2 watershed of wadi Koutine in southeast Tunisia, which receives about 200 mm annual 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 performed based on 38 runoff events recorded at the Koutine station between 1973 and 1985. The model predicted that the average annual watershed rainfall of the 12-year evaluation period (209 mm) was split into ET (72%), groundwater recharge (22%) and outflow (6%). The evaluation coefficients for calibration and validation were, respectively, R2 (coefficient of determination) 0.77 and 0.44; E (Nash-Sutcliffe coefficient) 0.73 and 0.43; and MAE (Mean Absolute Error) 2.6 mm and 3.0 mm, indicating that the model could reproduce the observed events reasonably well. However, the runoff record was dominated by two extreme events, which had a strong effect on the evaluation criteria. Discrepancies remained mainly due to uncertainties in the observed daily rainfall and runoff data. Recommendations for future research include the installation of additional rainfall and runoff gauges with continuous data logging and the collection of more field data to represent the soils and land use. In addition, crop growth and yield monitoring is needed for a proper evaluation of crop production, to allow an economic assessment of the different water uses in the watershed.

Aggregate Stability and Erosion Response to Antecedent Water Content of a Loess Soil

Abstract: Soil erosion processes are affected by the erodibility of the soil and by the erosivity of the rain. The effects of rain characteristics and invariant soil properties such as texture and organic matter content on soil erosion processes are well documented. However, the effect of antecedent soil-water content (θa) on aggregate breakdown, seal formation and subsequent soil erosion is much more disputable as opposing effects have been reported. We conducted lab experiments with a rainfall simulator on a Belgian silt loam soil. The objectives were to determine the effect of θa on seal formation, runoff and soil loss and to evaluate its effect on an empirical sediment transport equation. Air-dried soil aggregates were subjected to antecedent soil-water contents of 0.04 (air-dry aggregates), 0.12 and 0.19 m3 m-3. No runoff occurred on the soils with highest antecedent soil-water content, highest total runoff values were observed for the intermediate θa, while intermediate amounts of total runoff were noticed for the air-dry aggregates. Soil loss, however, showed a different trend: highest values were found for the lowest θa, intermediate values for the intermediate θa and no soil loss for the highest θa. We further observed that θa had no influence on the final runoff rates and on the final infiltration rate through the soil surface. In using a water discharge and stream power equation to predict sediment transport, the intercept and exponent of the regression equations were found to be lower for θa of 0.19 m3 m-3 compared to θa of 0.12 m3 m-3, indicating a decreasing erodibility with increasing θa. We therefore suggest including θa as an additional variable to assess soil erodibility in deterministic event-based water erosion models.

Effects on pesticide spray drift of the physicochemical properties of the spray liquid

Abstract: This research was on the effect of the physicochemical properties of the spray liquid on pesticide spray drift. Ten pesticide spray liquids with various physicochemical properties were selected for study. Some of these spray liquids were also examined with the addition of a polymer drift-retardant. In the first part, laboratory tests were performed to measure surface tension, viscosity, evaporation rate and density of the spray liquids. Subsequently, drift experiments were performed in a wind tunnel. From the results it was found that the dynamic surface tension is a major drift-determining factor, and also that the addition of a polymer drift-retardant can reduce drift significantly by increasing the viscosity. Drift reduction was found to be less effective with spray liquids of emulsifiable and suspendable formulation types than with spray liquids of water-dispersible granules and powders.

Hydraulic Conductivity as Influenced by Stoniness in Degraded Drylands of Chile

Abstract: Infiltration measurements in and, stony soils are notoriously variable in visually homogeneous areas, and have been reported to be influenced by embedded stone fragments. This Study aimed to identify the influence of rock fragment contents, orientation, and position within a small and watershed on hydraulic conductivity in northern Chile. Two different measurement techniques were used, a single-ring infiltrometer with constant ponding head and a tension infiltrometer, which were applied at both an undisturbed field site (44 locations along three transects) and on the disturbed < 2-mm soil fraction from the same locations. Variations in saturated and unsaturated hydraulic conductivities were observed when using different calculation methods, adding to the observed variability For saturated conditions, only small differences in conductivities were observed between two calculation methods, whereas unsaturated hydraulic conductivities calculated by five different methods showed more important variations. Stone fragment content correlated significantly with both saturated and unsaturated conductivities, probably due to a positive correlation between stone content and coarse lacunar pore space. Slope orientations with higher amounts of stone fragments gave higher infiltration rates, as well as transects with steeper slopes and more, but smaller, rock fragments. When evaluating differences in infiltration rates observed along three transects in the watershed, variability could be mainly attributed to stone fragment content influences.

On the influence of coarse fragments on soil water retention

Abstract: [1] The classical determination of the soil water retention curve (SWRC) by measuring soil water content θ at different matric potentials ψ using undisturbed soil samples is time consuming and expensive. Furthermore, undisturbed soil sampling can be an intricate task when coarse soil fragments (>2 mm) are present. The objective of this study was to test whether tension infiltrometry could be used to estimate the SWRC of stony soils and to investigate to what extent the coarse fragments affected the SWRC. Tension infiltrometer measurements were conducted at 44 sites with stony soils in arid Chile. Soil water retention curves obtained through inverse modeling were compared with laboratory-determined water retention (θ, ψ) data pairs. Differences were found to be small, confirming the applicability of the inverse modeling method. Rock fragments had a significant indirect influence on water retention for matric potentials higher than −0.30 kPa, which could be attributed to their direct influence on pore size distribution.

The effect of reduced tillage agriculture on carbon dynamics in silt loam soils

Abstract: Reduced tillage (RT) agriculture is an effective measure to reduce soil loss from soils susceptible to erosion in the short-term and is claimed to increase the soil organic carbon (SOC) stock. The change in distribution and total SOC stock in the 0–60 cm layer, the stratification of microbial biomass carbon (MB-C) content in the 0–40 cm layer and the carbon (C) mineralization in the upper 0–5 cm layer in silt loam soils in Western Europe with different periods of RT agriculture were evaluated. Ten fields at seven locations, representing the important RT types and maintained for a different number of years, and eight fields under conventional tillage (CT) agriculture with similar soil type and crop rotation were selected. RT agriculture resulted in a higher stratification of SOC in the soil profile than CT agriculture. However, the total SOC stock in the 0–60 cm layer was not changed, even after 20 of years RT agriculture. The MB-C was significantly higher in the 0–10 cm layer under RT agriculture, even after only 5 years, compared to CT agriculture. The higher SOC and MB-C content in the upper 0–5 cm layer of RT fields resulted in a higher C mineralization rate in undisturbed soil in the laboratory. Simulating ploughing by disturbing the soil resulted in inconsistent changes (both lower and higher) of C mineralization rates. A crop rotation with root crops, with heavy soil disturbance every 2 or 3 years at harvest, possibly limited the anticipated positive effect of RT agriculture in our research.

Using an inverse modelling approach to evaluate the water retention in a simple water harvesting technique.

Abstract: . 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. Nevertheless, few efforts were observed to quantify the water harvesting processes of these techniques and to evaluate their efficiency. In this study, a combination of detailed field measurements and modelling with the HYDRUS-2D software package was used to visualize the effect of an infiltration trench on the soil water content of a bare slope in northern Chile. Rainfall simulations were combined with high spatial and temporal resolution water content monitoring in order to construct a useful dataset for inverse modelling purposes. Initial estimates of model parameters were provided by detailed infiltration and soil water retention measurements. Four different measurement techniques were used to determine the saturated hydraulic conductivity (Ksat) independently. The tension infiltrometer measurements proved a good estimator of the Ksat value and a proxy for those measured under simulated rainfall, whereas the pressure and constant head well infiltrometer measurements showed larger variability. Six different parameter optimization functions were tested as a combination of soil-water content, water retention and cumulative infiltration data. Infiltration data alone proved insufficient to obtain high model accuracy, due to large scatter on the data set, and water content data were needed to obtain optimized effective parameter sets with small confidence intervals. Correlation between the observed soil water content and the simulated values was as high as R2=0.93 for ten selected observation points used in the model calibration phase, with overall correlation for the 22 observation points equal to 0.85. The model results indicate that the infiltration trench has a significant effect on soil-water storage, especially at the base of the trench.

Effects of different soil management practices on total P and Olsen-P sediment loss: A field rainfall simulation study

Abstract: Field rainfall simulations were conducted in 2002 and 2005 to study the effects of different soil management practices on the total phosphorous (TP) and Olsen-P losses by soil erosion and redistribution along a 15 m long slope in Luoyang, Henan province, China. Field plots were set up in 2001 and included the following soil management practices: subsoiling with mulch (SSM), no-till with mulch (NTM), reduced tillage (RT), and a conventional tillage control (CT). The results showed that there were no significant differences in TP and Olsen-P content in the sediment load between different plots after 6 years uniform tillage practices. The enrichment of TP and Olsen-P at the lower slope showed a clear redistribution along the slope. Effects of tillage practices on the temporal pattern of the enrichment ratio (ER) of TP and Olsen-P was not uniform. ERTP values were initially high and diminished after a short period of time and leveled to the end of the rainfall test in CT and RT plots, but remained ≥ 1. The ER of Olsen-P at the end of rainfall simulation showed a significant difference when compared to the initial stage, 0.78 to 1.60, respectively. However, the temporal loss rate of TP and Olsen-P showed a similar pattern because it was more depending on the sediment loss rate than on the concentration in the sediment. SSM resulted in 96% less TP and Olsen-P erosion loss compared to CT in 2002. Also, SSM showed the highest reduction in TP and Olsen-P loss after 4 years consistent practice. RT reduced TP and Olsen-P loss by 30%, although the runoff reduction was not significant. NTM was the best alternative with respect to TP and Olsen-P conservation, when considering its lower operational costs.

Average sand particle trajectory examined by the Raindrop Detachment and Wind‐driven Transport (RD‐WDT) process

Abstract: Recent studies of soil loss by the integrated action of raindrop impact and wind transport have demonstrated the significance of this mechanism. This paper presents data obtained during wind-tunnel experiments examining the ‘Raindrop Detachment and Wind-driven Transport’ (RD-WDT) process to investigate average sand particle trajectory and the spatial extent at which the process operates. In the experimental design, at the same time as the horizontal wind velocities of 6·4, 10, and 12 m s–1 passed through the tunnel, rainfall was simulated falling on very well sorted dune sand. The aspect and slope of the sand bed was varied to reproduce both windward (Ww) and leeward (Lw) slopes of 4o and 9o with respect to the prevailing wind direction. The average sand particle trajectories by the RD-WDT process () were estimated by a mass-distribution function, which was integrated over a 7-m uniform slope segment. The results showed that depended statistically upon the wind shear velocity (u*), and the effect of the slope gradient (θ) was insignificant on . This was different from that of the windless rain process (), ‘Raindrop Detachment and Splash-driven Transport’ (RD-ST), the spatial range of which relies strongly on θ. Additionally, was approximately 2·27 ± 2·2 times greater than the average path of a typical saltating sand particle of the rainless wind (), ‘Wind Erosion Saltation Transport’ (WE-ST). Copyright © 2009 John Wiley & Sons, Ltd.