Runoff Initiation Time Research Articles

Evaluating the influences hedgerow on soil erosion and nitrogen loss of purple soil sloping farmland under simulated rainfall

Hedgerow is a vital soil and water conservation technology for sloping farmland that can significantly reduce erosion and nutrient loss via their above- and below-ground parts. The effect of hedgerow on erosion and nutrient loss has been widely investigated, while the respective effects of their above- and below-ground parts are still unclear. Therefore, the purple soil from the Three Gorges Reservoir Area was used, and 3 slope conditions of control check, whole hedgerow and hedgerow roots only combined with 2 slope gradients (15° and 25°) were constructed and the simulated rainfall tests were researched at 3 rainfall intensities (60, 90 and 120 mm h−1). The runoff initiation time, runoff and erosion rates, and loss of nitrogen via runoff and sediment were analysed. In comparison to the control check slope condition, it was indicated that hedgerow increased the runoff initiation time by 43.38 %, decreased runoff and erosion by 15.59 % and 78.37 %, and decreased nitrogen loss via runoff by approximately 40 % and via sediment by approximately 70 % on average, respectively. The average contribution rates of the below-ground part of the hedgerow was 49.89 % for the increase in runoff initiation time, 33.99 % for runoff reduction, and 39.91 % for erosion reduction. In addition, more than 2/3 and 58.49 % of nitrogen loss reduction via runoff and sediment, respectively, was contributed by the above-ground part of the hedgerow. These results are beneficial for comprehending the control mechanism of hedgerow on soil erosion and nitrogen loss, thereby provide a scientific foundation for the sustainable and efficient utilization of soil and water resources on sloping farmland.

Effects of rainfall and the slope gradient on the soil and water loss in a purple soil area

Soil and water losses in purple soil area is becoming an increasingly severe problem, bringing enormous challenges to environmental protection in rural areas. In this study, simulated rainfall experiments were conducted to analyse the effects of rainfall and the slope conditions on the soil and water loss. Purple soil from a typical slope in the Beibei District of Chongqing was selected as the experimental soil. Twenty rainfall scenarios with varying rainfall intensities and slope conditions were created in the simulation. The results indicate that the runoff initiation time shortened with an increased rainfall intensity and slope gradient. There was a logarithmic relationship between the effect of the rainfall amount on both the runoff intensity and sediment yield intensity. Generally, both the runoff and sediment yield showed a positive linear relationship with the rainfall intensity under different slope gradient conditions. In terms of the same rainfall intensity, both the runoff intensity and sediment yield intensity increased with the slope. Furthermore, a critical slope gradient for the soil and water loss was found between 20° and 25°. This study aimed to provide a reference for soil and water conservation research in a purple soil area.

Efficacy of earthworm casts on sediment and nitrate loss with runoff in the Chinese Loess Plateau

The erosion of sediment and nutrients under rainfall conditions aggravated the degradation of soil quality in sloping farmland. It is very important to comprehensively control the sediment and nutrient loss of sloping farmland and improve the soil fertility of barren sloping farmland caused by soil erosion to improve the plant growth environment in the Loess Plateau of China. However, there is no research to combine the control of soil, water, and nutrient loss with the improvement of soil fertility. To address this issue, earthworm casts (ECs), an excellent organic soil amendment, was applied to the soil (silty loam). Ten rainfall simulation experiments were conducted in a 1.0 m × 1.0 m plot with two application methods (mixed and layered applications) and five application amounts (i.e., 0, 200, 400, 600, and 800 g/m2), and simulated rainfall for 1 h at a rate of 60 mm/h. The main results indicated that the ECs application significantly delayed the time of runoff initiation, reduced unit discharge and sediment yield rate in the early stage. The nitrate nitrogen concentration in runoff could be significantly reduced with the layered application method. The equivalent model of convection was more suitable for simulating nutrient transfer with runoff, and the effective mixing depth decreased with increased the ECs amounts. The ECs application increased the water content and nitrate nitrogen concentration of the soil profile from a depth of 0–20 cm and provided a suitable environment for vegetation growth. Runoff decreased by 18.16–33.47%, sediment decreased by 28.17–87.24%, and nitrate nitrogen loss in runoff decreased by 36.99–51.76% with the layered application. The layered application of ECs with 800 g/m2 had the significant regulation on runoff, sediment yield, and nitrate nitrogen loss. In conclusion, ECs can effectively improve the water erosion resistance of the soil, and enhance the water holding capacity and fertilizer retention capacity of the soil. The layered application of ECs can effectively control nitrogen loss with runoff. In the long run, ECs can provide sufficient nutrient sources for plant growth, improve regional vegetation carrying capacity, and fundamentally solve the problem of soil and water loss and soil degradation of bare slope farmland in the Loess Plateau of China.

Effects of anecic earthworms on runoff and erosion on the slope with soil from the Loess Plateau under a rainfall simulation experiment

Earthworms are ecological engineers that play an important role in hydrological processes and soil erosion by their burrowing and casting activities. Little is known, however, about the ecological function of the activities of an anecic species (Metaphire guillelmi) from the Loess Plateau in China where the soil is severely eroded. We conducted rain-simulation experiments on artificial slopes (mesocosms) filled with soil from Loess Plateau. Two rain intensities (90 and 120 mm h−1) and slope gradients (5° and 15°) were used to investigate the influences of earthworm activity on runoff and soil loss under multiple conditions. Data from 15 d of earthworm activity and 1 h of rain indicated that earthworm activity significantly reduced runoff but aggravated soil erosion. Runoff initiation time increased 2.7–3.1-fold, contributing to the promotion of water infiltration, and the amounts and rates of runoff were 35.8–61.6% and 35.1–60.8% lower under earthworm activity than the controls, respectively. Earthworms greatly influenced the physical and chemical properties of the soil, and these properties were strongly correlated with runoff initiation time and cumulative runoff. The surface casts produced by the earthworms on the soil surface were completely dispersed, increasing the cumulative sediment by a maximum of 169%. Both rain intensity and slope gradient greatly influence runoff and soil detachment, but with earthworm activity, slope gradient was more influential due to its superior contribution to sediment transport. This study quantified the effects of M. guillelmi on runoff and soil erosion and provides basic data for developing a more integrated control of soil erosion on the Loess Plateau.

Erosion process of loess slope and influencing factors in the loess hilly-gully region, China

Rainfall intensity, slope length, and slope gradient are the important factors affecting runoff and sediment yield. In order to quantitatively analyze the effects of rainfall intensity, slope length, and slope gradient on the erosion process of Ansai loess slope in loess hilly and gully region, we analyzed the variation of runoff and sediment yield on Ansai loess with two slope lengths (5, 10 m), three slopes (5°, 10°, 15°) and two rainfall intensities (60, 90 mm·h-1) in an indoor simulated rainfall experiment. The results showed that the initial runoff generation time decreased with the increases of slope length, though the overall change was not significant. The initial runoff generation time decreased with the increases of rainfall intensity. Compared with the intensity of 60 mm·h-1, the initial runoff generation time decreased by 5.7-18 min under the intensity of 90 mm·h-1. Among them, the runoff initiation time on the slope of 10° was the fastest. With the duration of rainfall, runoff yield rate increased rapidly at first, and then gradually fluctuated around a certain value. The sediment yield rate increased rapidly in a short period of time at the initial stage of runoff generation, and then decreased after reaching the maximum, and being gradua-lly stable. The rates of runoff and sediment yield increased with the increases of slope length and rainfall intensity, but the law of change with slope was not obvious. With the increases of rainfall intensity, slope length and gradient, the total sediment yield increased accordingly. Under the rainfall intensity of 90 mm·h-1, the slope surface with the length of 10 m and slope of 15° generated rill, leading to the highest total erosion amount (11885.66 g). Under the rainfall intensity of 60 mm·h-1, the erosion amount per unit area decreased with the increases of slope length, and there was a critical erosion slope length in 5-10 m slope section. Slope length, slope and rainfall intensity all played a promoting role in runoff process. Rainfall intensity, slope length, and their interaction contributed more to runoff yield rate and total erosion amount. Rainfall intensity contributed the most to runoff yield rate, with a contribution rate of 49.8%. The contribution rate of slope length to the total erosion was the largest, which reached 37.8%.

Initial effect of shifting from traditional to no-tillage on runoff retention and sediment reduction under rainfall simulation

Context Low precipitation and soil erosion are critical threats to sustainable agricultural development in the north-western coastal zone of Egypt. Conservation tillage may offer a good opportunity to mitigate these threats; however, switching from traditional tillage to conservation tillage causes initial challenges such as soil compaction and erosion. Aims This study was designed in order to assess the effects of various tillage practices on soil bulk density, volumetric water content, runoff rate, runoff initiation time, soil loss, sediment yield rate and wheat (Triticum aestivum L.) yield in a cultivated basin area. Furthermore, to investigate the efficacy of various rainfall intensities in generating runoff in a micro-catchment area. Methods Under rainfall simulation, five rainfall intensities (14, 21, 30, 36, and 45 mm h−1) and three tillage practices (contour tillage, CT; traditional tillage, TT; and no tillage, NT) were investigated. Key results Under various rainfall intensities, the CT treatment significantly reduced surface runoff compared with the TT and NT treatments. For the 30 mm h−1 rainfall intensity, the CT treatment decreased sediment yield rate by 58.7% and 49.4% compared with NT and TT treatments, respectively. Furthermore, the CT treatment significantly increased precipitation use efficiency by 11.8% and 19.9% compared with TT and NT treatments, respectively. Additionally, the CT increased grain yield by 12.3% more than TT and 21% more than NT. Conclusions and implications Consequently, it is preferable to encourage farmers to use CT practices when transitioning from traditional tillage to conservation tillage. Moreover, soil compaction and smoothing may contribute to enhance the generated runoff on the micro-catchment area.

Effect of straw-incorporation into farming soil layer on surface runoff under simulated rainfall

Returning crop straw into farmland is an important application and effective soil amendment method as it can increase soil organic matter to improve soil fertility and crop yield. In addition, this practice can help retain soil moisture and slow down the rainfall runoff rate, particularly on sloping farmland. This study uses laboratory experiments with a silt loam soil to examine the effects of wheat straw incorporation into cultivated farmland soil on rainfall-runoff. The experiments involved four straw incorporation rates (0 (control), 2, 4, and 8 t/ha), three rainfall intensities (80, 120 and 160 mm/h) and three slope gradients (10, 15 and 20°), carried out by a completely randomized combination design, with three repetitions. In all the experimental runs, the total rainfall amount was 100 mm per event. Our experimental results showed that the duration of runoff initiation time at straw incorporation rates of 2, 4 and 8 t/ha were increased by 1.63% to 104.93%, 6.16% to 111.67% and 15% to 141.25%, while the total runoff amounts decreased by 11.74% to 28.81%, 24.21% to 49.67% and 38.90% to 65.93%, compared with those of our control group (0 t/ha). The effects of straw incorporation on the runoff initiation delay time and runoff reduction were significant, particularly when the rainfall intensity was 120 mm/h and the slope was 10°. With increases in rainfall intensity and slope gradient, the runoff initiation time durations were decreased and the runoff rate increased. In conclusion, incorporating wheat straw into the farmland soil can delay the runoff initiation time and reduce runoff volume, to significantly increase rainwater storage into soil, thereby increasing the rainwater utilization rate and to benefit soil erosion control. This study can provide a data basis for farmland soil and water conservation research and practice.

Contributions of runoff from paved farm roads to soil erosion in karst uplands under simulated rainfall conditions

In upland areas, paved farm roads (PFRs) change surface hydrological characteristics and may affect soil erosion. The effect of runoff from PFR (hereafter, road runoff) on soil erosion at the road shoulder edge was investigated at two rainfall intensities (50 and 75 mm/h) under laboratory conditions. Two road shoulder edges (i.e., acute angle (AA) and right angle (RA) intersections between the road shoulder and soil surface) were simulated at a 10° slope, and road runoff rates were applied of 0.4 and 0.6 m3/h, which are typical rates for a 2 m wide road under 50 and 75 mm/h rainfall intensity, respectively. A surface without road runoff served as a control (CK). The experiments showed that at the 50 mm/h rainfall intensity, no surface runoff was generated for the CK, while the mean surface runoff was 0.34 and 0.38 m3/h for RA and AA, respectively; at the 75 mm/h rainfall intensity, the mean runoff and sediment yields increased to 9–15 times that of the CK. The road runoff caused rill erosion, shortening the surface runoff initiation time and greatly increasing the sediment loss for AA and RA. Moreover, road shoulder edge patterns impacted soil erosion by influencing the confluence patterns of road runoff, surface runoff and rill development. Because the soil surface is low for AA, it promotes a more concentrated flow along the road shoulder than RA, potentially limiting lateral erosion and downward erosion during rainfall. Indeed, compared to AA, on average, the rill length for RA was 13%-28% shorter, the rill depth and width were 9%-65% greater; and the sediment yield was 26%-64% higher. Therefore, road runoff increases soil loss near the road shoulder, and it is necessary to either divert road runoff away from the shoulder or reduce flow erosivity through appropriate land management.

Study on Runoff and Infiltration for Expansive Soil Slopes in Simulated Rainfall

In order to understand the hydrological process of expansive soil slopes, simulated rainfall experiments were conducted to study the effects of slope gradient and initial soil moisture content on runoff and infiltration for expansive soil slopes located in south China. The field program consisted of four neighboring slopes (70%, 47%, 32%, and 21%) instrumented by a runoff collection system and moisture content sensors (EC-5). Results from the monitored tests indicate that there was delay in the response of surface runoff. The runoff initiation time decreased with initial soil water content and increasing slope gradient. After the generation of runoff, the cumulative runoff per unit area and the runoff rate increased linearly and logarithmically with time, respectively. The greater the initial soil moisture content was, the smaller the influence of slope gradient on runoff. A rainfall may contribute from 39% to about 100% of its total rainfall as infiltration, indicating that infiltration remained an important component of the rainwater falling on the slope, despite the high initial soil water content. The larger the initial sealing degree of slope surface was the smaller the cumulative infiltration per unit area of the slope. However, the soil moisture reaction was more obvious. The influence of inclination is no longer discernible at high initial moisture levels. The greater the initial soil moisture content and the smaller the slope gradient, the weaker was the change of soil water content caused by simulated rainfall. The influence of initial soil moisture content and slope gradient on the processes of flow and changes of soil water content identified in this study may be helpful in the surface water control for expansive soil slopes.

Fertilizer Source Affects Nutrient Losses from Hybrid Bermudagrass during Surface Runoff

Controlled-release fertilizers (CRFs) provide an extended period of nutrient availability for turfgrass growth and may limit offsite nutrient losses compared with water-soluble fertilizers (WSFs). However, increasing temperatures and soil moisture accelerate nutrient release from many CRFs. As a result, turfgrass managers growing turfgrass in warm, humid climates with high rainfall question how effective CRFs are in reducing nutrient runoff losses while maintaining aesthetic quality. A study was conducted to examine the effect of three fertilizer treatments—an unfertilized control, a CRF applied at 87 lb/acre nitrogen (N), and a WSF applied at 87 lb/acre N as a split application (43.5 lb/acre N) at 0 and 45 d after initial fertilization (DAIF)—on nutrient losses from ‘Tifway’ hybrid bermudagrass (Cynodon dactylon × C. transvaalensis) during surface runoff events. Rainfall simulations were conducted 3, 28, 56, and 84 DAIF at an intensity of 3 inches per hour to induce 30 minutes of runoff. Water samples were analyzed for inorganic N and dissolved total phosphorus (DTP). Hybrid bermudagrass quality was similar among fertilizer treatments with CRF application, resulting in slightly higher quality. Across all fertilizer treatments, hybrid bermudagrass exhibited similar runoff initiation time and volumes within each rainfall simulation event. Nutrient losses from fertilized hybrid bermudagrass were greatest at the first runoff event at 3 DAIF, with WSF having the greatest losses. The subsequent application of WSF 45 DAIF did not result in greater N and DTP losses compared with CRF application, most likely a result of water incorporation applied to prevent wilting. Hybrid bermudagrass fertilized with a single application of CRF resulted in 23.6% and 55.6% reductions in cumulative inorganic N and DTP losses, respectively, compared with hybrid bermudagrass fertilized with the a split application of WSF.

Mulching effects on erosion from steep slopes and sediment particle size distributions of gully colluvial deposits

Mulching is an effective soil conservation practice for permanent gullies in southern China. Knowledge of the sediment characteristics that occur in mulched soils of colluvial deposits could improve the utility of mulching for soil conservation. A rainfall simulation experiment was designed to evaluate the effects of mulch on the runoff, erosion, and particle size distribution of eroded sediments. Straw mulch coverage of 0, 25, 50, 75, and 95% was tested with simulated rainfall. The effective particle size distribution of the sediment was compared with the ultimate particle size distribution to investigate the detachment and transport mechanisms involved in sediment mobilization. Mulching delayed the runoff initiation time and reduced the average runoff rate. Compared with bare soil, the increased mulch coverage decreased the soil loss rate by 13.0 to 90.3%. Moreover, the peak sediment concentration decreased from 80 to 200gL−1 under the different mulch coverage conditions. The optimal straw application rate was 1.5 to 3.0Mgha−1 in the permanent gully's deposits. The relationship between instantaneous kinetic energy of rainfall and the proportion of effective clay- and sand-sized particles was well represented using an exponential equation. The effective clay-sized sediments under the different mulch coverage conditions were 2 to 4 times more common than those of the original soil, although there were only 13.9% sand-sized particles in the sediment when the mulch coverage was 95%. The silt-sized sediment was transported as primary particles under the different mulch coverage conditions. The effective to ultimate ratio of silt-sized particles fluctuated around 1. There were depletions of clay and silt in the colluvial deposit soil with mulch cover, and the enrichment ratios of clay and silt were larger than 1 while most of the enrichment ratios for sand were <1.

Effects of tillage practices and slope on runoff and erosion of soil from the Loess Plateau, China, subjected to simulated rainfall

Soil erosion, particularly during summer fallow period, in sloped farmland has been identified as a critical threat to sustainable agricultural development in the Loess Plateau of China. However, the effects of varying tillage practices during the summer fallow period have not been fully investigated. The objective of this study was to determine the effects of tillage practices on runoff and sediment loss under plot (4.0m in length and 1.0m in width) rainfall simulations. Runoff initiation time, runoff amount, sediment loss and cumulative infiltration amount were recorded. One rainfall intensity (90mmh−1, 40min), three slopes (5°, 10°, and 15°) and four prevalent tillage practices (Artificial Digging, AD; Artificial Hoeing, AH; Contour Plow, CP; and Traditional Plow, TP) were studied. Two indices, runoff reduction benefits (RRB) and sediment reduction benefits (SRB), were selected to evaluate the effect of the practice on controlling runoff and sediment. Compared to TP treatment, the AD, AH and CP were more effective in reducing the magnitude of runoff amount and sediment loss as well as increasing the rain water infiltration amount. CP with a 15° slope was an exception in which the sediment loss increased. In general, the SRB was greater than the RRB for a given tillage practice under the same slope, suggesting that the benefits from sediment reduction were more effective than the benefits from runoff reduction. RRB and SRB were the largest for AD, followed by AH and CP, irrespective of slopes. The capacity of the three tillage practices to reduce runoff and sediment decreased as the slope increased. In particular, AD at a 5° slope had the best performance in reducing runoff and sediment loss; however, SRB and RRB were −57% and 1%, respectively, for a CP plot with a 15° slope. This finding suggested that CP had a higher sediment loss and a similar runoff amount compared to those of TP. These results of plot simulated rainfall will contribute to our knowledge about the effects of different tillage practices on soil erosion from sloped farmland.

Measurements of the initiation of post‐wildfire runoff during rainstorms using in situ overland flow detectors

AbstractOverland flow detectors (OFDs) were deployed in 2012 on a hillslope burned by the 2010 Fourmile Canyon fire near Boulder, Colorado, USA. These detectors were simple, electrical resistor‐type instruments that output a voltage (0–2·5 V) and were designed to measure and record the time of runoff initiation, a signal proportional to water depth, and the runoff hydrograph during natural convective rainstorms.Initiation of runoff was found to be spatially complex and began at different times in different locations on the hillslope. Runoff started first at upstream detectors 56% of the time, at the mid‐stream detectors 6%, and at the downstream detectors 38% of the time. Initiation of post‐wildfire runoff depended on the time‐to‐ponding, travel time between points, and the time to fill surface depression storage. These times ranged from 0·5–54, 0·4–1·1, and 0·2–14 minutes, respectively, indicating the importance of the ponding process in controlling the initiation of runoff at this site. Time‐to‐ponding was modeled as a function of the rainfall acceleration (i.e. the rate of change of rainfall intensity) and either the cumulative rainfall at the start of runoff or the soil–water deficit.Measurements made by the OFDs provided physical insight into the spatial and temporal initiation of post‐wildfire runoff during unsteady flow in response to time varying natural rainfall. They also provided data that can be telemetered and used to determine critical input parameters for hydrologic rainfall–runoff models. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Assessment of Soil Degradation Due to Compaction Resulting From Cattle Grazing Using Infiltration Parameters

The most essential effect of grazing is soil compaction due to animal traffic. The study was conducted to investigate the role of cattle grazing in soil degradation resulting from compaction using infiltration parameters at the Beef and Dairy Cattle Research Station of the Department of Animal Science of the Faculty of Agriculture, KNUST. Two fields, ungrazed and grazed (with a stocking rate of 120 cattle for three weeks) were used for the study. Physical properties such as soil texture, moisture content, bulk density, total porosity and aeration were determined. Field infiltration studies from which sorptivity (S) and steady state infiltrability (Ko) were determined were conducted with a double ring infiltrometer for one hour to determine the cumulative infiltration amount (I). The time-to-incipient ponding or runoff initiation time (tp) was calculated from the S and Ko values. Mean values of I were 1490 mm and 500 mm; S 2.72 mm/s 1/2 and 1.030 mm/s 1/2 ; Ko, 0.060 mm/s and 0.0080 mm/s for the ungrazed and grazed fields, respectively. The tp at a rainfall rate of 5 mm/h was recorded as 79.00 s on the grazed field and 419.00 s for the ungrazed field. It was observed that rainfall rates in excess of 10 mm/h would cause instantaneous ponding and/or runoff on both fields. Grazing by cattle was, thus, established to be deleterious to soil structure and infiltration due to soil compaction. Overall, infiltration parameters were found to be very useful tools for the evaluation of soil degradation due to compaction.

Soil surface roughness change and its effect on runoff and erosion on the Loess Plateau of China

As an important parameter in the soil erosion model, soil surface roughness (SSR) is used to quantitatively describe the micro-relief on agricultural land. SSR has been extensively studied both experimentally and theoretically; however, no studies have focused on understanding SSR on the Loess Plateau of China. This study investigated changes in SSR for three different tillage practices on the Loess Plateau of China and the effects of SSR on runoff and erosion yield during simulated rainfall. The tillage practices used were zero tillage (ZT), shallow hoeing (SH) and contour ploughing (CP). Two rainfall intensities were applied, and three stages of water erosion processes (splash erosion (I), sheet erosion (II) and rill erosion (III)) were analyzed for each rainfall intensity. The chain method was used to measure changes in SSR both initially and after each stage of rainfall. A splash board was used to measure the splash erosion at stage I. Runoff and sediment data were collected continuously at 2-min intervals during rainfall erosion stages II and III. We found that SSR of the tilled surfaces ranged from 1.0% to 21.9% under the three tillage practices, and the order of the initial SSR for the three treatments was ZT<SH<CP. For the ZT treatment, SSR increased slightly from stage I to III, whereas for the SH and CP treatments, SSR decreased by 44.5% and 61.5% after the three water erosion stages, respectively, and the greatest reduction in SSR occurred in stage I. Regression analysis showed that the changes in SSR with increasing cumulative rainfall could be described by a power function (R 2>0.49) for the ZT, SH and CP treatments. The runoff initiation time was longer in the SH and CP treatments than in the ZT treatment. There were no significant differences in the total runoff yields among the ZT, SH and CP treatments. Sediment loss was significantly smaller (P<0.05) in the SH and CP treatments than in the ZT treatment.

Water, sediment, and nutrient runoff from urban lawns established on disturbed subsoil or topsoil and managed with inorganic or organic fertilizers

Urban runoff has become an increasingly important environmental concern in recent years. With increasing urbanization, turfgrass area has substantially expanded in North America, and these lawns are often established on subsoil stripped of topsoil. In this study, 24 turfgrass-type tall fescue (Festuca arundinacea) plots were established on subsoil or topsoil, and managed with inorganic fertilizer (Scott’s Turf Builder®), organic fertilizer (Nature’s Touch® with enzymes), or no fertilizer (control). A one-hour simulated rainfall at 8.9 cm/hour was applied to the plots, and the time to runoff initiation and total runoff volume were measured. Runoff water samples were analyzed to quantify the amounts of sediment, N (NH4-N), P, K, and S losses. The results indicated that runoff initiation time was almost half in subsoil lawns (12.5 min) than in topsoil lawns (23 min). The total runoff volume and sediment loss were significantly larger in subsoil lawns (11,900 ml and 3,700 mg, respectively) than in topsoil lawns (2,200 ml and 900 mg, respectively). Although the N, P, K, and S losses in runoff were low, they were significantly higher from the subsoil-based than topsoil-based lawns, and were higher from inorganic fertilizer treated lawns than those treated with organic fertilizer. These results highlight the significance of topsoil preservation in city planning and urban development with respect to urban run-off and water quality and show distinct benefits of organic lawn management practices over the conventional inorganic practices for maintaining urban water quality.

TILLAGE AND RESIDUE EFFECTS ON RUNOFF AND EROSION DYNAMICS

The carry-over effects from one year to the next of surface residue and tillage management decisions on runoff and erosion are not clear. The dynamics of runoff and erosion processes during rainfall events are likely dependent on the tillage and residue management system. The objective of this study was to elucidate the effects of tillage practices and residue management, by removal of residue cover, on the properties that describe the dynamics of the runoff and erosion processes. Six-row, 12.2 m long . 5.5 m wide, plots under conventional tillage (CT) or no tillage (NT) corn (Zea mays L.) for nine years were used in this study. Plots had an average slope of 5.7% on a Grenada silt loam (Glossic Fragiudalf) soil. Rainfall simulations were conducted on a 10.7 m . 3.7 m area within each plot at a rate of 65 mm h -1 for 1 h under natural antecedent soil-water conditions (dry run), followed by a 0.5 h simulation 4 h later (wet run), and another 0.5 h application 30 min later (very wet run). The ten treatments consisted of an incomplete 2 . 2 . 3 factorial arrangement of two tillage histories (CTh and NTh), two tillage levels (tilled and not tilled), and three residue management levels (residue left, residue removed just prior to simulated rainfall, and residue removed one year prior to simulated rainfall). The missing treatments were the NTh-tilled and CTh-not tilled with residue left. The time of runoff initiation, maximum runoff rate, flow velocity, and maximum sediment concentration were used to describe differences in runoff and erosion dynamics. Residue removal resulted in significantly sooner runoff with the NT system. There was a significant carry-over effect of residue removal with runoff initiated 35% sooner the subsequent year of removal and sediment concentrations increasing by >100%. Maximum sediment concentrations were lower for the CTh land that was not tilled than for the tilled despite the untilled land experiencing sooner runoff and higher runoff rates. Tilling NTh land resulted in significantly lower sediment concentrations than tilling CTh land, suggesting that the soil quality of NT was not immediately lost when tilled, but these beneficial properties were fully lost within one year of residue removal.

Hydrologic Impacts of Disturbed Lands Treated with Dust Suppressants

This study presents research on changes in hydrologic characteristics of disturbed land surfaces that have been treated with dust suppressants. Disturbed land surfaces, such as construction sites and unpaved roads, are sources of fine particulate matter. The application of dust suppressants affects the runoff characteristics as well as the water quality of the runoff. The changes in runoff characteristics were investigated in the field using a rainfall simulator on plots treated with 11 different dust suppressants. The rainfall simulation system was able to provide a uniform distribution of rainfall over a 2.4×2.4 m (approximately) plot at relatively low rainfall intensities (21 mm/h). Results of the study indicate changes in runoff rates and volume, and the timing of runoff initiation. The majority of the plots had higher runoff volumes and an earlier time of runoff initiation as compared to the control plot. The total suspended solids in the runoff were reduced for the majority of the plots. Extrapolati...

Effects of pulp fibre on soil physical properties and soil erosion under simulated rainfall

Pulp fibre, a primary type of sludge of pulp and paper mills containing approximately 40% organic C, is usually disposed of in landfills causing a potential environmental problem. This material may be used as a soil amendment to restore the productivity of organic-matter-depleted potato-producing soils in Atlantic Canada. The effect of incorporating this material at rates equivalent to 0.5, 1.0, 2.0, and 4.0% organic matter in the plow layer of a gravelly loam soil on selected soil physical properties and soil erosion was evaluated. The objectives were to determine the effect of pulp fibre additions on selected soil properties, which are pertinent to water retention and movement and to evaluate its effectiveness in reducing runoff and soil loss, major contributing processes to soil degradation . Chemical analysis of pulp fibre revealed that all heavy metal concentrations were well below allowable concentrations for Category A compost. One year after incorporation, bulk density of the Ap horizon had decreased with increasing rates of organic matter addition. On the other hand, the saturated hydraulic conductivity and specific moisture content increased with increasing rates of treatments. Results on water-stable aggregates revealed that the organic matter in the pulp fibre combined smaller aggregates to form larger aggregates, resulting in a larger proportion of macropores as compared to micropores. In the 4% organic matter treatment, a 27% increase was found in the 1.0 to 5.0 mm-diameter aggregates whereas a 23% reduction was found in aggregates smaller than 1.0 mm diameter. In spite of the higher specific moisture content of the organic-matter-treated soils, soil moisture content measured immediately prior to the erosion test indicated that field soil moisture contents were lower than those of the control. Time of runoff initiation, rates of runoff and soil loss were greatly improved with the amendments. The beneficial effects of the 4% organic matter treatment include 2.1 times delay in runoff initiation, and 23 and 71% reduction in runoff and soil loss, respectively. Although the beneficial effects in soil and water conservation are apparent, a minor drawback appears to be lower field soil moisture content. Large-scale implementation of the addition of this material in potato fields should proceed only with caution. Key words: Saturated hydraulic conductivity, moisture retention, water stable aggregate, mean weight diameter, sediment yield, soil amendment

Herbicides in surface runoff: A rainfall simulation study on small plots in the field

The transport of the herbicides isoproturon, dichlorprop-p, and bifenox via surface runoff was investigated on small field plots with simulated rainfall at an intensity of about 70 mm/h. Isoproturon and dichlorprop-p, with water solubilities of 65 and 700 mg/l respectively, were transported mainly in the runoff water phase. Their runoff concentrations primarily depended on the preceding cumulative rainfall. Concentrations of runoff water and sediment decreased with increasing cumulative rainfall according to a power function. Total isoproturon and dichlorprop-p losses in runoff mainly depended on the time of runoff initiation as well as on total runoff and soil loss. Factors like soil type, vegetation, slope, or rainfall intensity affected total herbicide losses by influencing the time of runoff initiation as well as total water and soil losses. In most cases isoproturon losses were higher than losses of dichlorprop-p. Interflow resulted in increased herbicide concentrations in the runoff water. The increase was more pronounced for dichlorprop-p than for isoproturon. Bifenox, with a water solubility < 1 mg/l, was strongly adsorbed to the eroded sediment and moved of the plot almost exclusively in the sediment phase. Its concentration in the sediment mainly depended on the amount of preceding soil loss. For all runoff experiments the bifenox concentrations in the sediment of the first runoff litres were similar. The time of runoff initiation did not influence the bifenox concentration.