Field Rainfall Simulation Research Articles

Experimental Study on Slope Runoff, Erosion and Sediment under Different Vegetation Types

The relationships between precipitation, vegetation and erosion are important yet unresolved issues in the field of earth surface processes. Vegetation plays an important role in controlling soil erosion. Through field simulated rainfall experiments, we analyzed the characteristics, regulation of, and correlation among the slope rainfall-infiltration-runoff, erosion and sediment under different vegetation types. The results showed that the forest effectively improved soil structure, had stronger runoff and sediment regulation and was influenced less by rainfall intensity than those under other vegetative conditions. In addition, the efficiency and pattern of the regulation of runoff and sediment varied with vegetation types as did the mechanism of action. The soil and water conservation function of forest was water storage and sediment reduction by plant root systems to reduce erosion power, increase infiltration, decrease runoff and reduce flow speed. The function of grassland was direct sediment interception based on surface vegetation canopy for runoff and sediment regulation. The root contribution to runoff and sediment reduction was relatively greater than the shoot contribution under forest conditions, whereas, the effect of shoots and roots on soil loss was almost equivalent under grassland conditions. The different spatial structures of vegetation affected runoff and sediment regulation in different ways, and plant root systems were crucial for soil and water conservation. The cumulative sediment yield of the slopes increased as a statistically significant power function of cumulative runoff. The coefficient and curve shape of function were dependent on vegetation type, soil properties, rainfall intensity and surface roughness. The process of slope runoff and sediment was divided into development, active and stable stages. These stages correlated with each other to constitute a complete rainfall-runoff and erosion-sediment process, which exhibited their own features at each stage. This study furthers understanding of the relationships between vegetation, soil erosion and precipitation.

Using queuing theory to describe steady‐state runoff‐runon phenomena and connectivity under spatially variable conditions

Runoff‐runon occurs when spatially variable infiltration capacities result in runoff generated in one location potentially infiltrating downslope in an area with higher infiltration capacity. The runoff‐runon process is invoked to explain field observations of runoff ratios that decline with plot length and steady‐state infiltration rates that increase gradually with rainfall intensity. To illustrate the influence of spatial variability and runoff‐runon on net infiltration and runoff generation, we use both (i) field rainfall simulation on soil with a high infiltration capacity and (ii) numerical rainfall‐runoff‐runon simulations over a spatially variable area. Numerical simulations have shown that the spatial variability of soil infiltration properties affects surface runoff generation; however, it has proven difficult to represent analytically the associated runoff‐runon process. We argue that given some simplifying assumptions, the runoff‐runon phenomenon can be represented by queuing theory, well known in the literature on stochastic processes. Using this approach we report simple analytic expressions derived from the queuing literature that quantify the total runoff under steady‐state conditions from a spatially variable tilted 2‐D plane, and the runoff produced by the area connected with the lower boundary of the plane under these conditions. These quantities are shown to be equal to the waiting time and the “sampled” busy period, respectively, of a first‐in first‐out queue with exponentially distributed arrivals and service times. The queuing theory model is shown to be consistent with field observations of runoff; however, the approach requires some simplifying assumptions and restrictions that may negate the benefits of the reported analytic solutions.

Modeling Interrill Erosion on Unpaved Roads in the Loess Plateau of China

AbstractUnpaved roads play an important role in soil loss in small watersheds. In order to assess the impact of these unpaved roads in the Loess Plateau of China, runoff and sediment yields from road‐related sources must be quantified. Field rainfall simulation experiments were conducted under three slope gradients and five rainfall intensities on unpaved loess roads in a small watershed. Results showed that the runoff generation was very fast in loess road surface (time to runoff < 1 min) and produced a high runoff coefficient (mean value > 0·8). Soil loss rates were decreased as surface loose materials were washed away during a rainstorm. Rainfall intensity, initial soil moisture, and slope gradient are key factors to model surface runoff and sediment yield. Soil loss on loess road surface could be estimated by a linear function of stream power (R2 = 0·907). Four commonly interrill erosion models were evaluated and compared, and the interrill erodibility adopted in the Water Erosion Prediction Project model was determined as 1·34 × 106 (kg s m−4). A new equation taking into account different parameters like rainfall intensity, surface flow discharge, and slope gradient was established. Copyright © 2013 John Wiley & Sons, Ltd.

Sewer Lateral Electro Scan Field Verification Pilot

This research effort evaluated an innovative sewer lateral condition assessment tool in unique testing conditions, providing an opportunity for comparison to other traditional assessment approaches. This study field tested over 100 sanitary sewer lateral pipes for potential infiltration-generating defects using the Electro Scan ES-38TM technology according to ASTM F2550-006. Results of these inspections were compared to the results of other infiltration data produced in rainfall simulation tests of the same laterals and water exfiltration tests of each scanned pipe. The Electro Scan ES-38TM measurements were also compared to closed-circuit television (CCTV) inspection of laterals according to NASSCO Pipeline Assessment Certification Program (PACP) standards. Statistical comparisons of Electro Scan ES-38TM assessments to estimated leakage rates, from a field rainfall simulation test, were performed to determine the best means of correlating the two data sets. The research effort was used to test the Electro Scan approach against the dye water/rainfall simulation testing techniques that the City of Wauwatosa (Wauwatosa) has already used to derive convincing condition information in general and on specific properties within the proposed testing area. Prior to this research effort, Electro Scan technology had only been tested side-by-side against CCTV inspection information. The objectives of this proposed research effort were as follows: Test Electro Scan ES-38TM in the two pilot lateral rehabilitation project areas; 1. Compare Electro Scan ES-38TM results to pre-rehabilitation condition dye water/rainfall simulation tests; 2. Compare Electro Scan ES-38TM results to CCTV inspection results; 3. Perform water exfiltration tests and compare results to Electro Scan ES-38TM results; 4. Evaluate the feasibility of performing Electro Scan ES-38TM tests from basement cleanouts; and 5. Establish pros and cons of Electro Scan ES-38TM lateral condition evaluations, including estimated costs. This title belongs to WERF Research Report Series . ISBN: 9781780405063 (eBook)

Soil organic carbon mobilization by interrill erosion: Insights from size fractions

AbstractSediments mobilized by interrill erosion are often highly enriched in soil organic carbon (SOC) in comparison to source soils. This selectivity may lead to the preferential mobilization of SOC with specific properties, e.g., SOC that is especially susceptible to decomposition. This may then have important implications with respect to the role of soil erosion in the global carbon cycle. We addressed this issue by investigating the behavior of different SOC components in field rainfall simulation experiments on arable fields in loess‐derived soils. We characterized the mobilization of mineral‐bound organic carbon (MOC) and particulate organic carbon (POC) by interrill erosion using size fractionation and we used the C:N ratio as a tracer variable to determine the composition of the SOC in eroded sediments. MOC was found to be preferentially mobilized by interrill erosion in comparison to POC. The enrichment ratio (i.e., the ratio of the concentration of a soil constituent in the eroded sediment to its concentration in the original soil) of MOC decreased with increasing sediment concentration. The enrichment ratio of POC displayed a similar pattern to that of MOC but enrichment was less pronounced. Furthermore, sediments were found to be enriched in fine POC while they were impoverished with respect to coarse POC. The selective MOC mobilization together with the dominance of MOC in the total SOC pool in the soil explained the dominance of MOC in interrill eroded sediment. The fact that it is mainly MOC that is mobilized by interrill erosion implies that the SOC in the interrill eroded sediments is on average at least as recalcitrant than that in the source soils which may have important implications for the fate of the mobilized SOC. In order to understand the role of soil erosion in C cycling, MOC and POC need to be considered separately not only because they are chemically different but also because of their different behaviors with respect to geomorphic processes.

Characteristics of runoff and sediment generation of forest vegetation on a hill slope by use of artificial rainfall apparatus

We studied the impact of forest vegetation on soil erosion, surface runoff, and sediment generation by using field simulated rainfall apparatus. We measured runoff and sediment generation of five 4.5 × 2.1 m runoff plots (a bare soil as a control; two Pinus tabulaeformis forest plots and two Platycladus orientalis forest with row spacing of 1 m × 1 m and 1.5 m × 1.5 m, respectively) in Beijing Jiu Feng National Forest Park under three rainfall intensities (0.42, 0.83, 1.26 mm per minute). Forest vegetation significantly reduced soil erosion and sediment yield. Mean total runoff volume in the four tree stand plots was 93% of that in the control plot, demonstrating the limited effectiveness of forest vegetation in runoff control. With increasing rainfall intensity, runoff reduction in forest plots declined from 28.32% to 2.1%. Similar trends in runoff coefficient and the relationship between runoff volume and rainfall duration was observed. Mean total sediment yield and mean sediment yield reduction rate under different treatments was 55.05% and 43.17% of those in the bare soil control plot, respectively. Rainfall intensity played an important role in runoff and sediment generation processes, and had a greater impact on runoff than on soil erosion and sediment generation. When considering several factors in runoff and sediment transport processes, the P. tabulaeform plot with row spacing at 1 × 1 m had a greater effect on soil and water conservation than did other forested plots.

Rainfall simulator for field runoff studies

Summary Rain simulators (RSs) are used in soil crusting and soil erosion laboratory and field studies. The energy flux produced by RSs is usually high in respect to the intensity of the application. The high energy flux applied on the soil surface by these RSs becomes a crucial disadvantage when low intensity rainfall is considered. Moreover, crust formation under natural field conditions is very different from crusting in disturbed soil samples. The main purpose of this study was the design and the construction of a portable RS to be used in the field for simulating rainfalls that induce soil crusting and thus lead to the generation of runoff and eventually soil erosion. A high accuracy portable RS for field rainfall simulations was designed and built. The D50 of the drops is 1.5 mm with a ground hitting velocity that nearly matches the theoretical terminal velocity without the necessity of a tower ( Barros et al., 2008 ). The energy flux of the simulated rain is 76% of the energy flux expected for a natural rainfall of the same intensity. The spatial distribution of water is homogenous for a wide range of rain intensities. This RS can be a powerful tool for field infiltration, soil crusting and soil erosion field trials.

Influencia de las propiedades edáficas y la posición en el paisaje sobre la respuesta hidrológica de suelos pertenecientes a una cuenca de la Pampa Ondulada

Research in the Tala´s Creek Basin (Rolling Pampa, Argentina) including the monitoring of gauged watersheds and field rainfall simulation experiments is being carried out. It showed disagreement between the hydrological response of a small arable watershed compared to a basin of 400 km2 containing both arable soils and non arable sodic soils. The objective of this work was to assess the generation of surface runoff and soil erosion corresponding to four treatments whose soils and land use are representative of the studied region. The field trials consisted in the application of highintensity simulated rainfall on soils under bare surface condition. Unlike the rest of the treatments, the situation under livestock use with low organic carbon content, poor physical condition and high percentage of exchangeable sodium at the topsoil, showed the lowest final infiltration rate (1 mm h-1) and the largest sediment yield (349 g m-2). Due to its position close to the main stream, this site can pose an important risk to the studied water course because it is a source of physical, chemical and biological contaminants. These results show that sodic soils may be partially responsible for the lack of agreement between the small watershed and the basin’s hydrological response to rainfall events.

Comparative prediction schemes using conventional and advanced statistical analysis to predict microbial water quality in runoff from manured fields

Accurate estimations of indicator microorganisms’ concentrations are necessary to properly monitor water quality and manage contamination from agricultural land runoffs. In this study, Artificial Neural Networks (ANNs) and Multiple Regression Analysis (MRA) statistical methods were compared for accuracy in the prediction of manure-borne microorganisms’ concentrations in runoffs from agricultural plots (0.75 m × 2 m) treated with cattle or swine manure. Field rainfall simulation tests were initiated on days 4, 32, 62, 123, and 354 between June 2002 and May 2003. Each rainfall event produced 35 mm rainfall for 30 min at the intensity of 70 mm hr−1 at 24-intervals. Concentrations of microbial indicators were correlated with hydrological and environmental water quality parameters including water runoff, erosion, air temperature, relative humidity, solar radiation, pH, electric conductivity (EC) and turbidity to determine their impacts on microbial fate and transport. ANNs demonstrated a better ability to model the nonlinearity of land application of manure to ensure the safety of agricultural water environments.

Measuring Water-Extractable Phosphorus in Manures to Predict Phosphorus Concentrations in Runoff

Water-extractable phosphorus (WEP) in manures can influence the risk of phosphorus (P) losses in runoff when manures are land applied. We evaluated several manure handling and extraction variables to develop an extraction procedure for WEP that will minimize pre-analysis manure-sample-handling effects on WEP measurements. We also related manure WEP determinations to runoff dissolved reactive phosphorus (DRP) concentrations found in previously conducted field simulated rainfall experiments using the same manures to evaluate WEP as a predictor of P runoff losses. Dairy and poultry manure WEP concentrations increased with manure-to-water extraction ratio and shaking time. Relative to fresh manures, drying and grinding dairy manures before analysis usually decreased WEP concentrations, while WEP in poultry manures was often increased. Pre-analysis handling effects on WEP were minimized at the 1:1000 extraction ratio with a 1-h shaking time. Relationships between manure WEP and runoff DRP concentrations were strongly influenced by season of year and WEP extraction procedure. The best prediction of DRP concentration in spring runoff experiments was with manure WEP concentration at the 1:1000 extraction ratio. With fall runoff studies, DRP concentrations were best predicted with WEP application rate rather than concentration. These seasonal differences can be explained by the greater percentage of rainfall that ran off in the fall compared to the spring. For all studies, runoff DRP concentrations were strongly related (r2 = 0.82) to the ratio of runoff to rainfall volumes, confirming that models need to take runoff hydrology into account as well as manure WEP in P-loss risk assessments.

Post-fire overland flow generation and inter-rill erosion under simulated rainfall in two eucalypt stands in north-central Portugal

The aim of this study was to improve the existing knowledge of the runoff and inter-rill erosion response of forest stands following wildfire, focusing on commercial eucalypt plantations and employing field rainfall simulation experiments (RSE’s). Repeated RSE’s were carried out in two adjacent but contrasting eucalypt stands on steep hill slopes in north-central Portugal that suffered a moderate severity fire in July 2005. This was done at six occasions ranging from 3 to 24 months after the fire and using a paired-plot experimental design that comprised two pairs of RSE’s at each site and occasion. Of the 46 RSE’s: (i) 24 and 22 RSE’s involved application rates of 45–50 and 80–85 mm h −1, respectively; (ii) 22 took place in a stand that had been ploughed in down slope direction several years before the wildfire and 24 in an unploughed stand. The results showed a clear tendency for extreme-intensity RSE’s to produce higher runoff amounts and greater soil and organic matter losses than the simultaneous high-intensity RSE’s on the neighbouring plots. However, there existed marked exceptions, both in space (for one of the plot pairs) and time (under intermediate soil water repellency conditions). Also, overland flow generation and erosion varied significantly between the various field campaigns. This temporal pattern markedly differed from a straightforward decline with time-after-fire and rather suggested a seasonal component, reflecting broad variations in topsoil water repellency. The ploughed site produced less runoff and erosion than the unploughed site, contrary to what would be expected if the down slope ploughing had occurred after the wildfire instead of several years before it. Finally, sediment losses at both study sites were noticeably lower than those reported by other studies involving repeat RSE’s, i.e. in Australia and western Spain. This possibly reflected a history of intensive land use in the study region, including in more recent times after the widespread introduction of eucalypt plantations.

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

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

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. ER TP 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.

Assessment of marl properties effect on sediment and runoff rate at different rainfall intensity under field rainfall simulator

The objective of this study is to assess the effect of physical and chemical properties of Marl's formations on sediment and runoff rates at different rainfall intensities, based on using field rainfall simulator. For this purpose, first Marl's formations (Neocene's units) were separated to five units including Halite siltstone(NgSiH), Siltstone (NgSi), Mudstone (gy1C), Gypsum mudstone (gy1CG) and Halite clay stone (gy2CH), based on physical and chemical properties. Then runoff and sediment rates were determined in each unit at two intensities (30 and 60 mm/h) using rainfall simulator. Analysis of variance and Duncan's tests showed that Halite siltstone unit has produced the highest amount of runoff and sediment rates and then the runoff and sediment rates of other subunits in decreasing order are as follows: Siltstone, gy2CH, gylCG and gy1C are 5% significant level. The trend of induced runoff and sediment rates at different times showed that in Halite siltstone and Siltstone units the runoff amounts were fixed rapidly at 2nd ten minutes. And, on the other units, the runoff amounts were fixed at 3rd ten minutes and sediment yield was increased rapidly at 3rd ten minutes.

Soil management effects on runoff and soil loss from field rainfall simulation

ARTICLE I NFO Soil erosion from agricultural lands is a serious problem on the Chinese Loess Plateau. In total, 28 field rainfall simulations were carried on loamy soils under different management practices, namely conventional tillage (CT), no till with mulch (NTM), reduced tillage (RT), subsoiling with mulch (SSM), subsoiling without mulch (SS), and two crops per year (TC), to investigate (i) the effects of different soil management practices on runoff sediment and (ii) the temporal change of runoff discharge rate and sediment concentration under different initial soil moisture conditions (i.e. initially dry soil surface, and wet surface) and rainfall intensity (85 and 170 mm h �1 ) in the Chinese Loess Plateau. NTM was the best alternative in terms of soil erosion control. SSM reduced soil loss by more than 85% in 2002 compared to CT, and its effects on runoff reduction became more pronounced after 4 years consecutive implementation. SS also reduced considerably the runoff and soil loss, but not as pronounced as SSM. TC resulted in a significant runoff reduction (more than 92%) compared to CT in the initial 'dry' soil, but this effect was strongly reduced in the initial 'wet' soil. Temporal change of runoff discharge rate and sediment concentration showed a large variation between the different treatments. In conclusion, NTM is the most favorable tillage practices in terms of soil and water conservation in the Chinese Loess Plateau. SSM can be regarded as a promising measure to improve soil and water conservation considering its beneficial effect on winter wheat yield.

Is soil erosion in olive groves as bad as often claimed?

Alarming erosion rates have been reported in olive groves on sloping and mountainous land with some regional averages supposedly as high as 40–100 ton ha − 1 yr − 1 . These figures are based on empirical models that apply a simple multiplication of adverse environmental factors such as steep slopes, erodible soils and low vegetation cover. We present experimental data from rainfall simulations, runoff plot studies and field assessment of erosion symptoms that challenge the alarmist view. We suggest seven factors be taken into account, to achieve more realistic estimates of erosion: 1) increased surface roughness from tillage increases infiltration; 2) a cover of rock fragments protects the soil and reduces the slope effect on erosion; 3) grove undergrowth reduces sediment losses; 4) slope irregularities created by long term erosion allow runoff to infiltrate locally; 5) vegetative strips hamper rill and gully formation; 6) erosion mainly results from infrequent high intensity rainfall events, and 7) upscaling of experimental results leads to overestimation of erosion. These factors act and/or interact at different scales; although each pertains to a certain scale of analysis only and affects erosion processes differently, taken together the factors provide an argument for indicating more precisely when, where and for whom erosion constitutes a problem. A literature review (of various types of assessments) yielded erosion rates with upper and lower limits differing more than a factor of 10 000. In some individual experiments, differences between treatments (tillage versus non-tillage or vegetative strips) were still a hundredfold — frequently to the disadvantage of tillage operations. The results of our own experiments are also presented. In some runoff plots (7.5 × 15 m, previously tilled) the soil loss after cumulative rainfall of 104 mm was 17.3 g m − 2 for non-tilled against 8.5 g m − 2 for tilled conditions ( P < 0.05); in another runoff plot experiment (10 × 22 m, previously under a cover crop) tillage initially led to higher soil loss, but differences rapidly disappeared. Field rainfall simulations on soils with plant cover had significantly less soil loss than those without plant cover (recently tilled) (61 g m − 2 versus 218 g m − 2 , P < 0.001); runoff, however, was not significantly different. In consecutive rainfall simulations on soil with or without in situ rock fragments, the runoff, runoff coefficients and soil loss were significantly lower ( P < 0.01) in the case with rock fragments. On non-uniform slopes, runoff and soil loss were spatially different, and tillage led to variable responses, depending on location. Combining the findings from our individual experiments, we conclude that tillage applied judiciously in selected locations of a grove might reduce erosion. Localised erosion may still be controlled at field level by vegetative strips. Our results suggest that average soil erosion rates are unlikely to surpass 10 ton ha − 1 yr − 1 , which is nevertheless still more than the soil renewal by weathering (about 1 ton ha − 1 yr − 1 ). Any recommendations for improved soil management should ideally be tested at the appropriate scale and should capture the climatic (rainfall) conditions under which they are intended to mitigate soil erosion problems.

A New Polyacrylamide (PAM) Formulation for Reducing Erosion and Phosphorus Loss in Rainfed Agriculture

Soil erosion from agricultural lands and the subsequent transport of sediment and sediment-bound nutrients (particularly P) are serious problems contributing to surface water pollution and threatening agricultural sustainability. Raindrop impact on bare soil destabilizes soil aggregates and leads to surface sealing, increasing runoff volumes and soil loss. Surface-applied polyacrylamide (PAM) decreases soil erosion by stabilizing the soil structure and reducing surface sealing. Previous research has shown that surface-applied PAM reduces erosion at relatively high application rates (20 to 80 kg ha-1). The purpose of this study was to evaluate the effectiveness and longevity of a new liquid/emulsion PAM formulation to reduce runoff, sediment, and P loss from rainfed agricultural fields. The formulation was applied using a hand sprayer at a low PAM rate of 5 kg ha-1 (13,333 L of solution ha-1). Plot-scale field rainfall simulations (75 mm h-1) were conducted on individual test plots at three test intervals (rainfall simulated 2 days, 3 weeks, and 10 weeks after PAM application) on two soil types (Ashdale silt loam and Plano silt loam). The new polymer formulation, Soil Net EM-1000-50, reduced runoff volumes an average of 100% at the 2-day test interval, 59% at the 3-week test interval, and 55% at the 10-week test interval. Overall, larger rainfall depths were applied to treatment plots prior to runoff generation compared to controls. The most significant differences were observed at the 2-day test interval, when an average of 141 mm of rainfall was applied to the PAM-treated plots before runoff started, compared to 82 mm for the controls. These runoff reductions are not only important in terms of erosion but may also enhance water supply through increased infiltration. Sediment loss was reduced an average of 100% at the 2-day test interval, 80% at the 3-week test interval, and 74% at the 10-week test interval. Phosphorus loss was reduced an average of 100% at the 2-day test interval, 75% at the 3-week test interval, and 83% at the 10-week test interval. The polymer treatment was more effective on the Ashdale silt loam, which had received manure during the two years preceding the rainfall simulations. Manure application was the primary difference between the two soils (manure was not applied to the Plano silt loam), suggesting that the PAM treatment reacts more favorably to manured soils. The low cost of this new PAM technology (approx. $25 ha-1) coupled with its success in reducing runoff, sediment, and P loss over a 10-week period, make EM-1000-50 an attractive and economically feasible management practice for agricultural producers in rainfed regions.

Effects of tilling no-till soil on losses of atrazine and glyphosate to runoff water under variable intensity simulated rainfall

Herbicides released through agricultural activities to surface waters and drinking water systems represent a risk to human and environmental health, as well as a cost to municipalities for removal. This study focuses on the viability of glyphosate tolerant cropping systems as an alternative to atrazine-based systems, and the impact of tilling historically no-till ground on the runoff pollution potential of these systems. Variable intensity field rainfall simulations were performed on 2 m long × 1 m wide plots within a field in first-year disk and harrow following no-till (CT), and within a long-term no-tilled (NT) field, both treated with atrazine and glyphosate according to label. Rainfall sequence was: 50 mm h −1 for 50 min followed by 75 mm h −1 for 15 min, 25 mm h −1 for 15 min, and 100 mm h −1 for 15 min. Runoff was collected at regular time intervals during two simulated rainfall events and analyzed for herbicide concentration, sediment content, and volume. Maximum glyphosate concentration in runoff was 233 μg L −1 for NT and 180 μg L −1 for CT (approximately 33% and 26% of the maximum contaminant limit (MCL) for glyphosate (700 μg L −1), respectively, while maximum atrazine concentrations in runoff was 303 μg L −1 for NT and 79 μg L −1 for CT (approximately 100 times and 26 times the atrazine MCL (3 μg L −1)). Atrazine concentration and loading were significantly higher in runoff from NT plots than from CT plots, whereas glyphosate concentration and loading were impacted by tillage treatment to a much lesser degree. Results suggest that glyphosate-based weed management may represent a lower drinking water risk than atrazine-based weed management, especially in NT systems.

Evaluation of USLE and RUSLE Estimated Soil Loss on Rangeland

The Universal Soil Loss Equation (USLE) and the Revised Universal Soil Loss Equation (RUSLE 1.06) were evaluated with rainfall simulation data from a diverse set of rangeland vegetation types (8 states, 22 sites, 132 plots). Dry, wet, and very-wet rainfall simulation treatments were applied to the study plots within a 2-day period. The rainfall simulation rate was 65mm/hr for the dry and wet simulation treatments and alternated between 65-130 mm/hr for the very-wet treatment. Average soil loss for all plots for the representative simulation runs were: 0.011 kg/m2, 0.007 kg/m2, and 0.035 kg/m2 for the dry, wet, and very-wet simulation treatments, respectively. The Nash-Sutcliffe Model efficiencies (R2eff) of the USLE for the dry, wet, very-wet simulation treatments and sum of all soil loss measured in the three composite simulation treatments (pooled data) were negative. This indicates that the observed mean measured soil loss from the field rainfall simulations is better than predicted USLE soil loss. The USLE tended to consistently overpredict soil loss for all 3 rainfall simulation treatments. As the USLE predicted values increased in magnitude, the error variance between predicted and observed soil loss increased. Nash-Sutcliffe model efficiency for the RUSLE was also negative, except for the dry run simulation treatment [R2eff = 0.16 using RUSLE cover management (C) subfactor parameters from the RUSLE manual (C(table)), NRCS soil erodibility factor (K); and R2eff = 0.17 with C(table) and K estimated from the soil-erodibility nomograph]. In comparison to the USLE, there was less error between observed and RUSLE predicted soil loss. The RUSLE error variances showed a consistent trend of underpredicted soil loss among the 3 rainfall simulation treatments. When actual field measured root biomass, plant production and soil random roughness values were used in calculating the RUSLE C subfactors: the R2eff values for the dry, wet, very-wet rainfall simulation treatments and the pooled data were all negative. DOI:10.2458/azu_jrm_v56i3_spaeth

A comparison of rubber-tyred and steel-tracked skidders on forest soil physical properties

Compaction of a silty clay loam forest soil was compared for 2 types of log-skidding equipment, a rubber-tyred skidder and a flexible-steel-tracked skidder. Experiments involved the loaded skidders traversing marked laneways at zero, 2, 4, and 10 passes. Compaction was quantified in terms of 3 parameters: (1) bulk density to 25 cm depth measured gravimetrically, (2) penetration resistance using a field penetrometer, and (3) saturated hydraulic conductivity using a field rainfall simulator. Results showed no substantial difference in soil bulk density between the experimental treatments, regardless of skidder type or number passes. Penetration resistance of the traversed laneways was significantly higher than the surrounding undisturbed areas; however, there was no difference between skidder type. Rainfall simulation showed that the saturated hydraulic conductivity of all treatments was strongly reduced by trafficking, although this did not differ with skidder type. The results from this study highlight the dangers in assuming that reduced machine static ground pressures will automatically lead to reduced soil impacts. It is important to note that while this study did not find differences between the 2 skidder types when operated in a similar manner, differences in the operation of the two skidders may also influence impacts on soil properties.